Although previous reports have shown that the activation of both CD4+ and CD8+ cells subsets may be important for the killing of parasites in vaccinated mice using several parasite recombinant antigens [15], [32], [33], the present study's data suggest that CD4+ cells may contribute to a lesser extent to the induction of an IFN-γ mediated response elicited by immunization using B10 and C01 clones; being that the CD8+ T cells were the main resource of IFN-γ, and these cells could directly contribute to infection control through their direct cytotoxic effect. The gene discussed is CD8A; the disease is infection.