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Regulation of egg antigen-induced in vitro proliferative response by splenic suppressor T cells in murine Schistosoma japonicum infection

Beginning about 5 weeks after infection, C57BL/6J mice infected with Schistosoma japonicum developed granulomas around parasite eggs trapped in the liver. These granulomas attained peak size about 9 weeks after infection and then spontaneously regressed. This regression was also induced by the injection of serum immunoglobulin G1 but not lymphoid cells from chronically infected mice, but it was conceivable that lymphoid cells from mice infected for 10 weeks could also induce regression. We investigated the possibility of cellular suppression of egg antigen-induced immune responses by coculturing spleen cells from 5- to 6-week-infected mice with spleen cells from mice infected for 10 weeks or longer. Mitomycin C-resistant Thy 1.2+, Lyt 2.2+ splenic T cells from mice infected for 10 to 25 weeks consistently suppressed the egg antigen-stimulated proliferation of spleen cells from 5- to 6-week-infected mice. Suppression was dependent upon specific antigen and optimal concentrations of egg antigen and T suppressor cells. Once induced, the suppressor cells were nonspecific. Cultured T cells from uninfected mice also occasionally suppressed the acute spleen cell proliferative response, but these cells were mitomycin C sensitive. These in vitro observations suggest that granulomatous inflammation in vivo may also be down regulated by suppressor T cells and that these cells may also be implicated in the nonspecific depression of cellular and humoral responses to antigens observed during the course of this infection.