Final answer:
B cells are directed to the cortical regions of secondary lymphoid tissue by the chemotactic signal CXCL13.
Step-by-step explanation:
B cells follow chemotactic signals to migrate to the cortical regions of secondary lymphoid tissue. The specific chemotactic signal that guides B cells to these areas is CXCL13. This chemokine is essential for the homing of B cells to the follicles of lymphoid tissues, where they can encounter antigens and receive help from T follicular helper cells, enabling them to initiate the adaptive immune response.
These chemokines are secreted by stromal cells in the lymph nodes and attract B cells to the appropriate location.