Response of patients with mild and moderate hemophilia A and von Willebrand's disease to treatment with desmopressin

Desmopressin was administered intravenously to 68 patients with hemophilia and von Willebrand's disease of mild or moderate severity to assess the safety, reproducibility, and range of response to this new therapeutic alternative. A rise in factor VIII-von Willebrand factor levels was seen in 64 patients, and the magnitude was sufficient to provide normal hemostasis in 55 to 68 spontaneous or traumatic bleeding episodes, dental procedures, or operations. Thus, our experience shows that most patients with mild or moderate hemophilia and von Willebrand's disease can be treated effectively without plasma derivatives. Patients who had two or more infusions of desmopressin at different times had similar responses each time, and members of the same family also had similar responses after desmopressin infusions. Because this drug can be administered without significant side effects, it should have an important role in the management of patients with mild or moderate hemophilia and von Willebrand's disease.

Prenatal diagnosis of haemophilia A by factor VIII gene analysis

Cloned factor VIII deoxyribose nucleic acid (DNA) sequences were used as probes in the prenatal diagnosis of haemophilia A. Fetal DNA from cultured amniotic fluid cells was examined for a DNA polymorphism within the factor VIII gene which marked the haemophilia A gene in the pregnant obligate carrier. The fetus was predicted to be an affected male, and the diagnosis of haemophilia A was confirmed both in utero and after termination of the pregnancy.

Prenatal diagnosis of classic hemophilia (hemophilia A) by immunoradiometric assays

During the period from 1978 to 1983, 92 pregnancies have been evaluated by fetoscopy for the prenatal diagnosis of hemophilia A. Satisfactory fetal plasma samples were obtained in 80 instances and the diagnosis--or exclusion--of hemophilia was made by immunoradiometric assay of the factor VIII coagulant protein (VIII:CAg). The accuracy of the diagnosis established by fetoscopy has been verified after delivery or termination, and there have been no misdiagnoses resulting from laboratory error. Additional evidence for the accuracy of the analysis was the observation that the frequency of hemophilia in pregnancies of obligate carriers of the hemophilia gene, and of women whose plasma assays were indicative of the carrier state, was 29 of 59 fetuses at risk. In one case of cross-reacting material-positive hemophilia, samples obtained at fetoscopy and from the newborn infant had normal VIII:CAg levels but the infant had decreased factor VIII procoagulant activity. There were five fetal deaths resulting from fetoscopy in 55 pregnancies not intentionally terminated. Although only a small percentage of pregnant hemophilia carriers in the United States have elected to undergo fetoscopy for prenatal diagnosis, this procedure has allowed a number of pregnancies to go to term with delivery of normal males in families that were not willing to accept the risk of a hemophilic child. In eight instances, fetoscopic evaluation was sought for two successive pregnancies.

The effect of 1-deamino 8 D-arginine vasopressin (DDAVP) in a nonhaemophilic patient with an acquired type II factor VIII inhibitor

DDAVP (1-deamino 8 D-arginine vasopressin) was administered on two occasions to a patient with an acquired factor VIII inhibitor. Because the patient's autoantibody was low titre (1.8 Bethesda units) and had type II kinetic properties, it was expected that endogenous factor VIII/VWF released by DDAVP would be inactivated at a slow enough rate to permit satisfactory haemostasis during dental procedures. In both instances there was a 7-9-fold increase in factor VIII above the baseline level (13 units/dl), and factor VIII activity remained above 35 units/dl for 5 h after the infusion. The inhibitor could not be detected in his plasma during this period and the activated PTT was shortened into the normal range. Our experience with this patient suggests that DDAVP has a role in the management of some patients with low titre autoantibodies that inactivate factor VIII.

The idiotypic characteristics of human antibodies to factor VIII

We have prepared an antiidiotype antibody that specifically reacts with and inactivates a human autoantibody to factor VIII (VIII:C). The antiidiotype specificity of this rabbit antibody was evident in solution, as specific inhibition of anti-VIII:C activity, and in solid-phase studies. The antiidiotype antibody inhibited both plasma anti-VIII:C and Fab' fragments prepared from that plasma's IgG. Although the antibody had a greater inhibitory effect on the anti-VIII:C used for immunization than it did for other anti-VIII:C, partial inhibition was identified with ten of 25 other human anti-VIII:C. The demonstration that antiidiotype antibodies can be prepared to human anti-VIII:C indicates the feasibility of this approach to the immunochemical characterization of human anti-VIII:C inhibitors. Moreover, antiidiotype reagents have a potential role in the treatment of inhibitor patients.

