Trypanosoma cruzi-Induced Suppression of the Primary Immune Response in Murine Cell Cultures to T-Cell-Dependent and -Independent Antigens

In vitro antisheep erythrocyte (SRBC) and antitrinitrophenyl (TNP) antibody responses of spleen cells obtained from C57BL/6 mice infected with Trypanosoma cruzi were reduced as early as 6 days postinfection and not detectable after 18 days of infection. Lymph node cells had normal antibody responses to SRBC and TNP in vitro until the 11th day of infection, after which responses were diminished. By day 31 of infection, lymph node cells were unresponsive to both SRBC and TNP in vitro. Not only were the antibody responses of spleen and lymph node cells to T-cell-dependent and -independent an- tigens progressively reduced as the period of infection increased, but in addition, the effect of lymphoid cell density and antigen dose on antibody production underwent several sequential changes. As the infection advanced, low densities of cultured lymphoid cells and low doses of antigen were ineffective in eliciting a detectable immune response, whereas high densities of lymphoid cells and high doses of antigen resulted in responses approximately equivalent to that observed with normal cells under the same conditions. Results of cell mixing studies have shown that a plastic-adherent, macrophagelike cell plays a major role in the suppressed humoral responses observed in this host-parasite system. A number of viral, bacterial, protozoal, and metazoal infections of mammals effect states of nonspecific immunosuppression in their hosts. In some of these host-parasite relation