Enhanced LPS-induced apoptosis of nfkb1^−/− B cells is associated with defective ERK activation. (A) bim mRNA expression in wt (■) and nfkb1^−/− (□) B cells before and after LPS stimulation. bim expression in each sample determined by QRT-PCR was normalized relative to gapdh mRNA expression. The data represent the mean plus or minus SD of 3 experiments. (B) Western blots for Bim in wt and nfkb1^−/− B cells after LPS stimulation for 6, 12, and 18 hours. The data are representative of 4 experiments. (C) Bim Western blots for wt and nfkb1^−/− B cells left untreated or stimulated with LPS for 2 hours. (D) Bim Western blots for wt B cells, untreated or LPS-stimulated (2 hours) in the absence or presence of PD98059. (E) Tpl2 expression in wt and nfkb1^−/− B cells. (F) ERK and c-Raf S338 phosphorylation in wt and nfkb1^−/− B cells after LPS stimulation. Results shown for panels C through F are representative of 3 separate experiments.