Antibodies to prothrombin crossreact with plasminogen in patients developing myocardial infarction

Autoantibodies to plasminogen and their role in tumor diseases

Plasma level of IgG autoantibodies to plasminogen was measured by ELISA in patients with benign prostatic hyperplasia (n=25), prostatic cancer (n=17), lung cancer (n=15), and healthy volunteers (n=44). High levels of IgG to plasminogen were found in 2 (12%) of 17 healthy women, in 1 (3.6%) of 27 specimens in a healthy man, in 17 (68%) of 25 specimens in prostatic cancer, in 10 (59%) of 17 specimens in lung cancer, and in 5 (30%) of 15 specimens in benign prostatic hyperplasia. Comparison of plasma levels of anti-plasminogen IgG by affinity chromatography showed 3-fold higher levels in patients with prostatic cancer vs. healthy men.

In vitro thrombolytic activity of Dhamasa (Fagonia arabica Linn.), Kushta (Saussurea lappa Decne.), and Guduchi (Tinospora cordifolia Thunb.)

Introduction:

Thrombotic disorders are among the major fatal conditions affecting the society. Treatment modalities used for such disorders are either surgical interventions or use of drugs such as urokinase, streptokinase (SK), or tissue plasminogen activators to dissolve the blood clots. These modalities have their own limitations and side effects apart from being expensive. There is a need for safer and cost effective antithrombolytic agents.

Aim:

To evaluate in vitro thrombolytic property of Dhamasa (Fagonia arabica Linn.), Kushta (Saussurea lappa Decne.), and Guduchi (Tinospora cordifolia Thunb.) plant extract.

Materials and Methods:

Venous blood drawn from 20 healthy volunteers was allowed to form clots which was weighed and treated with the extract of test plant materials to disrupt the clots. Weight of clot after and before treatment provided a percentage of clot lysis. SK was used as a positive and water as a negative control.

Statistical Analysis Used:

The significance between % clot lysis of five groups by means of weight difference was tested by the one-way ANOVA.

Results:

Clot lysis observed were 68.06%, 14.85%, 25.01%, 92.54%, and 3.00% for Dhamasa, Kushta, Guduchi, SK, and distilled water, respectively.

Conclusion:

Herbal extracts possess thrombolytic properties and lyse blood clots in vitro.

Antibodies with dual reactivity to plasminogen and complementary PR3 in PR3-ANCA vasculitis

Patients with inflammatory vascular disease caused by anti-neutrophil cytoplasmic autoantibodies (ANCA) can harbor antibodies not only to the autoantigen proteinase 3 (PR3) but also to complementary PR3 (cPR3(105-201)), a recombinant protein translated from the antisense strand of PR3 cDNA. The purpose of this study was to identify potential endogenous targets of anti-cPR3(105-201) antibodies. Patients' plasmapheresis material was tested for the presence of antigens reactive with affinity-purified rabbit and chicken anti-cPR3(105-201) polyclonal antibodies. Antigen-containing fractions were tested with patients' anti-cPR3(105-201) affinity-purified IgG, and putative protein targets were sequenced by mass spectrometry. Unexpectedly, plasminogen was identified as a target of anti-cPR3(105-201). Reactivity of affinity-purified antibodies from two patients was lost when plasminogen was converted to plasmin, indicating restricted specificity. Antiplasminogen antibodies from five patients bound plasminogen at a surface-exposed loop structure within the protease domain. This loop contains an amino acid motif that is also found in a portion of recombinant cPR3(105-201); site-directed mutagenesis of this sequence decreased antibody reactivity by 30%. Functionally, antiplasminogen antibodies delayed the conversion of plasminogen to plasmin and increased the dissolution time of fibrin clots. Serologically, antiplasminogen antibody levels were higher in PR3-ANCA patients (n = 72) than healthy control subjects (n = 63), myeloperoxidase-ANCA patients (n = 34), and patients with idiopathic thrombosis (n = 57; P = 0.001). Of the patients with PR3-ANCA, nine had documented deep venous thrombosis events, five of whom were positive for antiplasminogen antibodies. In summary, capitalizing on interactions with complementary proteins, specifically complementary PR3, this study identified plasminogen as a previously undescribed autoantigen in PR3-ANCA vasculitis.

