Apoptosis of normal and IMF CD41⁺cells. The percentages of normal, IMF, and PV CD41⁺ cells undergoing apoptosis after 8, 11, and 15 days of culture are shown here. A progressive increase in the number of CD41⁺ cells undergoing apoptosis was observed in normal, IMF, and PV CD34⁺ cell cultures. The number of IMF CD41⁺ cells undergoing apoptosis was significantly smaller than that of normal CD41⁺ cells after 11 and 15 days of culture (P < .05; n = 8-12). Values are expressed as the mean ± SD.