An immunoradiometric assay for procoagulant factor VIII antigen: results in haemophilia, von Willebrand's disease and fetal plasma and serum

Inheritable molecular variants of moderate and mild hemophilia A

Factor VIII clotting activity (VIII:C) and factor VIII clotting antigen (VIII:CAg) were investigated in 54 patients with hemophilia A of moderate or mild severity. The patients belonged to 28 kindreds. The study showed a genetically determined molecular variation within hemophilia A of both moderate and mild forms. Each form can be classified into 3 types according to the content of demonstrable VIII:CAg. Type I has no demonstrable VIII:CAg, type IIa has VIII:CAg in an amount smaller than, or approximately equal to, that of VIII:C and type IIb has a larger amount of VIII:CAg than VIII:C. Affected members of one and the same kindred always have the same type of the disease.

Thrombin-catalyzed activation of factor VIII with His substituted for Arg372 at the P1 site

Thrombin-catalyzed proteolysis at Arg372 of factor VIII is essential for procofactor activation. However, hemophilia A patients with the missense mutation Arg372 to His possess a mild to moderate phenotype yet show no detectable cleavage at this bond. To evaluate this discrepancy, we prepared and stably expressed a recombinant, B-domainless factor VIII mutant (R372H) that possessed approximately 1% the specific activity of wild type. Cleavage at R372H by thrombin occurred with an approximately 80-fold decreased rate compared with wild type. N-terminal sequence analysis of the derived A2 subunit confirmed that cleavage occurred at the His372-Ser373 bond. Factor VIII R372H was activated slowly, attained lower activity levels, and exhibited an apparent reduced inactivation rate compared with factor VIII wild type. These observations were attributed to a reduced cleavage rate at His372. Factor Xa generation assays showed similar Michaelis-Menten constant (K(m), apparent) values for thrombin-catalyzed activation for either factor VIII form, but suggested an approximately 70-fold reduced maximum velocity (V(max)) for factor VIII R372H. However, prolonged reaction with thrombin yielded similar activity and stability values for the mutant and wild-type factor VIIIa forms. These results indicate a markedly reduced rate of cleavage following substitution at the P(1)Arg, and this property likely reflects the severity of the hemophilia A phenotype.

Understanding the hemostatic effects of recombinant factor VIIa by clot wave form analysis

The monitoring of coagulation-inhibitor bypassing agents, including recombinant factor VIIa (rFVIIa), remains a major issue in the management of clinical hemophilia. Clotting assays using prothrombin time (PT) and measurements of factor VII (FVII) activity do not always reflect the hemostatic effects of treatment. Thrombelastography can be used to observe the global effects of treatment on the overall coagulation process and is especially useful for observing the effects of hemostatic treatment in hemophilia patients with inhibitors. Waveform analysis is another technique for evaluating global hemostatic condition where changes in light transmission during routine clotting assays, such as the activated partial thromboplastin time (aPTT), are measured. We found that waveforms differed between individual patients with severe hemophilia A (FVIII:C < 1.0 IU/dL) with levels of sensitivity at below FVIII:C 1.0 IU/dL. Clot waveforms indicated dose-dependent improvements in clot formation after the addition of rFVIIa to both FVIII-deficient and factor IX (FIX)-deficient plasma. The improvements were further enhanced in the presence of both platelets and synthetic phospholipids, and were more pronounced with FVIII-deficient plasma than with FIX-deficient plasma. It appears that clot waveform analysis provides a very useful means for monitoring hemostasis in hemophilia A patients with inhibitors.

Assay of factor VIII antigen (VIII:CAg) in 294 haemophilia A patients by a new commercial ELISA using monoclonal antibodies

Monoclonal antibodies (MoAbs 833 and D4H1) directed against human factor VIII (FVIII) have been produced on a large scale to measure VIII:CAg by two-site ELISA (Asserachrom VIII:CAg, Diagnostica Stago). F(ab')2 from MoAb 833 were used for coating and bound VIII:CAg was revealed with MoAb D4H1 coupled to peroxidase. Control plasma (100 VIII:CAg U dL-1 by comparing with the International Standard) was used as reference. The assay sensitivity was 0.1 U dL-1 VIII:CAg. No apparent effect of the plasma proteins was observed provided plasma dilution was > or = 5. Thus this ELISA allowed us to estimate VIII:CAg levels of 0.5 U dL-1 in plasma. Levels of VIII:CAg were similar to those of VIII:C (correlation coefficient r = 0.87) in plasma from normal individuals (32 cases) and in patients with von Willebrand disease of various types (30 cases). Among 294 patients with haemophilia A (HA), 161 had severe HA (VIII:C < 1 U dL-1). Among those patients, 124 were cross-reacting material (CRM) negative with undetectable VIII:CAg and 37 were CRM+ (VIII:CAg 1-31 U dL-1). In 42 patients with moderate HA (VIII:C 1-5 U dL-1), 33 were CRM reduced (VIII:CAg 0.5-8 U dL-1) and nine were CRM+ with a VIII:CAg/VIII:C ratio of 6-91 (mean 34.3). In mild HA (91 cases with VIII:C > or = 6 U dL-1), 29 patients were classified as CRM+ (VIII:C 6-57 U dL-1, VIII:CAg 17-130 U dL-1 and VIII:CAg/VIII:C ratio 1.8-13.7 (mean 4.51)). In 62 CRM reduced patients there was a linear correlation between VIII:C (6-39 U dL-1) and VIII:CAg (2-36 U dL-1) levels (r = 0.88). In conclusion, this sensitive assay allows us to distinguish the quantitative CRM reduced and negative from the qualitative (CRM+) abnormalities in haemophilia A.

