Complement and tissue factor-enriched neutrophil extracellular traps are key drivers in COVID-19 immunothrombosis

Emerging data indicate that complement and neutrophils contribute to the maladaptive immune response that fuels hyperinflammation and thrombotic microangiopathy, thereby increasing coronavirus 2019 (COVID-19) mortality. Here, we investigated how complement interacts with the platelet/neutrophil extracellular traps (NETs)/thrombin axis, using COVID-19 specimens, cell-based inhibition studies, and NET/human aortic endothelial cell (HAEC) cocultures. Increased plasma levels of NETs, tissue factor (TF) activity, and sC5b-9 were detected in patients. Neutrophils of patients yielded high TF expression and released NETs carrying active TF. Treatment of control neutrophils with COVID-19 platelet-rich plasma generated TF-bearing NETs that induced thrombotic activity of HAECs. Thrombin or NETosis inhibition or C5aR1 blockade attenuated platelet-mediated NET-driven thrombogenicity. COVID-19 serum induced complement activation in vitro, consistent with high complement activity in clinical samples. Complement C3 inhibition with compstatin Cp40 disrupted TF expression in neutrophils. In conclusion, we provide a mechanistic basis for a pivotal role of complement and NETs in COVID-19 immunothrombosis. This study supports strategies against severe acute respiratory syndrome coronavirus 2 that exploit complement or NETosis inhibition.

Hydroxychloroquine reverses the prothrombotic state in a mouse model of antiphospholipid syndrome: Role of reduced inflammation and endothelial dysfunction

Antiphospholipid antibodies (aPL) promote endothelial dysfunction, inflammation and procoagulant state. We investigated the effect of hydroxychloroquine (HCQ) on prothrombotic state and endothelial function in mice and in human aortic endothelial cells (HAEC). Human aPL were injected to C57BL/6 mice treated or not with HCQ. Vascular endothelial function and eNOS were assessed in isolated mesenteric arteries. Thrombosis was assessed both in vitro by measuring thrombin generation time (TGT) and tissue factor (TF) expression and in vivo by the measurement of the time to occlusion in carotid and the total thrombosis area in mesenteric arteries. TGT, TF, and VCAM1 expression were evaluated in HAEC. aPL increased VCAM-1 expression and reduced endothelium dependent relaxation to acetylcholine. In parallel, aPL shortened the time to occlusion and extended thrombus area in mice. This was associated with an overexpression of TF and an increased TGT in mice and in HAEC. HCQ reduced clot formation as well as TGT, and improved endothelial-dependent relaxations. Finally, HCQ increased the p-eNOS/eNOS ratio. This study provides new evidence that HCQ improves procoagulant status and vascular function in APS by modulating eNOS, leading to an improvement in the production of NO.

Near-infrared photoimmunotherapy of pancreatic cancer using an indocyanine green-labeled anti-tissue factor antibody

AIM

To investigate near-infrared photoimmunotherapeutic effect mediated by an anti-tissue factor (TF) antibody conjugated to indocyanine green (ICG) in a pancreatic cancer model.

METHODS

Near-infrared photoimmunotherapy (NIR-PIT) is a highly selective tumor treatment that utilizes an antibody-photosensitizer conjugate administration, followed by NIR light exposure. Anti-TF antibody 1849-ICG conjugate was synthesized by labeling of rat IgG_2b anti-TF monoclonal antibody 1849 (anti-TF 1849) to a NIR photosensitizer, ICG. The expression levels of TF in two human pancreatic cancer cell lines were examined by western blotting. Specific binding of the 1849-ICG to TF-expressing BxPC-3 cells was examined by fluorescence microscopy. NIR-PIT-induced cell death was determined by cell viability imaging assay. In vivo longitudinal fluorescence imaging was used to explore the accumulation of 1849-ICG conjugate in xenograft tumors. To examine the effect of NIR-PIT, tumor-bearing mice were separated into 5 groups: (1) 100 μg of 1849-ICG i.v. administration followed by NIR light exposure (50 J/cm²) on two consecutive days (Days 1 and 2); (2) NIR light exposure (50 J/cm²) only on two consecutive days (Days 1 and 2); (3) 100 μg of 1849-ICG i.v. administration; (4) 100 μg of unlabeled anti-TF 1849 i.v. administration; and (5) the untreated control. Semiweekly tumor volume measurements, accompanied with histological and immunohistochemical (IHC) analyses of tumors, were performed 3 d after the 2^nd irradiation with NIR light to monitor the effect of treatments.

RESULTS

High TF expression in BxPC-3 cells was observed via western blot analysis, concordant with the observed preferential binding with intracellular localization of 1849-ICG via fluorescence microscopy. NIR-PIT-induced cell death was observed by performing cell viability imaging assay. In contrast to the other test groups, tumor growth was significantly inhibited by NIR-PIT with a statistically significant difference in relative tumor volumes for 27 d after the treatment start date [2.83 ± 0.38 (NIR-PIT) vs 5.42 ± 1.61 (Untreated), vs 4.90 ± 0.87 (NIR), vs 4.28 ± 1.87 (1849-ICG), vs 4.35 ± 1.42 (anti-TF 1849), at Day 27, P < 0.05]. Tumors that received NIR-PIT showed evidence of necrotic cell death-associated features upon hematoxylin-eosin staining accompanied by a decrease in Ki-67-positive cells (a cell proliferation marker) by IHC examination.

CONCLUSION

The TF-targeted NIR-PIT with the 1849-ICG conjugate can potentially open a new platform for treatment of TF-expressing pancreatic cancer.

Postprandial elevation of tissue factor antigen in the blood of healthy adults

Atherosclerosis is a dynamic disease involving lipid metabolism, inflammation and thrombosis. A key factor in thrombosis is tissue factor, a small transmembrane glycoprotein. Tissue factor binds FactorVIIa, and this complex converts Factor X to Factor Xa, leading to thrombin generation and fibrin formation. Inhibition of this pathway is by tissue factor pathway inhibitor (TFPI). Tissue factor is found sequestered within atherosclerotic plaques, and plaque rupture allows tissue factor exposure to the circulation, leading to formation of a thrombus. Tissue factor is also associated with membrane microparticles in the circulation, most likely released from monocytes activated by an inflammatory event. We hypothesize that consumption of a typical western diet that is moderate in fat content leads to elevated levels of circulating tissue factor that may act as a marker of a pro-thrombotic state. Healthy volunteers, aged 18-55, consumed a moderate (40%) fat meal, with blood taken before and 3.5 and 6 h after the meal. Plasma was isolated and assayed for plasma triglycerides, tissue factor, thrombin antithrombin (TAT) complexes, TFPI and TNFα. The levels of circulating tissue factor increased 56% (from 78 pg/ml to120 pg/ml) 3.5 h after the meal. Levels decreased, but had not returned to baseline 6 h postprandially. No significant differences in TAT, TFPI and TNFá levels were observed postprandially. These results demonstrate increased tissue factor levels in individuals who consumed a moderate fat diet. This suggests that the typical western diet may play a larger role in cardiovascular disease than merely altering lipid profiles.

Impact of haemostatic mechanisms on pathophysiology of preeclampsia

Preeclampsia (PE) is disorder of new onset hypertension and proteinuria during the second half of pregnancy. There is increasing evidence to implicate placental over-expression of tissue factor and PAR-1 in the pathophysiology of PE. Excessive activation of platelets, neutrophils and the complement system may also contribute to the placental pathology and maternal endothelial responsible for the symptoms of PE. Increased knowledge in this field may identify new therapeutic strategies for the treatment of PE.

Low frequency of elevated prothrombin times in patients with lupus anticoagulants when using a recombinant thromboplastin reagent: implications for dosing and monitoring of oral anticoagulant therapy

Many patients with lupus anticoagulants (LA) are treated with oral anticoagulation and monitored using the international normalised ratio (INR) derived from the prothrombin time (PT). Recent reports have produced conflicting conclusions about the extent to which LA interferes with PT determination. The degree of anticoagulation may be overestimated in a patient whose LA affects the PT. A number of reports conclude that specific thromboplastin reagents containing recombinant tissue factor are sensitive to the presence of LAs and should not be used to monitor oral anticoagulant therapy in these patients. These studies were performed on orally anticoagulated patients. The present retrospective study on 400 patients with LAs who were not receiving therapeutic anticoagulation was performed to ascertain the frequency of prolonged PT in these patients when using Innovin recombinant thromboplastin. Only 17 (4.3%) out of 400 had prolonged PT in the presence of LA. As this is a low prevalence, and not all patients with LAs will require anticoagulant therapy, it is concluded that baseline INR determination should be used to highlight the need to monitor individual patients with LA-insensitive reagents. As the use of moderate-intensity oral anticoagulation for patients with LAs and previous thrombosis is receiving wider acceptance, an informed approach to anticoagulant monitoring will reduce the possibility of under-anticoagulating patients receiving this therapy.

