Aplicación de la biología molecular en alergia a alimentos
Aplicación de la biología molecular en alergia a alimentos
Aplicación de la biología molecular en alergia a alimentos
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Alergol Inmunol Clin 2001;16 (Extraordinario Núm. 2):14-36<br />
Mo<strong>de</strong>rador: D. Barber<br />
Hernán<strong>de</strong>z<br />
ALK-Abelló. Madrid<br />
R. Sánchez-Monge,<br />
A. Díaz-Perales,<br />
G. García-Casado,<br />
G. Salcedo<br />
Unidad <strong>de</strong> Bioquímica.<br />
Departam<strong>en</strong>to <strong>de</strong><br />
Biotecnología. E.T.S. <strong>de</strong><br />
Ing<strong>en</strong>ieros Agrónomos.<br />
Universidad Politécnica.<br />
Madrid.<br />
14<br />
SESIÓN PLENARIA<br />
APLICACIÓN DE LA BIOLOGÍA<br />
MOLECULAR EN ALERGIA<br />
A ALIMENTOS<br />
Proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa y <strong>de</strong> reserva<br />
como alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos vegetales<br />
CARACTERIZACIÓN DE ALERGENOS:<br />
ASPECTOS BÁSICOS Y APLICADOS<br />
La cuestión c<strong>en</strong>tral <strong>en</strong> <strong>la</strong>s reacciones <strong>de</strong> hipers<strong>en</strong>sibilidad mediadas por IgE<br />
–¿por qué una proteína es alergénica?–, está lejos <strong>de</strong> ser contestada. La respuesta<br />
posiblem<strong>en</strong>te pasa por <strong>la</strong> purificación, clonación y expresión heteróloga <strong>de</strong> <strong>la</strong>s proteínas<br />
alergénicas.<br />
La caracterización <strong>de</strong> alerg<strong>en</strong>os, que incluye <strong>la</strong> <strong>de</strong>terminación <strong>de</strong> su secu<strong>en</strong>cia<br />
<strong>de</strong> aminoácidos o estructura primaria, su estructura tridim<strong>en</strong>sional y <strong>la</strong> posible exist<strong>en</strong>cia<br />
<strong>de</strong> modificaciones postraduccionales (como glicosi<strong>la</strong>ciones), así como el estudio<br />
<strong>de</strong> su estabilidad térmica y digestiva y el mapeo <strong>de</strong> epítopos (B o T) secu<strong>en</strong>ciales<br />
o conformacionales, permitirá esc<strong>la</strong>recer <strong>la</strong>s características que <strong>de</strong>terminan <strong>la</strong><br />
capacidad <strong>de</strong> una proteína para provocar <strong>la</strong> respuesta inmune.<br />
La expresión <strong>de</strong>l correspondi<strong>en</strong>te clon <strong>en</strong> sistemas heterólogos, normalm<strong>en</strong>te<br />
bacterias o levaduras, permite obt<strong>en</strong>er el alerg<strong>en</strong>o recombinante <strong>en</strong> cantida<strong>de</strong>s<br />
apreciables. Por mutagénesis dirigida se pue<strong>de</strong>n localizar los aminoácidos<br />
es<strong>en</strong>ciales para su alerg<strong>en</strong>icidad y obt<strong>en</strong>er formas hipoalergénicas <strong>de</strong> <strong>la</strong> proteína<br />
para su posible utilización <strong>en</strong> inmunoterapia o <strong>en</strong> <strong>la</strong> producción <strong>de</strong> alim<strong>en</strong>tos no<br />
alergénicos.<br />
A<strong>de</strong>más, y ésta es posiblem<strong>en</strong>te su aplicación más inmediata, <strong>la</strong> disponibilidad<br />
<strong>de</strong> alerg<strong>en</strong>os vegetales purificados, nativos o recombinantes, pue<strong>de</strong> ser <strong>de</strong> utilidad<br />
para el diagnóstico, tanto in vitro como in vivo, al permitir <strong>la</strong> estandarización <strong>de</strong>l<br />
material utilizado.<br />
PROTEÍNAS DE DEFENSA Y DE RESERVA<br />
COMO ALERGENOS VEGETALES<br />
La caracterización <strong>de</strong> alerg<strong>en</strong>os vegetales y su inclusión <strong>en</strong> familias <strong>de</strong> proteínas<br />
ampliam<strong>en</strong>te distribuidas <strong>en</strong> el reino vegetal permite pre<strong>de</strong>cir reactivida<strong>de</strong>s<br />
cruzadas <strong>en</strong>tre distintos alim<strong>en</strong>tos, o <strong>en</strong>tre éstos y pól<strong>en</strong>es u otro tipo <strong>de</strong>
Tab<strong>la</strong> I. Familias <strong>de</strong> proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa <strong>de</strong> p<strong>la</strong>ntas con<br />
miembros i<strong>de</strong>ntificados como alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos<br />
Familia/Especie Alerg<strong>en</strong>o<br />
Homólogos Bet v 1 (PR-10)<br />
Manzana Mal d 1<br />
Pera Pyr c 1<br />
Albaricoque Pru ar 1<br />
Cereza Pru av 1<br />
Avel<strong>la</strong>na Cor a 1<br />
Apio Api g 1<br />
Zanahoria Dau c 1<br />
Proteínas <strong>de</strong> transfer<strong>en</strong>cia <strong>de</strong> Lípidos (LTP) (PR-14)<br />
Manzana Mal d 3<br />
Melocotón Pru p 3<br />
Albaricoque Pru ar 3<br />
Cereza Pru av 3<br />
Cirue<strong>la</strong> Pru d 3<br />
Maíz Zea m 14<br />
Cebada (cerveza)<br />
Nuez Jug r 3<br />
Quitinasas <strong>de</strong> c<strong>la</strong>se I (PR- 3)<br />
Aguacate Prs a 1<br />
Castaña Cas s 5<br />
Plátano Mus a 1.1 y Mus a 1.2<br />
Proheveínas (PR-4)<br />
Nabo Bra r 2<br />
Taumatinas (PR-5)<br />
Manzana Mal d 2<br />
Cereza Pru av 2<br />
Pimi<strong>en</strong>ta Cap a 1<br />
Inhibidores <strong>de</strong> α-ami<strong>la</strong>sas/tripsina<br />
Trigo<br />
Cebada Hor v 1<br />
C<strong>en</strong>t<strong>en</strong>o Sec c 1<br />
Arroz RAP<br />
Inhibidores <strong>de</strong> proteasas (Kunitz)<br />
Soja<br />
Patata Solt t 2,3,4<br />
Peroxidasas<br />
Trigo<br />
Cebada<br />
Proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa y <strong>de</strong> reserva como alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos vegetales<br />
ag<strong>en</strong>tes ambi<strong>en</strong>tales (látex, etc.). Permite, asimismo, pre<strong>de</strong>cir<br />
<strong>la</strong> alerg<strong>en</strong>icidad <strong>de</strong> nuevos tipos <strong>de</strong> preparados alim<strong>en</strong>ticios<br />
o <strong>de</strong> alim<strong>en</strong>tos proce<strong>de</strong>ntes <strong>de</strong> organismos g<strong>en</strong>éticam<strong>en</strong>te<br />
modificados.<br />
Una mayoría <strong>de</strong> los alerg<strong>en</strong>os vegetales actualm<strong>en</strong>te<br />
caracterizados pue<strong>de</strong>n incluirse <strong>en</strong> familias <strong>de</strong> proteínas<br />
implicadas <strong>en</strong> <strong>la</strong> <strong>de</strong>f<strong>en</strong>sa <strong>de</strong> <strong>la</strong>s p<strong>la</strong>ntas fr<strong>en</strong>te a organismos<br />
predadores o situaciones <strong>de</strong> estrés abiótico (frío, calor,<br />
sequía, salinidad, etc.). A<strong>de</strong>más, varios alerg<strong>en</strong>os son proteínas<br />
<strong>de</strong> reserva <strong>en</strong> semil<strong>la</strong>s u otros órganos (ver Breit<strong>en</strong>e<strong>de</strong>r<br />
y Ebner 2001 1 para una revisión). En <strong>la</strong> Tab<strong>la</strong> I se resum<strong>en</strong><br />
<strong>la</strong>s familias <strong>de</strong> proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa <strong>de</strong> p<strong>la</strong>ntas <strong>en</strong> <strong>la</strong>s<br />
que se han i<strong>de</strong>ntificado alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos vegetales.<br />
La mayoría <strong>de</strong> estas familias están incluidas <strong>en</strong> <strong>la</strong>s <strong>de</strong>nominadas<br />
proteínas PR (pathog<strong>en</strong>esis re<strong>la</strong>ted o proteínas<br />
re<strong>la</strong>cionadas con <strong>la</strong> patogénesis) 2 . En <strong>la</strong> Tab<strong>la</strong> II aparec<strong>en</strong><br />
c<strong>la</strong>sificados por familias los alerg<strong>en</strong>os vegetales que son<br />
proteínas <strong>de</strong> reserva <strong>de</strong> semil<strong>la</strong>s.<br />
Tab<strong>la</strong> II. Familias <strong>de</strong> proteínas <strong>de</strong> reserva <strong>de</strong> p<strong>la</strong>ntas con<br />
miembros i<strong>de</strong>ntificados como alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos<br />
Familia/Especie Alerg<strong>en</strong>o<br />
Albúminas 2S<br />
Mostaza amaril<strong>la</strong> Sin a 1<br />
Mostaza ori<strong>en</strong>tal Bra j 1<br />
Colza Bra n 1<br />
Ricino Ric c 1<br />
Sésamo Ses i 1<br />
Nuez Jug r 1<br />
Nuez <strong>de</strong> Brasil Ber e 1<br />
Cacahuete Ara h 2, 6<br />
Girasol SFA8<br />
Vicilinas 7S<br />
Cacahuete Ara h 1<br />
Soja Gly m Bd 28 K y 60K<br />
L<strong>en</strong>teja Lec c 1<br />
Nuez Jug r 2<br />
Leguminas 11S<br />
Cacahuete Ara h 3<br />
Soja<br />
Proiaminas<br />
Trigo<br />
Cebada<br />
C<strong>en</strong>t<strong>en</strong>o<br />
15
R. Sánchez-Monge, et al<br />
Fig. 1. A: Pruebas cutáneas. B: Inmuno<strong>de</strong>tección (dot-blot) realizados<br />
con extractos proteicos <strong>en</strong>riquecidos <strong>en</strong> inhibidores WPI y BPI, y con<br />
proteínas purificadas <strong>de</strong> <strong>la</strong> familia <strong>de</strong> inhibidores <strong>de</strong> α-ami<strong>la</strong>sa/tripsina:<br />
W: trigo; B: cebada; TAI, DAI, y MAI: inhibidores tetráméricos,<br />
diméricos y monoméricos <strong>de</strong> α-ami<strong>la</strong>sa; TI: inhibidor monomérico <strong>de</strong><br />
tripsina. Los compon<strong>en</strong>tes glicosi<strong>la</strong>dos aparec<strong>en</strong> seña<strong>la</strong>dos con asterisco<br />
(*).<br />
A<strong>de</strong>más <strong>de</strong> <strong>la</strong>s proteínas incluidas <strong>en</strong> <strong>la</strong>s tab<strong>la</strong>s, también<br />
son importantes alerg<strong>en</strong>os vegetales <strong>la</strong>s profilinas y<br />
algunas tiol-proteasas. La profilinas son proteínas que un<strong>en</strong><br />
actina y participan <strong>en</strong> <strong>la</strong> organización <strong>de</strong>l citoesqueleto <strong>de</strong><br />
<strong>la</strong>s célu<strong>la</strong>s. Son panalerg<strong>en</strong>os implicados <strong>en</strong> reacciones cruzadas<br />
<strong>en</strong>tre pól<strong>en</strong>es y alim<strong>en</strong>tos. El alerg<strong>en</strong>o mayoritario<br />
<strong>de</strong> kiwi es una tiol-proteasa, actinidina (Act c 1), con<br />
homólogos responsables <strong>de</strong> pot<strong>en</strong>ciales reacciones cruzadas<br />
<strong>en</strong> otras frutas, como papaya, piña o higo. Uno <strong>de</strong> los<br />
principales alerg<strong>en</strong>os <strong>de</strong> <strong>la</strong> soja, Gly m 1 (antes Gly m Bd<br />
30K) es también una tiol- proteasa.<br />
LOS INHIBIDORES DE<br />
α-AMILASA/TRIPSINA DE HARINA DE<br />
CEREALES, IMPLICADOS EN ALERGIAS<br />
OCUPACIONALES, SON TAMBIÉN<br />
RESPONSABLES DE ALERGIAS<br />
ALIMENTARIAS<br />
Se han purificado y caracterizado diversos miembros<br />
<strong>de</strong> <strong>la</strong> familia <strong>de</strong> inhibidores <strong>de</strong> α-ami<strong>la</strong>sa/tripsina <strong>de</strong><br />
16<br />
trigo, cebada y c<strong>en</strong>t<strong>en</strong>o, y <strong>de</strong>mostrado su papel como<br />
alerg<strong>en</strong>os principales <strong>en</strong> <strong>la</strong> <strong>alergia</strong> ocupacional más<br />
importante asociada a <strong>la</strong> manipu<strong>la</strong>ción <strong>de</strong> harinas, <strong>de</strong>nominada<br />
“asma <strong>de</strong>l pana<strong>de</strong>ro” 3-6 . La mayoría <strong>de</strong> los miembros<br />
<strong>de</strong> <strong>la</strong> familia son reactivos, tanto in vitro como in<br />
vivo. Sin embargo, su capacidad <strong>de</strong> ligar IgE varía sustancialm<strong>en</strong>te<br />
(Figura 1). Son más reactivos los miembros<br />
que están glicosi<strong>la</strong>dos lo que ha permitido estudiar el<br />
papel <strong>de</strong> los N-oligosacáridos complejos <strong>de</strong> p<strong>la</strong>ntas <strong>en</strong> <strong>la</strong><br />
capacidad <strong>de</strong> unión <strong>de</strong> IgE, particu<strong>la</strong>rm<strong>en</strong>te el <strong>de</strong> los residuos<br />
<strong>de</strong> xilosa y fucosa, así como su implicación <strong>en</strong> reacciones<br />
cruzadas con glicoproteínas no re<strong>la</strong>cionadas<br />
secu<strong>en</strong>cialm<strong>en</strong>te 7-9 .<br />
Otro tipo <strong>de</strong> <strong>alergia</strong> ocupacional <strong>en</strong> el que está implicada<br />
<strong>la</strong> familia <strong>de</strong> inhibidores es <strong>en</strong> <strong>la</strong> industria ma<strong>de</strong>rera, <strong>en</strong> <strong>la</strong><br />
que se utilizan <strong>en</strong>grudos <strong>de</strong> cereales, habiéndose <strong>de</strong>mostrado<br />
<strong>la</strong> reactividad tanto in vivo como in vitro <strong>de</strong> varios <strong>de</strong> sus<br />
miembros 10-11 .<br />
A pesar <strong>de</strong> <strong>la</strong> importancia creci<strong>en</strong>te <strong>de</strong> <strong>la</strong> <strong>alergia</strong> alim<strong>en</strong>taria<br />
a diversos tipos <strong>de</strong> cereales, se sabe re<strong>la</strong>tivam<strong>en</strong>te<br />
poco <strong>de</strong> <strong>la</strong> naturaleza <strong>de</strong> los alerg<strong>en</strong>os implicados.<br />
Los datos acumu<strong>la</strong>dos sugier<strong>en</strong> un papel relevante <strong>de</strong> los<br />
miembros <strong>de</strong> <strong>la</strong> familia <strong>de</strong> inhibidores <strong>de</strong> α-ami<strong>la</strong>sa/tripsina.<br />
Diversos alerg<strong>en</strong>os localizados <strong>en</strong> el grano <strong>de</strong> arroz 12<br />
son homólogos a los inhibidores <strong>de</strong> trigo, cebada, y c<strong>en</strong>t<strong>en</strong>o.<br />
También es miembro <strong>de</strong> <strong>la</strong> familia el único alerg<strong>en</strong>o<br />
por ingestión localizado <strong>en</strong> trigo 13 . En un estudio reci<strong>en</strong>te<br />
(Arm<strong>en</strong>tia et al., datos sin publicar), los patrones <strong>de</strong> proteínas<br />
<strong>de</strong> extractos <strong>de</strong> trigo, cebada y c<strong>en</strong>t<strong>en</strong>o que ligan<br />
IgE son simi<strong>la</strong>res <strong>en</strong> paci<strong>en</strong>tes alérgicos a cereales por<br />
ingestión (niños y adultos) y por inha<strong>la</strong>ción (asma <strong>de</strong>l<br />
pana<strong>de</strong>ro).<br />
LTPs COMO PANALERGENOS VEGETALES<br />
EN POBLACIONES DEL ÁREA<br />
MEDITERRÁNEA<br />
En países <strong>de</strong>l c<strong>en</strong>tro y norte <strong>de</strong> Europa y <strong>de</strong> América<br />
<strong>de</strong>l Norte, <strong>la</strong> <strong>alergia</strong> a manzana y otros frutos <strong>de</strong> <strong>la</strong> familia<br />
