Thymus and activation-regulated chemokine (TARC) is a recently identified CC chemokine that is expressed constitutively in the thymus and transiently in stimulated peripheral blood mononuclear cells. TARC functions as a selective chemoattractant for T cells that express a class of receptors binding TARC with high affinity and specificity. The chemokine TARC is a ligand for the chemokine receptor CCR4 expressed on CD4 Th2 cells.