[Preparation and characterization of a monoclonal antibody against human tissue factor with anticoagulation activity]

OBJECTIVE

To prepare and characterize a monoclonal antibody (mAb) against human tissue factor (hTF) with anticoagulation activity.

METHODS

BALB/c mice were immunized with truncated recombinant protein (rhTF243). Hybridoma cell lines were generated from cell fusion, and screened using indirect ELISA and prothrombin time (PT). After ascites was developed in BALB/c mice, antibody titers were determined using indirect ELISA. Western blotting was performed to study the antibody specificity. Anticoagulant activity of the antibody was detected by PT assay.

RESULTS

A mAb to hTF with excellent anticoagulation activity was identified. Its immunoglobulin subclass belonged to IgG1. Titer of ascites fluid was 1:200 000. Western blotting and PT analysis confirmed the specificity and anticoagulant activity of the antibody. The mAb reacted specifically to both recombinant hTF243 and natural TF on SW620 colon cancer cell surface.

CONCLUSION

A hTF mAb with anticoagulation activity and high specificity has been successfully prepared.

Ischemia/reperfusion injury: effect of simultaneous inhibition of plasma cascade systems versus specific complement inhibition

Ischemia/reperfusion injury (IRI) may occur from ischemia due to thrombotic occlusion, trauma or surgical interventions, including transplantation, with subsequent reestablishment of circulation. Time-dependent molecular and structural changes result from the deprivation of blood and oxygen in the affected tissue during ischemia. Upon restoration of blood flow a multifaceted network of plasma cascades is activated, including the complement-, coagulation-, kinin-, and fibrinolytic system, which plays a major role in the reperfusion-triggered inflammatory process. The plasma cascade systems are therefore promising therapeutic targets for attenuation of IRI. Earlier studies showed beneficial effects through inhibition of the complement system using specific complement inhibitors. However, pivotal roles in IRI are also attributed to other cascades. This raises the question, whether drugs, such as C1 esterase inhibitor, which regulate more than one cascade at a time, have a higher therapeutic potential. The present review discusses different therapeutic approaches ranging from specific complement inhibition to simultaneous inhibition of plasma cascade systems for reduction of IRI, gives an overview of the plasma cascade systems in IRI as well as highlights recent findings in this field.

Prothrombotic state in Churg-Strauss syndrome: a case report

An increased risk of thrombosis has been described in patients with hypereosinophilic syndromes, including Churg-Strauss syndrome (CSS). We report the case of a 43-year-old man with CSS who presented with asthma, pansinusitis, blood eosinophilia (9650/microL), peripheral neuropathy, cutaneous eosinophilic vasculitis, and a positive result for antineutrophil cytoplasmic antibodies. An analysis of plasma during active disease revealed elevated levels of prothrombin fragment 1+2 (marker of thrombin generation) (832 pM; normal range, 68-229 pM) and D-dimer (marker of fibrin degradation) (2300 ng/mL; normal range, 130-250 ng/mL), which indicate an increased risk of thrombosis. Both parameters returned to normal values during remission after immunosuppressive treatment. Skin histology showed leukocytoclastic vasculitis with numerous eosinophils in the dermal infiltrate. Immunohistochemistry revealed expression of tissue factor by skin-infiltrating eosinophils, as confirmed by colocalization with eosinophil cationic protein, a classic marker of eosinophil granulocytes. In conclusion, we present a patient with active CSS and a prothrombotic state that reverted during remission achieved by immunosuppressive therapy.

Is preeclampsia an autoimmune disease?

Preeclampsia is a life-threatening hypertensive disease of pregnancy. The condition is characterized by the presence of autoantibodies that activate the major angiotensin receptor, AT(1). Research conducted during the past decade has shown that these autoantibodies activate AT(1) receptors on a variety of cell types and provoke biological responses that are relevant to the pathophysiology of preeclampsia. The introduction of these autoantibodies into pregnant mice results in hypertension, proteinuria and a variety of other features of preeclampsia including small fetuses and placentas. These findings demonstrate the pathophysiological role of these autoantibodies in preeclampsia. The biological properties of these autoantibodies can be blocked by a 7-amino acid peptide that corresponds to a specific sequence associated with the second extracellular loop of the AT(1) receptor. The fact that autoantibodies from different individuals are directed to a common epitope provides obvious diagnostic and therapeutic opportunities. Research reviewed here raises the intriguing possibility that preeclampsia may be a pregnancy-induced autoimmune condition characterized by the presence of disease-causing angiotensin receptor activating autoantibodies.

Tissue factor procoagulant activity of plasma microparticles is increased in patients with early-stage prostate cancer

Tissue factor (TF) plays a critical role in tumour growth and metastasis, and its enhanced release into plasma in association with cellular microparticles (MPs) has recently been associated with pathological cancer progression. We have previously demonstrated significantly elevated levels of plasma TF antigen as well as systemic coagulation and platelet activation in patients with localised prostate cancer. In this prospective study, we used a highly sensitive one-stage clotting assay to measure preoperative TF-specific procoagulant activity (PCA) of plasma MPs in 68 consecutive patients with early-stage prostate cancer to further explore the relevance of circulating TF in this tumour entity. Automated calibrated thrombography was used to monitor thrombin generation in cell-free plasma samples in the absence of exogenous TF or phospholipids. Compared to healthy male controls (n=20), patients had significantly increased levels of both D-dimer and TF-specific PCA of plasma MPs (p<0.001). Furthermore, MP-associated TF PCA was higher in patients with (n=29) than in those without (n=39) laboratory evidence of an acute-phase reaction (p=0.004) and decreased to normal levels within one week after radical prostatectomy. Overall, we found a significant correlation between TF-specific PCA of plasma MPs and plasma D-dimer (p=0.002), suggesting that plasma MPs contributed to in-vivo coagulation activation in a TF-dependent manner. Thrombin generation in plasma was also significantly increased in patients compared to controls (p<0.01). Collectively, our findings suggest that TF-specific PCA of plasma MPs contributes to intravascular coagulation activation in patients with early-stage prostate cancer and may represent a potential link between hypercoagulability, inflammation, and disease progression.

Tissue factor-bearing microparticles derived from tumor cells: impact on coagulation activation

BACKGROUND

Tissue factor (TF)-bearing microparticles (MP) from different origins are thought to be involved in the pathogenesis of cancer-associated thrombosis. However, the role of circulating tumor cell-derived TF is not well understood.

METHODS

TF antigen and activity were measured in MP generated in vitro from human TF-expressing cancer cells by ELISA and clotting or thrombin generation assays, respectively. TF antigen and activity were also measured in vivo in cell-free plasmas from mice previously injected with in vitro-generated MP or in cell-free plasmas from nude mice bearing orthotopically injected human cancer cells.

RESULTS

Tumor cell-derived MP (TMP) exhibited strong TF-dependent procoagulant activity (PCA) in vitro and in vivo. Injection of TMP into mice was associated with acute thrombocytopenia and signs of shock, which were prevented by prior heparinization. Human TF antigen and activity could be detected in mouse cell-free plasmas up to 30 min after TMP injections. Human TF was detected in the spleen of injected mice and its clearance from circulation was delayed in splenectomized mice, suggesting the involvement of the spleen in the rapid clearance of circulating MP in vivo. Detectable levels of TF-dependent PCA and thrombin-antithrombin complex were found in cell-free plasmas from mice growing pancreatic human tumors, suggesting that circulating tumor-derived TF causes coagulation activation in vivo.

CONCLUSIONS

MP derived from certain cancer cells exhibit TF-dependent PCA both in vitro and in vivo. These results provide new information about the specific contribution of tumor-derived MP to the hypercoagulable state observed in cancer.

