Interferon type II

A sole member makes up the type II IFNs that is called IFN-γ (gamma). Mature IFN-γ is an anti-parallel homodimer, which binds to the IFN-γ receptor (IFNGR) complex to elicit a signal within its target cell. IFNGR is made up of two subunits each of molecules designated IFNGR1 and IFNGR2.

Sources and functions
IFN-γ is involved in the regulation of the immune and inflammatory responses; in humans, there is only one type of interferon-gamma. It is produced in activated T-cells and natural killer cells. IFN-γ has some anti-viral and anti-tumor effects, but these are generally weak. However, this cytokine potentiates the effects of the type I IFNs. IFN-γ released by Th1 cells recruits leukocytes to a site of infection, resulting in increased inflammation. It also stimulates macrophages to kill bacteria that have been engulfed. IFN-γ released by Th1 cells is also important in regulating the Th2 response. As IFN-γ is vitally implicated in the regulation of immune response, its production can lead to autoimmune disorders.

Homologs of interferon-gamma are found in birds, frogs, and teleost fish. Thus it is likely that all bony fish/tetrapods encode IFN-γ. The gene structure of IFN-γ is identical to that of its structurally related cytokines, except that the intron between the third and fourth exons does not exist.

Notably, many teleost fish encode two distinct IFN-γ species (called IFN-γ1 and IFN-γ2) that appear to bind genetically and physically distinct IFN-γR1 chains. In all investigated tetrapods, there is a single IFN-γ gene that binds a unique IFN-γR1 chain and (in amniotes) a unique IFN-γR2 chain. Frogs appear to encode two distinct IFN-γR2 genes whose intracellular domains differ significantly.