Macrophage-derived chcmokine (MDC) is a member oi the CC ehemokine family. The receptor for MDC is CCR4, a G protein-coupled receptor expressed primarily on the TH2 subset of T lymphocytes and on developing T cells within the thymus. Consistent with this expression pattern, MDC is a chemoattrac-lanl for these cell types. MDC is also chemotactic for IL-2-activated NK cells, dendritic cells, and monocytes, although whether these effects are mediated through CCR4 or another, as yet to be identified receptor, is unclear. In vivo, MDC appears to be involved in the migration of developing T cells in the thymus, and of distinct subsets of mature T cells in the periphery. In the context of pathophysiology, MDC may play an important role in the migration of TH2 cells during allergic inflammation, and of С LA + T cells to the skin in conditions such as psoriasis.