IFN-gamma receptor beta chain is also known as IFN-gamma AF-1. This 60-65 kD class II cytokine receptor pairs with CDw119 to form the IFN-gamma receptor. CDw119 serves as the IFN-gamma-binding chain and associates with the IFN-gamma beta chain which is required for receptor signaling. The extracellular portion of both the IFN-gamma receptor alpha and beta chains must be species matched. The IFN-gamma receptor beta chain is expressed at low levels on T and B cells, NK cells, monocytes/ macrophages, and fibroblasts. Binding of IFN-gamma induces receptor dimerization, internalization, Jak1 and Jak2 protein kinase activation and, ultimately, STAT1 activation. IFN-gamma initiates and regulates a variety of immune responses.