Tissue Factor In Plasma Research Articles

PB1102 Evaluation of the Ability of Commercial ELISAs to Measure Tissue Factor in Human Plasma

PB1102 Evaluation of the Ability of Commercial ELISAs to Measure Tissue Factor in Human Plasma

Evaluation of four commercial ELISAs to measure tissue factor in human plasma

BackgroundUnder pathological conditions, tissue factor (TF)-positive extracellular vesicles (EVs) are released into the circulation and activate coagulation. Therefore, it is important to identify methods that accurately quantitate levels of TF in plasma. Enzyme-linked immunosorbent assays (ELISAs) are a fast and simple method to quantitate levels of proteins. However, there are several specific challenges with measuring TF antigen in plasma including its low concentration and the complexity of plasma. ObjectivesWe aimed to evaluate the ability of 4 commercial ELISAs to measure TF in human plasma. MethodsWe determined the ability of 4 commercial ELISAs (Imubind, Quantikine, Human SimpleStep, and CD142 Human) to detect recombinant human TF (Innovin) (12.5-100 pg/mL), TF-positive EVs isolated from the culture supernatant from a human pancreatic cancer cell line (57 pg/mL), TF in plasma containing low levels of EV TF activity (1.2-2.6 pg/mL) from lipopolysaccharide-stimulated whole blood, and plasma containing high levels of EV TF activity (151-696 pg/mL) from patients with acute leukemia. ResultsThe CD142 Human ELISA could not detect recombinant TF. Imubind and Quantikine but not Human SimpleStep detected recombinant TF spiked into plasma and TF-positive EVs isolated from the culture supernatant of a human pancreatic cancer cell line. Quantikine and Imubind could not detect low levels of TF in plasma from lipopolysaccharide-stimulated whole blood. However, Quantikine but not Imubind detected TF in plasma from acute leukemia patients with high levels of EV TF activity. ConclusionOur results indicate that commercial ELISAs have different abilities to detect TF. Quantikine and Imubind could not detect low levels of TF in plasma, but Quantikine detected TF in plasma with high levels of TF.

Inflammasome activation mediated by oxidised low-density lipoprotein in patients with sleep apnoea and early subclinical atherosclerosis.

Atherosclerosis is a common comorbidity of obstructive sleep apnoea (OSA) patients, caused by the interaction of dyslipidaemia and systemic inflammation. The OSA pro-inflammatory response is mediated by NLRP3 inflammasome activation, which requires a priming signal mediated by intermittent hypoxia (IH) and an activation signal provided by soluble stimulus present in plasma. Our objectives were to study oxidised low-density lipoprotein (oxLDL) expression in OSA patients with or without early subclinical atherosclerosis (eSA) as well as its contribution to NLRP3 activation and tissue factor (TF) release. We analysed oxLDL, key components of the NLRP3 inflammasome cascade and TF in plasma and monocytes from OSA patients and non-apnoeic subjects, with or without eSA as determined by increased carotid intima-media thickness without the appearance of atherosclerotic plaques. The oxLDL contribution to NLRP3 inflammasome activation was assessed using in vitro models. High levels of oxLDL were identified in plasma from OSA patients, particularly in those with eSA, as well as an overexpression of NLRP3 cascade components and TF. Furthermore, in vitro models showed that both oxLDL and plasma from OSA patients with eSA act synergistically with IH as a priming and activation signal of NLRP3 that enhances the inflammatory response, pyroptosis and TF release. OSA patients with eSA exhibit NLRP3 activation by IH and the presence of oxLDL capable of releasing TF, constituting a pathway for the interaction between dyslipidaemia and systemic inflammation in the development of atherosclerotic lesions.

Measurement of tissue factor-positive extracellular vesicles in plasma: strengths and weaknesses of current methods.

This review evaluates the different methods used to measure levels of tissue factor (TF) in plasma and on extracellular vesicles (EVs). Levels of TF-positive (TF+) EVs in blood are increased in a variety of diseases, such as cancer, sepsis, and viral infection, and are associated with thrombosis. Highly sensitive assays are required to measure the low levels of TF+ EVs in blood. TF antigen levels in plasma have been measured using standard ELISAs, SimpleStep ELISA technology, and solid-phase proximity ligation assay. Some studies reported the detection of TF+ EVs in plasma by flow cytometry. In addition, TF+ EVs can be captured onto beads and chips using anti-TF antibodies. Several assays have been developed to measure TF activity in EVs isolated from plasma. Importantly, activity-based assays are more sensitive than antigen-based assays as a single TF/FVIIa complex can generate large amounts of FXa. We recommend isolating EVs from plasma and measuring TF activity using a functional assay in the presence and absence of an anti-TF antibody. We do not recommend using antigen-based assays as these are not sensitive enough to detect the low levels of TF in plasma.

Correlation between Thrombin Generation, Standard Coagulation Assays, and Viscoelastic Assays for Hemostatic Assessment in Critically Ill Children.

Accurate assessment of hemostatic function is essential to guide care in critically ill children with acute and acquired coagulopathies. Thrombin generation (TG) provides a global assessment of procoagulant and anticoagulant factors and is commonly used in hemostasis research laboratories. Our objective was to determine the correlation of clinically available hemostasis assays with TG in critically ill children. Children (<18 years old, >3 kg in weight) in the intensive care unit were enrolled from March 2016 to December 2019 in a prospective 2-center study. Coagulation tests were prothrombin time, activated thromboplastin time, anti-Xa assay, viscoelastic assays (thromboelastography [TEG], rotational thromboelastometry [ROTEM]), and TG (induced by 20 pM tissue factor in platelet poor plasma and reported as endogenous thrombin potential [ETP; nM*min]). Data are reported as median (interquartile range) or Spearman coefficient (ρ). Patients (n = 106, age 10.2 years [3.8-15.3]) were divided into 3 groups: (a) no anticoagulation (n = 46), (b) anticoagulation (unfractionated heparin) without extracorporeal life support (n = 34), or (c) with extracorporeal life support (n = 26). ETP was decreased in anticoagulated compared to non-anticoagulated patients (group 1: 902.4 [560.8-1234], group 2: 315.6 [0.0-962.2], group 3: 258.5 [0.0-716.6]; P < 0.0001). Across all patients, ETP correlated best with TEG kinetic time (TEG-K), in min (ρ = -0.639), followed by TEG reaction time, in min (ρ = -0.596). By group, ETP correlated best with international normalized ratio for group 1 (ρ = -0.469), TEG-K time for group 2 (ρ = -0.640), and anti-Xa for group 3 (ρ = -0.793). Standard and viscoelastic assays have varying correlation with TG in critically ill children. TEG-K time had the most consistent moderate correlation with ETP across all groups.