IgG antibodies to plasminogen and their relationship to IgG anti-beta(2)-glycoprotein 1 antibodies and thrombosis

Reduced fibrinolytic activity has been described in primary antiphospholipid syndrome (PAPS) and may be responsible for thrombotic events. Some evidence supports a relationship between anti-plasminogen (PLG) antibodies, anti-beta(2)-glycoprotein 1 (beta(2)GP1) antibodies, and fibrinolysis, but their relationship is still unclear. The aim of study is to evaluate the association between IgG anti-beta(2)GP1 and IgG anti-PLG antibodies and thrombosis. Two groups of consecutive patients with PAPS and systemic lupus erythematosus (SLE): 32 patients with lupus anticoagulant (LAC), 32 patients without LAC, and 40 healthy controls were included. IgG against beta(2)GP1 and PLG antibodies were measured by enzyme-linked immunosorbent assay, and a value above the 99th percentile of the normal healthy control was considered as positive, and their interrelationship with thrombosis was evaluated by Pearson Chi-squared test. Cross-reactive antibodies binding to PLG and beta(2)GP1 were determined in a competitive and cross-inhibition assay. Levels of fibrinolytic activity in the presence of IgG fractions from patients and healthy controls were examined using a plasmin fluorogenic substrate assay. A high frequency of IgG anti-PLG antibodies (35.9%) was found in 64 patients, and its presence was associated with thrombosis (p = 0.001), which may be due to its ability to inhibit exogenous fibrinolysis. Coexistence of IgG anti-PLG and IgG anti-beta(2)GP1 antibodies was found in 11 of 64 patients and was related with thrombosis (p = 0.001). Cross-reactive antibody binding to PLG and beta(2)GP1 was found in IgG fractions from three patients and a monoclonal anti-beta(2)GP1 antibody BD4, and one of these three patients had thrombotic history. However, no significant association was found between IgG anti-PLG and IgG anti-beta(2)GP1 antibodies in patients. In conclusion, the prevalence of IgG anti-PLG was high in patients with PAPS and SLE and might relate with thrombosis. Cross-reactivity of IgG anti-beta(2)GP1 antibodies with PLG may occur in the sera of patients.

The clinical significance of anti-prothrombin antibodies for risk assessment of thromboembolism in patients with lupus anticoagulant

INTRODUCTION

Thromboembolism is a common manifestation of lupus anticoagulant (LA), however only a subgroup of LA-patients is affected by thrombosis. Study objective was to investigate whether anti-prothrombin antibodies can identify LA-patients at increased risk for thrombosis.

MATERIALS AND METHODS

In total 79 patients, 50 with (42 men/8 women) and 29 without thrombosis (21 men/8 women), were investigated for their presence of anti-prothrombin IgG and IgM antibodies using assays from two different manufacturers (Aeskulisa=assay I, CoaChrom=assay II).

RESULTS

The prevalence of elevated levels of anti-prothrombin IgG, IgM as well as IgG and/or IgM antibodies was 66% [assayI] (36% [assayII]), 38% (24%) and 72% (50%) in patients with thrombosis and 55% (24%), 28% (28%) and 66% (41%) in patients without thrombosis, respectively. Neither anti-prothrombin IgG or IgM nor IgG and/or IgM antibodies were found to indicate an increased risk for thrombosis. In the subgroup of patients with arterial or venous thrombosis there was also no association between anti-prothrombin antibodies and thrombosis. The comparison of median levels of IgG and IgM anti-prothrombin antibodies between patients with and without thrombosis yielded a borderline statistically significant difference only for anti-prothrombin IgG antibodies by using assay II (p=0.033), all other comparisons were not statistically significant.

