The specific anti-parasite immune responses of germ-free and conventional rats infected with Trypanosoma lewisi.
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.
D000818:Animals; D000953:Antigens, Protozoan / Q000276:immunology; D000955:Antigens, T-Independent / Q000276:immunology; D005260:Female; D005856:Germ-Free Life; D007074:Immunoglobulin G / Q000032:analysis; D007075:Immunoglobulin M / Q000032:analysis; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014350:Trypanosoma lewisi; D014352:Trypanosomiasis / Q000276:immunology*
D000953:Antigens, Protozoan; D000955:Antigens, T-Independent; D007074:Immunoglobulin G; D007075:Immunoglobulin M