TARC cDNA encodes a 94 amino acid precursor protein with a 23 amino acid residue signal peptide that is cleaved off to generate the 71 amino acid residue mature secreted protein. Along with CC chemokine family members， CCL-17 has approximately 24-29% amino acid sequence identity with RANTES， MIP-1a， MIP-1b， MCP-1， MCP-2， MCP-3 and I-309. TARC is expressed in thymus， and at a lower level in the lung， colon， and small intestine. TARC is in addition transiently expressed in stimulated peripheral blood mononuclear cells. Recombinant TARC has been shown to be chemotactic for T cell lines but not monocytes or neutrophils. CCL-17 was recently identified to be a specific functional ligand for CCR4， a receptor that is selectively expressed on T cells. CCL17 is one of quite a few Cys-Cys （CC） cytokine genes clustered on the q arm of chromosome 16. CCL17 shows chemotactic activity for T lymphocytes， but not monocytes or granulocytes. CCL17 binds to chemokine receptors CCR4 and CCR8. This chemokine plays important roles in T cell development in thymus as well as in trafficking and activation of mature T cells.
