Circulating factor VIII immune complexes in patients with type 2 acquired hemophilia A and protection from activated protein C-mediated proteolysis.

Factor VIII (FVIII) inhibitor antibodies are classified into 2 groups according to the kinetic pattern of FVIII inactivation. Type 2 antibodies are more commonly observed in patients with acquired hemophilia A and do not completely inhibit FVIII activity; in most cases, substantial levels of circulating FVIII are detected. Three type 2 autoantibodies from patients who had normal levels of FVIII antigen despite having low levels of FVIII activity were studied. The antibodies reacted exclusively with the light chain of FVIII but not with the C2 domain, and their epitopes were therefore ascribed to the regions in the A3-C1 domains. Heavy and light chains of FVIII were detected in plasma-derived immune complexes extracted by using protein G Sepharose. Direct binding assays using anhydro-activated protein C (anhydro-APC), a catalytically inactive derivative of activated protein C (APC) in which the active-site serine is converted to dehydroalanine, were used to examine the relation between immune complexes and APC. The intact FVIII, 80-kd light chain, and 72-kd light chain bound in a dose-dependent manner to anhydro-APC, with K(d) values of 580, 540, and 310 nM, respectively, whereas no appreciable binding was detected for the heavy chain. The 3 autoantibodies blocked FVIII binding to anhydro-APC by approximately 80% and consequently inhibited APC-induced FVIII proteolytic inactivation. These antibodies also bound to a synthetic peptide, His2009-Val2018, which contains the APC binding site. The findings suggest that binding of type 2 autoantibodies, recognizing residues His2009 to Val2018, protects FVIII from APC-mediated proteolysis and might contribute to the presence of FVIII immune complexes in the circulation.

Role of factor VIII C2 domain in factor VIII binding to factor Xa.

Factor VIII (FVIII) is activated by proteolytic cleavages with thrombin and factor Xa (FXa) in the intrinsic blood coagulation pathway. The anti-C2 monoclonal antibody ESH8, which recognizes residues 2248-2285 and does not inhibit FVIII binding to von Willebrand factor or phospholipid, inhibited FVIII activation by FXa in a clotting assay. Furthermore, analysis by SDS-polyacrylamide gel electrophoresis showed that ESH8 inhibited FXa cleavage in the presence or absence of phospholipid. The light chain (LCh) fragments (both 80 and 72 kDa) and the recombinant C2 domain dose-dependently bound to immobilized anhydro-FXa, a catalytically inactive derivative of FXa in which dehydroalanine replaces the active-site serine. The affinity (K(d)) values for the 80- and 72-kDa LCh fragments and the C2 domain were 55, 51, and 560 nM, respectively. The heavy chain of FVIII did not bind to anhydro-FXa. Similarly, competitive assays using overlapping synthetic peptides corresponding to ESH8 epitopes (residues 2248-2285) demonstrated that a peptide designated EP-2 (residues 2253-2270; TSMYVKEFLISSSQDGHQ) inhibited the binding of the C2 domain or the 72-kDa LCh to anhydro-FXa by more than 95 and 84%, respectively. Our results provide the first evidence for a direct role of the C2 domain in the association between FVIII and FXa.

Mapping of the minimal domain encoding a conformational epitope by lambda phage surface display: factor VIII inhibitor antibodies from haemophilia A patients.

Haemophilia A patients who receive repeated transfusion of fVIII concentrates often develop inhibitor alloantibodies, resulting in reduced efficacy of the therapy. Determination of fVIII epitopes for the alloantibodies is essential for an understanding of their inhibitory effect on blood coagulation. Random fragments of fVIII displayed on lambda phage particles were selected using two patient plasmas immobilized onto the surface of a microtiter plate. A set of clones defined the minimal domain that consisted of 157 amino acid residues including cysteine at both boundaries. The minimal domain absorbed most of the binding activities of the plasmas to fVIII, suggesting that the domain contains a major determinant for the plasmas. Site-directed mutagenesis and chemical denaturation of the domain confirmed that a tertiary structure formed by the disulfide bridge was recognized by the antibodies. The epitope domain defined overlaps with fVIII binding sites to vWf and phospholipid, and may play an important role in blood coagulation. Thus, the bacteriophage lambda surface display may be useful for mapping the minimal folding domain of various protein antigens that contain a conformational epitope.

The role of platelet von Willebrand factor in the binding of factor VIII to activated platelets.