Rosaceae aparece asociada con <strong>alergia</strong> al pol<strong>en</strong> <strong>de</strong> abedul,<br />
si<strong>en</strong>do los principales alerg<strong>en</strong>os miembros <strong>de</strong> <strong>la</strong> familia <strong>de</strong><br />
Bet v 1 y profilinas. En el área Mediterránea, con escasa<br />
pres<strong>en</strong>cia <strong>de</strong> abedules, los paci<strong>en</strong>tes alérgicos a este tipo <strong>de</strong><br />
frutos g<strong>en</strong>eralm<strong>en</strong>te no pres<strong>en</strong>tan IgE específica fr<strong>en</strong>te a<br />
Bet v 1. Tanto si <strong>la</strong> <strong>alergia</strong> aparece asociada a polinosis,<br />
como <strong>en</strong> paci<strong>en</strong>tes no polínicos, los principales alerg<strong>en</strong>os<br />
<strong>de</strong> manzana y melocotón son proteínas <strong>de</strong> alre<strong>de</strong>dor <strong>de</strong> 9
kDa, que fueron caracterizados como miembros <strong>de</strong> <strong>la</strong> familia<br />
<strong>de</strong> proteínas <strong>de</strong> transfer<strong>en</strong>cia <strong>de</strong> lípidos (LTPs) 14,15 . La<br />
utilidad <strong>de</strong> LTPs purificadas <strong>de</strong> distintas fu<strong>en</strong>tes <strong>en</strong> el diagnóstico<br />
<strong>de</strong> <strong>alergia</strong> a Rosáceas ha sido <strong>de</strong>mostrada <strong>en</strong> un<br />
estudio reci<strong>en</strong>te (García-Selles et al., datos sin publicar).<br />
Más <strong>de</strong>l 90% <strong>de</strong> los paci<strong>en</strong>tes alérgicos a melocotón y manzana<br />
reaccionan <strong>en</strong> pruebas cutáneas con <strong>la</strong> proteína correspondi<strong>en</strong>te<br />
(Pru p 3 y Mald d 3).<br />
Las LTPs son proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa ampliam<strong>en</strong>te distribuidas<br />
<strong>en</strong> distintos tejidos <strong>de</strong> <strong>la</strong>s p<strong>la</strong>ntas, lo que sugiere<br />
su pot<strong>en</strong>cial papel como panalerg<strong>en</strong>os responsables <strong>de</strong><br />
reacciones cruzadas <strong>en</strong>tre frutas, semil<strong>la</strong>s y pól<strong>en</strong>es 16,17 . La<br />
alta estabilidad térmica y digestiva <strong>de</strong> estas proteínas posibilita<br />
su actuación como alerg<strong>en</strong>os <strong>en</strong> alim<strong>en</strong>tos o bebidas<br />
e<strong>la</strong>boradas tales como zumo <strong>de</strong> melocotón 18 , vino 19 , o cerveza<br />
20 .<br />
A partir <strong>de</strong> clones cDNA <strong>de</strong> <strong>la</strong>s LTPs <strong>de</strong> melocotón<br />
y manzana 21 , se ha <strong>de</strong>ducido <strong>la</strong> secu<strong>en</strong>cia completa <strong>de</strong><br />
aminoácidos <strong>de</strong> <strong>la</strong>s proteínas maduras que muestran un<br />
82% <strong>de</strong> i<strong>de</strong>ntidad. La comparación con <strong>la</strong>s secu<strong>en</strong>cias <strong>de</strong><br />
otras proteínas <strong>de</strong> <strong>la</strong> familia permite localizar zonas conservadas<br />
y variables que pue<strong>de</strong>n formar parte <strong>de</strong> epítopos<br />
secu<strong>en</strong>ciales implicados <strong>en</strong> reactivida<strong>de</strong>s cruzadas. El<br />
mo<strong>de</strong><strong>la</strong>do <strong>de</strong> <strong>la</strong> estructura tridim<strong>en</strong>sional, como el pres<strong>en</strong>tado<br />
<strong>en</strong> <strong>la</strong> Figura 2, permitirá localizar zonas pot<strong>en</strong>cialm<strong>en</strong>te<br />
expuestas, candidatas a incluir epítopos conformacionales.<br />
El clon <strong>de</strong> melocotón ha sido expresado <strong>en</strong> <strong>la</strong> levadura<br />
Pichia pastoris 21 . La purificación <strong>de</strong> <strong>la</strong> proteína recombinante,<br />
ha <strong>de</strong>mostrado que, al m<strong>en</strong>os in vitro, su capacidad <strong>de</strong> ligar<br />
IgE es simi<strong>la</strong>r a <strong>la</strong> <strong>de</strong> <strong>la</strong> proteína nativa.<br />
LOS PANALERGENOS RESPONSABLES<br />
DEL SÍNDROME LÁTEX/FRUTAS<br />
SON QUITINASAS DE CLASE I<br />
Alre<strong>de</strong>dor <strong>de</strong> un 30-50% <strong>de</strong> los paci<strong>en</strong>tes alérgicos a<br />
látex pres<strong>en</strong>ta hipers<strong>en</strong>sibilidad a frutas, principalm<strong>en</strong>te<br />
aguacate, castaña, plátano y kiwi. La <strong>de</strong>nominación "síndrome<br />
látex/frutas" fue propuesta 22 para <strong>de</strong>scribir este tipo<br />
<strong>de</strong> reacción cruzada, que <strong>de</strong>be implicar <strong>la</strong> pres<strong>en</strong>cia <strong>de</strong> epítopos<br />
comunes <strong>en</strong> alguno <strong>de</strong> los alerg<strong>en</strong>os <strong>de</strong> látex y <strong>en</strong><br />
proteínas <strong>de</strong> <strong>la</strong>s frutas. La purificación y caracterización <strong>en</strong><br />
aguacate 23-25 , castaña 23,25 y plátano 26,27 <strong>de</strong> los alerg<strong>en</strong>os principales<br />
ha permitido concluir que son quitinasas <strong>de</strong> c<strong>la</strong>se I.<br />
Estas proteínas pose<strong>en</strong> <strong>en</strong> <strong>la</strong> zona N-terminal <strong>de</strong> su secu<strong>en</strong>cia<br />
un dominio heveína con cerca <strong>de</strong> un 70% <strong>de</strong> i<strong>de</strong>ntidad<br />
Proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa y <strong>de</strong> reserva como alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos vegetales<br />
Fig. 2. Mo<strong>de</strong><strong>la</strong>do <strong>de</strong> <strong>la</strong> LTP <strong>de</strong> melocotón, Pru p 3, a partir <strong>de</strong> su<br />
secu<strong>en</strong>cia <strong>de</strong> aminoácidos y tomando como refer<strong>en</strong>cia <strong>la</strong> LTP <strong>de</strong> maíz<br />
cuya estructura se ha <strong>de</strong>terminado por resonancia magnético nuclear.<br />
Ct y Nt seña<strong>la</strong>n los extremos carboxi y amino-terminal <strong>de</strong> <strong>la</strong> proteína.<br />
En colores se repres<strong>en</strong>tan los tramos <strong>de</strong> hélice α.<br />
con el alerg<strong>en</strong>o principal <strong>de</strong> látex, <strong>la</strong> heveína (Hev b 6.02).<br />
Este dominio no está pres<strong>en</strong>te <strong>en</strong> <strong>la</strong>s quitinasas <strong>de</strong> c<strong>la</strong>se II,<br />
que sin embargo pres<strong>en</strong>tan cerca <strong>de</strong>l 80% <strong>de</strong> i<strong>de</strong>ntidad <strong>de</strong><br />
secu<strong>en</strong>cia con el dominio catalítico <strong>de</strong> <strong>la</strong>s quitinasas <strong>de</strong> c<strong>la</strong>se<br />
I. En <strong>la</strong> Figura 3 se pres<strong>en</strong>tan los resultados <strong>de</strong> experim<strong>en</strong>tos<br />
<strong>de</strong> inmunoinhibición con <strong>la</strong>s quitinasas <strong>de</strong> ambas<br />
c<strong>la</strong>ses purificadas <strong>de</strong> castaña.<br />
El clonaje y expresión <strong>de</strong> <strong>la</strong> quitinasa <strong>de</strong> c<strong>la</strong>se I <strong>de</strong> castaña<br />
y <strong>de</strong> su dominio catalítico 28 ha permitido analizar el<br />
papel <strong>de</strong> los dos dominios <strong>de</strong> estas <strong>en</strong>zimas <strong>en</strong> su capacidad<br />
<strong>de</strong> ligar IgE. La importancia <strong>de</strong>l dominio heveína <strong>en</strong> dicho<br />
reconocimi<strong>en</strong>to es evi<strong>de</strong>nte pues <strong>la</strong> <strong>de</strong>leción <strong>de</strong>l mismo<br />
supone <strong>la</strong> pérdida completa <strong>de</strong> reactividad <strong>en</strong> <strong>en</strong>sayos <strong>de</strong><br />
inmuno<strong>de</strong>tección <strong>de</strong>spués <strong>de</strong> fraccionami<strong>en</strong>to por electroforesis<br />
<strong>en</strong> pres<strong>en</strong>cia <strong>de</strong> SDS (SDS-PAGE). Sin embargo, <strong>en</strong>sayos<br />
<strong>de</strong> RAST <strong>de</strong> inhibición <strong>en</strong> condiciones no <strong>de</strong>snaturalizantes<br />
sugier<strong>en</strong> <strong>la</strong> pres<strong>en</strong>cia <strong>de</strong> epítopos conformacionales <strong>en</strong><br />
el dominio catalítico.<br />
Las quitinasas <strong>de</strong> c<strong>la</strong>se I son proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa <strong>de</strong> <strong>la</strong>s<br />
p<strong>la</strong>ntas ampliam<strong>en</strong>te distribuidas. Son, por tanto, pot<strong>en</strong>ciales<br />
panalerg<strong>en</strong>os responsables <strong>de</strong> reacciones cruzadas <strong>en</strong>tre distintos<br />
tipos <strong>de</strong> alim<strong>en</strong>tos vegetales. Son proteínas termolábiles,<br />
<strong>de</strong>bido a lo cual sólo los alim<strong>en</strong>tos consumidos crudos,<br />
pero no los que se consum<strong>en</strong> tras ser cocinados o <strong>de</strong>spués <strong>de</strong><br />
ser sometidos a tratami<strong>en</strong>tos térmicos industriales, están asociados<br />
con el síndrome látex-frutas 29,30 . Por otra parte el nivel<br />
<strong>de</strong> este tipo <strong>de</strong> alerg<strong>en</strong>os pue<strong>de</strong> verse increm<strong>en</strong>tado <strong>de</strong>spués<br />
<strong>de</strong> <strong>de</strong>terminados tratami<strong>en</strong>tos, como es el caso <strong>de</strong>l etil<strong>en</strong>o utilizado<br />
para acelerar <strong>la</strong> maduración <strong>de</strong> frutas 30 .<br />
17
R. Sánchez-Monge, et al<br />
Fig. 3. A. Inmunoinhibición <strong>de</strong> un extracto proteico <strong>de</strong> castaña fraccionado<br />
por SDS-PAGE y electrotransferido a membranas <strong>de</strong> PVDF. El<br />
pool <strong>de</strong> sueros <strong>de</strong> paci<strong>en</strong>tes alérgicos a látex y frutas utilizado se<br />
preincubó con los sigui<strong>en</strong>tes inhibidores: Albúmina <strong>de</strong> suero bovino<br />
(BSA), quitinasas purificadas <strong>de</strong> castaña <strong>de</strong> c<strong>la</strong>se I (QI) y II (QII),<br />
extracto <strong>de</strong> látex (Hb). B. CAP <strong>de</strong> inhibición <strong>de</strong> castaña. Inhibidores:<br />
Extracto proteico <strong>de</strong> castaña CsT, preparación <strong>en</strong>riquecida <strong>en</strong> quitinasas<br />
<strong>de</strong> castaña (CsQ), quitinasas <strong>de</strong> c<strong>la</strong>se I (QI) y II (QII) purificadas<br />
<strong>de</strong> castaña, y extracto <strong>de</strong> <strong>la</strong>tex (Hb). Se utilizó un extracto comercial<br />
<strong>de</strong> D.pteronyssinus como control negativo.<br />
VICILINAS Y LA ALERGIA A LEGUMINOSAS<br />
EN LA ZONA MEDITERRÁNEA<br />
Las semil<strong>la</strong>s <strong>de</strong> leguminosas son una <strong>de</strong> <strong>la</strong>s principales<br />
causas <strong>de</strong> <strong>alergia</strong>s alim<strong>en</strong>tarias infantiles. En países<br />
anglosajones y <strong>en</strong> Japón, cacahuete y soja son <strong>la</strong>s principales<br />
especies causantes <strong>de</strong> reacciones <strong>de</strong> hipers<strong>en</strong>sibilidad,<br />
mi<strong>en</strong>tras que <strong>en</strong> <strong>la</strong> zona Mediterránea y <strong>en</strong> <strong>la</strong> India <strong>la</strong>s<br />
especies más implicadas son l<strong>en</strong>teja y garbanzo. Los aler-<br />
18<br />
1 29<br />
L<strong>en</strong> c 1 306 D D D E E E E Q E E E T S K Q V Q R Y R A K L S P G D V F 339<br />
Vic-50kd G K E N D K E E E Q E E E T S K Q V Q L Y R A K L S P G D V F V I<br />
Ara h 1 G R R EE E E D E D E E E S N R E V R R Y T A R L K E G D V F I M<br />
478 _ 512<br />
EG<br />
Fig. 4. Alineami<strong>en</strong>to <strong>de</strong> <strong>la</strong> secu<strong>en</strong>cia N-terminal <strong>de</strong>l alerg<strong>en</strong>o <strong>de</strong> l<strong>en</strong>teja<br />
(L<strong>en</strong> c 1) con secu<strong>en</strong>cias <strong>de</strong> una provicilina <strong>de</strong> guisante (∆ seña<strong>la</strong> el<br />
sitio <strong>de</strong> procesami<strong>en</strong>to) y <strong>de</strong>l alerg<strong>en</strong>o <strong>de</strong> cacahuete (Ara h 1).<br />
g<strong>en</strong>os principales <strong>de</strong> cacahuete y soja han sido ampliam<strong>en</strong>te<br />
estudiados pero no así los <strong>de</strong> l<strong>en</strong>teja y garbanzo.<br />
Se han caracterizado dos tipos <strong>de</strong> alerg<strong>en</strong>os <strong>en</strong> l<strong>en</strong>tejas<br />
cocidas 31 . Uno <strong>de</strong> ellos es un grupo <strong>de</strong> isoalerg<strong>en</strong>os <strong>de</strong><br />
12-16 kDa (L<strong>en</strong> c 1), que son variantes <strong>de</strong> γ-vicilinas, presumiblem<strong>en</strong>te<br />
producto <strong>de</strong>l procesami<strong>en</strong>to <strong>de</strong> un precursor<br />
<strong>de</strong> 50 kDa. Son reconocidos por un 65% <strong>de</strong> sueros <strong>de</strong><br />
niños alérgicos a l<strong>en</strong>teja. Pres<strong>en</strong>tan homología <strong>de</strong> secu<strong>en</strong>cia<br />
con <strong>la</strong> región C-terminal <strong>de</strong> vicilinas <strong>de</strong> guisante y con<br />
el alérg<strong>en</strong>o Ara h 1 <strong>de</strong> cacahuete, ambos <strong>de</strong> 50-60 kDa<br />
(ver Figura 4). El clonaje y secu<strong>en</strong>ciación <strong>de</strong> <strong>la</strong> vicilina <strong>de</strong><br />
l<strong>en</strong>teja permitirá su comparación con Ara h 1 (que es también<br />
una vicilina) <strong>de</strong>l que se ha <strong>de</strong>scrito el mapeo <strong>de</strong> epítopos<br />
IgE 32 .<br />
El otro alerg<strong>en</strong>o es una proteína biotini<strong>la</strong>da <strong>de</strong> 66 kDa<br />
(L<strong>en</strong> c 2). Proteínas homólogas han sido <strong>de</strong>scritas <strong>en</strong> guisante<br />
y otras especies.<br />
La pres<strong>en</strong>cia <strong>de</strong> homólogos para ambos tipos <strong>de</strong> alerg<strong>en</strong>os<br />
<strong>en</strong> otras especies <strong>de</strong> leguminosas pue<strong>de</strong> explicar <strong>la</strong>s reactivida<strong>de</strong>s<br />
cruzadas observadas 33,34 .<br />
AGRADECIMIENTOS<br />
Los autores <strong>de</strong>sean reconocer <strong>la</strong>s aportaciones <strong>de</strong> los<br />
sigui<strong>en</strong>tes investigadores: Drs. A. Arm<strong>en</strong>tia (Hospital Río<br />
Hortega, Val<strong>la</strong>dolid), L. Gómez (E.T.S. Ing<strong>en</strong>ieros <strong>de</strong> Montes,<br />
UPM), D. Barber (ALK-Abelló, Madrid) e I. Moneo<br />
