The chemokine (C-C motif) ligand 4 (CCL4), also known as Macrophage inflammatory protein 1β (MIP-1β), is a CC chemokine with specificity for CCR5 receptors. It is a chemoattractant for natural killer cells, monocytes and a variety of other immune cells. CCL4 expression can be induced in a variety of mouse cell types, including mast cells, endothelial cells, macrophages and CD8 T cells. Mouse CCL4 cDNA encodes a 92 amino acid (aa) residue precursor protein with a 23 aa residue signal peptide that is cleaved to generate the 69 aa residue secreted mature protein. CCL4 is a major HIV-suppressive factor produced by CD8 T cells. Chemokine activities are mediated by G-protein-coupled seven transmembrane domain receptors. These receptors, CCR1, 5, and 8 have been shown to mediate the biological activities of CCL4. CCL4 was reported to be twenty-fold less active than CCL3 on the same cell populations.