scholarly journals Microheterogeneity of beta-2 glycoprotein I: implications for binding to anionic phospholipids

1999 ◽  
Vol 340 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Timothy A. BRIGHTON ◽  
Yan-Ping DAI ◽  
Philip J. HOGG ◽  
Colin N. CHESTERMAN

Considerable interest is currently focused on the interactions of beta-2 glycoprotein I (β2GPI) and anti-phospholipid antibodies with anionic phospholipids in an attempt to understand the association between these antibodies and clinical diseases such as thrombosis. The interactions of β2GPI and anionic phospholipids have only been characterized partially, and the physiological role of this glycoprotein remains uncertain. In this study we have explored in detail the physical and phospholipid-binding characteristics of a number of β2GPI preparations. We have found (i) that perchloric acid-purification methods are damaging to β2GPI during purification, (ii) that the dissociation constants of the various preparations for phosphatidylserine vary between 0.1-2 μM and are considerably weaker than previously reported, (iii) that considerable differences in affinity of the various β2GPI preparations for anionic phospholipids are obtained when comparing anionic phospholipids immobilized to a solid-phase versus phospholipid assembled in unilamellar vesicles, (iv) that the integrity of the fifth domain of β2GPI is important for binding immobilized anionic phospholipid but not especially important in binding vesicular anionic phospholipid, and (v) that β2GPI preparations with differing isoelectric species content bind anionic phospholipids differently, suggesting that varying glycosylation and/or protein polymorphisms impact upon phospholipid binding. These results highlight the importance of assessing the determinants of the interaction of β2GPI with anionic phospholipids assembled in unilamellar vesicles.

Lupus ◽  
1998 ◽  
Vol 7 (2_suppl) ◽  
pp. 10-13 ◽  
Author(s):  
MI Kamboh ◽  
H Mehdi

Apolipoprotein H (apoH; also known as β2-glycoprotein I), is an essential cofactor for the binding of certain antiphospholipid antibodies (APA) to anionic phospholipid. The gene coding for apoH is polymorphic, with the occurrence of several common alleles in the general population. This genetically determined variation can effect the binding of apoH to anionic phospholipids and consequently the production of APA. Our group has identified two common mutations at codons 306 (Cys → Gly) and 316 (Trp → Ser) in the fifth domain of apoH which affect the binding of apoH to anionic phospholipids (phosphatidylserine or cardiolipin). ApoH from serum samples homozygous for each of these mutations or compound heterozygotes for both mutations showed no binding with anionic phospholipids on ELISA. In vitro mutagenesis and transient expression of these mutations in COS-1 cells followed by cardiolipin binding studies confirmed that Gly306 and Ser316 are causative mutations. Our data indicate that the fifth domain of apoH is essential for anionic phospholipid binding and genetically determined variation in this domain can affect the production of apoH-dependent APA.


1994 ◽  
Vol 179 (2) ◽  
pp. 457-462 ◽  
Author(s):  
E Matsuura ◽  
Y Igarashi ◽  
T Yasuda ◽  
D A Triplett ◽  
T Koike

Anticardiolipin antibodies (aCL) derived from the sera of individuals exhibiting the antiphospholipid syndrome (APS) directly bind to beta 2-glycoprotein I (beta 2-GPI), which is adsorbed to an oxidized polystyrene surface. Oxygen atoms were introduced on a polystyrene surface by irradiation with electron or gamma-ray radiation. X-ray photoelectron spectroscopy revealed the irradiated surfaces were oxidized to generate C-O and C = O moieties. aCL derived from either APS patients or (NZW x BXSB)F1 mice bound to beta 2-GPI coated on the irradiated plates, depending on the radiation dose. Antibody binding to beta 2-GPI on the irradiated plates was competitively inhibited by simultaneous addition of cardiolipin (CL)-coated latex beads mixed together with beta 2-GPI but were unaffected by addition of excess beta 2-GPI, CL micelles, or CL-coated latex beads alone. There was a high correlation between binding values of aCL in sera from 40 APS patients obtained by the anti-beta 2-GPI enzyme-linked immunosorbent assay (ELISA) using the irradiated plates and those by the beta 2-GPI-dependent aCL ELISA. Therefore, aCL have specificity for an epitope on beta 2-GPI. This epitope is expressed by a conformational change occurring when beta 2-GPI interacts with an oxygen-substituted solid phase surface.


2010 ◽  
Vol 104 (08) ◽  
pp. 335-341 ◽  
Author(s):  
Anhquyen Le ◽  
Anthony Prakasam ◽  
Hanan Abdel-Monem ◽  
Swapan Dasgupta ◽  
Perumal Thiagarajan

