B cells are deleted early in development because of NF-κB activation and escaping cells are immature. (A) Representative plots for Caspase 3 and 7 expression in development stage C and (B) summary data for Caspase 3 and 7 expression in different bone marrow B-cell development stages. Cells are gated on live B220⁺ cells and then subclassified using the Hardy system before Caspase 3 and 7 expression was assessed as a percentage in each developmental stage. Data are from n = 9 mice/genotype, shown as the mean ± SEM and were collected in 3 independent experiments. (C) Representative plots for mature and immature B cells in the spleen of LMC and mb1^DPWY mice. Cells are gated on live B220⁺ cells and stained for surface IgM and IgD, with immature cells being IgD^lo/− and mature cells being IgD⁺. (D) Summary data of the ratio of mature to immature B cells in the spleen of WT and mb1^DPWY mice, data are from n = 11 WT and n = 7 mb1^DPWY mice, shown as the mean ± SEM and were collected in 4 independent experiments. (E) Gene expression of Pax5, Ebf1, and Ikaros in Hardy group B cells, data are from n = 3 replicates/genotype (pooled from 2-3 mice/replicate). Data shown as fold induction compared with LMC controls. *P < .05, **P < .01, ***P < .001.