Cloning, expression and activity of B cell Activating Factor

Abstract

The preimmune antibody repertoire plays an important role in immune protection through out the life of the organism. In rabbits, B cells develop in the bone marrow and migrate to the gut associated lymphoid tissues (GALT), where in the presence of commensal bacteria, they are stimulated to proliferate, form organized follicles and develop -the primary antibody repertoire by Ig gene diversification. While the molecular events leading to Ig gene diversification in the bone marrow are well understood, little is known about the mechanisms regulating B cell proliferation and homeostasis in GALT. In a previous study to test whether B cell activating factor (BAFF) may play a role in stimulating GALT B cells, endogenous BAFF was neutralized in vivo using a soluble decoy receptor (TACI-Ig). This treatment greatly reduced the number and size of proliferating B cell follicles, demonstrating that BAFF is required for B cell development in GALT. However, it was not clear from this study, whether BAFF provided a proliferation signal or survival/maintenance signal. Therefore to address this question, I cloned, expressed and purified recombinant rabbit BAFF from E. coli, and tested its affect on B cells in vitro with a [3H]-thymidine incorporation assay. Purified rabbit BAFF induced splenocytes to undergo proliferation, but not B cells isolated from GALT. However, addition of BAFF to cultures of GALT B cells transiently prolonged their survival, suggesting that BAFF may provide a survival/maintenance signal for B cells in GALT.