Annexin V/propidium iodide (PI) analysis of CLL cells. Cells from CLL13 were incubated for 18 hours with the indicated additions. IL-4 was added at 10 ng/mL and PF-956980 at 1μM. Apoptosis was quantified by FACScan analysis of cells. Annexin V–FITC fluorescence is displayed on the vertical axis and PI fluorescence on the horizontal axis. Annexin V–positive/PI-negative cells in the lower right quadrant were considered as being apoptotic.