Hypoxia provokes leukotriene-dependent neutrophil sequestration in perfused rabbit hearts

Isolated rabbit hearts were perfused with salt solution containing autologous 111In-labeled neutrophils to determine whether 1) hypoxia provoked myocardial neutrophil sequestration, 2) neutrophil accumulation could be suppressed by inhibition of lipoxygenase and 3) hypoxic myocardium generated radioimmunoassayable leukotriene B4 (LTB4). Whereas accumulation of 111In-labeled neutrophils by normoxic hearts was minimal, induction of acute myocardial hypoxia by perfusion with hypoxic medium caused a rapid uptake of 111In-labeled neutrophils. Sequestered neutrophils were not released during a subsequent 20-min normoxic perfusion period. Hypoxia-induced neutrophil uptake was prevented by nordihydroguaiaretic acid (NDGA) or diethylcarbamazine (DEC), two structurally different inhibitors of lipoxygenase. Although no radioimmunoassayable LTB4 could be detected in neutrophil-free perfusate from normoxic or hypoxic preparations, hypoxia caused an approximate 2-fold increase in myocardial tissue levels of LTB4. Tissue levels of LTB4 reverted to control values after 20 min of normoxic perfusion. Infusion of exogenous LTB4 also provoked myocardial neutrophil uptake. Viewed collectively, these observations suggest that in isolated buffer-perfused rabbit hearts hypoxia induces LTB4 release from resident myocardial cells, which promotes avid neutrophil sequestration.     

Specific binding of soluble fibrin to macrophages

Guinea pig peritoneal macrophages were demonstrated to bind selectively soluble 125I-fibrin and fibrin/fibrinogen complexes as compared with fibrinogen, fibrinogen degradation products, and fibrin degradation products. Cellular uptake was considered to be surface receptor binding on the basis of removal of bound 125I-fibrin by trypsin and because uptake occurred in the presence of metabolic inhibitors. 125I-fibrin uptake could be blocked by nonradioactive fibrin but not by IgG or immune complexes. Binding was uneffected by prior treatment with plasmin or trypsin but was calcium dependent. Only limited reversibility of binding could be demonstrated after prolonged incubation. Scatchard plots permitted an estimate of the number of bound molecules. At saturation 6.92 X 10(6) 125I-fibrin molecules were bound per cell. Similar binding of fibrin was noted in polymorphonuclear leukocytes, but not lymphocytes or fibroblasts. Soluble fibrin binding may be a host defense mechanism whereby the reticuloendothelial system can remove fibrin from the blood before the development of microthrombi.     

穿心莲内酯抑制缺氧性肺动脉高压的实验研究

低氧可以诱发肺动脉高压,低氧环境下血管平滑肌增生和肥大导致的血管重塑是肺动脉高压的重要因素。因此研究血管平滑肌增生和肥大发生的原因、进程、以及如何抑制平滑肌的增生对低氧性肺动脉高压的预防和治疗具有重要的意义。本研究以NF-κB为研究目标,采用药物干预及基因敲除策略证明了NF-κB在低氧性肺动脉高压中被活化,而且NF-κB的抑制剂-穿心莲内酯具有延缓肺动脉高压进程的作用。     

Differential contributions of monocyte‐ and platelet‐derived microparticles towards thrombin generation and fibrin formation and stability

Summary. Background: Microparticles (MPs) are sub‐micron vesicles shed by activated or apoptotic cells, including platelets and monocytes. Increased circulating MPs are associated with thrombosis; however, their role in thrombogenesis is poorly understood. Objective: To determine how MPs promote thrombin generation and modulate fibrin density and stability. Methods: Platelets and monocytes were isolated from healthy donors. Platelets were stimulated with calcium ionophore, thrombin receptor agonist peptide (TRAP) or TRAP/convulxin. Monocytes and human monocytic THP‐1 cells were stimulated with lipopolysaccharide (LPS). MPs were isolated, washed by high‐speed centrifugation and assessed using the following: transmission electron microscopy (TEM), Nanoparticle Tracking Analysis (NTA), flow cytometry, tissue factor (TF) activity, prothrombinase activity, thrombin generation, and clot formation, density and stability. Results: MPs from monocytes (M‐MPs) and platelets (PMPs) had similar shapes and diameters (100–300 nm). M‐MPs had TF activity (16.7 ± 2.4 pm TF per 10⁶ MP), supported prothrombinase activity and triggered shorter thrombin generation lag times than buffer controls (5.4 ± 0.5 vs. 84.2 ± 4.8 min, respectively). Compared with controls, M‐MPs supported faster fibrin formation (0.24 ± 0.24 vs. 76.7 ± 15.1 mOD min^?1, respectively), 38% higher fibrin network density and higher clot stability (3.8‐fold higher turbidity in the presence of tissue plasminogen activator). In contrast, PMPs did not have TF activity and supported 2.8‐fold lower prothrombinase activity than M‐MPs. PMPs supported contact‐dependent thrombin generation, but did not independently increase fibrin network density or stability. Interestingly, PMPs increased rates of thrombin generation and fibrin formation (1.7‐ and 1.3‐fold, respectively) when mixed with THP‐1‐derived MPs. Conclusion: MPs from platelets and monocytes differentially modulate clot formation, structure and stability, suggesting unique contributions to thrombosis.     

