In contrast, Davila et al.100 showed that exosomes, defined as vesicles with a diameter of less than 100 nm, contribute to the overall procoagulant activity of tumor cell derived vesicles. They showed that approximately 20% of the TF coagulant activity was still present after filtration through a 0.1 μm filter, which would indicate a role for exosomes Pirfenidone concentration in coagulation

activation. Unfortunately, they did not investigate whether filtration enables removal of all vesicles larger than 0.1 μm, or whether larger vesicles are fragmented by such a procedure, making the distinction between exosomes and small MVs uncertain. Vesicles act at two levels regarding waste management. Vesicles can contain redundant intracellular components, thus acting as cellular waste disposal bags by their extrusion from the cell. In turn, such vesicles may be removed from the circulation by phagocytosis by other cells. It is tempting to speculate that EVs containing cellular waste are especially equipped to facilitate their clearance, e.g. by exposing

PS, thereby becoming easy targets for phagocytes. There is evidence that the spleen is involved in the clearance of MVs in vivo.100 Thirty minutes after injection click here of PS-exposing MVs from breast or pancreatic cancer cell lines into mice, both TF antigen and TF activity decreased by 72% and 90%, respectively, becoming undetectable 2 h after injection. Already 5 min after injection, the TF antigen was Amisulpride detectable in the spleen. In contrast, in splenectomized mice most of the human TF antigen was still detectable 30 min after injection, and 30% of the splenectomized mice did not survive 2 h after injection. In

humans, clearance of circulating vesicles exposing coagulant TF is extremely fast and efficient. We showed that human wound (pericardial) blood from patients undergoing open heart surgery contains exceptionally high levels of coagulant TF-exposing vesicles that trigger coagulation in vitro91 and thrombus formation in vivo.92 When this wound blood is retransfused, the TF-coagulant activity becomes undetectable in peripheral blood already after 20–30 min, revealing that also in humans clearance of vesicles must be very efficient.101 In pathological conditions, the waste management may not function properly. This could happen because of the failure of the phagocytes to recognize the danger signal[102] and [103] or because these phagocytes are impaired (apoptotic/necrotic).[104], [105] and [106] The consequence is that EVs containing redundant and unwanted biomolecules are not rapidly cleared from the circulation. Thus, these EVs are likely to play a role in the pathological conditions. Monocytes are phagocytes which expose a PS-specific receptor that recognizes PS-exposing vesicles.107 In an in vitro study, human monocytic leukemia cells (THP-1 cells) showed signs of apoptosis or possibly even necrosis after incubation with PS-exposing PMVs containing caspase 3.