Early versus late effects of SCF on HbF distribution.

Cells were analyzed after 2-week erythroid culture in (A) EPO alone on days 0 to 14, (B) EPO plus SCF on days 0 to 7 followed by EPO alone on days 7 to 14, and (C) EPO alone on days 0 to 7 followed by EPO plus SCF on days 7 to 14. Each panel shows the flow cytometric distribution of HbF after staining with fluorescent antibodies (y-axis) versus cell size (x-axis). A negative fluorescence level (below horizontal bar) was determined using isotypic control antibodies. The percentage of positive cells is shown on the upper right corner of each panel. The panels shown are representative of cultures from 3 separate blood donors demonstrating similar results.