CCL4 is a member of the CC- subfamily of chemokines and is most closely related to CCL3, or MIP-1 alpha. These proteins play critical roles in the recruitment of leukocytes to the site of inflammation. In addition to its chemotactic functions, CCL4 induces the release of proinflammatory cytokine, mast cells degranulation, and NK cell activation. CCL4 signaling is mediated by the G protein-coupled receptors CCR1, CCR4, and CCR5, which are shared with CCL3 and CCL5 (RANTES). CCR5 is the primary co-receptor for HIV entry, which the virus binds through the gp120 envelope protein. All CCR5 ligands demonstrate potent inhibition of virus entry into the cell, both through steric hindrance of gp120-CCR5 interaction, and ligand-mediated receptor internalization.