Tissue factor localization in non-human primate cerebral tissue

Tissue factor (TF), the principal procoagulant of human brain, resides in specific regions of the non-human primate central nervous system. Immunohistochemical studies employing murine anti-human TF monoclonal antibodies (MoAbs) detected TF antigen in the cortex, basal ganglia, cerebellum, and cervical spinal cord in three normal baboon subjects. Although significantly less prominent than human cortical gray matter, a distinct partition of TF in gray matter > white matter was noted. The gray matter predilection of TF was confirmed in primate temporal and parietal lobe cortex by both sandwich ELISA and one-stage coagulation assay. Variation in the relative quantity of TF antigen was observed by ELISA among the three subjects studied. Procoagulant activity followed the pattern of TF antigen (cortical gray matter > basal ganglia > or = cerebellum > cortical white matter), and was 96.5-98.5% inhibitable by a function inhibiting anti-human TF MoAb combination. TF antigen was associated with the microvasculature of all cerebral tissues studied, and spared capillaries most selectively in the cerebral cortex, basal ganglia, and cerebellum. These findings suggest a highly specific ordering of TF antigen and related procoagulant activity in the central nervous system of the baboon, confined primarily to gray matter parenchyma, and to the non-capillary microvasculature.

Monoclonal antibodies against the C-terminal peptide of human tissue factor for studies of the cytoplasmic domain

The carboxyl-terminal cytoplasmic domain of human tissue factor (the essential cofactor for coagulation factor VII) is a prospective regulatory domain through which viable cells may control the expression of tissue factor activity. Furthermore, this domain is subject to post-translational modifications of as yet unknown functional significance. Hybridomas producing antibodies against the C-terminal domain of tissue factor were obtained using splenocytes harvested from mice immunized with a synthetic peptide corresponding to the nine terminal residues of the protein sequence. These antibodies, C28 1.1 and C28 2.1, react with purified placental tissue factor, but not with a recombinant soluble tissue factor lacking the cytoplasmic and membrane-spanning domains. This confirms that tissue factor from biological membranes contains the entire cytoplasmic domain predicted from the cDNA sequence, and provides a mechanism to determine whether tissue factor used experimentally retains this proteolytically sensitive epitope. The antibodies have been employed to demonstrate selective proteolytic removal of the carboxyl-terminal peptide from tissue factor. Limited experiments indicate that they will be useful for characterizing the distribution of vesicles with regard to the possible orientations of tissue factor on their surface.

Immunohistochemical identification of tissue factor in solid tumors

Patients with cancer experience a much higher than expected incidence of thromboembolic disorders, commonly referred as Trousseau syndrome. Although this association has been well documented, the etiology of the hypercoagulable state is not known. The expression on tumor cells of tissue factor (TF), a membrane-bound lipoprotein that functions as a cofactor to factor VIIa in the initiation of the extrinsic pathway of blood coagulation, has been postulated as a possible mechanism. Whereas the distribution of TF in normal tissues is known, no large survey of TF expression in malignant tissues has been reported. In this study a polyclonal, monospecific rabbit anti-human TF IgG was used for immunohistochemical localization of TF antigen in 85 different tumor specimens. In general, cell types which normally express TF continued to do so after malignant transformation (41 of 60 epithelial tumor specimens were positive for TF). Tumors of nonepithelial origin frequently lacked TF, with only 3 of 19 specimens containing evidence of TF antigen. In addition five of six benign tumors did not express TF. Many tumor types commonly associated with Trousseau syndrome, for example lung, pancreatic, breast, colon and gastric carcinomas, stained positively for TF. Based on this survey, it appears that TF expression by tumors may be an important factor in the pathogenesis of a hypercoagulable state in some patients with cancer.

Tumor necrosis factor-induced endothelial tissue factor is associated with subendothelial matrix vesicles but is not expressed on the apical surface

Cultured endothelial cells can be induced by tumor necrosis factor/cachectin (TNF) and other cytokines to synthesize the procoagulant cofactor tissue factor (TF). Intact monolayers of TNF-treated endothelial cells showed only minimal TF activity. In contrast, after permeabilization of these monolayers with detergent (saponin, 0.02%), there was approximately 10- to 20-fold increase in TF-mediated, factor VIIa-dependent factor Xa formation. Extracellular matrix derived from TNF-treated endothelium, prepared after removing the cells by hypotonic lysis or ammonium hydroxide (0.1 N), also had similarly enhanced TF activity. Incubation with a blocking monoclonal antibody to TF inhibited the procoagulant activity of both TNF-stimulated endothelial cells, whether they were intact or permeabilized, and of their matrices. However, when the apical cell surface was pretreated with anti-TF antibody, washed, and then cells were lysed with water or permeabilized with saponin, similar augmentation of TF activity was still observed, suggesting the presence of a pool of TF to which the antibody did not initially gain access. Consistent with this concept, the presence of TF in the matrix of TNF-treated endothelial cells was shown by immunoblotting and morphologic studies; cultured endothelial monolayers and the native endothelium of aortic segments after exposure to TNF showed TF in extracellular matrix, associated with vesicles. In contrast, TF was virtually undetectable on the apical endothelial surface. Taken together, these findings suggest that endothelial TF can be present in a cryptic pool that only gains access to the blood after alteration in the integrity of the endothelial monolayer.

Antithrombotic effect of a monoclonal antibody against tissue factor in a rabbit model of platelet-mediated arterial thrombosis

Activation of the coagulation system by contact of circulating blood with tissue factor, a component of the extrinsic blood coagulation pathway that is produced in the vessel wall, may represent a pathway for the initiation of thrombosis in atherosclerotic vessels. This hypothesis was tested in vivo in a rabbit femoral artery eversion (inside-out) graft model, in which the adventitia, with its tissue factor, was exposed to circulating blood. Intra-arterial infusion of a neutralizing monoclonal antibody against tissue factor (D3) at a rate of 12 mg/kg over 15 minutes prevented thrombosis of a 7-8-mm eversion graft within a 2-hour observation period in four of five rabbits, whereas with a control antibody infusion (MA-15C5), occlusion occurred within 2 hours in five of six rabbits. In vitro immersion before reinsertion of the arterial segment in a solution containing 2 mg/ml of the control antibody for 30 minutes was associated with occlusion in all six rabbits, whereas pretreatment with D3 was associated with persistent patency in three of nine rabbits. Stepwise logistic-regression analysis of the results with perfusion status as the dependent variable and type of antibody (D3 or MA-15C5), application method (infusion versus immersion), and graft segment length as independent variables yielded a significant difference in frequency of occlusion with the two antibodies (p = 0.016). It is concluded that exposure of tissue factor to flowing blood may constitute a trigger mechanism for platelet-mediated arterial thrombosis.

