Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P02749 (beta2-glycoprotein I)
 836 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tissue factor is the membrane-associated protein which mediates activation of factors IX and X by factor VII. In a purified, reconstituted bovine system, factor X activation by the tissue factor-factor VIIa complex is inhibited by the mixed apoproteins from human high density lipoprotein (HDL) and by isolated apolipo-protein A-II (apo A-II). Other proteins found associated with plasma lipoproteins, apolipoprotein A-I (apo A-I), C-reactive protein (CRP), and beta 2-glycoprotein I (beta 2 GPI), have been examined for effects on the activation of factor X by tissue factor-factor VIIa. In these experiments, bovine tissue factor, reconstituted into phosphatidylserine-phosphatidylcholine (PS/PC; 30/70) vesicles, was used at a single concentration while factor X (the substrate), factor VIIa (the enzyme), and the potentially inhibitory proteins were varied in a continuous chromogenic assay. Apo A-II and CRP clearly inhibit tissue factor-factor VIIa activation of factor X, while apo A-I and beta 2 GPI have little or no effect. These results demonstrate that different lipid binding proteins vary in their effects on tissue factor activity.
 ...
PMID:Effects of lipid-binding proteins apo A-I, apo A-IL, beta 2-glycoprotein I, and C-reactive protein on activation of factor X by tissue factor--factor VIIa. 313 84

Antiphospholipid antibodies are a diverse group of immunoglobulins initially thought to have specificity to phospholipid epitopes. It is apparent that autoimmune anticardiolipin antibodies require a serum cofactor beta-2-glycoprotein I (beta 2GPI) for their binding to phospholipids. Lupus anticoagulant also may bind to phospholipids by beta 2GPI or by prothrombin. The description of binding to protein-phospholipid epitopes may explain several perplexing features of these antibodies both in vitro and in vivo. Antiphospholipid antibodies have a well-established association with clinical disease--in particular thrombosis, thrombocytopenia and recurrent fetal loss. The mechanism of the predisposition to thrombosis seen with these antibodies is poorly understood. It has been suggested that they may cause endothelial dysfunction by causing increased tissue factor expression, by inhibiting prostacyclin secretion or by inhibiting fibrinolysis. Various platelet-activating activities have also been described. The evidence that antiphospholipid antibodies promote thrombosis by effects on endothelium or platelets is inconclusive. Inhibition of protein C activation, or of activated protein C action, has been demonstrated in vitro. A poor correlation between thrombosis in vivo and these inhibitory effects has been found. Beta-2-glycoprotein I has been identified as a cofactor for binding to phospholipid by thrombogenic anticardiolipin antibodies. That beta 2GPI may be a natural anticoagulant of importance remains to be proved. Inhibition by antiphospholipid antibodies of this anticoagulant function could explain the propensity to thrombosis seen in association with these antibodies.
 ...
PMID:Antiphospholipid antibodies and thrombosis. 784

Great progress has been made within the past 10 years in characterizing, assaying, and describing mechanism(s) of action in vitro of antiphospholipid antibodies (a-PL Abs); three prominent members are reagin, anticardiolipin antibodies (a-CL Abs), and the lupus anticoagulants (LAC). The major focus of this review is on basic and current biochemical and immunologic research. First, the biochemistry, structural composition, and sources of anionic and dipolar ionic (zwitterionic) phospholipids are discussed together with several serum antibodies directed to these phospholipids. Cardiolipin, the most acidic phospholipid (net negative charge of 2 at pH 7.0) has been historically important as an antigen for testing reagin in syphilis serology, and currently is part of the antigenic composition used in the Venereal Disease Research Laboratory (VDRL) tests. In this connection, the chronic biological false-positive test for syphilis and the LAC are discussed in association with autoimmune disorders such as systemic lupus erythematosus. Second, a naturally occurring plasma anticoagulant in vitro and a critical cofactor for binding of purified autoimmune a-CL Abs to cardiolipin is considered, the beta 2-glycoprotein I (beta 2-gpI). This single-chain plasma polypeptide is highly glycosylated, has 326 amino acids, a molecular weight of 50 kD, and is characterized by repeating amino acid motifs or domains that structurally resemble multiple loops. The highly cationic C-terminal fifth domain binds to anionic phospholipids. The beta 2-gpI is a member of the short consensus repeat superfamily of proteins, and is compared with other proteins with similar domains. Third, experiments are detailed for defining LAC and distinguishing it from other a-CL Abs. Cofactors are also associated with LAC and include beta 2-gpI, prothrombin, protein C, protein S, tissue factor, and factor XI. Thus, LAC antibodies are heterogeneous, and no individual assay can detect all LACs. Because patients with syphilis and other infectious diseases have no cofactor associated with a-CL Abs, their plasma LACs are negative. The a-CL Abs found in infection are not associated with the clinical features of the antiphospholipid syndrome. LAC assays are important because of the pathogenetic association with clinical observations of venous and arterial thrombosis, thrombocytopenia, and recurrent fetal loss. Finally, reports leading to development of currently used direct solid-phase enzyme-linked immunosorbent assays (ELISA) for testing a-PL Abs are outlined; these developments have greatly increased understanding of the basic immunology of target antigens and their respective antibodies. Of significance, a-CL Abs cross-react with other anionic phospholipids. Additionally, the results of these assays led to the realization that high levels of circulating a-PL Abs over long periods are associated with a number of clinical problems now known collectively as the antiphospholipid syndrome.
 ...
PMID:Antiphospholipid antibodies: basic immunology and assays. 914 49

