Erk is phosphorylated in T2 B lymphocytes on anti-CD38 stimulation, and this effect requires PI3-kinase activity. Total splenocytes from CD38^−/− or wild-type mice were preincubated with DMSO or PD98059 for 30 minutes and then activated 10 minutes with rat-IgG (black line), anti-CD38 (gray histogram), or anti-IgM (dotted line). After activation, the cells were stained for B220, CD21, CD24, and pErk as described in “Erk phosphorylation.” (A) Phosphorylation of total or purified T2 B lymphocytes. (B) T2 B cells from wild-type mice were preincubated with DMSO, LY294002, or PD98059 for 30 minutes and then activated 1, 5, or 10 minutes with rat-IgG, anti-CD38, or anti-IgM. Erk phosphorylation was analyzed by Western blot as described in “Erk phosphorylation.”