In vitro generation of endothelial microparticles and possible prothrombotic activity in patients with lupus anticoagulant

Microparticles (MPs) resulting from vesiculation of platelets and other blo od cells have been extensively documented in vitro and have been found in i ncreased numbers in several vascular diseases, but little is known about MP s of endothelial origin. The aim of this study was to analyze morphological , immunological, and functional characteristics of MPs derived from human u mbilical vein endothelial cells (HUVECs) stimulated by TNF, and to investig ate whether these MPs are detectable in healthy individuals and in patients with a prothrombotic coagulation abnormality. Electron microscopy evidence d bleb formation on the membrane of TNF-stimulated HUVECs, leading to incre ased numbers of MPs released in the supernatant. These endothelial micropar ticles (EMPs) expressed the same antigenic determinants as the correspondin g cell surface, both in resting and activated conditions. MPs derived from TNF-stimulated cells induced coagulation in vitro, via a tissue factor/fact or VII-dependent pathway. The expression of E-selectin, ICAM-1, alpha v bet a 3, and PECAM-1 suggests that MPs have an adhesion potential in addition t o their procoagulant activity. In patients, labeling with alpha v beta 3 wa s selected to discriminate EMPs from those of other origins. We provide evi dence that endothelial-derived MPs are detectable in normal human blood and are increased in patients with a coagulation abnormality characterized by the presence of lupus anticoagulant. Thus, MPs can be induced by TNF in vit ro, and may participate in vivo in the dissemination of pro-adhesive and pr ocoagulant activities in thrombotic disorders.