Immunosuppression in mouse trypanosomiasis: inhibition of secondary antibody responses is dependent on the time of antigen priming.

Trypanosoma musculi-induced immunosuppression was examined in both congenitally athymic (nude) mice and their phenotypically normal, euthymic littermates using T-independent (polyvinylpyrrolidone = PVP) and T-dependent (sheep erythrocyte = SE) antigens. T. musculi-infected nude mice had significantly diminished direct (IgM) plaque-forming cell (PFC) responses to PVP. In euthymic mice, T. musculi parasitemia significantly inhibited the direct PFC response to both PVP and SE. Trypanosoma musculi-infected euthymic mice had significantly diminished indirect (IgG) SE-specific PFC responses if priming occurred during parasitemia; however, T. musculi parasitemia did not significantly decrease indirect SE-specific PFC responses in euthymic mice if the mice were primed before infection.