Antiphospholipid Syndrome: Diagnostic Aspects of Lupus Anticoagulants

2001 ◽  
Vol 86 (07) ◽  
pp. 83-91 ◽  
Author(s):  
J. Arnout
Keyword(s):  
Monoclonal Antibodies ◽  
Antiphospholipid Syndrome ◽  
Autoimmune Disorder ◽  
Coagulation Factors ◽  
Laboratory Diagnosis ◽  
Anticardiolipin Antibodies ◽  
Lupus Anticoagulants ◽  
Glycoprotein I ◽  
Antigen Antibody

SummaryAntiphospholipid syndrome (APS) is an autoimmune disorder in which antiphospholipid antibodies (aPL) are thought to be involved in the development of venous and/or arterial thrombosis. APL found in this syndrome are antibodies directed against a variety of phospholipid (PL) binding-proteins of which β2-glycoprotein I (β2GPI) and prothrombin are considered to be the major antigens. Some of these antibodies prolong PL-dependent clotting reactions and are termed lupus anticoagulants (LA). Autoimmune aPL which bind through β2GPI to cardiolipin are called anticardiolipin antibodies (aCL). Clinical studies indicate that LA is a stronger risk factor for thrombosis than aCL. The production of monoclonal antibodies against β2GPI and prothrombin has enabled us to understand the mechanism by which LA prolong coagulation in vitro. LA form bivalent antigen-antibody complexes with increased affinity for PL which compete with coagulation factors for the same catalytic surface. These LA positive monoclonal antibodies may be helpful in further improving the laboratory diagnosis of LA.

Mechanism of action of Lupus anticoagulants

2001 ◽  
Vol 21 (02) ◽  
pp. 44-49 ◽  
Author(s):  
J. Arnout
Keyword(s):  
Binding Proteins ◽  
Fetal Loss ◽  
Coagulation Factors ◽  
Anticardiolipin Antibodies ◽  
Heparin Induced Thrombocytopenia ◽  
Glycoprotein I ◽  
Direct Binding ◽  
Initial Activation ◽  
The Complement System

SummaryThe antiphospholipid syndrome (APS) is defined as the association of antiphospholipid antibodies (aPL) with thrombosis, fetal loss or thrombocytopenia. Some aPL can be detected via coagulation assays where they present as an aspecific inhibitor termed the lupus anticoagulant (LA). Others can be measured via direct binding to cardiolipin and are termed anticardiolipin antibodies. aPL found in APS patients bind to a variety of PL-binding proteins such as beta-2-glycoprotein I (β2GPI) and prothrombin bound to PL surfaces. LA retard coagulation reactions in vitro by forming stable bivalent immune complexes on coagulation active phospholipids. These complexes have increased affinity for PL and compete with coagulation factors for the same catalytic surface. Animal experimental work has provided evidence that aPL are pathogenic. Based on similarities with heparin induced thrombocytopenia, another thrombotic syndrome, the following mechanism might be proposed. As a consequence of an initial activation, anionic PL exposed on bloodcells, endothelium or trophoblasts may promote the formation of bivalent complexes of aPL and PL-binding proteins. In this way, aPL concentrate on the cell surface, activate cellular FcγRII receptors or the complement system and induce thrombosis.

Monoclonal Antibodies against Beta-2-Glycoprotein I: Use as Reference Material for Lupus Anticoagulant Tests

1998 ◽  
Vol 79 (05) ◽  
pp. 955-958 ◽  
Author(s):  
J. Arnout ◽  
M. Vanrusselt ◽  
C. Wittevrongel ◽  
J. Vermylen
Keyword(s):  
Monoclonal Antibodies ◽  
Laboratory Diagnosis ◽  
Poor Agreement ◽  
Control Material ◽  
Lupus Anticoagulants ◽  
Glycoprotein I ◽  
Coefficients Of Variation ◽  
And Control ◽  
Murine Monoclonal Antibodies ◽  
Control Batch

SummaryThe laboratory diagnosis of lupus anticoagulants (LA) remains difficult despite internationally accepted guidelines for its detection. Several interlaboratory surveys have shown poor agreement between laboratories. Further standardization of LA testing will to a large extent depend on better insights on the mechanisms by which LA affect phospholipid-dependent coagulation assays as well as on the availability of well characterized and internationally accepted reference materials and control specimens. We recently raised a series of murine monoclonal antibodies against human β2GPI (anti-β2GPI moabs), a phospholipid-binding protein directly involved in the interaction between certain lupus anticoagulants and phospholipids. In this study we report on the use of LA positive anti-β2GPI moabs as easy to handle reference and control material. The relative LA responsiveness of various phospholipid-dependent clotting assays was determined on plasmas spiked with such moabs and compared well with that determined on LA positive plasma samples. Plasmas spiked with LA positive anti-β2GPI moabs were also used as control specimens to study the interlaboratory precision of LA testing. With these control specimens, low interassay coefficients of variation were obtained. Our results indicate that LA positive anti-β2GPI moabs have potential for the production of control specimens that could be made available to routine hemostasis laboratories to assess intra-laboratory precision of LA testing and to manufacturers to control batch-to-batch variability of their reagents.

