Effect of cytokines on the production of MK by CD34⁺CD41⁺ progenitors. Highly purified CD34⁺CD41⁺ BM cells (30,000/mL) were incubated for 7 days in a serum-free synthetic culture media containing various combinations of cytokines. After culture, cells were counted and analyzed for CD41 and PI by flow cytometry. The resulting two-parameter histogram was gated on CD41⁺ cells with DNA content ≥2N to exclude cell fragments and other debris. The total number of CD41⁺ cells recovered from each well has been plotted. Each bar represents the mean of two to four experiments. The error bars indicate the standard deviation of the mean and are shown for all results in which three or more values were available.