Low factor V level ameliorates bleeding diathesis in patients with combined deficiency of factor V and factor VIII

AbstractCombined factor V (FV) and FVIII deficiency (F5F8D) is a rare autosomal-recessive bleeding disorder caused by mutations in lectin mannose binding-1 (LMAN1) and multiple coagulation factor deficiency-2 (MCFD2). Six causative homozygous mutations (5 in LMAN1 and 1 in MCFD2) were identified in 6 patients with F5F8D. A thrombin-generation assay, triggered with tissue factor (1 pM) in F5F8D plasma, paradoxically exhibited enhanced thrombin generation compared with normal plasma. Significantly lower free tissue factor pathway inhibitor (fTFPI) was found in F5F8D patients compared with healthy controls (P < .01). Normalizing tissue factor pathway inhibitor α (TFPIα) in F5F8D plasma greatly delayed and reduced thrombin generation. Increasing FV concentrations by adding plasma FV to F5F8D plasma only caused a gradual decrease in thrombin generation, suggesting that low levels of TFPIα and FV cocontributed to the elevated thrombin generation by reducing anticoagulant effects. On the contrary, thrombin generation in F5F8D platelet-rich plasma (PRP) was significantly lower than in normal controls (P < .05); however, it was fully corrected by normalizing FVIII or after 1-deamino-8-d-arginine vasopressin (DDAVP) infusion, indicating that the hypocoagulable state of F5F8D patients is associated with low FVIII levels. In addition, plasma and platelet FV in F5F8D PRP were sufficient to support normal thrombin generation, and low TFPIα may have no effect on thrombin generation. DDAVP infusion induced a complete response in 5 F5F8D patients and a partial response in the remaining patient. Based on our findings, we suggest that DDAVP may be considered a potential substitute for FVIII concentrates, and fresh-frozen plasma (FFP) infusion may not be necessary for F5F8D patients with minor bleeding challenges.

Targeting protease nexin-1, a natural anticoagulant serpin, to control bleeding and improve hemostasis in hemophilia

AbstractHemophilia A and B, diseases caused by the lack of factor VIII (FVIII) and factor IX (FIX) respectively, lead to insufficient thrombin production, and therefore to bleeding. New therapeutic strategies for hemophilia treatment that do not rely on clotting factor replacement, but imply the neutralization of natural anticoagulant proteins, have recently emerged. We propose an innovative approach consisting of targeting a natural and potent thrombin inhibitor, expressed by platelets, called protease nexin-1 (PN-1). By using the calibrated automated thrombin generation assay, we showed that a PN-1-neutralizing antibody could significantly shorten the thrombin burst in response to tissue factor in platelet-rich plasma (PRP) from patients with mild or moderate hemophilia. In contrast, in PRP from patients with severe hemophilia, PN-1 neutralization did not improve thrombin generation. However, after collagen-induced platelet activation, PN-1 deficiency in F8−/−mice or PN-1 blocking in patients with severe disease led to a significantly improved thrombin production in PRP, underlining the regulatory role of PN-1 released from platelet granules. In various bleeding models, F8−/−/PN-1−/− mice displayed significantly reduced blood loss and bleeding time compared with F8−/−mice. Moreover, platelet recruitment and fibrin(ogen) accumulation were significantly higher in F8−/−/PN-1−/− mice than in F8−/−mice in the ferric chloride-induced mesenteric vessel injury model. Thromboelastometry studies showed enhanced clot stability and lengthened clot lysis time in blood from F8−/−/PN-1−/− and from patients with hemophilia A incubated with a PN-1-neutralizing antibody compared with their respective controls. Our study thus provides proof of concept that PN-1 neutralization can be a novel approach for future clinical care in hemophilia.

Histones Induce the Release of Extracellular Hemoglobin and Red Blood Cell-Derived Microvesicles with Procoagulant Activity

BackgroundHistones are nuclear proteins that can be released extracellularly following cell death or certain mechanisms of cell activation. Infusion of high doses of histones into mice causes lethality. Circulating levels of extracellular histones are elevated in several disease states associated with inflammation and thrombosis. The mechanisms by which extracellular histones induce morbidity and mortality are not fully understood. Histones may activate or be toxic to several cell types in vitro. Most of these activities have been shown to be dependent on histone signaling through toll-like receptors (TLRs). Red blood cells (RBC) do not express TLRs. However, previous studies have reported that histones promote RBC aggregation, increase shear-dependent RBC fragility, reduce deformability under flow and cause hemolytic anemia in mice. Histones also induce calcium influx and promote PS expression on RBC membranes thereby supporting the prothrombinase activity and shortening clotting times in plasma. Histones may insert into cell membranes (independently of TLRs), and form pore-like structures similar to ionophore. The role of this process in histone-induced RBC toxicity has not been fully investigated.ObjectiveWe assessed the ability of individual histones to promote the release of extracellular hemoglobin (Ex-Hb) and RBC-derived microvesicles (RBC-MVs), as well as RBC-MVs' ability to initiate or propagate thrombin generation (TG) in MV-free plasma.MethodsRBCs were isolated from citrated whole blood from healthy volunteers, and were re-suspended in buffer with or without 10uM A23187 (calcium ionophore), recombinant histones H2A, H2B, H3 or H4 for 1 hour at 37°C.To assess histone binding, RBCs were washed and dual-stained with fluorophore-conjugated anti-glycophorin A (GPA) and anti-panhistone antibodies. Stained RBCs were analyzed using imaging flow cytometry, and were considered positive for histone binding if the fluorescence intensity was > 95th percentile of RBCs processed in the absence of histones.RBCs were removed by centrifugation at 2,500g for 15 minutes x2. RBC-MVs present in the supernatant were pelleted by centrifugation at 20,000g for 30 min. Isolated RBC-MVs were then re-suspended in buffer to assess PS exposure using the microparticle activity assay (Hyphen Biomed). RBC-MVs were also re-suspended in re-calcified MV-free plasma supplemented with 4uM 41%PC/44%PE/15%PS lipid vesicles to assess their ability to initiate TG by monitoring the activity of thrombin on a fluorogenic substrate over time. To assess their ability to propagate TG, coagulation was initiated by 1pM tissue factor in MV-free plasma containing histone-induced RBC-MVs without addition of synthetic lipid vesicles. In this condition, phospholipids present on the surface of histone-induced RBC-MVs are the limiting factor for TG.The supernatant collected after pelleting RBC-MVs was used to measure Ex-Hb by absorbance at 540 nm.ResultsThe percentage of RBCs positive for histone binding was 21.6%, 2.3%, 76.9% and 98.1% for H2A, H2B, H3 and H4, respectively. Representative images of RBC staining for GPA and histone H4 is shown in Figure 1A.All histone types induced the release of Ex-Hb (Fig. 1B) and RBC-MVs that possess PS activity (Fig. 1C) in a dose-dependent manner, with the highest PS activity observed with H2A. RBC-MVs released by H2A or H2B clearly initiated TG in MV-free normal pool plasma (Fig.1D). They also significantly enhanced TF-initiated TG in the absence of additional lipid vesicles. The release of Ex-Hb and procoagulant RBC-MVs induced by histones were re-capitulated by ionophore to a greater degree, as expected (Fig.1B-E).ConclusionsAll 4 types of core histones bind to RBCs and induce the release of Ex-Hb. Our findings suggest that despite their lower binding to RBCs, histones H2A and H2B may have a greater ability to induce the release of procoagulant RBC-MVs that can initiate and propagate TG in plasma. The reason for the differential toxicity of histone types on RBCs and the discrepancy between the relative effect of histone-induced RBC-MVs on PS equivalents and TG are unknown. Histone-induced RBC toxicity appears to mimic calcium ionophore, supporting the idea that histones may insert and form functional pores in cell membranes. The contribution of Ex-Hb and procoagulant RBC-MVs to the morbidity and mortality of extracellular histones in vivo requires further studies. [Display omitted] DisclosuresMonroe:Novo Nordisk A/S: Honoraria, Research Funding.