CONCLUSIONS

In conclusion, presence of anti-prothrombin antibodies was not associated with thromboembolism in LA-patients.

Current concepts on the pathogenesis of the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an important cause of acquired thrombophilia. It is characterized by the core clinical manifestations of thrombosis, either venous or arterial, and in women it can also be associated with recurrent fetal loss. The detection of persistently elevated levels of antiphospholipid antibodies (aPL Abs) is a requisite laboratory feature for the diagnosis to be made. The dominant antigenic targets in APS are beta 2-glycoprotein I (β2-GPI) and prothrombin. There is an accumulating body of experimental evidence that suggests that specific subgroups of aPL Abs may directly contribute to disease pathogenesis. This review critically examines the experimental evidence underlying the various propositions made to explain how these antibodies may predispose to disease in humans. Furthermore, it also examines the evidence relating to the immunologic mechanisms that may contribute to the breakage of peripheral tolerance in this disorder. Delineating the strengths and limitations of the experimental evidence accumulated thus far will hopefully stimulate further experimentation toward achieving the ultimate goal of precisely defining the dominant pathogenic mechanisms operational in APS. This may pave the way for the development of improved therapies.

Autoantibodies and self-reported health complaints in relatives of systemic lupus erythematosus patients: a community based approach

First-degree relatives (FDRs) and spouses to a population-derived cohort of lupus patients were investigated for the occurrence of selected autoantibodies and self-reported health complaints. A healthy reference population was included. The lupus population consisted of 103 index cases. A total of 275/375 available relatives accepted to enter the study. Two hundred and twenty-six/315 (72%) were FDRs and 49/60 (82%) were spouses. Serum was analysed for ANA using indirect immunofluorescence on Hep-2 cells at the following dilutions: 1:40, 1:80 and 1:160 and in addition sera were tested for anti-dsDNA, IgM RF, ACA (IgM, IgG), anti-beta2GPI (IgM, IgG) and antibodies to prothrombin. ANA positivity occurred more frequently in FDRs compared with spouses and controls at serum dilution 1:160 (10 versus 0% and 2.5%, respectively, P = 0.04 and P < 0.01), 1:80 (24 versus 4% and 5%, respectively, P = 0.003 and P < 0.001) and 1:40 (31 versus 10% and 10%, respectively, P = 0.006 and P < 0.0001). ANA positivity in FDRs occurred randomly, irrespective of family relationship. Fifty-three/184 versus 2/32 FDRs to patients with definite SLE (D-SLE) and incomplete SLE (I-SLE), respectively, tested ANA positive at 1:80 (P < 0.05). FDRs with ANA titer at 80 were affiliated to lupus probands with high SLICC scores (P < 0.05). Self-reported health complaints, cardiovascular/thromboembolic events in particular, were more frequent among FDRs than in spouses. The population-based approach adopted in the present study supports previous clinic-based evidence of an increased propensity for autoantibody occurrence in relatives to SLE patients. In FDRs, present ANA positivity was associated with increased prevalence of health complaints and ANA positivity in FDRs was related to the criterial burden and cumulated damage in corresponding lupus probands. The low ANA frequency among spouses of SLE patients argues against a significant autoantibody triggering effect of shared environment in adult life.

Identification of Anti-Plasmin Antibodies in the Antiphospholipid Syndrome That Inhibit Degradation of Fibrin

