CCL5/RANTES is a secreted beta-chemokine that plays a primary role in the inflammatory immune response through chemoattraction and activation of leukocytes that express CCR1, 3, 4, or 5. The two N-terminal residues of CCL5 can be removed by CD26/DPPIV, generating a protein that functions as a chemotaxis inhibitor. The deposition of CCL5 on activated vascular endothelial cells is crucial for monocyte adhesion to damaged vasculature. CCL5 is upregulated in breast cancer and promotes tumor progression through the attraction of proinflammatory macrophages in addition to its actions on tumor cells, stromal cells, and the vasculature. In humans, CCR5 binding to CCL5 inhibits the infectivity of R5 (M-tropic) but not X4 (T-tropic) strains of HIV-1.