In the cases of infection with blood-stage P. chabaudi and P. yoelii parasites, genetically IFN-γ-deficient or IFN-γ receptor (IFN-γR)-deficient mice or anti-IFN-γ antibody-treated mice on a C57BL/6 or CBA background show delayed elimination of the parasites (36, , –39). This evidence concerns the gene IFNG and infection.