(a) MK grown for 7 days from CD34⁺CD38⁺ progenitors in the presence of Mpl-l: numerous microparticles (arrows) surround this platelet-shedding mature MK. (b) Cultured MK having undergone thrombin activation (1 U/mL for 5 min): the plasma membrane is bristled with numerous pseudopods (p). However, unlike platelet-shedding MKs, only a few microparticle profiles are seen around the cell surface (arrows), probably corresponding to some pseudopod transverse sections.