Many faces of lupus anticoagulants

Lupus ◽  
1998 ◽  
Vol 7 (2_suppl) ◽  
pp. 18-22 ◽  
Author(s):  
DA Triplett
Keyword(s):  
Fetal Loss ◽  
Laboratory Diagnosis ◽  
Anticardiolipin Antibodies ◽  
Screening Tests ◽  
Factor Viii Inhibitor ◽  
Lupus Anticoagulants ◽  
Venous Thromboembolic Events ◽  
Venous Thromboembolic ◽  
Confirmatory Tests

Lupus anticoagulants (LA) are immunoglobulins which inhibit one or more of the in-vitro phospholipid (PL) dependent tests of coagulation. Virtually any physician may encounter LA-positive patients. Such patients present with a variety of diagnostic challenges including arterial and venous thromboembolic events, recurrent fetal loss, TIAs, livedo reticularis, etc. LA and anticardiolipin antibodies (ACA) are the most common cause of acquired thrombophilia. Consequently, it is imperative for clinicians and laboratorians to work together in establishing the diagnosis of LA/ACA. The laboratory diagnosis of LA requires careful adherence to the SSC Subcommittee on Lupus Anticoagulants/Phospholipid-dependent Antibodies guidelines. Four sequential steps are required, including: screening tests, mixing studies (to establish the presence of an inhibitor), confirmatory tests based on increased or altered PL concentrations, and ruling out other coagulopathies (for example, factor VIII inhibitor).

scholarly journals Beta 2-glycoprotein I is a requirement for anticardiolipin antibodies binding to activated platelets: differences with lupus anticoagulants

Blood ◽  
1993 ◽  
Vol 81 (5) ◽  
pp. 1255-1262 ◽  
Author(s):  
W Shi ◽  
BH Chong ◽  
CN Chesterman
Keyword(s):  
Cross Reactivity ◽  
Anticardiolipin Antibodies ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Glycoprotein I ◽  
Activated Platelets ◽  
Major Interest ◽  
Thrombin Activation ◽  
Beta 2

Abstract Antiphospholipid (aPL) antibodies are of major interest not only because the lupus anticoagulant (LA) causes an inhibition of in vitro blood coagulation, but also because the presence of aPL antibodies confers a risk of thrombosis. The inhibition of in vitro phospholipid- dependent coagulation (LA) is thought to be caused by the binding of LA to procoagulant phospholipid surfaces, thus impeding the clotting process. Another class of aPL antibodies are those originally described to be directed against negatively charged phospholipids, in particular cardiolipin (ACA). ACA are usually directed against a complex antigen consisting of negatively charged phospholipid and a plasma protein, beta 2-glycoprotein I (beta 2-GPI). Further, there is antibody heterogeneity even within individual patients so that ACA and LA are separable using physicochemical techniques such as ion exchange chromatography and chromatofocusing. Using such techniques we have enriched Ig fractions for LA and ACA from two patient plasmas. The majority of Ig with LA activity had a pI of 7.2 to 7.3 whereas ACA had a pI of 5.0 to 5.2. Using these enriched fractions labeled with [125I]- iodine we have shown that LA binds to platelets in a specific and saturable manner. Binding is dependent on thrombin activation. [125I]- ACA behaves differently. Like LA, binding is specific and dependent on thrombin activation but in this case requires the presence of beta 2- GPI. ACA, in the presence of beta 2-GPI, competes for binding with LA suggesting the same or contiguous site. There is no cross-reactivity of these antibodies with GPIIb/IIIa and the most likely binding site is phospholipid. In neither case does LA nor ACA have an effect on thrombin-induced release of serotonin or beta-thromboglobulin nor do they affect platelet aggregation induced by a number of agonists. This antibody binding may play an etiological role in thrombocytopenia associated with aPL, but does not explain thrombosis on the basis of hyperaggregability or increased platelet release.