(Instituto <strong>de</strong> Salud Carlos III, Madrid), <strong>en</strong> el caso <strong>de</strong> los<br />
inhibidores <strong>de</strong> α-ami<strong>la</strong>sa/tripsina <strong>de</strong> cereales y su re<strong>la</strong>ción<br />
con asmas ocupacionales y <strong>alergia</strong> alim<strong>en</strong>taria; Drs. C.<br />
B<strong>la</strong>nco y T. Carrillo (Hospital Dr Negrín, Las Palmas <strong>de</strong><br />
Gran Canaria), y C. Aragoncillo y C. Col<strong>la</strong>da (E.T.S. Ing<strong>en</strong>ieros<br />
<strong>de</strong> Montes, UPM), <strong>en</strong> <strong>la</strong> i<strong>de</strong>ntificación <strong>de</strong> quitinasas<br />
<strong>de</strong> c<strong>la</strong>se I como panalerg<strong>en</strong>os asociados al síndrome látexfrutas;<br />
Drs. D. Barber y M. Lombar<strong>de</strong>ro (ALK-Abelló,<br />
Madrid), F.J. García Sellés (Hospital Virg<strong>en</strong> <strong>de</strong> <strong>la</strong> Arrixaca,<br />
Murcia), M. Fernán<strong>de</strong>z-Rivas (Hospital Fundación Alcorcón,<br />
Madrid), y J. Fernán<strong>de</strong>z Crespo y J. Rodríguez (Hospital<br />
12 <strong>de</strong> Octubre, Madrid) <strong>en</strong> el establecimi<strong>en</strong>to <strong>de</strong> LTPs
como pot<strong>en</strong>ciales panalerg<strong>en</strong>os vegetales; Drs. C. Pascual y<br />
M. Martín-Esteban (Hospital Infantil La Paz, Madrid) <strong>en</strong> <strong>la</strong><br />
i<strong>de</strong>ntificación <strong>de</strong> alerg<strong>en</strong>os <strong>de</strong> l<strong>en</strong>teja.<br />
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20<br />
S. B. Lehrer, G. Reese*<br />
Research Professor of<br />
Medicine<br />
Section of Clinical<br />
Immunology, Allergy, and<br />
Rheumatology<br />
Departm<strong>en</strong>t of Medicine<br />
Tu<strong>la</strong>ne University School of<br />
Medicine. New Orleans,<br />
EE.UU.<br />
* Paul-Ehrlich-Institut,<br />
Departm<strong>en</strong>t of Allergology<br />
Lang<strong>en</strong>. Germany<br />
Applications of Molecu<strong>la</strong>r Biology in<br />
Food Allergy Allerg<strong>en</strong>s of Animal Origin<br />
INTRODUCTION<br />
das E. Hypers<strong>en</strong>sitivity to members of the botanical or<strong>de</strong>r Fabales<br />
(legumes). J Investig Allergol Clin Immunol 2000; 10: 187-<br />
199.<br />
34. Pascual CY, Crespo JF, Pérez PG, Esteban NM. Food allergy and<br />
intolerance in childr<strong>en</strong>. An update. Eur J Clin Nutr 2000; 54: S75-<br />
S78.<br />
The mortality and morbidity resulting from hypers<strong>en</strong>sitivity reactions to<br />
foods 1 <strong>de</strong>monstrate that food allergy can be a very serious problem. Avoidance, traditionally<br />
recomm<strong>en</strong><strong>de</strong>d as treatm<strong>en</strong>t for food allergies, may not always be possible<br />
since some food products contain compon<strong>en</strong>ts that are seemingly unre<strong>la</strong>ted to<br />
their original source. Furthermore, there is concern about the safety and pot<strong>en</strong>tial<br />
allerg<strong>en</strong>icity of newly <strong>de</strong>veloped transg<strong>en</strong>ic crops 2 since these g<strong>en</strong>etically altered<br />
p<strong>la</strong>nts and their products may contain unknown allerg<strong>en</strong>s 3,4 . Despite r<strong>en</strong>ewned interest<br />
in food allergy, the immunochemical analysis of food allerg<strong>en</strong>s <strong>la</strong>gs behind<br />
that of injected allerg<strong>en</strong>s such as insect v<strong>en</strong>oms and inhaled aeroallerg<strong>en</strong>s such as<br />
poll<strong>en</strong>, dust mites, and cockroaches. Thus, it is important to i<strong>de</strong>ntify and characterize<br />
food allerg<strong>en</strong>s to elucidate the structural features that separate them from nonallerg<strong>en</strong>s<br />
and <strong>de</strong>velop better diagnosis and therapeutic regim<strong>en</strong>s for food allergic<br />
subjects.<br />
GENERAL PROPERTIES OF FOOD ALLERGENS<br />
Although allerg<strong>en</strong>ic foods may contain over 10,000 differ<strong>en</strong>t proteins, only a<br />
few (g<strong>en</strong>erally 10-20) elicit allergic reactions. The structural properties that are responsible<br />
for the allerg<strong>en</strong>icity of a food protein are g<strong>en</strong>erally still poorly <strong>de</strong>fined, although<br />
some broad characteristics of food allerg<strong>en</strong>s have be<strong>en</strong> i<strong>de</strong>ntified. These<br />
inclu<strong>de</strong> abundance of a giv<strong>en</strong> protein in a particu<strong>la</strong>r food; physicochemical properties,<br />
such as molecu<strong>la</strong>r weight (10-70 kD), acidic isoelectric point, and glycosy<strong>la</strong>tion;<br />
and resistance to heat and digestion 5 . Although these characteristics have be<strong>en</strong> associated<br />
with the allerg<strong>en</strong>icity of proteins, some if not all of these properties characterize<br />
a vast number of nonallerg<strong>en</strong>ic proteins as well and thus are not unique to food<br />
allerg<strong>en</strong>s.<br />
Food allerg<strong>en</strong>s frequ<strong>en</strong>tly account for a major fraction of the total protein cont<strong>en</strong>t<br />
within a giv<strong>en</strong> food. For example, the major shrimp allerg<strong>en</strong>, P<strong>en</strong> a 1, accounts<br />
for about 25%-30% of the total shrimp tail muscle protein 6 . An exception to this rule<br />
is the major allerg<strong>en</strong> of codfish Gadus cal<strong>la</strong>rias, Gad c 1; this molecule, i<strong>de</strong>ntified<br />
as parvalbumin, is not a dominant protein in cod muscle 7 . There are three aspects of
molecu<strong>la</strong>r size that may contribute to a protein allerg<strong>en</strong>icity.<br />
First, the molecule must be <strong>la</strong>rge <strong>en</strong>ough to elicit an immune<br />
response; second, it must be a suffici<strong>en</strong>t size for at least two<br />
IgE binding sites to bridge mast cell-bound IgE; third, the protein<br />
must be small <strong>en</strong>ough to cross the gut mucosal membrane<br />
barrier. Most known food allerg<strong>en</strong>s have molecu<strong>la</strong>r weights<br />
betwe<strong>en</strong> 10 and 70 kD, thus fulfilling these requirem<strong>en</strong>ts.<br />
Most allerg<strong>en</strong>s are glycoproteins with an acidic isoelectric<br />
point (pI). However, these characteristics are not<br />
unique to allerg<strong>en</strong>s and many nonallerg<strong>en</strong>ic proteins also<br />
exhibit them. Heat resistance is probably the most common<br />
feature of pot<strong>en</strong>t food allerg<strong>en</strong>s. Although heat <strong>de</strong>naturation<br />
may cause loss of the native protein’s conformation,<br />
pati<strong>en</strong>ts’ IgE antibodies can still react with these<br />
<strong>de</strong>natured food proteins, suggests that the allerg<strong>en</strong>s epitopes<br />
are not <strong>de</strong>p<strong>en</strong><strong>de</strong>nt on the native conformation.<br />
The ability of food allerg<strong>en</strong> to cross the mucosal<br />
membrane of the intestinal tract is most likely an important<br />
feature. As m<strong>en</strong>tioned earlier, size is one parameter in<br />
this context; another may be a resistance to digestion. The<br />
results of one study which used a gastric mo<strong>de</strong>l of mammalian<br />
digestion to study the digestibility of food allerg<strong>en</strong>s<br />
point in this direction 8 . In the study, the digestibility<br />
of allerg<strong>en</strong>s from egg, milk, peanut, soybean, and mustard<br />
Table I. I<strong>de</strong>ntified Major Allerg<strong>en</strong>s of Animal Origin 5,9-11<br />
Applications of Molecu<strong>la</strong>r Biology in Food Allergy Allerg<strong>en</strong>s of Animal Origin<br />
was evaluated. Food allerg<strong>en</strong>s tested resisted digestion for<br />
up to 1 hour, whereas nonallerg<strong>en</strong>s were digested within 1<br />
minute. However, there is still insuffici<strong>en</strong>t information to<br />
conclu<strong>de</strong> that the resistance to digestion is a major property<br />
that characterizes food allerg<strong>en</strong>s since <strong>la</strong>bile proteins<br />
can be allerg<strong>en</strong>ic and not all stable proteins are allerg<strong>en</strong>s.<br />
EXAMPLES OF COMMON FOOD ALLERGEN<br />
OF ANIMAL ORIGIN<br />
Of the eight major common allerg<strong>en</strong>ic foods, 4 (milk, egg,<br />
fish, and crustacea) are <strong>de</strong>rived from animal sources. An additional<br />
eight foods (abalone, beef, chick<strong>en</strong>, cuttlefish, oysters, pork, squid,<br />
and turkey) members of three major food groups (mollusks, fowl,<br />
mammalian meat) have be<strong>en</strong> m<strong>en</strong>tioned as less common allerg<strong>en</strong>ic<br />
foods 9 . Major allerg<strong>en</strong>s that have be<strong>en</strong> sequ<strong>en</strong>ced are summarized<br />
in Table I. The common allerg<strong>en</strong>ic foods of animal origin and their<br />
i<strong>de</strong>ntified allerg<strong>en</strong>s are <strong>de</strong>scribed as follows in more <strong>de</strong>tail.<br />
Cow’s Milk Allerg<strong>en</strong>s<br />
Cow’s milk, a very complex mixture of proteins, is<br />
one of the most common food allerg<strong>en</strong>s. Two major groups<br />
Food Allerg<strong>en</strong> Source Molecu<strong>la</strong>r weight Sequ<strong>en</strong>ce Comm<strong>en</strong>ts<br />
MILK Bos d 8 Bos Tauris (Cow’s Milk) 20-30 kDa C Caesins family of chemically<br />
re<strong>la</strong>ted proteins<br />
Bos d 5 Bos tauris (Cow’s milk) 18 kDa C Beta <strong>la</strong>ctoglobulin<br />
Most abdundant whey protein<br />
EGG Gal d 1 Gallus domesticus (chick<strong>en</strong>) 22.6 kDa C Ovomucoid<br />
Gal d 2 Gallus domesticus (chick<strong>en</strong>) 42.8 kDa C Ovalbumin<br />
Gal d 3 Gallus domesticus (chick<strong>en</strong>) 77.8 kDa C Ovotransferrin, conalbumin<br />
Gal d 4 Gallus domesticus (chick<strong>en</strong>) 16.2 kDa C Lysozyme C<br />
FISH Gad c 1 Gadus cal<strong>la</strong>rias (Baltic Cod) 12.1 kDa C Parvalbumin beta<br />
Sal s 1 Salmo sa<strong>la</strong>r (At<strong>la</strong>ntic salmon) C Parvalbumin<br />
CRUSTACEA Met e 1 Metap<strong>en</strong>aeus <strong>en</strong>sis (greasyback shrimp) 34.0 kDa C Tropomyosin<br />
P<strong>en</strong> a 1 Panaeus aztecus (brown shrimp) 36.0 kDa C Tropomyosin<br />
P<strong>en</strong> i 1 Panaeus indicus (Indian shrimp) 34.0 kDa P Tropomyosin<br />
Hom a 1 Homarus americanus (American lobster) 32.8 kDa C Tropomyosin<br />
Pan s 1 Panulirus stimpsoni (spiny lobster) 32.8 kDa C Tropomyosin<br />
Cha f 1 Charybdis feriatus (crab) 32.8 kDa C Tropomyosin<br />
21
S. B. Lehrer, et al<br />
of cow’s milk proteins, caseins and ß-<strong>la</strong>ctoglobulin, have<br />
be<strong>en</strong> i<strong>de</strong>ntified as major allerg<strong>en</strong>s. The caseins are a family<br />
of chemically re<strong>la</strong>ted proteins. The frequ<strong>en</strong>cy of reactivity<br />
to differ<strong>en</strong>t casein variants has not be<strong>en</strong> systematically studied.<br />
ß-<strong>la</strong>ctoglobulin is a whey protein that composes approximately<br />
20% of total milk proteins. It has a molecu<strong>la</strong>r<br />
weight of 18 kD, and at least six g<strong>en</strong>etic variants have be<strong>en</strong><br />
i<strong>de</strong>ntified. The whey proteins α-<strong>la</strong>ctalbumin and bovine<br />
serum albumin (BSA) have be<strong>en</strong> i<strong>de</strong>ntified as minor cow’s<br />
milk allerg<strong>en</strong>s 9 .<br />
Egg Allerg<strong>en</strong>s<br />
Food allergy to proteins from egg of the domestic chick<strong>en</strong><br />
(Gallus domesticus) is one of the most frequ<strong>en</strong>tly implicated<br />
causes of immediate food allergic reactions of childr<strong>en</strong><br />
in the United States and Europe 12 . Ovomucoid has be<strong>en</strong> i<strong>de</strong>ntified<br />
as the major egg white allerg<strong>en</strong> Gal d 1. It is a glycoprotein<br />
with a molecu<strong>la</strong>r weight of 28 kD and an isoelectric<br />
point of 4.1. Ovalbumin has be<strong>en</strong> i<strong>de</strong>ntified as the major egg<br />
white allerg<strong>en</strong> Gal d 2. It is a monomeric phosphoglycoprotein<br />
with a molecu<strong>la</strong>r weight betwe<strong>en</strong> 43 and 45 kD and an isoelectric<br />
point of 4.5. Ovotransferrin or conalbumin has be<strong>en</strong><br />
i<strong>de</strong>ntified as the major allerg<strong>en</strong> from egg white Gal d 3 with a<br />
molecu<strong>la</strong>r weight of 77 kD and an isoelectric point of 6.0.<br />
Lysozyme (Gal d 4) from egg has a molecu<strong>la</strong>r weight of 14.3<br />
kD and an isoelectric point of 10.7. In addition, a variety of<br />
other egg proteins have be<strong>en</strong> <strong>de</strong>scribed as minor allerg<strong>en</strong>s.<br />
These inclu<strong>de</strong> Ovomucin, Ovoinhibitor, Ovaf<strong>la</strong>voprotein<br />
(ribof<strong>la</strong>vin-binding protein), Apovitell<strong>en</strong>in I, and Apovitell<strong>en</strong>in<br />
VI.<br />
Fish Allerg<strong>en</strong>s<br />
The consumption of fish 13 is a frequ<strong>en</strong>t cause of IgEmediated<br />
reactions. Fish is one among the most commonly<br />
implicated allerg<strong>en</strong>ic foods and has be<strong>en</strong> incriminated in<br />
fatal anaphy<strong>la</strong>ctic reactions. Species-specific analysis of<br />
IgE reactivities has not be<strong>en</strong> performed and most studies<br />
refer only to cod or g<strong>en</strong>erally to fish. One of the first and<br />
most compreh<strong>en</strong>sive analysis of a food allerg<strong>en</strong> was the<br />
purification and characterization of the major codfish<br />
allerg<strong>en</strong>, Gad c 1. Gad c 1, originally <strong>de</strong>signated allerg<strong>en</strong><br />
M, from Baltic cod, Gadus cal<strong>la</strong>rias, has be<strong>en</strong> docum<strong>en</strong>ted<br />
to be the major codfish allerg<strong>en</strong>. It belongs to a group<br />
of muscle proteins called parvalbumins 7 and constitutes<br />
approximately 0.05% to 0.1% of the white cod muscle tissue.<br />
Minor cod fish allerg<strong>en</strong>s distinct from Gad c 1 were<br />
i<strong>de</strong>ntified by CRIE but have not yet be<strong>en</strong> further characterized.<br />
22<br />
Crustacea Allerg<strong>en</strong>s<br />
The c<strong>la</strong>ss Crustacea belongs to the phylum Arthropoda<br />
and inclu<strong>de</strong>s shrimp, prawns, crabs, lobster, and crawfish.<br />
