Cynomolgus Monkey (Macaca fascicularis) CCL5 (C–C motif chemokine ligand 5, also known as RANTES – Regulated upon Activation, Normal T cell Expressed and Secreted) is a proinflammatory chemokine that regulates immune cell recruitment, antiviral responses, and inflammatory signaling in nonhuman primates. CCL5 belongs to the CC chemokine family, which also includes CCL3 (MIP-1α), CCL4 (MIP-1β), and CCL2 (MCP-1), chemokines that coordinate leukocyte trafficking during immune activation. In cynomolgus monkeys, CCL5 is produced primarily by activated T lymphocytes, macrophages, dendritic cells, platelets, epithelial cells, and endothelial cells in response to infection, inflammatory stimuli, or tissue injury. CCL5 exerts its biological effects mainly through binding to the chemokine receptors CCR1, CCR3, and CCR5, promoting chemotaxis and activation of T cells, monocytes/macrophages, eosinophils, and natural killer (NK) cells at sites of infection or inflammation. Because cynomolgus monkeys are widely used as preclinical animal models for human infectious diseases and immunology, CCL5 has been studied in models of viral infections such as HIV/SIV, dengue, and other emerging pathogens, where chemokine-mediated recruitment of immune cells plays an important role in antiviral immunity and inflammatory pathology. Due to their close genetic and immunological similarity to humans, cynomolgus monkey CCL5 is important for translational research on chemokine signaling, immune regulation, and development of immunomodulatory therapies targeting pathways such as CCR5-mediated leukocyte trafficking.