Interferon-γ (IFN-γ, also known as Type II interferon or immune interferon) is a cytokine produced primarily by T-lymphocytes and natural killer cells. The protein shares no significant homology with IFN-β or the various IFN-α family proteins. Mature IFN-γ exists as noncovalently-linked homodimers. Human IFN-γ is highly species specific and is biologically active only in human and primate cells.
IFN-γ was originally characterized based on its antiviral activities. The protein also exerts anti-proliferative, immunoregulatory and proinflammatory activities and is thus important in host defense mechanisms. IFN-γ induces the production of cytokines, up-regulates the expression of class I and II MHC antigens, Fc receptor and leukocyte adhesion molecules. It modulates macrophage effector functions, influences isotype switching and potentiates the secretion of immunoglobulins by B cells. IFN-γ also augments Helper T cell expansion and may be required for Helper T cell differentiation.
IFN-γ exerts its biological activities by binding to specific cell surface receptors with high-affinity binding sites. The IFN-γ receptor is present on almost all cell types except mature erythrocytes and has been cloned and characterized. The IFN-γ receptor is structurally related to the IL-10 receptor.