Human 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 plays a central role in immune cell recruitment, antiviral defense, and inflammatory signaling. CCL5 belongs to the CC chemokine family, which also includes CCL3 (MIP-1α), CCL4 (MIP-1β), and CCL2 (MCP-1), chemokines that regulate leukocyte trafficking during immune responses. In humans, 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. It exerts its biological effects mainly through binding to the chemokine receptors CCR1, CCR3, and CCR5, triggering intracellular signaling pathways that promote chemotaxis and activation of T cells, monocytes/macrophages, eosinophils, basophils, and natural killer (NK) cells at sites of infection or inflammation. Human CCL5 is involved in immune responses against viral, bacterial, and parasitic pathogens, and dysregulated CCL5 signaling has been implicated in chronic inflammatory and immune-mediated diseases such as asthma, rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease, as well as in tumor progression and metastasis through effects on the tumor microenvironment. Because CCL5 interacts with CCR5, which is also a key co-receptor for HIV entry, the CCL5–CCR5 signaling pathway has been extensively studied in immunology, infectious disease, cancer biology, and therapeutic development, including the design of CCR5-targeted drugs and immunomodulatory therapies.