Human Chemokine (C-C Motif) Ligand 3 (CCL3) is a small cytokine belonging to the CC chemokine family. CCL3 is primarily expressed in T cells, B cells, and monocytes after antigen or mitogen stimulation. CCL3 exhibits chemoattractive and adhesive effects on lymphocytes. CCL3 exerts multiple effects on hematopoietic precursor cells and inhibits the proliferation of hematopoietic stem cells in vitro as well as in vivo. CCR1 and CCR5 have been identified as functional receptors for CCL3.

C-C Motif Chemokine 3-Like 1 (CCL3L1) is a secreted protein that belongs to the intercrine beta (chemokine CC) family. CCL3L1 is a ligand for CCR1, CCR3 and CCR5. CCL3L1 binds to several chemokine receptors including chemokine binding protein 2 and chemokine (C-C motif) receptor 5 (CCR5). CCR5 is a co-receptor for HIV, and binding of this protein to CCR5 inhibits HIV entry. The processed form LD78-beta (3-70) shows a 20-fold to 30-fold higher chemotactic activity and is a very potent inhibitor of HIV-1-infection. The copy number of this gene varies among individuals: most individuals have 1-6 copies in the diploid genome, although rare individuals have zero or more than six copies. The human genome reference assembly contains two full copies of the gene (CCL3L3 and CCL3L1) and a partial pseudogene. This record represents the more centromeric full-length gene.