The key role of IFNγ in generation of protective immunity to mycobacterial infections and other intracellular infections is highlighted by the fact that genetically inherited disorders of the IFNγ pathway, including IFNGR1, IFNGR2 and STAT1 (reviewed in [54]) lead to overwhelming infections with intracellular organisms of low pathogenicity such as the Bacille Calmette Guerin (BCG) vaccine, or non-tuberculous mycobacterial (NTM) species. Here, IFNG is linked to infection.