Effect of p110δ inactivation on IL-4 signaling in primary splenic B cells. (A) Cells were stimulated with or without IL-4 for 15 minutes, followed by assay of PI3K activity in IRS-2 immunoprecipitates. (B) Percent of viable cells in a culture of B cells treated with or without IL-4 or anti-CD40 for 24 hours. (C) Left panel: Cells were stimulated with IL-4 at different time points, followed by analysis of signaling proteins in total-cell lysates. Right panel: WT B cells were stimulated with IL-4 for 15 minutes with or without the indicated PI3K inhibitors.