Emicizumab, A Bispecific Antibody to Factors IX/IXa and X/Xa, Does Not Interfere with Antithrombin or TFPI Activity In Vitro.

Emicizumab is a humanized bispecific antibody that binds simultaneously to factor (F) IXa and FX replacing the cofactor function of FVIIIa. Because emicizumab recognizes FIX/FIXa and FX/FXa, a question may arise whether emicizumab competes with antithrombin (AT) and/or tissue factor pathway inhibitor (TFPI), thereby enhancing overall hemostatic potential by blocking their antihemostatic effects. To address this question, we performed enzymatic assays using purified coagulation factors to confirm whether emicizumab interferes with the action of AT on FIXa or FXa, or with the action of TFPI on FXa. In those assays, we found no interference of emicizumab on the actions of AT and TFPI. We next assessed emicizumab's influences on the anticoagulation actions of AT or TFPI in thrombin generation assays triggered with FXIa or tissue factor (TF) in AT-depleted or TFPI-depleted plasma supplemented with AT or TFPI in vitro. In those assays, we employed anti-FIXa and anti-FX monospecific one-armed antibodies derived from emicizumab instead of emicizumab itself so as to prevent emicizumab's FVIIIa cofactor activity from boosting thrombin generation. Consequently, we found that neither anti-FIXa, anti-FX monospecific antibody, nor the mixture of the two interfered with the anticoagulation actions of AT or TFPI in plasma. Although emicizumab can bind to FIXa and FXa, our results showed no interference of emicizumab with the action of AT or TFPI on FIXa or FXa. This indicates that the presence of emicizumab is irrelevant to the action of AT and TFPI, and thus should not alter the coagulant/anticoagulant balance related to AT and TFPI.

Effect of Andexanet-TFPI Interaction on in Vitro Thrombin Formation and Coagulation Markers in the TF-Pathway

Background: Tissue factor pathway inhibitor (TFPI) plays a major role in regulation of tissue factor (TF)-initiated coagulation in a FXa-dependent manner. Andexanet alfa (AnXa) is a modified, recombinant, catalytically inactive form of human FXa being developed to reverse the anticoagulant activity of FXa inhibitors in patients during episodes of major bleeding. As a modified FXa, AnXa retained high binding affinity to fXa inhibitors, including TFPI. Our previous in vitro studies demonstrated that AnXa reverses rivaroxaban-induced inhibition of thrombin generation (TG) initiated by either the extrinsic or intrinsic pathways. However, the thromboelastography (TEG) results showed that AnXa-TFPI interaction enhanced thrombin formation at low TF conditions, which suggested potential increase in the fibrin degradation product in the presence of recombinant tissue plasminogen activator (rtPA) (Lu, G., et al, ASH2016). In the current study, we further characterized the differential effect of AnXa on thrombin formation and clot lysis via the two different pathways, and correlated the TG and TEG parameters with the coagulation markers in the TF-initiated reaction in plasma, including prothrombin fragment (F1+2), thrombin-antithrombin complex (TAT), and fibrin degradation product (D-dimer).Methods: TF-initiated TG in human plasma was measured using a calibrated automated thrombogram (TF-CAT) and the PPP-reagent (5 pM TF, Diagnostica Stago). Non-TF-initiated TG was measured using CAT and an aPTT reagent, Actin FS (Siemens Healthcare) as the activator (Actin FS-CAT). Clot formation was measured in plasma using a TEG 5000 analyzer (Haemonetics). TF (1 pM) and Actin FS (1:240 final dilution) were used as the activators with or without rtPA (150 ng/mL). Time-dependent thrombin formation and clot lysis were monitored by quenching samples at various times (0, 2.5, 5, 10, 15, 30, 60 min) following initiation of the reaction by TF (1 pM) in plasma with or without rtPA (150 ng/mL) and AnXa (4.0 µM). Corn trypsin inhibitor (CTI, 50 µg/mL) was added to block contact activation. F1+2, TAT and D-dimer were quantified according to manufacturers' recommendations.Results: The effect of AnXa on TF-CAT and Actin FS-CAT were compared side-by-side with AnXa at low (0 - 20 nM) and high (0 - 4.0 µM) concentration ranges. AnXa (5 nM) increased TF-CAT parameters sensitive to TFPI activity (i.e., peak thrombin), with less effect on endogenous thrombin potential (ETP). No further increase in these parameters was observed at AnXa therapeutic concentrations (e.g., 2.0 and 4.0 µM), consistent with the expected effect of AnXa on the activity of TFPI, which is present at low plasma concentration (~2.4 nM). In contrast, AnXa did not significantly affect the Actin FS-CAT parameters.The effect of AnXa-TFPI interaction on coagulation and fibrinolytic pathways in human plasma were compared using TEG, with or without rtPA. AnXa (4.0 µM) reduced the TF-TEG-R parameter (lag time, equivalent to clotting time) and resulted in an increased area under the fibrinolytic profile with rtPA as previously shown. In contrast, AnXa and the buffer controls had similar profiles in the Actin FS-TEG assay under similar conditions, with or without rtPA (150 ng/mL) in the current studies, suggesting lack of an AnXa-TFPI effect.We further investigated the effect of AnXa-TFPI interaction on coagulation markers following TF (1pM)-initiated thrombin formation in plasma. AnXa (4 µM) increased F1+2 and TAT levels at early time points following initiation (2.5, 5, 10, 15 min), but had no difference at or after 30 min, compared to buffer control. A similar pattern was observed for D-dimer level when exogenous rtPA (150 ng/mL) was added. Compared to buffer control, AnXa caused elevation of D-dimer level at early time points but had no difference at or after 30 min following initiation of the reaction.Conclusions: AnXa-TFPI interaction can modulate the TF/TFPI activity in the initiation phase of the extrinsic coagulation pathway and increase parameters sensitive to TFPI activity in the TF-CAT and TF-TEG assays, but has minimal effect on the later phase of the reactions and the overall thrombin formation potential. Consistent with clinical observations, AnXa-TFPI interaction increased the F1+2 and TAT levels, as well as D-dimer level in the presence of rtPA in the early phase of the reaction following initiation of the reaction by TF. DisclosuresLu:Portola Pharmaceuticals, Inc.: Employment. Lin:Portola Pharmaceuticals, Inc.: Employment. Curnutte:3-V Biosciences: Equity Ownership; Sea Lane Biotechnologies: Consultancy; Portola Pharmaceuticals, Inc.: Employment, Equity Ownership, Patents & Royalties. Conley:Portola Pharmaceuticals, Inc.: Employment, Equity Ownership, Patents & Royalties.

