Expression of CD62 on the surface of platelets produced in vitro from CD34⁺ cells (A) or CD34⁺CD41⁺ (B). MKs were cultured either from CD34⁺ in the presence of PEG-rHuMGDF (A) or CD34⁺ CD41⁺ in the presence of PEG-rHuMGDF or the combination of IL-3, SCF, and IL-6 (B). At day 13 or 7 for cultures deriving from CD34⁺ or CD34⁺CD41⁺, respectively, cells were stimulated for 10 minutes at 37°C with 2 U/mL thrombin. Activated and nonactivated platelets were incubated with phycoerythrin (PE) anti-CD62 and FITC-TAB and analyzed relative to PE-conjugated IgG1MoAb control by flow cytometry in a morphological gate corresponding to blood platelets. (A) Serum-free cultures in the presence of PEG-rHuMGDF (10 ng/mL) from CD34⁺ cells. Expression of CD62 (solid line) in thrombin-activated platelets in comparison with nonactivated platelets (broken line). (B) Serum-free cultures in the presence of PEG-rHuMGDF (10 ng/mL) or rHuSCF (50 ng/mL), rHuIL-6 (100 U/mL), and rHuIL-3 (100 U/mL) from CD34⁺ CD41⁺ cells. Expression of CD62 in thrombin-activated platelets from PEG-rHuMGDF (thick solid line) or SCF, IL-3, and IL-6 (thin solid line). Isotype control is shown (broken line).