Human CCL2 (C-C motif chemokine ligand 2, also known as monocyte chemoattractant protein-1, MCP-1) is a pro-inflammatory chemokine that plays a critical role in recruitment and activation of monocytes, macrophages, dendritic cells, and memory T cells during immune responses. CCL2 primarily signals through the CCR2 receptor, activating intracellular pathways that promote leukocyte migration, cytokine production, and coordination of innate and adaptive immunity at sites of infection, tissue injury, or inflammation. In humans, CCL2 is produced by a variety of cells including endothelial cells, fibroblasts, epithelial cells, and immune cells in response to inflammatory stimuli such as infection or tissue damage. While CCL2-mediated recruitment of monocytes is essential for host defense and tissue repair, dysregulated or excessive expression contributes to chronic inflammatory diseases including atherosclerosis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and chronic kidney disease. CCL2 also plays an important role in cancer biology, where it promotes recruitment of tumor-associated macrophages that can support tumor growth, angiogenesis, and metastasis. As a key regulator of monocyte trafficking and inflammatory signaling, human CCL2 is widely studied as both a biomarker of inflammation and a therapeutic target in autoimmune disease, cardiovascular disease, cancer, and other chronic inflammatory conditions.