Examination of sorted MKs. After 8 days of culture, the cells were sorted on their CD41 expression and on their ploidy by Hoechst staining into two cell fractions corresponding to 2N-4N and >4N MKs. The quality of the sorted cells was checked by examination with a fluorescence microscope (original magnification × 100) under UV light (a and b). The polyploid fraction with multilobulated nuclei (b) was slightly contamined by some cell agregates. In the 2N-4N fraction (a), the cells were smaller. Cells were also reanalyzed by flow cytometry. A typical experiment is shown in (c), (d), and (e). In (c), the ploidy histogram of the CD41⁺ cells before sorting is shown with 14% >4N MKs. The ploidy histogram of the 2N-4N cell fraction is shown in (d). The purity of this fraction is greater than 99.9%. In (e), the ploidy histogram of >4N is shown with a purity of greater than 93%. It is noteworthy that contaminant cells (5%) are only 2N cells. The width of the peak is slightly larger than in the unfractionated cells due to a slight efflux of the Hoechst during cell sorting.