Correlation between factor (F)XIa, FIXa and tissue factor and trauma severity.

It has been observed that trauma patients often display elevated procoagulant activity that could be caused, in part, by tissue factor (TF). We previously observed that trauma patients with thermal, blunt, and penetrating injuries have active FIXa and FXIa in their plasma. In the current study, we evaluated the effect of injury severity, with or without accompanying shock, on the frequency and concentration of TF, FIXa, and FXIa in plasma from trauma patients. Eighty trauma patients were enrolled and divided equally into four groups based on their Injury Severity Score and base deficit:Blood was collected at a 0 time-point (first blood draw upon arrival at hospital) and citrate plasma was prepared, frozen, and stored at -80 °C. FXIa, FIXa, and TF activity assays were based on a response of thrombin generation to corresponding monoclonal inhibitory antibodies. The frequency and median concentrations of TF were relatively low in non-severe injury groups (17.5% and 0 pM, respectively) but were higher in those with severe injury (65% and 0.5 pM, respectively). Although FXIa was observed in 91% of samples and was high across all four groups, median concentrations were highest (by approximately fourfold) in groups with shock. FIXa was observed in 80% of plasma samples and concentrations varied in a relatively narrow range between all four groups. No endogenous activity was observed in plasma from healthy individuals. (1) Frequency and concentration of TF is higher in patients with a higher trauma severity. (2) Concentration of FXIa is higher in patients with shock. (3) For the first time reported, the vast majority of plasma samples from trauma patients contain active FIXa and FXIa. Prognostic/epidemiological study, level II.

Andexanet Alfa, a Universal Antidote Under Development for Factor Xa Inhibitors, Reverses Rivaroxaban-Induced Inhibition of Thrombin Generation Initiated By the Intrinsic Coagulation Pathway Independent of TFPI

Background: Andexanet alfa (AnXa) is a modified, recombinant human fXa molecule being developed to reverse the anticoagulant activity of fXa inhibitors in patients during episodes of major bleeding. As a modified fXa, AnXa retained high binding affinity to fXa inhibitors and had no significant interaction with major plasma coagulation proteins, except for tissue factor pathway inhibitor (TFPI), an endogenous fXa inhibitor with sub-nanomolar affinity to both fXa and AnXa. In previous in vitro and clinical studies in healthy volunteers, AnXa has shown dose-dependent and complete reversal of both direct and indirect fXa inhibitors in tissue factor (TF)-initiated thrombin generation (TG). To delineate the contribution of AnXa-TFPI interactions to TG, we compared rivaroxaban (Riva)-induced inhibition of TG initiated via the extrinsic pathway (TF) versus the intrinsic pathway (non-TF). The differential effect of AnXa on TG and clot formation via the two pathways was further studied in the context of recombinant tissue plasminogen activator (rtPA)-induced fibrinolysis using thromboelastography (TEG).Methods: TF-initiated TG in human plasma was measured using a calibrated automated thrombogram (CAT) and the PPP-reagent (5 pM TF). Non-TF-initiated TG was measured using CAT and Actin FS, an aPTT reagent. Anti-fXa activity was measured using a modified anti-fXa chromogenic assay with reagents from the Coamatic Heparin kit (DiaPharma). Riva was used as the standard. Pooled human plasma was spiked with Riva (0 - 2 µM) or Riva (1 µM)+AnXa (0 - 4 µM), and TG and anti-fXa activity were measured. Clot formation with or without AnXa was measured in plasma using a TEG 5000 analyzer. The functional fibrinogen (TF) and Kaolin reagents (both from Haemonetics) were used according to the manufacturer’s instruction. For low TF-initiated clot formation, the PPP-reagent (5 pM TF) was diluted in phospholipid (4.0 µM) followed by measuring the TEG profiles with 0.25, 0.5 and 1.0 pM TF.Results: The potential contribution of AnXa-TFPI interaction to TG was studied under similar conditions using TF or Actin FS in human plasma containing AnXa, Riva or Riva+AnXa. AnXa alone had minimal effect on the endogenous thrombin potential (ETP) in either assay. AnXa was able to fully reverse Riva-induced anticoagulation in the Actin FS TG assay, independent of AnXa-TFPI interaction that primarily modulates TF activity. The modulation of TF activity could be assessed by correlating ETP vs. the anti-fXa activity in samples containing Riva or Riva+AnXa. Riva dose-dependently inhibited TF-initiated TG as anti-fXa activity increased. At similar anti-fXa levels (i.e., similar free Riva concentration), Riva+AnXa had higher ETP than Riva alone. As expected, this difference was not observed in the Actin FS TG assay.To further investigate the role of AnXa-TFPI interaction on coagulation and fibrinolytic pathways, the profile of clot formation was studied in human plasma using TEG without Riva. AnXa (4 µM) had no effect on the TEG parameters in the kaolin assay or the functional fibrinogen assay containing high TF, with or without rtPA (150 ng/mL). When low TF (0.25, 0.5, and 1.0 pM) was used to initiate clot formation in the absence of rtPA, AnXa reduced the TEG-R parameter (lag time equivalent to clotting time), but had no effect on maximum amplitude (MA). The fibrin clot formed under each condition (±AnXa) was lysed slowly at low rtPA (75 ng/mL, ~1 nM), resulting in well-segregated processes of coagulation and fibrinolysis. However, rtPA at 150 ng/mL (~2 nM) dramatically changed the lysis profiles that overlapped the fibrin formation, possibly due to the higher rtPA activity ratio, relative to the major plasma inhibitor PAI-1 (<1 nM). With the optimal rtPA, fibrin clot formed at each TF concentration (±AnXa) was compensated by the fibrinolytic activity of rtPA resulting in an increased fibrin degradation product.Conclusions: In the absence of a fXa inhibitor, AnXa had minimal effect on TF or Actin FS-initiated TG with no direct interaction or effect on rtPA function. AnXa dose-dependently and completely reversed Riva-induced inhibition of TG initiated by either the intrinsic or extrinsic pathway, but had different effect on ETP due to the AnXa-TFPI interaction that mainly modulates TF function. AnXa-TFPI interaction may enhance TF-initiated TG at low TF conditions with increased fibrin degradation product in the presence of rtPA. DisclosuresLu:Portola Pharmaceuticals, Inc.: Employment. Lin:Portola Pharmaceuticals, Inc.: Employment. Curnutte:3-V Biosciences: Equity Ownership; Sea Lane Biotechnologies: Consultancy; Portola Pharmaceuticals: Employment, Equity Ownership, Patents & Royalties, Research Funding. Conley:Portola Pharmaceuticals, Inc.: Employment.

