Function and clinical significance of platelet-derived microparticles

Microparticles released from platelets (PMPs) may play a role in the normal hemostatic response to vascular injury because they demonstrate prothrombinase activity. PMPs were first observed as released vesicles from platelets following adhesion to vessel walls, and flow cytometry is now the most widely used method for studying PMPs. PMPs are thought to play a role in clinical disease because they express phospholipids that function as procoagulants. High shear stress can initiate both platelet aggregation and shedding of procoagulant-containing PMP, suggesting that PMP generation by high shear stress occurs in small diseased arteries and arterioles under various clinical conditions. In addition, the possibility that PMPs evoke cellular responses in their immediate microenvironments has recently been suggested. Despite many interesting findings, the significance of PMPs in various clinical conditions remains controversial. For example, it is not known whether PMPs found in peripheral blood vessels cause thrombosis, or if they are the results of thrombosis. There has been some question about whether the PMPs found in thromboses are consumed locally, meaning that PMPs circulating in the peripheral blood are not functionally important. Currently, the number of clinical disorders associated with elevated PMPs is increasing. Int J Hematol. 2001:74:397-404. (C) 2001 The Japanese Society of Hematology.