Serum soluble CTLA-4 levels are increased in diffuse cutaneous systemic sclerosis

OBJECTIVE

To determine serum levels of soluble cytotoxic T-lymphocyte associated molecule-4 (sCTLA-4) and clinical association in patients with systemic sclerosis (SSc).

METHODS

Serum sCTLA-4 levels from 32 patients with diffuse cutaneous SSc (dSSc) and 27 patients with limited cutaneous SSc (lSSc) were examined by enzyme-linked immunosorbent assay (ELISA). For a longitudinal study, 211 sera from 30 SSc patients were analysed (follow-up 2.1-7.0 yr).

RESULTS

Serum sCTLA-4 levels were elevated in dSSc patients compared with normal controls (n = 41), lSSc patients and patients with active systemic lupus erythematosus (SLE) (n = 23). By contrast, sCTLA-4 levels in patients with lSSc or SLE were normal. SSc patients with elevated sCTLA-4 levels had a shorter disease duration and more frequent presence of digital pitting scars, contracture of phalanges, diffuse pigmentation, pulmonary fibrosis and decreased percentage vital capacity (%VC) than those with normal sCTLA-4 levels. sCTLA-4 levels correlated positively with the extent of skin fibrosis, serum IgG levels and anti-topoisomerase I antibody levels. In a longitudinal study, sCTLA-4 levels decreased on a parallel with improvement of skin sclerosis in five dSSc patients. Skin sclerosis did not improve in two of six dSSc patients with high sCTLA-4 levels throughout the follow-up, while the remaining four patients showed improvement of skin sclerosis.

CONCLUSION

These results suggest that sCTLA-4 correlates with disease severity and activity of SSc and that sCTLA-4 plays a role in immunological abnormalities of SSc, since sCTLA-4 may augment humoral immune responses as well as T-cell responses by interfering with B7-CTLA-4 interactions that induce negative signals in T and B cells.

Schwannoma in the sublingual space

In this report, we present CT and MRI findings of a case of a schwannoma that developed in the floor of the oral cavity. A 49-year-old woman visited our hospital with a painless swelling in the oral floor. CT and MRI revealed a well circumscribed oval mass in the sublingual space, which showed cystic degeneration in most of the lesion. In addition, a thickened wall that strongly enhanced after injection of contrast medium and formation of fluid level were observed in the mass. The mass was removed and was histopathologically diagnosed as schwannoma. Only a few cases of schwannoma in the oral floor have been reported. However, when the characteristic findings are observed on CT and MRI, schwannoma should be added to the differential diagnosis.

Identification of protein Sα gene mutations including four novel mutations in eight unrelated patients with protein S deficiency

Eight distinct and potentially causative mutations were identified in eight unrelated Japanese patients with protein S (PS) deficiency, by direct DNA sequencing of the protein Salpha (PSalpha) gene-specific polymerase chain reaction products of all 15 exons and exon/intron boundaries. There were five missense mutations, including two novel mutations (Cys80Tyr and Arg314His), and three showed a major impact on the expected gene products: novel mutations of a 5-bp deletion (delCTCTG887:Cys206Stop) and a nonsense mutation (Glu208Stop), as well as a previously reported splice site (exon 10 +5 A-->G) mutation. One of the patients showed compound heterozygosity for delCTCTG887 and 732A-->G. Investigation for the cosegregation state of these two mutations with PS deficiency in the patient's family suggested that the delCTCTG887 mutation was responsible for the abnormal phenotype and that the 732A-->G (Lys155Glu) mutation did not appear to play a key role. However, we also identified the same 732A-->G (Lys155Glu) mutation in an unrelated patient with apparent PS deficiency with severe pulmonary embolism, and found that this mutation seemed to cosegregate with a PS-deficient state in her family members. These data implied that unknown factor(s) other than the 732A-->G mutation itself might influence phenotypic expression of PS status in different individuals.

