Abstract
It is now recognized that all circulating blood cells, as well as endothelial cells (EC), continuously shed small membranous vesicles (microparticles [MPs]), which are approximately less than 1 µm, and that levels of circulating MPs are sensitive indicators of disease activity. The first type extensively studied in patients was platelet MP (PMPs) (1). Currently, endothelial-derived MP (EMPs) have risen to the fore as sensitive markers of EC perturbation, recently reviewed (2) and further considered in this article. Although other reviews may differ in viewpoint and emphasis (3,4), it is generally agreed that circulating MPs comprise different subspecies of membrane vesicles released from endothelium and blood cells, such as platelets, leukocytes, and red blood cells (RBCs). MPs containing negatively charged phospatidylserine (PS) and/or tissue factor are highly procoagulant. MPs that express specific adhesion molecules are capable of interacting with leukocytes and endothelia to initiate inflammatory responses.