Activated protein C up-regulates IL-10 and inhibits tissue factor in blood monocytes

The protective effect of recombinant activated protein C therapy in patients with severe sepsis likely reflects the ability of recombinant activated protein C to modulate multiple pathways implicated in sepsis pathophysiology. In this study, we examined the effects of recombinant activated protein C on the anti-inflammatory cytokine IL-10 and on the procoagulant molecule tissue factor (TF) in LPS-challenged blood monocytes. Treatment of LPS-stimulated monocytes with recombinant activated protein C resulted in an up-regulation of IL-10 protein production and mRNA synthesis. The up-regulation of IL-10 required the serine protease activity of recombinant activated protein C and was dependent on protease-activated receptor-1, but was independent of the endothelial protein C receptor. At the intracellular level, p38 MAPK activation was required for recombinant activated protein C-mediated up-regulation of IL-10. We further observed that incubation of LPS-stimulated monocytes with recombinant activated protein C down-regulated TF Ag and activity levels. This anticoagulant effect of recombinant activated protein C was dependent on IL-10 since neutralization of endogenously produced IL-10 abrogated the effect. In patients with severe sepsis, plasma IL-10 levels were markedly higher in those treated with recombinant activated protein C than in those who did not receive recombinant activated protein C. This study reveals novel regulatory functions of recombinant activated protein C, specifically the up-regulation of IL-10 and the inhibition of TF activity in monocytes. Our data further suggest that these activities of recombinant activated protein C are directly linked: the recombinant activated protein C-mediated up-regulation of IL-10 reduces TF in circulating monocytes.

C5a and TNF-alpha up-regulate the expression of tissue factor in intra-alveolar neutrophils of patients with the acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by the presence of fibrin-rich inflammatory exudates in the intra-alveolar spaces and the extensive migration of neutrophils into alveoli of the lungs. Tissue factor (TF)-dependent procoagulant properties of bronchoalveaolar lavage fluid (BALF) obtained from ARDS patients favor fibrin deposition, and are likely the result of cross-talk between inflammatory mediators and hemostatic mechanisms. However, the regulation of these interactions remains elusive. Prompted by previous findings suggesting that neutrophils, under certain inflammatory conditions, can express functional TF, we investigated the contribution of intra-alveolar neutrophils to the procoagulant properties of BALF from patients with ARDS. Our results confirm that the procoagulant properties of BALF from ARDS patients are the result of TF induction, and further indicate that BALF neutrophils are a main source of TF in intra-alveolar fluid. We also found that BALF neutrophils in these patients express significantly higher levels of TF than peripheral blood neutrophils. These results suggest that the alveolar microenvironment contributes to TF induction in ARDS. Additional experiments indicated that the ability of BALF to induce TF expression in neutrophils from healthy donors can be abolished by inhibiting C5a or TNF-alpha signaling, suggesting a primary role for these inflammatory mediators in the up-regulation of TF in alveolar neutrophils in ARDS. This cross-talk between inflammatory mediators and the induction of TF expression in intra-alveolar neutrophils may be a potential target for novel therapeutic strategies to limit ARDS-associated disturbances of coagulation.

Expression of human tissue factor under the control of the mouse tissue factor promoter mediates normal hemostasis in knock-in mice

BACKGROUND

Tissue factor (TF) is expressed widely at the subluminal surface of blood vessels and serves as the primary cellular initiator of the extrinsic pathway of blood coagulation. Lack of TF in mice resulted in lethality in utero, but human TF (huTF) expressed at low levels from a human minigene rescued null mice from prenatal death. Although these low-TF expressing transgenic mice developed to term, they had a significantly shorter life span and exhibited hemorrhage and fibrosis in the heart.

METHODS

Human TF knock-in (TFKI) mice were generated by replacing the first two exons of the mouse (murine) TF (muTF) gene with the huTF complete coding sequence, thus placing it under the control of the endogenous muTF promoter.

RESULTS

Expression of huTF in the TFKI mice was similar to muTF in wild-type (wt) mice. The TFKI mice showed no microscopic evidence of spontaneous hemorrhage in the heart, nor cardiac fibrosis at up to 18 months of age. Immunohistochemistry showed that huTF was expressed in cells surrounding blood vessels in TFKI mice. Coagulation activity of brain homogenates from TFKI mice was comparable with that from wt brain. Cardiac hemorrhage similar to that of the low-TF transgenic mice occurred in the TFKI mice when huTF was blocked by a neutralizing anti-huTF monoclonal antibody.

CONCLUSION

We generated a transgenic mouse line that expresses huTF under the control of the endogenous muTF promoter at physiological levels. Our results suggest that huTF can fully reconstitute the murine coagulation system and mediate normal hemostasis.

Anti-human tissue factor antibody ameliorated intestinal ischemia reperfusion-induced acute lung injury in human tissue factor knock-in mice

Background

Interaction between the coagulation and inflammation systems plays an important role in the development of acute respiratory distress syndrome (ARDS). Anti-coagulation is an attractive option for ARDS treatment, and this has promoted development of new antibodies. However, preclinical trials for these antibodies are often limited by the high cost and availability of non-human primates. In the present study, we developed a novel alternative method to test the role of a humanized anti-tissue factor mAb in acute lung injury with transgenic mice.

Methodology/Principal Findings

Human tissue factor knock-in (hTF-KI) transgenic mice and a novel humanized anti-human tissue factor mAb (anti-hTF mAb, CNTO859) were developed. The hTF-KI mice showed a normal and functional expression of hTF. The anti-hTF mAb specifically blocked the pro-coagulation activity of brain extracts from the hTF-KI mice and human, but not from wild type mice. An extrapulmonary ARDS model was used by intestinal ischemia-reperfusion. Significant lung tissue damage in hTF-KI mice was observed after 2 h reperfusion. Administration of CNTO859 (5 mg/kg, i.v.) attenuated the severity of lung tissue injury, decreased the total cell counts and protein concentration in bronchoalveolar lavage fluid, and reduced Evans blue leakage. In addition, the treatment significantly reduced alveolar fibrin deposition, and decreased tissue factor and plasminogen activator inhibitor-1 activity in the serum. This treatment also down-regulated cytokine expression and reduced cell death in the lung.

Conclusions

This novel anti-hTF antibody showed beneficial effects on intestinal ischemia-reperfusion induced acute lung injury, which merits further investigation for clinical usage. In addition, the use of knock-in transgenic mice to test the efficacy of antibodies against human-specific proteins is a novel strategy for preclinical studies.

Tissue factor: a critical role in inflammation and cancer

A series of coordinated enzymatic reactions takes place in the body whenever blood clots. The major physiological initiator of these reactions is a membrane-bound glycoprotein known as tissue factor (TF), which is normally separated from the bloodstream by the vascular endothelium. Bleeding, caused by injury or tissue damage, activates a complex enzyme cascade as TF becomes exposed to the bloodstream. In disease states, leukocytes or the vascular endothelium may abnormally express TF to cause intravascular coagulation. The blood-coagulation cascade is also relevant to diseases such as hemophilia, in which patients are deficient in blood proteins necessary for clotting, and is linked to vascular diseases such as heart attack and stroke, in which clotting can lead to the occlusion of blood vessels. Coagulation is also activated in inflammation and cancer. In this article, we discuss characteristics of TF and review its role in inflammation and cancer.

Tissue factor: a link between C5a and neutrophil activation in antiphospholipid antibody induced fetal injury

Fetal loss in patients with antiphospholipid (aPL) antibodies has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically activation of complement with generation of the anaphylotoxin C5a, is an essential trigger of fetal injury. In this study, we analyzed the role of the procoagulant molecule tissue factor (TF) in a mouse model of aPL antibody-induced pregnancy loss. We found that either blockade of TF with a monoclonal antibody in wild-type mice or a genetic reduction of TF prevented aPL antibody-induced inflammation and pregnancy loss. In response to aPL antibody-generated C5a, neutrophils express TF potentiating inflammation in the deciduas and leading to miscarriages. Importantly, we showed that TF in myeloid cells but not fetal-derived cells (trophoblasts) was associated with fetal injury, suggesting that the site for pathologic TF expression is neutrophils. We found that TF expression in neutrophils contributes to respiratory burst and subsequent trophoblast injury and pregnancy loss induced by aPL antibodies. The identification of TF as an important mediator of C5a-induced oxidative burst in neutrophils in aPL-induced fetal injury provides a new target for therapy to prevent pregnancy loss in the antiphospholipid syndrome.