Cofactor residues lysine 165 and 166 are critical for protein substrate recognition by the tissue factor-factor VIIa protease complex

High affinity binding of factor VIIa (VIIa) to its cellular receptor tissue factor (TF), as well as association of factor X with phospholipid are required for optimal assembly of the extrinsic activation complex. In addition to the interactions of substrate with phospholipid and enzyme, we here provide evidence that cofactor residues Lys-165 and Lys-166 specifically contribute to the recognition of macromolecular substrate. Ala for Lys replacement in TFA165A166 was compatible with high affinity binding of VIIa when analyzed on cell surfaces as well as in the absence of phospholipid. Dissociation of TFA165A166.VIIa did not occur with a faster rate compared to TF.VIIa, further supporting unaltered VIIa binding function of TFA165A166. Cleavage of chromogenic peptidyl substrate by TFA165A166.VIIa complexes was not diminished, demonstrating that TFA165A166 supported enhancement of catalytic function of the VIIa protease domain. In contrast, factor X activation was reduced in the presence and absence of phospholipid. Further, TFA165A166 effectively competed with wild-type TF in the cleavage of factor X at limited VIIa concentrations. Selective reduction in macromolecular substrate hydrolysis combined with normal VIIa binding by TFA165A166 indicates that the cofactor TF does contribute, either directly or indirectly via specific interactions with VIIa, to factor X recognition.

Glomerular tissue factor stimulates thromboxane synthesis in human platelets via thrombin generation

We have investigated whether or not tissue factor (TF) which is present in the supernatant of isolated glomeruli, is responsible for the stimulatory activity of TXB2 production by isolated human platelets. Reconstituted TF stimulated TXB2 synthesis in platelets in a dose-dependent manner. This effect was potentiated in the presence of a mixture of the major fatty acids found in glomerular supernatants. Addition of a neutralizing anti-TF monoclonal antibody abolished both the procoagulant activity and the platelet-TXB2 stimulatory activity of reconstituted TF and of glomerular supernatants. Anti-factor VII/VIIa (F VII/VIIa) Fab inhibited in a dose-dependent manner the platelet-TXB2 stimulatory activity of an identical dilution of reconstituted TF and of glomerular supernatants, providing evidence that the functional complex TF. VIIa and not TF itself was the active agent. Pretreatment of platelets, TF or glomerular supernatant by hirudin, an inhibitor of thrombin, as well as by antithrombin III heparin, which inhibits both activated factor X and thrombin also markedly inhibited the synthesis of TXB2 by platelets in the presence of either TF or glomerular supernatant. Taken together, these results demonstrate that the stimulatory activity for TXB2 production by platelets which is released by the glomerular cells is attributable to TF. TF does not act directly. Its effect is mediated by thrombin which is formed de novo at the platelet surface in the presence of even traces of the plasma coagulation proteins associated with platelets. TXB2 formation in platelets correlates well with TF concentration in the glomerular supernatant. The possibility of a similar set of mechanisms associated with glomerular injury may require consideration.

Mechanisms of binding of recombinant extrinsic pathway inhibitor (rEPI) to cultured cell surfaces. Evidence that rEPI can bind to and inhibit factor VIIa-tissue factor complexes in the absence of factor Xa

Extrinsic pathway inhibitor plays a key role in modulating tissue factor-dependent blood coagulation. We have studied binding of radioiodinated recombinant extrinsic pathway inhibitor (rEPI) to cultured cell surfaces. rEPI in the absence of added reactants bound to a limited extent to three cell lines studied. Binding of rEPI to two cell lines possessing surface tissue factor, but not to a cell line lacking surface tissue factor, was markedly increased in the presence of both factor VIIa and factor Xa, and calcium ions. Moreover, some increased tissue factor-dependent binding was also demonstrated with factor VIIa alone. Binding isotherms of rEPI to factor VIIa-tissue factor obtained with an ovarian carcinoma cell line were hyperbolic. Scatchard plots indicated the following: a Kd value of 4.5 +/- 1.5 nM and 335,000 +/- 84,000 sites/cell when factor Xa was present; a Kd value of 11.9 +/- 3.5 nM and 236,000 +/- 68,000 sites/cell when factor Xa was absent. In functional studies, high concentrations of rEPI, e.g. 27-67.5 nM, were found to inhibit factor VIIa-tissue factor-catalyzed release of activation peptide from tritiated factor IX in the absence of factor Xa. Whereas factor Xa was thus shown not to be required for rEPI to inhibit factor VIIa-tissue factor catalytic activity, its presence markedly enhanced rEPI's inhibitory function. Since the local concentration of extrinsic pathway inhibitor achieved at a site of tissue injury is unknown, the physiologic significance of the observation of extrinsic pathway inhibitor-induced inhibition of factor VIIa-tissue factor activity in the absence of factor Xa is not clear. However, factor Xa-independent inhibition could play a significant role when large doses of rEPI are administered in experimental studies of thrombosis.

An anti-tissue factor monoclonal antibody which inhibits TF.VIIa complex is a potent anticoagulant in plasma

Tissue factor (TF) functions as the receptor and cofactor for factor VIIa (VIIa) to form a proteolytically active TF.VIIa complex on cell surfaces. We here demonstrate that most MAbs against human TF were poor inhibitors of TF function in plasma and that they inhibited preformed TF.VIIa complex at a slow rate which was dependent on dissociation of VIIa from the cell surface TF. An exception was defined by one MAb (TF8-5G9) which was an effective immediate anticoagulant in plasma. Binding of TF8-5G9 to TF.VIIa inhibited catalytic function prior to dissociation of the TF.VIIa complex. This analysis thus establishes two distinct mechanisms by which MAbs interfere with TF function. The MAb TF8-5G9 introduces a therapeutic principle for rapid arrest of inappropriate triggering of coagulation by TF as well as the TF.VIIa complex in vivo.