Levels of microparticle tissue factor activity correlate with coagulation activation in endotoxemic mice

Summary.  Background: Tissue factor (TF) is present in blood in various forms, including small membrane vesicles called microparticles (MPs). Elevated levels of these MPs appear to play a role in the pathogenesis of thrombosis in a variety of diseases, including sepsis. Objective: Measure levels of MP TF activity and activation of coagulation in control and endotoxemic mice. Materials and methods: MPs were prepared from plasma by centrifugation. The procoagulant activity (PCA) of MPs was measured using a two-stage chromogenic assay. We also measured levels of thrombin-antithrombin and the number of MPs. Results: Lipopolysaccharide (LPS) increased MP PCA in wild-type mice; this PCA was significantly reduced by an anti-mouse TF antibody (1H1) but not with an anti-human TF antibody (HTF-1). Conversely, in mice expressing only human TF, MP PCA was inhibited by HTF-1 but not 1H1. MPs from wild-type mice had 6-fold higher levels of PCA using mouse factor (F)VIIa compared with human FVIIa, which is consistent with reported species-specific differences in FVIIa. Mice expressing low levels of human TF had significantly lower levels of MP TF activity and TAT than mice expressing high levels of human TF; however, there were similar levels of phosphatidylserine (PS)-positive MPs. Importantly, levels of MP TF activity in wild-type mice correlated with levels of TAT but not with PS-positive MPs in endotoxemic mice. Conclusion: These results suggest that the levels of TF-positive MPs can be used as a biomarker for evaluating the risk of disseminated intravascular coagulation in endotoxemia.     

Hypoxia-induced increases in pulmonary transvascular protein escape in rats. Modulation by glucocorticoids.

Pulmonary edema after ascent to altitude is well recognized but its pathogenesis is poorly understood. To determine whether altitude exposure increases lung vascular permeability, we exposed rats to a simulated altitude of approximately 14,500 feet (barometric pressure [Pb] 450 Torr) and measured the pulmonary transvascular escape of radiolabeled 125I-albumin corrected for lung blood content with 51Cr-tagged red blood cells (protein leak index = PLI). Exposures of 24 and 48 h caused significant increases in PLI (2.30 +/- 0.08 and 2.40 +/- 0.06) compared with normoxic controls (1.76 +/- 0.06), but brief hypoxic exposures of 1-13 h produced no increase in PLI, despite comparable increases in pulmonary artery pressure. There were associated increases in gravimetric estimates of lung water in the altitude-exposed groups and perivascular edema cuffs on histologic examination. Normobaric hypoxia (48 h; fractional inspired oxygen concentration [FIO2] = 15%) also increased lung transvascular protein escape and lung water. Dexamethasone has been used to prevent and treat altitude-induced illnesses, but its mechanism of action is unclear. Dexamethasone (0.5 or 0.05 mg/kg per 12 h) started 12 h before and continued during 48 h of altitude exposure prevented the hypoxia-induced increases in transvascular protein escape and lung water. Hemodynamic measurements (mean pulmonary artery pressure and cardiac output) were unaffected by dexamethasone, suggesting that its effect was not due to a reduction in pulmonary artery pressure or flow. The role of endogenous glucocorticoid activity was assessed in adrenalectomized rats that showed augmented hypoxia-induced increases in transvascular protein escape, which were prevented by exogenous glucocorticoid replacement. In summary, subacute hypoxic exposures increased pulmonary transvascular protein escape and lung water in rats. Dexamethasone prevented these changes independent of reductions of mean pulmonary artery pressure or flow, whereas adrenalectomy increased pulmonary vascular permeability and edema at altitude. Increases in vascular permeability in hypoxia could contribute to the development of high-altitude pulmonary edema and endogenous glucocorticoids may have an important influence on pulmonary vascular permeability in hypoxia.     

