IFN‐γ is detectable in splenic homogenates as early as 24 h after infection with nonlethal P. yoelii strains (but not after infection with lethal strains) 34; IFN‐γ  is also detectable (although at reduced concentrations) in athymic mice lacking T cells 34 but is reduced in animals depleted of NK cells by administration of anti‐asialo GM1 antibody 5, 34. This evidence concerns the gene IFNG and infection.