Inhibits hemopoiesis and stimulates chemotaxis. Chemotactic in vitro for thymocytes and activated T-cells, but not for B-cells, macrophages, or neutrophils. Potent mesangial cell chemoattractant. Shows preferential activity towards naive T-cells. May play a role in mediating homing of lymphocytes to secondary lymphoid organs. Binds to CCR7 and to CXCR3. Interacts with PDPN; relocalizes PDPN to the basolateral membrane. Expressed strongly in lung, spleen, thymus, peripheral and mesentric lymph nodes. Also expressed in the testis, kidney, liver, and heart. Three genes code for Ccl21 in mouse. Ccl21b and Ccl21c produce identical proteins while the protein produced by Ccl21a differs at only one position. Ccl21b and Ccl21c have Leu-65 (6Ckine-Leu) while Ccl21a has 'Ser-65' (6Ckine-Ser). Belongs to the intercrine beta (chemokine CC) family.