BAFF-R expression correlates with positive selection of immature B cells



The interaction between BAFF and BAFF-R is crucial for the development of mature B cells. Here, we report that the expression of BAFF-R is first detectable on a fraction of mouse CD19+ CD93+ IgM+ CD23 and human CD19+ CD10+ IgM+ BM B cells. This BAFF-R+ BM B-cell population shows higher levels of surface IgM expression and decreased RAG-2 transcripts than BAFF-R immature B cells. When cultured, mouse BAFF-R, but not BAFF-R+ immature B cells spontaneously undergo B-cell receptor editing. However, BAFF-R+ immature B cells cultured in the presence of an anti-κ light chain antibody are induced to undergo receptor editing. This receptor editing correlates with down-modulation of surface BAFF-R expression and the up-regulation of RAG-2 at the RNA level. B-cell receptor (BCR) cross-linking on splenic T1 B cells results in down-modulation of the BAFF-R, and receptor editing and RAG-2 up-regulation in a minor fraction of B cells. BCR cross-linking on splenic T2/3 B cells results in partly down and partly up-modulation of BAFF-R expression and no evidence for receptor editing. Overall, our data indicate that BAFF-R expression is tightly regulated during B-cell development in mouse and human and its expression is correlated with positive selection.