IFNG and viral infectious disease: While IFN γ is produced in T cells, its upregulation has also occurred in T cell deficient nude mice, leading to the conclusion that macrophages can also play a role in this in vivo response of IFN-γ secretion [52], [53], and during viral infections, macrophages are among the first cells in any organ to be exposed and are likely the major producers of IFN-γ soon after infection.