Role of CXCL12 and its receptor, CXCR4, in diversification of the rabbit primary antibody repertoire (133.3)

Abstract

Abstract The antibody repertoire of early postnatal rabbits is of limited diversity due to preferential V gene usage during VDJ gene rearrangement. Early in life, rabbit B cells expand this repertoire by diversifying their VDJ genes in gut-associated lymphoid tissue. VDJ gene diversification begins around 1 week of age, in B cells located in the basolateral region of nascent follicles. Because these B cells share similarities with B cells in germinal center dark zones, we hypothesized that activated B cells localize to the basolateral region in response to the chemokine CXCL12. To test this hypothesis, we examined B cell expression of CXCR4, the CXCL12 receptor, by in situ hybridization. We found that B cells in the basolateral region, but not those located elsewhere in the follicle, expressed CXCR4. Because antibody repertoire diversification requires signals derived from intestinal commensals, we further examined CXCR4 expression in appendices that were kept sterile by surgical ligation at birth. We found that B cells in these appendices did not express CXCR4 and did not diversify their VDJ genes. By contrast, we detected CXCL12 expression in both conventional and sterile appendices, demonstrating that it is not dependent on commensal-derived signals. Our results suggest that B cells activated by microbial-derived signals upregulate CXCR4 and migrate to the basolateral region of the follicle, likely in response to CXCL12, where they proliferate and diversify their VDJ genes.