Inhibition of tissue factor signaling suppresses tumor growth

Coagulation activation by tissue factor (TF) is implicated in cancer progression, cancer-associated thrombosis and metastasis. The role of direct TF signaling pathways in cancer, however, remains incompletely understood. Here we address how TF contributes to primary tumor growth by using a unique pair of isotype-matched antibodies that inhibit either coagulation (monoclonal antibody [Mab]-5G9) or direct signaling (Mab-10H10). We demonstrate that the inhibitory antibody of direct TF-VIIa signaling not only blocks TF-VIIa mediated activation of PAR2, but also disrupts the interaction of TF with integrins. In epithelial and TF-expressing endothelial cells, association of TF with beta1 integrins is regulated by TF extracellular ligand binding and independent of PAR2 signaling or proteolytic activity of VIIa. In contrast, alpha3beta1 integrin association of TF is constitutive in breast cancer cells and blocked by Mab-10H10 but not by Mab-5G9. Mab-5G9 has antitumor activity in vivo, but we show here that Mab-10H10 is at least as effective in suppressing human xenograft tumors in 2 different models. Breast tumor growth was also attenuated by blocking PAR2 signaling. These results show that tumor cell TF-PAR2 signaling is crucial for tumor growth and suggest that anti-TF strategies can be applied in cancer therapy with minor impairment of TF-dependent hemostatic pathways.

Fibrin formation by wounded bronchial epithelial cell layers in vitro is essential for normal epithelial repair and independent of plasma proteins

BACKGROUND

The bronchial epithelium is in contact with, and continually damaged by, the environment. Animal models have indicated that normal epithelial repair is rapid and supported by the formation of a provisional fibrin matrix that is exclusively plasma-derived.

OBJECTIVES

Our objectives were to demonstrate the ability of normal human bronchial epithelial (NHBE) cells to produce coagulation cascade proteins and form fibrin in response to damage, independently of plasma proteins, and to show that formation of a cross-linked fibrin matrix is essential for normal epithelial repair in vitro.

METHODS

Primary NHBE cells and cells of the 16HBE 14o- bronchial epithelial cell line were grown and maintained in vitro prior to mechanical wounding of confluent monolayers in serum-free media. Tissue factor (TF) and factor XIII (FXIII) were visualized on 16HBE 14o- monolayers using immunohistochemistry. The time-dependent expression of TF, factor VII (FVII), factor X (FX), fibrinogen, soluble fibrin, FXIII subunit A (FXIIIA) and D-dimers following wounding of confluent 16HBE 14o- monolayers was investigated using immunoassays. TF and FVII expression at the mRNA level was investigated by RT-PCR. The role of coagulation cascade proteins in the repair response of NHBE and 16HBE 14o- monolayers was investigated using neutralizing antibodies.

RESULTS

Active TF was constitutively expressed in 16HBE 14o- cells. Levels of FVII, FX, fibrinogen, soluble fibrin, FXIIIA and D-dimers in culture supernatants increased rapidly and were maximal 20 min after wounding the monolayers. Expression of TF and FVII mRNA was significantly increased 10 and 4 h, respectively, after wounding. Neutralizing antibodies to TF, fibrinogen and FXIIIA significantly inhibited repair of NHBE and 16HBE 14o- cell layers.

CONCLUSIONS

The bronchial epithelium has the potential to respond rapidly to mechanical damage by forming a cross-linked fibrin matrix that is essential for normal epithelial repair, independently of plasma proteins.

Tissue factor around dermal vessels has bound factor VII in the absence of injury

BACKGROUND

'Idling' or ongoing low-level activity of the tissue factor (TF) pathway is a postulated mechanism by which the coagulation process can become active without a lag period at sites of injury.

OBJECTIVE

To determine whether TF around cutaneous vessels has bound factor VIIa in the absence of injury, and thus could participate in the idling process.

METHODS

Immunostaining of mouse skin with antibodies against a 15-residue peptide from the sequence of mouse TF, and against the whole extracellular portion of TF.

RESULTS

The whole TF antibody recognized TF in squamous epithelium and around vessels in the dermis. By contrast, the monospecific antibody only recognized TF in the squamous epithelium, but not around vessels. We also found that biotinylated, active site-inhibited FVIIa (FVIIai) bound to tissue sections in the same areas in which TF was recognized by the monospecific antibody (squamous epithelium), but did not bind around vessels. Molecular modeling revealed that FVIIa and FX binding to TF masked a significant part of the surface of the target peptide.

CONCLUSIONS

In the aggregate, these data are most consistent with the interpretation that TF in perivascular sites has bound FVIIa, even in the absence of any injury. The presence of endogenously bound FVIIa prevents the subsequent binding of the monospecific antibody or exogenous FVIIai to perivascular TF.

CNTO 859, a humanized anti-tissue factor monoclonal antibody, is a potent inhibitor of breast cancer metastasis and tumor growth in xenograft models

Thromboembolic complications are frequently associated with advanced cancer. Interestingly, one of the major initiators of blood coagulation, tissue factor (TF), is reported to be overexpressed in several tumor types and can be found on both tumor cells and tumor vasculature. Although the exact mechanisms have yet to be elucidated, TF expressed on tumor cells can trigger intracellular signaling events through various pathways that can lead to tumor angiogenesis, proliferation, and metastasis. There exists preclinical evidence that disruption of TF dependent signaling can effectively inhibit tumor cell migration, metastasis, and angiogenesis. Here, we report for the first time that an antibody to tissue factor can also prevent tumor growth in vivo. Prophylactic administration of CNTO 859, a humanized anti-human TF antibody, was shown to inhibit experimental lung metastasis of MDA-MB-231 human breast carcinoma cells by over 99% compared to a control antibody. Furthermore, therapeutic doses of CNTO 859 were shown to reduce tumor incidence and growth of orthotopically implanted MDA-MB-231 cells.

Monocyte IL-10 produced in response to lipopolysaccharide modulates thrombin generation by inhibiting tissue factor expression and release of active tissue factor-bound microparticles

Lipopolysaccharide (LPS)-stimulated monocytes are known to have a procoagulant effect. This property is currently explained by the fact that monocytes, in response to LPS, can express tissue factor (TF) and undergo a process of membrane microvesiculation. Interleukin-10 (IL-10) has been shown to downregulate TF expression and inhibit procoagulant activity (PCA). In order to further characterize the inhibitory effect of IL-10 on LPS-induced PCA, we used the integrated system of analysis of kinetics of thrombin generation in normal plasma (thrombinography). For this, we developed an original method of elutriation allowing to obtain a highly purified monocyte preparation, under endotoxin-free conditions. Thrombin generation was measured using a highly sensitive and specific fluorogenic method which we adapted to inhibit the contact factor pathway. Results show that recombinant human IL-10 decreased the kinetics of thrombin generation in a dose-dependent manner. Furthermore, the inhibition of endogenous IL-10 released by monocytes in response to LPS is associated with an increase in the kinetics of thrombin generation. We demonstrated that this effect was a consequence of the up-regulation of TF expression and TF-bound microparticle release. In conclusion, we report that IL-10 can regulate thrombin generation in conditions close to physiology as allowed by thrombinography, and that endogenous IL-10 regulates TF expression and release of active TF-bound microparticles by a negative feed back loop through IL-10 receptor alpha.

Toll-like receptor and antiphospholipid mediated thrombosis: in vivo studies

OBJECTIVE

A study was undertaken to investigate the in vivo pathogenic role of Toll-like receptor 4 (TLR-4) in the antiphospholipid syndrome (APS) by studying the thrombogenic antiphospholipid (aPL) activity in lipopolysaccharide (LPS) non-responsive (LPS-/-) mice and the association between tlr4 gene polymorphisms and APS in patients.

METHODS

IgGs from two patients with APS, one with aPL negative systemic lupus erythematosus (SLE) and one with normal human serum (NHS), were evaluated for thrombosis, tissue factor (TF) activity and endothelial cell activation in LPS-/- mice displaying a tlr4 spontaneous mutation vs LPS responsive (LPS+/+) mice. Human tlr4 Asp299Gly and Thr399Ile polymorphisms were evaluated by allele-specific PCR in 110 patients with APS with arterial/venous thrombosis and in 220 controls of the same ethnic origin.

RESULTS

IgG-APS produced significantly larger thrombi and more leucocytes (WBC) adhering to endothelial cells in the cremaster muscle microcirculation of LPS+/+ mice than IgG-NHS or aPL negative SLE-IgG. These effects were abrogated after absorption of the anti-beta(2)glycoprotein I activity by an affinity column. The two IgG-APS induced significantly smaller thrombi and fewer WBC adhering to endothelial cells in LPS-/- mice than in LPS+/+ mice. IgG-APS induced higher TF activity in carotid artery homogenates of LPS+/+ mice than in LPS-/- mice. The prevalence of Asp299Gly and Thr399Ile tlr4 polymorphisms was significantly lower than in controls.