Mild haemophilia A in Iceland: clinical genetic studies of three families with the same mutation

OBJECTIVES

The aim of the study was to define the phenotype in three families with mild haemophilia A and to determine restriction fragment length polymorphisms (RFLP), which could support a hypothesis of a common progenitor of the families.

DESIGN

Family survey.

SETTING

Index cases were identified in and outside hospital and a family survey for symptoms and signs of bleeding in family members and sampling for coagulation and RFLP studies were mostly carried out in the field.

SUBJECT

Family members with and without symptoms of bleeding were selected for investigation and normal spouses and unrelated individuals were investigated for control.

INTERVENTIONS

Medical advice regarding affected family members were given to the families and their physicians.

MAIN OUTCOME MEASURES

Bleeding time, factor VIII activity, quantification of factor VIII:Ag, von Willebrand factor (vWF) Ag and vWF ristocetin assay. Typing of RFLP polymorphisms for genetic homogeneity.

RESULTS

Bleeding manifestations are present in both sexes in the three families although more frequent and more severe in the males. The level of factor VIII activity is between 10 and 20% in most affected males whereas 35-60% is found approximately in 2/3 of female carriers and in 1/3 of them factor VIII activity is within the normal range. It is suggested that screening for this mild haemophilia A gene by a molecular genetic method would be of clinical value now, its mutation having been detected.

CONCLUSIONS

Transmission of mild haemophilia A through six to seven generations is demonstrated by the study. The mild haemophilia A type described is the most prevalent of haemophilia A types in Iceland (population 260,000, 1992). The founder effect was confirmed by studies of RFLP polymorphisms.

Abnormal factor VIII Hiroshima: defect in crucial proteolytic cleavage by thrombin at Arg1689 detected by a novel ELISA

We have established an ELISA for detecting thrombin cleavage of the FVIII light chain at Arg1689. The method used a coating alloantibody which recognized amino acid residues 2248-2312 in the C2 domain, together with a second monoclonal antibody, NMC-VIII/10, which recognized residues 1675-1684 in the amino-terminal region of the light chain. FVIII antigen (FVIII:Ag) was measured after treatment of plasma with various concentrations of thrombin. The FVIII:Ag of normal plasma was reduced in a dose-dependent manner by the thrombin, falling to 28% in the presence of 100 U/ml enzyme. The concentration of thrombin that achieved 50% reduction (IC50) was approximately 1.0 U/ml. The plasma of four haemophilia A positive (A+) and two haemophilia A reduced (AR) patients were analysed. The IC50 of all patients was more than 1.0 U/ml, indicating that thrombin cleavage of the FVIII light chain was defective. One haemophilia A+ plasma did not respond to thrombin in this ELISA system. The patient (TI) was a haemophiliac with FVIII coagulant activity of 0.04 U/ml and FVIII:Ag of 1.78 U/ml. In addition, immunoblotting of the purified FVIII from TI showed that thrombin cleavage of the 80 kilodalton (kD) light chain was impaired. The patient's DNA was amplified using the polymerase chain reaction with a set of synthetic oligonucleotide primers spanning amino acid residues 1646-1714. Sequence analysis of the amplified DNA fragments revealed a cytosine to thymine transition, converting an arginine 1689 to cysteine. This abnormal FVIII was designated as FVIII Hiroshima. Our ELISA system is a simple and useful method of evaluating the proteolytic cleavage by thrombin at Arg1689.

Development, optimization and use of an enzyme linked immunosorbent assay (ELISA) to measure factor VIII antigen utilizing monoclonal antibodies

An enzyme linked immunosorbent assay (ELISA) has been developed to measure VIII:Ag in plasma and concentrates. The assay utilizes two commercially available monoclonal antibodies to VIII:Ag and provides an alternative to the established immunoradiometric assay (IRMA). It has the advantage of not requiring the use of radioactive material and human antibodies. The assay sensitivity is 0.006 u/ml and the interassay coefficient of variation is 6.3%. Forty-eight samples with VIII:Ag levels ranging from 0.006 to 1.5 u/ml were assayed by both ELISA and IRMA. The coefficient of correlation between the two assays was 0.89. In addition to measuring human VIII:Ag, it is also possible to detect antigen in several animal plasma and sera.

How do carriers of hemophilia experience prenatal diagnosis (PND)? Carriers' Immediate and later reactions to amniocentesis and fetal blood sampling

A semistructured personal interview was performed with 29 carriers of hemophilia A or B, 1-5 years after a pregnancy in which prenatal diagnosis (PND) was performed by fetal blood sampling. Fetal blood sampling by fetoscopy was significantly more often reported by the women to the more trying than expected than was ultrasound-guided heart puncture. Of 29 women 13 was classified as having experienced the PND process (amniocentesis and fetal blood sampling) as distressing, having had mental or psychosomatic symptoms associated with it. All of the women who had abortion/miscarriage after PND reported a very high frequency of psychological sequelae during the 6 months that followed PND. Of 22 women who continued their pregnancy with a healthy fetus after PND 8 experienced the period until delivery as trying and felt that their emotional and somatic status influenced their daily life activities. This was particularly common among women who after fetoscopy received routine profylactic terbutalin treatment and had continuous sickleave until the 36th gestational week, 17/29 would consider going through PND in the future. Qualified psychological assistance must be offered both before and after PND.

