Examination of morphology (A) and counts (B) of platelets released in the culture supernatants by CD34-derived megakaryocytes. (A) shows semithin sections with the presence of apoptotic (arrows) megakaryocytes surrounded by clusters of platelet-size fragments (*). OM × 40. In (B), gel-filtered platelets were counted at different culture times. Data are expressed as the means ± SD of three separate experiments performed in duplicate.