Human CCL3 (C-C motif chemokine ligand 3, also known as MIP-1α, macrophage inflammatory protein-1 alpha) is a pro-inflammatory chemokine that plays a central role in immune cell recruitment and activation during inflammatory and infectious responses. CCL3 primarily signals through the CCR1 and CCR5 receptors, promoting chemotaxis of monocytes, macrophages, dendritic cells, natural killer (NK) cells, and activated T lymphocytes to sites of infection, tissue injury, or immune activation. In humans, CCL3 is produced by activated macrophages, dendritic cells, T cells, epithelial cells, and endothelial cells in response to inflammatory stimuli such as microbial products and cytokines including TNF-α and IL-1β. CCL3 contributes to host defense by coordinating leukocyte trafficking and amplifying inflammatory signaling, but dysregulated or sustained expression is associated with chronic inflammatory and immune-mediated diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and psoriasis. CCL3 is also involved in viral infections such as HIV, where it can influence viral entry by competing for the CCR5 coreceptor, and in cancer, where it contributes to immune cell infiltration and tumor microenvironment remodeling. Because of its key role in immune cell migration and inflammatory signaling, human CCL3 is widely studied as both a biomarker of inflammation and a potential therapeutic target in infectious disease, autoimmune disorders, and cancer immunology.