Edoxaban, a direct factor Xa inhibitor, suppresses tissue-factor induced human platelet aggregation and clot-bound factor Xa in vitro: Comparison with an antithrombin-dependent factor Xa inhibitor, fondaparinux

IntroductionTissue factor-induced platelet aggregation and factor Xa (FXa) activity bound to clot contribute to the formation and growth of thrombus. The effects of edoxaban, a direct FXa inhibitor, on these responses were determined and compared with that of fondaparinux, an antithrombin-dependent (indirect) FXa inhibitor. Material and methodsHuman platelet aggregation was induced by human tissue factor (Dade Innovin or RecombiPlasTin) in platelet-rich plasma spiked with edoxaban or fondaparinux. Clot formed from human whole blood was incubated with 0.9μM prothrombin in the absence or presence of FXa inhibitors. As the index of FXa activity, the amount of prothrombin fragment F1+2 was measured with an ELISA. Free FXa activity was measured using human FXa and its chromogenic substrate S-2222. ResultsEdoxaban inhibited tissue factor-induced platelet aggregation in a concentration-dependent manner with the IC50 values of 150 and 110nM for Dade Innovin and RecombiPlasTin-induced platelet aggregation, respectively. At 1μM, edoxaban completely inhibited the aggregation. Fondaparinux inhibited RecombiPlasTin-induced aggregation with the IC50 of 9.3μM, but did not show complete inhibition up to 30μM and had no effect on Dade Innovin-induced aggregation. Edoxaban inhibited both free and clot-bound FXa with the IC50 of 2.3 and 8.2nM, respectively. Fondaparinux inhibited free FXa (IC50 5.4nM), but 40-times higher concentration were required to inhibit clot-bound FXa (IC50 217nM). ConclusionsEdoxaban, a direct FXa inhibitor, was a more potent inhibitor of tissue factor-induced platelet aggregation and clot-bound FXa than fondaparinux, an indirect FXa inhibitor.

Correlation between Factor (F)XIa, FIXa and Tissue Factor and Trauma Severity

Background. It has been observed that trauma patients often display an elevated procoagulant activity. This activity has been hypothesized to be caused in part by tissue factor (TF) located on the endothelium, blood cells and microparticles. We also observed in our previous studies that trauma patients with thermal, blunt and penetrating injuries have active FIXa and FXIa in their plasma, often persistent for several days to weeks. What is not known is the effect of injury type and severity on TF release after trauma. In the current study we evaluated how the severity of an injury with or without accompanying shock affects the frequency and concentration of TF, FIXa and FXIa in plasma from trauma patients.Methods. Eighty trauma patients presenting to a major urban level 1 trauma center (47 with blunt trauma and 33 with penetrating trauma) were enrolled. 62 patients were male and 18 female. The age of patients varied between 18 and 90 years (average 42.6±19.2 years) and the Injury Severity Score (ISS) varied between 1 and 75 (average 19.3±17.2). Blood was collected immediately upon emergency department arrival prior to any resuscitation or blood product transfusion. For analysis our cohort was divided into 4 groups (20 patients/group) based on their ISS and presence of shock (base deficit BD):Group 1: Non-severe injury, no shock (ISS≤15; BD>-6)Group 2: Non-severe injury, with shock (ISS≤15; BD≤-6)Group 3: Severe injury, no shock (ISS>15; BD>-6)Group 4: Severe injury, with shock (ISS>15; BD≤-6)Citrate plasma was prepared, frozen and stored at -80°C. No additional freeze/thaw cycles were involved prior to FXIa, FIXa and TF activity assays. The assays were based on a response of thrombin generation to corresponding monoclonal inhibitory antibodies (αFXIa-2, αFIXa-91 and αTF-5, respectively; all at 0.1 mg/mL).Results. The frequency of TF in less injured patients was relatively low (table) and increased by at least 3-fold in patients with severe injury (groups 3 and 4). The concentration of TF varied in a wide range in all 4 groups, but was the lowest in group 1 patient samples and the highest in groups 3 and 4. FXIa was observed in 91% of plasma samples and was high in all 4 groups of patients. Similar to TF, the concentration of FXIa varied in a wide range in the entire study population. Unlike TF however, FXIa was present in patients with shock at a higher concentration and did not correlate with the severity of injury. Only 9 of 20 group 1 plasma samples had detectable FIXa, whereas in groups 2-4 only 1 or 2 plasma samples had no FIXa activity. The median concentration of this protein varied in a relatively narrow range between all 4 groups, although the lowest was observed in group 1. For the entire cohort, there was a good correlation between FIXa and FXIa concentrations (R2 =0.33), but no correlation between TF and FIXa or FIXa. These data suggest that FXIa in trauma patient blood is generated primarily through the contact pathway, although the input of the TF pathway to FXI activation cannot be excluded. Table 1Patient GroupTFFXIaFIXaFrequencyConcentration (pM)FrequencyConcentration (pM)FrequencyConcentration (pM)RangeMedianRangeMedianRangeMedian14/20 (20%)0.1 - >6.40.2818/20 (90%)0.9 - >647.39/20 (45%)73 - >100017523/20 (15%)0.5 - >6.41.0019/20 (95%)3.2- >6423.418/20 (90%)38 - >1000270312/20 (60%)0.3 - >6.43.5017/20 (85%)0.7 - >6411.118/20 (90%)75 - >1000252414/20 (70%)0.2 - >6.42.4819/20 (95%)1.8 - >6426.519/20 (95%)26 - >1000205Overall33/80 (41%)0.1 - >6.41.0173/80 (91%)0.7 - >10017.064/80 (80%)26 - >1000250Conclusions. 1) Frequency and concentration of TF is higher in patients with a higher trauma severity, but it is independent of shock; 2) The vast majority of plasma samples from trauma patients contain active FIXa and FXIa; 3) Concentration of FXIa is higher in patients with shock and does not appear to be affected by the trauma severity. Taken together, these data suggest separate mechanisms for contact pathway activation after injury driven by shock and TF pathway activation driven by tissue injury. DisclosuresNo relevant conflicts of interest to declare.

