Microparticles (MPs) (also known as microvesicles) are small membrane vesicles that are released from activated and apoptotic cells. They are defined as 0.1-1 μm in diameter and are therefore larger than exosomes. Formation of MPs requires activation of an ATP-dependent lipid transporter called scramblase that translocated phosphatidylserine (PS) from the inner to outer leaflet. Subsequent membrane blebbing is followed by release of a MP. MPs are procoagulant because the exposed PS provides a docking site for the assembly of different coagulation protease complexes. In addition, the presence of the transmembrane glycoprotein called tissue factor (TF) increases their procoagulant activity. Levels of TF-positive MPs are increased in a variety of diseases, including acute coronary syndromes, sepsis, diabetes, sickle cell disease and cancer. Hyperlipidemia induces TF expression in circulating monocytes and these cells subsequently release TF-positive MPs that may contribute to arterial thrombosis after rupture of atherosclerotic plaques. In cancer, tumors release high levels of TF-positive MPs into the circulation and they may trigger venous thrombosis. These studies suggest that levels of TF-positive MPs can be used clinically to assess thrombotic risk in different diseases.
Disclosure of Interest N. Mackman Consultant for: Merck