Factor VIII influences binding of factor IX and factor X to intact human platelets

To investigate the influence of factor VIII on the binding of factors IX and X to the surface of intact human platelets, washed collagen-stimulated platelets were incubated with factor IX and factor X in the presence or absence of factor VIII. Platelets were then lysed and IX:Ag and X:Ag were determined in the platelet lysate. Platelet bound IX:Ag was higher after incubation of platelets with factor IX in the presence of native or activated factor VIII than after incubation of platelets with factor IX alone. Thrombin degraded factor VIII did not support binding of factor IX to stimulated platelets. Preactivation of factor IX enhanced binding to platelets; influence by factor VIII on binding to platelets was greater with native factor IX than with preactivated factor IX. Presence of native or activated factor VIII also increased binding of factor X to platelets. In contrast to factor IX, preactivation of factor X did not influence binding to platelets, but in the presence of factor VIII preactivation of factor X increased binding of factor X to platelets. Our data suggest that mediation of binding of factors IX and X to the surface of platelets is one of the mechanisms by that factor VIII exerts its cofactor function in the activation of factor X.

Direct characterization of factor VIII in plasma: detection of a mutation altering a thrombin cleavage site (arginine-372----histidine)

An immunoadsorbent method has been developed for the direct analysis of normal and variant plasma factor VIII. Using this method, the molecular defect responsible for mild hemophilia A has been identified for a patient whose plasma factor VIII activity is 0.05 unit/ml, even though the factor VIII antigen content is 3.25 units/ml. Although the variant factor VIII has an apparently normal molecular mass and chain composition, the 92-kDa heavy chain accumulates when the variant protein is incubated with thrombin and the 44-kDa heavy chain fragment cannot be detected. In contrast, thrombin cleavage of the 80-kDa light chain to the 72-kDa fragment is normal. As these data indicate a loss of factor VIII cleavage by thrombin at arginine-372, the genetic defect was determined by polymerase-chain-reaction amplification of exon 8 of the factor VIII gene and direct sequencing of the amplified product. A single-base substitution (guanine----adenine) was identified that produces an arginine to histidine substitution at amino acid residue 372. These data identify the molecular basis of an abnormal factor VIII, "factor VIII-Kumamoto," that lacks procoagulant function because of impaired thrombin activation.

The combined use of monoclonal antibody-based enzyme-linked immunosorbent assays (ELISA) for factor VIII antigen (VIII:Ag) and von Willebrand factor antigen (vWF:Ag) for the detection of carriers of haemophilia A

Enzyme-linked immunosorbent assays (ELISA) for factor VIII antigen (VIII:Ag) and von Willebrand factor antigen (vWF:Ag) have been developed, each employing monoclonal antibodies. In the majority of severe haemophilic plasmas tested, VIII:Ag was undetectable by ELISA and also by immunoradiometric assay (IRMA) using haemophilic VIII:C antibodies. In haemophilic plasmas with mild/moderate deficiency of coagulant factor VIII (VIII:C), there was no significant difference between the two immunoassays although there was a general trend for ELISA VIII:Ag results to be higher. Assay of von Willebrand's disease (vWd) plasmas with the ELISA for vWF:Ag demonstrated reduced levels of this antigen in type I vWd, normal levels in type IIA, and a severe reduction of vWF:Ag in type III vWd. The discrimination of obligate carriers of haemophilia from normal was determined using ratios of factor VIII/vWF. Factor VIII antigen/von Willebrand factor antigen measured by IRMA and Laurell immunoelectrophoresis respectively, gave a superior discriminant to that of VIII:C/vWF:Ag (Laurell), but optimal discrimination was obtained with the combination of ELISAs for VIII:Ag and vWF:Ag.

Factor VIII polypeptide specificity of monoclonal anti-factor VIII antibodies

Four monoclonal antibodies against factor VIII, NMC-VIII/1, NMC-VIII/2, NMC-VIII/3 and NMC-VIII/4, were produced. The first three antibodies were of the IgG1 immunoglobulin subclass, while the fourth was IgM. The affinity of each antibody for factor VIII was high and anti-factor VIII clotting activity was detected in NMC-VIII/2, NMC-VIII/3 and NMC-VIII/4. NMC-VIII/1 had no inhibitory effect on factor VIII clotting activity. Immunoblotting using purified intact and thrombin-treated factor VIII identified the antibodies' factor VIII polypeptide specificities. With thrombin-treated factor VIII the factor VIII fragments for NMC-VIII/1 and NMC-VIII/2 were 80 kDa and 54 kDa, respectively, while both NMC-VIII/3 and NMC-VIII/4 recognised a 44 kDa fragment. With intact factor VIII, antibodies NMC-VIII/2-4 bound to polypeptides larger than 90 kDa, especially NMC-VIII/2, which reacted with a chain of 330 kDa thought to be a mature form of factor VIII protein. We also detected a mature form of factor VIII in hepatic sinusoidal endothelial cells by immunoperoxidase staining. Identification of the factor VIII polypeptides bearing these fragments enabled us to clarify the localization of the factor VIII thrombin cleavage site, and suggested the existence of factor VIII in hepatic sinusoidal endothelial cells.

Hemostatic effect of a heat-treated factor VIII concentrate (Haemate P) in von Willebrand's disease

A heat-treated factor VIII (F VIII) concentrate (Haemate P) has been administered to patients with various types of von Willebrand's disease (vWD). The 4 activities of F VIII/vWF as well as change in the multimeric structure of vWF were then studied. In 4 patients with type I vWF who were given a Ristocetin cofactor (Rcof) dose of 42-78 U/kg, there was a clear reduction of the bleeding time and an increase of F VIII: C, F VIII: Ag, Rcof and vWF: Ag for several hours. The recovery of Rcof. after 1 h was 50-75%. Although the multimeric composition of vWF in these patients was similar to that of normal plasma, the density of each multimer band was very low. After infusion, however, the density of all multimer bands increased for several hours, to decrease again after 24 h. In 4 patients with type II A vWD who received a dose of Rcof of 55-76 U/kg, the 4 activities of F VIII/vWF increased similarly as was the case in type I. All patients had only 3-4 smaller multimer bands. New larger and intermediate multimers appeared for several hours after infusion of the preparation. Two patients with type III vWD who received doses of Rcof of 52 and 65 U/kg showed also a similar increase in the 4 activities of F VIII/vWF after infusion. All the multimers lacking in these patients appeared for several hours after infusion.

