TypIIInterferon

Type II interferon, commonly referred to as interferon-gamma (IFN-γ), is a cytokine in the interferon family that plays a central role in innate and adaptive immunity. It is produced mainly by natural killer (NK) cells and T lymphocytes, especially CD4+ Th1 and CD8+ cytotoxic T cells, in response to infection or antigen stimulation. It is the only member of the type II interferons and, unlike type I interferons, is produced later in immune responses and acts primarily to activate macrophages and coordinate cellular immunity.

Molecularly, IFN-γ is a homodimer that binds to a receptor complex consisting of IFNGR1 and IFNGR2. Receptor engagement activates JAK1 and JAK2, leading to phosphorylation and dimerization of STAT1, which translocates to the nucleus and binds gamma-activated sequence (GAS) elements to induce gene expression. This signaling promotes expression of genes involved in antigen presentation, antimicrobial activity, and inflammatory responses, including IRF1 and various chemokines.

Functionally, IFN-γ enhances macrophage microbicidal activity, upregulates MHC class II expression, and improves antigen presentation to T cells. It supports Th1 differentiation, augments phagocytosis and intracellular killing of pathogens such as Mycobacterium, and can exert anti-proliferative and anti-angiogenic effects in some contexts. It also acts synergistically with other cytokines, including TNF-α, to shape immunity and inflammation. Antiviral effects are generally indirect, via activation of infected cell defenses and immune effector cells.

Clinically, IFN-γ deficiency or dysregulation can increase susceptibility to intracellular infections. Recombinant IFN-γ has therapeutic use in certain conditions, notably chronic granulomatous disease and other severe infections, under controlled settings. Immunologically, IFN-γ release assays use T-cell production of IFN-γ as a readout for exposure to Mycobacterium tuberculosis antigens.