Bim-deficiency led to prolonged survival and abnormal accumulation of antigen-specific B cells. Mice (wt and bim^−/−) were injected intraperitoneally with 100 μg of NP coupled to KLH; 28 days later, leukocytes were collected from the spleen and stained with the indicated antibodies and analyzed by flow cytometry. (A) Viable cells were gated on dump-channel negative (IgM⁻IgD⁻Gr-1⁻Mac-1⁻) and B220⁺ cells (R1). Among the cells in R1, those that had switched isotype to IgG1 and possessed the ability to bind the immunizing hapten NP coupled to the fluorescent protein allophycocyanin (APC) result in a population of antigen-specific IgG1⁺NP⁺ B cells (R2). These gated cells (R1R2) were then analyzed for CD38 expression to discriminate between memory (CD38^high) and GC B cells (CD38^low). The total numbers of antigen-specific IgG1⁺NP⁺ B cells in the spleen (B) and their percentages in blood (D) were determined as illustrated in (A). Data represent the mean (± SD) of n = 4 to 8 mice; (*P ≤ .05). (C) B220⁺ enriched B cells from immunized wt (□) and bim^−/− (■) mice were cultured for the indicated times in simple medium, harvested, and stained to enumerate antigen-specific IgG1⁺NP⁺ B cells as shown in (A). The initial number of viable IgG1⁺NP⁺ B cells at time 0 h was set as 100%, and the proportion of viable cells remaining after the different times in culture is displayed (n.c. = no cells). Data represent means (± SD) of n = 3 mice. (*P < .02).