Effect of lipoprotein-associated coagulation inhibitor (LACI) on thromboplastin-induced coagulation of normal and hemophiliac plasmas

Lipoprotein-associated coagulation inhibitor (LACI) is a plasma-derived protein that inhibits the tissue factor/factor VIIa/calcium/phospholipid complex in a factor Xa-dependent manner. Recombinant LACI (rLACI) added exogenously to plasma prolonged the activated partial thromboplastin time (APTT) and prothrombin time (PT) as a function of rLACI concentration in linear and curvilinear manners, respectively. Under these standard assay conditions, the amounts of rLACI required to double the APTT and PT were approximately 350- and 90-fold the plasma concentration of LACI, respectively. Likewise, addition of antibodies against LACI to pooled normal, factor VIII-deficient, or factor IX-deficient plasma had no effect on their respective APTTs and PTs, demonstrating the insensitivity of these assays to endogenous LACI. The prothrombin time assay was modified by using dilute thromboplastin. Unlike the standard prothrombin time assay, the clotting times were prolonged for factors VIII- or IX-deficient plasma relative to pooled normal plasma in this modified PT assay. Additionally, the degree of factor deficiency, as determined by the APTT assay, was correlated with that determined by the modified PT assay using dilute thromboplastin. When antibodies against LACI were added to pooled normal, factor VIII-deficient, or factor IX-deficient plasma and the prothrombin time assay initiated using dilute thromboplastin, the clotting times for antibody-treated plasma were shorter than for the corresponding plasma in the absence of antibodies. Moreover, the clotting times for factors VIII- and IX-deficient plasmas treated with antibodies raised against LACI were at least as fast as pooled normal plasma in the absence of LACI antibodies when dilute thromboplastin was used to initiate clotting. These results suggest that the prothrombin time assay using dilute thromboplastin may more accurately reflect what occurs in vivo and that LACI may play an important role in the prolonged bleeding of those with hemophilia A or B.

The anticoagulant effect in heparinized blood and plasma resulting from interactions with extrinsic pathway inhibitor

The influence of Extrinsic pathway inhibitor (EPI) on global clotting times of plasma was studied using activity-blocking IgG antibodies. Dilute tissue thromboplastin (TP) clotting times in plasma collected after intravenous injection of heparin were dramatically shortened by the addition of anti-EPI IgG. Anti-EPI IgG shortened the TP times to a lesser degree in plasma heparinized in vitro. Compared to plasma heparinized in vitro, the TP clotting times were markedly prolonged in post-heparin plasma of equal heparin concentration. Addition of anti-antithrombin IgG reduced the clotting times somewhat more than did anti-EPI IgG, particularly in normal plasma. In plasma from patients with cancer, about equal effect was obtained by blocking either EPI or antithrombin. These clotting time studies suggested that much of the anticoagulant effect caused by injection of heparin depended on EPI. This was confirmed by recording the release of fibrinopeptide A (FPA), as marker of thrombin generation, following addition of TP and CaCl2 to citrated blood. Thrombin generation was delayed and markedly reduced in post-heparin blood compared to that in normal blood. After incubating post-heparin citrated blood with anti-EPI IgG, the generation of FPA was more rapid; the amounts released 30 seconds after addition of TP were 6 times greater (36 vs 6 ng/ml) than in post-heparin blood without anti-EPI IgG. The subsequent FPA values were midway between pre-injection and post-heparin values. In conclusion, between one third and one half of the inhibition of TP-initiated coagulation in post-heparin plasma depends on EPI. This inhibition is mainly due to inactivation of the factor VIIa-TP complex. A small, but distinct contributing effect observed in the APTT assay (and hence no TP) indicates that even increased inactivation of activated factor X contributes. In cancer patients, these EPI-heparin interactions contribute even more to the anticoagulant effects of heparin.

Inhibition of extrinsic pathway inhibitor shortens the coagulation time of normal plasma and of hemophilia plasma

An increasing amount of evidence suggests that coagulation factors VIII and IX play a role not only in the intrinsic but also in the extrinsic pathway of coagulation. In this context the influence of the Extrinsic Pathway Inhibitor (EPI) on the coagulation time of hemophilia plasma lacking FVIII or FIX has been investigated. The coagulation time was measured in a dilute thromboplastin assay. Addition of recombinant EPI (rEPI) prolonged the coagulation time of normal plasma while the addition of an inhibitory antibody against EPI shortened the coagulation time. At low concentrations of thromboplastin the coagulation time of hemophilia plasma was prolonged and at all dilutions of thromboplastin, addition of anti-EPI IgG normalized the coagulation time of a hemophilia plasma. Analysis of 10 individual donor plasma samples and 8 individual hemophilia samples showed that addition of anti-EPI IgG shortened the coagulation time more in hemophilia plasma than in normal plasma. This illustrates the importance of a powerful extrinsic FVII dependent pathway to achieve hemostasis in the case of FVIII or FIX deficiency (hemophilia A and B).

Antibody mapping of tissue factor implicates two different exon-encoded regions in function

Tissue Factor (TF), a small transmembrane glycoprotein, is the cellular receptor for the zymogen Factor VII and the serine protease Factor VIIa (VIIa). TF provides cofactor function for VIIa in the catalytically active (TF: VIIa) binary complex. To explore the structural loci of TF that are responsible for binding of VII and VIIa, monoclonal antibodies (MAbs) and sequence-specific polyclonal antibodies to the native TF protein were analysed for inhibition of VII binding. Two independent epitopes of MAbs were localized by reciprocal competition and by binding of the MAbs to different proteolytic fragments of TF. The epitopes were also characterized in part by progressive C-terminal deletional mutation of the TF protein. Reactivity of the anti-(locus II) MAb TF9-6G4 is consistent with epitope localization in residues Thr40-Val83, encoded by exon 3. In contrast, the anti-(locus I) MAb TF9-5G9 was reactive with fragments encompassing exon 4 (Thr106-Lys165). Antibodies to linear sequences encoded by the same two exons also inhibited VII binding. These data suggest a minimum requirement for two of the four exon-encoded regions of TF for the functional integrity of this receptor cofactor with respect to ligand recognition and high-affinity binding.

Extrinsic activation of human coagulation factors IX and X on the endothelial surface

In previous kinetic studies, the catalytic efficiency of the activation of human coagulation factors IX and X by factor VIIa in the presence of purified tissue factor apoprotein was found to be essentially equal. These activation reactions were now studied on the surface of human umbilical vein endothelial cells. The cells were stimulated with endotoxin to express tissue factor. This tissue factor activity was saturable with factor VIIa and could be inhibited by rabbit antibodies against human tissue factor apoprotein. Only stimulated cells supported factor VIIa activity. No difference in the reactivity of factor VII and VIIa was observed in the presence of factor X, due to rapid feedback activation of factor VII by factor Xa. However, the activation of factor IX by factor VII shows a 10 min lag-phase, which reflects that the activation of factor VII by factor IXa is a less efficient process. The kinetic parameters for the factor VIIa dependent activation of factor IX and factor X on the endothelial surface were: Km 0.09 microM, Vmax 0.13 pmol/min, and Km 0.071 microM, Vmax 0.41 pmol/min, respectively. The same ratio between the Vmax for factor X and factor IX activation was observed as in a cell free system. However, the Km of factor IX was 4-fold higher on the endothelial surface than in the cell free system. Together, these kinetic parameters will favour factor X activation 5-fold over factor IX activation at physiological concentrations of these proteins. The activation of factor X by factor VIIa on the endothelial surface was characterized by a short lag-phase, which was absent in factor IX activation.(ABSTRACT TRUNCATED AT 250 WORDS)

