Extracellular vesicles (EVs) are spherical particles enclosed by a phospholipid bilayer and have a diameter ranging from 30 nm up to 5 μm. EVs are present in body fluids and fractions thereof, such as serum and a conditioned medium of cultured cells. The concentration of EVs in human body fluids may be over 1010/mL under normal, physiological conditions. The classification of EVs is not straightforward, with substantial confusion throughout the literature, mainly because detection of single vesicles is cumbersome. However, major improvements in the detection of EVs have been made recently. Because EVs contribute to health and disease, the clinical interest in EVs as noninvasive biomarkers for diagnosis or prognosis is emerging. Also, EVs may have several potential therapeutic applications, which are currently being explored.
This chapter provides an overview of current knowledge on EVs, with a focus on properties, functions, and clinical applications of EVs.