Crustacea are common causes of hypers<strong>en</strong>sitivity. Like that of<br />
fish allergy, a higher inci<strong>de</strong>nce of crustacea allergy would be<br />
expected in geographic areas where greater amounts of shellfish<br />
are consumed on a regu<strong>la</strong>r basis. A 36 kD allerg<strong>en</strong>, <strong>de</strong>signated<br />
P<strong>en</strong> a 1, was iso<strong>la</strong>ted from boiled brown shrimp, P<strong>en</strong>aeus<br />
aztecus. Sequ<strong>en</strong>cing of a 21 amino acid Lys-C pepti<strong>de</strong> of<br />
P<strong>en</strong> a 1 <strong>de</strong>monstrated significant homology (60%-85%) with<br />
tropomyosin from various species consist<strong>en</strong>t with the conclusion<br />
that P<strong>en</strong> a 1 is tropomyosin 6 . P<strong>en</strong> a 1 constitutes 20% of<br />
the soluble protein and accounts for approximately 80% of<br />
pooled shrimp-allergic sera reactivity to shrimp meat extract.<br />
More than 80% of allergic subjects reacted to this allerg<strong>en</strong> 6 .<br />
P<strong>en</strong> a 1 was cloned and sequ<strong>en</strong>ced; its cDNA sequ<strong>en</strong>ce showed<br />
26 base pair substitutions wh<strong>en</strong> compared with the<br />
sequ<strong>en</strong>ce of Met e 1; these base pair substitutions resulted in<br />
only one amino acid substitution in position 69. Homologous<br />
proteins P<strong>en</strong> i 1, and Met e 1 from Indian shrimp P<strong>en</strong>aeus<br />
indicus and greasyback shrimp Metap<strong>en</strong>aeus <strong>en</strong>sis respectively<br />
have also be<strong>en</strong> studied 14,15 .<br />
EPITOPES IN ALLERGENS OF ANIMAL<br />
ORIGIN: STUDY OF SHRIMP TROPOMYOSIN<br />
Tropomyosin is a major muscle protein pres<strong>en</strong>t in all<br />
living creatures. These molecules appears to be highly conserved<br />
by the substantial amino acid sequ<strong>en</strong>ce i<strong>de</strong>ntity of tropomyosins<br />
from unre<strong>la</strong>ted species. For example, shrimp tropomyosin<br />
amino acid sequ<strong>en</strong>ce shares homology of<br />
approximately 60% with non-allerg<strong>en</strong>ic tropomyosins of vertebrates.<br />
Tropomyosin has a rather unique structure in that it is<br />
composed of two polypepti<strong>de</strong> chains each in alpha helix formation<br />
coiled around one another in the coiled-coil formation<br />
16 . Although the structure of tropomyosin is well known,<br />
little information about its B cell epitopes (IgE-binding epitopes)<br />
and no information about the T cell epitopes was avai<strong>la</strong>ble<br />
until rec<strong>en</strong>tly.<br />
In or<strong>de</strong>r to i<strong>de</strong>ntify areas of the tropomyosin molecule<br />
that contain important IgE binding regions, the following strategy<br />
was used by Ayuso et al 17 . Thirty-six over<strong>la</strong>pping pepti<strong>de</strong>s<br />
(15 amino acids long, offset 6 amino acids) were synthesized<br />
that spanned the <strong>en</strong>tire sequ<strong>en</strong>ce of P<strong>en</strong> a 1, shrimp<br />
tropomyosin allerg<strong>en</strong>. Testing the sera from 18 shrimp-allergic<br />
subjects, reactive to P<strong>en</strong> a 1, these synthetic pepti<strong>de</strong>s were<br />
scre<strong>en</strong>ed for IgE antibody reactivity. Based on the preval<strong>en</strong>ce
and int<strong>en</strong>sity of IgE antibody binding, five major IgE binding<br />
regions were i<strong>de</strong>ntified in shrimp tropomyosin (P<strong>en</strong> a 1) 17 .<br />
Further efforts were directed at i<strong>de</strong>ntification of the IgE binding<br />
epitopes (<strong>de</strong>fined as the smallest sequ<strong>en</strong>ce of amino acids<br />
that yields maximal IgE binding) within each region. The<br />
same system of over<strong>la</strong>pping synthetic pepti<strong>de</strong>s was employed<br />
using shorter pepti<strong>de</strong> l<strong>en</strong>gths with varying sizes to i<strong>de</strong>ntify the<br />
minimal pepti<strong>de</strong> that binds IgE. All pepti<strong>de</strong>s were synthesized<br />
and tested as <strong>de</strong>scribed previously.<br />
Using sera from 3 to 8 shrimp-allergic individuals who<br />
recognized a particu<strong>la</strong>r region, 8 IgE-binding epitopes were<br />
i<strong>de</strong>ntified within the 5 IgE-binding regions of P<strong>en</strong> a 1: epitope<br />
1 in region 1, epitope 2 in region 2, epitopes 3a and 3b in<br />
region 3, epitope 4 in region 4 and epitopes 5a, 5b and 5c in<br />
region 5 18 . In some cases the same epitope was recognized<br />
with maximal int<strong>en</strong>sity by all subjects showing IgE reactivity<br />
to a certain region. In other cases, a common sequ<strong>en</strong>ce was<br />
i<strong>de</strong>ntified (common core), recognized by all subjects tested to<br />
that particu<strong>la</strong>r region but the l<strong>en</strong>gth of the whole epitope<br />
recognized pres<strong>en</strong>ted personal variability. IgE binding sites<br />
varied from 8 to 15 amino acid long pepti<strong>de</strong>s, <strong>de</strong>p<strong>en</strong>ding on<br />
the region and the subject studied.<br />
MOLECULAR BASIS AND CLINICAL<br />
SIGNIFICANCE OF CROSS-REACTIVITIES<br />
OF FOOD ALLERGENS OF ANIMAL ORIGIN<br />
Cross-reactivities are found among foods of re<strong>la</strong>ted phylog<strong>en</strong>etic<br />
origin and betwe<strong>en</strong> foods and seemingly unre<strong>la</strong>ted<br />
nonfood allerg<strong>en</strong>s. Milk, eggs, crustacea and fishes are examples<br />
of phylog<strong>en</strong>etically re<strong>la</strong>ted cross-reacting allerg<strong>en</strong>s existing<br />
in certain food families. Nonfood allerg<strong>en</strong>s that crossreact<br />
with foods <strong>de</strong>rived from animals are insects and dust<br />
mites 19 . The origin of food allerg<strong>en</strong> cross-reactivity is still not<br />
clear. The clinical relevance of food allerg<strong>en</strong> cross-reactivity<br />
<strong>de</strong>p<strong>en</strong>ds on the food in question. For example, cross-reactivities<br />
among crustacea are thought to be clinically relevant, since<br />
shrimp allergic subjects can react with crawfish, lobster and<br />
crab; however, although the reactivity to differ<strong>en</strong>t fishes by<br />
RAST and skin test suggests cross-reactivity, the majority of<br />
fish-allergic subjects can eat other fish species or do not react<br />
during food chall<strong>en</strong>ge 20,21 , indicating that the in vitro crossreactivity<br />
may be of limited clinical relevance.<br />
The substantial cross-reactivity among Crustacea appears<br />
to be clinically important 22 ; shrimp-allergic subjects can<br />
react to other crustaceans without additional s<strong>en</strong>sitization. The<br />
cause of this cross-reactivity is probably due to the major<br />
Applications of Molecu<strong>la</strong>r Biology in Food Allergy Allerg<strong>en</strong>s of Animal Origin<br />
allerg<strong>en</strong> tropomyosin, a highly conserved muscle protein.<br />
Allerg<strong>en</strong>ic tropomyosin (P<strong>en</strong> a 1, P<strong>en</strong> i 1, and Met e 1) has<br />
be<strong>en</strong> i<strong>de</strong>ntified in three shrimp species: brown shrimp (P<strong>en</strong>aeus<br />
aztecus) 6 , Indian shrimp (P. indicus) 14 , and greasyback<br />
shrimp (Metap<strong>en</strong>aeus <strong>en</strong>sis) 15 . P<strong>en</strong> a 1-like proteins were<br />
<strong>de</strong>tected in crab, crawfish, and lobster using sera of shrimpallergic<br />
subjects and P<strong>en</strong> a 1-specific monoclonal antibodies 23 .<br />
The amino acid sequ<strong>en</strong>ce simi<strong>la</strong>rity among these differ<strong>en</strong>t<br />
shrimp tropomysosins is very high; for example, the amino<br />
acid sequ<strong>en</strong>ces of Met e 1 and P<strong>en</strong> a 1 only differ in one position.<br />
Inspite of the substantial cross reactivity among p<strong>la</strong>nt<strong>de</strong>rived<br />
allerg<strong>en</strong>s or among animal <strong>de</strong>rived allerg<strong>en</strong>s as <strong>de</strong>scribed<br />
above, there is little if any reports of cross reactivity betwe<strong>en</strong><br />
p<strong>la</strong>nt <strong>de</strong>rived and animal <strong>de</strong>rived allerg<strong>en</strong>s. Certainly from a<br />
phylog<strong>en</strong>etic and structural viewpoint, this makes s<strong>en</strong>se.<br />
Assessm<strong>en</strong>t of IgE antibody reactivity to foods and its<br />
re<strong>la</strong>tionship to specific food-allergic responses may be complicated<br />
by cross-reactivity that can occur among certain food<br />
families and betwe<strong>en</strong> foods and seemingly unre<strong>la</strong>ted allerg<strong>en</strong>s.<br />
Based on the fact that tropomyosin allerg<strong>en</strong>s have be<strong>en</strong> i<strong>de</strong>ntified<br />
in invertebrates such as cockroaches, dust mites, and<br />
shrimp, IgE antibody reactivity to the major shrimp allerg<strong>en</strong><br />
P<strong>en</strong> a 1 was assessed in an unexposed popu<strong>la</strong>tion of Orthodox<br />
Jews who observe Kosher dietary <strong>la</strong>ws that prohibit eating<br />
shellfish 24 . Sera from 9 subjects reporting to an allergy clinic<br />
located in a strictly orthodox town (Bnay Braq, Israel), who<br />
<strong>de</strong>monstrated positive skin tests to shrimp extract, were selected<br />
for study. Subjects were strictly observant with no prior<br />
exposure to seafood (regar<strong>de</strong>d as non-Kosher). Six/9 reported<br />
symptoms of asthma, atopic <strong>de</strong>rmatitis, rhinitis and/or sinusitis.<br />
All had positive skin prick tests to shrimp (P<strong>en</strong>aeus setiferous),<br />
and dust mite (Dematophagoi<strong>de</strong>s farinae, Dematophagoi<strong>de</strong>s<br />
pteronissynus or both); 2/7 subjects tested for<br />
cockroach (mix of B<strong>la</strong>ttel<strong>la</strong> germanica and Perip<strong>la</strong>neta americana)<br />
were found positive.<br />
All sera were tested for IgE antibody reactivity to<br />
shrimp and the major shrimp allerg<strong>en</strong> P<strong>en</strong> a 1 by radioallergosorb<strong>en</strong>t<br />
test (RAST) and immunoblot assay (IB). Crossreactivity<br />
of mite and/or cockroach with shrimp allerg<strong>en</strong>s was<br />
assessed by RAST and immunoblot inhibition assays. Three/9<br />
subjects <strong>de</strong>monstrated positive IgE antibody responses to both<br />
shrimp (RAST 7.0 to 15.2%), and to P<strong>en</strong> a 1 (6.3% to 24.1%).<br />
Significant IgE reactivity to P<strong>en</strong> a 1 and to mite extract was<br />
<strong>de</strong>monstrated in the 3 sera by IB. IgE binding to P<strong>en</strong> a 1 was<br />
inhibited with either mite or cockroach extracts as <strong>de</strong>monstrated<br />
by both RAST (Table II) and IB inhibition analysis. These<br />
studies indicate that IgE antibody reactivity to a major food<br />
23
S. B. Lehrer, et al<br />
Table II. Inhibition of P<strong>en</strong> a 1 IgE reactivity<br />
allerg<strong>en</strong>, shrimp, can occur in an unexposed popu<strong>la</strong>tion of<br />
individuals; subjects allergic to house dust mite and/or cockroach<br />
show substantial reactivity to the major shrimp allerg<strong>en</strong><br />
P<strong>en</strong> a 1 (tropomyosin). Based on inhibition with cockroach<br />
and/or dust mite extracts, this reactivity appears to be due<br />
to exposure to cross-reacting tropomyosins in indoor aeroallerg<strong>en</strong>s.<br />
This observation suggests that individuals may become<br />
inadvert<strong>en</strong>tly s<strong>en</strong>sitized to certain foods without prior<br />
exposure. Furthermore, it may exp<strong>la</strong>in the fact that many skin<br />
test positive individuals do not necessarily <strong>de</strong>velop clinically<br />
significant allergic reactivity to foods.<br />
SUMMARY AND CONCLUSIONS<br />
Although the mortality and morbidity resulting from<br />
food allergy can be quite serious, avoidance has be<strong>en</strong> traditionally<br />
the only recomm<strong>en</strong><strong>de</strong>d treatm<strong>en</strong>t. In<strong>de</strong>ed, our un<strong>de</strong>rstanding<br />
of the immunopathog<strong>en</strong>esis of ev<strong>en</strong>ts leading to induction<br />
of a food allergic reaction, and the molecu<strong>la</strong>r structure of<br />
those molecules, inducing such reactions has only rec<strong>en</strong>tly<br />
begun to be un<strong>de</strong>rstood. Of the 8 major food types or groups<br />
that cause food induced allergic reactions, 4 are of animal origin.<br />
In addition, there are some reports of other groups of animals,<br />
namely mollusks, meat of mammals, and avian meat<br />
that also may cause allergic reactions. In spite of the <strong>la</strong>ck of<br />
interest in the past concerning food allerg<strong>en</strong>s, rec<strong>en</strong>tly there<br />
has be<strong>en</strong> r<strong>en</strong>ewed efforts in better un<strong>de</strong>rstanding the structure<br />
24<br />
Inhibitor % Inhibition<br />
Allerg<strong>en</strong> Conc<strong>en</strong>tration (µg/ml) Orthodox Jews Shrimp Allergic Subjects<br />
White Shrimp 10 105.7 102.8<br />
(Panaeus setiferus) 1 90.3 92.8<br />
0.1 61.2 73.5<br />
0.01 53.1 48.6<br />
Dust Mite 800 63.0 82.1<br />
(Dermatophagoi<strong>de</strong>s farinae) 100 12.0 60.1<br />
10 0.0 31.6<br />
American Cockroach 720 95.7 96.8<br />
(Perip<strong>la</strong>neta americana) 100 37.8 53.8<br />
10 15.6 39.3<br />
Peanut 800 2.3 0.0<br />
of these molecules in re<strong>la</strong>tionship to <strong>de</strong>veloping improved<br />
diagnostic and therapeutic regim<strong>en</strong>s. The adv<strong>en</strong>t of molecu<strong>la</strong>r<br />
biology and its application to studies of food allerg<strong>en</strong>s has helped<br />
advance our knowledge. The major codfish allerg<strong>en</strong>, Gad<br />
c 1, was the first allerg<strong>en</strong> to be thoroughly investigated in the<br />
premolecu<strong>la</strong>r biology era 7 . The allerg<strong>en</strong> structure was accurately<br />
<strong>de</strong>termined, and the epitopes to which IgE antibodies bind<br />
i<strong>de</strong>ntified. This project occurred over a period of approximately<br />
5 years in contrast to curr<strong>en</strong>t allerg<strong>en</strong> i<strong>de</strong>ntification and<br />
characterization studies that now take months rather than years<br />
to complete.<br />
As an example of characterization of a major food allerg<strong>en</strong><br />
from an animal source, we reviewed our investigations of<br />
the major shrimp allerg<strong>en</strong>, shrimp tropomyosin. The i<strong>de</strong>ntification<br />
