Influence of normal microbiota on some aspects of the immune response during experimental infection with Trypanosoma cruzi in mice

To study the influence of normal associated microbiota on systemic immunological responses during experimental Chagas' disease, germ-free and conventional NIH Swiss mice were infected with Y strain of Trypanosoma cruzi. Although no statistical differences in mortality and parasitaemia were found, conventional mice showed IFN-gamma, TNF-alpha and NO production (P < 0.05) by spleen cell cultures and higher blood levels of immunoglobulins of the IgG2a isotype (P < 0.05) when compared to their germ-free counterparts. Moreover, higher levels of IgG1 were also found in conventional animals. On the other hand, no differences in IL10 production were found between germ-free and conventional mice after infection (P < 0.05). Interestingly, spleen cell cultures from non-infected germ-free mice spontaneously produced higher levels of IL10 than cultures from conventional mice. Moreover, cultures from non-infected germ-free mice responded to T. cruzi antigens with IFN-gamma production, contrary to cultures from conventional animals. In conclusion, the presence of the normal microbiota skews the immune response towards production of inflammatory cytokines during experimental infection with T. cruzi in mice. However, the increase in production of cytokines that is linked to resistance to this parasite did not alter the outcome of infection significantly, probably due to high virulence of the Y strain.