Fig. 1.

Microvesicle shedding. Microvesicles are formed by the outward budding of the plasma membrane, as shown. Not all plasma-membrane proteins are incorporated into shed vesicles, although the topology of membrane proteins remains intact. Membrane proteins such as oncogene and other growth-factor receptors, intergrin receptors and MHC class I molecules, soluble proteins such as proteases and cytokines, as well as nucleic acids, have been found in microvesicles. Microvesicles appear to be enriched in some lipids such as cholesterol, whereas phosphatidylserine is relocated to the outer membrane leaflet specifically at sites of microvesicle shedding.