Interferon gamma (IFNG or IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. Through cell signaling, interferon gamma plays a role in regulating the immune response of its target cell. A key signaling pathway that is activated by type II IFN is the JAK-STAT signaling pathway. IFNG plays an important role in both innate and adaptive immunity. Type II IFN is primarily secreted by adaptive immune cells, more specifically CD4+ T helper 1 (Th1) cells, natural killer (NK) cells, and CD8+ cytotoxic T cells. The expression of type II IFN is upregulated and downregulated by cytokines. By activating signaling pathways in cells such as macrophages, B cells, and CD8+ cytotoxic T cells, it is able to promote inflammation, antiviral or antibacterial activity, and cell proliferation and differentiation. Type II IFN has played a role in the development of cancer immunotherapy treatments due to its ability to prevent tumor growth.