Immunochemical characterization of factor VIII inhibitors

Factor VIII inhibitors are antibodies, predominantly of the IgG class, that inactivate factor VIII procoagulant activity. They do not fix complement and cannot be detected by standard immunoprecipitin assays. Their immunochemical properties are unusual, for the alloantibodies have consistent light chain restriction (kappa) and most allo- and auto- anti-VIII:C are predominantly or exclusively IgG4. This property may be responsible for the lack of complement fixation and immunoprecipitation. Human anti-VIII:C react with several different VIII:C antigenic determinants, and recent studies have begun to characterize the major epitopes. In addition, anti-VIII:C idiotypes have been identified using both rabbit anti-idiotype serum and monoclonal antibodies. These reagents provide a new way to obtain more precise immunochemical characterization.

Von Willebrand factor multimer patterns in von Willebrand's disease

The von Willebrand factor antigen (factor VIII-related antigen, VIIIR:Ag) multimer pattern has been analysed by SDS-agarose electrophoresis of plasmas from 116 patients (47 families) with von Willebrand's disease. In addition to previously recognized patterns, a subclassification was established between plasmas that had a type Ia pattern (VIIIR:Ag multimer pattern like that of normal plasma) and those that had a type Ib pattern in which there was a relative reduction in the concentration of the larger VIIIR:Ag multimers even though all multimeric forms were present. The different patterns were consistent within families and were inherited by autosomal dominant transmission. Von Willebrand's disease heterogeneity was apparent in the distribution of these plasmas: type Ia, 43 patients in 18 families; type Ib, 39 patients in 15 families; type II, 22 patients in 10 families, one of which was further classified as type IIB, one of which was type IIC, and three were IIA. Seven patients with severe von Willebrand's disease were also studied. In general, the interpretation of SDS-agarose multimer patterns corresponded to those previously obtained by crossed immunoelectrophoresis, but the former technique was more sensitive and could identify differences that were not apparent by crossed immunoelectrophoresis.

Development of an inhibitor specific to factor VIII: coagulant activity in a patient with platelet-type von Willebrand's disease

Platelet-type von Willebrand's disease is a recently described autosomal dominant bleeding disorder characterized by decreased ristocetin cofactor activity, lack of the higher molecular weight von Willebrand Factor (vWF) multimers on SDS agarose gel electrophoresis, increased platelet aggregation with low concentrations of ristocetin, and increased ristocetin-induced binding of normal vWF to patient platelets. In this report the authors describe a 17-month-old male with Platelet-type von Willebrand's disease, inherited from the paternal side of his family, who developed an inhibitor specific to Factor VIII:C. The patient's plasma inhibited normal plasma VIII:C and partially purified VIII:C; it did not appear directed against normal VIIIR:Ag or ristocetin cofactor. This antibody is therefore similar to inhibitors that develop in some transfused hemophilia A patients. Since low VIII:C, VIII:CAg, and VIII:C/VIIIR:Ag ratio were encountered in his mother, it is likely that this patient has inherited hemophilia A in addition to Platelet-type von Willebrand's disease.

Detection of hemophilia carriers during pregnancy

The accuracy of hemophilia A carrier detection during pregnancy has been determined using combined measurement of VIII:CAg and VIIIR:Ag. These immunoassays detect determinants that are sufficiently stable in plasma that the assays could be done on frozen samples that had been obtained when women were seen for antenatal diagnosis studies (carrier women) or for routine prenatal care (controls). A linear discriminant was calculated that best separated the data for 32 normal women and 25 obligate carriers of the hemophilia gene. Twenty-three of 25 carriers (92%) and all 32 control women were correctly identified in this analysis. The overall classification accuracy (55/57, 96%) is comparable to that obtained by VIII:C and VIIIR:Ag measurements using freshly drawn blood samples in nonpregnant individuals. This study demonstrates that hemophilia A carriers can be detected during pregnancy with sufficient accuracy that the information may be used for genetic counseling.

