The CXC chemokinc BLC/BCA-1 is conslilutively expressed in lymphoid follicles of secondary lymphoid organs. Il binds to the chemokine receptor CXCR5, which is found on mature В cells and a small sub-populalion of T memory cells. By attracting В cells. BLC/BCA-1 essentially contributes to В cell homing and proper positioning of these cells within the micro-anatomic compartments of secondary lymphoid organs.