of eight IgE binding epitopes in this molecule and the<br />
fact that tropomyosin may be an important inha<strong>la</strong>nt allerg<strong>en</strong> in<br />
house dust mite and cockroach may exp<strong>la</strong>in our finding that<br />
an unexposed popu<strong>la</strong>tion of orthodox Jews has reactivity to<br />
shrimp tropomyosin. Most likely this is due to cross reactivity<br />
betwe<strong>en</strong> invertebrate tropomyosins since these individuals are<br />
also allergic to house dust mite, and cockroach. This observation<br />
is very important since it may exp<strong>la</strong>in the fact that some<br />
pati<strong>en</strong>ts who are skin test positive to a variety of foods, do not<br />
necessarily have clinical reactivity. It also suggests that perhaps<br />
we may need to further elevate the level by which allerg<strong>en</strong><br />
reactivity is measured. Could those epitopes to which<br />
pati<strong>en</strong>ts react <strong>de</strong>termine the course of their disease? It is possible<br />
that the affinity and/or spacial configuration of epitopes
to which IgE reacts affects the occurr<strong>en</strong>ce or severity of allergic<br />
diseases? The application of molecu<strong>la</strong>r biology to the<br />
study of food allerg<strong>en</strong>s of animal origin will help us further<br />
elucidate this.<br />
ACKNOWLEDGEMENT<br />
The authors wish to thank Pat Constance and Patricia<br />
Kirsch Duboue in preparation of this manuscript. Support for<br />
writing this article was provi<strong>de</strong>d by the National Fisheries Institute<br />
and the Departm<strong>en</strong>t of Medicine, Tu<strong>la</strong>ne University<br />
School of Medicine.<br />
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14. Shatin KN, Martin BM, Nagpal S, Metcalfe DD, Sabba-Rao PV.<br />
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press.<br />
Pot<strong>en</strong>cial diagnóstico <strong>de</strong> los alerg<strong>en</strong>os<br />
purificados <strong>de</strong> alim<strong>en</strong>tos<br />
La r<strong>en</strong>tabilidad diagnóstica <strong>de</strong> <strong>la</strong>s pruebas in vivo e in vitro realizadas<br />
con alim<strong>en</strong>tos vegetales (especialm<strong>en</strong>te frutas y hortalizas) es baja,<br />
si<strong>en</strong>do uno <strong>de</strong> los factores cruciales <strong>la</strong> calidad <strong>de</strong> los extractos empleados.<br />
En <strong>la</strong> última década se ha producido un gran avance <strong>en</strong> el conocimi<strong>en</strong>to <strong>de</strong><br />
los alerg<strong>en</strong>os <strong>de</strong> alim<strong>en</strong>tos vegetales, habiéndose i<strong>de</strong>ntificado, clonado y se-<br />
25
M. Fernán<strong>de</strong>z-Rivas<br />
cu<strong>en</strong>ciado un notable número <strong>de</strong> proteínas alergénicas. Sin<br />
embargo, por el mom<strong>en</strong>to, esto no ha redundado <strong>en</strong> una<br />
mejora <strong>de</strong> <strong>la</strong>s pruebas diagnósticas accesibles al alergólogo.<br />
En <strong>la</strong> actualidad, <strong>en</strong> <strong>la</strong> Unidad <strong>de</strong> Alergia <strong>de</strong> <strong>la</strong> Fundación<br />
Hospital Alcorcón, estamos llevando a cabo un trabajo<br />
<strong>de</strong> investigación (FIS 00/0179) sobre <strong>la</strong> utilidad diagnóstica<br />
<strong>de</strong> los alerg<strong>en</strong>os purificados <strong>de</strong> melocotón. La base<br />
ci<strong>en</strong>tífica y los resultados iniciales con el alerg<strong>en</strong>o mayor<br />
<strong>de</strong> melocotón Pru p 3 (proteína transportadora <strong>de</strong> lípidos)<br />
aplicado <strong>en</strong> pruebas cutáneas, son el objeto <strong>de</strong> esta pres<strong>en</strong>tación.<br />
PROBLEMÁTICA ACTUAL EN EL<br />
DIAGNÓSTICO<br />
DE LA ALERGIA A FRUTAS<br />
La <strong>alergia</strong> a frutas frescas es <strong>la</strong> causa más frecu<strong>en</strong>te<br />
<strong>de</strong> <strong>alergia</strong> a alim<strong>en</strong>tos <strong>en</strong> paci<strong>en</strong>tes adultos 1-3 . Las más frecu<strong>en</strong>tem<strong>en</strong>te<br />
implicadas son <strong>la</strong>s pert<strong>en</strong>eci<strong>en</strong>tes a <strong>la</strong> familia<br />
Rosaceae, que compr<strong>en</strong><strong>de</strong> frutas <strong>de</strong> amplio consumo <strong>en</strong><br />
nuestro país como son melocotón, manzana, pera, albaricoque,<br />
cereza y cirue<strong>la</strong>, <strong>en</strong>tre otras 1,2,4 . De todas <strong>la</strong>s rosáceas,<br />
<strong>la</strong> que induce reacciones con mayor frecu<strong>en</strong>cia <strong>en</strong> nuestro<br />
área es el melocotón 4,5 (Fig. 1).<br />
26<br />
1989 paci<strong>en</strong>tes mayores <strong>de</strong> 14 años estudiados<br />
76 alérgicos a alim<strong>en</strong>tos<br />
76/1989 = 3,82%<br />
57 alérgicos a frutas<br />
57/76 = 75%<br />
39 alérgicos a rosáceas<br />
(>90% melocotón)<br />
39/57 = 68,42%<br />
39/1989 = 1,96%<br />
Fig. 1. Frecu<strong>en</strong>cia <strong>de</strong> <strong>alergia</strong> a rosáceas. Datos <strong>de</strong> <strong>la</strong> Unidad <strong>de</strong><br />
Alergia <strong>de</strong>l Hospital Ntra. Sra. <strong>de</strong> Sonsoles <strong>de</strong> Ávi<strong>la</strong>, años 1996-97.<br />
El diagnóstico se estableció por historia clínica junto con prueba<br />
cutánea y/o CAP y/o provocación oral abierta positiva.<br />
Para llevar a cabo el diagnóstico <strong>de</strong> <strong>alergia</strong> a un alim<strong>en</strong>to<br />
es necesario comprobar que éste es <strong>la</strong> causa <strong>de</strong> los<br />
síntomas referidos por el paci<strong>en</strong>te mediante una prueba <strong>de</strong><br />
provocación, si<strong>en</strong>do <strong>la</strong> mejor prueba diagnóstica <strong>la</strong> provocación<br />
oral doble ciego contro<strong>la</strong>da con p<strong>la</strong>cebo (PODCCP).<br />
A<strong>de</strong>más, es necesario <strong>de</strong>mostrar que existe un mecanismo<br />
inmunológico subyac<strong>en</strong>te mediado por IgE, mediante <strong>la</strong><br />
realización <strong>de</strong> pruebas cutáneas (PC) y <strong>de</strong>terminación <strong>de</strong><br />
IgE específica sérica 6,7 .<br />
Sin embargo, <strong>en</strong> <strong>la</strong> <strong>alergia</strong> a frutas <strong>la</strong> aplicación <strong>de</strong><br />
esta metodología ti<strong>en</strong>e unas limitaciones importantes. Las<br />
pruebas diagnósticas serológicas y cutáneas ti<strong>en</strong><strong>en</strong> una baja<br />
eficacia diagnóstica <strong>de</strong>bido a <strong>la</strong> inestabilidad <strong>de</strong> los alerg<strong>en</strong>os<br />
<strong>de</strong> frutas, y a su importante reactividad cruzada con<br />
otros alim<strong>en</strong>tos y pól<strong>en</strong>es.<br />
La mayoría <strong>de</strong> los alerg<strong>en</strong>os <strong>de</strong> frutas son muy s<strong>en</strong>sibles<br />
a <strong>la</strong> temperatura y pH, y pier<strong>de</strong>n su alerg<strong>en</strong>icidad con<br />
el almac<strong>en</strong>ami<strong>en</strong>to, y durante los procesos habituales <strong>de</strong><br />
extracción 8 . Esto conduce a una rápida <strong>de</strong>gradación y pérdida<br />
<strong>de</strong> <strong>la</strong> actividad biológica, produci<strong>en</strong>do resultados falsam<strong>en</strong>te<br />
negativos. Para subsanarlo se utiliza <strong>la</strong> prueba<br />
cutánea con <strong>la</strong> fruta fresca: el prick-prick 9 . Esta prueba es<br />
<strong>de</strong> realización simple, reproducible, fiable, y ti<strong>en</strong>e una r<strong>en</strong>tabilidad<br />
diagnóstica superior a <strong>la</strong>s PC realizadas con<br />
extractos comerciales 6,7,10-12 (Tab<strong>la</strong> I). Sus principales inconv<strong>en</strong>i<strong>en</strong>tes<br />
son <strong>la</strong> imposibilidad para su estandarización, y <strong>la</strong><br />
<strong>de</strong>p<strong>en</strong><strong>de</strong>ncia <strong>de</strong> <strong>la</strong> disponibilidad <strong>de</strong> <strong>la</strong> fruta, lo que supone<br />
una notable limitación <strong>en</strong> el caso <strong>de</strong> frutas estacionales.<br />
Existe una importante reactividad cruzada <strong>en</strong>tre los<br />
alerg<strong>en</strong>os <strong>de</strong> rosáceas, y <strong>de</strong> éstas con pól<strong>en</strong>es, <strong>la</strong> cual conduce<br />
a frecu<strong>en</strong>tes resultados positivos <strong>en</strong> paci<strong>en</strong>tes tolerantes.<br />
Estos “falsos positivos” son sujetos que aunque pres<strong>en</strong>tan<br />
IgE específica para el alerg<strong>en</strong>o, toleran <strong>la</strong> ingestión<br />
<strong>de</strong> <strong>la</strong> fruta.<br />
En resum<strong>en</strong>, <strong>la</strong> <strong>la</strong>bilidad <strong>de</strong> los alerg<strong>en</strong>os <strong>de</strong> frutas<br />
conduce a una importante pérdida <strong>de</strong> <strong>la</strong> s<strong>en</strong>sibilidad (Se)<br />
(aum<strong>en</strong>to <strong>de</strong>l número <strong>de</strong> falsos negativos), y <strong>la</strong> reactividad<br />
cruzada a una pérdida <strong>de</strong> especificidad (Es) (aum<strong>en</strong>to <strong>de</strong><br />
los falsos positivos) (Fig. 2). En <strong>la</strong> Tab<strong>la</strong> I se recog<strong>en</strong> datos<br />
<strong>de</strong> s<strong>en</strong>sibilidad y especificidad <strong>de</strong> pruebas cutáneas y serológicas<br />
con difer<strong>en</strong>tes frutas. Debido a <strong>la</strong>s limitaciones <strong>de</strong><br />
<strong>la</strong> capacidad diagnóstica <strong>de</strong> estas pruebas el diagnóstico<br />
<strong>de</strong>finitivo so<strong>la</strong>m<strong>en</strong>te se realiza con pruebas <strong>de</strong> provocación,<br />
si<strong>en</strong>do el gold standard <strong>la</strong> PODCCP.<br />
La PODCCP es una técnica compleja, que requiere<br />
gran número <strong>de</strong> personal sanitario y consume mucho tiempo,<br />
lo que limita su uso <strong>en</strong> <strong>la</strong> práctica clínica habitual. La<br />
ya com<strong>en</strong>tada <strong>la</strong>bilidad <strong>de</strong> los alerg<strong>en</strong>os obliga a <strong>la</strong> prepa-
Tab<strong>la</strong> I. S<strong>en</strong>sibilidad (%) <strong>de</strong> <strong>la</strong>s pruebas diagnósticas <strong>en</strong> <strong>la</strong> <strong>alergia</strong> a rosáceas<br />
ración <strong>de</strong> <strong>la</strong> fruta y el vehículo <strong>en</strong> el que va escondida,<br />
inmediatam<strong>en</strong>te antes <strong>de</strong> <strong>la</strong> administración al paci<strong>en</strong>te. El<br />
disponer <strong>de</strong> ciertas frutas so<strong>la</strong>m<strong>en</strong>te durante unos meses al<br />
año constituye un inconv<strong>en</strong>i<strong>en</strong>te adicional. Por todas estas<br />
razones, <strong>la</strong> PODCCP se utiliza casi exclusivam<strong>en</strong>te con<br />
fines <strong>de</strong> investigación. A<strong>de</strong>más, el diagnóstico se basa <strong>en</strong> <strong>la</strong><br />
inducción <strong>de</strong> una reacción alérgica (bajo condiciones contro<strong>la</strong>das),<br />
cuya int<strong>en</strong>sidad no es pre<strong>de</strong>cible. Sería, por tanto,<br />
<strong>de</strong>seable disponer <strong>de</strong> una técnica diagnóstica fácil <strong>de</strong><br />
realizar, ex<strong>en</strong>ta <strong>de</strong> riesgos, y eficaz.<br />
Pot<strong>en</strong>cial diagnóstico <strong>de</strong> los alerg<strong>en</strong>os purificados <strong>de</strong> alim<strong>en</strong>tos<br />
Serie Fruta Prick-prick Prick test con IgE específica<br />
Fruta fresca extracto comercial sérica<br />
Orto<strong>la</strong>ni et al. 2 Melocotón 86 11 59<br />
Manzana 84 4 70<br />
Orto<strong>la</strong>ni et al. 10 Melocotón 59 14 –<br />
Manzana 81 2 70<br />
Pera 43 0 –<br />
Cuesta et al. 11 Melocotón 100 4; 5; 13; 74<br />
Rodríguez et al. 12 Melocotón 71 – 68<br />
Manzana 53 – 65<br />
Pera 53 – 29<br />
Albaricoque 41 – 53<br />
Cirue<strong>la</strong> 56 – 47<br />
Fresa 38 – 41<br />
Fig. 2.<br />
Prueba<br />
diagnóstica<br />
Diagnóstico (gold standard)<br />
+<br />
–<br />
+<br />
–<br />
a b<br />
c d<br />
n 1<br />
a: verda<strong>de</strong>ros positivos<br />
b: falsos positivos<br />
c: falsos negativos<br />
d: verda<strong>de</strong>ros negativos<br />
n 2<br />
m 1<br />
m 2<br />
T<br />
S<strong>en</strong>sibilidad (Se): a/n 1<br />
Especificidad (Es): d/n 2<br />
Efici<strong>en</strong>cia: a+d/T<br />
ALERGENOS DE ROSÁCEAS<br />
Los principales alerg<strong>en</strong>os hasta ahora implicados <strong>en</strong><br />
<strong>la</strong> <strong>alergia</strong> a rosáceas son <strong>la</strong>s proteínas homólogas <strong>de</strong> Bet<br />
v 1, <strong>la</strong>s profilinas, y <strong>la</strong>s proteínas transportadoras <strong>de</strong> lípidos<br />
(PTL). Proteínas <strong>de</strong> estos tres grupos han sido clonadas<br />
y secu<strong>en</strong>ciadas <strong>en</strong> difer<strong>en</strong>tes frutas y pól<strong>en</strong>es. Se ha<br />
podido <strong>de</strong>mostrar que <strong>de</strong>ntro <strong>de</strong> cada grupo ti<strong>en</strong><strong>en</strong> una<br />
homología importante <strong>en</strong> sus secu<strong>en</strong>cias <strong>de</strong> aminoácidos,<br />
lo que explica <strong>la</strong> reactividad cruzada a nivel <strong>de</strong> epítopos<br />
IgE.<br />
La <strong>alergia</strong> a rosáceas <strong>en</strong> los países <strong>de</strong>l C<strong>en</strong>tro y Norte<br />
<strong>de</strong> Europa, zonas ricas <strong>en</strong> abedules, se asocia a <strong>la</strong> polinosis<br />
<strong>de</strong> abedul. Esto es <strong>de</strong>bido a que <strong>en</strong> esas frutas se<br />
expresan unas proteínas altam<strong>en</strong>te alergénicas re<strong>la</strong>cionadas<br />
con <strong>la</strong> patogénesis (proteínas PR), que pres<strong>en</strong>tan una alta<br />
homología <strong>en</strong> sus secu<strong>en</strong>cias con el Bet v 1, alerg<strong>en</strong>o<br />
mayor <strong>de</strong>l pol<strong>en</strong> <strong>de</strong> abedul. Los alerg<strong>en</strong>os homólogos <strong>de</strong><br />
Bet v 1 están implicados <strong>en</strong> más <strong>de</strong>l 90% <strong>de</strong> los paci<strong>en</strong>tes<br />
alérgicos a rosáceas <strong>de</strong>l Norte y C<strong>en</strong>tro <strong>de</strong> Europa 13-18 . En<br />
