IFNG and Mendelian susceptibility to mycobacterial diseases: In conclusion, while mice lacking IFN-γ were shown to be susceptible to infection by both viruses and bacterial pathogens capable of surviving macrophage-mediated phagocytosis [180,181], the study of MSMD patients has shown that human IFN-γ is primarily a macrophage-activating factor and appears less important for anti-viral immunity.