Radioimmunoassay for quantitative measurement of factor VIII-heavy chain

An immunoassay has been developed for the measurement of factor VIII heavy chain (FVIII-HC). IgG from a human inhibitor plasma with specificity for FVIII-HC and FVIII-light chain (FVIII-LC) was coated to microplates with loose wells. After washing, the plates were incubated with sample and after another wash 125I-FVIII-HC was added so that the amount of bound tracer was dependent on the amount of FVIII-HC in sample. When EDTA was included in the assay buffer the assay response was increased 3-fold for normal human plasma. This indicated that the antibody was reactive with a determinant hidden in the FVIII-HC/FVIII-LC complex as EDTA splits the complex. The sensitivity of the assay was 0.004 units/ml (1 unit/ml in normal human plasma pool). Together with a previously published assay for FVIII-LC it has now become possible to measure the relative amounts of FVIII-HC and FVIII-LC in haemophilia A plasma and to study the separate expression of FVIII-HC and FVIII-LC by recombinant DNA technology. Patients with severe haemophilia A had FVIII-HC levels below 0.01 units/ml. However, inhibitor patients in high dose FVIII-treatment showed up to 50 times higher levels of FVIII-HC than FVIII-LC and FVIII:C, indicating the presence of FVIII/anti-FVIII-LC immune complexes. Thus, dependent on assay specificity plasma samples can show very variable content of FVIII:antigen.

In vitro characterization of various heat-treated prothrombin complex concentrates (PCC)

All of 6 heat-treated prothrombin complex concentrates (PCC) tested contained adequate levels of factor IX but factor VII content was low. Levels of factors II, X, protein C and protein S were variable and antigen levels were always greater than those of functional activities. On crossed-immunoelectrophoresis factor IX showed variable anodal shift in all concentrates tested and in some activated factor IX was demonstrated by immunoblotting technique. These findings suggested some activation and/or denaturation during production and/or heating. Modest amount of factor VIII clotting activity by solid-phase amidolytic method and of factor VIII antigen was demonstrated in some concentrates but none contained more than a trace factor VIII inhibitor bypassing activity. The results suggested that heat-treated PCC should provide safe therapeutic products for hemophilia B.

Factor VIII coagulant moiety binds to platelets by binding to phospholipids of the platelet membrane

Washed human platelets were incubated with commercial factor VIII concentrate, or with purified factor VIII coagulant moiety. Platelets were then washed again and lysed by sonication. VIII:Ag and vWf:Ag were measured in the platelet lysate prior to and after incubation of the lysate with phospholipase C (PL-C). Platelet bound VIII:Ag was significantly higher after incubation of washed platelets with factor VIII concentrate than after incubation with buffer. Platelet bound VIII:Ag was further increased when platelets had been incubated with concentrate in the presence of thrombin and collagen. In contrast, only a slight increase in platelet bound vWf:Ag was observed after incubation of platelets with concentrate. When washed platelets had been incubated with factor VIII coagulant moiety, also significantly more platelet bound VIII:Ag was observed than after incubation with buffer. Measurable VIII:Ag, but not vWf:Ag, increased significantly after incubation of the platelet lysate with PL-C. When intact washed platelets had been treated with PL-C prior to the incubation with concentrate, binding of VIII:Ag to platelets was nearly completely abolished. Our data suggest that the factor VIII coagulant moiety binds to phospholipids of the platelet membrane and thereby contributes to the assembly of the factor X activating complex on the platelet surface.

Molecular pathology and immunology of factor VIII (hemophilia A and factor VIII inhibitors)

Factor VIII is a large procoagulant glycoprotein that circulates in plasma in a noncovalent complex with von Willebrand factor. It is essential for the efficient cleavage of coagulation factor X by factor IXa, and its absence causes a severe bleeding disorder. Plasma factor VIII is reduced from the normal range of approximately 100 to 200 ng/ml in patients with the hereditary coagulation defect, hemophilia A, as well as in patients who develop autoantibodies that inactivate factor VIII. The understanding of factor VIII structure has been enhanced by recent studies that have characterized the X chromosome gene responsible for its synthesis, and preliminary information is now available about specific genetic defects. The basis for antibody formation in approximately 15 per cent of repeatedly transfused hemophilic patients is less clear at this time, however, for these individuals appear to have a variety of genetic defects that are not characteristically different from the patients who do not develop inhibitors. Although the antibodies cause a serious problem for affected individuals, they have been very useful in characterizing normal factor VIII and nonfunctional factor VIII-like protein that is found in the plasmas of 10 per cent of patients with mild hemophilia. Moreover, they are very useful reagents that can be used for immunoassay of factor VIII that has been modified in ways that have destroyed its procoagulant function.

