Endotoxin induced platelet microvesicle formation measured by flow cytometry

Endotoxin (lipopolysaccharide, LPS) is a major component of the outermost membrane of gram-negative bacteria. Endotoxin is an important mediator of septic shock and it is involved in the development of disseminated intravascular coagulation (DIC), which is a dreaded complication of gram-negative bacterial infections. Platelet microvesicles are platelet derived vesicles that are formed during platelet activation. These microvesicles are too small to be detected by cell counters used in clinical laboratories, but they are active in haemostasis and may thus contribute to the development of DIC. We have used flow cytometry to study the in vivo effect of endotoxin on platelet microvesicle formation in clinical material and in a porcine model. We found increased levels of platelet microvesicles in patients with gram-negative bacterial sepsis. Endotoxin infusion in pigs caused microvesicle formation of up to four times the initial value. Thus, the formation of such microvesicles, which are associated with increased coagulation activity, may be initiated by endotoxin.