Cellular distribution of HbF. Flow cytometric analysis of cells cultured in EPO for (A) 7 days or (B) 14 days versus matched cultures in EST for (C) 7 days or (D) 14 days. The x-axis indicates the forward scatter of cells (size) and y-axis, the HbF fluorescence from the cells stained with anti-HbF antibodies. The horizontal bar marks the level of fluorescence 2 standard deviations above that of the isotypic controls. At least 5000 cells were analyzed in each sample. The percentage of HbF-positive cells is shown in the top right corner of each panel.