esta zona <strong>la</strong> rosácea más inductora <strong>de</strong> reacciones es <strong>la</strong> manzana,<br />
<strong>de</strong>bido a <strong>la</strong> alta homología <strong>en</strong>tre Bet v 1 y Mal d 1,<br />
el alerg<strong>en</strong>o mayor <strong>de</strong> manzana. Sin embargo, <strong>en</strong> <strong>la</strong> zona<br />
C<strong>en</strong>tro <strong>de</strong> España, área virtualm<strong>en</strong>te <strong>de</strong>sprovista <strong>de</strong> abedules,<br />
<strong>la</strong> s<strong>en</strong>sibilización a Bet v 1 se <strong>de</strong>tecta <strong>en</strong> m<strong>en</strong>os <strong>de</strong>l<br />
10% <strong>de</strong> los alérgicos a rosáceas 19,20 .<br />
Otro alerg<strong>en</strong>o implicado <strong>en</strong> <strong>la</strong> <strong>alergia</strong> a rosáceas es <strong>la</strong><br />
profilina, proteína altam<strong>en</strong>te conservada, pres<strong>en</strong>te <strong>en</strong> todas<br />
<strong>la</strong>s célu<strong>la</strong>s eucariotas, que forma complejos con <strong>la</strong> actina<br />
(profi<strong>la</strong>ctina). La profilina se comporta como alerg<strong>en</strong>o <strong>en</strong><br />
27
M. Fernán<strong>de</strong>z-Rivas<br />
pól<strong>en</strong>es y <strong>en</strong> una gran variedad <strong>de</strong> alim<strong>en</strong>tos <strong>de</strong> orig<strong>en</strong><br />
vegetal, incluy<strong>en</strong>do <strong>la</strong>s frutas rosáceas 21-23 . Su importancia<br />
también varía con el área geográfica. En los paci<strong>en</strong>tes<br />
alérgicos a pol<strong>en</strong> <strong>de</strong> abedul y rosáceas <strong>de</strong>l C<strong>en</strong>tro y Norte<br />
<strong>de</strong> Europa <strong>la</strong> profilina es un alerg<strong>en</strong>o m<strong>en</strong>or (
<strong>en</strong>ing para <strong>de</strong>tectar s<strong>en</strong>sibilización a melocotón. A cualquier<br />
punto <strong>de</strong> corte, <strong>la</strong> Se <strong>de</strong> <strong>la</strong> PC con Pru p 3 es inferior<br />
a <strong>la</strong> <strong>de</strong>l prick-prick, pero <strong>la</strong> Es es c<strong>la</strong>ram<strong>en</strong>te superior. Respecto<br />
al CAP <strong>la</strong>s difer<strong>en</strong>cias <strong>en</strong> Se y Es son m<strong>en</strong>os marcadas.<br />
Es notable <strong>la</strong> alta Es (92%) <strong>de</strong> <strong>la</strong> PC con Pru p 3 cuando<br />
se consi<strong>de</strong>ra positivo un tamaño igual o superior al<br />
control <strong>de</strong> histamina: el VPP es <strong>de</strong>l 92%, <strong>de</strong> manera que<br />
so<strong>la</strong>m<strong>en</strong>te 8 <strong>de</strong> cada 100 paci<strong>en</strong>tes diagnosticados <strong>de</strong> <strong>alergia</strong><br />
sin PODCCP estarían mal c<strong>la</strong>sificados. La baja Se<br />
(33%) a ese nivel imposibilita su uso como scre<strong>en</strong>ing <strong>de</strong><br />
s<strong>en</strong>sibilización. Globalm<strong>en</strong>te, <strong>la</strong> efici<strong>en</strong>cia <strong>de</strong> <strong>la</strong> PC con Pru<br />
p 3, es <strong>de</strong>cir <strong>la</strong> capacidad para c<strong>la</strong>sificar correctam<strong>en</strong>te a<br />
los paci<strong>en</strong>tes como verda<strong>de</strong>ros positivos y negativos, <strong>de</strong>crece<br />
al subir el punto <strong>de</strong> corte (61%, 59%, 50%).<br />
La utilización <strong>de</strong> Pru p 3 <strong>en</strong> el diagnóstico <strong>de</strong> <strong>la</strong> <strong>alergia</strong><br />
a melocotón ti<strong>en</strong>e <strong>la</strong> v<strong>en</strong>taja <strong>de</strong> que pue<strong>de</strong> ser estandarizado<br />
y ofrecer una alta reproducibilidad, características que<br />
<strong>la</strong> fruta fresca y los extractos hasta ahora comercializados<br />
no pres<strong>en</strong>tan. A<strong>de</strong>más, su disponibilidad durante todo el año<br />
está garantizada. A <strong>la</strong> luz <strong>de</strong> los datos <strong>de</strong> que ahora disponemos,<br />
<strong>la</strong> PC con Pru p 3 no parece ofrecer v<strong>en</strong>tajas <strong>en</strong> Se,<br />
pero su superior Es es atractiva. La conc<strong>en</strong>tración <strong>de</strong> Pru p<br />
3 testada <strong>de</strong>mostró una Se superior (91%, IC95%: 80%-<br />
98%) <strong>en</strong> un estudio previo 32 . La proce<strong>de</strong>ncia <strong>de</strong> <strong>la</strong> mitad <strong>de</strong><br />
los paci<strong>en</strong>tes allí estudiados <strong>de</strong> un área geográfica difer<strong>en</strong>te<br />
(Murcia), y el no haberse establecido el diagnóstico por<br />
PODCCP pue<strong>de</strong>n explicar <strong>la</strong> difer<strong>en</strong>te Se. La Se <strong>de</strong> PC con<br />
conc<strong>en</strong>traciones superiores <strong>de</strong> Pru p 3 está si<strong>en</strong>do investigada<br />
<strong>en</strong> <strong>la</strong> actualidad. Adicionalm<strong>en</strong>te, es necesario ampliar el<br />
tamaño muestral para po<strong>de</strong>r establecer conclusiones <strong>de</strong>finitivas.<br />
La utilización combinada <strong>de</strong> otros alerg<strong>en</strong>os importantes<br />
<strong>en</strong> nuestros paci<strong>en</strong>tes alérgicos al melocotón, como <strong>la</strong><br />
profilina, pue<strong>de</strong> mejorar <strong>la</strong> efici<strong>en</strong>cia diagnóstica.<br />
Pot<strong>en</strong>cial diagnóstico <strong>de</strong> los alerg<strong>en</strong>os purificados <strong>de</strong> alim<strong>en</strong>tos<br />
Tab<strong>la</strong> II. S<strong>en</strong>sibilidad (Se), especificidad (Es) y valores predictivos positivo (VPP) y negativo (VPN), y efici<strong>en</strong>cia (Ef) <strong>de</strong> <strong>la</strong>s<br />
pruebas diagnósticas <strong>en</strong> <strong>la</strong> <strong>alergia</strong> a melocotón<br />
Prueba diagnóstica Punto <strong>de</strong> corte Se (%) Es (%) VPP (%) VPN (%) Ef (%)<br />
Prick-prick 7 mm2 88 15 73 33 67<br />
Melocotón fresco 50% control histamina 79 39 77 42 67<br />
(piel) 100% control histamina 61 62 80 38 61<br />
CAP 0,35 kU/L 58 46 73 30 54<br />
0,70 kU/L 55 62 78 35 57<br />
3,5 kU/L 27 85 82 31 43<br />
Prick test con 7 mm2 61 62 80 38 61<br />
Pru p 3 50% control histamina 55 69 82 38 59<br />
100% control histamina 33 92 92 35 50<br />
AGRADECIMIENTOS<br />
A Rosa Rodríguez Pérez, por su trabajo <strong>en</strong> <strong>la</strong> purificación<br />
<strong>de</strong> Pru p 3, y a Eloína González Mancebo, por el<br />
trabajo clínico realizado. A los Dres. Rosa Sánchez-Monge<br />
y Gabriel Salcedo <strong>de</strong> <strong>la</strong> E.T.S. <strong>de</strong> Ing<strong>en</strong>ieros Agrónomos<br />
<strong>de</strong> Madrid por su ayuda <strong>en</strong> <strong>la</strong> purificación <strong>de</strong> Pru p 3.<br />
A los Dres. Mª Dolores Alonso, Ana Rosado, Miguel<br />
Angel Tejedor y Concepción Vi<strong>la</strong>, <strong>de</strong> <strong>la</strong> Unidad <strong>de</strong> Alergia<br />
<strong>de</strong> <strong>la</strong> FHA por su contribución <strong>en</strong> el estudio clínico. Este<br />
proyecto <strong>de</strong> investigación ha sido financiado con una beca<br />
FIS (00/0179), y ha recibido el Premio a <strong>la</strong> Investigación<br />
KPMG-Fundación Hospital Alcorcón <strong>de</strong>l año 2000.<br />
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Repercusión clínica <strong>de</strong> <strong>la</strong> reactividad<br />
cruzada<br />
INTRODUCCIÓN<br />
D<strong>en</strong>tro <strong>de</strong>l sistema inmunológico, una <strong>de</strong> <strong>la</strong>s características principales <strong>de</strong> los<br />
anticuerpos es su gran especificidad. Sin embargo, se sabe que una <strong>de</strong>terminada IgE
pue<strong>de</strong> reconocer antíg<strong>en</strong>os difer<strong>en</strong>tes. La base etiopatogénica<br />
<strong>de</strong> este hecho está <strong>en</strong> que el anticuerpo reconoce tan solo una<br />
ca<strong>de</strong>na corta <strong>de</strong> aminoácidos <strong>de</strong>l antíg<strong>en</strong>o (son sufici<strong>en</strong>tes<br />
unos 10 aminoácidos para constituir un epítopo), por lo que<br />
basta que dos proteínas se asemej<strong>en</strong> <strong>en</strong> unos cuantos aminoácidos<br />
para que pueda existir reactividad cruzada (RC) <strong>en</strong>tre<br />
el<strong>la</strong>s. Por lo tanto y <strong>de</strong>ntro <strong>de</strong> nuestra especialidad, <strong>en</strong>t<strong>en</strong><strong>de</strong>mos<br />
por RC al reconocimi<strong>en</strong>to <strong>de</strong> distintos antíg<strong>en</strong>os por un<br />
mismo anticuerpo IgE. La RC se <strong>de</strong>muestra <strong>en</strong> <strong>la</strong>boratorio por<br />
experim<strong>en</strong>tos <strong>de</strong> inhibición <strong>de</strong> captación <strong>de</strong> IgE (inhibición <strong>de</strong><br />
ELISA, inhibición <strong>de</strong> inmuno<strong>de</strong>tección, etc.). Si lo que se<br />
quiere es i<strong>de</strong>ntificar a los alerg<strong>en</strong>os responsables <strong>de</strong> <strong>la</strong> RC, se<br />
<strong>de</strong>be recurrir a técnicas más complejas que <strong>en</strong>tran <strong>en</strong> el campo<br />
<strong>de</strong> <strong>la</strong> <strong>biología</strong> molecu<strong>la</strong>r, como por ejemplo a <strong>la</strong> utilización<br />
<strong>de</strong> anticuerpos monoclonales o antíg<strong>en</strong>os recombinantes.<br />
Des<strong>de</strong> el punto <strong>de</strong> vista clínico y c<strong>en</strong>trándonos <strong>en</strong> <strong>la</strong><br />
<strong>alergia</strong> a alim<strong>en</strong>tos, <strong>la</strong> RC se traduce <strong>en</strong> <strong>alergia</strong>s asociadas<br />
<strong>de</strong> forma estadísticam<strong>en</strong>te significativa. Por ejemplo, los<br />
paci<strong>en</strong>tes alérgicos a gambas suel<strong>en</strong> serlo también a <strong>la</strong>ngosta,<br />
si<strong>en</strong>do fácil <strong>de</strong>mostrar <strong>en</strong> <strong>la</strong>boratorio que <strong>de</strong>trás <strong>de</strong><br />
esta <strong>alergia</strong> asociada existe una RC <strong>en</strong>tre los antíg<strong>en</strong>os <strong>de</strong><br />
ambas especies. El problema es más complejo, porque con<br />
frecu<strong>en</strong>cia <strong>la</strong> RC se traduce <strong>en</strong> pruebas cutáneas positivas<br />
que se asocian <strong>de</strong> forma significativa <strong>en</strong> grupos <strong>de</strong> alim<strong>en</strong>tos,<br />
sin que esto t<strong>en</strong>ga trasc<strong>en</strong><strong>de</strong>ncia clínica alguna. En<br />
este caso, se hab<strong>la</strong> <strong>de</strong> s<strong>en</strong>sibilizaciones asociadas, que son<br />
muy frecu<strong>en</strong>tes <strong>en</strong> <strong>alergia</strong> a alim<strong>en</strong>tos. Para complicar mis<br />
el panorama, po<strong>de</strong>mos <strong>de</strong>mostrar RC in vitro que no t<strong>en</strong>ga<br />
ninguna repercusión in vivo, <strong>en</strong> cuyo caso se trataría <strong>de</strong><br />
simples hal<strong>la</strong>zgos <strong>de</strong> <strong>la</strong>boratorio que no se traduc<strong>en</strong> <strong>en</strong><br />
s<strong>en</strong>sibilizaciones o <strong>alergia</strong>s asociadas.<br />
El estudio <strong>de</strong> <strong>la</strong> RC y <strong>de</strong> su repercusión clínica ha<br />
sido uno <strong>de</strong> los temas principales <strong>de</strong> preocupación <strong>en</strong> <strong>alergia</strong><br />
a alim<strong>en</strong>tos a lo <strong>la</strong>rgo <strong>de</strong> los últimos años 1,2 . La reci<strong>en</strong>te<br />
aplicación <strong>de</strong> técnicas <strong>de</strong> <strong>biología</strong> molecu<strong>la</strong>r ha permitido<br />
i<strong>de</strong>ntificar diversos alerg<strong>en</strong>os responsables <strong>de</strong><br />
síndromes clínicos <strong>de</strong> <strong>alergia</strong>s asociadas, que hasta hace<br />
pocos años eran <strong>de</strong> difícil explicación. A continuación se<br />
resum<strong>en</strong> <strong>de</strong> forma sucinta algunos <strong>de</strong> los conceptos básicos<br />
y avances <strong>en</strong> el campo <strong>de</strong> <strong>la</strong> RC <strong>en</strong> <strong>alergia</strong> a alim<strong>en</strong>tos.<br />
LA REACTIVIDAD CRUZADA EN FAMILIAS<br />
DE ALIMENTOS<br />
A priori parece razonable que exista RC <strong>en</strong>tre antíg<strong>en</strong>os<br />
<strong>de</strong> especies filog<strong>en</strong>éticam<strong>en</strong>te cercanas. Por ejemplo,<br />
Repercusión clínica <strong>de</strong> <strong>la</strong> reactividad cruzada<br />
es lógico que una misma IgE reconozca una insulina humana<br />
y otra porcina, habida cu<strong>en</strong>ta <strong>de</strong> <strong>la</strong> gran similitud <strong>en</strong> su<br />
secu<strong>en</strong>cia <strong>de</strong> aminoácidos. La experi<strong>en</strong>cia <strong>en</strong> <strong>alergia</strong> a alim<strong>en</strong>tos<br />
indica que con frecu<strong>en</strong>cia el paci<strong>en</strong>te que sufre<br />
reacciones con un alim<strong>en</strong>to concreto <strong>de</strong> una familia <strong>de</strong>terminada,<br />
suele t<strong>en</strong>er problemas con otros miembros <strong>de</strong> <strong>la</strong><br />
misma familia. Hoy <strong>en</strong> día se conoc<strong>en</strong> varios <strong>de</strong> los alerg<strong>en</strong>os<br />
principales responsables <strong>de</strong> esta RC, que se traduce clínicam<strong>en</strong>te<br />
<strong>en</strong> s<strong>en</strong>sibilización o <strong>alergia</strong> asociada a una familia<br />
<strong>de</strong> alim<strong>en</strong>tos concreta 1,2 .<br />
Des<strong>de</strong> el punto <strong>de</strong> vista práctico, al paci<strong>en</strong>te que pres<strong>en</strong>ta<br />
<strong>alergia</strong> a un miembro <strong>de</strong> una familia alim<strong>en</strong>taria <strong>en</strong> <strong>la</strong><br />
que se sabe que existe RC, se le prohibe el resto <strong>de</strong> los<br />
compon<strong>en</strong>tes <strong>de</strong> dicha familia hasta que por medio <strong>de</strong>l<br />
estudio alergológico se <strong>de</strong>muestra <strong>la</strong> pres<strong>en</strong>cia o aus<strong>en</strong>cia<br />
<strong>de</strong> <strong>alergia</strong> a cada uno <strong>de</strong> ellos. Dicho estudio se basa <strong>en</strong> <strong>la</strong><br />
historia clínica <strong>de</strong> consumo y posible tolerancia a cada uno<br />