HLA-DR is a procoagulant

Numerous incidents of thromboembolic complications have been documented in cancer patients and in recipients of mismatched organ transplants. Tumor procoagulants have also been implicated in the process of metastasis. Two protein bands of 35,000 and 28,000 daltons isolated from human ovarian carcinoma possessed procoagulant activity. The 35,000 dalton protein had an amino terminal sequence identical to that of the major histocompatibility antigen HLA-DR. Further, isolation of the protein using immunoaffinity column chromatography with monoclonal antibody to HLA-DR resulted in the isolation of procoagulant activity. The immunoaffinity purified protein enhanced thrombin generation in recalcified normal plasma approximately 20- fold. HLA-DR procoagulant activity was completely inhibited by Staphylococcal enterotoxin A. We propose that the procoagulant nature of HLA-DR may contribute to thrombotic disorders in several cancers and in association with graft rejection. The ability of enterotoxin A to inhibit this procoagulant may lead to development of future therapeutic strategies.

A sulfated rabbit endothelial cell glycoprotein that inhibits factor VIIa/tissue factor is functionally and immunologically identical to rabbit extrinsic pathway inhibitor (EPI)

Colburn and Buonassisi (In Vitro Cell Dev. Biol. 24, 1133-1136, 1988) have isolated a single chain sulfated glycoprotein inhibitor of factor VIIa/tissue factor-catalyzed activation of factor X from conditioned media of an established rabbit endothelial cell line. We report herein that their endothelial cell-derived inhibitor and extrinsic pathway inhibitor (EPI) isolated from rabbit plasma have identical functional properties with respect to their interactions with factor Xa and with factor VIIa/tissue factor. In addition, the endothelial cell inhibitor and rabbit plasma EPI migrate with the same apparent molecular weights on non-reduced SDS-PAGE and contain similar amounts of N-linked carbohydrate. Like the endothelial cell inhibitor the EPI of rabbit plasma exists as a single chain molecule. Furthermore, the endothelial cell inhibitor is recognized and neutralized by a polyclonal antibody raised against rabbit plasma EPI. We therefore conclude that cultured rabbit endothelial cells produce an inhibitor of factor VIIa/tissue factor activity that is functionally and immunologically identical to rabbit plasma EPI.

Lethal E. coli septic shock is prevented by blocking tissue factor with monoclonal antibody

Gram-negative bacteremia poses a major health problem, causing one-half of cases of lethal septic shock acquired during hospitalization. Bacterial lipopolysaccharide (LPS) and the inflammatory cytokines, tumor necrosis factor (TNF) and interleukin-1 (IL-1), have been shown to be essential mediators of septic shock. Among the effects of these mediators is a coagulopathy that may be triggered by induced expression of tissue factor (TF) on macrophages and endothelial cells. We now report that 500 micrograms/kg of either immunoglobulin G (IgG) or Fab fragments of a monoclonal antibody against TF administered to baboons as a pretreatment attenuates the coagulopathy and protects against LD100 Escherichia coli. This study provides direct evidence of an essential effector role for TF in septic shock.

Depletion of extrinsic pathway inhibitor (EPI) sensitizes rabbits to disseminated intravascular coagulation induced with tissue factor: evidence supporting a physiologic role for EPI as a natural anticoagulant

Although in vitro experiments have established that extrinsic pathway inhibitor (EPI) is the only known plasma inhibitor of factor VIIa-tissue factor (TF) catalytic activity of potential physiologic significance, evidence of its function in vivo has been lacking. TF-induced intravascular coagulation may occur in patients despite normal plasma levels of EPI and, in our earlier studies, normal plasma EPI levels did not protect rabbits from intravascular coagulation induced by an infusion of purified TF (1 microgram/kg). Studies have now been carried out in which plasma EPI levels were reduced in rabbits to below 20% of the initial level by injection of anti-rabbit EPI IgG. Infusion into such animals of purified rabbit TF apoprotein (0.25 microgram/kg) reconstituted into phospholipid vesicles induced substantial disseminated intravascular coagulation. Infusion of control saline or phospholipid vesicles not containing TF was without significant effect as was infusion of TF (0.25 microgram/kg) into animals injected with nonimmune goat IgG. These data establish that EPI can dampen TF-induced intravascular coagulation in rabbits. They support the hypothesis that EPI plays a significant role in regulating coagulation resulting from the exposure of blood to trace concentrations of TF during the illnesses and minor injuries of normal existence.

Monoclonal antibody analysis of a unique macrophage procoagulant activity induced by murine hepatitis virus strain 3 infection

A panel of 24 IgG2ak monoclonal antibodies was produced against murine hepatitis virus strain 3 (MHV-3)-induced procoagulant activity (PCA) from murine macrophages. The antibodies were specific and did not react in an enzyme-linked immunosorbent assay with purified MHV-3; lipopolysaccharide-induced PCA; crude mouse, human, or rabbit tissue factor, or unstimulated murine macrophages. Sixteen of 24 monoclonal antibodies inhibited functional PCA expression in a one-stage clotting assay. More detailed studies on one monoclonal antibody, 3D4.3, demonstrated that it inhibited prothrombin cleavage at concentrations of greater than or equal to 0.1 microgram/ml, and by Western blot this antibody reacted with proteins of a molecular mass of 140, 74, and 70 kDa on nonreduced gels and 74 and 70 kDa on reduced gels distinct from tissue factor known to have a molecular mass of 47 kDa. Induction of PCA was dependent on both host RNA and protein synthesis. Immunofluorescence studies showed specific binding to MHV-3-stimulated PCA-positive macrophage membranes. Both numbers of positive macrophages and intensity of staining correlated with multiplicity of infection. These monoclonal antibodies will be useful in isolation and characterization of the unique viral-induced PCA as well as in determining its biologic role in MHV infection and other diseases in which the prothrombinase has been implicated.

