CCL17 also known as TARC, Small-inducible cytokine A17, Thymus and activation-regulated chemokine and SCYA17, is encoded by the CCL17 gene located on the chromosome 8. Among CC chemokine family members, CCL17 has approximately 24 – 29 % amino acid sequence identity with RANTES, MIP-1α, MIP-1β, MCP-1, MCP-2, MCP-3 and I-309. CCL17 is a secreted protein and expressed by thymus cells constitutively and phytohemagglutinin-stimulated peripheral blood mononuclear cells transiently. It signals through the chemokine receptors CCR4 and CCR8 and displays chemotactic activity for T lymphocytes and some other leukocytes. CCL17 play an important role in skin diseases such as atopic dermatitis, bullous pemphigoid and mycosis fungoides. Recombinant CCL17 has been shown to be chemotactic for T cell lines but not monocytes or neutrophils.