Inactivation of factor VIII coagulant activity by two different types of human antibodies

Human antibodies that inactivate factor VIII procoagulant activity (VIII:C) are heterogeneous in their kinetic properties. We report there here the properties of four type I and four type II antibodies classified according to Biggs et al. Type I antibodies have second-order inactivation kinetics and completely destroy VIII:C when present in high concentration; type II antibodies have more complex kinetics and do not completely inactivate VIII:C even when tested undiluted. The latter properties correspond to the in vivo finding in some patients that there is detectable VIII:C, even though there is also a significant inhibitor titer. It has been suggested that the antibody-antigen complex in these patients retains some VIII:C activity. This is unlikely, however, since protein-A-Sepharose (PAS) did not adsorb any VIII:C activity from mixtures of type II antibodies with normal human plasma. An alternate possibility, reduced VIII:C inactivation due to a steric effect the factor-VIII-related protein (VIIIR, von Willebrand factor), appears to be a more important factor, since three of four type II antibodies had inactivating properties like type I antibodies when they were tested with separated VIII:C instead of plasma. Although the fourth type II antibody did not completely inactivate separated VIII:C the residual coagulant activity was adsorbed from this mixture by PAS. These data indicate that type II anti-VIII:C react with different antigenic determinants than type I antibodies and that these determinants are partially blocked in the factor VIII complex by VIIIR.

Cultured endothelial cells derived from the human iliac arteries

Cells derived from the endothelium of human iliac arteries were cultured in vivo. The cells were isolated, grown, and subcultured in HEPES buffered Medium 199 supplemented with 20% heat inactivated human whole blood serum, human alpha-thrombin, and commercial endothelial cell growth supplement derived from bovine brain. The cells were viable in culture for 8 to 10 passages at a split ratio of 1:3. After the 10th passage, the cells began to enlarge and their growth rate was reduced. No cultures were viable after the 12th passage. The cells were determined to be of endothelial origin by their morphology at confluence; their ultrastructural characteristics, including the presence of Weibel-Palade bodies; the production and release of factor VIII-related antigen; and by their maintenance of a surface that prevented platelet attachment. The cultured arterial endothelial cells released prostacyclin in response to challenge with thrombin and protamine sulfate but not in response to bradykinin or the platelet-derived growth factor. Although the cultures described in this report were derived from patients with varying degrees of atherosclerotic disease, there were no significant differences in morphological or physiological parameters among these cultures or in comparison with commonly studied cells derived from human umbilical veins.

Distribution of plasma fibronectin (cold-insoluble globulin) and components of the factor VIII complex after heparin-induced precipitation of plasma

Factor VIII procoagulant (VIII:C) activity, factor VIII coagulant antigen (VIII:CAg), von Willebrand ristocetin cofactor (VIIIR:RC) activity, factor VIII-related antigen (VIIIR:Ag), and plasma fibronectin (CIg; cold-insoluble globulin) were measured in the heparin precipitable fraction (HPF) and heparin supernatant fraction (HS) of normal human plasma. Following heparin induced precipitation, most measurable VIII:C activity (77% +/- 24%) was recovered in the HS. Although there was little VIII:C activity (less than 1%) in the HPF, 20% +/- 6.5% VIII:CAg was present as well as CIg (81% +/- 5.6%). VIIIR:RC activity (72% +/- 12%), and VIIIR:Ag (34 +/- 5.2%). As assessed by Na dodecyl SO4 glyoxyl agarose electrophoresis, the multimeric forms of plasma VIIIR:Ag could be resolved into a series of bands. Larger multimers tended to precipitate with the HPF whereas the smaller multimers tended to remain supernatant. Plasma from a subject with congenital afibrinogenemia was also studied. Although the afibrinogenemic HPF contained CIg, neither VIIIR:RC activity nor VIIIR:Ag was precipitated. However, both were present in the HPF from afibrinogenemic plasma to which fibrinogen had been added, suggesting that they are incorporated in this precipitate because of an affinity for fibrinogen. The ability of heparin to induce precipitation of CIg while leaving most VIII:C activity in the supernatant plasma may be useful in the preparation of procoagulant-rich plasma subfractions, since VIII:C can subsequently be recovered in good yield by cryoprecipitation.

