Progenitor contents according to CD9 expression. CFU-MK frequency is increased in the CD34⁺CD9^high and CD34⁺CD9^mid cell fractions.

CD34⁺CD41^neg bone marrow cells were sorted according to CD9 expression: CD9^low, CD9^mid, and CD9^high (gates A, B, and C, respectively). Sorted cells were plated in duplicate or triplicate. For CFU-MK cultures, cells were plated at a density of 10⁴ cells/mL in serum-free collagen culture. For the other myeloid progenitors (CFU-GEMM, BFU-E, CFU-GM, CFU-M, and CFU-Mast) assays, cells were plated at a density of 2000 cells/mL in methylcellulose culture. The growth factor cocktail used was adapted according to the type of progenitor cultures as described in “Materials and methods.” The histogram values represent the average number of colonies obtained per plate in one experiment; standard deviations between plates were less than 5%. Bars corresponded to 4 to 5 individual experiments using different CD34⁺ bone marrow samples. ND, not determined.