Evidence against Collagen Activation of Platelet-Associated Factor XI as a Mechanism for Initiating Intrinsic Clotting

Collagen activation of platelet-associated Factor XI has been proposed as a mechanism for initiating intrinsic clotting independent of Factor XII. Since this could explain the lack of bleeding in patients with hereditary Factor XII deficiency, pre-kallikrein deficiency and high molecular weight kininogen deficiency, we subjected the hypothesis to rigorous testing. Incubation of isolated platelets with collagen and calcium ions failed to generate activity shortening the clotting time of an acivated Factor XI (XI_a) assay that had been modified to eliminate effects due to platelet-associated activated Factor V. Nor could generation of traces of Factor XI_a in such mixtures be detected by incubation with purified Factor IX and testing for the generation of activated Factor IX (IX_a) in clotting and amidolytic assays. Moreover, when blood or platelet-rich plasma containing added ¹²⁵I-Factor IX was incubated with calcium ions and collagen and then subjected to reduced sodium.dodecyl sulfate poly-acrylamide gel electrophoresis, the radioactivity profiles revealed only native ¹²⁵I-Factor IX without evidence of the polypeptide chains of Factor IX_a. The negative results of this study mitigate against the hypothesis that collagen activation of platelet-associated Factor XI represents a physiologically significant mechanism for initiating clotting independent of Factor XII.     

Activation of factor VII bound to tissue factor: a key early step in the tissue factor pathway of blood coagulation.

Whether the factor VII/tissue factor complex that forms in tissue factor-dependent blood coagulation must be activated to factor VIIa/tissue factor before it can activate its substrates, factor X and factor IX, has been a difficult question to answer because the substrates, once activated, back-activate factor VII. Our earlier studies suggested that human factor VII/tissue factor cannot activate factor IX. Studies have now been extended to the activation of factor X. Reaction mixtures were made with purified factor VII, X, and tissue factor; in some experiments antithrombin III and heparin were added to prevent back-activation of factor VII. Factor X was activated at similar rates in reaction mixtures containing either factor VII or factor VIIa after an initial 30-sec lag with factor VII. In reaction mixtures with factor VII a linear activation of factor X was established several minutes before cleavage of 125I-labeled factor VII to the two-chain activated molecule was demonstrable on gel profiles. Adding antithrombin III and heparin blocked activation of factor X by factor VII/tissue factor but not by factor VIIa/tissue factor. When the antithrombin III and heparin were added 1 min after the other reagents, factor VII/tissue factor activation of factor X was not blocked. These data suggest that factor VII/tissue factor cannot activate measurable amounts of factor X over several minutes. Overall, our results support the hypothesis that a rapid preferential activation of factor VII bound to tissue factor by trace amounts of factor Xa is a key early step in tissue factor-dependent blood coagulation.     

Activation of factor IX by the reaction product of tissue factor and factor VII: additional pathway for initiating blood coagulation.

A study was carried out on mechanisms, independent of activated Factor XI, capable of activating Factor IX. The reaction product of tissue factor and Factor VII functioned as a potent Factor IX activator in the assay system used. Activated Factor IX itself activated Factor X; thrombin failed to activate Factor IX. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis confirmed that the reaction product of tissue factor and Factor VII activated Factor IX, with replacement of the band corresponding to native factor IX [molecular weight (Mr) 55,000] by bands corresponding to the heavy chain (Mr 27,000) and light chain (Mr 17,000) of activated Factor IX. When either Factor VII or calcium ions were left out of incubation mixtures, the band of native Factor IX persisted unchanged. Contact of blood with tissue factor represents a second mechanism, bypassing activated Factor XI, for the activation of Factor IX during hemostasis. It may help to explain the discrepancy between the mild bleeding of hereditary Factor XI deficiency and the severe bleeding of hereditary Factor IX deficiency.     

