The key role of IFNγ in generation of protective immunity to mycobacterial infections and other intracellular infections is underscored by the fact that mutations of genes encoding IFNGR1 and IFNGR2, (the ligand-binding and intracellular, signaling subunits, respectively, of the IFNγ receptor), and STAT1 (Signal Transducer and Activator of Transcription 1), that is downstream of the IFNγ receptor, often lead to severe infections with intracellular organisms of low pathogenicity such as the Bacille Calmette Guerin (BCG) vaccine or non-tuberculous mycobacterial (NTM) species (45). Here, STAT1 is linked to infection.