Chemokine (C-C motif) ligand 1 (CCL1),  also known as I-309, is a small glycoprotein secreted by activated T cells that belongs to the family ofchemokines. Human CCL1 has been assumed to be a homologue of mouse TCA3. While the two proteins share only approximately 42% amino acid sequence identity, both chemokines contain an extra pair of cysteine residues not found in most other chemokines. CCL1 attracts monocytes, NK cells, immature B cells and dendritic cells by interacting with the cell surface chemokine receptor CCR8. This chemokine resides in a large cluster of CC chemokines on human chromosome 17.
Recombinant Human I-309/CCL1 produced in E.coli is a single non-glycosylated polypeptide chain containing 74 amino acids. A fully biologically active molecule, rhI-309/CCL1has a molecular mass of 8.5 kDa analyzed by reducing SDS-PAGE and is obtained by chromatographic techniques at ExCell Bio.