CONCLUSIONS

These findings in LPS-/- mice and the reduction in the "protective" polymorphism in patients with APS with thrombosis suggest that TLR-4 is involved in the interaction of aPL with endothelial cells in vivo.

Amplified anticoagulant activity of tissue factor-targeted thrombomodulin: in-vivo validation of a tissue factor-neutralizing antibody fused to soluble thrombomodulin

Tissue factor (TF) exposure is a potent pro-thrombotic trigger that initiates activation of the coagulation cascade, while thrombomodulin (TM) is a potent anticoagulant protein that limits the extent of activation. Both TF neutralizing antibodies and soluble TM (sTM) are effective anticoagulants. We have developed a novel anticoagulant fusion protein, Ab(TF)-TM, by fusing a TFneutralizing single-chain antibody, Ab(TF), to an active fragment of TM. Ab(TF)-TM is a novel anticoagulant targeting to sites of TF exposure with a dual mechanism of action. The Ab(TF) portion of the molecule inhibitsTF/factorVIIa mediated activation of FIX and FX, and the TM portion of the molecule acts as a cofactor for activation of protein C. In-vitro coagulation assays show that Ab(TF)-TM more potently inhibits TF-initiated coagulation (prothrombin time) than can its individual components, Ab(TF) (20-fold) and sTM (80-fold) alone, or in combination (10-fold). In contrast, the potency of Ab(TF)-TM in the activated partial thromboplastin and thrombin clotting time assays was similar to sTM alone. In a rat model of disseminated intravascular coagulation (DIC), intravenous injection of a human TF-containing thromboplastin reagent (0.5 ml/kg) resulted in an immediate death in approximately 60% of the animals and a clinical score of approximately 2.5. Pre-injection of Ab(TF)-TM or Ab(TF) and sTM, given alone or in combination, showed dose-dependent efficacy. At a dose of 0.7 nmol/kg, Ab(TF)-TM completely prevented death and reduced clinical scores by 79%, while neitherAb(TF) nor sTM, given alone or in combination, showed significant therapeutic effects. Calculated effective doses that reduced mortality by 50% relative to that in the control group (ED(50), nmol/kg) were 0.21 for Ab(TF)-TM, 3.2 for an equimolar mixture of Ab(TF) and sTM, 4.3 for sTM and 20 for Ab(TF). Thus, Ab(TF)-TM presented 10- to 100-fold enhancement of the anticoagulant potency, relative to the ED(50) in Ab(TF) and sTM given either alone or in combination, in a rat DIC model.

A novel anti-tissue factor monoclonal antibody with anticoagulant potency derived from synthesized multiple antigenic peptide through blocking FX combination with TF

Tissue factor (TF) has been implicated in the pathogenesis of various thrombotic disorders. Monoclonal antibodies (mAb) that specifically target TF may have potential as antithrombotic therapy. We designed a unique TF peptide (TFP) that was specific for the binding site to factor X (FX). This peptide was used to develop TF mAb that block the coagulation cascade by interfering with the combination of FX with the TF/FVIIa complex. Chemically synthesized TFP coupled to polylysine matrix was used as multiple antigenic peptide (TF-MAP) and this was used to immunize Balb/c mice for the preparation of hybridomas. One hybridoma cell line released an antibody, named TF4A12, which had high anticoagulant potency (by dilute prothrombin time assay). Western blotting showed that TF4A12 could bind TF-MAP and the soluble TF extracellular domain (sTF(1-219)). Results of FX activation assay and amidolytic activity assay showed that the anticoagulant ability of TF4A12 is due to blocking FX, but not FVII, binding to TF. Our study identified an efficient method of developing TF mAb that could block the coagulation cascade.

Antithrombotic action of annexin V proved as efficient as direct inhibition of tissue factor or thrombin

The role of phospholipid platelet membrane and tissue factor in thrombin generation and thrombus formation is accepted. In the present study we have explored antithrombotic action of strategies aimed to block exposure of negatively charged phospholipids and we compared effects with those obtained through tissue factor or a direct thrombin inhibition. Type III collagen was exposed to flowing blood (5 min, 300 s(-1)). Effects of inhibition of platelet deposition by annexin A5 (ANXA5), hirudin (HIR) or by an antibody against tissue factor (TF) were evaluated. Prothrombin fragment F1 + 2 (F1 + 2) was monitored. Pre-incubation of whole blood with HIR or ANXA5 resulted in a statistically significant reduction of platelet deposition (12.2 +/- 0.6% in control experiments vs. 8.3 +/- 0.4% and 8.5 +/- 0.5%, respectively, P < 0.05). A similar decrease was found when blood was incubated with an antibody against TF. Furthermore, ANXA5 and HIR inhibited the recruitment of platelets into forming aggregates. The height of platelet aggregates generated was decreased in the presence of HIR or ANXA5, but only incubation with both inhibitors reached levels of statistical significance. The presence of ANXA5 or HIR decreased levels of F1 + 2 suggesting a reduced activation of the coagulation system. In our experimental studies, the inhibitory potential of ANXA5 on platelet-thrombus formation was as effective as that of a direct thrombin inhibitor, as HIR, or an antibody against TF. Negatively charged phospholipids exposed on activated platelets potentiate the formation of platelet aggregates on a collagen surface and further suggest that inhibition of platelet procoagulant activity might be a specific target for antithrombotic drugs.

Immunologic quantitation of tissue factors

The large number of conflicting reports on the presence and concentration of circulating tissue factor (TF) in blood generates uncertainties regarding its relevance to hemostasis and association with specific diseases. We believe that the source of these controversies lies in part in the assays used for TF quantitation. We have developed a highly sensitive and specific double monoclonal antibody fluorescence-based immunoassay and integrated it into the Luminex Multi-Analyte Platform. This assay, which uses physiologically relevant standard and appropriate specificity controls, measures TF antigen in recombinant products and natural sources including placenta, plasma, cell lysates and cell membranes. Comparisons of reactivity patterns of various full-length and truncated TFs on an equimolar basis revealed quantitative differences in the immune recognition of TFs by our antibodies in the order of TF 1-263 > 1-242 > 1-218 > placental TF. Despite this differential recognition, all TF species are quantifiable at concentrations < or = 2 pM. Using a calibration curve constructed with recombinant TF 1-263 and plasma from healthy individuals (n = 91), we observed the concentration of TF antigen in plasma to be substantially lower than that generally reported in the literature: TF antigen in plasma of 72 individuals (79%) was below 2 pM (quantitative limit of our assay); TF antigen levels between 2.0 and 5.0 pM could be detected in six individuals (7%); and in 14% (13 plasmas), the non-specific signal was higher than the specific signal, and thus TF levels could not be determined. These differential recognition patterns affect TF quantitation in plasma and should be considered when evaluating plasma TF-like antigen concentrations.

Optimization of conditions for in vitro production of radical oxygen species and expression of tissue factor by canine mononuclear cells and granulocytes for use in high-throughput assays

The purpose of this study was to optimize conditions for high throughput measurement of radical oxygen species (ROS) production and expression of tissue factor, also termed procoagulant activity, by canine leukocytes. Granulocytes and mononuclear cells were separated by density gradient centrifugation from peripheral blood collected on several occasions from three healthy large breed dogs. To determine optimal conditions for ROS production, granulocytes were incubated for 1 or 3h in PBG (PBS containing 0.5% BSA and 5mM glucose) or RPMI containing 10% fetal bovine serum (FBS); lipopolysaccharide (LPS), zymosan, peptidoglycan (PGN) and phorbol myristate acetate (PMA) were used as stimuli. ROS was assessed by conversion of the nonfluorescent dye dihydrorhodamine 123 to fluorescent rhodamine 123 by radical species released into the media. To identify optimal conditions for expression of tissue factor, mononuclear cells were incubated for 5h in RPMI containing different concentrations of heat-inactivated FBS (HI-FBS), and LPS, zymosan, PGN or PMA as stimuli. Expression of tissue factor was determined using a one-stage recalcification assay performed in an automated nephelometric coagulation analyzer. Neither LPS nor zymosan increased ROS production by granulocytes incubated in PBG media. In contrast, granulocytes incubated in RPMI had dose-dependent increases in ROS production in response to zymosan and PGN. ROS production was significantly increased by incubation with concentrations of LPS of 0.01microg/ml or greater, and by zymosan concentrations of 0.1microg/ml or greater. ROS production in response to incubation with PMA was significantly increased starting at 10(-7)M, and was significantly greater for cells incubated in RPMI than cells incubated in PBG. LPS-, zymosan- and PGN-stimulated procoagulant activity increased in a dose-dependent manner, whereas PMA-stimulated procoagulant activity peaked at 10(-7)M. Increasing concentrations of HI-FBS significantly increased LPS-, zymosan- and PGN-induced procoagulant activity of mononuclear cells. Results obtained in this study indicate production of ROS by canine granulocytes is optimal when these cells are incubated for 3h in RPMI with LPS (0.1microg/ml), zymosan (10 microg/ml), PGN (10 microg/ml), and PMA (10(-7)M). Furthermore, canine mononuclear cells express procoagulant activity in response to LPS, zymosan, PGN, and PMA, and responses to LPS, zymosan and PGN are enhanced by the addition of HI-FBS. These findings suggest that HI-FBS retains important serum proteins that facilitate interactions between each of these bacterial or yeast derived products and the mononuclear cells. Consequently, future studies regarding the regulation of procoagulant activity by canine mononuclear cells should be performed in the presence of HI-FBS. Both assays utilized in this study allow high throughput of samples, and therefore are appropriate choices for rapid screening of conditions and/or therapeutic interventions affecting the canine inflammatory system.

