Identification and characterization of MVs. (A) MVs were identified by evaluating their ability to bind annexin V by flow cytometry. Annexin positivity is shown by histogram from 2 representative MV preparations from CLL plasma. (B) Heterogeneity and sizes of the MVs were determined by electron microscopy after negative membrane staining with phosphotungstic acid (magnification level is indicated by the horizontal bar). (C) Plasma levels of MVs were determined by measuring the total protein content and presented as micrograms of MV per milliliter of plasma (isolated from CLL patients [n = 58] or healthy human subjects [n = 5]). (D-E) MVs isolated from CLL patients at various disease stages as indicated were phenotypically characterized by the use of CD61 for platelet-derived or CD19 for B lymphocyte–derived cell-surface marker by flow cytometry. Results from individual patients are presented with mean values.