Factor VIII binds to activated platelets and contributes to the tenase complex assembled on the platelet membrane surface. We have examined the role of platelet von Willebrand factor in the binding of factor VIII to platelets using a platelet captured enzyme-linked immunosorbent assay. Purified factor VIII bound to activated normal platelets in a dose dependent manner. Factor VIII also bound to platelets obtained from a patient with Type 2N von Willebrand disease, although in this case the binding was reduced to approximately 50% of that seen with control platelets. Furthermore, factor VIII bound to Type 3 von Willebrand disease platelets in the absence of detectable von Willebrand factor. In this instance the binding reaction appeared to be approximately 30% of that seen with the same number of normal platelets. An anti-A3 domain monoclonal antibody, NMC-VIII/10, which recognizes the amino-terminal acidic region of the factor VIII light chain, and an anti-C2 domain monoclonal antibody, NMC-VIII/5, which also moderates the binding of factor VIII to phosphatidylserine, inhibited the association between factor VIII and platelets. Inhibition was more remarkable with NMC-VIII/5 than with NMC-VIII/ 10 but not complete. The findings suggest that the binding of factor VIII to activated platelets is not based on a single ligand-receptor relationship, although a predominant role exists for the platelet von Willebrand factor. Furthermore, both the amino-terminal acidic region of the A3 domain and the C2 domain participate in the binding of factor VIII to activated platelets.

The canine factor VIII cDNA and 5' flanking sequence.

Factor VIII is a trace plasma glycoprotein involved as a cofactor in the activation of factor X by factor IXa. Inherited deficiency of factor VIII results in the X-linked bleeding disorder hemophilia A which has been documented in humans, horses, sheep and dogs. In this report, the putative proximal promoter, 5' untranslated region, complete coding sequence and 3' untranslated region of the canine factor VIII gene have been characterized. When compared to the human gene, the 5' flanking region shows conservation of transcription factor binding sites in the 5' untranslated region. Alignment of the amino acid sequence with that of the previously reported human, mouse and pig proteins demonstrates sequence identity of between 77 and 92% for the A1, A2, A3, C1 and C2 domains but an identity of only between 44 and 62% for the central B domain. The three thrombin cleavage sites are conserved in the canine sequence as are the protein C cleavage sites and the von Willebrand factor binding region. In addition, all six tyrosine residues that are known to undergo sulfation in the human protein are conserved in the dog. The 3' untranslated region of the canine gene extends 1.5 kilobases. The initial 700 basepairs of this sequence are highly GC rich and the sequence terminates with 2 alternative potential polyadenylation sites. The knowledge of this sequence, in combination with a well described canine model of hemophilia A, provides the necessary starting point for studies addressing the long-term evaluation of factor VIII gene therapy using a homologous transgene.

Factor VIII gene analysis in Japanese CRM-positive and CRM-reduced haemophilia A patients by single-strand conformation polymorphism.

Haemophilia A is the most common X-linked blood coagulation disorder; it is caused by deficiency of factor VIII activity (FVIII:C). Half of the affected patients do not have detectable levels of FVIII protein in their plasma, whereas about 5% have normal levels of the FVIII antigen (FVIII:Ag) (> 50 u/dl), and are called cross-reacting material (CRM) positive (CRM+ or A+). About 45% of patients have reduced levels of the FVIII:Ag (1-50 u/dl), classified as CRM reduced (CRM[R] or A[R]). We screened the FVIII gene of 13 Japanese patients (five CRM+ and eight CRM[R]) by single-strand conformation polymorphism, and identified 11 different mutations in 13 patients by analysing all 26 exons (Trp255Cys, Tyr473Cys, Gly479Arg, Arg531His, Thr667Arg, Arg1689Cys, Arg1941Gln, Arg2150His, Arg2159Cys, Thr2245Ala and Gly2285Val). Seven mutations were identified in the A domains (four in the A2 domain). All the mutations are point mutations resulting in missense codons. Four mutations (Trp255Cys, Thr667Arg, Thr2245Ala and Gly2285Val) have not been described previously.

Factor VIII Ise (R2159C) in a patient with mild hemophilia A, an abnormal factor VIII with retention of function but modification of C2 epitopes.