<strong>de</strong> los miembros <strong>de</strong> <strong>la</strong> familia <strong>en</strong> cuestión, con fecha posterior<br />
a <strong>la</strong> reacción motivo <strong>de</strong> consulta. La historia clínica<br />
se complem<strong>en</strong>ta con pruebas in vivo e in vitro (prick con<br />
extractos comerciales, prick <strong>en</strong> fresco con los alim<strong>en</strong>tos,<br />
<strong>de</strong>terminación <strong>de</strong> IgE específica) para <strong>de</strong>mostrar <strong>la</strong>s s<strong>en</strong>sibilizaciones<br />
exist<strong>en</strong>tes. Por último y <strong>en</strong> los casos <strong>en</strong> que<br />
esté indicado, <strong>la</strong>s pruebas <strong>de</strong> provocación oral dilucidan <strong>la</strong><br />
tolerancia a aquellos alim<strong>en</strong>tos a los que se ha <strong>de</strong>mostrado<br />
s<strong>en</strong>sibilización 3 .<br />
Es fundam<strong>en</strong>tal recordar que, mi<strong>en</strong>tras que <strong>la</strong> aus<strong>en</strong>cia<br />
<strong>de</strong> s<strong>en</strong>sibilización es un indicador muy fiable <strong>de</strong> tolerancia,<br />
<strong>la</strong> pres<strong>en</strong>cia <strong>de</strong> s<strong>en</strong>sibilización a un <strong>de</strong>terminado<br />
alim<strong>en</strong>to <strong>de</strong>be seguirse <strong>de</strong> una prueba <strong>de</strong> provocación oral<br />
si se quiere <strong>de</strong>terminar si el paci<strong>en</strong>te es o no alérgico al alim<strong>en</strong>to<br />
<strong>en</strong> cuestión. Esto es así por ser muy frecu<strong>en</strong>tes <strong>la</strong>s<br />
s<strong>en</strong>sibilizaciones asintomáticas a alim<strong>en</strong>tos. Por supuesto,<br />
el estudio alergológico <strong>de</strong>scrito <strong>de</strong>be realizarse <strong>en</strong> unida<strong>de</strong>s<br />
capacitadas para ello, es <strong>de</strong>cir, que cu<strong>en</strong>t<strong>en</strong> con el personal,<br />
<strong>la</strong> experi<strong>en</strong>cia y los medios precisos para tratar todo<br />
tipo <strong>de</strong> reacciones alérgicas. Pasamos a <strong>en</strong>umerar brevem<strong>en</strong>te<br />
<strong>la</strong>s RC que con más frecu<strong>en</strong>cia <strong>en</strong>contramos <strong>en</strong><br />
familias <strong>de</strong> alim<strong>en</strong>tos, con m<strong>en</strong>ción a los posibles alerg<strong>en</strong>os<br />
implicados, <strong>en</strong> los casos <strong>en</strong> los que se haya podido<br />
i<strong>de</strong>ntificar (Tab<strong>la</strong> I).<br />
Crustáceos<br />
La RC <strong>en</strong>tre los mariscos es frecu<strong>en</strong>te y bi<strong>en</strong> conocida<br />
4 . Pue<strong>de</strong> implicar no sólo a los crustáceos, sino también<br />
a los cefalópodos y a los bivalvos. Los síntomas abarcan<br />
todo el espectro posible, <strong>de</strong>s<strong>de</strong> reacciones leves hasta <strong>la</strong>s<br />
más graves, si<strong>en</strong>do muy frecu<strong>en</strong>tes <strong>la</strong>s s<strong>en</strong>sibilizaciones<br />
31
C. B<strong>la</strong>nco<br />
Tab<strong>la</strong> I. La reactividad cruzada <strong>en</strong> familias <strong>de</strong> alim<strong>en</strong>tos. Resum<strong>en</strong> <strong>de</strong> <strong>la</strong>s familias implicadas con más frecu<strong>en</strong>cia y <strong>de</strong> los<br />
posibles alerg<strong>en</strong>os responsables<br />
Familia <strong>de</strong> alim<strong>en</strong>tos Alerg<strong>en</strong>os responsables Peso molecu<strong>la</strong>r ~Kd Refer<strong>en</strong>cias<br />
Crustáceos Tropomiosinas 34-36 4-6<br />
Pescados Parvalbúminas 12 7-10<br />
Leguminosas Vicilinas 12-16 11-13<br />
asintomáticas. La base molecu<strong>la</strong>r <strong>de</strong> esta RC estriba <strong>en</strong> <strong>la</strong><br />
tropomiosina, proteína muscu<strong>la</strong>r y alerg<strong>en</strong>o principal <strong>de</strong> <strong>la</strong><br />
gamba 5 . Se han i<strong>de</strong>ntificado tropomiosinas pot<strong>en</strong>cialm<strong>en</strong>te<br />
alergénicas <strong>en</strong> todos los crustáceos investigados, a<strong>de</strong>más <strong>de</strong><br />
<strong>en</strong> moluscos, insectos, ácaros <strong>de</strong>l polvo y nemátodos, s<strong>en</strong>tando<br />
<strong>la</strong> base <strong>de</strong> un síndrome clínico que se m<strong>en</strong>cionará<br />
más a<strong>de</strong><strong>la</strong>nte 6 . Otra proteína muscu<strong>la</strong>r, <strong>la</strong> paramiosina,<br />
podría también jugar un papel.<br />
Pescados<br />
Los pescados son una causa frecu<strong>en</strong>te <strong>de</strong> <strong>alergia</strong> a alim<strong>en</strong>tos<br />
y, a su vez, un c<strong>la</strong>ro ejemplo <strong>de</strong> RC. De hecho, se<br />
ha <strong>de</strong>mostrado <strong>la</strong> exist<strong>en</strong>cia <strong>de</strong> RC clínicam<strong>en</strong>te relevante<br />
<strong>en</strong>tre varias especies <strong>de</strong> pescados 7,8 . El más estudiado <strong>de</strong>s<strong>de</strong><br />
el punto <strong>de</strong> vista antigénico es el baca<strong>la</strong>o, cuyo alerg<strong>en</strong>o<br />
principal Gad c 1 es una parvoalbúmina, proteína transportadora<br />
<strong>de</strong> calcio. La s<strong>en</strong>sibilización a homólogos <strong>de</strong> Gad c<br />
1 parece ser responsable <strong>de</strong> <strong>la</strong> RC <strong>en</strong>tre los distintos pescados<br />
9,10 .<br />
Legumbres<br />
Si bi<strong>en</strong> <strong>la</strong> mayoría <strong>de</strong> los paci<strong>en</strong>tes alérgicos a<br />
cacahuete toleran el resto <strong>de</strong> <strong>la</strong>s legumbres 11 , los alérgicos<br />
a otras leguminosas <strong>de</strong> mayor consumo <strong>en</strong> el área mediterránea,<br />
como por ejemplo <strong>la</strong>s l<strong>en</strong>tejas, suel<strong>en</strong> ser alérgicos<br />
a otros miembros <strong>de</strong> <strong>la</strong> familia 12 . Reci<strong>en</strong>tem<strong>en</strong>te se ha<br />
caracterizado a dos c<strong>la</strong>ses distintas <strong>de</strong> alerg<strong>en</strong>os <strong>en</strong> l<strong>en</strong>tejas<br />
cocidas, posibles responsables <strong>de</strong> <strong>la</strong> RC 13 . L<strong>en</strong> c 1 ha<br />
resultado pert<strong>en</strong>ecer a un grupo <strong>de</strong> proteínas <strong>de</strong> reserva<br />
<strong>de</strong>nominadas vicilinas, mi<strong>en</strong>tras que L<strong>en</strong> c 2 se correspon<strong>de</strong><br />
con una proteína fijadadora <strong>de</strong> biotina específica <strong>de</strong><br />
semil<strong>la</strong>s.<br />
32<br />
Proteínas biotini<strong>la</strong>das 66<br />
Frutos secos Albúminas 2S 9 14, 15<br />
Frutas rosáceas PTL 9 16-18<br />
Cereales Inhibidores <strong>de</strong> <strong>la</strong> α-ami<strong>la</strong>sa 14-16 19, 20<br />
Gliadinas 65<br />
Frutos secos<br />
La <strong>alergia</strong> a cacahuete se asocia significativam<strong>en</strong>te<br />
con <strong>alergia</strong> a frutos secos como <strong>la</strong> avel<strong>la</strong>na y <strong>la</strong> nuez 14 . En<br />
<strong>la</strong> práctica clínica, el paci<strong>en</strong>te con reacción alérgica a un<br />
fruto seco suele mostrar s<strong>en</strong>sibilización a otros frutos<br />
secos, que <strong>en</strong> muchos casos ti<strong>en</strong>e una c<strong>la</strong>ra repercusión clínica.<br />
Sin embargo, por el mom<strong>en</strong>to se <strong>de</strong>sconoc<strong>en</strong> los antíg<strong>en</strong>os<br />
responsables <strong>de</strong> esta RC, si bi<strong>en</strong> se ha <strong>de</strong>mostrado <strong>la</strong><br />
alerg<strong>en</strong>icidad <strong>de</strong> unas proteínas <strong>de</strong> reserva <strong>de</strong>nominadas<br />
albúminas 2S <strong>en</strong> varios frutos secos y semil<strong>la</strong>s comestibles<br />
15 . Estas proteínas podrían dar cu<strong>en</strong>ta <strong>de</strong> <strong>la</strong> RC <strong>en</strong>tre los<br />
distintos frutos secos, así como <strong>en</strong>tre éstos y el cacahuete.<br />
Frutas rosáceas<br />
La <strong>alergia</strong> a frutas rosáceas como el melocotón, el<br />
albaricoque, <strong>la</strong> cirue<strong>la</strong> y <strong>la</strong> cereza, es una asociación bi<strong>en</strong><br />
conocida 16 . La clínica característica es el síndrome <strong>de</strong> <strong>alergia</strong><br />
oral (SAO), sobre todo cuando esta <strong>alergia</strong> se asocia a<br />
polinosis (ver más a<strong>de</strong><strong>la</strong>nte). Sin embargo, <strong>en</strong> el área Mediterránea<br />
se observa con re<strong>la</strong>tiva frecu<strong>en</strong>cia <strong>alergia</strong> a rosáceas<br />
sin polinosis asociada, <strong>en</strong> cuyo caso <strong>la</strong> clínica varía<br />
<strong>de</strong>s<strong>de</strong> SAO hasta reacciones graves 17 . Reci<strong>en</strong>tem<strong>en</strong>te, se ha<br />
<strong>de</strong>mostrado que los alerg<strong>en</strong>os principales reconocidos por el<br />
suero <strong>de</strong> los paci<strong>en</strong>tes alérgicos a rosáceas sin polinosis asociada<br />
son <strong>la</strong>s proteínas trasportadoras <strong>de</strong> lípidos (PTL) 18 .<br />
Cereales<br />
La mayoría <strong>de</strong> los estudios sobre RC <strong>en</strong>tre cereales se<br />
han realizado con suero <strong>de</strong> paci<strong>en</strong>tes con <strong>alergia</strong> respiratoria<br />
por inha<strong>la</strong>ción <strong>de</strong> harinas (asma <strong>de</strong>l pana<strong>de</strong>ro), i<strong>de</strong>ntificándose<br />
como principales alerg<strong>en</strong>os responsables a inhibidores<br />
<strong>de</strong> <strong>la</strong> α-ami<strong>la</strong>sa 19 . Con respecto a <strong>la</strong> ingestión <strong>de</strong>
cereales, parece existir RC al m<strong>en</strong>os <strong>en</strong>tre trigo, cebada y<br />
c<strong>en</strong>t<strong>en</strong>o, habiéndose <strong>de</strong>mostrado reci<strong>en</strong>tem<strong>en</strong>te que una<br />
gliadina <strong>de</strong> trigo reacciona <strong>de</strong> forma cruzada con otras proteínas<br />
<strong>de</strong> cereales 20 .<br />
LOS SÍNDROMES DE REACTIVIDAD<br />
CRUZADA ENTRE AEROALERGENOS<br />
Y ALIMENTOS<br />
L<strong>la</strong>ma po<strong>de</strong>rosam<strong>en</strong>te <strong>la</strong> at<strong>en</strong>ción el hecho <strong>de</strong> que<br />
exista RC <strong>en</strong>tre alerg<strong>en</strong>os <strong>de</strong> especies que no ti<strong>en</strong><strong>en</strong><br />
re<strong>la</strong>ción taxonómica directa <strong>en</strong>tre sí. En los últimos<br />
años, se han <strong>de</strong>scrito varios síndromes <strong>de</strong> <strong>alergia</strong>s asociadas<br />
<strong>en</strong>tre especies distantes, g<strong>en</strong>eralm<strong>en</strong>te <strong>de</strong> aeroalerg<strong>en</strong>os<br />
y alim<strong>en</strong>tos, habiéndose <strong>de</strong>mostrado <strong>la</strong> exist<strong>en</strong>cia<br />
<strong>de</strong> RC <strong>en</strong>tre el<strong>la</strong>s. La aplicación <strong>de</strong> técnicas <strong>de</strong><br />
<strong>biología</strong> molecu<strong>la</strong>r al estudio <strong>de</strong> estos síndromes clínicos<br />
ha permitido i<strong>de</strong>ntificar distintas familias <strong>de</strong> antíg<strong>en</strong>os<br />
que reaccionan <strong>de</strong> forma cruzada, tanto <strong>en</strong> el reino<br />
animal como <strong>en</strong> el vegetal. Reci<strong>en</strong>tem<strong>en</strong>te se ha acuñado<br />
el término panalerg<strong>en</strong>o para <strong>de</strong>finir a estos antíg<strong>en</strong>os,<br />
responsables <strong>de</strong> RC <strong>en</strong>tre diversas especies que no<br />
se re<strong>la</strong>cionan <strong>de</strong> forma directa <strong>en</strong>tre sí 21 . Des<strong>de</strong> el punto<br />
<strong>de</strong> vista clínico, los síndromes <strong>de</strong> <strong>alergia</strong> asociada <strong>en</strong>tre<br />
aeroalerg<strong>en</strong>os y alim<strong>en</strong>tos son <strong>de</strong> difícil diagnóstico y<br />
manejo, si no se conoce una serie <strong>de</strong> conceptos básicos<br />
sobre ellos. Por lo tanto, es fundam<strong>en</strong>tal familiarizarse<br />
con estos síndromes para po<strong>de</strong>r hacer un diagnóstico<br />
correcto y dar unas indicaciones terapéuticas a<strong>de</strong>cuadas.<br />
La i<strong>de</strong>ntificación <strong>de</strong> diversos panalerg<strong>en</strong>os y <strong>la</strong> actual<br />
disponibilidad diagnóstica <strong>de</strong> algunos <strong>de</strong> ellos ha<br />
Repercusión clínica <strong>de</strong> <strong>la</strong> reactividad cruzada<br />
Tab<strong>la</strong> II. Los síndromes <strong>de</strong> reactividad cruzada <strong>en</strong>tre aeroalerg<strong>en</strong>os y alim<strong>en</strong>tos. Resum<strong>en</strong> <strong>de</strong> los alim<strong>en</strong>tos implicados con más<br />
frecu<strong>en</strong>cia y <strong>de</strong> los posibles panalerg<strong>en</strong>os responsables<br />
Síndrome Alim<strong>en</strong>tos implicados Panalerg<strong>en</strong>os responsables Refer<strong>en</strong>cias<br />
Abedul-manzana Manzana, zanahoria, patata, kiwi, otros Familia Bet v 1 21, 25-27<br />
Profilinas<br />
Artemisa-apio- Múltiples alim<strong>en</strong>tos vegetales Profilinas 28, 29<br />
zanahoria-especias ¿Homólogos Art v 1?<br />
Gramíneas-melocotón Rosáceas Profilinas 31, 32<br />
Látex-frutas Aguacate, castaña, plátano, kiwi, otros Quitinasas <strong>de</strong> c<strong>la</strong>se I 34-41<br />
Ácaros-mariscos Crustáceos, moluscos Tropomiosina 6, 42-47<br />
PTL<br />
supuesto un gran avance <strong>en</strong> este s<strong>en</strong>tido. En un futuro<br />
no lejano, será posible <strong>la</strong> aplicación terapéutica <strong>de</strong><br />
dichos panalerg<strong>en</strong>os.<br />
Con respecto a <strong>la</strong> etiopatog<strong>en</strong>ia, los panalerg<strong>en</strong>os suel<strong>en</strong><br />
ser proteínas conservadas por <strong>la</strong> evolución, <strong>de</strong>bido a<br />
que <strong>de</strong>sempeñan una función muy importante <strong>en</strong> <strong>la</strong>s especies<br />
animales o vegetales correspondi<strong>en</strong>tes. Por ejemplo,<br />
los panalerg<strong>en</strong>os hasta ahora i<strong>de</strong>ntificados se <strong>en</strong>cuadran <strong>en</strong><br />
grupos <strong>de</strong> proteínas <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa, proteínas <strong>de</strong>l citoesqueleto<br />