Identification of the Amino Acid Residues of the Platelet Glycoprotein Ib (GPIb) Essential for the von Willebrand Factor Binding by Clustered Charged-to-Alanine Scanning Mutagenesis

At the site of vascular injury, von Willebrand factor (VWF) mediates platelet adhesion to subendothelial connective tissue through binding to the N-terminal domain of the alpha chain of platelet glycoprotein Ib (GPIbalpha). To elucidate the molecular mechanisms of the binding, we have employed charged-to-alanine scanning mutagenesis of the soluble fragment containing the N-terminal 287 amino acids of GPIbalpha. Sixty-two charged amino acids were changed singly or in small clusters, and 38 mutant constructs were expressed in the supernatant of 293T cells. Each mutant was assayed for binding to several monoclonal antibodies for human GPIbalpha and for ristocetin-induced and botrocetin-induced binding of 125I-labeled human VWF. Mutations at Glu128, Glu172, and Asp175 specifically decreased both ristocetin- and botrocetin-induced VWF binding, suggesting that these sites are important for VWF binding of platelet GPIb. Monoclonal antibody 6D1 inhibited ristocetin- and botrocetin-induced VWF binding, and a mutation at Glu125 specifically reduced the binding to 6D1. In contrast, antibody HPL7 had no effect for VWF binding, and mutant E121A reduced the HPL7 binding. Mutations at His12 and Glu14 decreased the ristocetin-induced VWF binding with normal botrocetin-induced binding. Crystallographic modeling of the VWF-GPIbalpha complex indicated that Glu128 and Asp175 form VWF binding sites; the binding of 6D1 to Glu125 interrupts the VWF binding of Glu128, but HPL7 binding to Glu121 has no effect on VWF binding. Moreover, His12 and Glu14 contact with Glu613 and Arg571 of VWF A1 domain, whose mutations had shown similar phenotype. These findings indicated the novel binding sites required for VWF binding of human GPIbalpha.

Crystal Structure and Magnetic Interactions in Nickel(II) Dibridged Complexes Formed by Two Azide Groups or by Both Phenolate Oxygen−Azide, −Thiocyanate, −Carboxylate, or −Cyanate Groups

Tridentate/tetradentate Schiff base ligands L(1) and L(2), derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L(1))(micro(1,1)-N(3))Ni(L(1))(N(3))(OH(2))].H(2)O (1), [[Ni(L(1))(micro(1,1)-NCS)Ni(L(1))(NCS)(OH(2))][Ni(L(1))(micro-CH(3)COO)Ni(L(1))( NCS) (OH(2))]] (2) [[2A][2B]], [Ni(L(1))(micro(1,1)-NCO)Ni(L(1))(NCO)(OH(2))].H(2)O (3), and [Ni(L(2)-OMe)(micro(1,1)-N(3))(N(3))](2) (4), where L(1) = Me(2)N(CH(2))(2)NCHC(6)H(3)(O(-))(OCH(3)) and L(2) = Me(2)N(CH(2))(2)NCHC(6)H(3)N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a micro(1,1) mode and micro(2)-phenolate oxygen ion for 1-3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic susceptibility (chi(M)) versus temperature measurements. The chi(M) nus T plot reveals that compounds 1 and 4 are strongly ferromagnetically coupled, 3 shows a weak ferromagnetic behavior, and 2 is very weakly antiferromagnetically coupled.

Irreversible and reversible adhesion between virus particles and hydrolyzing-precipitating aluminium: a function of coagulation

The infectivity of viruses (Qbeta, MS2, T4, and P1) after dosing virus-contaminated water with 4 types of aluminium coagulant was investigated. The concentrations of infectious viruses were determined after dissolving aluminium hydroxide flocs in alkaline solution. The concentration of infectious viruses did not recover to the initial value after a short floc-dissolution time (5 s). Although the infectious virus concentration increased as the floc-dissolution time was extended to 5 h, it did not recover fully. Irreversible adhesion between virus particles and aluminium coagulant is responsible for the insufficient recovery. We interpret this phenomenon as a virucidal activity of the aluminium coagulant. All tested aluminium coagulants (PACl, alum, and reagent grade aluminium chloride and aluminium sulfate) inactivated all types of viruses tested. PACl had the highest virucidal activity. The virucidal activity of aluminium coagulants was lower in river water, presumably owing to the presence of natural organic matter.

