CCL1, also known as I-309 or TCA-3, is a member of the chemokine (C-C motif) ligand family. Human CCL1 was initially identified by subtractive hybridization as a transcript that was present in a gamma /δ T cell line but not in EBV-transformed B cells. CCL1 cDNA encodes a 96 amino acid residue precursor protein with a hydrophobic signal peptide that is cleaved to yield a 73 amino acid residue mature protein. CCL1 interacts with the G protein-linked transmembrane chemokine receptors CCR8 and induces biochemical events that may result in the control of chemotaxis, proliferation, apoptosis and adhesion. It has been demonstrated that CCL1 displays chemotactic activity for monocytes and other cell types such as NK cells and dendritic cells, but not for neutrophils. Furthermore, as the only known physiological ligand for CCR8, CCL1 was identified as a potent inhibitor of HIV-1 envelope-mediated cell-cell fusion and virus infection. CCL1 induces significant levels of LTC4 from elicited eosinophils.