o proteínas muscu<strong>la</strong>res, todas el<strong>la</strong>s con funciones relevantes<br />
22 . Por otra parte, es muy interesante consi<strong>de</strong>rar que<br />
mi<strong>en</strong>tras que los niños se s<strong>en</strong>sibilizan a alim<strong>en</strong>tos por vía<br />
digestiva y <strong>de</strong>bido a un fallo <strong>de</strong>l mecanismo <strong>de</strong> tolerancia<br />
inmunológica, los adultos con <strong>alergia</strong> asociada a aeroalerg<strong>en</strong>os<br />
y alim<strong>en</strong>tos probablem<strong>en</strong>te se s<strong>en</strong>sibilic<strong>en</strong> al panalerg<strong>en</strong>o<br />
por vía respiratoria. Como consecu<strong>en</strong>cia <strong>de</strong> <strong>la</strong> RC<br />
<strong>en</strong>tre el aeroalerg<strong>en</strong>o y los antíg<strong>en</strong>os alim<strong>en</strong>tarios, dicha<br />
s<strong>en</strong>sibilización daría lugar a reacciones alérgicas a <strong>de</strong>terminados<br />
alim<strong>en</strong>tos 23 . A continuación se resum<strong>en</strong> brevem<strong>en</strong>te<br />
algunos <strong>de</strong> los conceptos básicos sobre los síndromes <strong>de</strong><br />
RC <strong>en</strong>tre aeroalerg<strong>en</strong>os y alim<strong>en</strong>tos mejor conocidos (Tab<strong>la</strong><br />
II).<br />
Alergia a alim<strong>en</strong>tos vegetales y polinosis<br />
Una <strong>de</strong> <strong>la</strong>s formas más frecu<strong>en</strong>tes <strong>de</strong> <strong>alergia</strong> a alim<strong>en</strong>tos<br />
<strong>en</strong> paci<strong>en</strong>tes adultos es el SAO por alim<strong>en</strong>tos vegetales<br />
<strong>en</strong> polínicos 24 . Los alim<strong>en</strong>tos implicados con más frecu<strong>en</strong>cia<br />
pert<strong>en</strong>ec<strong>en</strong> a <strong>la</strong>s familias <strong>de</strong> rosáceas y<br />
umbelíferas, mi<strong>en</strong>tras que los pól<strong>en</strong>es habitualm<strong>en</strong>te implicados<br />
son los <strong>de</strong> abedul y <strong>de</strong> artemisa. En <strong>la</strong> mayoría <strong>de</strong> los<br />
casos, los síntomas respiratorios por pól<strong>en</strong>es prece<strong>de</strong>n a <strong>la</strong><br />
aparición <strong>de</strong> <strong>la</strong>s reacciones adversas a alim<strong>en</strong>tos, lo que<br />
33
C. B<strong>la</strong>nco<br />
sugiere que <strong>la</strong> s<strong>en</strong>sibilización primaria es por vía respiratoria.<br />
Con respecto a <strong>la</strong> polinosis por abedul, característica<br />
<strong>de</strong>l norte <strong>de</strong> Europa, es muy frecu<strong>en</strong>te que se asocie con<br />
SAO por manzana y otros alim<strong>en</strong>tos vegetales 25 . Este síndrome<br />
abedul-manzana se basa <strong>en</strong> <strong>la</strong>s familias <strong>de</strong>l Bet v 1<br />
y <strong>de</strong> <strong>la</strong>s profilinas 26 . El Bet v 1 es una proteína <strong>de</strong> <strong>de</strong>f<strong>en</strong>sa<br />
que se comporta como alerg<strong>en</strong>o principal <strong>de</strong>l abedul,<br />
habiéndose <strong>de</strong>mostrado homólogos <strong>en</strong> diversos alim<strong>en</strong>tos<br />
vegetales como <strong>la</strong> manzana 27 . Las profilinas son unas proteínas<br />
<strong>de</strong>l citoesqueleto <strong>de</strong> los eucariotas, ubicuas <strong>en</strong> el reino<br />
vegetal, a <strong>la</strong> cual pert<strong>en</strong>ece el alerg<strong>en</strong>o 2 <strong>de</strong> abedul (Bet<br />
v 2) 21 . Si bi<strong>en</strong> <strong>la</strong> profilina <strong>de</strong> abedul se comporta como un<br />
alerg<strong>en</strong>o m<strong>en</strong>or, el paci<strong>en</strong>te s<strong>en</strong>sibilizado a Bet v 2 suele<br />
mostrar también pruebas cutáneas positivas a pól<strong>en</strong>es <strong>de</strong><br />
gramíneas y malezas, es <strong>de</strong>cir, suele estar polis<strong>en</strong>sibilizado.<br />
Por su parte, <strong>en</strong> el c<strong>en</strong>tro <strong>de</strong> Europa se ha <strong>de</strong>scrito el<br />
síndrome artemisa-apio-zanahoria-especias, que se manifiesta<br />
con clínica variable <strong>de</strong>s<strong>de</strong> SAO hasta reacciones graves<br />
28 . En este caso no están implicados los homólogos a Bet<br />
v 1, <strong>de</strong>l que carece <strong>la</strong> artemisa, mi<strong>en</strong>tras que <strong>la</strong>s profilinas<br />
parec<strong>en</strong> jugar un papel. A<strong>de</strong>más, hay otro grupo <strong>de</strong> antíg<strong>en</strong>os<br />
<strong>de</strong> peso molecu<strong>la</strong>r alto y función <strong>de</strong>sconocida, <strong>en</strong> el<br />
rango <strong>de</strong>l alerg<strong>en</strong>o principal <strong>de</strong> artemisa Art v 1, que podrían<br />
también participar <strong>en</strong> <strong>la</strong> RC 29 . En nuestro medio, dado<br />
que el consumo <strong>de</strong> apio y especias es más limitado que <strong>en</strong><br />
el c<strong>en</strong>tro <strong>de</strong> Europa, no se suele diagnosticar este síndrome.<br />
Sin embargo, es frecu<strong>en</strong>te observar múltiples <strong>alergia</strong>s a alim<strong>en</strong>tos<br />
vegetales (frutos secos, rosáceas, crucíferas, leguminosas)<br />
<strong>en</strong> paci<strong>en</strong>tes polínicos por artemisa, con expresión<br />
clínica variable 30 . También <strong>en</strong> el sur <strong>de</strong> Europa, <strong>la</strong><br />
<strong>alergia</strong> a gramíneas se asocia con SAO por melocotón u<br />
otras rosáceas 31 . Los alerg<strong>en</strong>os responsables <strong>de</strong> esta RC<br />
parec<strong>en</strong> ser <strong>la</strong>s profilinas y <strong>la</strong>s PTL 32 . A<strong>de</strong>más, es frecu<strong>en</strong>te<br />
el SAO por cucurbitáceas <strong>en</strong> polínicos por p<strong>la</strong>ntago o<br />
gramíneas, pudi<strong>en</strong>do estar implicadas <strong>la</strong>s profilinas 33 .<br />
Alergia a látex y frutas<br />
Durante <strong>la</strong> última década, <strong>la</strong> <strong>alergia</strong> mediada por IgE<br />
al látex ha sido reconocida como un problema médico <strong>de</strong><br />
<strong>en</strong>orme trasc<strong>en</strong><strong>de</strong>ncia. Esto es <strong>de</strong>bido al aum<strong>en</strong>to observado<br />
<strong>en</strong> su preval<strong>en</strong>cia, a su pres<strong>en</strong>tación como <strong>en</strong>fermedad<br />
profesional <strong>en</strong>tre trabajadores que usan guantes y a <strong>la</strong> gravedad<br />
pot<strong>en</strong>cial <strong>de</strong> <strong>la</strong>s reacciones que induce. En el año<br />
1994 se <strong>de</strong>scribió <strong>la</strong> exist<strong>en</strong>cia <strong>de</strong> un síndrome látex-frutas,<br />
al evi<strong>de</strong>nciarse una asociación clínica significativa <strong>en</strong>tre<br />
estas <strong>alergia</strong>s 34 . De hecho, diversos estudios han <strong>de</strong>mostrado<br />
que <strong>en</strong>tre un 20% y un 60% <strong>de</strong> los paci<strong>en</strong>tes alérgicos a<br />
látex pres<strong>en</strong>tan reacciones mediadas por IgE a una amplia<br />
34<br />
variedad <strong>de</strong> alim<strong>en</strong>tos, principalm<strong>en</strong>te a frutas como el plátano,<br />
el aguacate, <strong>la</strong> castaña y el kiwi 35 . La variedad y proporción<br />
<strong>de</strong> alim<strong>en</strong>tos implicados varía <strong>en</strong> función <strong>de</strong>l consumo<br />
re<strong>la</strong>tivo <strong>de</strong> los mismos <strong>en</strong> cada zona. Muchos <strong>de</strong> los<br />
paci<strong>en</strong>tes muestran <strong>alergia</strong> simultánea a 3 o más alim<strong>en</strong>tos.<br />
Las manifestaciones clínicas <strong>de</strong> estas reacciones pue<strong>de</strong>n<br />
variar <strong>de</strong>s<strong>de</strong> SAO hasta reacciones anafilácticas. Si bi<strong>en</strong> <strong>la</strong><br />
clínica con látex suele prece<strong>de</strong>r a <strong>la</strong>s reacciones adversas a<br />
alim<strong>en</strong>tos, <strong>en</strong> algunos casos se observa lo contrario.<br />
Reci<strong>en</strong>tem<strong>en</strong>te, se ha logrado caracterizar a algunos <strong>de</strong><br />
los alerg<strong>en</strong>os comunes responsables <strong>de</strong> <strong>la</strong> RC <strong>en</strong>tre el látex<br />
y <strong>la</strong>s frutas. Estos panalerg<strong>en</strong>os han resultado ser quitinasas<br />
<strong>de</strong> c<strong>la</strong>se I, que pose<strong>en</strong> un dominio heveína N-terminal 36 . La<br />
heveína es uno <strong>de</strong> los alerg<strong>en</strong>os principales <strong>de</strong>l látex, al<br />
m<strong>en</strong>os <strong>en</strong> paci<strong>en</strong>tes adultos, por lo que existe RC <strong>en</strong>tre <strong>la</strong>s<br />
quitinasas <strong>de</strong> los alim<strong>en</strong>tos vegetales y <strong>la</strong> heveína <strong>de</strong>l látex 37 .<br />
Hasta el mom<strong>en</strong>to, se ha <strong>de</strong>mostrado <strong>la</strong> exist<strong>en</strong>cia <strong>de</strong> quitinasas<br />
alergénicas <strong>en</strong> castaña, aguacate y plátano, a<strong>de</strong>más <strong>de</strong><br />
<strong>en</strong> otros alim<strong>en</strong>tos implicados <strong>en</strong> el síndrome con m<strong>en</strong>or<br />
frecu<strong>en</strong>cia 38,39 . Puesto que <strong>la</strong>s quitinasas son proteínas <strong>de</strong><br />
<strong>de</strong>f<strong>en</strong>sa <strong>de</strong> los vegetales 40 , su expresión aum<strong>en</strong>ta con <strong>de</strong>terminados<br />
estímulos, como por ejemplo al tratar <strong>la</strong>s p<strong>la</strong>ntas<br />
con óxido <strong>de</strong> etil<strong>en</strong>o 41 . Este producto se emplea para estimu<strong>la</strong>r<br />
cultivos y madurar frutas, por lo que es posible que<br />
<strong>la</strong>s frutas que se consum<strong>en</strong> hoy <strong>en</strong> día t<strong>en</strong>gan un cont<strong>en</strong>ido<br />
alergénico muy superior a <strong>la</strong>s que se consumían años atrás.<br />
Este hecho podría explicar, al m<strong>en</strong>os <strong>en</strong> parte, el aum<strong>en</strong>to<br />
observado <strong>en</strong> <strong>la</strong> preval<strong>en</strong>cia <strong>de</strong>l síndrome látex-frutas. Por el<br />
contrario, el tratami<strong>en</strong>to térmico inactiva <strong>la</strong>s quitinasas, lo<br />
que explica qué alim<strong>en</strong>tos que expresan quitinasas pot<strong>en</strong>cialm<strong>en</strong>te<br />
alergénicas, pero que se suel<strong>en</strong> comer cocinados<br />
(como <strong>la</strong>s judías ver<strong>de</strong>s), no caus<strong>en</strong> problemas clínicos <strong>en</strong><br />
paci<strong>en</strong>tes afectos <strong>de</strong>l síndrome látex-frutas 41 .<br />
Alergia a crustáceos/moluscos y <strong>alergia</strong> respiratoria<br />
a ácaros<br />
Des<strong>de</strong> hace años se sabe que <strong>la</strong> <strong>alergia</strong> respiratoria a ácaros<br />
<strong>de</strong>l polvo se asocia con re<strong>la</strong>tiva frecu<strong>en</strong>cia con <strong>alergia</strong> alim<strong>en</strong>taria<br />
a mariscos 42 . La clínica con mariscos varía <strong>de</strong>s<strong>de</strong><br />
SAO hasta reacciones graves, si<strong>en</strong>do frecu<strong>en</strong>tes <strong>la</strong>s s<strong>en</strong>sibilizaciones<br />
asintomáticas 43 . Más raram<strong>en</strong>te, los paci<strong>en</strong>tes afectos<br />
pres<strong>en</strong>tan reacciones clínicas con moluscos bivalvos o cefalópodos.<br />
A<strong>de</strong>más, estos paci<strong>en</strong>tes suel<strong>en</strong> mostrar prueba cutánea<br />
positiva a cucaracha, cuya significación clínica es incierta 44 .<br />
Tal y como se com<strong>en</strong>tó anteriorm<strong>en</strong>te, <strong>la</strong> tropomiosina<br />
es el panalerg<strong>en</strong>o responsable <strong>de</strong> esta RC 6 . A<strong>de</strong>más <strong>de</strong><br />
ser el alerg<strong>en</strong>o principal <strong>de</strong> <strong>la</strong> gamba, se han i<strong>de</strong>ntificado<br />
tropomiosinas alergénicas <strong>en</strong> otros crustáceos, ácaros <strong>de</strong>l
polvo, insectos, caracoles y nemátodos 45,46 . Por otra parte, se<br />
conoce <strong>la</strong> exist<strong>en</strong>cia <strong>de</strong> RC <strong>en</strong>tre moluscos, crustáceos y<br />
<strong>de</strong>terminados insectos, causada por <strong>de</strong>terminantes carbohidratados<br />
que reaccionan <strong>de</strong> forma cruzada (CCD), si bi<strong>en</strong><br />
su trasc<strong>en</strong><strong>de</strong>ncia clínica es más que dudosa 47 .<br />
Otros síndromes <strong>de</strong> reactividad cruzada<br />
Aunque <strong>en</strong> este caso no se trate <strong>de</strong> RC <strong>en</strong>tre especies<br />
distantes, convi<strong>en</strong>e m<strong>en</strong>cionar otros síndromes <strong>en</strong>cuadrados<br />
<strong>de</strong>ntro <strong>de</strong> <strong>la</strong> RC <strong>en</strong>tre aeroalerg<strong>en</strong>os y alim<strong>en</strong>tos. En primer<br />
lugar, el síndrome ave-huevo, que <strong>de</strong>staca por su trasc<strong>en</strong><strong>de</strong>ncia<br />
clínica 48 . Se caracteriza por <strong>la</strong> asociación <strong>en</strong>tre reacciones<br />
alérgicas por ingestión <strong>de</strong> huevo y <strong>alergia</strong> respiratoria<br />
por inha<strong>la</strong>ción <strong>de</strong> antíg<strong>en</strong>os <strong>de</strong>rivados <strong>de</strong> aves, si<strong>en</strong>do<br />
más frecu<strong>en</strong>te <strong>en</strong> paci<strong>en</strong>tes adultos. Se ha i<strong>de</strong>ntificado a <strong>la</strong><br />
seroalbúmina <strong>de</strong> aves o α-livetina como <strong>la</strong> responsable <strong>de</strong><br />
esta RC 49 .<br />
Del mismo modo, se ha <strong>de</strong>scrito <strong>la</strong> asociación <strong>de</strong> <strong>alergia</strong><br />
respiratoria a animales con reacciones alérgicas por<br />
ingestión <strong>de</strong> carne. Un ejemplo es el síndrome gato-cerdo,<br />
<strong>en</strong> el que paci<strong>en</strong>tes con <strong>alergia</strong> respiratoria a gato pres<strong>en</strong>tan<br />
reacciones por ingestión <strong>de</strong> carne <strong>de</strong> cerdo 50 . En éste y <strong>en</strong><br />
otros casos <strong>de</strong> reacciones cruzadas por ingestión <strong>de</strong> carnes<br />
parece estar implicada <strong>la</strong> seroalbúmina animal.<br />
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