Cynomolgus Monkey (Macaca fascicularis) CCL4 (C-C motif chemokine ligand 4, also known as MIP-1β, macrophage inflammatory protein-1 beta) is a pro-inflammatory chemokine that regulates recruitment and activation of immune cells during inflammatory and antiviral immune responses in nonhuman primates. CCL4 primarily signals through the CCR5 receptor, promoting chemotaxis of monocytes, macrophages, dendritic cells, natural killer (NK) cells, and activated T lymphocytes to sites of infection or tissue injury. In cynomolgus monkeys, CCL4 is produced by activated macrophages, dendritic cells, epithelial cells, and lymphocytes in response to inflammatory stimuli such as pathogen-associated molecules and cytokines including TNF-α and IL-1β. Because cynomolgus monkeys are widely used in preclinical infectious disease and immunology research, CCL4 is frequently studied in models of viral infections such as dengue, influenza, HIV/SIV, and SARS-CoV-2, where chemokine-mediated recruitment of immune cells contributes to antiviral defense and inflammatory responses. CCL4 signaling through CCR5 also influences immune cell trafficking and immune activation during vaccine responses and therapeutic evaluation. As a regulator of leukocyte migration and inflammatory signaling, cynomolgus monkey CCL4 provides an important translational model for understanding chemokine-mediated immune responses, host–pathogen interactions, and immunomodulatory therapies relevant to human disease.