We found a patient with mild hemophilia A who had no detectable factor VIII antigen (FVIII:Ag), as shown by two-site ELISA using inhibitor alloantibodies (TK). We then analyzed A2, A2/B, and C2 antigen of the patient's DDAVP-induced FVIII using several anti-FVIII monoclonal antibodies. Factor VIII activity (FVIII:C) was increased from 12 to 42 U/dl by the administration of DDAVP. The DDAVP-induced increases in the A2 and A2/B antigens were 40 and 36 U/dl, respectively. However, the increase in the C2 antigen was only 7.5 U/dl. SSCP analysis and subsequent sequencing demonstrated an Arg to Cys transition at codon 2159. The anti-FVIII:C titer of monoclonal antibody, NMC-VIII/5 which recognized the C2 domain, against normal plasma was 450 Bethesda U/mg of IgG. However, the titer against DDAVP-treated patient's plasma was only 15 Bethesda U/mg. We also tested DDAVP-induced increase in the FVIII:Ag in another mild hemophilia A patient with the same mutation at Arg2159. Increase in his C2 antigen levels was only 19% of those in the A2 and A2/B antigen. We designate this abnormal FVIII as FVIII Ise. Our results show that a missense mutation at Arg2159 to Cys modifies the antigenicity of the C2 domain.

Preschool sarcoidosis mimicking juvenile rheumatoid arthritis: the significance of gallium scintigraphy and skin biopsy in the differential diagnosis.

Preschool sarcoidosis occurring in children less than 6 years old is rare and characterized by the triad of skin, joint and eye manifestations without any pulmonary lesion. Because of similar clinical manifestations, the diagnosis of preschool sarcoidosis and juvenile rheumatoid arthritis (JRA) is confusing. A girl with preschool sarcoidosis, initially diagnosed and treated as having JRA, is reported here. Ophthalmologic examinations revealed posterior involvement of the eye. A gallium scintigram of the head showed panda appearance. Biopsy of the cutaneous lesion demonstrated non-caseating granuloma. Gallium scanning may be an important clue to correct diagnosis.

Anti-factor VIII inhibitor alloantibodies recognizing the A2 domain in the human factor VIII heavy chain poorly bind to porcine factor VIII.

Anti-factor VIII (FVIII) inhibitor alloantibodies from 11 patients with hemophilia A, along with five anti-FVIII neutralizing monoclonal antibodies, were examined for differences in their reactivities with the A2 and C2 domains of human and porcine FVIII. None of the patients had been previously treated with porcine FVIII. Six inhibitors which specifically recognized the human FVIII C2 domain bound to both the 76-kDa porcine FVIII light chain and its 69-kDa proteolyzed fragments, showing cross-reactivity against porcine FVIII between 33 and 100%. Two A2-specific inhibitors did not react with porcine FVIII. The cross-reactivity was low (0-0.5%). The inhibitors recognizing both C2 and A2 reacted with the 76- and 69-kDa bands of porcine FVIII light chain, with cross-reactivity of between 11 and 33%. Monoclonal antibodies recognizing A1 (C-5) and A2 (JR8) did not react with the porcine FVIII. No anti-porcine FVIII neutralizing activity was detected in these antibodies. Monoclonal antibodies to the amino-terminal portion of A3 (NMC-VIII/10 and C-2) poorly reacted with the 76-kDa band, the cross-reactivities being 0 and 0.5%, respectively. NMC-VIII/5 recognizing C2 which competes with the C2-specific inhibitor, reacted with both the 76- and 69-kDa fragments showing cross-reactivity of 13%. These findings suggest that porcine A2 is antigenically different from human A2. The A2-specific inhibitor is a useful indicator for therapy with porcine FVIII.

Factor IX inhibition and epitope localization of factor IX inhibitor antibodies in haemophilia B patients with anaphylactoid reactions.

We describe the results of immunological studies, reaction kinetics and epitope localization of six inhibitor antibodies to factor IX (FIX) developed in severe haemophilia B patients. Three of the six patients had suffered recent anaphylactoid reactions to FIX concentrates, two others had in the past and one had none. All six inhibitors rapidly inactivated FIX activity in vitro, and the prominent immunoglobulin (IgG) subclass of the antibody was IgG4 when analysed with ELISA. Interestingly, we found an additional IgG1 component in the antibody samples from the patients who had recently experienced anaphylactoid reactions to FIX. When analysed with Western blotting in these three patients, the IgG4 antibody bound with enhanced affinity to the heavy chain or the light chain of FIX, and in two of the three the IgG1 antibody also bound strongly to the FIX heavy chain. The results suggest that the heavy chain of FIX might play a more significant role than the light chain in the pathogenesis of anaphylactoid reactions in haemophilia B patients with FIX inhibitors.

Measurement of anti-factor IX IgG subclasses in haemophilia B patients who developed inhibitors with episodes of allergic reactions to factor IX concentrates.

