Quantitative evaluation of apoptosis in CD34-derived megakaryocytes by the TUNEL technique. In (A) and (B), the intensity of fluorescence in the whole cell population was shown by flow cytometry at day 18 of liquid culture. (A) represents a negative control: cells treated with avidin-FITC. (B) shows a typical double profile in which the left area represents viable cells overlapping the negative control and the right area represents apoptotic cells that incorporate the biotin-UTP FITC-avidin complex. The × axis shows the relative fluorescence intensity. The y axis shows the relative number of cells. (C) shows the percentage of apoptosis evaluated by TUNEL technique and shown by flow cytometry at different culture times. Data are expressed as the means ± SD of four separate experiments performed in duplicate. In (D), apoptotic megakaryocytes appeared as intensively yellow-green fluorescent cells at confocal microscopy.