Characterization of microparticles in raw, treated, and distributed waters by means of elemental and particle size analyses

The elemental composition and particle size distribution of suspended particles in raw water, treated water, and distributed water were determined to understand the behavior of particles during the water treatment-distribution process. The weight of suspended particles collected on a 0.6-microm filter was 1.1 times (raw water), 1.4 times (treated water), and 1.5 times (distributed water) that collected on a 2.7-microm filter, suggesting that smaller particles may remain after conventional water treatment. Organic suspended particles were removed less efficiently than inorganic suspended particles. After sand filtration, the Al content in the fixed suspended solids (FSS) markedly increased, indicating that either a small percentage of aluminium floc passed through during sand filtration or dissolved aluminum precipitated after sand filtration. The Mn and Fe concentrations increased after chlorination. The percentages of carbon and nitrogen in the volatile suspended solids (VSS) were roughly the same in the raw, treated, and distributed waters. The carbon/nitrogen/phosphate/VSS ratios indicated that the VSS of the suspended particles consisted of organic matter originating from microorganisms. The major constituents of the FSS in the treated and distributed waters were compounds of Fe, Al, Ca, Mg, and Mn, but these compounds accounted for only 16% or less of the FSS in raw water, indicating the existence of Si compounds. In distribution pipes, the total suspended solids concentration, especially the FSS concentration, was higher than that of water just after treatment. The Fe concentration in distributed water increased, probably due to oxidation and rusting of iron pipes.

Production of adrenomedullin from synovial cells in rheumatoid arthritis patients

It was recently reported that plasma levels of adrenomedullin (AM), identified as a vasorelaxant peptide, are significantly higher in rheumatoid arthritis (RA) patients than in osteoarthritis (OA) patients. The objective of the present study was to elucidate AM production in synovial cells from patients with RA. Adrenomedullin mRNA was detected in cultured synovial cells from RA patients by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemical analysis demonstrated the presence of AM in synovial cells from RA patients. In addition, we investigated AM levels in knee joint fluids from RA and OA patients. Those from RA patients were elevated approximately threefold over those of OA patients. In this study, we demonstrated for the first time AM expression in synovial cells from RA patients and high levels of AM production in RA joint fluid.

Cyclic tensile stretch loaded on bovine chondrocytes causes depolymerization of hyaluronan: involvement of reactive oxygen species

OBJECTIVE

We have previously demonstrated that reactive oxygen species (ROS) are involved in cartilage degradation. Decreased size of hyaluronan (HA), the major macromolecule in synovial fluid, to which it imparts viscosity, is reported in patients with arthritis. The purpose of this study was to determine the alteration in the molecular weight range of HA as a result of mechanical deformation loaded on the chondrocytes, as well as the involvement of ROS in this action.

METHODS

ROS were generated via the oxidation of hypoxanthine by xanthine oxidase. Cyclic tensile stretch was loaded using a vacuum-operated instrument. Levels of HA were measured using a sandwich enzyme-binding assay. Superoxide dismutase (SOD) activity and ROS were measured using water-soluble tetrazolium and a chemiluminescent probe, respectively.

RESULTS

ROS depolymerized HA molecules. Cyclic tensile stretch depolymerized HA and induced ROS. SOD inhibited not only ROS induction but also HA depolymerization caused by the mechanical stress.

CONCLUSION

ROS play an important role in mechanical stress-induced HA depolymerization.

Compound heterozygosity for two novel mutations in a severe factor XI deficiency

We identified two novel mutations in an asymptomatic 25-year-old Japanese patient with severe factor XI deficiency. Direct sequencing analysis of PCR products from his factor XI gene revealed a G to T transversion in exon 12, resulting in the nonsense mutation (Glu447Stop) and a G insertion in five consecutive guanine nucleotides ((501)Trp(TGG)-(502)Gly(GGG)) in exon 13 that is expected to lead to the substitution of the last 105 amino acids ((503)Tyr-(607)Val) with 32 abnormal amino acid residues ((503)Val-(534)Thr) followed by stop codon. We also demonstrated that two mutations are associated with the separate alleles in this patient, indicating compound heterozygosity for these mutations. Both mutations lead to the disruption of the catalytic domain structure of the FXI molecule and thus are responsible for his deficiency of factor XI.

Trisomy X in Philadelphia chromosome-negative cells during the course of Philadelphia chromosome-positive chronic myelocytic leukemia

A Philadelphia chromosome-negative (Ph(-)) clone with trisomy X appeared in the bone marrow cells from a patient with Ph(+) chronic myelocytic leukemia in the chronic phase after hydroxyurea and interferon-alpha treatment.