We have established a simple enzyme-linked immunosorbent assay (ELISA) for the detection of anti-factor IX IgG subclasses in haemophilia B patients with inhibitors. The assay was performed using immobilized purified factor IX. Specific IgG subclasses were detected by peroxidase-conjugated anti-human IgG1,2,3 and 4. Ten plasma samples from 6 haemophilia B patients with inhibitors ranging from 1.0 to 253 Bethesda Units/ml were analyzed. All samples were positive for IgG4. Six out of 10 samples were positive only for IgG4. Three samples were positive for IgG2. Five of the 6 patients had previously had allergic reactions to factor IX concentrates. Three patients had allergic episodes within the past month. Three samples from these latter patients taken on the day when the allergy had occurred showed positive also for IgG1. In later samples, however, taken at 4 days and 4 weeks respectively from two of these same patients. IgG1 was not detected. In two of the five patients in whom allergic reactions had occurred more than one month previously IgG1 was not detected. The results suggested that allergic reactions in patients with haemophilia B treated with factor IX concentrates were associated with the development of the specific IgG1 subclass of antibody to factor IX.

Common inhibitory effects of human anti-C2 domain inhibitor alloantibodies on factor VIII binding to von Willebrand factor.

Factor VIII (FVIII) inhibitor alloantibodies obtained from seven severe haemophilia A patients were examined for their binding regions and their effects on FVIII binding to von Willebrand factor (vWF). Immunoblotting analysis with a panel of recombinant fragments demonstrated that the binding regions of antibodies in cases 1-5 were contained in the C2 domain of the light chain. Antibodies from cases 1 and 2, which recognized an epitope within residues 2248-2312, completely inhibited FVIII/vWF binding in an ELISA (IC50: 5.0 and 9.0 micrograms/ml, respectively). Antibodies from case 3 recognizing 2170-2312 and case 5 recognizing 2170-2327 also inhibited FVIII/vWF binding (IC50: 110 and 400 micrograms/ml, respectively). Case 4 antibodies recognizing 2218-2307 showed barely detectable inhibition and cases 6 and 7 antibodies recognizing the 44 kD heavy chain, did not inhibit. Our results demonstrate that all anti-C2 alloantibodies with epitopes that extend to the residue 2312 inhibit vWF binding and that an overlap of the inhibitor epitope with residues 2308-2312 is critical for maximal inhibition of vWF binding. Prevention of FVIII/vWF binding appears to be a common property of anti-C2 domain inhibitor alloantibodies.

Measurement of anti-factor VIII IgG, IgG4 and IgM alloantibodies in previously untreated hemophilia A patients treated with recombinant factor VIII. Kogenate Japanese Clinical Study Group.

Using enzyme-linked immunosorbent assay (ELISA), we measured anti-factor VIII immunoglobulin G (IgG), IgG4 and IgM in serum samples obtained from hemophilia A patients treated with a recombinant factor VIII (rFVIII) preparation (Kogenate). Twelve pre- and post-treatment serum samples from 3 previously untreated patients who developed an inhibitor (alloantibody) were evaluated. Both rFVIII and plasma-derived factor VIII (pdFVIII) were used as antigen. Serum samples were diluted 37.5-fold. For the measurement of IgM antibody, protein A Sephadex suspension was added to the patients' serum samples and the supernatant was assayed. Anti-human IgG, IgG4, and IgM monoclonal antibodies labelled with peroxidase were added and absorbance at 450nm was determined. The reactivity of the IgG antibody with rFVIII and pdFVIII was extremely low. Samples containing the IgG4 inhibitor with a neutralizing activity of approximately 7.5 Bethesda units (BU)/ml resulted in absorbance values of 0.451-0.551, thus demonstrating a considerably high degree of sensitivity. The correlation between the neutralizing activity and reactions of the IgG4 antibody with rFVIII and pdFVIII antigens was high, with correlation coefficients of 0.912 and 0.966, respectively. Furthermore, the correlation coefficient between the measured absorbance values for the antibody reacted with pdFVIII and rFVIII was 0.961. No correlation was found between the reactivity of IgM to rFVIII and pdFVIII.

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.

A factor VIII neutralizing monoclonal antibody and a human inhibitor alloantibody recognizing epitopes in the C2 domain inhibit factor VIII binding to von Willebrand factor and to phosphatidylserine.

