Extracellular vesicles (EV) are small membrane-enclosed cell fragments, which are released from almost all prokaryotic and eukaryotic cells during health and disease. Although they are quite heterogenous, EV can be classified into 3 major groups (i) the exosomes, which originate from endosomal compartments. They are small in size 40-100 nm and often contain endosomal markers e.g. CD9, CD63, Tsg101 and Alix. (ii) the microvesicles, which originate from the outer membrane by budding and are larger than the exosomes (100-800 nm). The microvesicles often carry markers that are retained from their parent cells. (iii) the apoptotic bodies, that are generated upon cell apoptosis and are larger than 1 µm. Almost all biologic fluids contain EV. Although this has been recognized for over 4 decades, EV have become in focus as physiologic players only during the past 15 years. Since EV do not only contain quantitative information (i.e. counts per ml body fluid), but also qualitative information (size, content, surface markers), they have the potential to become excellent biomarkers. However, EV are quite difficult to accurately determine and to isolate. Platelets, neutrophils, monocytes and red blood cells release EV after activation and these EV are thought to have functional roles in the initiation and propagation of thrombosis. In addition, platelet-derived EV can also influence the behavior and phenotype of monocytes or smooth muscle cells, a process that might be important for the pathophysiology of atherosclerosis.
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