Regulation of the procoagulant activity within the bronchoalveolar compartment of normal human lung

The nature of the procoagulant activity of normal bronchoalveolar fluid was examined both qualitatively and quantitatively. Unconcentrated, cell-free lavage freshly obtained from normal volunteers clotted normal plasma in a mean of 84 +/- 20 s. The procoagulant activity was initiated by Factor VII-tissue factor complexes as judged by differential activity in various plasmas genetically deficient in single clotting factors, by neutralization of the procoagulant activity with antibodies to either Factor VII or tissue factor, and by a Factor X activation assay. Preincubation of the lavage with calcium was required to demonstrate Factor VII activity in unconcentrated samples. The cell-free fluid contained about 8,500 thromboplastin units/mg protein, equivalent to a third of the thromboplastin standard and indicating high amounts of cofactor. Quantitation of Factor VII was estimated by functional analysis in coagulation and amidolytic assays with reference to dilutions of normal plasma of known Factor VII concentration. When lavage and diluted plasma were adjusted to yield equivalent amidolytic activities, the average ratio of the Factor VII-clotting activity of the alveolar fluid relative to plasma Factor VII was 19 +/- 7, suggesting the presence of Factor VIIa in lavage. In contrast to previous reports with serum or activated plasma, immunoblots of concentrated lavage revealed only single-chain Factor VII, and 125I-Factor VII added to the fluid was not converted to 125I-Factor VIIa, suggesting a unique control mechanism in the lung compartment which differs from plasma. When equivalent Factor VII amidolytic activities in diluted plasma and cell-free lavage were compared, the rates of Factor Xa formation were very similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of human factor VII in the initiation of tissue factor- dependent coagulation

We have used activation peptide release assays to compare factor VII and activated factor VII (VIIa) activation of factor X, normal factor IX (IXN), and a variant factor IX (IXBmLE), which, after activation, is unable to back-activate factor VII. In purified systems, factor VII and VIIa each rapidly activated factor X, but after a one minute lag for factor VII. VIIa also readily activated both IXN and IXBmLE. Factor VII initially failed to activate substantial amounts of either IXN or IXBmLE; on further incubation factor VII activated IXN but not IXBmLE. Activation of IXN began when approximately 10% of factor VII had been converted to VIIa, as measured by 125I-factor VII radioactivity profiles. Adding factor VII to VIIa slowed its activation of IXBmLE. However, in the presence of factor X, factor VII alone rapidly activated IXBmLE. Unlike purified systems, 1 nmol/L VIIa added to factor VII-deficient plasma failed to activate factor IX. Increasing factor VII to 10 nmol/L (plasma concentration) either as native VII or VIIa yielded similar activation curves for factor IX and similar activation curves for factor X. Adding 5% VIIa to factor X-deficient plasma and to factor XII-deficient plasma substantially shortened the dilute tissue factor clotting time of only the former. These data support the hypothesis that factor VII/tissue factor complex initiates tissue factor-dependent clotting through a minimal generation of Xa. This Xa then rapidly back-activates a small amount of factor VII, following which the rates of activation of both factors IX and X increase dramatically.     

Activation of human factor VII during clotting in vitro

We have studied factor VII activation by measuring the ratio of factor VII clotting to coupled amidolytic activity (VIIc/VIIam) and cleavage of 125I-factor VII. In purified systems, a low concentration of Xa or a higher concentration of IXa rapidly activated 125I-factor VII, yielding a VIIc/VIIam ratio of 25 and similar gel profiles of heavy and light chain peaks of VIIa. On further incubation, VIIa activity diminished and a third 125I-peak appeared. When normal blood containing added 125I- factor VII was clotted in a glass tube, the VIIc/VIIam ratio rose fivefold, and 20% of the 125I-factor VII was cleaved. Clotting normal plasma in an activated partial thromboplastin time (APTT) system yielded a VIIc/VIIam ratio of 25 and over 90% cleavage of 125I-factor VII. Clotting factor XII-deficient plasma preincubated with antibodies to factor X in an APTT system with added XIa yielded a VIIc/VIIam ratio of 19 and about 60% cleavage, which indicates that IXa, at a concentration achievable in plasma, can effectively activate factor VII. Clotting normal plasma with undiluted tissue factor yielded a VIIc/VIIam ratio of 15 to 20 and 60% cleavage of 125I-factor VII, whereas clotting plasma with diluted tissue factor activated factor VII only minimally. We conclude that both Xa and IXa can function as significant activators of factor VII in in vitro clotting mixtures but believe that only small amounts of factor VII may be activated in vivo during hemostasis.     

Evidence against collagen activation of platelet-associated factor XI as a mechanism for initiating intrinsic clotting.