Abnormalities in gap junctions and Ca2+ dynamics in cardiomyocytes at the border zone of myocardial infarcts

Abnormalities in gap junction function and Ca2+ dynamics are believed to be important factors in arrhythmogenesis after myocardial infarction. To elucidate the relationship between changes in Ca2+ dynamics and gap junctions, we analyzed by real-time in situ Ca2+ imaging of fluo-3 loaded whole hearts the spatiotemporal occurrence of Ca2+ waves and the localization of connexin43 (Cx43) at the border zone of myocardial infarcts induced in the rat by coronary ligation. At early time points (2-4 hours postligation), different regions of the left ventricle showed distinct changes in cytosolic free Ca2+ concentrations [Ca2+]i. While some cardiomyocytes of infarcted regions exhibited high levels of resting fluo-3 fluorescence, at border zones frequent Ca2+ waves were observed. Some of the waves were abolished by spontaneous Ca2+ transients and others were not. Intact myocardium apart from infarcted regions exhibited homogenous Ca2+ transients. Confocal imaging of Cx43 and actin filaments in the rat heart fixed 2 hours after coronary ligation revealed that Cx43 was markedly decreased in the area of myocyte necrosis with contraction bands and in the neighboring myocardium. These results suggest that abnormal expression and function of gap junctions could be associated with Ca2+ waves at the border zone of myocardial infarcts, possibly through Ca2+ overload.

Enzyme immunoassay for measurement of murine plasminogen activator inhibitor-1, employing a specific antibody produced by the DNA vaccine method

We developed a sensitive immunoassay to determine the concentration of mouse plasminogen activator inhibitor-1. The assay was a non-competitive sandwich enzyme-linked immunosorbent assay (ELISA) based on the production of a specific polyclonal antibody against mouse plasminogen activator inhibitor type-1 (PAI-1) used both as a trapping and detecting antibody. This antibody was raised in a rabbit by direct introduction of the expression vector plasmid DNA encoding mouse PAI-1, instead of conventional immunization with the purified protein. The standard curve was constructed with a recombinant glutathione S-transferase (GST)-mouse PAI-1 fusion protein (GST-mPAI-1) and dose-response of the assay was linear for GST-mPAI-1 between 6.25 and 100 pM. In order to assess the consistency of the assay, we measured PAI-1 antigen in normal mouse pooled plasma several times. We found that the intra-assay and inter-assay coefficients of variation (CV) were 4.8% and 9.2%, respectively, indicating that the ELISA would be sufficiently repeatable and reproducible. In this assay, lipopolysaccharide (LPS)-injected mice showed substantially higher levels (22-fold) of plasma PAI-1 antigen than did control mice (12.5+/-2.4 vs. 0.58+/-0.16 nM), similar to results reported elsewhere. Taken together, the DNA vaccine method is extremely useful for preparing specific antibodies against mouse PAI-1, which can be utilized to establish the ELISA and analyze the profile of PAI-1 distributions in mice under various conditions. This approach might also be useful for immunological investigation of other coagulation factors and related proteins.

Immunofluorescence analysis of neutrophil nonmuscle myosin heavy chain-A in MYH9 disorders: association of subcellular localization with MYH9 mutations