Tissue specific modulation of beta-adrenoceptor number in rats with chronic hypoxia with an attenuated response to down-regulation by salbutamol

The number of beta-adrenoceptors and their affinity for the radioligand 125I-labelled cyanopindolol (125I-CYP) were measured in crude membrane preparations of left ventricle, spleen and lung from Wistar rats exposed to 28 days continuous hypoxia. beta-Adrenoceptor density in the left ventricle was not significantly altered after exposure to chronic hypoxia (binding site maxima, Bmax.: normoxic control 36 SEM 5, hypoxic 24.8 SEM 2 fmol/mg of protein). There was no change in beta-adrenoceptor number in the spleen in response to chronic hypoxia (Bmax.: normoxic control 76 SEM 19 fmol/mg of protein, hypoxic 80 SEM 15 fmol/mg of protein). Chronic hypoxia resulted in a significant increase in beta-adrenoceptor number in lung tissue (binding site maxima, Bmax.: normoxic control 406 (SEM 31) fmol/mg of protein; hypoxic 535 (SEM 30) fmol/mg of protein, P less than 0.01 without change in the dissociation constant (KD) of the radioligand. beta-Adrenoceptor subtypes in lung homogenates were studied by establishing displacement curves for 125I-CYP by ICI 118551 (a selective beta 2-antagonist). A significant difference was seen in the proportion of beta 1-/beta 2-adrenoceptor subtypes after hypoxia (normoxic control 66 SEM 2.5%, hypoxic 79 SEM 2.4% beta 2-adrenoceptors, P less than 0.01). alpha 1-Adrenoceptor number in lung membranes was measured with 125I-labelled 2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone (125I-HEAT). No difference was seen in the number of alpha 1-receptors in normoxia and in chronic hypoxia [Bmax.: normoxic control 48 (SEM 3), hypoxic 48 (SEM 5) fmol/mg of protein].(ABSTRACT TRUNCATED AT 250 WORDS)     

Phytoestrogens restore nitric oxide-mediated relaxation in isolated pulmonary arteries from chronically hypoxic rats

Phytoestrogens derived from soybeans reverse endothelial dysfunction in a number of animal models of systemic vascular disease. Based on these studies, we hypothesized that phytoestrogens would reverse chronic hypoxia-induced endothelial dysfunction in rat pulmonary arteries. To test this hypothesis we examined the effect of genistein, the major phytoestrogen found in soybeans, on carbachol-induced relaxation in phenylephrine-constricted pulmonary artery rings isolated from normoxic rats and rats exposed to 14 days of hypobaric hypoxia. Compared with that in normoxic rats, the response to carbachol was impaired in pulmonary arteries isolated from rats exposed to chronic hypoxia. In normoxic rat pulmonary arteries, genistein (30 microM) did not change the maximum relaxation to carbachol. In contrast, genistein significantly enhanced the relaxation response to carbachol in pulmonary arteries from hypoxic rats, restoring it to the levels seen in normoxic rats. 17beta-estradiol (10 microM) and daidzein (30 microM), a structural analog of genistein lacking inhibitory effects on tyrosine kinases, also restored the relaxation response to carbachol in hypoxic rat pulmonary arteries. The nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine (100 microM) completely blocked the genistein, daidzein, and 17beta-estradiol-induced restoration of the relaxation response to carbachol, whereas the estrogen receptor antagonist ICI 182,780 (10 microM) had no effect on the relaxation responses. We conclude that the phytoestrogens genistein and daidzein act like estrogen in restoring nitric oxide-mediated relaxation in chronically hypoxic rat pulmonary arteries and that this effect does not appear to be mediated by inhibition of tyrosine kinases or by known estrogen receptors.     

