C-C motif chemokine 17 (CCL17) is a novel CC chemokine, it belongs to the intercrine beta (chemokine CC) family. CCL17 is expressed at high levels in thymus, and at a lower level in lung, colon, and small intestine. CCL17 is also transiently expressed in stimulated peripheral blood mononuclear cells. 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 and MCP-3. CCL17 has been identified to be Chemotactic factor for T-lymphocytes but not monocytes or granulocytes. CCL17 plays a role in T-cell development in thymus and in trafficking and activation of mature T-cells.