Enzyme linked immunosorbent assay (ELISA) for the measurement of factor VIII coagulant antigen (CAg) using haemophilic antibodies

A method for the quantitation of factor VIII clotting antigen (VIII:CAg) has been developed based on a micro enzyme linked immunosorbent assay (ELISA) principle employing antibodies from two polytransfused haemophilia A patients. Solid polystyrene support bound IgG fraction of inhibitor plasma extracted VIII:CAg from normal plasma and samples. Bound VIII:CAg was detected by peroxidase labelled F(ab')2 fragment of the IgG used for solid phase. Two assays, each based on its particular inhibitor antibody, were set up. The F VIII clotting antigen in plasma of 30 healthy persons was found identical with the two VIII:CAg assays (r=0.97) and closely correlating with clotting activity (VIII:C) (r=0.84). Serum VIII:CAg was 67% (+/-14.5%) of the corresponding plasma value. In severe haemophilia A, 17 out of 19 had VIII:CAg values less than 1 U/dl. Two patients with cross-reactive material (CRM+) were found. In some milder cases of haemophilia A, higher values of VIII:CAg than VIII:C was recorded. The sensitivity of the method was 0.08 U/dl. Inter assay coefficient of variation at the 100 U/dl level was 9.5% (CV%), at the 2 U/dl level 16.4% (CV%). Mainly due to the great stability of enzyme conjugated antibody compared to the natural decay of radioiodinated material and subsequent loss of detecting material, ELISA was found superior to immunoradiometric assay (IRMA).

Hemophilia A. Detection of molecular defects and of carriers by DNA analysis

To understand the molecular basis of hemophilia A and to provide heterozygote detection and prenatal diagnosis by DNA analysis, we used cloned factor VIII:C DNA fragments to study 10 affected families. In four of these families, inhibitors of factor VIII:C had developed in affected persons. In one such family a deletion of approximately 80 kb within the factor VIII:C gene was identified. Carriers of the deletion were identified through detection of an abnormal DNA fragment located at the deletion end points. In another family a single nucleotide change in the coding region of the factor VIII:C gene produced a nonsense codon leading to premature termination of factor VIII:C synthesis. Carrier detection was performed in eight female members of this four-generation family. In a third family a small change in the size of a restriction-endonuclease fragment correlated with the presence of the mutant gene, and in the other seven families the molecular defect has not yet been identified. In addition, we used two common polymorphic sites in the factor VIII:C gene to differentiate the normal from the defective gene in four of six obligate female carriers from families with patients in whom inhibitors did not develop. Carrier detection was possible in other members of these families. These data suggest that DNA analysis of the factor VIII:C gene provides an accurate method of carrier detection and, potentially, of prenatal diagnosis in at least 50 per cent of the pedigrees affected by hemophilia A.

Dissociation of the Factor-VIII complex during clotting: role of thrombin and phospholipids

To study the dissociation of the two moieties of the factor-VIII complex during clotting, plasma, concentrate and serum were chromatographed on 4% agarose. In plasma and concentrate factor-VIII coagulant activity (VIII C), factor-VIII coagulant antigen (VIII C:Ag), and factor-VIII-related antigen (VIII R:Ag) eluted together in the void volume, but some VIII C:Ag eluted after the void volume. The amount of VIII C:Ag eluting after the void volume was made smaller by adding proteinase inhibitors. In serum nearly all VIII C:Ag eluted after the void volume. From factor-VIII complex immunoadsorbed by means of an antibody against VIII R:Ag no VIII C:Ag was dissociated by thrombin or by thrombin and physiologic CaCl2 concentrations. Radiolabelled human thrombin did not bind to the VIII C:Ag of immunoadsorbed factor-VIII complex. VIII C:Ag displaying VIII C was dissociated from immunoadsorbed factor-VIII complex by human brain thromboplastin or by phosphatidyl-serine. Our results suggest that VIII C:Ag and VIII R:Ag dissociate during clotting. This dissociation seems not to be mediated by thrombin, but may be mediated by phospholipids.

Effects of growth hormone on the factor VIII complex in patients with growth hormone deficiency

Factor VIII activity (VIII C), factor VIII coagulant antigen (VIII C:Ag), factor VIII-related antigen (VIII R:Ag), Ristocetin cofactor (R:Cof), and growth hormone were studied in eight children with growth hormone deficiency prior to, and 60, 120, and 180 minutes after administration of human growth hormone (Crescormone, Kabi), 4 U/m2. Growth hormone has been administered for 1.0 to 6.8 years but was stopped one week prior to this investigation. Basal levels of VIII C, VIII C:Ag, VIII R:Ag, and R:Cof were within the normal limits. After administration of human growth hormone, VIII C, VIII C:Ag, VIII R:Ag, and R:Cof showed a significant rise. Our study shows that growth hormone is not necessary to maintain the basal levels of the factor VIII complex within the normal limits. However, out data suggest that growth hormone has some influences on the levels of the factor VIII complex. The mechanisms for the rise of the factor VIII complex--whether this is a direct effect of growth hormone or not--are not clear at this point.

Anti-idiotypic suppression of autoantibodies to factor VIII (antihaemophilic factor) by high-dose intravenous gammaglobulin

In two patients with high-titre autoantibodies to antihaemophilic factor (VIIIc), treatment with high-dose intravenous immunoglobulin (IVIg) resulted in rapid and prolonged, although not total, suppression of antibody. IVIg also inhibited anti-VIIIc activity in patients' plasma in vitro; IVIg and F(ab')2 fragments from IVIg inhibited anti-VIIIc activity of the IgG fraction and of the Fab'2 fragments of the IgG fraction from patients' plasma, indicating that the in-vivo effect of IVIg was due to the presence in the therapeutic immunoglobulins of anti-idiotypic antibodies against idiotypes expressed by anti-VIIIc autoantibodies. In contrast, IVIg had little or no effect on antibody titre in two haemophilic patients with anti-VIIIc alloantibodies. These observations suggest that IVIg contains anti-idiotypes against autoantibodies and may be effective in the treatment of some autoimmune diseases through idiotypic/anti-idiotypic interactions.

Acquired factor VIII:C inhibitor (IgG) and positive direct Coombs' test (IgM) in a patient with lung carcinoma. Clinical course and immunochemical studies

A 73-year-old man with lung squamous-cell carcinoma simultaneously developed a factor VIII:C inhibitor and a transient positive direct Coombs' test. The factor VIII:C inhibitor was characterized as a mixture of IgG1, IgG2, IgG4 with kappa and lambda light chains. The Coombs' test was IgM-specific.