A neutralizing monoclonal antibody, NMC-VIII/5, recognizing the 72 kDa thrombin-proteolytic fragment of factor VIII light chain was obtained. Binding of the antibody to immobilized factor VIII (FVIII) was completely blocked by a light chain-specific human alloantibody, TK, which inhibits FVIII activity. Immunoblotting analysis with a panel of recombinant protein fragments of the C2 domain deleted from the amino-terminal or the carboxy-terminal ends demonstrated binding of NMC-VIII/5 to an epitope located between amino acid residues 2170 and 2327. On the other hand, the epitope of the inhibitor alloantibody, TK, was localized to 64 amino acid residues from 2248 to 2312 using the same recombinant fragments. NMC-VIII/5 and TK inhibited FVIII binding to immobilized von Willebrand factor (vWF). The IC50 of NMC-VIII/5 for the inhibition of binding to vWF was 0.23 micrograms/ml for IgG and 0.2 micrograms/ml for F(ab)'2. This concentration was 100-fold lower than that of a monoclonal antibody NMC-VIII/10 which recognizes the amino acid residues 1675 to 1684 within the amino-terminal portion of the light chain. The IC50 of TK was 11 micrograms/ml by IgG and 6.3 micrograms/ml by F(ab)'2. Furthermore, NMC-VIII/5 and TK also inhibited FVIII binding to immobilized phosphatidylserine. The IC50 for inhibition of phospholipid binding of NMC-VIII/5 and TK (anti-FVIII inhibitor titer of 300 Bethesda units/mg of IgG) was 10 micrograms/ml.

Changes in polypeptide-specific factor VIII antigen levels during whole blood clotting.

The time-course of factor VIII (FVIII) proteolysis during whole blood coagulation was monitored using polypeptide-specific enzyme-linked immunosorbent assays (ELISAs) developed with monoclonal antibodies to FVIII. Such assays of whole blood from normal subjects revealed that, within 30 min after coagulation had started, levels of the amino-terminal region of FVIII light chain and in the middle region of FVIII heavy chain had decreased to baseline in parallel with factor VIII procoagulant activity, but that levels of the 70 kDa thrombin digest decreased more slowly, with 75 U/dl of FVIII antigen (FVIII:Ag) remaining even after 2 h. Similar analysis of the blood of a patient with congenital hypoprothrombinemia indicated a lag phase of 20 min before proteolysis started. No significant change was observed until 1 h after calcium chloride was added to prothrombin-depleted plasma. On the other hand, in the presence of tissue thromboplastin, levels of FVIII:Ag in all ELISAs decreased rapidly. These results indicate a requirement for thrombin generation in the proteolysis of FVIII during the process of whole blood clotting.

Epitope localization of monoclonal antibodies against factor VIII light chain which inhibit complex formation by factor VIII with von Willebrand factor.

We obtained three clones of monoclonal antibodies against factor VIII by immunization with purified human factor VIII. The anti-factor VIII procoagulant activity of these antibodies ranged from 2 to 53 Bethesda units/mg of IgG. According to an immunoblotting study, all antibodies reacted with the 80 kDa light chain but not with 72 kDa peptides derived from thrombin digestion of factor VIII. We attempted to localize the antigenic epitopes of these antibodies by a competitive blocking assay using synthetic peptides and recombinant fragments of the amino-terminal region of factor VIII light chain. In the former assay, a 50 microM peptide containing the fifteen amino acid residues from the Val1670-Glu1684 completely inhibited the binding of the three monoclonal antibodies to immobilized factor VIII. In the latter experiment, 13 reactive recombinant peptides were obtained. Sequences of these peptides revealed fourteen overlapped amino acid residues from Glu1675 to Pro1688. All three antibodies at a final concentration of around 10 micrograms/ml completely inhibited the binding of 125I-labelled factor VIII to immobilized von Willebrand factor (vWF). We conclude that ten amino acid residues, 1675EDFDIYDEDE1684 in the factor VIII light chain are important for complex formation with vWF.

[Properties of factor VIII/von Willebrand factor in two highly-purified factor VIII concentrates, Hemofil M and Monoclate, using monoclonal antibodies].

Properties of F. VIII/vWF in highly-purified factor VIII concentrates were examined using monoclonal antibodies. The F. VIII: C levels obtained with the chromogenic assay agreed with those obtained with the one-stage clotting method. The ratio between F. VIII: Ag and F. VII: C in Hemofil M and Monoclate was 1.09 and 1.34, respectively. The F. VIII: Ag levels assayed by monoclonal ELISAs were the same as those assayed by polyclonal ELISA, except that those assayed by C 5-ELISA tended to be higher. The ratio between F. VIII: Ag and vWF: Ag in Hemofil M and Monoclate was 105 and 45, respectively. Both concentrates lacked the large multimers of vWF and showed the intensification of the satellite bands. SDS-PAGE patterns showed almost no contamination. Immunoblot analysis revealed that F. VIII in both concentrates could react with 6 kinds of monoclonal antibodies to F. VIII. These results suggest that the fundamental structure of F. VIII molecule for coagulant activity in both concentrates are preserved.