The autosomal dominant macrothrombocytopenia with leukocyte inclusions, May-Hegglin anomaly, Sebastian syndrome, and Fechtner syndrome, are rare human disorders characterized by a triad of giant platelets, thrombocytopenia, and characteristic Döhle body-like cytoplasmic inclusions in granulocytes. Epstein syndrome is another autosomal dominant macrothrombocytopenia associated with Alport syndrome but without leukocyte inclusions. These disorders are caused by mutations in the same gene, the MYH9, which encodes the nonmuscle myosin heavy chain-A (NMMHCA). The term, MYH9 disorders, has been proposed, but the clinicopathologic basis of MYH9 mutations has been poorly investigated. In this study, a total of 24 cases with MYH9 disorders and suspected cases were subjected to immunofluorescence analysis by a polyclonal antibody against human platelet NMMHCA. Abnormal subcellular localization of NMMHCA was observed in every neutrophil from individuals with MYH9 mutations. Comparison with May-Grünwald-Giemsa staining revealed that the NMMHCA always coexisted with the neutrophil inclusion bodies, suggesting that NMMHCA is associated with such bodies. In three cases, neutrophil inclusions were not detected on conventional May-Grünwald-Giemsa-stained blood smears but immunofluorescence analysis revealed the abnormal NMMHCA localization. In contrast, cases with Epstein syndrome and the isolated macrothrombocytopenia with normal NMMHCA localization had no MYH9 mutations. An antibody that recognizes the C-terminal 12 mer peptides showed similar immunoreactivity from the patients heterozygous for truncated mutations that abolished the C-terminal epitope, suggesting that normal NMMHCA dimerizes with abnormal NMMHCA to form inclusion bodies. We further propose that the localization pattern can be classified into three groups according to the number, size, and shape of the fluorescence-labeled NMMHCA granule. Immunofluorescence analysis of neutrophil NMMHCA is useful as a screening test for the clear hematopathologic classification of MYH9 disorders.

Novel nonsense mutation in the platelet glycoprotein Ibbeta gene associated with Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS) is an autosomal recessive bleeding disorder caused by quantitative or qualitative abnormalities in the glycoprotein (GP) Ib/IX/V complex, the platelet receptor for von Willebrand factor. This complex is composed of four subunits, GPIbalpha, GPIbbeta, GPIX, and GPV, and the coordinated assembly of GPIbalpha, GPIbbeta, and GPIX is required for the efficient surface expression of a functional complex. We report here a novel nonsense mutation of the GPIbbeta gene associated with BSS. Flow cytometric analysis of the patient's platelets showed markedly reduced GPIbalpha and absent GPIX surface expression. Immunoblot analysis of solubilized platelets showed that a small amount of GPIbalpha was detected; however, GPIbbeta and GPIX were undetectable. DNA sequencing analysis revealed a novel nonsense mutation of the GPIbbeta gene that converts Trp (TGG) to a stop codon (TAG) at residue 123. Transient transfection studies revealed that the mutant GPIbbeta polypeptide was not detected in the transfected 293T cells, suggesting that null expression of the mutant GPIbbeta impairs expression of the GPIbalpha and GPIX subunits and results in a BSS phenotype in the patient.

Epstein-Barr virus-associated T-cell lymphoma: a case of eyelid swelling and intramuscular infiltration mimicking dermatomyositis

Association with Epstein-Barr virus (EBV) infection has been noted in various types of cutaneous lymphoproliferative disorders. We report a 57-year-old Japanese woman with T-cell lymphoma mimicking dermatomyositis that was associated with chronic active EBV infection. She presented with low-grade fever, bilateral erythematous swellings on the eyelids, and necrotic papules on the face. Serum creatine kinase levels were elevated and a diffuse reticular shadow was detected in both lung fields. The infiltrate of atypical lymphocytes found in skin and muscle, which contained EBV-encoded small nuclear RNA-1 and EBV, was also detected in the CD4+ peripheral blood cells. Treatment with prednisolone resolved her lesions with no relapse for 3 years, after which there was a recurrence in her left lung. Combination chemotherapy was not effective against the lung lesion and she died with multiple organ failure 2 months after the recurrence.

Increased expression of plasminogen activator inhibitor-1 with fibrin deposition in a murine model of aging, "Klotho" mouse

Although aging accompanies specific pathological changes, including thrombosis and organ sclerosis, the underlying mechanisms of these processes remain to be elucidated. In the present study, we analyzed the gene expression of plasminogen activator inhibitor-1 (PAI-1), a key molecule in the development of thrombosis, in a murine model of aging, klotho mutant ( kl/kl) mice. Active PAI-1 antigen in plasma and PAI-1 mRNA in several tissues were strikingly elevated in kl/kl mice as compared with wild-type mice. This increased PAI-1 expression was age dependent and linked to the development of ectopic calcification and glomerular fibrin deposition in the kidneys. In situ hybridization analysis of kl/kl mice demonstrated that strong signals for PAI-1 mRNA were localized in renal tubular epithelial cells, cardiomyocytes, adrenal medullar cells, and smooth muscle and endothelial cells in Mönckeberg's arteriosclerotic vessels. Renal glomerular fibrin deposition, as evaluated immunohistochemically, was occasionally observed only in kl/kl mice, and the number of fibrin-positive glomeruli increased as the kl/kl mice aged. These observations suggest that in the process of aging the PAI-1 gene expression is increased, contributing to the development of thrombosis.

