Increased proliferation and altered function of patient B cells after stimulation. (A) Proliferation of naive B cells purified from patients and controls was measured by [³H]thymidine incorporation in response to various B cell–activating stimuli. Patient responses were significantly higher than controls for all stimuli (P < 0.03) except SAC. Data show mean ± standard deviation of triplicate wells. (B) Representative protein expression of three NF-κB–responsive surface markers (CD86, CD25, and CD83) was quantified in naive B cells by flow cytometry, before or after polyclonal stimulation with anti-IgM or SAC + 200 U/ml IL-2. MFI values are listed for each histogram shown. With the exception of SAC, patient responses were significantly higher than controls. (C) Purified naive B cells from a normal control donor (C1), P2, and P3 were stimulated with BAFF and IL-21 ± 1 µg/ml anti-CD40 Ab for 10 d. The percentage of IgD⁻CD38^hi plasma cells generated is highlighted in red for the lower right quadrant. (A–C) Data are representative of two (C) or three (A and B) independent experiments.