Procoagulant microparticles: 'criminal partners' in atherothrombosis and deleterious cellular exchanges.

Procoagulant microparticles (MP) constitute valuable hallmarks of vascular cell damage at the crossroad of atherothrombosis processes. Detectable at low concentrations in the blood flow of healthy individuals, elevated levels of procoagulant microparticles are characteristic features of most cardiovascular risk factors. Circulating MP support cellular cross-talk leading to vascular inflammation, endothelial dysfunction, leukocyte adhesion and recruitment possibly contributing to plaque growth with consecutive development of local thrombosis and altered vasomotion. Within the plaque, MP shed by apoptotic monocytes and smooth muscle cells are major determinant of plaque thrombogenicity mainly through the presence of tissue factor (TF) activity. Besides this procoagulant potential, trapped MP could contribute to plaque vulnerability through multiple pathways including angiogenesis, extracellular matrix proteolysis, recruitment of inflammatory cells, smooth muscle cell and endothelial apoptosis. Having long been considered sufficient to initiate coagulation following plaque disruption, the role assigned to plaque-bound TF does not appear physically realistic at a macroscopic scale, the swift growth of the thrombus probably involving blood-borne TF conveyed by circulating MP. As participants in crucial steps of atherosclerotic disease, MP can now be viewed as "partners in crime" in acute ischemic syndromes.