Collagen activation of platelet-associated Factor XI has been proposed as a mechanism for initiating intrinsic clotting independent of Factor XII. Since this could explain the lack of bleeding in patients with hereditary Factor XII deficiency, prekallikrein deficiency and high molecular weight kininogen deficiency, we subjected the hypothesis to rigorous testing. Incubation of isolated platelets with collagen and calcium ions failed to generate activity shortening the clotting time of an activated Factor XI (XIa) assay that had been modified to eliminate effects due to platelet-associated activated Factor V. Nor could generation of traces of Factor XIa in such mixtures be detected by incubation with purified Factor IX and testing for the generation of activated Factor IX (IXa) in clotting and amidolytic assays. Moreover, when blood or platelet-rich plasma containing added 125I-Factor IX was incubated with calcium ions and collagen and then subjected to reduced sodium dodecyl sulfate polyacrylamide gel electrophoresis, the radioactivity profiles revealed only native 125I-Factor IX without evidence of the polypeptide chains of Factor IXa. The negative results of this study mitigate against the hypothesis that collagen activation of platelet-associated Factor XI represents a physiologically significant mechanism for initiating clotting independent of Factor XII.     

Newer concepts of blood coagulation

Summary. In this report we describe an in vitro model of blood coagulation reactions that mimics as closely as possible the in vivo condition. Our model indicates that the tissue factor—factor VIIa complex initiates coagulation by activating small amounts of both factor IX and factor X in the environment of the tissue factor bearing cell. Factor Xa and factor IXa formed in the initial reaction then play very distinct roles in the subsequent interactions of the clotting mechanism leading to a burst of thrombin generation on the platelet surface. Our results also indicate that factor XI can be activated by thrombin in the absence of factor XII and that the function of factor XI is simply to enhance conversion of factor IX to factor IXa resulting in enhanced thrombin generation on the platelet surface.     

Pharmacokinetic study of a high-purity factor IX concentrate (Factor IX Grifols®) with a 6-month follow up in previously treated patients with severe haemophilia B

Summary. Optimal replacement treatment in haemophilia B patients requires a good understanding of the pharmacokinetics of factor IX (FIX). The aim of this study was to compare the pharmacokinetic profile of Factor IX Grífols^®, a highly purified human FIX concentrate with two specific pathogen inactivation/removal steps, to that of available FIX preparations. The study was an open, non‐randomized trial including 25 male subjects older than 12 years of age with severe haemophilia B. Pharmacokinetic profile of the FIX preparation regularly used by the subjects was determined as control. Pharmacokinetic profile of Factor IX Grifols^® was determined twice, one 7–15 days after control assessment and second after a 6 months period had elapsed. Results showed that all products had peak plasma levels of FIX:C within 30 min. Mean recovery was 1.3 ± 0.3 IU dL⁻¹ per IU kg⁻¹ for Factor IX Grifols^® and 1.0 ± 0.3 IU dL⁻¹ per IU kg⁻¹ for control products (P < 0.001). The mean terminal half‐life (t_1/2) for Factor IX Grifols^® was 26.7 h and 26.8 h for control product. Pharmacokinetic parameters after 6 months of treatment with Factor IX Grifols^® did not statistically differ from the parameters obtained with the first infusion. There were no adverse events related to Factor IX Grifols^® for the duration of the study. In conclusion, Factor IX Grifols^® has adequated pharmacokinetic properties comparable to the control plasma‐derived FIX and these parameters remain stable after 6 months of treatment. Factor IX Grifols^® can be an effective and safe plasma‐derived FIX concentrate for replacement therapy in haemophilia B patients.     

Inhibition of tissue factor/factor VIIa activity in plasma requires factor X and an additional plasma component

A study was carried out to explore requirements for the inhibition of tissue factor-factor VIIa enzymatic activity in plasma. Reaction mixtures contained plasma, 3H-factor IX or 3H-factor X, tissue factor (vol/vol 2.4% to 24%), and calcium. Tissue factor-factor VIIa activity was evaluated from progress curves of activation of factor IX or factor X, plotted from tritiated activation peptide release data. With normal plasma, progress curves exhibited initial limited activation followed by a plateau indicative of loss of tissue factor-factor VIIa activity. With hereditary factor X-deficient plasma treated with factor X antibodies, progress curves revealed full factor IX activation. Adding only 0.4 micrograms/mL factor X (final concentration) could restore inhibition. Inhibition was not observed in purified systems containing 6% to 24% tissue factor, factor VII, 0.5 micrograms/mL, factor IX, 13 micrograms/mL, and factor X up to 0.8 micrograms/mL, but could be induced by adding barium-absorbed plasma to the reaction mixture. Thus, both factor X and an additional material in plasma were required for inhibition. The amount of factor X needed appeared related to the concentration of tissue factor; adding more tissue factor at the plateau of a progress curve induced further activation. These results also indicate that inhibited reaction mixtures contained active free factor VII(a). Preliminary data suggest that inhibition may stem from loss of activity of the tissue factor component of the tissue factor- factor VII(a) complex.     

