Syntenin modulates eosinophil differentiation. (A) CD34⁺ cells were isolated from cord blood, and cultured for 3 days in FLT-3, SCF, IL-3, and GM-CSF before the medium was supplemented with IL-3 in the presence or absence of IL-5. Cells were transduced with EGFP control virus at days 1 and 2. At day 17, EGFP⁺ cells were sorted, cytospins were prepared, and cells were stained by May-Grünwald-Giemsa. Percentage of eosinophils was scored in 4 independent experiments using different donors (± SD). (B) Eosinophil differentiations of 3 independent donors upon transduction with EGFP control protein or syntenin and incubation with IL-5 as described in panel A. Eosinophil numbers after EGFP transduction were set at 100%, and the fold increase upon syntenin transduction was calculated per donor (± SD). (C) Representative cytospins at day 17 of EGFP or syntenin-transduced CD34⁺ cells that were differentiated toward eosinophils. EGFP-positive cells were sorted and stained by May-Grünwald-Giemsa. (D) CD34⁺ cells were transduced with retroviral vectors expressing control shRNA or syntenin-targeting shRNA and differentiated toward eosinophils. At day 17, fold increase of the percentage of eosinophils for each donor (n = 3, data show average ± SD) after control shRNA transductions (set at 100%) or syntenin-targeting shRNA transduction was determined. **P < .01. (E) Surface IL-5Rα expression of primary CD34⁺ cells transduced with EGFP or syntenin (3 donors) or control or syntenin-targeting shRNA (2 donors). Eosinophil cultures were analyzed at day 14 for IL-5Rα expression by flow cytometry (PE-channel). Nontransduced and transduced cells were indicated by EGFP transduction and IL-5Rα staining was compared with isotype staining. Numbers represent geometric mean fluorescent intensities of the boxed region in the PE channel. Identical results were obtained for all donors and 1 representative sample is shown.