Binding site on human von Willebrand factor of bitiscetin, a snake venom-derived platelet aggregation inducer

Bitiscetin, a C-type lectin-like heterodimeric snake venom protein purified from Bitis arietans, binds to human von Willebrand factor (VWF) and induces the platelet membrane glycoprotein (GP) Ib-dependent platelet agglutination in vitro similar to botrocetin. In contrast with botrocetin which binds to the A1 domain of VWF, the A3 domain, a major collagen-binding site of VWF, was proposed to be a bitiscetin-binding site. In the competitive binding assay, neither bitiscetin nor botrocetin had an inhibitory effect on the VWF binding to the immobilized type III collagen on a plastic plate. The anti-VWF monoclonal antibody NMC-4, which inhibits VWF-induced platelet aggregation by binding to alpha4 helix of the A1 domain, also inhibited bitiscetin binding to the VWF. Binding of VWF to the immobilized bitiscetin was competitively inhibited by a high concentration of botrocetin. A panel of recombinant VWF, in which alanine-scanning mutagenesis was introduced to the charged amino acid residues in the A1 domain, showed that the bitiscetin-binding activity was reduced in mutations at Arg632, Lys660, Glu666, and Lys673 of the A1 domain. Those substituted at Arg629, Arg636, and Lys667, which decreased the botrocetin binding, showed no effect on the bitiscetin binding. These results indicate that bitiscetin binds to a distinct site in the A1 domain of VWF spanning over alpha4a, alpha5 helices and the loop between alpha5 and beta6 but close to the botrocetin- and NMC-4-binding sites. Monoclonal antibodies recognizing the alpha-subunit of bitiscetin specifically inhibited bitiscetin-induced platelet agglutination without affecting the binding between VWF and bitiscetin, suggesting that the alpha-subunit of bitiscetin is located on VWF closer to the GPIb-binding site than the beta-subunit is. Bitiscetin and botrocetin might modulate VWF by binding to the homologous region of the A1 domain to induce a conformational change leading to an increased accessibility to platelet GPIb.

Identification of the regulatory elements of the human von Willebrand factor for binding to platelet GPIb. Importance of structural integrity of the regions flanked by the CYS1272-CYS1458 disulfide bond

In vitro platelet glycoprotein Ib (GPIb) binding of the human von Willebrand factor (VWF) increases markedly by exogenous modulators such as ristocetin or botrocetin, and the binding does not occur in normal circulation. GPIb binding sites have been assigned in the VWF A1 domain, which consists of a disulfide loop Cys1272(509)-Cys1458(695) where amino acid residues are numbered from the starting methionine as +1. The previous numbering from the N-terminal Ser of the mature processed VWF is indicated in parentheses. In contrast, several gain-of-function mutations have been found in two regions comprised of the disulfide loop and its N- and C-terminal flanking regions. In this study, Cys1222(459)-Tyr1271(508), Gln1238(475)-Tyr1271(508), Glu1260(497)-Tyr1271(508), and Asp1459(696)-Asp1472(709) were sequentially deleted of full-length multimeric recombinant VWF. Deletions at either side resulted in normal GPIb binding, indicating that the flanking regions are not GPIb binding sites. However, the addition of a mutation at Arg1308(545) on each deletion mutant resulted in spontaneous GPIb binding without requiring modulators, suggesting that both regions are important for the inhibition of GPIb binding. Spontaneous binding was completely inhibited by monoclonal antibodies that recognize the GPIb binding sites. Interestingly, mutant proteins with N-terminal but not C-terminal deletions lost binding to monoclonal antibodies B328, B710, and 23C7, which selectively inhibit ristocetin-induced GPI binding. Their epitopes were found at His1268(505) or Asp1269(506). The crystallographic structure of the A1 domain suggests that GPIb binding is influenced by the molecular interface between the two regions and that the antibody binding to the interface inhibits binding.