IFNG and parasitic infectious disease: However, testosterone may reduce NK cell activity as previously reported (Hou and Zheng, 1988) because NK cells produce IFN-γ in mice infected with Plasmodium (Mohan et al., 1997), and this cytokine promotes parasite elimination via phagocytosis (Roetynck et al., 2006), which would at least partially explain the reduction in IFN-γ in the group that received letrozole + testosterone as well as the increase in parasitemia and anemia in the same group.