CXCR4 promotes B cell egress from Peyer's patches.

Peyer's patches (PPs) play a central role in supporting B cell responses against intestinal antigens, yet the factors controlling B cell passage through these mucosal lymphoid tissues are incompletely understood. We report that, in mixed chimeras, CXCR4-deficient B cells accumulate in PPs compared with their representation in other lymphoid tissues. CXCR4-deficient B cells egress from PPs more slowly than wild-type cells, whereas CXCR5-deficient cells egress more rapidly. The CXCR4 ligand, CXCL12, is expressed by cells adjacent to lymphatic endothelial cells in a zone that abuts but minimally overlaps with the CXCL13(+) follicle. CXCR4-deficient B cells show reduced localization to these CXCL12(+) perilymphatic zones, whereas CXCR5-deficient B cells preferentially localize in these regions. By photoconverting KikGR-expressing cells within surgically exposed PPs, we provide evidence that naive B cells transit PPs with an approximate residency half-life of 10 h. When CXCR4 is lacking, KikGR(+) B cells show a delay in PP egress. In summary, we identify a CXCL12(hi) perilymphatic zone in PPs that plays a role in overcoming CXCL13-mediated retention to promote B cell egress from these gut-associated lymphoid tissues.