TREATMENT

blood transfusions (packed red cells), cyclophosphamide and prednisone. Bleeding subsided without factor VIII-replacement therapy. Before death, in spite of the tumour-mass progression, factor VIII:C was normal.

Measurement of factor VIII CAg by immunoradiometric assay in human tissue extracts

Samples of normal tissues taken from three patients within 24 hours of death were physically disrupted, washed and extracted. Centrifuged supernatants were tested for factor VIII coagulant antigen (VIII CAg) and factor VIII related antigen (VIII RAg) by radioimmunoassays using homologous and heterologous antisera respectively. VIII RAg was readily washed out by isotonic saline whereas VIII CAg required 1.5 M sodium chloride for optimal extraction from tissue homogenates. Highest levels of VIII CAg were detected in some lymph nodes followed by lung, liver and spleen. There was rapid loss of VIII CAg from most tissues in the absence of proteolytic inhibitors.

The relationship of biological and immunological activities of factor VIII

Factor VIII is an essential blood clotting factor which consists of two protein moieties, each with distinct biological functions and antigenic determinants. The immunological markers were originally seen as indicators of the biological activities; however this view has been increasingly challenged. We have investigated the biological and immunological properties of Factor VIII to clarify these relationships. Plasma stored at room temperature for 21 days lost biological activity, but retained immunological activity: The procoagulant activity was reduced to 35% and the ristocetin cofactor activity to 75.4% of their original levels; but the reactivities of both procoagulant antigen and Factor VIII related antigen were maintained. A dissociation of activities was also demonstrated in serum, in which the procoagulant activity was 10% and the procoagulant antigen 72% of corresponding plasma values. These results indicate that the antigenic reactivities are not appropriate markers for Factor VIII biological activity.

An enzyme immunoassay (ELISA) for the quantitation of human factor VIII coagulant antigen (VIII:CAg)

For the purposes of prenatal diagnosis and carrier detection of haemophilia A, an enzyme linked immunosorbent assay (ELISA) was developed for the quantitation of plasma Factor VIII coagulant antigen (VIII:CAg). It is based upon a human antibody. Results are compared to assays for Factor VIII coagulant activity (VIII:C) and Factor VIII related antigen (VIIIR:Ag) in plasma from 30 normal female individuals, 5 fetuses from mothers normal with respect to bleeding status, 10 obligate carriers of haemophilia A, 10 patients with haemophilia A, 5 with von Willebrand's disease, and 5 with haemophilia B. The ELISA developed is simpler than previously published VIII:CAg methods owing to its use of total IgG instead of immunologically affinity-purified antibodies. It is specific (as judged from clinical results), sensitive (detection limit: 0.005 units/ml), and sufficiently precise (between-assay coefficient of variation: 11%) for the purposes mentioned. The coefficient of correlation between VIII:CAg and VIII:C results is 0.86. The introduction of ELISA for quantitating VIII:CAg represents an advantage as compared to existing immunoradiometric assays (IRMA) mainly due to the stable and non-radioactive reagents used in the ELISA.

The interaction between factor VIII clotting antigen (VIIICAg) and phospholipid

The interaction between factor VIII clotting antigen (VIIICAg) and phospholipid (PL) was studied using a two-site solid phase immunoradiometric assay (IRMA) for VIII CAg. Incubation (2 h, 37 degrees C) of normal plasma, cryoprecipitate or factor VIII concentrate with Diagen PL (0.5 mg/unit VIIICAg) resulted in 80-90% loss of IRMA-measurable VIIICAg. No loss of factor VIII related antigen (VIIIRAg) or factor VIII clotting activity (VIIIC) was seen. Treatment of factor VIII concentrate with purified PLs showed greatest VIIICAg reduction with phosphatidylserine, less with phosphatidylethanolamine, and very little with phosphatidylcholine. The action of phospholipase-C (PL-C) on VIIICAg-PL complexes was investigated, with enzyme activity being monitored by thin-layer chromatography. Treatment of normal plasma, cryoprecipitate or factor VIII concentrate with PL-C (5 u/unit VIIICAg) resulted in 25%, 25% and 30% increases in VIIICAg. No increase in VIIIC or VIIIRAg was seen. Preincubation of factor VIII concentrate with PL, followed by PL-C incubation, resulted in 70-80% recovery of measurable VIIICAg. Incubation of 'activated' prothrombin complex with PL-C increased VIIICAg by 44% (Autoplex) and 80% (FEIBA), indicating VIIICAg-PL complexes are present. Incubation of factor VIII concentrate with fresh platelet lysate led to a reduction in VIIICAg (100 u/dl to 21 u/dl). In fresh platelet lysate alone low VIIICAg levels were detectable (0.71 X 10(-3) u/10(9) plt). After PL-C incubation VIIICAg levels increased to 9.8 X 10(-3) u/10(9) plt) (14-fold increase). Thus VIIICAg in platelets may be hidden by VIIICAg-PL complexes.

The stability of VIII:C in frozen stored plasma samples--re-examined

VIII procoagulant activity (VIII:C) was estimated by a two-stage assay method, on 100 pre- and post-transfusion samples obtained from severe haemophiliacs receiving regular treatment with a variety of VIII concentrate preparations. Close and significant correlation (r = 0.97 P less than 0.01) was obtained between freshly tested samples and samples stored for one month at -35 degrees C. No significant difference between the two samples was demonstrated by Student's paired-t-test. Forty-nine of the stored samples were also measured for VIII procoagulant antigen (VIII:C Ag) level. A similar close and significant correlation was found for this parameter (r = 0.9 P less than 0.01), when compared with the VIII:C of the freshly tested samples. On average the VIII:C Ag value was 10% lower than the corresponding VIII:C value, although the difference was not statistically significant.

