Research Group Heussler (Malaria I) - Bernhard-Nocht-Institut für ...

Medical Microbiology Section
Murine Chagas’ disease: Requirements for Th1 inducing
cytokines and NK cell activity in an effective immune response
Zusammenfassung
Der einzellige Parasit Trypanosoma cruzi ist der Erreger
der Chagas-Krankheit des Menschen. Immunität
des Wirtes ist abhängig von einer proinflammatorischen
T-lymphozytären Immunreaktion. Wir haben in
IL-12- bzw. IL-18- defizienten Mäusen untersucht, ob
diese unterschiedlich suszeptibel gegenüber dem
Parasiten sind. Während IL-12-/- Mäuse auch sehr
niedrigen Infektionsdosen erlagen, waren IL-18-/-
Mäuse vergleichbar resistent wie Wildtyp Kontrollen.
Parasitäre Gewebslasten wurden an Tag 14 in einer
quantitative PCR verglichen. In Geweben von IL-12-/-
Mäuse waren sie deutlich erhöht, v.a. in der Leber;
bei IL-18-/- Mäusen waren sie mit denen von Kontrollmäusen
vergleichbar. Die Expression von IL-12
ist demnach essentiell in der Immunabwehr gegenüber
T. cruzi, während die Expression von IL-18 nicht
zu einer Steigerung der Resistenz führt. IL-12 ist u.a.
für die Aktivierung von NK-Zellen notwendig. Die Parasitämie
in NK-Zell-depletierten Mäuse war signifikant
erhöht, wenngleich Gewebslasten nicht verändert
waren. Dieser Effekt war Perforin-unabhängig.
Summary
The protozoan pathogen Trypanosoma cruzi causes
Chagas’ disease in man. A protective immune response
by the host depends on pro-inflammatory Tcell reactivity.
We investigated the requirements for expression of IL-
12 and IL-18 in C57BL/6 mice in instigating such a
response. IL-12-/- mice were susceptible to very low
infectious doses, whereas IL-18-/- mice resisted an
infection to the same extent as wildtype controls.
Parasite tissue burdens were compared on day 14
by real time quantitative PCR. Parasite infiltration was
vastly increased in tissues of IL-12-/- mice, most notably
in the liver, wheras in IL-18-/- mice, it was comparable
to wildtype controls. Thus, IL-12 is essential for protective
immunity to T. cruzi in this model, while IL-18 is
dispensable. NK cells (that are activated by IL-12)
showed contact-dependent effector function against
free trypanosomes in vitro. Parasitaemia in NK celldepleted
mice was significantly increased, but tissue
parasite burdens were not altered. This effect was
found to be perforin-independent.
Figure 1. Course of T. cruzi infection in mice deficient of either
IL-12 or IL-18. Mice were infected with an intermediately lethal
dose (10 3 trypomastigotes). Tissue parasite burdens were determined
by quantitative real-time PCR. Relative T. cruzi loads
are expressed as ratio of parasite DNA to host ß-actin DNA.
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Introduction
Chagas’ disease is a major cause of morbidity and mortality
in endemic countries of Latin America. The pathogenesis
of the disease is not fully understood, but both
host and parasite factors are known to contribute to defining
the severity of the disease. Chronic inflammation
is possibly mediated by parasite persistence. Aquired T
cell mediated immunity and Th1 type cytokines are crucial
in host resistance, whereas the role of innate immune
responses are less well understood. Using N2
backcross offspring of susceptible C57BL/6 and resistant
B6D2F1 mice, we mapped three genetic loci to
chromosomes 5, 13 and 17 that are linked to suceptibility
to lethal experimental T. cruzi infection. A real time
PCR assay for quantitative comparison of parasite tissue
burdens was established. Susceptible mice har-