Murine malaria: cellular interactions in the immune response.

The cellular and humoral interactions that contribute to protective immunity in Plasmodium yoelii malaria were studied by adoptive transfer of selective cell populations or hyperimmune serum into sublethally irradiated syngeneic C57BL/6 mice. For some experiments pools of mononuclear spleen cells were depleted of T or B lymphocytes and cells that take up silica were inactivated by standard procedures. Unfractionated immune spleen cells, but not nonimmune spleen cells, protected recipients from lethal P. yoelii challenge. Analysis of the protective capacity of subpopulations of immune spleen cells showed that levels of immunity similar to those seen after transfer of unfractionated immune cells were present only in those instances where immune macrophages, i.e., cells not previously inactivated with silica, were transferred concomitantly with either immune T (supplemented with nonimmune B) or immune B (supplemented with nonimmune T) cells. The requirement for immune macrophages could not be met by transferring mononuclear cells from a nonimmune donor. The results support the hypothesis that an immune 5,000 R-radioresistant, silica-inactivated, non-T, non-B cell, probably a macrophage, must act in concert with immune T and B lymphocytes in the optimal expression of transferred immunity to P. yoelii.