Platelet activation microvesicles

Platelet activation leads to the formation of platelet-derived microparticles derived from the platelet surface. These microvesicles typically account for 25% to 30% of platelet procoagulant activity and factor V binding sites (34,39),... 

Such microvesicles have size variable between 50 nm to 1 (xm and differ from other vesicles (like exosomes (30-100 nm)). In general, microparticles are phospholipids vesicles derived from eukaryotic cells as a result of different types of stimulation. Microparticles can also be defined as phospholipids microvesicles containing certain membrane proteins originating from the parental cell. Microparticles circulate in the blood and contribute to numerous physiological processes. MPs have been described in various haematopoietic cells as platelets (Heijnen et al. 1999), T-cells (Blanchard et al. 2002), polynuclear neutrophils (Mesri and Altieri 1999) or dendritic cells. After have been considered as cell dust, MPs are now considered to reflect cell activation. Platelet derived microparticles have been the most extensively studied until now. They are now accepted to play an important role in the procoagulant... 

Heijnen, H.F., Schiel, A.E., Fijnheer, R., Geuze, H.J. and Sixma, J.J. (1999) Activated platelets release two types of membrane vesicles microvesicles by surface shedding and exosomes derived from exocytosis of multivesicular bodies and alpha-granules. Blood 94, 3791-3794. 

Platdet-activating factor (PAF) is formed fi om the membrane phospholipid l-O-alkyl-2-acyl-sn-glycero-3-phosphocholine by the consecutive actions of PLAj and acyltransferase (Qiao and Olson, 1993) and binds to its receptor on human platelets oprogge and Akkerman, 1985 Kloprogge et al. 1986). Rat and mouse platelets lack this receptor (Bairea, 1984 Siess 1989). It has been shown that 87 % of the PAF produced is contained in the microvesicles that are shed fiom the platelets during the activation process (Iwamoto etal, 1996). 

---