SummaryThe majority of the antiphospholipid antibodies, present in patients with antiphospholipid syndrome, are directed against conformational epitopes in β2-glycoprotein I. β2-glycoprotein I is an anionic phospholipid- binding 50-kDa plasma protein whose physiological role is not clear. Here we investigate the role of β2-glycoprotein I in the phagocytosis of phosphatidylserine-expressing platelet microvesicles and the effect of autoantibodies to β2-glycoprotein I on this process. We labelled the glycans of β2-glycoprotein I with BODIPY (4,4-difluoro- 4-bora-3a,4a-diaza-s-indacene)-hydrazide without affecting its phospholipid binding capacity. BODIPY-β2-glycoprotein I bound to platelet microvesicles in a concentration-dependent manner and promoted the phagocytosis of platelet microvesicles by THP-1 derived macrophages in vitro at physiological plasma concentrations with a half maximal effect at ∼10 μg/ml. β2-glycoprotein I-stimulated phagocytosis was inhibited by annexin A5 and the phosphatidylserine-binding C1C2 fragment of lactadherin. Furthermore, immunoaffinity purified β2-glycoprotein I-dependent antiphospholipid antibodies from five patients with antiphospholipid syndrome inhibited the phagocytosis in a concentration- dependent manner. These studies suggest that the binding of β2-glycoprotein I to phosphatidylserine-expressing procoagulant platelet microvesicles may promote their clearance by phagocytosis and autoantibodies to β2-glycoprotein I may inhibit this process to induce a procoagulant state.


Author(s):  
David Green

The antiphospholipid syndrome is characterized by antibodies directed against phospholipid-binding proteins and phospholipids attached to cell membrane receptors, mitochondria, oxidized lipoproteins, and activated complement components. When antibodies bind to these complex antigens, cells are activated and the coagulation and complement cascades are triggered, culminating in thrombotic events and pregnancy morbidity that further define the syndrome. The phospholipid-binding proteins most often involved are annexins II and V, β2-glycoprotein I, prothrombin, and cardiolipin. A distinguishing feature of the antiphospholipid syndrome is the “lupus anticoagulant”. This is not a single entity but rather a family of antibodies directed against complex antigens consisting of β2-glycoprotein I and/or prothrombin bound to an anionic phospholipid. Although these antibodies prolong in vitro clotting times by competing with clotting factors for phospholipid binding sites, they are not associated with clinical bleeding. Rather, they are thrombogenic because they augment thrombin production in vivo by concentrating prothrombin on phospholipid surfaces. Other antiphospholipid antibodies decrease the clot-inhibitory properties of the endothelium and enhance platelet adherence and aggregation. Some are atherogenic because they increase lipid peroxidation by reducing paraoxonase activity, and others impair fetal nutrition by diminishing placental antithrombotic and fibrinolytic activity. This plethora of destructive autoantibodies is currently managed with immunomodulatory agents, but new approaches to treatment might include vaccines against specific autoantigens, blocking the antibodies generated by exposure to cytoplasmic DNA, and selective targeting of aberrant B-cells to reduce or eliminate autoantibody production.


1999 ◽  
Vol 340 (1) ◽  
pp. 59 ◽  
Author(s):  
Timothy A. BRIGHTON ◽  
Yan-Ping DAI ◽  
Philip J. HOGG ◽  
Colin N. CHESTERMAN

Hematology ◽  
2014 ◽  
Vol 2014 (1) ◽  
pp. 321-328 ◽  
Author(s):  
Steven A. Krilis ◽  
Bill Giannakopoulos

Abstract This chapter reviews several important themes pertaining to the antiphospholipid syndrome (APS), including a description of the clinical features, a discussion of the main autoantigen, beta 2-glycoprotein I (β2GPI), and insights into the characteristics of the pathogenic anti-β2GPI autoantibodies. Evidence-based considerations for when to test for APS are explored, along with the clinical significance of patients testing positive on multiple APS assays, so-called triple positivity. A detailed review of recently published laboratory guidelines for the detection of lupus anticoagulant and the solid-phase anticardiolipin and anti-β2GPI ELISAs is undertaken. Finally, a brief review of nonclassification criteria laboratory assays with potential future diagnostic utility is presented.


2010 ◽  
Vol 22 (9) ◽  
pp. 34
Author(s):  
C. A. Viall ◽  
L. W. Chamley ◽  
Q. Chen

Women with antiphospholipid antibodies (aPL) are at an increased risk of preeclampsia, recurrent miscarriage, stillbirth and intrauterine growth restriction. Antiphospholipid antibodies may predispose to these pathologies by damaging the placenta, although exactly how is not understood. Recently, a novel pathogenic mechanism was suggested by work which showed that aPL are specifically internalised by placental trophoblasts where they caused aberrant trophoblast death. Internalisation may occur via an endocytic receptor called megalin in a process that seems to involve at least one of the two components of the antigen for aPL, the anionic phospholipid-binding protein β2 glycoprotein I (β2GPI). However, whether internalisation is also dependent upon anionic phospholipids is unknown. Identifying the receptor pathway responsible for aPL internalisation may provide insight into the pathogenesis of aPL in the placenta. To investigate the process of aPL internalisation, first trimester placental explants were cultured with fluorescently-labeled monoclonal aPL, or a control antibody and/or β2GPI or acetylated β2GPI, which can not bind anionic phospholipids. The explants were then sectioned and the localisation of the aPL, β2GPI, or acetylated β2GPI was determined by confocal microscopy. The localisation of megalin expression in placental explants was determined by immunohistochemistry. Megalin was expressed throughout the syncytiotrophoblast but more strongly in some regions. After an overnight incubation, both aPL and β2GPI, but not control antibodies were co-localised in the cytoplasm of the syncytiotrophoblast. Acetylated β2GPI was not internalised and partially blocked aPL uptake. These results suggest that aPL are internalised into the synctiotrophoblast by a receptor-dependent mechanism involving β2GPI, anionic phospholipids and megalin. This work forms the first step to understanding how aPL are internalised by trophoblasts. Further investigation of this mechanism and the subsequent intracellular effects of aPL may lead to a new therapeutic strategy for aPL-positive pregnant women by preventing the pathogenic effect of aPL on the placenta.


