Effect of TRAIL on erythroid maturation. CD34⁺ cells were cultured in the presence of EPO + IL-3 + SCF for 6 days and then cells were either left untreated or treated with TRAIL. At the indicated times, cultures were analyzed for glycophorin A expression and cell morphology. In panels A-B, surface glyophorin A expression, reported either as percentage of positive cells (A) or as mean fluorescence intensity (MFI) (B), was measured by flow cytometry. Data represent the means ± SDs of 4 independent experiments performed in duplicate; *P < .01. In panels C-D, representative cell phenotype and cell morphology, examined on day 12 of culture by flow cytometry and by light microscopy after May-Grunwald-Giemsa staining, respectively, are shown. In panel D, some mature (arrowheads) and immature (arrows) erythroblasts are indicated in the untreated (i) and TRAIL-treated (ii) cultures. Original magnification, × 40. Similar results were observed in 3 independent experiments performed in duplicate.