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

Carrier detection in haemophilia a by immunological measurement of factor VIII related antigen (VIIIRAg) and factor VIII clotting antigen (VIIICAg)

23 obligate carriers of mild and severe haemophilia A and 26 normal females were bled on three occasions, and their plasmas assayed for procoagulant factor VIII (VIIIC), factor VIII related antigen (VIIIRAg) and factor VIII clotting antigen (VIIICAg). A comparison of the ratios VIIIC/VIIIRAg and VIIICAg/VIIIRAg indicated that, although the two ratios gave the same proportional misclassification of carriers as normals (four of 23), the latter ratio showed greater discriminatory power when an unequal variances predictive method was used to calculate likelihood ratios (for carrier status). This greater power was shown to be due to a greater reproducibility between visits for the VIIICAg/VIIIRAg ratio. Discrimination was considerably better when the median of the three median values for each variable was analysed, compared to the median value obtained at the first visit. There was also no statistical difference between VIIICAg/VIIIRAg (or VIIIC/VIIIRAg) ratios obtained from carriers of severe compared to mild haemophilia.

Analysis of factor VIII coagulant antigen in normal, thrombin-treated, and hemophilic plasma

The relationship between Factor VIII coagulant antigen (VIII:CAg) and Factor VIII-associated von Willebrand factor (VIII:vWF), and the effect of thrombin on VIII:CAg have been determined in plasma by using complexes of VIII:CAg and 125I-labeled human anti-VIII:CAg-Fab. Antibody-treated plasma samples were electrophoresed on NaDodSO4/polyacrylamide agarose gels and analyzed by autoradiography. The major VIII:CAg-125I-labeled Fab complex that persisted in NaDodSO4 had Mr 3.2 x 10(5). This Mr value was confirmed by column chromatography and sucrose density centrifugation and is presumed to reflect a free VIII:CAg of Mr 2.7 x 10(5). Minor bands were also present on autoradiograms of normal plasma corresponding to Mr values of 2.5, 1.85, and 1.7 x 10(5) (free VIII:CAg related proteins with Mr values of 2.0, 1.35, and 1.2 x 10(5), respectively). None of the VIII:CAg bands was present in plasma samples from five patients with severe hemophilia A. No radioactivity was associated with VIII:vWF multimers on NaDodSO4 gels. Thrombin treatment of normal plasma eliminated the radioactive band at 3.2 x 10(5) and increased the intensity of a band of Mr 1.7 x 10(5). Generation of this presumed VIII:CAg fragment of Mr is approximately equal to 1.2 x 10(5) coincided with a thrombin-induced increase in Factor VIII coagulant activity. These data demonstrate that the form of VIII:CAg detected in normal plasma is not covalently linked to VIII:vWF multimers and is absent in plasma from five hemophilia A patients. Thrombin-induced proteolysis of VIII:CAg can be detected in microliter quantities of normal plasma.

Factor VIII:C and VIII:CAg response in patients with haemophilia A and von Willebrand's disease after administration of different factor VIII concentrates or plasma

Factor VIII procoagulant activity (VIII:C) and factor VIII procoagulant antigen (VIII:CAg) were studied in seven patients with haemophilia A after administration of three different factor VIII concentrates or plasma. The in vivo recovery of VIII:CAg was less than that of VIII:C and the disappearance rate of VIII:CAg was much higher either when concentrates or plasma were given. The half-life of VIII:C was thus about 12 h but of VIII:CAg only about 3 h or less. Six patients with von Willebrand's disease were studied after administration of AHF-Kabi. In contrast to haemophilia A the discrepancy between VIII:C and VIII:CAg disappearance rates was not present in von Willebrand's disease, since both VIII:C and VIII:CAg showed a typical progressive increase. We conclude that factor VIII:C given to haemophilia patients does not behave like native VIII:C, not even when fresh plasma is used. Patients with von Willebrand's disease are capable of forming a normal VIII:C when appropriately stimulated.

