Cynomolgus Monkey Interferon-γ (IFN-γ) is a type II interferon cytokine that plays a central role in cell-mediated immunity and regulation of antimicrobial and inflammatory responses in cynomolgus monkeys (Macaca fascicularis). IFN-γ is produced primarily by activated T helper 1 (Th1) cells, cytotoxic T lymphocytes, and natural killer (NK) cells following stimulation by intracellular pathogens or immune signaling molecules such as IL-12 and IL-18. Cynomolgus monkey IFN-γ binds to the interferon-γ receptor (IFNGR1/IFNGR2) expressed on many immune and non-immune cells, activating intracellular signaling through the JAK–STAT pathway, particularly STAT1, which induces expression of numerous interferon-stimulated genes involved in antigen presentation, macrophage activation, and antimicrobial defense. In cynomolgus monkeys, IFN-γ is critical for activation of macrophages, enhancement of MHC class I and II expression, and control of intracellular pathogens, including mycobacteria, viruses, and certain parasites, and it is widely studied in nonhuman primate models of infectious disease, vaccine development, and immunotherapy due to the close immunological similarity between cynomolgus monkeys and humans.