Normal pregnancy in a patient with a prior postpartum factor VIII inhibitor: with observations on pathogenesis and prognosis

A 22-yr-old primigravada developed a hemorrhagic diathesis 6 days after delivering a normal female infant and was found to have an immunoglobulin inhibitor of factor VIII (15 Bethesda units). The patient was treated with prednisone and the bleeding stopped soon thereafter. Her inhibitor titer decreased over the next 8 mo, at which time no inhibitor was detectable. Nine months later she became pregnant again and proceeded to have an uneventful pregnancy and delivery of a normal female infant without evidence of a recurrence of the inhibitor. Studies of 3H-thymidine incorporation into the patient's lymphocytes in the presence of her own plasma or plasmas from her husband, normals, a von Willebrand patient, and a hemophilic patient yielded equivocal results. Analysis of VIII:CAg using 2 different antisera failed to discern immunologic differences between the VIII:CAg of the patient, her husband, or her first child. A review of the literature revealed that there were no recurrences with second pregnancies in any of the 8 patients with postpartum factor VIII inhibitors whose inhibitors had completely disappeared prior to delivery. While the pathogenesis of this disorder remains uncertain, the apparently favorable prognosis for such patients should be considered in counselling with regard to future pregnancies.

The factor VIII complex: structure and function

Normal human plasma contains a complex of two proteins that are important in hemostasis and coagulation. The factor VIII procoagulant protein (antihemophilic factor) and the factor VIII-related protein (von Willebrand factor) are under separate genetic control, have distinct biochemical and immunologic properties, and have unique and essential physiologic functions. While the nature of their interaction and the details of the biochemical structures remain to be determined, the information now available permits a preliminary understanding of the molecular defects in hemophilia and von Willebrand's diseases.

Synthesis and release of factor VIII by cultured human endothelial cells

Endothelial cells (ECs) derived from human umbilical veins were cultured in order to study the physiological control of factor VIII synthesis and release. The culture media were studied from multiple replicate cultures at confluence. Factor VIII related antigen (VIIIR:Ag) and factor VIII coagulant antigen (VIII:CAg) were measured by sensitive immunoradiometric assays. De novo synthesis of factor VIII related protein (VIII:R) was quantitated by incorporation of labelled amino acids into specific protein subunits. The following agents were added to the culture medium in a range of concentrations from physiological to pharmacological: adrenaline, 5 hydroxytryptamine, 2,3-DPG, cyclic AMP, thyroxine, hydrocortisone, and human growth hormone. None of them had any effect at any concentration on the rate of accumulation of VIIIR:Ag in the culture medium. Addition of exogenous factor VIII had no effect on do novo synthesis of VIII:R. VIII:CAg was found to be stable under the conditions of culture but none was released from the ECs. Long-term monocyte cultures also failed to release VIII:CAg. It appears that VIII:R is a constitutive gene product of umbilical vein endothelial cells and that VIII:CAg is not made by these cells.

The effect of thrombin on human factor VIII. Cleavage of the factor VIII procoagulant protein during activation

Human VIII: C has been partially purified by immunoabsorbent chromatography and agarose gel filtration in the presence of 2 mM DFP. The ratio of VIII:C to VIIIR:Ag in these preparations was greater than 1000:1, and the VIII:C procoagulant and immunologic (VIII:CAg) activities eluted together from Sephadex G-200 with a Kav of 0.05, a value consistent with a Stokes radius of 88 A. The molecular weight estimated from this measurement and sucrose density-gradient centrifugation studies (8.2S) is 285,000. VIII:C activation was detected when the purified procoagulant was incubated with 2 x 10(-5) to 10(-2) U/ml highly purified human alpha-thrombin. Although 2 mM DEP inhibits VIII:C activation by alpha-thrombin, DFP added after activation did not prevent subsequent loss of activity. When VIII:C was incubated for 4 hr with dilute alpha-thrombin, 2 x 10(-5) to 2 x 10(-3) U/ml, the activated procoagulant (VIII:C/VIII:CAg > 1) eluted from Sephadex G-200 with a Kav of about 0.2 This gel filtration pattern corresponds to a protein with a Stokes radius of 60 A and, taken together with a preliminary estimate of sedimentation properties (5S), suggests a molecular weight of about 116,000. Higher concentration of thrombin, 10(-3) to 10(-1) U/ml, inactivated VIII:C in these experiments, and the nonfunctional protein was identified by VIII:CAg immunoassay. The inactivated VIII:CAg eluted from Sephadex G-200 in a broad peak of Kav approximately 0.3. THese data suggest that alpha-thrombin activates and inactivates human VIII:C by proteolytic modification of VIII:C structure and that thrombin-activated VIII:C is smaller than the unactivated procoagulant.

