Human thymus and activation-regulated chemokine (TARC) also known as CCL17, is a novel CC chemokine identified using a signal sequence trap method. Mouse CCL17 was discovered as a dendritic cell (DC) specific gene by differentiation RNA display. Among CC chemokine family members, CCL17 has approximately 24-29% amino acid sequence identity with RANTES, MIP-1 alpha, MIP-1 beta, MCP-1, MCP-2, MCP-3, and I-309. The gene for human CCL17 has been mapped to chromosome 16q13 rather than chromosome 17 where the genes for many human CC chemokines are clustered. Recombinant CCL17 has been shown to be chemotactic for T cell lines and antigen-primed T helper cells. In humans, CCL17 was identified to be a specific functional ligand for CCR4 and CCR8, receptors that are selectively expressed on T cells.