The 'primary' antiphospholipid syndrome: antiphospholipid antibody pattern and clinical features of a series of 23 patients

Twenty-three patients with the 'primary' antiphospholipid syndrome were studied over 2-6 years. Twenty-two (96%) had antiphospholipid antibodies detected by ELISA (87% had antibodies to thromboplastin and 70% to cardiolipin), and 18 out of the 21 tested patients (86%) had lupus anticoagulant activity by coagulative assays. Mean age of the cohort was 29.9 years and the sex ratio (female:male) 4.75:1. Eleven patients presented 18 venous and/or arterial thrombosis and 13 had 25 foetal losses (84% occurred during the second and third trimester). Other clinical features were migraine, livedo reticularis, and epilepsy. Three patients had relatives with systemic lupus erythematosus. Thrombocytopaenia was seen in 33%, antinuclear antibodies in low or moderate titre in 30%, and haemolytic anaemia in 13%. During the follow-up, two patients presented recurrent thrombosis despite anticoagulant therapy, one of them dying because of recurrent pulmonary thromboembolism. Four patients achieved successful term pregnancies after treatment with aspirin and a further patient after treatment with aspirin and low dose prednisolone. No patient developed systemic lupus erythematosus or any other definable connective tissue disease. The 'primary' antiphospholipid syndrome may exist as a distinct clinical entity and all younger patients presenting with thrombotic events, foetal losses and/or thrombocytopaenia, without any evidence of a well defined disease, should be tested for antiphospholipid antibodies in order to rule out this syndrome.

Heparin requires both antithrombin and extrinsic pathway inhibitor for its anticoagulant effect in human blood

Heparinization of blood inhibited the generation of fibrinopeptide A (FPA) after addition of thromboplastin (TP). Heparinization was more effective when performed in vivo than in vitro; the amounts of FPA at 60 s incubation were 8% and 32%, respectively, of control values in nonheparinized blood. When monospecific, neutralizing IgG against extrinsic pathway inhibitor (anti-EPI) were added to heparinized blood prior to TP, the amount of FPA increased to 65%. When monospecific IgG blocking antithrombin (anti-AT) was used, the amount of FPA increased to values similar to those in nonheparinized blood. When anti-AT and anti-EPI were both added to heparinized blood, FPA was generated about 25% faster than in normal blood. These results show that EPI contributes significantly to the anticoagulant effect of heparin in human blood.

Flow cytometric analysis of tissue factor (TF) expression on stimulated monocytes--comparison to procoagulant activity of mononuclear blood cells

Whereas tissue factor (TF), a 47 kDa transmembrane glycoprotein, is constitutively present in certain tissues such as epithelial tissue, brain, and placenta, it is normally not expressed by cells within the vasculature. However, inflammatory mediators including bacterial lipopolysaccharide (LPS) can stimulate the expression of cell surface procoagulant activity (PCA) on monocytes. In our present study the kinetics (over 24 h) of molecular TF expression on LPS-stimulated monocytes analyzed by flow cytometry corresponds closely to functional PCA of human mononuclear blood cells (MBC). Both PCA and TF expression on monocytes were rapid events reaching their maximum after about 6 h of stimulation. At this time approximately 70-80% of monocytes had also achieved maximum anti-TF MAb receptor density. For certain analytical applications, monitoring of molecular TF expression on monocytes by flow cytometry using anti-TF MAb is favorable because there is no influence by PCA inhibitors.

Detection of lupus-like anticoagulants by an enzyme-linked immunosorbent assay using a partial thromboplastin as antigen; a comparative study

Clotting assays allow qualitative rather than quantitative detection of the lupus anticoagulant. We have therefore studied the usefulness of an ELISA using a commercial partial thromboplastin, Throombofax, as antigen; the results obtained on 146 selected patient plasmas were compared to the results of coagulation tests (kaolin clotting time, tissue thromboplastin inhibition test, activated partial thromboplastin time) and of ELISAs using cardiolipin or phosphatidylserine as antigen. While satisfactory agreement was found within the group of coagulation tests or that of ELISAs, only a moderate agreement was obtained between clotting tests and ELISAs, the best being with the partial thromboplastin ELISA using low plasma dilutions. The study further indicates that ELISA techniques cannot entirely replace coagulation tests for the detection of a lupus anticoagulant, even when a partial thromboplastin is used as antigen. On the other hand, coagulation tests are less sensitive than ELISAs for the detection of antiphospholipid antibodies.

Localization of human tissue factor antigen by immunostaining with monospecific, polyclonal anti-human tissue factor antibody

Tissue factor, the cofactor for factor VIIa-catalyzed activation of factors IX and X, plays an important role in the initiation of hemostasis. However, the distribution of tissue factor in the body has not been defined until recently. In the present study frozen sections of non-malignant human tissues were immunostained using polyclonal, monospecific rabbit anti-human tissue factor antibodies. Specificity of the anti-tissue factor antibody was established by Western blotting. Sensitivity of the immunostaining technique for tissue factor antigen was confirmed by correlating staining of non-perturbed and perturbed cultured human umbilical vein endothelial cells with their surface membrane tissue factor coagulant activity. Brain, lung and placenta, all known to possess large amounts of tissue factor procoagulant activity, stained strongly for tissue factor, as did peripheral nerves and autonomic ganglia. Epithelium of skin, mucosa, and glomeruli also stained; however, epithelium lining excretory ducts failed to stain. Skeletal muscle did not stain, but cardiac muscle stained faintly. Smooth muscle also did not stain except for the muscularis mucosa of the esophagus, which stained brightly. Fibroblasts varied in stainability; those found in the adventitia of vessels stained strongly. The endothelium, tunica intima and tunica media of blood vessels consistently failed to stain. The distribution of tissue factor antigen as demonstrated by immunostaining supports the hypothesis that maintenance of a physical barrier between tissue factor activity and blood is key to the normal regulation of hemostasis.

Tissue factor: identification and characterization of cell types in human placentae

This is an immunohistologic study of tissue factor (TF) in snap frozen, unfixed, human normal-term placentae. Antibodies to TF were a monoclonal to human brain TF purified on a factor VII-agarose affinity column, and a polyclonal to a synthetic polypeptide representing the carboxyl-terminal nine amino acids of human TF. The results detail the localization and distribution of TF and characterize the cells in which it is found. TF was not observed in trophoblast, trophoblastic basement membranes, or noncellular components of connective tissue. TF was identified in some but not all macrophages, most fibroblast-like cells, and occasionally in perivascular cells and endothelium. The most consistent and intense reactions were obtained with vimentin-positive fibroblast-like cells in loose connective tissue. TF usually was not identified in fetal stem vessel endothelial cells, but TF reactivity was found in some of these cells in chorionic villi with histologic evidence of chronic inflammation. Such areas are uncommonly found in normal-term placentae. The vast majority of TF-reactive cells did not react with antibody to factor VII and were not in contact with blood. The biologic purpose of producing relatively great amounts of TF in areas remote from circulating factor VII is not known.