Human polymorphonuclear leukocytes produce and express functional tissue factor upon stimulation

BACKGROUND

Blood-borne tissue factor (TF) plays a crucial role in thrombogenesis.

AIM

To study whether polymorphonuclear leukocytes (PMN) are a source of TF.

METHODS AND RESULTS

Human PMN were carefully separated from other blood cells and stimulated for 3 min with purified P-selectin or the chemotactic peptide formyl-MetLeuPhe (fMLP): they expressed both TF procoagulant activity, as identified by specific TF MoAb and inactivated factor VIIa blockade; and TF:Ag (four to six times), as shown by flow-cytometry and immunocytochemistry. About 40% of permeabilized PMN, both resting and stimulated, contained TF:Ag, indicating that stimulation only modifies the location of TF:Ag within PMN. By real time-polymerase chain reaction (RT-PCR), a very low amount of TF mRNA was detectable in resting PMN, but a 3- to 5-fold increase was observed after 1-h stimulation with P-selectin or fMLP, respectively.

CONCLUSIONS

These findings suggest that TF is not constitutively expressed in peripheral PMN, but can be up-regulated and produced upon stimulation and specific gene transcription, as for instance during contact with activated platelets or endothelium. The stored TF is rapidly expressed in vitro as a functional molecule on the surface of activated PMN. The availability of PMN TF supports the relevance of inflammatory cells and their interaction with platelets for fibrin deposition and thrombus formation.

Discrepancy between tissue factor activity and tissue factor expression in endotoxin-induced monocytes is associated with apoptosis and necrosis

Tissue factor (TF), the main initiator of blood coagulation, contributes to the manifestation of disseminated intravascular coagulation following septic shock in meningococcal infection. Since a direct relationship between disease severity and lipopolysaccharide (LPS) concentration in the circulation has been shown, we hypothesized that the procoagulant and cytotoxic effects of endotoxin also in vitro were related to its concentration. In vitro studies, however, have frequently used much higher LPS concentrations than those observed in clinical samples. Using elutriation-purified human monocytes, we observed that LPS up to 1000 ng/ml exerted a concentration-dependent increase in TF activity (tenase activity, fibrin formation in plasma). Although there was a dose-dependent increase in TF activity, there was not a concomitant increase in TF expression at LPS concentrations above 1 ng/ml (flow cytometry, Western blotting, TF mRNA). Flow cytometry revealed that this discrepancy between TF activity and TF expression at endotoxin concentrations above 1 ng/ml, coincided with an LPS dose-dependent increase in cell surface phosphatidylserine (PS), considered to promote coagulation. The increased PS expression was associated with an increased number of 7-AAD-positive cells indicating cell death. We conclude that enhancement of monocyte procoagulant activity in vitro by high concentrations of LPS may result from increased PS exposure due to apoptosis and necrosis. Therefore, the LPS concentrations used to examine monocyte procoagulant activity in vitro, should be carefully chosen.

State and diagnostic value of plasma tissue factor in early-hospitalised patients with chest pain

To study the state and diagnostic value of plasma tissue factor (TF) in patients with acute coronary syndromes (ACS), we quantitatively compared plasma TF antigen and TF activity in 90 early-hospitalised patients with chest pain. Using high-affinity antibodies, a sensitive assay for TF antigen was developed with a detection limit of 40 fmol/l. One of the antibodies was used to capture TF from plasma and, after elution and dialysis-free reconstitution in phospholipid-glucoside micelles, absolute amounts of TF activity could be measured with a detection limit of 80 fmol/l. All TF in plasma was found to be exposed, and a value of 2.5(1.1-14.8) pmol/l (median with range) was found for TF antigen. Most of this TF antigen (70-80%) circulated in a (potentially) functional state. Left in its in vivo state, however, TF captured from plasma was totally inactive, probably because of the lack of a procoagulant matrix. Compared with controls with non-cardiac chest pain, TF activity was unchanged and TF antigen about 25% elevated in ACS patients. Combined with the markers prothrombin fragment F1+2 and fatty acid-binding protein, TF did not improve the early diagnosis of ACS.

Radiotherapy of human xenograft NSCLC tumors in nude mice with a 90Y-labeled anti-tissue factor antibody

Tissue factor (TF) is a type I transmembrane protein and the initiator of the extrinsic blood coagulation pathway. TF plays a critical role in tumor development and its overexpression is observed in many tumors. To understand the prevalence and relative level of TF expression in non-small-cell lung cancer (NSCLC), we analyzed 50 NSCLC tumors by immunohistochemical staining and found that 88% of human NSCLC tumors overexpressed TF. We then generated a high affinity anti-TF antibody, TF278, which specifically binds TF on the surface of cells and is internalized upon binding. An 111In-labeled TF278 demonstrated favorable tumor accumulation in an SW-900 xenograft tumor model with a maximum mean percent of injected dose per gram of tissue (%ID/g) of 73.1% at 96 hours postinjection. In addition, we labeled the antibody with 90Y and tested its ability to inhibit the growth of tumors in an SW-900 xenograft tumor model in immunocompromised mice. The 90Y-TF278 slowed the growth of SW-900 tumors at a 50 microCi dose and completely regressed SW-900 tumors at a 150 microCi dose with little toxicity.

Clotting time analysis of citrated blood samples is strongly affected by the tube used for blood sampling

Our aim was to establish whether differences in clotting times for recalcified blood and plasma samples might be explained by the use of different blood collection tubes. Samples obtained from different plastic vacuum tubes were recalcified and clotting times determined by free oscillation rheometry. The clotting times for blood collected in Vacutainer (Becton Dickinson, Rutherford, New Jersey, USA) or Vacuette (Greiner Bio-One, Kremsmünster, Austria) tubes decreased with time, with maximal effect after 30 min. Blood from Monovette (Sarstedt, Nümbrecht, Germany) tubes displayed longer clotting times, which did not decrease with time. Clotting times for plasma prepared after 1 h storage in Vacutainer or Vacuette tubes were unaffected by subsequent addition of corn trypsin inhibitor to inhibit factor XIIa, although an antibody against factor XI prolonged the clotting time markedly. In Monovette plasma, both corn trypsin inhibitor and anti-factor XI effectively prolonged the clotting time. When corn trypsin inhibitor or anti-factor XI was added to the tubes before blood collection, but both additions clearly prolonged the clotting times in all types of tubes, even though corn trypsin inhibitor was less effective in whole blood. Antibodies against human tissue factor did not affect the clotting times. The amounts of platelet or leukocyte microparticles in plasma were low and similar in all tubes. This indicates that blood collection in Vacutainer or Vacuette tubes induces a rapid activation of factor XII and factor XI.

