Analysis of apoptosis and cell division in unilineage erythroid bulk culture. Freshly purified PKH26 labeled CD34⁺Lin⁻ cells were stained with Annexin V-FITC (day 0) or transferred to unilineage erythroid culture and stained with Annexin V at days 2 and 6. (A) FSC/SSC of day-0, -2, and -6 cells. (B) Ungated cells stained with PKH26 and Annexin V-FITC. Day 0: note that only a minority of freshly isolated CD34⁺Lin⁻ cells scored apoptotic when stained with Annexin V. Day 2: virtually all cells are still PKH26⁺ (nondividing cells), but more than 50% stain with Annexin V. Day 6: the majority of cells are proliferating because they stain barely or do not stain with PKH26. Some of these cells are Annexin V⁺, ie, they are apoptotic. Gates R1, R2, and R3: dead, apoptotic cells with low FSC.