Acquired von Willebrand's disease: demonstration of a circulating inhibitor to the factor VIII complex in four cases

We have studied four patients suffering from acquired von Willebrand's disease. All patients had a severe bleeding diathesis with recurrent life-threatening haemorrhages. Three of the patients had a monoclonal gammopathy and one of these developed multiple myeloma. In three patients tested, a plasma inhibitor to ristocetin cofactor activity was detected. In each case this was localized to the IgG fraction of plasma. In addition, VIII:C activity was found to be associated with the IgG fraction of patients' plasma and altered mobility of VIII:C was detected on Laurell immunoelectrophoresis. Furthermore, plasma from all four patients and the IgG fraction therefrom resulted in a dissociation of normal VIII:C into two components separable by gel-filtration on Sepharose 6B. Finally the circulating half-life of the three factor VIII activities was found to be markedly reduced in the patients with acquired von Willebrand's disease. We conclude that in the patients studied the coagulation defect was related to the presence of a circulating inhibitor to the factor VIII complex and that this inhibitor was associated with the IgG fraction of plasma.

An electroblotting technique for the detection of factor VIII/von Willebrand factor multimers in plasma

A new, relatively simple technique has been developed in order to study the multimers of factor VIII/von Willebrand factor (VIII/vWF). It involves electrophoresis on SDS agarose gels and electrophoretic transfer (electroblotting) of the separated protein bands onto nitrocellulose membranes, to which they are non-covalently bound. VIII/vWF multimers are then detected by 125I-labelled antibodies to VIII/vWF, and autoradiography. Optimum electrophoretic transfer occurred at 0.5 A, for 18 h, on 0.8% agarose gels, thus enabling detection of the multimeric profile of VIII/vWF in 5 microliters of normal plasma. The multimeric profile for haemophilia A patients was identical to that for normal plasma. In plasma from patients with von Willebrand's disease (vWd), various patterns were seen, with a preponderance of smaller multimers in type II (atypical) vWd, similar to those seen in cryosupernatant. Heterogeneity within a particular type of vWd was also evident. Investigation of commercial factor VIII concentrates showed the presence of 'doublets' of VIII/vWF. Unlike other reported techniques, the rapid transfer and fixing of the protein bands to the nitrocellulose, minimizes loss of resolution, and handling of the paper is easier. It is possible to cut a sample electrophoresis strip into several areas, for incubation with different antibodies. Preliminary experiments also suggest that double antibody techniques are possible, or even removal of a first radiolabelled antibody by low pH, and then incubation of the separated proteins with a second, unrelated antibody.

Studies on the stability of factor VIII coagulant antigen (VIII:CAg) in the presence of VIII:C antibodies

The stability of factor VIII coagulant antigens (VIII:CAg) at 56 degrees C was investigated using an immunoradiometric assay for VIII:CAg. In normal or CRM+ haemophilic plasmas VIII:CAg was rapidly inactivated at 56 degrees C. VIII:CAg in spontaneous VIII:C inhibitor plasmas and in post-treatment samples from haemophiliacs with VIII:C inhibitor was resistant to inactivation at 56 degrees C, indicating the presence of heat stable VIII:CAg-anti VIII:CAg complexes. In vitro VIII:CAg-anti VIII:CAg complexes were formed by incubation of diluted VIII:C antibodies and normal plasma and the stability of these complexes at 56 degrees C was studied. Haemophilic VIII:CAg antibodies formed heat stable immune complexes over a narrow range of inhibitor dilutions whilst some spontaneous VIII:CAg antibodies formed these stable complexes over a much wider range of dilutions emphasizing the difference in the properties of these antibodies.

Quantitation of coagulant antigens and inhibition of activated protein C in combined factor V VIII deficiency

Inhibition of activated human protein C was assessed in an amidolytic assay system using normal human plasma and samples from patients with hereditary coagulation abnormalities. In eight experiments normal plasma inhibited 63.5% (+/- 15.6%) protein C activity. Plasma from patients with haemophilia A or isolated factor V deficiency gave results which were not significantly different from normal. However, plasma from patients with combined factor V and factor VIII deficiencies inhibited an average of 24.5% (+/- 13.6%) of the amidolytic activity (P less than 0.01). Two of these plasma samples failed to inhibit any protein C activity. The relationship between the level of inhibitor and those of factor V and factor VII coagulant antigens (VCAg and VIIICAg) in the combined defect was investigated. There was no significant correlation between the level of inhibitor and any of the coagulation immunoassays on these stored samples but there was significant correlation between VCAg and VIIICAg in some assay systems. The levels of VCAg and VII CAg was low in most samples from patients with the combined defect which was in contrast to the results obtained when normal plasma was incubated with activated protein C in vitro. The findings are consistent with the presence of biochemical similarities between factors V and VIIIC molecules, but the role of activated protein C and its inhibitor in hereditary combined factor V/VIII deficiency remains to be firmly established.

Heterogeneity of haemophilia A: a study with three different antisera

One human and one rabbit antibody against VIII:C--in a fluid-phase, inhibitor neutralization assay (INA)--and one human antibody--in a solid-phase, immunoradiometric assay (IRMA)--were used to investigate a group of 59 patients with severe, moderate and mild haemophilia A. Patients were classified as haemophilia A+ when the VIII:C/VIIIAG ratio was less than 0.4 while the absolute VIII:C antigen (VIIICAG) value exceeded 0.25 u/ml. Three haemophiliacs (from two pedigrees) were classified as A+ in all three assay systems. 50% of the patients were classified as haemophilia A+ on the basis of at least one assay. The other 50%, including 66% of the patients with severe haemophilia, were shown to be A- by all three assay systems. Combining the data obtained with the three different antibodies four different categories could be distinguished, in addition to the classification based on severity.

