Interferon gamma (IFNγ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. In humans, the IFNγ protein is encoded by the IFNG gene.

IFNγ, or type II interferon, is a cytokine that is critical for innate and adaptive immunity against viral, some bacterial and protozoal infections. IFNγ is an important activator of macrophages and inducer of Class II major histocompatibility complex (MHC) molecule expression. Aberrant IFNγ expression is associated with a number of autoinflammatory and autoimmune diseases. The importance of IFNγ in the immune system stems in part from its ability to inhibit viral replication directly, and most importantly from its immunostimulatory and immunomodulatory effects.

Cellular responses to IFNγ are activated through its interaction with a heterodimeric receptor consisting of Interferon gamma receptor 1 (IFNGR1) and Interferon gamma receptor 2 (IFNGR2). IFNγ binding to the receptor activates the JAK-STAT pathway. IFNγ also binds to the glycosaminoglycan heparan sulfate (HS) at the cell surface.