Nonspecific suppression of primary antibody responses and presence of plastic-adherent suppressor cells in Toxoplasma gondii-infected mice.

The effect of Toxoplasma infection on primary antibody responses to both T-dependent and T-independent antigens was examined in mice. Drastic suppression of primary responses to sheep erythrocytes (SRBC) occurred when mice were immunized 7 days after infection. The suppression was observed in both 2-mercaptoethanol-sensitive and -resistant hemagglutinin responses. Anti-dinitrophenol (DNP) immunoglobulin E and G1 responses to DNP-conjugated keyhole limpet hemocyanin were also suppressed by infection. It was suggested that the suppressive effect is nonspecific for the antigens and immunoglobulin classes produced. Anti-DNP responses to DNP-Ficoll, a T-independent antigen, were suppressed by infection, but the suppressive effect was weaker than that on the responses to SRBC. This suggests that both T and B cells are suppressed by infection. In vitro responses of infected mouse spleen cells to SRBC and DNP-Ficoll confirmed the results of in vivo experiments. In addition, the presence of plastic-adherent suppressor cells was demonstrated in the spleen cells of infected mice, which suppressed the ability of normal mouse spleen cells to mount an SRBC-specific plaque-forming cell response. These plastic-adherent suppressor cells appeared to be a major cause of nonspecific suppression of primary antibody responses in Toxoplasma-infected mice.