Blastogenic response of Toxoplasma-infected mouse spleen cells to T- and B-cell mitogens.

In order to differentially test the function of lymphocytes in Toxoplasma gondii-infected mice, the in vitro blastogenic response of spleen cell cultures to non-specific mitogens was studied. Phytohaemagglutinin (PHA) and concanavalin A (Con A) stimulation were used as tests of thymus-dependent lymphocyte (T cell) function and bacterial endotoxin lipopolysaccharide (LPS) was used as a probe of bursal equivalent lymphocyte (B cell) function. For the first 3 weeks following T. gondii infection, the uptake of tritiated thymidine ([3H]TdR) by spleen cells cultured with all three mitogens was markedly reduced in comparison to the uptake in spleen cells from uninfected control mice. Thereafter, the response to LPS returned to normal while stimulation by the T-cell mitogens (PHA and Con A) remained depressed. It is postulated that T. gondii infection either: (1) diluted out T cells in the spleen with unreactive cells; (2) modified T cells in such a way that they were less responsive to mitogens; (3) depleted the peripheral lymphoid tissues of T cells; (4) induced non-specific suppressor cells, which inhibited the T-cell function assays; or (5) activated macrophages which depressed T-cell function non-specifically.