Effect of p110δ inactivation on BCR-driven early signaling in primary splenic B cells. (A) Primary splenic B cells were cultured with or without anti-IgM for 5 minutes, followed by cell lysis and immunoblot analysis of whole-cell lysates for the presence of phosphotyrosine. (B) Calcium flux was determined in presence or absence of PI3K inhibitors in response to stimulation with 10 μg/mL anti-IgM in presence or absence of LY294002 (5 μM) or IC87114 (0.1 μM). (C) lysates from control or anti-IgM–treated B cells were analyzed by immunoblot for the indicated signaling molecules. In the right panel, cells were treated with various PI3K inhibitors prior to 5-minute stimulation with anti-IgM.