Cynomolgus Monkey Interleukin-16 (IL-16) is a proinflammatory cytokine that plays an important role in regulating immune cell recruitment and activation in cynomolgus monkeys (Macaca fascicularis). IL-16 is produced by several cell types, including CD8⁺ T cells, mast cells, eosinophils, and epithelial cells, in response to immune stimulation or inflammatory signals. Cynomolgus monkey IL-16 functions primarily as a chemoattractant for CD4⁺ immune cells by binding to the CD4 receptor, promoting migration and activation of T helper cells, monocytes, and dendritic cells to sites of infection or inflammation. Through these actions, IL-16 contributes to coordination of immune responses and modulation of inflammatory signaling pathways. In cynomolgus monkeys, IL-16 participates in immune responses against viral, bacterial, and parasitic infections and may influence inflammatory processes in tissues such as the respiratory and gastrointestinal tracts. In cell culture, recombinant cynomolgus monkey IL-16 is commonly used to study chemotaxis of CD4⁺ immune cells, investigate mechanisms of immune cell recruitment and activation, and evaluate cytokine-mediated regulation of inflammatory pathways. Due to the close immunological similarity between cynomolgus monkeys and humans, IL-16 is also studied in nonhuman primate models of infectious disease and immunology, including research on immune regulation, inflammation, and host–pathogen interactions relevant to translational biomedical studies.