Microvesicles (or MVs) are plasma membrane-derived vesicles released from most eukaryotic cells constitutively during early apoptosis or at higher levels after chemical or physical stress conditions. This review looks at some of the functions of MVs in terms of intercellular communication and ensuant signal transduction, including the transport of proteins (unconventional protein export) as well as of mRNA and microRNA. MVs also have roles in membrane repair, the removal of misfolded proteins, and in the control of apoptosis. We also discuss the role MVs have been shown to have in invasive growth and metastasis as well as in hypoxia in tumours and cerebral ischaemia. The association of MVs in infectious and autoimmune disease is also summarised together with their possible use as therapeutic agents.

The methods of Plasma Membrane-derived Vesicle (PMV) isolation and quantification vary considerably in the literature and a new standard needs to be defined. This study describes a novel filtration method to isolate PMVs in plasma, which avoids high speed centrifugation, and to quantify them using a Becton Dickinson (BD) FACS Calibur™ flow cytometer, as annexin V-positive vesicles, larger than 0.2 μm in diameter. Essentially microvesicles (which comprise a mixture of PMVs and exosomes) from citrate plasma were sonicated to break up clumped exosomes, and filtered using Millipore 0.1 μm pore size Hydrophilic Durapore membranes in Swinnex 13 mm filter holders. Phosphatidylserine-positive PMVs detected with annexin V-PE were quantified using combined labelling and gating strategies in conjunction with Polysciences Polybead Microspheres (0.2 μm) and BDTrucount tubes. The PMV absolute count was calculated on the analysis template using the Trucount tube lot number information and expressed in PMV count/ml. Having estimated a normal reference range (0.51×10(5)-2.82×10(5) PMVs/ml) from a small sample of human donors, using the developed method, the effect of certain variables was investigated. Variations such as freezing of samples and gender status did not significantly alter the PMV absolute count, and with age plasma PMV levels were only marginally reduced. Smokers appeared to have reduced PMV levels. Nicotine, as for calpeptin was shown to dose-dependently (from 10 up to 50 μM) reduce levels of early apoptosis in THP-1 monocytes and to decrease the level of PMV release. Fasting individuals had 2-3 fold higher PMV absolute counts compared to non-fasting subjects.

Plasma membrane-derived vesicles (PMVs) also known as microparticles, are small membrane-bound vesicles released from the cell membrane via blebbing and shedding. PMVs have been linked with various physiological functions as well as pathological conditions such as inflammation, autoimmune disease and cardiovascular disease. PMVs are characterised by the expression of phosphatidylserine (PS) on the plasma membrane. PS, also expressed on apoptotic cells (ACs) enables macrophages to phagocytose ACs. As it is widely known that PMV production is increased during apoptosis, we were able to show that PMVs could compete dose dependently with ACs for the PS receptor on macrophages, so reducing phagocytosis of ACs. In a clinical setting this may result in secondary necrosis and further pathological conditions. In SLE in which there are raised PMV levels, there is an anti-phospholipid-mediated increase in PMV release, which can be abrogated by depletion of IgG. Our work provides an insight into how PMVs may play a role in the aetiology of autoimmune disease, in particular SLE.