Immunosuppression associated with visceral leishmaniasis of hamsters

Immunosuppression was demonstrated during the course of Leishmania donovani infection of outbred and inbred hamsters. Proliferative responses of splenic lymphocytes to the mitogen concanavalin A (Con A) and to promastigote antigens were used as indicators of immune responsiveness. Although splenic lymphocyte proliferative responses to parasite antigens were demonstrable 3 weeks after challenge, antigen specific lymphocyte responses diminished as the infection progressed. Two types of immunosuppression were demonstrable. The first was a non-specific anergy of splenic lymphocytes to Con A stimulation. Thus, spleen cells from infected animals did not actively suppress the Con A responses of normal lymphocytes in mixed cultures A second immunosuppression mechanism, specific for leishmania antigens was mediated by a nylon wool non-adherent cell population. The suppressor, tentatively identified as a T cell population, inhibited the proliferation of parasite antigen sensitized responder lymphocytes in mixed culture. Elimination of the parasite burden by glucantime therapy restored responsiveness of lymphocytes to parasite antigens. Con A responses, however, remained suppressed 1 week after drug cure.