Caspase activation and GATA-1 cleavage in normal and PV erythroblasts. Erythroid precursors derived from CD34⁺ cells of healthy donors (N) and patients with PV (PV) characterized for the JAK2 V617F mutation (as in Figure 2) were cultivated in standard erythroid medium. At day 7 of culture, cells were stimulated with 250 ng/mL anti-CD95 antibodies for 24 hours in standard erythroid medium containing 0.5 U/mL EPO and were analyzed for caspase activation (P < .01) (A) and GATA-1 protein levels (B). Results shown in panel B were obtained with a pool of erythroblasts obtained from 3 healthy donors (N) and are representative of experiments performed with erythroblasts derived from 6 patients with PV harboring the JAK2 V617F mutation. Horizontal bars in panel A indicate the mean value of the N and PV caspase activation.