Mammalian cell transient expression of tissue factor for the production of antigen

We describe a mammalian cell expression system used to rapidly produce microgram quantities of a membrane protein used as an immunogen. A fusion protein expression vector was constructed which contained the signal sequence and 27 amino acids of the Herpes simplex virus glycoprotein D (gD), followed by a factor VIII (fVIII) thrombin cleavage site and the mature tissue factor (TF) sequence. This fusion protein was transiently expressed and then purified using an antibody to gD. The purified fusion protein, gDTF, was incubated with thrombin to remove the gD-fVIII moiety and the resulting rTF served as antigen for the generation of TF-specific antibodies. The antibodies produced were then used for a comparison of the turnover rates of the constitutively and transiently produced fusion protein. In addition, sensitivity to glycosidases indicated that the transiently and constitutively produced recombinant proteins do not contain identical carbohydrate structures.

Disseminated intravascular coagulation in rabbits induced by administration of endotoxin or tissue factor: effect of anti-tissue factor antibodies and measurement of plasma extrinsic pathway inhibitor activity

Rabbits were given polyclonal anti-tissue factor (TF) immunoglobulin G (IgG) before an injection of endotoxin to test the hypothesis that TF triggers disseminated intravascular coagulation (DIC) after endotoxin. The rabbits had been prepared with cortisone to develop DIC after one injection of endotoxin. Anti-TF IgG substantially reduced the falls in fibrinogen, factors V and VIII, and platelets noted in control rabbits given preimmune IgG before endotoxin. At autopsy 24 hours later, fibrin was present in glomerular capillaries of 4 of 5 control rabbits, but in none of 11 rabbits given anti-TF IgG. DIC was also induced in a second group of rabbits by the infusion, over 4 hours, of 1 microgram/kg of purified, reconstituted rabbit brain TF. This resulted in striking falls in plasma fibrinogen, factors V, and VIII that were diminished, but not prevented by prior treatment with anti-TF IgG. Circulating activated factor VII, induced by either TF infusion or endotoxin, could not be detected after DIC. Mean plasma extrinsic pathway inhibitor (EPI) activity did not fall significantly after endotoxin, and only to about 65% of the preinfusion after infusion of TF. Thus, DIC induced by both agents proceeded despite nearly normal plasma EPI levels. Because EPI neutralizes factor VIIa/TF in vitro only after a short lag period, the DIC that persisted for up to 6 hours after injection of endotoxin suggests that TF activity continued to be generated during this period on cells to which the circulating blood was exposed. All animals given endotoxin became ill with cyanosis, tachypnea, cold ears, and diarrhea, regardless of whether they had received anti-TF IgG to attenuate DIC. Infusion of TF caused some animals to die acutely with pulmonary arterial thromboses, but surviving animals did not appear ill. The findings support the hypothesis that exposure of blood to TF triggers DIC after endotoxin, but is not important for the pathogenesis of endotoxin-induced shock.

Purification and characterization of rabbit tissue factor

Anti-human tissue factor IgG column was used to partially purify rabbit tissue factor. The rabbit tissue factor was then further purified on SDS-polyacrylamide gel electrophoresis to prepare an essentially homogeneous rabbit tissue factor. This was used as an antigen to raise a high titer, monospecific, polyclonal antiserum for rabbit tissue factor. Immunostaining of a crude Triton extract of rabbit brain acetone powder and purified tissue factor with the anti-rabbit tissue factor IgG yielded a single major band with an apparent molecular weight of 45 kD, which corresponds to the mobility on SDS-PAGE of purified rabbit tissue factor apoprotein. The anti-rabbit tissue factor IgG was coupled to Affi-Gel-15 and used as an immunoadsorbent column to purify large amounts of rabbit brain tissue factor in a rapid, one-step technique.

Correlation between antigenic and functional expression of tissue factor on the surface of cultured human endothelial cells following stimulation by lipopolysaccharide endotoxin

Previous studies indicated that E. coli lipopolysaccharide (LPS) induces human umbilical vein endothelial cells (HUVEC) to express tissue factor activity. Using a radiolabeled anti-tissue factor monoclonal antibody to assess cell-surface tissue factor apoprotein antigen and a two-stage amidolytic assay to assess functional tissue factor activity, we have investigated the temporal relationship between antigenic expression and functional expression of tissue factor on the surface of LPS-stimulated HUVEC. Maximum tissue factor apoprotein antigenic expression on the surface of LPS-stimulated HUVEC was achieved in four hours after LPS treatment, while maximum functional tissue factor activity occurred after 6 hours. Specific binding of radiolabelled human factor VIIa to LPS-stimulated HUVEC paralleled the time course of the expression of tissue factor functional activity. Thus, these data indicate that the presence of of newly-synthesized tissue factor apoprotein antigen on the cell surface is insufficient by itself for maximal factor VIIa binding to occur, and provide presumptive evidence for the posttranslational processing of tissue factor apoprotein on the cell surface prior to its acquisition of ligand binding function.

Monoclonal antibody analysis of purified and cell-associated tissue factor

Tissue factor (TF), one of the cell-surface initiators of blood coagulation, has been implicated as the major molecule of this type and as a critical controlling molecule in hemostasis, thrombosis and inflammation. Analysis of the expression of human TF by cells has been hampered by the lack of suitable molecular probes. We have prepared a library of twenty-four murine hybridomas which stably secrete monoclonal antibodies to human TF. Based on their characteristics, these monoclonals can be categorized into a minimum of five distinct groups. Twenty-three of the hybridoma antibodies strongly inhibited TF activity, which was attributable to blocking of formation of the bimolecular complex of TF and factor VII. We have used these antibodies to demonstrate directly that TF is the sole high affinity factor VII receptor on an intact cell. We have also demonstrated the immunologic relationship between constitutive and induced expression of the protein responsible for TF-like activity by several cells and tissues. Most of the antibodies were found to inhibit TF activity expressed by other primate species, and the potential in vivo therapeutic use of monoclonal antibodies of differing intramolecular specificity is discussed.

Characterization of anti-tissue factor antibody and its use in immunoaffinity purification of human tissue factor

Human brain tissue factor apoprotein was recently purified to homogeneity in this laboratory by affinity chromatography utilizing factor VII bound to immobilized anti-factor VII (Anal Biochem 165, 365-370, 1987). A potent polyclonal anti-tissue factor antibody has now been raised to the purified apoprotein. Immunostaining of purified tissue factor with this polyclonal IgG yielded a single major band with an apparent molecular weight of 47,000, which corresponds to the mobility on SDS-PAGE of tissue factor apoprotein. Immunostaining of a crude Triton extract of brain tissue yielded two additional bands, with apparent molecular weights of 54,000 and 40,000 Da. An anti-tissue factor IgG was coupled to Affi-Gel-15 to prepare an immunoadsorbant column. The two additional proteins in the crude Triton extract recognized by Western blotting did not bind to the column. This permitted its use to develop a simple, efficient technique for purification of human tissue factor apoprotein.

