Involvement of the Th1 Subset of CD4+ T Cells in Acquired Immunity to Mouse Infection with Trypanosoma Equiperdum

Heat- or merthiolate-inactivated Trypanosoma equiperdum was administered to recipient mice that were subsequently challenged with viable inocula of the same stabilate. Only mice inoculated with merthiolate-killed parasites were completely protected from a challenge inoculum of 10(3) trypanosomes, an effect that was abolished by prior immunosuppression of mice. Immune sera from protected animals contained high levels of interferon (IFN)-gamma and specific IgG2a antibodies. Spleen cells from these mice produced high amounts of interleukin (IL)-2 and IFN-gamma in vitro in response to specific antigen or concanavalin A, whereas splenocytes from mice receiving heat-killed parasites produced high amounts of IL-6. In contrast, the production of tumor necrosis factor (TNF)-alpha and colony-stimulating activity (CSA) was not significantly different in mice receiving either killed parasite preparation. The protection in immunized mice was associated with the detection of strong delayed-type hypersensitivity (DTH) to T. equiperdum antigens, an effect that could be adoptively transferred onto naive recipients by specifically immune CD4+ lymphocytes. These results suggest that the development of protective immunity in mice to T. equiperdum by our immunization protocol may involve the activity of helper/DTH T cells, particularly those of the Th1 subset.