Consumption of Serum Factors and Prothrombin During Intravascular Clotting in Rabbits

We have studied the effect of experimental intravascular clotting upon Factors II, VII, IX, and X in rabbits. Animals were given sodium warfarin intravenously to block the synthesis of these factors and, 4 hours later, were infused with either dilute tissue thromboplastin or saline. The tissue thromboplastin induced intravascular clotting extensive enough to halve fibrinogen and platelet levels and to reduce markedly Factor V and Factor VIII levels. These changes resulted from a consumption during clotting of about 10 per cent of the available prothrombin. Each of the serum factors fell further during the infusion of tissue thromboplastin than during the infusion of saline; apparently, serum factors activated during clotting do not circulate in the rabbit. Net losses due to intravascular clotting equalled about 15 to 30 per cent of the Factors VII, IX, and X initially present. These data suggest that consumption during intravascular clotting may account for the low levels of Factors VII, IX, and X described in patients with diffuse intravascular clotting complicating septicaemia. The evidence of consumption of Factor IX raises the possibility that tissue thromboplastin may activate intrinsic clotting during hemostasis in vivo.     

Characterization of a cDNA coding for human factor VII.

Factor VII is a precursor to a serine protease that is present in mammalian plasma. In its activated form, it participates in blood coagulation by activating factor X and/or factor IX in the presence of tissue factor and calcium. Clones coding for factor VII were obtained from two cDNA libraries prepared from poly(A) RNA from human liver and Hep G2 cells. The amino acid sequence deduced from the cDNAs indicates that factor VII is synthesized with a prepro-leader sequence of 60 or 38 amino acids. The mature protein that circulates in plasma is a single-chain polypeptide composed of 406 amino acids. The amino acid sequence analysis of the protein and the amino acid sequence deduced from the cDNAs indicate that factor VII is converted to factor VIIa by the cleavage of a single internal bond between arginine and isoleucine. This results in the formation of a light chain (152 amino acids) and a heavy chain (254 amino acids) that are held together by a disulfide bond. The light chain contains a gamma-carboxyglutamic acid (Gla) domain and two potential epidermal growth factor domains, while the heavy chain contains the serine protease portion of the molecule. Factor VII shows a high degree of amino acid sequence homology with the other vitamin K-dependent plasma proteins.     

Studies of the activation of factor VII bound to tissue factor [see comments]

Experiments were performed to evaluate activation of factor VII bound to relipidated tissue factor (TF) in suspension and to TF constitutively expressed on the surface of an ovarian carcinoma cell line (OC-2008). Activation was assessed by measuring cleavage of 125I- factor VII and by the ability of unlabeled factor VII to catalyze activation of a variant factor IX molecule that, after activation, cannot back-activate factor VII. Factor Xa was found to effectively activate factor VII bound to TF relipidated in either acidic or neutral phospholipid vesicles. Autoactivation of factor VII bound to TF in suspension was dependent on the preparation of TF apoprotein used and the technique of its relipidation. This highlights the need for caution in extrapolating data from TF in suspension to the activation of factor VII bound to cell surfaces during hemostasis. A relatively slow activation of factor VII bound to OC-2008 monolayers in the absence of added protease was observed consistently. Antithrombin in the presence or absence of heparin prevented this basal activation, whereas TF pathway inhibitor (TFPI/factor Xa complexes had only a limited inhibitory effect. Adding a substrate concentration of factor X markedly enhanced basal activation of factor VII, but both TFPI/factor Xa and antithrombin/heparin abolished this enhancement. Overall, our data are compatible with the hypothesis that not all factor VII/TF complexes formed at a site of tissue injury are readily activated to factor VIIa (VIIa)/TF complexes during hemostasis. The clinical significance of this is discussed.     

Proteolytic interactions of factor IXa with human factor VIII and factor VIIIa.