The effect of storage of whole blood on the association of factor VIII-related antigen and factor VIII-coagulant antigen

To evaluate the extent of denaturation of factor VIII-coagulant activity (VIII: C) during production of factor VIII concentrates, the factor VIII-coagulant antigen (VIII: CAg)/VIII: C ratio was measured in plasma, cryoprecipitate and cryosupernatant from fresh and stored blood. This ratio was close to unity for both cryoprecipitate and other concentrates, suggesting that VIII: CAg is lost concurrently with VIII: C during cryoprecipitation and further fractionation. Storage of blood (18 h, 22 degrees C) before processing resulted in a 30% loss of VIII: C from the separated plasma; however, VIII: CAg was not affected. In cryoprecipitate prepared from this plasma, VIII: C and VIII: CAg both were 30% lower than when prepared from fresh plasma. In the corresponding cryosupernatant, however, more VIII: CAg but less VIII: C was present compared with fresh material. Gel chromatography revealed that the rise of VIII: CAg in cryosupernatant prepared from stored blood, was due to an increased amount of VIII: CAg of low molecular weight, not being associated with factor VIII-related antigen. Such an increase in dissociated VIII: CAg was not detected in the plasma prior to cryoprecipitation. It is concluded that during storage of blood, molecular changes are induced in the factor VIII-VWF complex, possibly by limited proteolysis, which make the complex more liable to dissociation during subsequent cryoprecipitation.

Simplified immunoradiometric assay for factor VIII coagulant antigen

A simplified, non-competitive, solid phase immunoradiometric assay has been developed for the quantitation of factor VIII coagulant antigen (VIII:CAg)--the antigenic counterpart of FVIII coagulant activity (VIII:C). Both homologous and heterologous antibodies to human factor VIII (FVIII) were used in this assay. Initially, FVIII in a test sample was attached to immobilized, human IgG obtained from a polytransfused haemophilia A patient with a high titre antibody to VIII:C. The bound FVIII was then detected using rabbit 125I-IgG specific for human FVIII. The concentration of VIII:CAg correlated well with VIII:C levels in the plasma from normal donors (r = 0.84, n - 15). Homozygote von Willebrand's disease patients had undetectable levels of VIII:CAg in their plasma. Patients with severe haemophilia A (VIII:C less than 0.01 u/ml) could be divided into groups on the basis of the VIII:CAg levels, i.e. those having undetectable VIII:CAg and other with measurable VIII:CAg. VIII:CAg detected in normal serum was less than 0.002 u/ml. In this assay the use of human antibody to FVIII is considerably decreased compared to other methods for VIII:CAg, and the time-consuming steps to immunopurify human anti-FVIII antibody are eliminated.

The 'in vivo' survival characteristics of factor VIII procoagulant antigen (VIII:C Ag) in haemophilia A subjects

Initial half disappearance times and biological half-lives were determined for factor VIII procoagulant antigen (VIII:C Ag) and compared with VIII procoagulant (VIII:C) survival for each of two commercial concentrates, transfused into seven severe (less than 1 i.u./dl) non-bleeding haemophiliacs. The results show that VIII:C Ag has similar half disappearance and biological half-life to that of factor VIII:C. The relevance of these results to recently published findings is discussed.

Precipitating anti-VIII:C antibodies in two patients with haemophilia A

IgG from the plasmas of two haemophilia A patients with anti-VIII:CAg antibodies (1000 and 200 u/ml) was isolated and labelled with 125I. The specific labelled anti-VIII:CAg IgG was further purified by binding to and elution from immobilized factor VIII/von Willebrand factor (F.VIII/vWF). When studied by immunodiffusion and autoradiography, both antibodies gave a precipitin line with normal plasma, serum, cryoprecipitate, purified F.VIII/vWF and the plasmas of two patients with haemophilia A+. No precipitin line was observed with the plasmas of 11 patients with haemophilia A- or four patients with severe von Willebrand's disease. Levels of VIII:CAg obtained by radioelectroimmunoassay were in agreement with those obtained by immunoradiometric assay. This study demonstrates that, contrary to previous evidence, human anti-VIII:CAg antibodies are precipitating as well as neutralizing when studied by highly sensitive techniques.

Factor VIII clotting antigen (VIIICAg) in haemophilia measured by two immunoradiometric assays (IRMA) using different antibodies, and the measurement of inhibitors to procoagulant factor VIII (VIIIC) by IRMA

Factor VIII clotting antigen (VIIICAg) was measured by immunoradiometric assay (IRMA) using two different antibodies. Both antibodies arose in polytransfused severe haemophiliacs and had similar titres against VIIIC. In 12 normal plasmas there was no significant difference in VIIICAg values obtained (VIIICAg (AbI) = VIIICAg (AbII)). In the majority of 15 severe haemophiliacs tested VIIICAg was undetectable by both antibodies. In 28 mild to moderate haemophiliacs VIIICAg (AbII) was significantly greater than VIIICAg (AbI) (P less than 0.01) suggesting different antigenic determinants. The difference, however, was small and does not affect diagnosis of haemophilia. A modified IRMA has been used to measure anti VIIIC inhibitors by competition of the inhibitor with 125I labelled VIIICAg antibodies for common antigenic determinants. Using an inhibitor of 225 Bethesda units as a standard, results by IRMA of inhibitors in severe haemophiliacs have been similar to those obtained by clotting assay, but with a sensitivity of 0.01 u/ml suggesting the possible use in the detection of weak inhibitors.