Effect of MV generated under different conditions of stimulation on the expression of megakaryocytic differentiation markers by K562 cells. MVs were obtained from CEM T cells treated with either medium (control) or PHA (A), PMA (B), act D (C-D), and added at the indicated concentration to K562-cell culture. After 72 hours of treatment, expression of α_IIbβ₃ or CD42b was analyzed by flow cytometry, and morphology was examined by phase-contrast microscopy (original magnification, ×100). In panels A-C results are expressed as the mean ± SEM (error bars).