TNF-α inhibits the generation of megakaryocytic progenitors but increases the number of nonmegakaryocytic cells from CD34⁺ cells supported by TPO. (A) Human CD34⁺ cells at 7.5 × 10⁵/mL were cultured with 100 ng/mL TPO in the presence of various concentrations of TNF-α ranging from 0 to 250 ng/mL. Seven days later, the total numbers of recovered cells (•) were counted, and CD41 (○), CD42b (□), and CD61 (⋄) expressions were examined by a cytofluorometer. The cell yields were represented as the percent relative to the total number of cells without TNF-α. Marker-positive cells were also shown as the percent of the total number of cells in an individual group. The result shown is representative of 3 independent experiments. (B) CD34⁺ cells were cultured as in panel A in the presence (•) or absence (○) of 100 ng/mL TNF-α. Cell counts and phenotype analyses were performed at various time points. The results shown are representative of 3 independent experiments. (C) Morphologic differences in the cells differentiated by TPO with and without TNF-α as in panel B. Cytospin specimens were stained with May-Grünwald-Giemsa solution at the indicated time points (× 1000).