Death of CD27⁺- and CD27⁻-derived plasma cells during differentiation in vitro. (A-B) At the indicated time points, cells were stained with trypan blue, and the absolute number of live (open diamonds with black lines) and dead (open circles with gray lines) cells were counted. (C) The percentage of living cells at each culture day for CD27⁻ (open triangles with thin line) and CD27⁺ (open squares with thick line) cells. (D) Western blot analysis of bcl-2 protein expression during in vitro plasma-cell differentiation from naive (thin line) and memory (solid line) B-cell precursors. (A-D) Error bars are mean ± standard error for all plots (n = 2 experiments from 2 subjects).