Thrombin generation induced by tissue factor plus ADP in human platelet rich plasma: A potential new measurement to assess the effect of the concomitant use of an oral factor Xa inhibitor edoxaban and P2Y12 receptor antagonists

IntroductionPatients with atrial fibrillation undergoing percutaneous coronary intervention may require combination therapy with anticoagulants and antiplatelet agents. The objectives of this study were to establish an assay which can evaluate the effects of both anticoagulants and P2Y12 receptor antagonists and determine the effects of edoxaban, a direct factor Xa inhibitor, and P2Y12 receptor antagonists (clopidogrel and ticagrelor) alone and when combined. Material and methodsHuman platelet-rich plasma (PRP) from healthy subjects was stimulated with adenosine diphosphate (ADP) plus tissue factor. Thrombin generation was measured by means of calibrated automated thrombography. ResultsCombination of 10μM ADP and low concentration (0.25 pM) tissue factor induced reproducible thrombin generation in human PRP. Edoxaban (40 and 80ng/mL), active metabolite of clopidogrel (AM-clopidogrel, 10 and 20μg/mL), and ticagrelor (3μg/mL) alone inhibited ADP plus tissue factor-induced thrombin generation. Edoxaban suppressed all 5 parameters (lag time, peak, time to peak, endogenous thrombin potential, and maximum rate), whereas AM-clopidogrel and ticagrelor inhibited 4 and 3 parameters, respectively. Concomitant treatment with edoxaban and AM-clopidogrel or ticagrelor produced an additive inhibition of thrombin generation compared to the single treatments. ConclusionsThe thrombin generation assay induced by ADP plus tissue factor can detect the activities of both edoxaban and P2Y12 receptor antagonists. Combination of edoxaban and a P2Y12 receptor antagonist shows additive inhibition. These results suggest that ADP plus tissue factor-induced thrombin generation may be a useful measurement to assess the combination effects of anticoagulants and P2Y12 receptor antagonists in a single assay.

A TFPI Inhibitory Half Life Extended Fusion Peptide Proves Efficacy in FVIII Knock out Mice and Marmoset Monkeys