Factor VIII-related protein circulates in normal human plasma as high molecular weight multimers

The size of human factor VIII-related protein in plasma has been determined by sodium dodecyl sulfate (SDS) glyoxyl agarose electrophoresis. The protein was immobilized after the electrophoresis by coupling it to the modified agarose, and it was identified by autoradiography using purified rabbit anti-factor VIII-related antigen (VIIR:Ag). A series of multimeric forms was identified with Mr of 0.85-12 x 10(6). The distribution of VIIR:Ag multimers was the same in heparin and citrate anticoagulated plasmas and in serum, and the pattern was the same after freezing as in plasma kept at 37 degrees C from the time of venipuncture until the electrophoresis was complete. These observations indicate that VIIR:Ag circulates in normal plasma as a population of very large multimers and that the size distribution is not an artifact induced by purification methods, freezing, or calcium chelation.

Prenatal diagnosis of classic hemophilia

Prenatal diagnosis of classic hemophilia (hemophilia A) in mid-trimester was achieved by means of immunoradiometric assays for factor VIII on fetal plasma and amniotic-fluid mixtures obtained by fetoscopy. Samples were analyzed from six male fetuses at risk for severe hemophilia and from nine control fetuses for which fetoscopy was carried out to attempt prenatal diagnosis of other genetic disorders. The factor VIII coagulant-antigen values for the control (non-hemophilic) samples were 17 to 94, and the factor VIII related-antigen concentrations were 50 to 155 U per deciliter. Three of the fetuses at risk for hemophilia had factor VIII values in the control range, and these infants were normal at birth. The other three fetuses had low concentrations of factor VIII coagulant antigen but normal concentrations of factor VIII related antigen. These values and the diagnoses of severe hemophilia were confirmed with blood from the abortuses.

Immunoradiometric measurement of the factor VIII procoagulant antigen

A fluid-phase immunoradiometric assay has been developed which identifies an antigen on the Factor VIII (antihemophilic factor) procoagulant protein. This sensitive and quantitative assay is not influenced by levels of Favor VIII-related antigen (von Willebrand factor) or other plasma proteins. There is a close correlation of procoagulant activity and immunologically detectable protein in normal and von Willebrand's disease plasmas. In contrast, several different patterns have been identified in hemophilic plasmas. Neither procoagulant activity nor procoagulant antigen is detectable in plasmas from patients with severe classic hemophilia. Patients with mild and moderate hemophilia have either comparable plasma concentrations of procoagulant activity and procoagulant antigen or relatively greater levels of immunologically detectable protein.

Thrombin activation of factor VIII. II. A comparison of purified factor VIII and the low molecular weight factor VIII procoagulant

The current experiments examine the reaction between purified human alpha-thrombin and purified human factor VIII and compare this with the reaction between alpha-thrombin and the low molecular weight factor VIII procoagulant activity obtained by high ionic strength dissociation. The reaction patterns of both procoagulants are similar, demonstrating in initial increase in factor VIII activity followed by a decay of procoagulant activity. The extent of activation which is observed in the initial phase decreases with lower temperatures and with lower thrombin concentrations. A pseudo-first order relationship is demonstrated for the activation phase. The labile factor VIII procoagulant activity produced by the initial action of thrombin appears to be intrinsically unstable, since the addition of hirudin or diisopropylfluorophosphate does not prevent the subsequent decay of the procoagulant activity. The similar activation and decay patterns of purified factor VIII and the dissociated low molecular weight factor VIII procoagulant support the concept that the low molecular weight procoagulant itself represents the functional coagulant moiety of the factor VIII complex.