On the origin of urinary fibrin-fibrinogen-related antigen in glomerulonephritis

A model of antiglomerular basement membrane nephritis in the rat was used to elucidate the origin of urinary fibrin-fibrinogen-related antigen (FRA). The intrarenal distribution and excretion of 125I-rat fibrinogen was examined to determine whether there was increased filtration of bibrinogen or fibrin degradation products (FDP) or lysis of intraglomerular fibrin. 125I-protein appeared in the urine immediately after injection of 125I-fibrinogen and fell in parallel with the fall in plasma 125I-fibrinogen. Renal retention of 125I-fibrin averaged less than 0.2 percent of the administered dose of 125I-fibrinogen. The infusion of epsilon aminocaproic acid (EACA) had no significant effect on either FRA excretion or 125I-protein excretion. Plasma FDP levels and the elution patteren of 125I-protein from the urine were not significantly changed by EACA infusion. These observations support the view that ruinary FRA excretion in glomerulonephritis is derived predominantly from increased filtration of plasma fibrinogen rather than from breakdown of intraglomerular fibrin.     

Tissue factor‐bearing microparticles and inflammation: a potential mechanism for the development of venous thromboembolism in cancer

Summary

Cancer is associated with an increased risk of venous thromboembolism (VTE); the exact mechanisms for the induction of VTE remain to be fully elucidated, but it is widely acknowledged that tissue factor (TF)‐bearing microparticles (TF‐MPs) may play a significant role. However, TF‐MPs have yet to be accepted as a genuine biomarker for cancer‐associated VTE, as the presence of elevated TF‐MP levels is not always accompanied by thrombosis; interestingly, in certain cases, particularly in pancreatic cancer, VTE seems to be more likely in the context of acute inflammation. Although several potential mechanisms for the development of VTE in cancer have been postulated, this review explores the homeostatic disruption of TF‐MPs, as the main reservoir of bloodborne TF, in the context of cancer and inflammation, and considers the abrogated responses of the activated endothelium and mononuclear phagocyte system in mediating this disruption.

     

Cyclooxygenase-2-linked attenuation of hypoxia-induced pulmonary hypertension and intravascular thrombosis

Exogenous prostacyclin is effective in reducing pulmonary vascular resistance in some forms of human pulmonary hypertension (PH). To explore whether endogenous prostaglandins played a similar role in pulmonary hypertension, we examined the effect of deleting cyclooxygenase (COX)-gene isoforms in a chronic hypoxia model of PH. Pulmonary hypertension, examined by direct measurement of right ventricular end systolic pressure (RVESP), right ventricular hypertrophy (n = 8), and hematocrit (n = 3), was induced by 3 weeks of hypobaric-hypoxia in wild-type and COX-knockout (KO) mice. RVESP was increased in wild-type hypoxic mice compared with normoxic controls (24.4 +/- 1.4 versus 13.8 +/- 1.9 mm Hg; n = 8; p < 0.05). COX-2 KO mice showed a greater increase in RVESP following hypoxia (36.8 +/- 2.7 mm Hg; p < 0.05). Urinary thromboxane (TX)B(2) excretion increased following hypoxia (44.6 +/- 11.1 versus 14.7 +/- 1.8 ng/ml; n = 6; p < 0.05), an effect that was exacerbated by COX-2 gene disruption (54.5 +/- 10.8 ng/ml; n = 6). In contrast, the increase in 6-keto-prostacyclin(1alpha) excretion following hypoxia was reduced by COX-2 gene disruption (29 +/- 3 versus 52 +/- 4.6 ng/ml; p < 0.01). Tail cut bleed times were lower following hypoxia, and there was evidence of intravascular thrombosis in lung vessels that was exacerbated by disruption of COX-2 and reduced by deletion of COX-1. The TXA(2)/endoperoxide receptor antagonist ifetroban (50 mg/kg/day) offset the effect of deleting the COX-2 gene, attenuating the hypoxia-induced rise in RVESP and intravascular thrombosis. COX-2 gene deletion exacerbates pulmonary hypertension, enhances sensitivity to TXA(2), and induces intravascular thrombosis in response to hypoxia. The data provide evidence that endogenous prostaglandins modulate the pulmonary response to hypoxia.     

