CCL4 (C-C motif chemokine ligand 4), also known as macrophage inflammatory protein-1β (MIP-1β), is a pivotal chemokine that governs immune cell migration and activation. By binding primarily to its receptor CCR5, it directs the recruitment of monocytes, dendritic cells, natural killer (NK) cells, and T lymphocytes to sites of inflammation and infection. CCL4 plays a crucial role in antiviral defense, antitumor immunity, and inflammatory responses. However, dysregulated CCL4 signaling is implicated in the pathogenesis of chronic inflammatory diseases, autoimmune disorders, and cancer progression. Notably, due to its shared use of the CCR5 receptor with HIV-1, CCL4 also participates in HIV pathogenesis. This dual role as a mediator of both protective immunity and pathology positions CCL4 as a significant biomarker and a promising therapeutic target in immunology and medicine.