Cynomolgus Monkey Macrophage Colony-Stimulating Factor (M-CSF) is a cytokine that regulates the development, proliferation, and survival of monocytes and macrophages in cynomolgus monkeys (Macaca fascicularis). M-CSF is produced by several cell types, including fibroblasts, endothelial cells, epithelial cells, and stromal cells, in response to tissue signals and inflammatory stimuli. Cynomolgus monkey M-CSF binds to the colony-stimulating factor-1 receptor (CSF1R), a receptor tyrosine kinase expressed on monocytes and macrophage lineage cells, activating intracellular signaling pathways such as PI3K–AKT, ERK/MAPK, and JAK–STAT that promote differentiation and maintenance of macrophage populations. Through these mechanisms, M-CSF supports macrophage-mediated immune surveillance, phagocytosis, tissue homeostasis, and inflammatory responses. Because macrophages play a central role in host defense and immune regulation, M-CSF–mediated macrophage function is important for maintaining immune health and responding to infection or tissue injury in nonhuman primates. In cell culture, recombinant cynomolgus monkey M-CSF is commonly used to promote differentiation of cynomolgus monkey monocytes into macrophages and to support macrophage proliferation and functional assays in vitro. Cynomolgus monkeys are widely used in nonhuman primate research models, making M-CSF an important tool for studying macrophage biology, immune responses, and host–pathogen interactions in translational biomedical studies.