Characterization of microvesicles released from cells constitutively and upon stimulation

Constitutively released microvesicles (cMVs) are released as a part of normal cell physiology. However, stimulated microvesicles (sMVs) are released as a result of a number of possible stress factors. We found sMVs to be released in higher numbers than cMVs, typically 10-fold higher numbers, in the same time frame, and where the stress factor was a pharmacological agent, the microvesiculation was an attempt to release this chemical stress factor. Using a mass sensing technique, the sMVs were released over a 15-minutes period after stimulation. Using sizing beads on a flow cytometer and by transmission electron microscopy, the cMVs were typically smaller (less than 300 nm in diameter) than sMVs (300500 nm in diameter). However, cMVs were found to carry more protein. By contrast, phosphatidylserine expression was greater on the larger sMVs, which also more effectively inhibited complement-mediated lysis.