Surface expression of TfR1 is influenced by differentiation status, ELT concentration, and iron availability in culture. The surface expression of TfR1 was determined by FACS at day 7 of culture. (A) Representative flow cytometry results showing the gating strategy and histogram showing the changes in TfR1 expression (MFI) during MK differentiation. (B) TfR1 MFI levels in different cell types based on CD34 and CD41 expression, showing the highest levels in CD34⁺CD41⁺ cells. The iron availability in the media in which cells were cultured had a nonsignificant effect on TfR1 expression level. (C) Representative FACS results showing dose-dependent upregulation of TfR1 by ELT in all 3 cell types studied. (D) In CD34⁺CD41⁺ and CD34⁻CD41⁺ cells treated with ELT6 and ELT30, iron availability had a significant effect: Increased iron reduced TfR1 MFI in cells treated with ELT6, but it had the opposite effect on cells treated with ELT30. Data reflect the mean ± SD from 5 independent experiments. *P < .05; **P < .01; ***P < .001.