The beta2-glycoprotein I (beta2-GPI) is known for its procoagulant as well as anticoagulant properties. The influence of beta2-GPI on tissue factor (TF) activity was investigated by chromogenic assays for both factor Xa generation and factor VIIa activity. When 1.36 mg/mL beta2-GPI was added to phospholipids prior to the addition of TF and factor VIIa, the TF activity was moderately inhibited by beta2-GPI in a concentration-dependent manner. Inhibition of TF activity by beta2-GPI required incubation for at least 20 min. When beta2-GPI was added to the mixture of phospholipids and TF followed by the addition of factor VIIa, the TF activity was little affected by the addition of beta2-GPI. The TF activity was inhibited when beta2-GPI was added after forming a complex with TF and factor VIIa. The results suggest that beta2-GPI inhibits both the reconstitution of TF with phospholipids and factor Xa generation by the TF factor-VIIa complex but does not affect the formation of a TF factor-VIIa complex.
 ...
PMID:The influence of beta2-glycoprotein I on tissue factor activity. 970 50

Anti-beta 2-glycoprotein I antibodies bind to endothelial cells through beta 2-GPI. The antibodies are present in patients with systemic lupus erythematosus and antiphospholipid syndrome and are associated with the pathogenesis of the disease. Anti-endothelial cell antibodies that react with constitutive antigens on ECs are present in patients with vasculiditis and other diseases. Both types of antibodies can activate ECs. Frequent findings in APLS and vasculitis are fibrin deposits and thromboembolic phenomena. These indicate that the coagulation system is activated. However, the mechanism of activation is not clear. ECs generate tissue factor upon stimulation with various substances. In the present study we report that monoclonal anti-beta 2-GPI antibodies and AECAs, derived from a patient with primary APLS and a patient with Takayasu's arteritis, respectively, induce a potent tissue factor in ECs. The production of TF activity, TF antigen and TF mRNA is dose and time dependent. The TF activity was induced also by F(ab)2 but not by Fc fragments and was abolished completely by pre-incubation with ant-TF antibodies. The TF that is induced in ECs by AECAs with and without beta 2-GPI specificity may activate the coagulation and thereby play a major role in the pathogenesis of fibrin deposition and thrombus formation in diseases that are associated with the presence of these antibodies.
 ...
PMID:Anti-beta 2-glycoprotein I antibodies and anti-endothelial cell antibodies induce tissue factor in endothelial cells. 1090 14

Expression of tissue factor activity on cells in contact with flowing blood is the trigger for physiological coagulation as well as many types of thrombosis. A number of older observations and considerable recent data suggest that increased tissue factor activity is an important cause of hypercoagulability in the antiphospholipid syndrome. Potential mechanisms contributing to upregulation of the tissue factor pathway include increased expression of tissue factor due to increased transcription, increased functional activity of tissue factor molecules due to de-encryption and decreased activity of tissue factor pathway inhibitor. Autoantibodies and/or immune complexes appear to play a major role in enhanced tissue factor activity, although increased levels of inflammatory cytokines may also contribute. Anti-beta 2-glycoprotein I autoantibodies have been specifically implicated in the antibody-mediated enhancement of tissue factor activity.
 ...
PMID:Tissue factor pathway and the antiphospholipid syndrome. 1096 13

