An attempt at an epidemiological explanation - Epib.nl

Chapter 4The reference strains of the L3/L1/L8 group of ITs did not show "pure" reactionpatterns: strain 126E (Ll) also reacted with the LS group of moabs, strain M978 (LS)with the L3 group and 6275 (L3), though weakly, also with the LS group (Table 1).None of our isolates showed a "pure" Lt reaction pattern, but strain no. 892385(Table 3) reacted solely with the L3 group of moabs. Strain no. 900714 (Table 3)seems to perform better than the original LS reference strain M978 (Table 1),although it reacted weakly with 2 of the L3 group of moabs. The same reasoning mayapply to strain no. 900100 as a reference for LlD. Therefore, the above-mentionedstrains from our series could, for the time being, be used as new references until newreference strains which express a single immunotype have been constructed byrecombinant DNA technology.With the chemical structure in mind, the dissimilarity between the L2/L4 andL3/L1/L8 categories is based on the location of the phosphoethanolamine group, anda shift of ITs between those 2 categories is very unlikely. We have not found ITs ofthese 2 unrelated categories in the same pair of any of the 116 isolates which werecultured twice. Among the 112 pairs of isolates, obtained from both the blood andCSF of the same patient, in the on ly instance in which the CSF isolate (U) and theblood isolate (L1,8) of the same patient belonged to those unrelated categories, thereaction patterns of the 2 isolates differed completely, and in such a way that anerroneous interchange of isolates of 2 different patients seems to be the most likelyexplanation. The occurrence of Ll among L2 or L4 isolates is theoretically possible.We have found this combination only rarely, and we somewhat doubt its trueexistence.From 1989 to 1990 U, L3 and L4 were Ille most prevalent ITs among serogroup Band C meningococci in the Netherlands. Among these 2 serogroups, 2 main categoriesof related serotypes, subtypes and immunotypes could be distinguished duringthis period: the serotypes 4 and 15, the subtypes P1.4, P1.5, Pl.15, Pl.16 and P1.7,16,and the immunotypes of the L3/L1/L8 category on the one hand, and the serotypes 2aand 2b, the subtypes P1.2 and P1.5,2, and the immunotypes U and L4 on the other.The first category was typical for serogroup B, and the second for serogroup C. TheB:4:P1.4 phenotype, which is at present the most prevalent in the Netherlands,"belonged almost exclusively to the L3 complex, which also applies to the "Norwegian"B:15:P1.7,16 phenotype in the Netherlands."The LOS IT is considered to be a virulence determinant. 1o Isolates of ITs with aterminal lacto-N-neotetraose unit (U, L3, L4, LS, L7 and L9) are capable of endogenouslysialylating their LOS, which renders them seroresistent by down-regulatingthe alternative complement pathway.1.l 25 Ll, L6 and LS strains are not structured intbis way, and are serosensitive 13 25 Theoretically, strains of tbe latter ITs will beisolated more often among carriers, as was indeed the case in Great Britain.lOHowever, a relatively large proportion (13%) of Ll, Ll,8 and LS strains, not or onlyweakly expressing L3, was found among our patient isolates in the period 1989 to1990. It might be possible that a carrier strain of the Ll/L8 category shifts to the L3group during colonization, which enables the isolate to evade the host defense58