MICROVESICLES IN BLOOD COMPONENTS - LABORATORY AND CLINICAL ASPECTS

There is ample evidence for the presence of microvesicles (MV) of diff erent sizes and functions in various blood components. A variety of me chanisms have been proposed for the formation of MV. These include mec hanical injury, shear stress, cell activation, activation of complemen ts, hypoxia, and the cell aging process. While MV share many biologica l properties and surface receptors of their parental cells, they demon strate significant differences in membrane asymmetry of the inner memb rane phospholipid, in particular phosphatidylserine (PS). This provide s high-affinity binding sites for the components of the prothrombinase complex. To what extent these MV contribute to hemostatic effectivene ss, immudomodulation, and some untoward effects of the transfused bloo d components remains to be fully elucidated. Several methods for quali tative and semiquantitative characterization of MV are now available. Although in most cases it is necessary to separate MV from the intact cells for improved characterization, recent advances in flow cytometry make it possible to accurately differentiate MV in the presence of th eir parental cells on the basis of light scattering and fluorescent in tensity. This review focuses on four main areas of MV in blood compone nts: (1) the proposed mechanisms of platelet vesiculation, (2) factors influencing the formation of MV, (3) laboratory analysis of MV, and ( 4) the clinical impact of the presence of MV in blood components.