Mechanism of action of β2-glycoprotein I-dependent lupus anticoagulants

Lupus ◽  
1998 ◽  
Vol 7 (2_suppl) ◽  
pp. 23-28 ◽  
Author(s):  
J Amout ◽  
J Vermylen
Keyword(s):  
Mechanism Of Action ◽  
Molecular Basis ◽  
Current Knowledge ◽  
Indirect Evidence ◽  
Integrated Model ◽  
Anticardiolipin Antibodies ◽  
Pathogenic Role ◽  
Lupus Anticoagulants ◽  
Glycoprotein I

There is accumulating evidence showing that lupus anticoagulants (LA) are more strongly associated with thrombosis than anticardiolipin antibodies. In addition, indirect evidence has been presented indicating that β2GPI-dependent LA are more strongly associated with thrombosis than prothrombin-dependent LA. From this, one may assume that anti-β2GPl antibodies with LA activity are more pathogenic than anti-β2GPI antibodies without LA activity. Therefore, it is of the utmost importance to understand the molecular basis on which some anti-β2GPI antibodies behave as LA. In this presentation, the current knowledge on the interaction of β2GPI with phospholipids and with anti-β2GPI antibodies is reviewed and an integrated model for the anti-β2GPI - dependent LA activity is proposed with implications for a pathogenic role of these particular antibodies.

Anticardiolipin Antibodies Block the Inhibition by β2-Glycoprotein I of the Factor Xa Generating Activity of Platelets

1993 ◽  
Vol 70 (02) ◽  
pp. 342-345 ◽  
Author(s):  
Wei Shi ◽  
Beng H Chong ◽  
Philip J Hogg ◽  
Colin N Chesterman
Keyword(s):  
Antiphospholipid Antibodies ◽  
Lupus Anticoagulant ◽  
Fetal Loss ◽  
Factor Xa ◽  
Anticardiolipin Antibodies ◽  
Recurrent Fetal Loss ◽  
Glycoprotein I ◽  
Activated Platelets ◽  
Inhibit Factor

SummaryAntiphospholipid antibodies, defined either by lupus anticoagulant (LA) activity or positive anticardiolipin immunoabsorbent assay (ACA) are associated with a predisposition to thromboses, recurrent fetal loss or thrombocytopenia. The mechanisms for these predispositions remain undefined. We have enriched immunoglobulin fractions from two patient plasmas to obtain antibodies with LA activity but no ACA, or conversely, with ACA positivity but no LA, in order to investigate in vitro characteristics which might explain a thrombotic propensity. β2-glycoprotein I (β2-GPI), the plasma cofactor required for ACA binding to negatively charged phospholipid, has previously been shown to inhibit prothrombinase generation in the presence of activated platelets (8). We now report that β2-GPI, at physiological concentrations, inhibits the generation of factor Xa in the presence of activated gel-filtered platelets. Further, ACA interferes with this inhibition, resulting in protracted, unopposed factor Xa generation. This interference with β2-GPI, a natural anticoagulant component of plasma, is potentially prothrombotic. LA immunoglobulins behave differently and inhibit factor Xa generation in a manner similar to β2-GPI. These findings provide the basis for a previously unsuspected mechanism for thrombosis in patients with aPL.

scholarly journals Antiphospholipid syndrome: a clinical and laboratorial challenge

2014 ◽  
Vol 60 (2) ◽  
pp. 181-186 ◽  
Author(s):  
Luci Maria Santana Dusse ◽  
Fernanda Dias e Silva ◽  
Letícia Gonçalves Freitas ◽  
Danyelle Romana Alves Rios ◽  
Sandra Cristina Armond ◽  
...  
Keyword(s):  
Antiphospholipid Syndrome ◽  
Fetal Loss ◽  
Anticardiolipin Antibodies ◽  
Major Protein ◽  
Protein Targets ◽  
Clinical Criteria ◽  
Glycoprotein I ◽  
Increased Sensitivity ◽  
Commercial Kits ◽  
Positive Results

Antiphospholipid syndrome (APS) is an acquired autoimmune thrombophilia characterized by the presence of a heterogeneous family of antibodies that bind to plasma proteins with affinity for phospholipid surfaces. The two major protein targets of antiphospholipid antibodies are prothrombin and β2-glycoprotein I (β2GPI). APS leads to aprothrombotic state, and it is characterized by the occurrence of arterial, venous or microvascular thrombosis or recurrent fetal loss. The diagnosis of APS is based on a set of clinical criteria and the detection of lupus anticoagulant (LA), anticardiolipin antibodies (ACA) or anti-β2GPI in plasma. Although laboratory tests are essential for APS diagnosis, these tests have limitations associated with the robustness, reproducibility and standardization. The standardization of diagnostic tests for detection of APLAs has been a challenge and a variety of results have been obtained using different commercial kits and in-house techniques. An increased sensitivity of the ELISA kits for detection of ACA effectively has contributed to APS diagnosis. However, the lack of specificity associated with a high number of false-positive results is a clinical and laboratorial challenge, since such results may lead to mistaken clinical decisions, such as prescription of oral anticoagulant, leading to the risk of hemorrhaging. Furthermore, clinicians are often unfamiliar with these tests and have difficulty interpreting them, requiring interaction between clinical and laboratory professionals in order to ensure their correct interpretation.

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