Chemokines direct B cells from follicles (left) to the B/T border (right).


Bcells troll for antigens in lymphoid organ follicles, but once they have paired up with their antigen, they need help from T cells, which are found in separate T-rich zones. Karin Reif, Jason Cyster (University of California, San Francisco, CA), and colleagues report that activated B cells increase their production of CCR7, a T-zone chemokine receptor, so that they can migrate toward the T-rich zone. Activation of both CCR7 and CXCR5, the receptor for B-zone chemokines, strikes a balance so that the B cells end up at the border of the two zones.Overexpression of the T-zone receptor CCR7 was sufficient to drive nonactivated B cells to the B/T border, whereas overexpression of the B-zone receptor CXCR5 kept activated B cells in the B-rich follicles. But the two chemokine systems are not the only determinants of B cell position. Cells lacking the B-zone receptor CXCR5 still localized to the B/T border after activation. “They're actually being kept out of the center [of the T zone] by something else,” says Cyster. He suggests that the B cells may be less responsive than T cells to the T-zone chemokines, or the adhesive properties of the B cells and their later arrival may keep them layered outside of the main mass of T cells. ▪


Reif, K., et al.