Immunoradiometric assay of factor VIII: coagulant antigen using four human antibodies. Study of 27 cases of haemophilia A

Immunoradiometric assay (IRMA) of VIII:C antigen was performed using either IgG or monovalent Fab fragments from four antibodies arisen in polytransfused haemophilia A patients (titre between 100 and 1500 U/ml). Using IgG isolated by a solid or a liquid phase system, only the high titre (greater than or equal to 1000 U/ml) antibodies could be used for IRMA, with a sensitivity of 0.2% VIII:CAg. Using Fab fragments isolated by liquid phase, high and low (less than or equal to 150 U/ml) titre antibodies could be used and the IRMA was significantly improved with a 10-fold higher sensitivity. The affinity of the antibodies for VIII:CAg, studied by displacement curves using a modification of the IRMA, was found not to depend upon the titre of the antibody. Comparative levels of VIII:C and VIII:CAg in 27 cases of haemophilia A emphasize the heterogeneity of this disorder, two types of severe and three types of mild haemophilia being observed.

A radial immunodiffusion method for the assay of factor VIII:C Antigen (VIII:C Ag) in plasma

A method has been developed for the immunological quantitation of factor VIII:C Ag using a medium titre (50 new Oxford units) factor VIII:C antibody arising in a severe multitransfused haemophiliac. The method, which utilizes clotting inhibition in an agarose gel medium, gave close and significant correlation with the two-stage factor VIII:C procoagulant assay (r=0.83, P less than 0.01) for 54 normal subjects. Similar or higher values were found in 19 mild, moderate and severe haemophiliacs with 2-30% average normal plasma levels of factor VIII:C (r=0.72, P less than 0.01). Four mild von Willebrand patients gave similar results by immunoassay and procoagulant assay methods. A previously identified patient with cross reacting material (CRM+) gave an immunoassay within the normal range (66%) with only 4% VIII:C activity detectable. The method offers a simple, sensitive and apparently reliable procedure for the assay of plasma factor VIII:C Ag which may prove useful in the further investigation of factor VIII:C Ag and antibody heterogeneity. The procedure offers an alternative to immunoradiometric assay and may be of potential use in the assessment of the haemophilia carrier state and possibly the early detection of thrombosis.

Dual diagnosis of prenatal haemophilia A by measurement of fetal factor VIIIC and VIIIC antigen (VIIICAg)

Procoagulant factor VIII (VIIIC) and procoagulant factor VIII antigen (VIIICAg) were measured in 20 samples of pure fetal blood obtained by fetoscopy at mid-term from non-haemophilic fetuses. VIIIC levels ranged from 25 to 89 U/dl (mean 43.5) and VIIICAg from 11 to 43 U/dl (mean 22.3). Samples from 39 consecutive fetuses at risk of haemophilia A gave results indicating haemophilia in 11, and these pregnancies were terminated at the parents' request. Of the remaining 28, 18 have resulted in normal births, 8 still await delivery, and 2 pregnancies were terminated for non-haematological reasons. The results confirm that pure fetal blood can be aspirated fetoscopically for plasma assays of both VIIIC and VIIICAg. Dual measurement enhances the reliability of predicting or excluding haemophilia A, and makes prenatal diagnosis a dependable option for known or potential carriers seeking this information.

Immunoradiometric assay of procoagulant factor VIII antigen (VIIICAG)

An immunoradiometric assay of procoagulant factor VIII antigen was developed using a human antibody to the procoagulant activity of factor VIII (VIII:C). The assay measures specifically the antigen related to factor VIII procoagulant activity (VIIICAG) both in plasma and in serum. VIII:C and VIIICAG were measured in a group of healthy individuals and in a group of haemophilia A patients. In haemophilia A at least four groups can be recognised on the basis of the presence or absence of VIII:C and VIIICAG and the VIII:C/VIIICAG ratio.

Coagulation factors in the human fetus of about 20 weeks of gestational age

In plasma samples of 11 fetuses of about 20 weeks of gestational age the following coagulation factors have been determined (mean values found are given in parentheses): fibrinogen (0.30 U/ml), prothrombin (+/-0.17 U/ml), factor V (0.28 U/ml), factor VII (0.21 U/ml), factor VIII coagulant activity (factor VIII:C) (0.12 U/ml), factor VIII-related antigen (factor VIIIR:Ag) (1.04 U/ml), coagulant factor VIII-related antigen (factor VII:CAg) (0.19 U/ml), factor IX coagulant activity (0.05 U/ml), factor IX antigen (less than or equal to 0.03 U/ml), factor X (0,19 U/ml) and antithrombin III (AT-III) (0.23 U/ml). Our data support the evidence that prenatal diagnosis of haemophilia A is at present possible; less optimism is warranted where haemophilia B is concerned. the number of samples is sufficient to establish normal values for the age group. Means of quality control of the sample-which is often difficult to obtain-are disscussed.

