Inhibits hemopoiesis and stimulates chemotaxis. Chemotactic in vitro for thymocytes and activated T-cells, but not for B-cells, macrophages, or neutrophils. Shows preferential activity towards naive T-cells. May play a role in mediating homing of lymphocytes to secondary lymphoid organs. Binds to atypical chemokine receptor ACKR4 and mediates the recruitment of beta-arrestin (ARRB1/2) to ACKR4. Monomer. Binds to CCR7. Interacts with PDPN; relocalizes PDPN to the basolateral membrane (PubMed:14978162). Interacts with TNFAIP6 (via Link domain). Highly expressed in high endothelial venules of lymph nodes, spleen and appendix. Intermediate levels found in small intestine, thyroid gland and trachea. Low level expression in thymus, bone marrow, liver, and pancreas. Also found in tonsil, fetal heart and fetal spleen. Belongs to the intercrine beta (chemokine CC) family. CCL21 entry