CD40-mediated B-cell proliferation and up-regulation of surface markers. (A) Proliferation was measured in splenic B cells treated with IL-4 either with or without hCD40L for 3 days. Cultures were pulsed with [³H]TdR for the last 8 hours of culture (*P = .005; **P = .008). (B) For the induction of surface markers, splenic B cells were cultured in vitro for 48 hours with or without hCD40L (400 ng/mL). Cells were harvested and stained for CD23 and CD80 followed by FACS analysis. Data are representative of more than 3 independent experiments as the average ± standard deviation (SD).