The properties of immune complexes formed by human antibodies to factor VIII

Although human antibodies to Factor VIII inactivate its procoagulant activity, they do not form immunoprecipitates when tested with this antigen. To understand this observation, we have examined the interaction of normal human Factor VIII with four high-titer human anti-Factor VIII, two from transfused hemophiliacs and two "spontaneous" antibodies from nonhemophilic individuals. An estimate of the size of complexes formed by these antibodies has been obtained by agarose gel filtration of mixtures of anti-Factor VIII with cryoprecipitate. Complexed anti-Factor VIII was detected by the method of Allain and Frommel: acid dissociation of complexes at pH 3.5. Complexed anti-Factor VIII was detected in column fractions eluting between the void volume and those which correspond to the elution volume of human IgG. In contrast, Factor VIII procoagulant activity was restricted to void volume fractions when separations were carried out in antigen excess, and free anti-Factor VIII was limited to late-eluting fractions when separations were carried out in antibody excess. A small proportion of the complexed anti-Factor VIII was present in void volume fractions; the quantity was directly related to the ratio of antibody to antigen.Thus, although some complexed anti-Factor VIII is detected in void volume fractions, as would be expected for complexes formed with a very large plasma protein, most immune complexes elute in fractions that indicate interaction with a smaller antigen. These findings suggest that human anti-Factor VIII inactivates procoagulant activity by forming a complex with a small, apparently univalent, component of Factor VIII. This property may prevent immunoprecipitate formation.

Stabilization of factor VIII in plasma by the von Willebrand factor. Studies on posttransfusion and dissociated factor VIII and in patients with von Willebrand's disease

In normal plasma, the ratio of the procoagulant activity of factor VIII (VIII(AHF)) to that of the von Willebrand factor activity (ristocetin cofactor, VIII(VWF)) or factor VIII antigen (VIII(AGN)) is approximately 1, but ratios > 1 (e.g., VIII(AHF) > VIII(VWF) or VIII(AGN)) may be observed in some patients with von Willebrand's disease and in the "late" posttransfusion plasmas of patients with this disorder. The lability of VIII(AHF) was studied by incubating plasma, diluted 1:10 in imidazole buffer pH 7.1, for 6 h at 37 degrees C. With normal plasmas, 77+/-12% (SD) of the original VIII(AHF) activity remained after incubation. VIII(AHF) was labile (e.g., 35-55% residual activity) in the "late" posttransfusion plasmas (VIII(AHF) >> VIII(VWF)) of a patient with von Willebrand's disease, but not in the "early" posttransfusion plasmas (VIII(AHF) approximately VIII(VWF)). VIII(AHF) was also labile in the (base-line) plasmas of three patients with von Willebrand's disease in whom the ratios of VIII(AHF) to VIII(VWF) were 4.4 to 8.1, but not in the plasmas of four other patients in whom the ratio was approximately 1. The electrophoretic mobility of factor VIII antigen was increased in two of the three patients with labile VIII(AHF). In both of these patients, and in the late posttransfusion plasmas, labile VIII(AHF) activity could be stabilized by the addition of purified von Willebrand factor (lacking VIII(AHF) activity) or by hemophilic plasma, but not by plasmas of patients with severe von Willebrand's disease. Thus, VIII(VWF) may serve to stabilize VIII(AHF) and this might explain the posttransfusion findings in von Willebrand's disease.

Thrombin activation of factor VIII: the effect of inhibitors

Factor VIII is a large glycoprotein which can be separated into a high molecular weight component which retains factor VIII-related antigens and supports ristocetin-induced platelet agglutination, and a low molecular weight component which has procoagulant activity. It has been suggested that this separation, observed in high ionic strength buffers, might be the consequence of proteolysis by plasma proteins. To consider this possibility, we have examined the interaction of the proteolytic enzyme thrombin with factor VIII. This study, carried out with highly purified materials, has used thrombin-mediated factor VIII proagulant activation as an indicator of this interaction. Several proteolytic inhibitors have been studied to determine their ability to inhibit factor VIII activation by thrombin. Under the current experimental conditions, diisopropylfluorophosphate (DFP) and hirudin inhibited the reaction, while heparin was an effective inhibitor only when plasma proteins were added. Benzamidine inhibited factor VIII activation when used at high concentrations, and phenylmethyl sulphonylfluoride and soybean trypsin inhibitor were found to be ineffective. These results show that DFP and hirudin prevent thrombin alteration of factor VIII and will be useful in purification and characterization studies of the factor VIII molecule.

