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 active form of IFN-γ is an antiparallel dimer that interacts with the receptor IFN-γR1 and sets off IFN-γ/JAK/STAT pathway. IFN-γ signaling does diverse biological functions primarily related to host defense and immune regulation, including antiviral and antibacterial defense, apoptosis, inflammation, and innate and acquired immunity. While IFN-γ–induced inflammatory cascade summons a variety of immune-related cell types, such as macrophages, natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), IFN-γ is also implicated in resistance to NK cell and CTL responses and in immune escape in a variety of cancers.