Factor VII and fibrinolytic response to deamino-8-D-argenine vasopressin in normal subjects and dissociate response in some patients with haemophilia and von Willebrand's disease

Deamino-8-D-argenine vasopressin (DDAVP) was given by intravenous infusion to normal subjects, haemophiliacs and patients with von Willebrand's disease (vWd) and the factor VIII and plasminogen activator response was studied. In normal subjects and most patients with mild haemophilia and mild (intermediate) von Willebrand's disease there was an increase in plasminogen activator and all factor VIII related activities. In patients with mild vWd the prolonged bleeding time was shortened by DDAVP despite only a modest rise in factor VIII related Ristocetin cofactor activity (VIIIR:RiCoF). Sub-groups of patients have been characterized in whom atypical responses was observed. In two brothers with clinically severe haemophilia, but with 5--6 u/dl procoagulant factor VIII (VIIIC), there was an increase in VIIIC but no rise of the corresponding antigen, suggesting increased release of an antigenically abnormal poorly functioning molecule. A patient with intermediate vWd was studied in whom neither DDAVP, adrenaline infusion, nor venous occlusion resulted in an increase in either plasminogen activator or factor VIII related antigen (VIIRAg), although there was a significant increase in VIIIC. In a further patient with severe vWd, DDAVP failed to elicit any plasminogen activator or VIII response. The results obtained from these two patients suggested that in some individuals the presumed endothelial cell abnormality in vWd may be more extensive than a defect in VIIIRAg synthesis. Sub-groups of patients have been identified for whom treatment with factor VIII concentrates would be more appropriate than DDAVP prior to minor surgery.

Characterization of procoagulant activity produced by cultures of human monocytes and lymphocytes separated in colloidal silica-polvinylpyrrolidone gradients

Human peripheral blood leucocytes were examined for their ability to synthesize procoagulant activity in tissue culture. A method was developed utilizing silica coated with polyvinylpyrrolidone (Percoll) to separate monocytes from lymphocytes prior to culture. Coagulation activity was demonstrated in all mononuclear cell cultures after 24 hours incubation. This activity was inhibited by phospholipase C which suggested that tissue thromboplastin was the major source of activity. Specific immunoradiometric assays failed to demonstrate synthesis of factor VIII related antigen (FVIIIRAG) or factor VIII coagulant antigen. The results indicate that under conditions of this study factor VIII was not synthesized in mononuclear cell cultures.

Characteristics of the factor VIII protein and Factor XIII in various factor VIII concentrates

The in vitro properties of 5 factor VIII preparations (AHF-Kabi, Hemofil Hyland, AHF-Profilate Abbott, Kryobulin Immuno and Factorate High Purity Armour) and an ordinary cryoprecipitate were studied with reference to factor VIII clotting activity (VIII:C), factor VIII clotting antigen (VIII:CAg), factor VIII related antigen (VIIIR:Ag) (EI, IRMA, CIE), ristocetin cofactor activity (VIIIR:RCF), fibrinogen and factor XIII. All the preparations with the exception of Factorate had higher levels of VIII:CAg than VIII:C indicating inactivation of the biological activity of VIII:C during the procedure. AHF-Kabi (fraction I-0) and the cryoprecipitate, the only preparations capable of normalising the defect in patients with von Willebrand's disease, showed the same level of VIIIR:Ag determined by EI and by IRMA, while all the other preparations (i.e. cryoprecipitates purified further in different ways) had considerably lower levels of VIIIR:Ag determined by IRMA than by EI. Based on these in vitro techniques it seems to be possible to predict which preparations can be used successfully in patients with von Willebrand's disease, while no such conclusions can be made from VIIIR:RCF determinations. EI yielded similar concentrations of factor XIII a subunit in all the preparations tested. 3 functional assays showed high factor XIII activities in AHF-Kabi but low or no activities in the others. Thus, considerable differences were found on the in vitro properties of the proteins in 5 factor VIII concentrates and a cryoprecipitate. The action of proteases and the techniques used in the purification procedure are probably of crucial importance for the properties of the various factors.