Classification and Nomenclature of Extracellular Vesicles

Extracellular vesicle (EV) is a generic term recommended by the International Society for Extracellular Vesicles for “particles naturally released from the cell that are delimited by a lipid bilayer and cannot replicate.” Almost all cell types secrete EVs, which perform physiological and pathological roles. The diameter of EVs typically ranges from 30 nm to 1 μm. In the past few decades, dozens of different names for EVs have been coined based on their cellular origins, biological functions, or biogenesis pathways. Based on biogenesis, EVs have been classified into three main subgroups: exosomes, microvesicles, and apoptotic bodies. Because EVs are heterogeneous, with different sizes, densities, and intracellular sources, and because there are no universal molecular markers or methods that can discriminate among different subtypes of EVs, it is quite challenging to classify and determine the nomenclature of EV subtypes.