A co-operative study for the detection of the carrier state of classic hemophilia

To determine the specificity and sensitivity of current technics for detecting carriers of classic hemophilia, three investigators simultaneously tested obligate carriers and noncarriers for immunologic and procoagulant factor VIII activity. Overall correct classification ranged from 72 per cent (36 of 50) to 94 per cent (47 of 50). The maximum accuracy obtained with the same linear-discriminant-function method on all data was 90 per cent (26 of 29) in detecting carriers without misclassifying normal persons as carriers (none of 21). Lowest accuracy by the same technic was 66 per cent (19 of 29) carrier detection while misclassifying 19 per cent (four of 21) normal persons. Precision of testing for both factor VII activity and antigen was high (standard deviations from 0.004 to 0.026 on a log scale). Differences between participants seemed related to laboratory technics rather than to statistical methods. The factor VIII activity/antigen measurement is a valid technic for detecting in the carrier state of hemophilia A.

von Willebrand's disease and hemorrhagic telangiectasia: association of two complex disorders of hemostasis resulting in life-threatening hemorrhage

The clinical and laboratory findings in a patient with uncontrolled gastrointestinal bleeding secondary to combined hemostatic defects (von Willebrand's disease and hemorrhagic telangiectasia) are described. Evidence for von Willebrand's disease was found in five family members, but no other affected relative was found to have hemorrhagic telangiectasia. Complete assestivity, factor VIII antigen and von Willebrand factor levels. The patient described also was evaluated for her response to transfusion utilizing these same measurements. Previous reports of the coexistence of hemostatic defects with hereditary hemorrhagic telangiectasia are reviewed. The importance of complete hemostatic evaluation of patients with mucocutaneous bleeding is stressed in light or current knowledge of the diagnostic specificity of available laboratory tests.

Rabbit factor VIII: identification of size heterogeneity

Two forms of rabbit factor VIII procoagulant activity, distinguishable by size on gel filtration and ultracentrifugation, have been identified in normal rabbit plasma. These studies have been carried out with citrate-anticoagulated rabbit plasma obtained by cardiac puncture. Two peaks of factor VIII activity were obtained on agarose gel chromatography, using physiologic ionic strength buffers: a high molecular weight peak eluting at the void volume and a second peak eluting with smaller plasma proteins. The presence of high and low molecular weight factor VIII activities was confirmed by sucrose density gradient centrifugation. The two peaks of factor VIII activity remained distinct when proteolytic inhibitors were added to the plasma and eluting buffers. Both the high and low molecular weight factor VIII procoagulant activities were inhibited by antibodies to human and rabbit factor VIII, and both were activated by thrombin. The identification of size heterogeneity of factor VIII in normal rabbit plasma, in the absence of any modification by ionic strength, may permit more satisfactory study of the relationship of factor VIII size to function.

The effects of epinephrine infusion in patients with von Willebrand's disease

Epinephrine infusion causes variable increases in the components of the Factor VIII (antihemophilic factor) complex in patients with von Willebrand's disease. The increase in antihemophilic factor procoagulant activity was greater than that of Factor VIII-related antigen and von Willebrand factor activity in two patients with von Willebrand's disease. Similar increases in the three individual factors were demonstrated in two other patients. A 4-10-fold increase in Factor VIII-related properties was identified in each of these individuals after infusion. One patient has been studied with very severe von Willebrand's disease; none of the Factor VIII-related properties increased despite two infusions of epinephrine. Bleeding times were normalized or remained normal in the two patients whose von Willebrand factor activity was greater than 25 U/100 ml. It remained prolonged in those three patients whose von Willebrand factor activity levels remained below that concentration. The increase in procoagulant activity was transient in all patients and t 1/2 values were estimated to be between 0.8 and 3.4 h.

