Developmental regulation of apoptosis and BCL-2/BAX expression during B lymphopoiesis in normal and RAG-2-/- mouse bone marrow

Abstract

B cell genesis in mouse bone marrow (BM) represents a finely controlled balance between cell production and apoptotic cell selection. However, the molecular signals that modulate B cell selection in BM are unclear. In the present study, we have examined Bcl-2 and Bax protein expression among precursor B cells at phenotypically defined differentiation stages in normal mouse BM cell suspensions using Western blotting and flow cytometry. The mean concentration of Bcl-2 and Bax per cell changed during successive stages of B cell development, high Bax/Bcl-2 ratios generally correlating with high incidences of hypodiploid apoptotic cells detected by flow cytometry among large pre-B cells and immature B lymphocytes, respectively. Further, the B220+μ- early precursor B cells in RAG-2-/- mouse BM showed a high apoptotic incidence ex vivo and an accelerated rate of entry into the apoptotic pathway in short term culture, together with an elevated Bax/Bcl-2 protein ratio. Changes in Bax/Bcl-2 ratio, similarly correlated with modified apoptotic rates among precursor B cells, were also observed in interleukin-7 gene modified mice. These findings suggest that Bcl-2 family proteins are implicated in regulating apoptotic selection of precursor B cells during their development in mouse BM.