The Specific Anti-Parasite Immune Responses of Germ-Free and Conventional Rats Infected with Trypanosoma lewisi

Abstract

To test the hypothesis that the rapid immune response of rats to Trypanosoma lewisi is elicited by prior exposure to cross-reacting environmental antigens, the early immune response to infection with this nonpathogenic protozoan was studied in germ-free and conventional rats. In germ-free rats, initial levels of both IgG and IgM were significantly lower than those of conventional rats. After infection, the germ-free rats made more immunoglobulins of both classes, and made them more quickly, than did conventional rats. Trypanosome-specific antibodies appeared earlier and in higher titers in the germ-free rats. Because they lacked intestinal microflora, it is unlikely that the germ-free rats' responses had been primed; thus, these observations indicated that the conventional rats' responses to some trypanosome antigens had been down-regulated by their prior exposure to environmental antigens. However, protective antibodies that inhibited parasite reproduction (ablastin) may have been primed, because these appeared in sera 2 days earlier in conventional rats. Despite much lower rates of production of trypanosome-specific antibodies, the conventional rats had the same peak parasitemias and times to crisis as germ-free rats. Thus it is apparent that protective immunity to this nonpathogenic parasite is not down-regulated by prior exposure to environmental antigens, as would be predicted.

The effect of iron nutritional status on Trypanosoma cruzi infection in germfree and conventional mice

“…The GN group, therefore, produced more IgG and IgM than their CV counterparts. Higher titers of immunoglobulins were observed in GN rats infected with T. lewisi (Giannini, 1987) and in GN mice infected with T. cruzi (Furarah et al, 1991) than in their CV counterparts. This confirms the hypothesis that the difference in levels of TIBC between CV and GN mice may be due to differences in immunological responses.…”