Effect of hydroxyethyl starch on vascular leak syndrome and neutrophil accumulation during hypoxia

OBJECTIVE: Several studies have suggested that intravenous hydroxyethyl starch treatment may dampen acute inflammatory responses. It is well documented that limited oxygen delivery to tissues (hypoxia) is common in acute inflammation, and numerous parallels exist between acute responses to hypoxia and to inflammation, including the observation that both are associated with increased vascular leakage and neutrophil infiltration of tissues. Therefore, we compared functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. DESIGN: Laboratory study. SETTING: University hospital. SUBJECTS: Cultured human microvascular endothelial cells and mice (C57BL/6/129 svj). INTERVENTIONS: We measured functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. MEASUREMENTS AND MAIN RESULTS: Studies to assess endothelial barrier function in vitro indicated that the addition of hydroxyethyl starch promotes endothelial barrier in a dose-dependent fashion and hydroxyethyl starch-barrier effects are increased following endothelial hypoxia exposure (human microvascular endothelial cells, 48 hrs, 2% oxygen). Treatment of human microvascular endothelial cells with hydroxyethyl starch resulted in a dose-dependent increase in 157-phosphorylated vasodilator-stimulated phosphoprotein, a protein responsible for controlling the geometry of actin-filaments. Neutrophil adhesion was decreased in the presence of physiologically relevant concentrations of hydroxyethyl starch in vitro, particularly after endothelial hypoxia exposure. Using a murine model of normobaric hypoxia, increases in vascular leakage and pulmonary edema associated with hypoxia exposure (4 hrs at 8% oxygen) were decreased in animals treated with intravenous hydroxyethyl starch. Increases of tissue neutrophil accumulation following hypoxia exposure were dampened in hydroxyethyl starch-treated mice. CONCLUSIONS: Taken together, these results indicate that hypoxia-induced increases in vascular leakage and acute inflammation are attenuated by hydroxyethyl starch treatment.     

Hypoxia increases human keratinocyte motility on connective tissue.

Re-epithelialization of skin wounds depends upon the migration of keratinocytes from the cut margins of the wound and is enhanced when human keratinocytes are covered with occlusive dressings that induce hypoxia. In this study, two independent migration assays were used to compare cellular motility on connective tissue components under normoxic or hypoxic conditions. Human keratinocytes apposed to collagens or fibronectin exhibited increased motility when subjected to hypoxic (0.2 or 2% oxygen) conditions compared with normoxic (9 or 20% oxygen) conditions. When compared with normoxic cells, hypoxic keratinocytes exhibited increased expression and redistribution of the lamellipodia-associated proteins (ezrin, radixin, and moesin). Furthermore, hypoxic keratinocytes demonstrated decreased secretion of laminin-5, a laminin isoform known to inhibit keratinocyte motility. Hypoxia did not alter the number of integrin receptors on the cell surface, but did induce enhanced secretion of the 92-kD type IV collagenase. These data demonstrate that hypoxia promotes human keratinocyte motility on connective tissue. Hypoxia-driven motility is associated with increased expression of lamellipodia proteins, increased expression of collagenase and decreased expression of laminin-5, the locomotion brake for keratinocytes.     

Platelet‐ and erythrocyte‐derived microparticles trigger thrombin generation via factor XIIa

See also Shapiro S, Laffan M. Making contact with microparticles. This issue, pp 1352–4. Summary. Background: The procoagulant properties of microparticles (MPs) are due to the of the presence of phosphatidylserine (PS) and tissue factor (TF) on their surface. The latter has been demonstrated especially on MPs derived from monocytes. Objectives: To investigate the relative contribution of TF and factor (F)XII in initiating coagulation on MPs derived from monocytes, platelets and erythrocytes. Methods: Microparticles were isolated from calcium ionophore‐stimulated platelets, erythrocytes and monocytic THP‐1 cells. MPs were quantified, characterized for cell‐specific antigens and analyzed for TF, PS exposure and their thrombin‐generating potential. Results: The MP number was not proportional to PS exposure and the majority of the MPs exposed PS. TF activity was undetectable on platelet‐ and erythrocyte‐derived MPs (< 1 fm nm ^?1 PS), whereas monocyte‐derived MPs exposed TF (32 fm nm ^?1 PS). Platelet‐, erythrocyte‐ and monocyte‐derived MPs, but not purified phospholipids, initiated thrombin generation in normal plasma in the absence of an external trigger (lag time < 11 min). Deficiency or inhibition of FVII had no effect on thrombin generation induced by platelet‐ and erythrocyte‐derived MPs, but interfered with monocyte MP‐triggered coagulation. Platelet‐ and erythrocyte‐derived MPs completely failed to induce thrombin generation in FXII‐deficient plasma. In contrast, monocyte‐derived MPs induced similar thrombin generation in normal vs. FXII‐deficient plasma. Conclusion: MPs from platelets and erythrocytes not only propagate coagulation by exposing PS but also initiate thrombin generation independently of TF in a FXII‐dependent manner. In contrast, monocyte‐derived MPs trigger coagulation predominantly via TF.     