Resolution of monomeric and heterodimeric forms of tissue factor, the high-affinity cellular receptor for factor VII

Tissue factor (TF) is the high affinity cell surface receptor and obligatory cofactor for plasma coagulation factor VII. Purification of TF from human brain and placenta has recently been reported to yield both a monomeric 47 kDa protein as well as a 58 kDa heterodimeric form. In this study, the TF glycoprotein was isolated from human brain by immunoaffinity chromatography using a newly developed monoclonal antibody, TF8-5G9, and was compared to TF isolated by factor VII-affinity chromatography. Except for the greater efficiency of the immunoaffinity method, both methods yielded TF with similar specific activities, and both preparations contained the monomeric and heterodimeric forms of TF. The 58 kDa form was established to be a disulfide-linked heterodimer composed of TF and the alpha chain of hemoglobin. From these results and from studies of immunoprecipitation of TF from cultured fibroblast cells, we conclude that the 47 kDa monomeric form of TF is the naturally occurring cellular form of TF, and that heterodimer formation is a secondary event. The potential significance of the proclivity of TF to form a heterodimer with hemoglobin is discussed.

Glomerular procoagulant activity in human proliferative glomerulonephritis

Mechanisms for initiation of glomerular fibrin deposition were studied using renal tissue obtained from two patients with rapidly progressive, crescentic glomerulonephritis. Histological examination showed extensive glomerular monocyte infiltration and fibrin deposition in both patients. Sonicated cell suspensions of isolated glomeruli from these patients contained markedly augmented levels of procoagulant activity (PCA) compared with the levels found in normal glomeruli. This PCA was characterized as tissue factor by its functional dependence on Factors VII and V, independence of Factors VIII and XII, inhibition by concanavalin A and phospholipase C, and association with cell membranes. Its coagulant activity was also inhibited by a specific monoclonal anti-human tissue factor antibody. Tissue factor could be identified in glomeruli from these two patients by indirect immunofluorescence using this antibody. These studies implicate extrinsic pathway activation via tissue factor in intraglomerular deposition of fibrin in these patients. Activated monocytes, known to be a potent source of procoagulant activity and seen in large numbers within glomeruli from these patients, are a likely source of this tissue factor.

An inhibitory monoclonal antibody against human tissue factor

We obtained a hybridoma using immune spleen cells from a mouse injected with human brain tissue factor that had been purified on a factor VII-agarose affinity column. This monoclonal IgG1, HTF1-7B8, inhibits tissue factor procoagulant activity. The concentration of HTF1-7B8 producing half-maximal inhibition is influenced by the concentration of factor VIIa, suggesting that the antibody and enzyme compete for the cofactor. The antibody was successfully used to detect both human and bovine tissue factor on nitrocellulose dot blots, indicating that the epitope recognized by this antibody is conserved in both species. This antibody clearly reveals tissue factor on a Western blot. An HTF1-7B8 affinity column was used to purify tissue factor from both human brain and placenta. The electrophoretic mobilities in polyacrylamide gels in the presence of sodium dodecyl sulfate (SDS) and the amino acid compositions of the purified tissue factor from brain and placenta are indistinguishable, as are their specific procoagulant activities in reconstituted systems. This antibody will be useful for immunopurification and characterization of tissue factor structure and mechanism.

The development of monospecific antibodies against human thromboplastin apoprotein (apoprotein III) and their application in the immunocytochemical detection of the antigen in blood cells

Human thromboplastin apoprotein (apoprotein III) purified by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) was purified a further 2-4 fold by PAGE in the presence of digitonin. Subsequent line immunoelectrophoresis of the protein revealed several lines, only one of which contained inhibitory antibodies. New inhibitory antibodies which were raised by using this particular line to immunize rabbits produced only a single line in immunoelectrophoresis of apoprotein III, with precipitated inhibitory antibodies being present only in the line. When these antibodies were used in electroblot immunobinding studies of crude thromboplastin after SDS-PAGE staining was found mainly in a single band of MW about 50,000, but also to some extent in immunologically related higher MW material. Prior deglycosylation of the thromboplastin using trinitrobenzenesulfonic acid resulted in a shift of the bulk of the main band representing an apparent MW reduction of 16%, and a corresponding shift in the position of protein with the capacity to bind inhibitory antibodies. Besides being a good criterion of specificity of the antibodies this also suggests that non-carbohydrate parts of apoprotein III may be involved in the interaction with Factor VII. Immunoperoxidase staining of unstimulated or endotoxin stimulated blood cells using the antibodies revealed the presence of significant amounts of apoprotein III only in stimulated monocytes, apparently available on the surface of the cells since it was detectable also by preembedding staining of fixed cells in suspension. The result is strong evidence that apoprotein III is synthesized de novo in monocytes upon endotoxin stimulation.

Tissue factor induction in human monocytes. Two distinct mechanisms displayed by different alloantigen-responsive T cell clones

One component of the cellular immune response to antigens is the expression of procoagulant activity (PCA) by monocytes and macrophages. Induction of human monocyte PCA in response to alloantigenic stimulation requires the collaboration of HLA-DR-responsive T cells. In mixed lymphocyte cultures (MLCs), the induction of monocyte tissue factor appears to be mediated exclusively by a T cell-derived lymphokine. We have used a soft agar cloning method to generate alloantigen-responsive T cell clones from MLCs between irradiated Daudi lymphoblastoid cells and human peripheral blood mononuclear cells. Developing clones were screened for the ability to induce PCA in fresh autologous monocytes in response to Daudi stimulator cells. PCA induction was observed with some, but not all, proliferating T cell clones and two modes of induction were apparent. Some T cell clones mediated PCA induction exclusively by lymphokine production, whereas other clones delivered induction signals by direct cellular collaboration with the monocyte effector cells. These two inductive pathways were represented in distinct, non-inclusive functional subsets of T cell clones. Constitutive production of soluble inducer signals was not observed in T inducer clones. The magnitude of the monocyte PCA response increased in response to an increase in the allogeneic stimulator/T clone responder ratio, and third-party allogeneic cells were unable to elicit the PCA-inducing lymphokine signals from T inducer clones. Both modes of induction were shown to generate tissue factor protein activity in monocytes. Collectively, these results suggest that PCA induction can be initiated in response to alloantigens through collaboration with certain OKT3+, OKT4+, OKT8-, OKM1- T inducer clones, and that induction can be mediated by at least two different functional subsets of human T cells. Stimulation with the appropriate alloantigen may elicit both lymphokine and T cell-contact pathways of induction of tissue factor in human monocytes.

