CD40-mediated rescue of BCR-driven desensitization of ErkMAPkinase correlates with generation of arachidonate-derived metabolites such as PGE₂. (A) WEHI-231 B cells were stimulated in the presence and absence of anti-IgM (1 μg/mL) and/or anti-CD40 (10 μg/mL) for 24 hours and then cell lysates were prepared and PGE₂ levels were estimated by enzyme-linked immunosorbent assay (ELISA) and presented as means ± SD, n = 3 as described in “Materials and methods.” In the insert panel, such lysates were probed for Cox2 expression by Western blot analysis. (B) WEHI-231-Neo (□) and -Bcl-x_L (▪) B cells were stimulated in the presence and absence of 1 μg/mL anti-IgM for up to 48 hours before estimating intracellular levels of PGE₂. Each anti-Ig–treated time point sample is expressed as a percent of its unstimulated control and data are presented as means ± SD, n = 3. (C) WEHI-231 B cells were stimulated with anti-CD40 (10 μg/mL) for up to 48 hours in the presence and absence of NS-398 plus EDBC (both at 10 μM), and cell lysates were prepared. ErkMAPkinase activity was determined by Western blot analysis of phospho-Erk and total Erk reactivity as described in “Materials and methods.” The data presented are representative of at least 3 independent experiments.