The combined presence of anti-phospholipid Ab (aPL) and thrombosis is recognized as the antiphospholipid syndrome (APS). The aPL represent a heterogeneous group of Ab that recognize various phospholipids (PL), PL-binding plasma proteins, and/or PL-protein complexes. Recently, we found the presence of antithrombin Ab in some APS patients and that some of these anti-thrombin Ab could inhibit thrombin inactivation by antithrombin. Considering that thrombin is homologous to plasmin, which dissolves fibrin, we hypothesize that some APS patients may have Ab that react with plasmin, and that some anti-plasmin Ab may interfere with the plasmin-mediated lysis of fibrin clots. To test this hypothesis, we searched for anti-plasmin Ab in APS patients and then studied those found for their effects on the fibrinolytic pathway. The results revealed that seven of 25 (28%) APS patients have IgG anti-plasmin Ab (using the mean OD plus 3 SD of 20 normal controls as the cutoff) and that six of six patient-derived IgG anti-thrombin mAb bind to plasmin with relative K(d) values ranging from 5.6 x 10(-8) to 1 x 10(-6) M. These K(d) values probably represent affinities in the higher ranges known for human IgG autoantibodies against protein autoantigens. Of these mAb, one could reduce the plasmin-mediated lysis of fibrin clots. These findings suggest that plasmin may be an important driving Ag for some aPL B cells in APS patients, and that the induced anti-plasmin Ab may act either directly, by binding to plasmin and inhibiting its fibrinolytic activity, or indirectly, by cross-reacting with other homologous proteins in the coagulation cascade to promote thrombosis.

Lupus-Derived Antiprothrombin Autoantibodies from a V Gene Phage Display Library Are Specific for the Kringle 2 Domain of Prothrombin

Autoantibodies to prothrombin are common in patients with systemic lupus erythematosus. Although their presence is a risk factor for thrombosis, neither their origin nor their precise role in inducing the procoagulant state is known. We have developed a phage-display antibody library from patients with systemic lupus erythematosus with antiprothrombin antibodies, and we have selected two single-chain Fv antibody fragments (ScFvs) by panning on a prothrombin-coated surface. In prothrombin activation assays using purified components, these antibodies promoted prothrombin activation. These ScFvs, termed AN78 and AN129, bound to immobilized prothrombin in a concentration-dependent specific manner but not to other anionic phospholipid binding proteins such as beta2-glycoprotein I or annexin V. Phosphatidylserine-bound prothrombin, but not soluble prothrombin, inhibited the binding suggesting that the epitope is available only on immobilized prothrombin. To localize the epitope, prothrombin was treated with thrombin or factor Xa and various prothrombin activation fragments were subsequently isolated and tested in ELISA with the ScFvs. Both AN78 and AN129 bound to prethrombin I (the fragment lacking the Gla domain and the first kringle domain), to fragment 1.2 (containing Gla and the two kringle domains only) and to fragment 2 but not to thrombin, thus localizing the cognate epitope to the kringle 2 domain in prothrombin. Analysis of the cDNA sequences of these antibodies show clustered mutational patterns in the complementarity determining region, suggesting that variable domains are the products of antigen-driven B cell clonal maturation.

Anti-prothrombin antibodies cause thrombosis in a novel qualitative ex-vivo animal model

Anti-prothrombin antibodies (aPT) are associated with thrombotic manifestations, and their association with reproductive failure is debatable. The aim of this study was to examine whether aPT could induce thrombosis and other clinical manifestations of the anti-phospholipid syndrome (APS). Mice were immunized with either prothrombin, beta2-glycoprotein-I (beta2GPI), or beta2GPI followed by prothrombin. The presence of clinical manifestation of APS, including thrombocytopenia, lupus anticoagulant and fetal resorption rates, was evaluated in all mice groups compared with nonimmunized mice. Thrombosis was studied in a novel ex-vivo model in which the aorta was sutured for 1 min and the presence or absence of visible thrombus was qualitatively evaluated. Immunized mice developed high autoantibody levels directed towards their immunizing autoantigens. The groups immunized with beta2GPI or beta2GPI/prothrombin, but not with prothrombin alone, developed prolonged aPTT, thrombocytopenia and increased fetal resorption rate. All prothrombin-immunized mice as well as most beta2GPI/prothrombin-immunized mice developed visible thrombus within the aorta. Some beta2GPI immunized mice developed very mild thrombus. None of the CFA/PBS-injected or the nonimmunized mice developed such thrombus. Active immunization with prothrombin or beta2GPI/prothrombin is associated with prothrombotic activity of blood in an ex-vivo model. This is the first direct evidence for thrombus induction by aPT.

