The follicular versus marginal zone B lymphocyte cell fate decision is regulated by Aiolos, Btk, and CD21

Most splenic B cells in mice that lack Aiolos are mature IgD(hi)IgM(lo) fol licular lymphocytes, suggesting that maturation signals delivered via the B CR are enhanced in the absence of Aiolos. The enhanced maturation of follic ular B cells is accompanied by the absence of MZ B lymphocytes and the down regulation of CD21 expression in follicular B cells, all of which depend on the generation of signals via Btk, which is in epistasis to Aiolos. The in verse relationship between the strength of BCR signaling and MZ B cell deve lopment is supported by an examination of MZ B cells in CD21 null mice. The se data support the view that antigens tin contrast to "tonic" signals) dri ve the development of naive B cells.