Effects of IFN-α2b on colony formation and DNA ploidy of primary human megakaryocytes. (A) Human bone marrow–derived CD34⁺ cells were treated with 10 ng/mL TPO and 0, 1, or 10 ng/mL IFN-α2b for 10 days. (Left graph) Total number of CFU-MK. The average number was calculated from 3 independent experiments. (Right graph) Number of CFU-MK that included one or more megakaryocytes more than 100 μm in diameter. Diameters were measured under a microscope using a microscale within an eyepiece. Data are means plus or minus SEM from the results of 3 independent experiments (*P < .05 vs 0 ng/mL IFN-α2b). (B) Effects of IFN-α2b on DNA ploidy of megakaryocytes in vitro. Human bone marrow–derived CD34⁺ cells were cultured with 10 ng/mL of TPO in combination with 0, 1, or 10 ng/mL IFN-α2b. Megakaryocytes were stained with antihuman CD41a-PE antibody and 7-AAD dye, and examined by 2-color cytometry. Data are means plus or minus SEM from the results of 3 independent experiments (*P < .05 vs 0 ng/mL IFN-α2b).