IntroductionTissue factor pathway inhibitor (TFPI) is an important inhibitor of the extrinsic coagulation pathway as it inhibits factor Xa (FXa) and the tissue factor (TF) – FVIIa complex. Inhibition of TFPI with blocking antibodies, aptamers, or peptide inhibitors improves hemostasis and may become an option to treat patients with hemophilia including those with inhibitors. We developed a TFPI-antagonistic fusion peptide (FP) consisting of a linear and a cyclic peptide connected by a linker. The two peptide entities bind to different epitopes on TFPI and together synergistically inhibit TFPI. The FP was further improved by half-life extending (HL) non-covalent albumin binding. HL-FP was characterized for in vitroinhibition of TFPI, pharmacokinetics, and improvement of coagulation in animal models of hemophilia.MethodsHL-FP was characterized in a set of in vitro assays for binding to and inhibition of TFPI. Interaction with immobilized TFPI was studied by BiaCore. Functional inhibition was analyzed in model assay systems such as inhibition of FXa and FX activation by TF/FVIIa and plasma assays according to the calibrated automated thrombography (CAT) protocol at low TF in hemophilia plasma. Addition of TFPI simulated conditions of potentially elevated TFPI plasma concentrations. In a single dose PK study, mice (n=6 per time point) received 400 nmol/kg of the HL-FP intravenously (i.v.) or subcutaneously (s.c.). Plasma was sampled up to 38 h after dosing and HL-FP level quantified by a compound specific LC-MS protocol. To provide an ex vivo activity measure, FVIII inhibitory antibodies were added to mouse plasma to mimic a hemophilic condition and then analyzed by calibrated automated thrombography (CAT). A 2-week repeated i.v. dose study in mice investigated TFPI accumulation due to HL-FP. HL-FP was dosed at 40, 400, and 2000 nmol/kg and mouse plasma TFPI levels determined by ELISA. The efficacy of the HL-FP was studied in a hemophilia A mouse tail cut model and in a marmoset monkey model of ex vivoimprovement of coagulation. FVIII knockout mice (n=16 per group) were dosed i.v. with 12-400 nmol/kg HL-FP in the presence of a sub-therapeutic level of recombinant FVIII (10 U/kg) and blood loss (mg) was assessed. Marmoset monkeys (N=4) received 400 nmol/kg HL-FP i.v. and plasma samples obtained 1 h after dosing were analyzed by CAT in the presence of FVIII inhibitory antibodies.ResultsHL-FP bound to and efficiently inhibited TFPI as demonstrated in several in vitro test systems. Binding affinity of < 1nM correlated well with functional inhibition of TFPI in model assays, resulting in IC50s of ~0.7nM. The HL-fusion peptide (HL-FP) efficiently inhibited plasma TFPI, which resulted in an improvement of all thrombin generation parameters in plasma of hemophilia A and B patients, with EC50s ranging from 6 to 20nM. HL-FP increased peak thrombin levels of hemophilia plasma to or slightly above a range established for individual normal plasma. Non-covalent binding to albumin substantially increased the half-life to ~4 h with ~ 50% s.c. bioavailability in mice. The ex vivo procoagulant activity determined by CAT correlated well with HL-FP plasma concentrations. In the repeated dose study, the HL-FP was well tolerated and did not accumulate TFPI, which strongly indicates that HL-FP did not interfere with TFPI clearance receptor interactions. HL-FP significantly reduced bleeding in the hemophilia mouse tail cut bleeding model at a dose as low as 40 nmol/kg. In marmoset monkeys, HL-FP efficiently improved ex vivo plasma thrombin generation, even at low peptide plasma concentrations (25- 55 nM).SummaryWe developed a TFPI inhibitor composed of two TFPI antagonistic peptides that completely inhibits TFPI. Introduction of an entity non-covalently bound to albumin provides intermediate half-life extension and s.c. bioavailability. This HL-FP improved coagulation and hemostasis in animal models of hemophilia and did not interfere with TFPI clearance receptor interactions. TFPI-antagonistic peptides with a prolonged half-life, resistance to elevated TFPI, and minimal interference with TFPI clearance. Our HL-FP appears to be useful in preventing bleeding in hemophilia and provides a FVIII and FIX independent approach for non-i.v. treatment. DisclosuresDockal:Baxter Innovations GmbH, Vienna, Austria: Employment. Hartmann:Baxter Innovations GmbH, Vienna, Austria: Employment. Polakowski:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Panholzer:Baxter Innovations GmbH, Vienna, Austria: Employment. Kammlander:Baxter Innovations GmbH, Vienna, Austria: Employment. Osterkamp:3B Pharmaceuticals, Berlin, Germany: Employment. Reineke:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Schiviz:Baxter Innovations GmbH, Vienna, Austria: Employment. Hoellriegl:Baxter Innovations GmbH, Vienna, Austria: Employment. Scheiflinger:Baxter Innovations GmbH, Vienna, Austria: Employment.

Bothrops jararaca venom metalloproteinases are essential for coagulopathy and increase plasma tissue factor levels during envenomation.

Background/AimsBleeding tendency, coagulopathy and platelet disorders are recurrent manifestations in snakebites occurring worldwide. We reasoned that by damaging tissues and/or activating cells at the site of the bite and systemically, snake venom toxins might release or decrypt tissue factor (TF), resulting in activation of blood coagulation and aggravation of the bleeding tendency. Thus, we addressed (a) whether TF and protein disulfide isomerase (PDI), an oxireductase involved in TF encryption/decryption, were altered in experimental snake envenomation; (b) the involvement and significance of snake venom metalloproteinases (SVMP) and serine proteinases (SVSP) to hemostatic disturbances.Methods/Principal FindingsCrude Bothrops jararaca venom (BjV) was preincubated with Na2-EDTA or AEBSF, which are inhibitors of SVMP and SVSP, respectively, and injected subcutaneously or intravenously into rats to analyze the contribution of local lesion to the development of hemostatic disturbances. Samples of blood, lung and skin were collected and analyzed at 3 and 6 h. Platelet counts were markedly diminished in rats, and neither Na2-EDTA nor AEBSF could effectively abrogate this fall. However, Na2-EDTA markedly reduced plasma fibrinogen consumption and hemorrhage at the site of BjV inoculation. Na2-EDTA also abolished the marked elevation in TF levels in plasma at 3 and 6 h, by both administration routes. Moreover, increased TF activity was also noticed in lung and skin tissue samples at 6 h. However, factor VII levels did not decrease over time. PDI expression in skin was normal at 3 h, and downregulated at 6 h in all groups treated with BjV.ConclusionsSVMP induce coagulopathy, hemorrhage and increased TF levels in plasma, but neither SVMP nor SVSP are directly involved in thrombocytopenia. High levels of TF in plasma and TF decryption occur during snake envenomation, like true disseminated intravascular coagulation syndrome, and might be implicated in engendering bleeding manifestations in severely-envenomed patients.

Microparticle association and heterogeneity of tumor‐derived tissue factor in plasma: is it important for coagulation activation?

Tumor-derived tissue factor (TF) activates coagulation in vitro and in vivo in an orthotopic model of human pancreatic cancer. Here, we further characterized tumor-derived TF in this model. Conditioned medium (CM) of L3.6pl human pancreatic tumor cells and plasma from nude mice bearing L3.6pl tumors were ultracentrifuged, and the pellets were filtered through membranes with different pore sizes. The size distribution of particles was analyzed in CM or plasma fractions with nanoparticle tracking and dynamic light scattering. Human TF antigen and activity were measured in pellets and supernatants with ELISA and clotting or thrombin generation assays, respectively. Human alternatively spliced TF (asTF) was measured with ELISA. Human TF and thrombin-antithrombin complex (TAT) concentrations were assessed in plasma of mice injected with filtered fractions of CM. Particles in both CM and plasma were < 0.4 μm. TF antigen and activity in the CM were mainly associated with microparticles (MP). Approximately 50% of antigen and 20% of activity were associated with particles of < 0.1 μm. Injection of < 0.1 μm particles into mice caused a 30% drop in platelet counts and an increase in TAT levels. In contrast, ~ 90% of TF antigen in tumor-bearing mice plasmas was non-sedimentable, whereas TF activity was exclusively associated with MP. Particles of < 0.1 μm and the supernatants of both CM and plasma gained TF activity after addition of exogenous phospholipids. Although asTF was found in MP-free CM supernatants, it was also present in CM and plasma pellets. Tumor-derived particles of < 0.1 μm and non-sedimentable TF are or can become procoagulant in the presence of phospholipids, and may contribute to the procoagulant potential of circulating TF.