Tissue factor in microvesicles shed from U87MG human glioblastoma cells induces coagulation, platelet aggregation, and thrombogenesis

Microvesicles (diameter ca 200 nm) from the cell-free supernatant of U87MG human glioblastoma cell caused platelet aggregation and coagulation in a manner identical with that previously shown for the intact cells. Both activities were inhibited by dansylarginine -N-(3-ethyl-1,5-pentanediyl) amide (DAPA), confirming the thrombin-dependent nature of both activities. The specific activities per microgram of protein were 2-10 times greater in the microvesicles than in the plasma membrane fraction, suggesting localization in specific membrane domains. Sucrose density centrifugation gave a single protein peak (density 1.14) with congruent procoagulant and platelet aggregating activities. Both activities required the extrinsic pathway, as shown by studies with factor-deficient plasmas, and both were inhibited by heating (60 min/100 degrees C), by reduction and alkylation, and by incubation of the microvesicles with rabbit anti-bovine brain tissue factor antibody. These observations were confirmed using microvesicles from the HL-60 human promyelocytic leukemia cells, which are known to contain tissue factor activity. The results suggest that both procoagulant and proaggregating activities are causally related through the presence of tissue factor in the microvesicles. Studies with the Baumgartner perfusion apparatus showed that U87MG microvesicles increased the size of adherent thrombi nearly tenfold and that these thrombi were associated with nucleated cells from the blood. The increase in adherent thrombi did not occur if perfusion was carried out in the presence of DAPA, confirming the role of thrombin in their formation.

Occurrence of fibrin and tissue factor antigen in human small cell carcinoma of the lung

Fibrin was detected by specific immunofluorescence in tissue obtained from five of six cases of small cell carcinoma of the lung. Dense specific fluorescence was observed in the connective tissue stroma surrounding metastatic tumor nodules and frequently in the scant extracellular stroma surrounding individual viable tumor cells and small tumor cell clusters. When observed by electron microscopy, the fibrin hugged tumor cell plasma membranes and, in some areas, seemed to envelop the cells. Fluorescent staining of tumor cells, but not the stroma, was observed with an antibody to tissue factor. These findings suggest that local activation of coagulation occurs in small cell carcinoma of the lung. Deposited fibrin may contribute to the growth and spread of this particular type of cancer.

The production and availability of tissue thromboplastin in cellular populations of whole blood exposed to various concentrations of endotoxin. An assay for detection of endotoxin

These studies were undertaken to determine the type and availability of the procoagulant activities generated in blood incubated with endotoxin. The shortening of the recalcification time of blood incubated with endotoxin was directly correlated with the increase in synthesis of tissue thromboplastin in the monocytes. The procoagulant activity which resulted in the shortening of the clotting time was shown to be almost totally blocked by tissue thromboplastin antibodies. Thus, no additional procoagulant activity was generated in platelets during the 5 h incubation of blood with endotoxin. However, lysed platelets enhanced the synthesis of tissue thromboplastin in blood monocytes in the presence of endotoxin. Lysed red blood cells or granulocytes had no such effect. In endotoxin stimulated monocytes the main part of the newly synthesized tissue thromboplastin appeared to be exposed on the cellular surface. Thus, only 25% of the tissue thromboplastin activity was recovered when tissue thromboplastin antibodies had been present during the stimulation. Unstimulated monocytes were also found to possess tissue thromboplastin activity, but this low activity was not affected by tissue thromboplastin antibodies unless the monocytes were disrupted by sonication. The high percentage of tissue thromboplastin exposed on the surface of the endotoxin stimulated monocytes in whole blood may contribute significantly to the rapid induction of disseminated intravascular coagulation in gram negative sepsis.

Evaluation of the 'Mason' (continuous-thaw-siphon) method for cryoprecipitate production

A comparison was made of the factor VIII recovery in cryoprecipitate made by the continuous-thaw-siphon technique of Mason [1], by our routine method of overnight thawing at 4 degrees C and by a fast-thaw method. The siphon method resulted in a mean recovery of 71% of the factor VIII. This is at least double the yield obtained by the routine method and could not be solely attributed to the faster processing as cryoprecipitate prepared by the fast-thaw method gave a factor VIII yield of 53%, which was significantly less than the Mason product. This product also contained increased amounts of factor VIII-related antigen and fibrinogen. Characterisation of the thaw-siphon cryoprecipitate factor VII by gel filtration, electrophoretic mobility, stability and measurement of isoagglutinin titre did not reveal any significant qualitative differences from cryoprecipitate produced by other methods.

Properties of canine tissue thromboplastins from brain, lung, arteries, and veins

Properties of the protein moieties of canine tissue thromboplastins (TTP's) from brain (BTTP), lung (LTTP), arteries (ATTP), AND VEINS (VTTP) were determined. The maximum specific activity of each protein moiety after its relipidation was obtained when the phospholipid-delipidated TTP ratio was 0.32 and was 1,395 U/mg BTTP, 1,130 U/mg LTTP, 630 U/mg VTTP, and 435 U/mg ATTP. The amino acid contents of the protein moieties of LTTP, ATTP, and VTTP were closely similar, but that of BTTP was significantly different. The Ouchterlony analysis showed that BTTP did not react at all with the antibody against VTTP, but that three other TTP's did and showed the reaction of complete identity. Then, the reactivity of 125-I-labeled TTP's with the anti-VTTP antibody was studied. The results showed that 0.79 +/- 0.01 (SD) % of [125I]BTTP, 10.24 +/- 0.5 (SD) % of [125I]LTTP, 19.4 +/- 0.2 (SD) % of [125I]VTTP, and 5.88 +/- 0.4 (SD) % of [125I]ATTP added were bound to the antibody in 2 h. Next, the molecular weight of each was determined by Sephadex G-200 filtration, which averaged 80,000 +/- 4,000 (SD) ([125I]BTTP), 113,000 +/- 5,000 (SD) ([125I]LTTP), 62,000 +/- 3,000 (SD) ([125I]ATTP), and 47,000 +/- 2,000 (SD) ([125I]VTTP). Finally, the plasma behavior of each was studied in four dogs. The plasma half-life averaged 8.1 +/- 0.24 (SD) h ([125I]BTTP), 14.6 +/- 0.5 (SD) h ([125I]LTTP), 7.38 +/- 0.48 (SD) h ([1252]ATTP), and 24.3 +/- 0.9 (SD) h ([125I]VTTP). These results indicate that the protein moieties of canine TTP's from brain, lung, arteries, and veins are closely similar in some aspects but dissimilar in others and are definitely not identical.