组织因子阳性微粒在凝血及血栓形成中的作用

微粒是真核细胞活化或凋亡时释放的直径约为0.1～1.0 μm的双层脂质膜囊泡,来源于血小板、白细胞、红细胞、单核细胞、内皮细胞及肿瘤细胞等.组织因子(TF)是一种跨膜糖蛋白,是体内凝血途径的启动因子.TF主要以在微粒上表达的形式存在,这种微粒称为组织因子阳性微粒(TF+MPs).TF+ MPs具有较高的促凝活性,其表达水平可在血栓性疾病和相关凝血性疾病中升高.因此,测定TF+MPs可能作为血栓性疾病的有效监测指标.     

Complex formation of platelet thrombospondin with plasminogen. Modulation of activation by tissue activator.

Thrombospondin (TSP), a multifunctional alpha-granule glycoprotein of platelets, binds fibrinogen, fibronectin, heparin, and histidine-rich glycoprotein and thus may play an important role in regulating thrombotic influences at vessel surfaces. In this study we have demonstrated that purified human platelet TSP formed a complex with purified human plasminogen (Plg). Complex formation was detected by rocket immunoelectrophoresis of mixtures of the purified radiolabeled proteins. Significant complex formation of fluid-phase Plg with adsorbed TSP was also demonstrated by enzyme-linked immunosorbent assay (ELISA). The complex formation was specific, saturable, and inhibited by excess fluid-phase TSP, with an apparent KD of approximately 35 nM. In both ELISA and rocket immunoelectrophoresis systems, complex formation was inhibited by 10 mM epsilon-amino-n-caproic acid, implying that there is a role for the lysine binding sites of Plg in mediating the interaction. TSP also formed a complex with plasmin as detected by ELISA but did not directly inhibit plasmin activity measured with a synthetic fluorometric substrate or with a 125I-fibrin plate assay. TSP, when incubated with Plg before addition to 125I-fibrin plates significantly inhibited the generation of plasmin activity by tissue plasminogen activator (TPA) in a manner that was calcium dependent. A kinetic study of Plg activation by TPA in the presence of TSP demonstrated that Michaelis-Menten kinetics were followed and that TSP acted as a noncompetitive inhibitor. These studies support the hypothesis that TSP, acting as a multifunctional regulator in focal areas of active hemostasis, could serve as a prothrombotic influence, leading to increased deposition of fibrin.     

Intravenous somatic gene transfer with antisense tissue factor restores blood flow by reducing tumor necrosis factor-induced tissue factor expression and fibrin deposition in mouse meth-A sarcoma.

Fibrin is deposited on the endothelial cell surface in the vasculature of murine methylcholanthrene A-induced sarcomas after injection of tumor necrosis factor (TNF). Capillary endothelial cells of the tumor vascular bed become positive for tissue factor after TNF injection, based on immunocytochemistry and in situ hybridization. Intravascular clot formation was not dependent on tissue factor derived from tumor cells, since in vessels of tumors not expressing tissue factor, TNF also induced fibrin/fibrinogen deposition. However, the time course of fibrin/fibrinogen deposition after TNF differed in tumors expressing no, little, or greater amounts of tissue factor. Fibrin/fibrinogen deposition was more rapid in tumors in which the neoplastic cells expressed tissue factor than in tumors not expressing tissue factor. In the tumors not expressing tissue factor, activation of coagulation was dependent on TNF-induced synthesis of tissue factor by host cells, i.e., endothelium or monocytes/macrophages. Intravenous somatic gene transfer with tissue factor cDNA in the antisense orientation (but not sense or vector alone) reduced intravascular fibrin/fibrinogen deposition and restored blood flow to the tumor, showing that de novo tissue factor expression is central in TNF-induced activation of the coagulation mechanism.