Factor IXa was shown to inactivate both factor VIII and factor VIIIa in a phospholipid-dependent reaction that could be blocked by an antifactor IX antibody. Factor IXa-catalyzed inactivation correlated with proteolytic cleavages within the A1 subunit of factor VIIIa and within the heavy chain (contiguous A1-A2-B domains) of factor VIII. Furthermore, a relatively slow conversion of factor VIII light chain to a 68-Kd fragment was observed after prolonged incubation. Sites of cleavage were identified within the A1 domain at Arg336-Met337 and within the factor VIII light chain at Arg1719-Asn1720. Factor IXa failed to cleave isolated factor VIII heavy chains, yet cleaved isolated factor VIII light chain. In addition, the purified A1/A3-C1-C2 dimer derived from factor VIIIa was a substrate for factor IXa; however, cleavage of the A1 subunit occurred at less than 30% the rate of cleavage of A1 in trimeric factor VIIIa. These data suggest that factor VIII light chain contributes to the binding site for factor IXa and also support a role for a heavy chain determinant located within the A2 subunit in the association of factor VIIIa with factor IXa. Furthermore, the capacity of factor IXa to proteolytically inactivate its cofactor, factor VIIIa, suggests a mode of regulation within the intrinsic tenase complex.     

Congenital Haemorrhagic Condition Similar but Not Identical to Factor X Deficiency

A 23-year-old white male with a bleeding tendency since early childhood presented a congenital coagulation defect similar but not identical to factor X deficiency. A first and second stage defect were demonstrated, characterized by a prolonged prothrombin time, prolonged partial thromboplastin time, abnormal thromboplastin generation, abnormal prothrombin consumption. The Stypven clotting time was slightly prolonged on fresh plasma but was normal on frozen plasma. Factors I, II, V, VIII, IX, XI, and XII were all within normal limits; factor VII was at the lower limits of normally or slightly decreased. Mr. Stuart's plasma failed to correct the defect of the patients plasma; however, a known factor VII deficient plasma was able to correct the abnormality. Factor X levels showed low (3–13%) only when assayed using tissue whole thromboplastin or tissue partial thromboplastin; the factor X assay using a Stypven-cephalin mixture yielded normal or near normal values. The factor II + factor X level using a Stypven-cephalin mixture appeared normal also. The significance of the findings is discussed. The results are tentatively interpreted as being due to an abnormal factor X rather than to a real deficiency.     

Coagulation Factor IX concentrate: method of preparation and assessment of potential in vivo thrombogenicity in animal models

Thrombosis and/or disseminated intravascular coagulation (DIC) are complications specifically associated with the use of factor IX complex in some patients. Assuming that these complications might result from zymogen overload, we have produced, using diethylaminoethyl (DEAE)- Sephadex (Pharmacia, Piscataway, NJ) and sulfated dextran chromatography, a factor IX concentrate (coagulation factor IX) that is essentially free of prothrombin, factor VII, and factor X. Factor IX specific activity is at least 5 U/mg protein, a 250-fold purification compared to plasma. Amounts of factors II, VII, and X are less than 5 units each per 100 units of factor IX. The concentrate is essentially free of activated clotting factors and contains no added heparin. In the rabbit stasis model, a dose of 200 factor IX U/kg was less thrombogenic than 100 factor IX U/kg of the DEAE-Sephadex eluate from which the concentrate was derived. Infusion of 200 factor IX U/kg did not induce DIC in the nonstasis rabbit model, whereas 100 factor IX U/kg of the DEAE-Sephadex eluate resulted in DIC in this model. Several factor IX lots were found to have shortened nonactivated partial thromboplastin times (PTTs), but were nonthrombogenic in both animal models. These data indicate that coagulation factor IX concentrate is less thrombogenic than factor IX complex.     

Activation of a Proteolytic System by a Membrane Lipoprotein: Mechanism of Action of Tissue Factor

