The crucial role of IFN-γ in clearing intracellular infections has been demonstrated using either antibody-mediated neutralization assays, IFN-γ receptor α chain, or IFN-γ gene knockout (KO) mice for infections with M. tuberculosis [16], Chlamydia [17], Plasmodium [18], Francisella tularensis [19], Leishmania [20], and Rickettsia spp. Here, IFNG is linked to infection.