Splenomegaly, enhanced phagocytosis, and anemia are thymus-dependent responses to malaria.

Immunologically competent mice and mice with defined immunological deficiencies were infected with Plasmodium yoelii. Splenomegaly, enhanced phagocytosis, and anemia were most marked in infected mice having intact thymic tissue. Whereas the spleens of infected nude mice increased minimally in size, the relative blood hemoglobin levels and the rates of carbon clearance in these mice were similar to those of noninfected, immunologically intact mice. Thymus-reconstituted nude mice and B-cell-deficient mice responded to infection in a manner similar to that of infected immunocompetent mice. These data demonstrate that the hallmarks of malaria, i.e., splenomegaly, enhanced phagocytosis, and anemia, are thymus-dependent responses to infection.