Clotting time analysis of citrated blood samples is strongly affected by the tube used for blood sampling

Our aim was to establish whether differences in clotting times for recalcified blood and plasma samples might be explained by the use of different blood collection tubes. Samples obtained from different plastic vacuum tubes were recalcified and clotting times determined by free oscillation rheometry. The clotting times for blood collected in Vacutainer (Becton Dickinson, Rutherford, New Jersey, USA) or Vacuette (Greiner Bio-One, Kremsmünster, Austria) tubes decreased with time, with maximal effect after 30 min. Blood from Monovette (Sarstedt, Nümbrecht, Germany) tubes displayed longer clotting times, which did not decrease with time. Clotting times for plasma prepared after 1 h storage in Vacutainer or Vacuette tubes were unaffected by subsequent addition of corn trypsin inhibitor to inhibit factor XIIa, although an antibody against factor XI prolonged the clotting time markedly. In Monovette plasma, both corn trypsin inhibitor and anti-factor XI effectively prolonged the clotting time. When corn trypsin inhibitor or anti-factor XI was added to the tubes before blood collection, but both additions clearly prolonged the clotting times in all types of tubes, even though corn trypsin inhibitor was less effective in whole blood. Antibodies against human tissue factor did not affect the clotting times. The amounts of platelet or leukocyte microparticles in plasma were low and similar in all tubes. This indicates that blood collection in Vacutainer or Vacuette tubes induces a rapid activation of factor XII and factor XI.

Blockade of tissue factor-factor X binding attenuates sepsis-induced respiratory and renal failure

Tissue factor expression in sepsis activates coagulation in the lung, which potentiates inflammation and leads to fibrin deposition. We hypothesized that blockade of factor X binding to the tissue factor-factor VIIa complex would prevent sepsis-induced damage to the lungs and other organs. Acute lung injury was produced in 15 adult baboons primed with killed Escherichia coli [1 x 10(9) colony-forming units (CFU)/kg], and then 12 h later, they were given 1 x 10(10) CFU/kg live E. coli by infusion. Two hours after live E. coli, animals received antibiotics with or without monoclonal antibody to tissue factor intravenously to block tissue factor-factor X binding. The animals were monitored physiologically for 34 h before being killed and their tissue harvested. The antibody treatment attenuated abnormalities in gas exchange and lung compliance, preserved renal function, and prevented tissue neutrophil influx and bowel edema relative to antibiotics alone (all P < 0.05). It also attenuated fibrinogen depletion (P < 0.01) and decreased proinflammatory cytokines, e.g., IL-6 and -8 (P < 0.01), in systemic and alveolar compartments. Similar protective effects of the antibody on IL-6 and -8 expression and permeability were found in lipopolysaccharide-stimulated endothelial cells. Blockade of factor X binding to the tissue factor-factor VIIa complex attenuates lung and organ injuries in established E. coli sepsis by attenuating the neutrophilic response and inflammatory pathways.

Prognostic significance of tissue factor in pancreatic ductal adenocarcinoma

Tissue factor (TF) is a transmembrane glycoprotein that plays roles in the blood coagulation and intracellular signaling pathways, and has also been suggested to modulate the biological behavior of cancer cells. In order to examine the clinicopathologic significance of TF expression in pancreatic ductal adenocarcinoma, TF expression was determined by immunohistochemistry using a newly raised anti-TF monoclonal antibody in 113 patients who had undergone surgical resection of pancreatic ductal adenocarcinoma. According to the incidence of tumor cell immunopositivity, patients were divided into "negative TF" (0%), "weak TF" (<25%), or "high TF" (25% or more) groups, which accounted for 11.6% (n = 13), 44.2% (n = 50), and 44.2% (n = 50) of the total, respectively. Increased TF expression was correlated with the extent of the primary tumor (P = 0.0043), lymph node metastasis (P = 0.0043), lymphatic distant metastasis (P = 0.0039), advanced tumor-node-metastasis stage (P = 0.0002), and high tumor grade (P = 0.0164). Multivariate analysis using the Cox proportional hazards model showed that high TF expression was an independent negative predictor for survival (hazard ratio, 2.014; P = 0.0076). Moreover, patients with TF-negative tumors had a significantly better prognosis even if lymph node metastasis was present (P < 0.0001). We also showed that TF knockdown by RNA interference suppressed the invasiveness of a pancreatic adenocarcinoma cell line in vitro. These results indicate that TF expression may contribute to the aggressiveness of pancreatic ductal adenocarcinoma by stimulating tumor invasiveness, and that evaluation of the primary tumor for TF expression may identify patients with a poor prognosis.

Generation of a polyclonal rabbit anti-mouse tissue factor antibody by nucleic acid immunisation

Tissue factor (TF) the cellular receptor and cofactor for factor VII, initiates coagulation and has also been implicated in several coagulation-independent functions, including inflammation, angiogenesis and tumour metastasis. Investigations of TF expression in mouse models of these processes has been limited by the availability of antibodies that specifically recognise mouse TF. We have generated a rabbit polyclonal antibody to mTF by DNA immunisation. This has yielded an antiserum that recognises native mTF in immunohistochemical and flow cytometric analyses. Furthermore, the antiserum is inhibitory in coagulation assays. This antiserum will be a valuable investigative tool in the analysis of mTF expression.

IgG immune response to tumor-associated carbohydrate antigens (TF, Tn, alphaGal) in patients with breast cancer: impact of neoadjuvant chemotherapy and relation to the survival

AIM

To study the humoral immune response to tumor-associated carbohydrate epitopes (TF, Tn and alphaGal) in patients with breast cancer and healthy donors, the putative impact of the chemotherapy and to evaluate if the level of antibody to these epitopes might be beneficial or detrimental for the patients with breast cancer.

MATERIALS AND METHODS

The humoral immune response to TF, Tn and alphaGal was studied in 133 patients with breast cancer, including the patients at stage II-III (n = 44) before and after neoadjuvant chemotherapy (10 patients received cyclophosphamide/methotrexate/fluorouracyl (CMF) chemotherapy regimens, 34 patients received cyclophosphamide/doxorubicin/fluorouracil (CAF)), and in controls (healthy donors and patients with fibroadenoma). Fully synthetic carbohydrate hapten-polyacrylamide conjugates were used as antigens in ELISA for anti-carbohydrate antibody determination. The correlation analysis between the level of anti-carbohydrate antibodies and the stage of cancer, histological grade, expression of TF and alphaGal epitopes in tumor tissue, patient's survival was performed.

RESULTS

The level of anti-carbohydrate antibodies varied between individuals with no significant correlation between IgG immune response to the three epitopes. Lower levels of antibodies were observed at advanced stages of cancer. Neoadjuvant chemotherapy stimulated antibody production to Tn and alphaGal epitopes (increase > 50%) in about one third of patients. Immunosuppression, decrease in antibody levels, was observed only in 4.5-13.6% of cases. High levels of TF-antigen specific IgG antibody before surgery were associated with a better survival time of stage II breast cancer patients.

CONCLUSION

The widely used regimens of neoadjuvant chemotherapy (such as CMF, CAF) can stimulate the immune response to tumor-associated carbohydrate epitopes in some patients. The high levels of anti-TF antibody before surgery are associated with a better survival of stage II breast cancer patients. This may indicate that the selection of immunopotentiating regimens of neoadjuvant chemotherapy might be beneficial for the host.

Role of Fibrinogen-Like Protein 2 Prothrombinase/Fibroleukin in Experimental and Human Allograft Rejection

Immune coagulation is a major contributor to the pathogenesis of xenograft rejection, viral-induced hepatocellular injury and cytokine-induced fetal loss syndrome. In this study, we investigated the contribution of the novel gene product, fibrinogen-like protein 2 (fgl2) prothrombinase, in mediating immune injury in experimental and human acute allograft rejection. Using a mouse heterotopic cardiac transplant model, mouse fgl2(mfgl2)/fibroleukin mRNA transcripts and protein were highly expressed in macrophages, CD4- and CD8-positive T lymphocytes, and endothelial cells in rejecting cardiac allografts in association with deposits of fibrin. Although mfgl2-deficient mice rejected allografts at similar rates to littermate controls, survival of grafts from mfgl2-deficient mice were prolonged and deposition of intravascular fibrin was diminished. Treatment of wild-type mice with a neutralizing anti-fgl2 Ab ameliorated histological evidence for allorejection and intravascular fibrin deposition, and resulted in an increase in graft survival. To address further the relevance of fgl2 in acute allograft rejection, we examined kidney biopsies from patients who had undergone renal transplantation. Human fgl2 mRNA transcripts and protein were markedly expressed mainly in renal tubule cells, infiltrating lymphoid cells including macrophages, CD8(+) T cells, mature B cells (plasma cells), and endothelial cells. Dual staining showed fibrin deposition was localized mainly to blood vessels, in the glomerulus and interstitium and the lumen of tubules, and occurred in association with human fgl2 expression. These data collectively suggest that fgl2 accounts for the fibrin deposition seen in both experimental and human allograft rejection and provide a rationale for targeting fgl2 as adjunctive therapy to treat allograft rejection.