Effect Of Combined Heparin- and Antithrombin-Binding Exosite Mutations On Human Factor IX(a) Coagulant Activity, Thrombin Generation, and Protease Half-Life In Human Plasma

IntroductionHemophilia B is an X-linked genetic disorder characterized by defective factor IX activity. Recombinant factor IX (rFIX) is employed as protein replacement for the treatment and prophylaxis of bleeding episodes. Antithrombin is the primary plasma inhibitor of activated factor IX (FIXa), and inhibition is enhanced by heparin/heparan sulfate. We hypothesize that selective disruption of protease interactions with heparin and antithrombin via mutations in the respective heparin- and antithrombin-binding exosites may enhance rFIX(a) efficacy by prolonging protease half-life in vivo. AimTo assess the effect of mutations in the FIX(a) heparin- and antithrombin-binding exosites on traditional coagulant activity, thrombin generation, and protease half-life in human plasma. MethodsHuman FIX cDNA constructs with alanine substitutions (chymotrypsinogen numbering) in the heparin exosite (K126A, K132A, K126A/K132A), antithrombin exosite (R150A), or both (K126A/R150A, K132A/R150A, K126A/K132A/R150A) were expressed in HEK293 cell lines. Recombinant zymogens were purified from conditioned media, and a portion activated to protease with human factor XIa. Zymogen and protease forms were characterized in APTT-based clotting assays, and tissue factor (TF) and FIXa-initiated thrombin generation (TG) assays in pooled human FIX-deficient plasma, respectively. Comparisons were made with human plasma-derived factor IX (pFIX) and recombinant FIX wild type (WT). Protease half-life in pooled, citrated human plasma was determined using a novel assay that detects FIXa activity by TG response. ResultsZymogen coagulant activities (% WT ± S.E) were: pFIX 105.2 ± 2.8, WT 100 ± 7.1, K132A/R150A 75.8 ± 3.4, K126A 63.3 ± 2.3, R150A 62.4 ± 4.0, K132A 30.9 ± 1.0, K126A/R150A 27.0 ± 2.1, K126A/K132A 20.6 ± 9.2, and K126A/K132A/R150A 7.3 ± 3.8. Similarly, protease coagulant activities were: WT 100 ± 6.1, pFIXa 98.4 ± 11.4, K132A 91.4 ± 1.6, K132A/R150A 84.9 ± 2.8, R150A 77.1 ± 5.8, K126A 39.5 ± 2.4, K126A/R150A 25.3 ± 2.8, K126A/K132A/R150A 10.9 ± 0.6, and K126A/K132A 9.3 ± 0.6. In contrast to their relative coagulant activities, FIX K126A (1.9-fold), R150 (1.6-fold), and K132A/R150A (1.3-fold) supported increased peak thrombin concentrations during TF-triggered TG; pFIX, FIX K132A and K126A/R150A were similar to WT; and FIX K126A/K132A/R150A (0.6-fold) and K126A/K132A (0.2-fold) demonstrated marked reductions in peak thrombin relative to WT. In the FIXa-initiated TG assay, FIXa K126A/R150A and K132A/R150A (1.5-fold) demonstrated significantly increased peak thrombin concentrations; pFIXa, FIXa K132A, R150A, and K126A (0.8-1.0 fold) were similar to WT; while FIXa K126A/K132A and K126A/K132A/R150A demonstrated markedly reduced (0.2-0.3 fold) and delayed peak thrombin concentrations. In pooled, citrated FIX-deficient plasma, FIXa WT (40.9 ± 1.4 min) and K126A/K132A (37.2 ± 0.7 min) demonstrated similar half-lives, while FIXa R150A, K126A/R150A, and K132A/R150A all had half-lives > 2 hr. ConclusionsSingle exosite mutations resulted in mild to moderate reductions in coagulant activity, while the double mutation in the heparin exosite (K126A/K132A) markedly reduced activity, likely due to a synergistic effect on cofactor binding. Traditional coagulant activity did not accurately represent the ability of the mutant proteins to support thrombin generation. Despite variable reductions in coagulant activity, FIX K126A, K132A, R150A, K126A/R150A and K132A/R150A supported levels of plasma thrombin generation that were equal to or greater than FIX WT. The plasma half-life of FIXa WT activity was remarkably lengthy, and while mutations in the heparin exosite had negligible effects, R150A in the antithrombin exosite substantially increased protease half-life, consistent with a primary role for antithrombin in the plasma inhibition of FIXa. Thus, single exosite mutations did not significantly disrupt the procoagulant function of human FIX(a), and combined exosite mutations (K126A/R150A and K132A/R150A) maintain or enhance plasma thrombin generation while disrupting exosite-mediated regulatory mechanisms. The combination of intact procoagulant function with disruption of antithrombin- and heparin-mediated regulation of FIX(a) will potentially enhance in vivo recovery, prolong plasma half-life, and enhance the efficacy of hemophilia B replacement therapy. Disclosures:Sheehan:Novo Nordisk Access to Insight Basic Research Grant: Research Funding; Bayer Hemophilia Awards Program: Research Funding; Diagnostica Stago: reagents, reagents Other.

Use of immuno-magnetic beads for direct capture of nanosized microparticles from plasma

Increased microparticle tissue factor (TF) activity is not only found in cancer patients, but also in patients with cardiovascular and inflammatory diseases. Methods such as flow cytometry and impedance-based flow cytometry allow the analysis of microparticle subsets but provide no insight on which microparticles carry active TF. Conversely, the microparticle-TF activity itself does not reveal the cellular origin of the microparticles carrying the active TF.For this reason, we developed an immuno-magnetic bead method to capture subsets of microparticles directly from plasma. The method was optimized for capture of platelet-derived microparticles (PMPs) from plasma. Only 100 μl platelet-poor plasma (PPP) was needed in combination with 135 μl (27 μg) of biotinylated antihuman CD41 monoclonal antibody (MoAb) and 200 μl of streptavidin beads to achieve complete separation of PMPs from plasma. As a control, biotinylated mouse IgG1 isotype control MoAb was used instead of the anti-CD41 MoAb. Using biotinylated anti-CD14 MoAb, CD14-positive microparticles were captured from normal plasma spiked with microparticles isolated from the supernatant of lipopolysaccharide-stimulated monocytes (MoMPs). TF activity was found both in the positive (selected) and negative (depleted) fractions indicating that both CD14-positive and negative MoMPs carry active TF. We propose that this method can be used in the future to investigate the source of microparticles carrying active TF in plasma of patients with cancer and other diseases.