Plasmodium yoelii: the thymus-dependent lymphocyte in mice immunodepressed by malaria

Euthymic mice, athymic nude mice, and mice treated with antithymocyte serum were infected with Plasmodium yoelii and immunized 10 days postinfection with pneumococcal polysaccharide (SSSIII). As a control, uninfected mice were also immunized with SSSIII. Splenic plaque-forming cells as well as serum antibody titers to SSSIII were measured 5 days after immunization. In infected euthymic mice, both plaque-forming cells (PFC) and serum antibody were severely depressed. In contrast, plaque-forming cells and serum antibody were approximately normal in infected nude mice and in infected mice treated with antithymocyte serum. Splenic adherent cells from infected euthymic mice failed to function as accessory cells in the in vitro antibody response to a second antigen, the sheep erythrocyte. Moreover, they lacked suppressor activity when cultured with spleen cells from uninfected mice. In contrast, adherent spleen cells from infected mice treated with antithymocyte serum displayed accessory cell function.