Characterization of Human Tissue Factor (TF)–Specific Monoclonal Antibodies Prepared Using a Rapid Immunization Protocol

Tissue factor (TF) plays an important, physiological role in hemostasis. Recent studies have demonstrated the over-expression of TF in a number of solid tumor types and its pathological roles in angiogenesis and tumor metastasis. In this study, we report the development and characterization of a panel of murine MAbs that are specific for human TF, but do not inhibit TF-mediated blood coagulation. By using a modified repetitive immunizations at multiple sites (RIMMS) protocol in conjunction with an efficient hybridoma cloning procedure, anti-TF MAbs were generated within a relatively short time frame of 5-6 weeks. Following primary screening by ELISA, the binding of the MAbs to the native form of human TF was demonstrated in flow cytometry using a stable cell line expressing human TF. Several of these TF-specific MAbs did not inhibit blood coagulation in a blood coagulation assay and bound with high affinity (0.5-2 nM) to human TF in BIAcore analyses. Importantly, this study represents an independent evaluation of the RIMMS strategy for MAb generation and demonstrates that class-switched, high-affinity MAbs can be generated rapidly and reliably using RIMMS.

Potent inhibition of thrombin with a monoclonal antibody against tissue factor (Sunol-cH36): results of the PROXIMATE-TIMI 27 trial

AIMS

Exposure of tissue factor (TF) is a critical proximal step in the pathogenesis of acute coronary syndromes. Sunol-cH36, a chimaeric monoclonal antibody to TF, blocks binding of factor X to the TF:VIIa complex. This report describes the first completed trial of Sunol-cH36 in humans.

METHODS AND RESULTS

We assessed the safety and pharmacokinetics of Sunol-cH36 in an open-label, dose-escalating trial among subjects with stable coronary artery disease. The safety analysis included all adverse events with a focus on overt or occult bleeding. Five doses of Sunol-cH36 (0.03, 0.06, 0.08, 0.1, 0.3 mg/kg) were administered as a single intravenous bolus to 26 subjects (three to eight subjects per dose tier). No major bleeding (> or =2 g/dL haemoglobin decline) occurred. Spontaneous minor bleeding was observed with a dose-related pattern. Notably, the majority of spontaneous bleeding episodes were clinically consistent with platelet-mediated bleeding (e.g. gum, tongue) without thrombocytopenia. The median terminal half-life was 72.2 (25th, 75th: 28.4, 72.5) h.

CONCLUSION

Sunol-cH36 exhibited dose-dependent anticoagulant effects. We postulate that the mucosal bleeding observed with this potent inhibitor of thrombin generation may reflect antiplatelet effects resulting from networking between the coagulation cascade and platelet pathways that could prove clinically relevant with this novel class of anticoagulants.

Tissue factor activity in whole blood

Tissue factor (TF) is an integral membrane protein essential for hemostasis. During the past several years, a number of studies have suggested that physiologically active TF circulates in blood at concentrations greater than 30 pM either as a component of blood cells and microparticles or as a soluble plasma protein. In our studies using contact pathway-inhibited blood or plasma containing activated platelets, typically no clot is observed for 20 minutes in the absence of exogenous TF. An inhibitory anti-TF antibody also has no effect on the clotting time in the absence of exogenous TF. The addition of TF to whole blood at a concentration as low as 16 to 20 fM results in pronounced acceleration of clot formation. The presence of potential platelet TF activity was evaluated using ionophore-treated platelets and employing functional and immunoassays. No detectable TF activity or antigen was observed on quiescent or ionophore-stimulated platelets. Similarly, no TF antigen was detected on mononuclear cells in nonstimulated whole blood, whereas in lipopolysaccharide (LPS)-stimulated blood a significant fraction of monocytes express TF. Our data indicate that the concentration of physiologically active TF in non-cytokine-stimulated blood from healthy individuals cannot exceed and is probably lower than 20 fM.

Fibrin independent proinflammatory effects of tissue factor in experimental crescentic glomerulonephritis

BACKGROUND

Tissue factor initiated glomerular fibrin deposition is an important mediator of injury in crescentic glomerulonephritis. Recent data have suggested noncoagulant roles for tissue factor in inflammation.

METHODS

To test the hypothesis that in addition to its effects in initiating coagulation, tissue factor has proinflammatory effects in glomerulonephritis, rabbits given crescentic anti-glomerular basement membrane (GBM) antibody-induced glomerulonephritis were defibrinogenated with ancrod. One group of defibrinogenated rabbits was also given anti-tissue factor antibodies. Comparisons were made between these groups, as well as a third group that was neither defibrinogenated with ancrod nor given anti-tissue factor antibodies.

RESULTS

Defibrinogenation alone abolished glomerular fibrin deposition, reduced crescent formation, and limited renal impairment (ancrod-treated, serum creatinine 274 +/- 37 micromol/L; untreated 415 +/- 51 micromol/L; P < 0.01). Tissue factor inhibition in defibrinogenated rabbits resulted in further protection of renal function (creatinine 140 +/- 19 micromol/L, P < 0.01) and reduced proteinuria (0.4 +/- 0.2g/day, untreated 2.6 +/- 0.4 g/day, P <0.01), which was significantly increased by defibrinogenation alone (ancrod-treated, 5.6 +/- 1.2 g/day). Anti-tissue factor antibodies (but not defibrinogenation alone) attenuated glomerular T-cell and macrophage recruitment, and major histocompatibility complex (MHC) class II expression.

CONCLUSION

These results demonstrate important proinflammatory effects of tissue factor in crescentic glomerulonephritis that are fibrin independent and provide in vivo evidence for tissue factor's proinflammatory effects on MHC class II expression and leukocyte accumulation.

Properties of proteins in cancer procoagulant preparations that are detected by anti-tissue factor antibodies

Cancer procoagulant (CP) and tissue factor (TF; only in complex with Factor VIIa (FVIIa)) can activate FX to FXa. Controversy still exists whether or not CP is an entity different from TF, or whether CP activity is due to contamination of CP preparations with TF/FVIIa complex. We therefore looked for proteins in CP preparations that were detected by anti-TF antibodies and then sequenced these proteins. One- and two-dimensional gels of CP and TF were used to identify proteins immunoreactive to monoclonal anti-CP and anti-TF antibodies (Mabs). Those proteins in the CP preparation recognized by anti-TF antibodies were sequenced. Angiotensinogen precursor, alpha-1-antitrypsin precursor, and vitamin D-binding protein were identified along with one so far unidentified sequence; however, no TF-sequences were identified. Also, no proteins with the correct molecular weight for TF were identified using anti-TF antibodies. It seems possible that CP preparations contain proteins that have some epitopes similar to the epitopes recognized in TF by anti-TF Mab. However, these proteins do neither have the molecular weight nor the amino acid sequence of TF.

Effect of interleukin-6 blockade on tissue factor-induced coagulation in human endotoxemia

OBJECTIVE

Clinical trials show that interleukin (IL)-6 represents a predictive marker in human sepsis. Furthermore, IL-6 has been proposed as a candidate mediator for endotoxin (lipopolysaccharide)-induced coagulation activation: In a primate model, an (alphaIL-6 antibody (alphaIL-6 Ab) almost abolished lipopolysaccharide-induced coagulation activation. Therefore, we wished to determine if an alphaIL-6 Ab (B-E8) may also attenuate lipopolysaccharide-induced activation of coagulation in humans.

DESIGN

The study was a randomized, double blind, placebo-controlled parallel group trial (n = 12 per group).

SETTING

University medical center.

PATIENTS

Healthy volunteers.

INTERVENTIONS

Healthy volunteers were randomized to receive either 80 mg of a monoclonal anti-IL-6 Ab (B-E8) or placebo intravenously before bolus infusion of 2 ng/kg lipopolysaccharide.

MEASUREMENTS AND MAIN RESULTS

B-E8 effectively decreased IL-6 bioactivity as measured by a Bg-bioassay in vitro and concentrations of C reactive protein. However, B-E8 did not decrease lipopolysaccharide-induced tissue factor-messenger RNA transcription or plasma concentrations of downstream coagulation variables (prothrombin fragment 1 + 2, thrombin-antithrombin III complexes, and D-dimer concentrations). Similarly, tumor necrosis factor-alpha concentrations, fibrinolytic activity (plasmin-antiplasmin complexes), endothelial activation (soluble E-selectin), and IL-10 were unaffected.

CONCLUSION

IL-6 does not appear to mediate early-phase lipopolysaccharide-induced coagulation activation in humans.