Microvesicles: intercellular vectors of biological messages.

Cells communicate directly by cell-cell contact and indirectly via the release of mediators. But gaining a greater appreciation recently is the identification and characterization of intercellular communication through the secretion of microvesicles (MVs). MVs—small vesicles that comprise microparticles (MPs) and exosomes (1) —released from a wide variety of cells, can be considered micro-messengers. Whereas exosomes are released into the extracellular compartment by exocytosis, MPs are shed from the blebbing plasma membrane, and the composition and effects of both on target cells differ depending on the cell from which originate and the type of stimulus involved in their formation. MVs are obtained after several steps of centrifugation, whereby MPs are defined as the MVs obtained by centrifugation at 100,000 × g. Because the processes by which exosomes and MPs work are different, some researchers have claimed that such broad observations impede the defining and understanding of MV actions (2).