BCR cross-linking and apoptosis. (A) Apoptosis assessed by Annexin V–FITC staining for 1 healthy control and 2 CLL patients (nonresponder and high responder). (Top and bottom left) Time before stimulation (T0). (upper right) Overlay unstimulated (T0) and stimulated (T6H, in translucent blue). (Bottom right) Integration of the 2 curves unstimulated and stimulated (T6H), calculation of the percentage of cells undergoing apoptosis after stimulation compared to basal (Overton). (B) Flow cytometry analysis of Annexin V–FITC and propidium iodine double staining before stimulation (T0), at 6 hours, and at 24 hours after BCR stimulation of a representative CLL high responder. Cells remains viable (Annexin V positive/PI negative) at 6 hours after stimulation.