1997 ◽  
Vol 77 (03) ◽  
pp. 486-491 ◽  
Author(s):  
Monica Galli ◽  
Gianluca Beretta ◽  
Maria Daldossi ◽  
Edouard M Bevers ◽  
Tiziano Barbui

SummaryLupus anticoagulant (LA) antibodies are acquired inhibitors of coagulation belonging – together with anticardiolipin (aCL) antibodies – to the family of antiphospholipid antibodies. Since LA antibodies affect coagulation reactions via recognition of the complex of lipid-bound prothrombin, they may be better named anti-prothrombin antibodies. We studied their immunological properties in the plasma of 59 patients with antiphospholipid antibodies by means of specific ELISA systems that allowed the characterization of the interaction of these antibodies with human prothrombin and anionic phospholipids. The mode of presentation of prothrombin was found to greatly influence the reactivity of anti-prothrombin antibodies. In fact, when plain polystyrene plates were used to immobilize prothrombin, virtually no binding was observed. Conversely, when prothrombin was coated on high-activated PVC ELISA plates, 34 samples (58%) contained antibodies that recognize human prothrombin in solid phase. In particular, IgG antibodies were found in 21 plasmas and IgM in 22; both IgG and IgM isotypes were present in 9 of these cases. A higher prevalence was observed in the ELISA for the detection of the antibodies directed at the calcium- mediated complex of phosphatidylserine (PS)-bound prothrombin: 53 samples (90%), preadsorbed with cardiolipin liposomes to remove aCL antibodies, showed the presence of IgG and/or IgM anti-prothrombin antibodies. When the results were analyzed according to the immunoglobulin isotypes, 44 (75%) and 39 (66%) samples were found to contain IgG and IgM anti-prothrombin antibodies, respectively. Both IgG and IgM were present in the plasma of 30 patients. Only half of these samples reacted also with PVC-bound prothrombin. Apparently, the higher rate of positivity of the ELISA for the detection of antibodies to the complex of PS-bound prothrombin was not due to differences in the amount of antigen available in the 2 systems, as judged by binding experiments performed with a rabbit polyclonal anti-human prothrombin antiserum.Finally, the anticoagulant properties of 14 total IgG preparations (12 of them contained anti-prothrombin antibodies positive in both ELISA systems, whereas the other 2 cases reacted either with PVC-bound prothrombin only or with PS-bound prothrombin only) were evaluated by diluted Russell’s Viper Venom Time and by diluted activated Partial Thromboplastin Time. To rule out the β2-glycoprotein I (β2-GPI)-de- pendent anticoagulant effect of the aCL antibodies contained in the preparations, the coagulation tests were performed in (β2-GPI deficient plasma. Six preparations failed to show anticoagulant activity in both assay systems, suggesting that 2 types of IgG anti-prothrombin antibodies exist, that differ with respect to their anticoagulant properties. These findings suggest that anti-prothrombin antibodies resemble aCL antibodies with respect to the behaviour in “in vitro” coagulation reactions and underline the wide heterogeneity of antiphospholipid antibodies.


1994 ◽  
Vol 72 (04) ◽  
pp. 578-581 ◽  
Author(s):  
T McNally ◽  
S E Cotterell ◽  
I J Mackie ◽  
D A Isenberg ◽  
S J Machin

Summaryβ2 glycoprotein-I (β2GPI), a cofactor for antiphospholipid antibody (aPA) binding, binds to many anionic macromolecules including heparin. The nature of this interaction with heparin is not well understood and its effect on the purported biological functions of β2GPI is unknown.We have examined the interactions of dermatan sulphate (DS) and different pharmaceutical preparations of heparin with β2GPI by crossed immunoelectrophoresis (CIE) and investigated the effect of these agents on plasma levels of p2GPI antigen (β2GPI: Ag) by a standardised enzyme linked immunosorbent assay (ELISA). P2GPI aPA cofactor activity (β2GPI:Cof) was also measured using a modified solid phase an-ti-phosphatidylserine (aPS) ELISA. CIE results confirmed a heparin-β2GPI interaction with unfractionated (UF) heparin. β2GPI:Ag levels were unaffected by any of the preparations investigated. There were no significant differences in β2GPI:Cof activities of the samples containing LMW heparins or DS but levels of β2GPI:Cof were increased in samples containing UF sodium and calcium heparin preparations (0.5 IU/ml Monoparin, p <0.05, and 10 IU/ml Liquemin and Calcipa-rine, p <0.05).


Sign in / Sign up

Export Citation Format

Share Document