May play a role in the trafficking of activated/effector T-lymphocytes to inflammatory sites and other aspects of activated T-lymphocyte physiology. Chemotactic for monocytes, dendritic cells and natural killer cells. Mild chemoattractant for primary activated T-lymphocytes and a potent chemoattractant for chronically activated T-lymphocytes but has no chemoattractant activity for neutrophils, eosinophils, and resting T-lymphocytes. Binds to CCR4. Processed forms MDC(3-69), MDC(5-69) and MDC(7-69) seem not be active. Highly expressed in macrophage and in monocyte-derived dendritic cells, and thymus. Also found in lymph node, appendix, activated monocytes, resting and activated macrophages. Lower expression in lung and spleen. Very weak expression in small intestine. In lymph node expressed in a mature subset of Langerhans' cells (CD1a+ and CD83+). Expressed in Langerhans' cell histiocytosis but not in dermatopathic lymphadenopathy. Expressed in atopic dermatitis, allergic contact dermatitis skin, and psoriasis, in both the epidermis and dermis. The N-terminal processed forms MDC(3-69), MDC(5-69) and MDC(7-69) are produced by proteolytic cleavage after secretion from monocyte derived dendrocytes. Belongs to the intercrine beta (chemokine CC) family. CCL22 entry