We used C57BL6 mice with targeted gene deletions to evaluate the importance of CD4 T cells, B cells, IFN-γ receptor (IFN-γ receptor KO), inducible nitric oxide synthase (iNOS) and pattern recognition receptor signaling (myeloid differentiation primary response 88 [MyD88]) KO mice), in the regulation of peak parasitemia and parasite clearance (resolution of infection). This evidence concerns the gene CD4 and parasitic infectious disease.