Thalidomide induced fetal hemoglobin expression. Cells were cultured in EPO on days 0 to 6 and then were treated with the indicated concentration of thalidomide (A) or 100 μM thalidomide in the presence or absence of catalase (4000 U/mL), DMTU (10 mM), or SB203580 (5 μM) (B) from days 6 to 14. On day 14, cells were stained with fluorescently labeled anti-HbF antibodies and analyzed by flow cytometry. Panels represent fluorescence signal (y-axis) versus cell size (x-axis); the percentage of positive cells is shown in the top right corner of each panel. The panels shown are representative of the results for cultures from 3 separate donors.