Determination of the von Willebrand's disease antigen (factor VIII-related antigen) in plasma by quantitative immunoelectrophoresis

Measurement of the von Willebrand's disease antigen (factor viii-related antigen) has become an increasingly useful tool in the differential diagnosis of those disorders of hemostasis characterized by an abnormality of factor viii procoagulant activity. Optimal conditions for assay of the von Willebrand's disease antigen in plasma by the quantitive immunoelectrophoretic technique are described. Potential sources ofsystematic error have been evaluated and a dilution effect has been identified.

Implications of immunologic methods for measuring antihemophilic factor (factor VIII)

Recent immunologic studies have provided important new information about the nature of AHF deficiency diseases and the structure and synthesis of this protein. They provide, moreover, a considerably improved ability to identify the carrier state in hemophilia A. Additional progress may be possible in the identification of carriers and of hemophilic patients at risk of antibody formation, but it will require a different approach to these problems. While preliminary goals have been obtained by using antibodies that identify antigenic determinants shared by normal and nonfunctional AHF, further progress will require the capacity to identify differences between the normal protein and the nonfunctional AHF-like molecules in hemophilic plasma.

Immunofluorescent localization of antihemophilic factor antigen and fibrinogen in human renal diseases

Tissue localization of antihemophilic factor (AHF, factor VIII) antigen and fibrinogen by immunofluorescent microscopy was determined in 146 specimens of normal and diseased kidneys. AHF antigen was present in the endothelial cells of glomeruli, peritubular capillaries, arteries, and veins of normal kidneys; a distribution similar to that in other tissues. In scleroderma and malignant hypertension, deposition of AHF antigen and fibrinogen was limited to the markedly thickened endothelial layers of arteries. More extensive intense deposition of both AHF antigen and fibrinogen in glomeruli and in arterial walls were present in hyperacute renal homograft rejection, hemolyticuremic syndrome, postpartum renal failure, and in some cases of acute homograft rejection. In contrast, deposition of fibrinogen was observed in glomerular epithelial cresents in severe proliferative glomerulonephritis, but AHF deposition was not present in these lesions. Glomerular deposition of fibrinogen without increased AHF standing was also detected in renal tissue from patients with anaphylactoid purpura nephritis and in recurrent macroscopic hematuria with focal glomerulonephritis. Increased staining of peritubular capillaries with anti-AHF was seen in diseased kidneys irrespective of etiology. Immunofluorescent localization of AHF, a participant in the intrinsic coagulation pathway, offers a new way by which to analyze the mechanisms responsible for fibrinogen deposition in disease.

Synthesis of von Willebrand factor by cultured human endothelial cells

Cultured human endothelial cells synthesize and secrete a protein(s) which has Factor VIII antigen but which lacks Factor VIII clot-promoting activity (J. Clin. Invest. 52, 2757-2764, 1973). Von Willebrand factor activity has been identified in medium from cultured human endothelial cells. This activity was demonstrated by the ability to correct the defect in platelet adhesiveness of blood obtained from patients with von Willebrand's disease. This activity also supported ristocetin-induced aggregation of washed normal human platelets. The von Willebrand factor activity from cultured endothelial cells has physicochemical and immunologic properties like those of the von Willebrand factor activity and the Factor VIII antigen present in human plasma and the Factor VIII antigen synthesized by human endothelial cells in vitro. Rabbit antibody to chromatographic fractions containing endothelial cell von Willebrand factor inhibits the platelet retention of normal blood in glass bead columns.

Antihemophilic factor antigen. Localization in endothelial cells by immunofluorescent microscopy

The tissue localization of antihemophilic factor (AHF, Factor VIII) has been determined by immunofluorescent studies using monospecific rabbit antibody to human AHF. Specific staining demonstrating AHF antigens has been identified in endothelial cells of a wide range of human tissues. The staining pattern was observed in endothelial cells of arteries, capillaries, and veins as well as the cells lining hepatic and splenic sinusoids. Specific fluorescence was limited to these endothelial cells in sections of kidney, liver, spleen, lymph node, cardiac and smooth muscle, thyroid, umbilical cord, and skin. Absorption studies established that the staining was specific for cells in which there were proteins that had AHF antigens. The demonstration of fluorescence within the cytoplasm of endothelial cells suggests that these cells synthesize proteins that have AHF antigens.