One pathway of blood coagulation, the extrinsic system, is initiated by a specific interaction between tissue factor, which is a membrane lipoprotein, and factor VII, one of the plasma coagulation factors. Factor VII was prepared from bovine plasma by adsorption onto and elution from BaSO(4). The eluate was chromatographed on DEAE-Sephadex and purified by preparative disc-gel electrophoresis. Factor VII complexed with purified bovine-brain tissue factor and, when eluted from the complex, factor VII had a greater mobility in acrylamide-gel electrophoresis in the presence of sodium dodecyl sulfate, i.e., it had a reduced molecular weight. Factor VII was also cleaved in the presence of orthophenanthroline, an inhibitor of the peptidase activity of tissue factor. Prior treatment of factor VII with diisopropylphosphorofluoridate, however, completely blocked its cleavage and the development of coagulant activity, although factor VII treated with diisopropylphosphorofluoridates complexed equally well as the native protein with tissue factor. Factor VII in whole bovine plasma was also inhibited by the drug. Factor VII labeled with [(32)P]diisopropylphosphorofluoridate and radioautographed after electrophoresis in gels showed two major components, only one of which was labeled. We conclude that tissue factor initiates blood coagulation by facilitating a proteolytic attack within the factor VII "complex." The most likely mechanism is proteolysis of one form of factor VII by the diisopropylphosphorofluoridate-sensitive enzyme, although additional intramolecular proteolysis may be involved.     

A Factor VII Concentrate for Therapeutic Use

S ummary . A concentrate of factor VII suitable for therapeutic use has been prepared from human plasma by a method forming part of a comprehensive scheme of large-scale plasma fractionation. Factor VIII was separated as cryoprecipitate and factors II, IX and X were adsorbed on DEAE-cellulose. Most of the factor VII remained in the supernatant. By batch adsorption on DEAE-Sepharose, followed by elution on a chromatographic column, factor VII was concentrated about 25-fold, and purified about 50-fold compared with original plasma, without the need for further dialysis or concentration steps. Data are presented from 10 batches, each from 80-120 kg plasma. Following doses of factor VII to six congenitally deficient patients, the mean rise in plasma factor VII was 95–100% of theoretical; the half-disappearance time was about 4 h. The treatment of four patients with acquired deficiency of factor VII is also described. No untoward side effects were observed.     

An open clinical study assessing the efficacy and safety of Factor IX Grifols®, a high‐purity Factor IX concentrate,in patients with severe haemophilia B

Summary. Factor IX Grifols^® is a new high‐purity plasma‐derived FIX concentrate with two specific pathogen elimination steps. Until this study was performed, there were no detailed reports with an adequate number of patients on the clinical evaluation of this product. To determine the efficacy and safety of Factor IX Grifols^® for replacement therapy in previously treated patients with severe haemophilia B, this open, multicentre and non‐randomized study included 25 male subjects over the age of 12 with severe haemophilia B. Patients underwent prophylaxis and treatment of bleeding episodes with Factor IX Grifols^® for 1 year. The clinical efficacy and safety of this product were assessed. Forty percent of the patients were children and adolescents (12–17 years old). During the 12 months follow‐up, 1 446 000 IU of Factor IX Grifols^® were administered in 961 infusions (range 12–83 infusions per patient): 31% for prophylaxis and 69% for bleeding episodes. Only five major bleeding events were reported in two patients. These haemorrhages were successfully treated with a mean of 2900 IU per bleed (range 1500–4000 IU), and 1–3 infusions per bleed. The average time elapsed from the first infusion to resolution of bleeding was 43 h (median). Overall, haemostasis was rated as excellent or good by the investigator in 96% of the infusions. No product‐related adverse events were reported. Factor IX Grifols^® is an effective and safe Factor IX concentrate and can be considered as a first line option for replacement therapy in haemophilia B patients.     

Differential Consumption of Coagulation Factors Resulting from Activation of the Extrinsic (Tissue Thromboplastin) or the Intrinsic (Foreign Surface Contact) Pathways

1. The consumption of coagulation Factors IX, X, and XI was studied innormal whole blood clotted with celite (intrinsic activation) or tissue thromboplastin (extrinsic activation).

2. During these studies an assay method for Factor XI was developed whichwas not influenced by the presence of tissue thromboplastin. The assay methodis based on the thromboplastin generation principle.

3. When blood clotted in silicone treated tubes, the serum and plasma concentrations of Factors IX, X, and XI were almost identical, indicating that littleconsumption or activation of these factors had occurred.

4. In the presence of celite, coagulation Factors IX and XI are consumed,whereas Factor X is consumed only slightly.

5. In the presence of tissue thromboplastin, Factor X is consumed, whereasFactors IX and XI are not consumed.

6. In the presence of both celite and thromboplastin, the thromboplastindecreased the consumption of Factors IX and XI produced by celite.

7. The study of serum coagulation factor levels may provide evidence as towhether the coagulation process had been initiated by the intrinsic (foreignsurface contact) or extrinsic (thromboplastin) pathways.

Submitted on May 9, 1966 Accepted on July 21, 1966