On the basis of the role of immuno-mediated inflammation in atherosclerosis we investigated, (1) the prevalence of anti-endothelial cell antibodies (AECA) in ischaemic heart disease (IHD); (2) if beta2-glycoprotein I (beta2-GPI) was the target antigen of AECA; (3) the relationship between AECA, tissue factor (TF) and tissue factor pathway inhibitor (TFPI). In 93 consecutive IHD patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and 105 controls AECA were detected by ELISA on human umbilical vein endothelial cells (HUVEC). AECA positive sera were evaluated for anti-beta2-GPI antibodies by ELISA. TF and TFPI plasma levels were assessed by ELISA. Twelve of 93 (12.9%) IHD patients and only one of 105 controls (0.95%) were AECA positive. The prevalence of AECA was higher in unstable angina (UA) than in effort angina (EA) (P=0.01). Three of 12 AECA positive sera resulted positive for anti-beta2-GPI and showed a marked decrease in EC-binding when tested on HUVEC cultured in serum-free medium. The binding was restored by the addition of beta2-GPI. TF and TFPI levels were similar in AECA positive and AECA negative patients. The rate of angiographically documented clinical recurrences was 66.7% in the AECA positive and 14.8% in the AECA negative group (P=0.0004) with a significant relationship between restenosis and AECA (P<0.0001), unchanged by the inclusion of cardiovascular risk factors in the regression model. Our results suggest a 'role' for AECA in the immune-mediated inflammation in UA beta2-GPI is not the only AECA target antigen. AECA are not responsible for high TF and TFPI levels. The high rate of clinical recurrences after PTCA, confirmed by angiography, in AECA positive patients is in line with such a role and suggests further large-scale 'ad hoc' studies.
 ...
PMID:Activation of the immune system and coronary artery disease: the role of anti-endothelial cell antibodies. 1116 76

It is well known that monocytes may play an active role in thrombogenesis, since they may express on their surface tissue factor, the major initiator of the clotting cascade. The results of this investigation demonstrate beta-2-glycoprotein I (beta2-GPI) mRNA expression by human peripheral blood monocytes, indicating that these cells synthesize beta2-GPI. In addition, we show beta2-GPI expression on cell surface of these cells by flow cytometric analysis, and the presence of this protein in cell lysate by Western blot. Interestingly, beta2-GPI expression on monocytes is significantly increased in patients with anti-phospholipid syndrome (APS) or systemic lupus erythematosus (SLE) as against healthy blood donors and correlates with tissue factor expression on monocytes. These findings support the view that monocytes are able to synthesize beta2-GPI and suggest that patients with APS may have increased beta2-GPI exposure on cell surface, which leads to persistently high monocyte tissue factor expression and consequently to a prothrombotic diathesis.
 ...
PMID:Beta-2-glycoprotein I expression on monocytes is increased in anti-phospholipid antibody syndrome and correlates with tissue factor expression. 1278 Jul

Autoantibodies to beta2-glycoprotein I (beta2GPI) are believed to be the primary cause of coagulation abnormalities in patients with antiphospholipid syndrome (APS). Clinical features include a range of life-threatening thrombotic events and microangiopathies affecting multiple organ systems. Current standard of care relies on long-term, high-intensity anticoagulation and is associated with a high risk for serious bleeding events. The relation between autoantibodies and the pathophysiology of APS is not clearly understood, but numerous in vitro studies have characterized the effects of antiphospholipid autoantibodies on various components of the coagulation cascade, including tissue factor and the protein C pathway. The fine specificity of autoantibodies to beta2GPI is a subject of considerable debate; however, a body of evidence may offer resolution by integrating concepts of antibody affinity and assay sensitivity with carefully designed molecular studies. An investigational new therapy for APS is based on the approach that pathogenic antibodies may be reduced via depletion of circulating autoantibodies and induction of immune tolerance at the B-cell level. Preliminary results from a phase I/II clinical trial with LJP 1082, a B-cell toleragen, indicate the drug was well tolerated and may warrant further development for reduction of thrombotic events in patients with APS.
 ...
PMID:Therapeutic potential of toleragens in the management of antiphospholipid syndrome. 1537 72

The expression of tissue factor (TF) activity to flowing blood is the trigger for physiological coagulation as well as many types of thrombosis. A growing body of evidence suggests that increased tissue factor activity is a significant contributor towards the hypercoagulability associated with the antiphospholipid syndrome (APS). The increase in tissue factor activity appears to be due to increased transcription and translation of nascent tissue factor molecules but is not due to de-encryption of existing tissue factor molecules on cells. Autoantibodies and/or immune complexes circulating in APS patients appear to enhance the expression of tissue factor activity on monocytes and endothelial cells. Anti-beta2-glycoprotein I (beta2GPI) autoantibodies have been specifically implicated in the antibody-mediated enhancement of tissue factor activity. The presence of antibodies against tissue factor pathway inhibitor (TFPI) in certain APS patients suggests that negative regulation of tissue factor activity might also be impaired in these patients. Given a mechanism involving increased tissue factor activity in APS-associated thrombosis, agents specifically targeting tissue factor activity may be a novel and efficacious therapy that is safer than current approaches to the management of APS.
 ...
PMID:Mechanisms of autoantibody-induced monocyte tissue factor expression. 1550 69


1 2 3 Next >>