Antibodies to tissue-type plasminogen activator (tPA) in patients with antiphospholipid syndrome: evidence of interaction between the antibodies and the catalytic domain of tPA in 2 patients

The causes of thrombosis and pregnancy loss in antiphospholipid syndrome (APS) are still unknown, although several hypotheses have been proposed and hypofibrinolysis has been implicated. Anti-tissue-type plasminogen activator (tPA) antibodies may induce fibrinolytic defects and preliminary data indicate an association with thrombosis in APS. We measured plasma anti-tPA antibody levels in 91 consecutive patients with APS, 91 healthy controls, 40 patients with antiphospholipid antibodies without APS symptoms, and 23 patients with systemic lupus erythematosus (SLE) without antiphospholipid antibodies and APS symptoms. Patients with APS had anti-tPA antibody levels higher than controls (P = .0001), patients with SLE (P = .0001), and asymptomatic antiphospholipid patients (P = .05). A subgroup of 53 patients had plasma levels of tPA antigen higher (P = .0001) and tPA activity lower (P = .05) than controls, with an inverse correlation (r = -0.454; P = .003) between anti-tPA antibody levels and tPA activity and no correlation with tPA antigen. The 2 patients with the highest antibody levels had tPA activity below the normal range. Their antibodies were, respectively, IgG1 and IgG3; both recognized human tPA, recombinant tPA, and the catalytic domain of tPA, but not beta 2-glycoprotein I, prothrombin, or plasminogen. Our data indicate that anti-tPA antibodies specifically interacting with the catalytic domain of tPA can be found in patients with APS, representing a possible cause of hypofibrinolysis.

Current status and implications of autoimmune antiphospholipid antibodies in relation to thrombotic disease

This review briefly describes the development of the concepts of antiphospholipid antibody and of antiphospholipid syndrome. It focuses on the two main antigenic targets, beta2 glycoprotein I and prothrombin. An excessive production of natural antibodies rather than an immune response to exogenous antigen is proposed as pathogenetic for the development of these antibodies. The review attempts to explain how some of these antibodies are anticoagulant in vitro yet prothrombotic in vivo. The final section discusses when to test for such antibodies, how to test and how to consider treatment of patients with the antiphospholipid syndrome.

A study on associations between antiprothrombin antibodies, antiplasminogen antibodies and thrombosis

Anti-prothrombin antibodies are a frequent cause of lupus anticoagulant (LAC), a thrombotic risk factor. Prothrombin shares structural homology with plasminogen, a kringle protein with an important role in fibrinolysis. Cross-reactivity between antiprothrombin antibodies and plasminogen has been described. To study associations between LAC, IgG and IgM class antiprothrombin and antiplasminogen antibodies, plasminogen activity levels and thrombosis in selected patients with systemic autoimmune diseases. Patients included forty-six consecutive LAC-positive patients (29 with systemic lupus erythematosus (SLE); 33 with a thrombotic history), 38 patients without LAC (36 with SLE; seven with a history of thrombosis) and 40 healthy controls. In the total group of 84 patient samples, the prevalence of antiprothrombin and antiplasminogen antibodies was 30 and 38%, respectively. There was no significant relationship between the presence of these antibodies. In contrast to presence of antiplasminogen antibodies, presence of antiprothrombin antibodies was statistically significant related to thrombosis. Thirteen samples had antiprothrombin and antiplasminogen antibodies of similar isotype (IgG, n= 4; IgM, n= 9). Of these, all but one had LAC and 11/13 came from patients with a history of thrombosis. Simultaneous presence of IgM-class antiprothrombin and antiplasminogen antibodies had a significant association with thrombosis. Levels of plasminogen activity were similar in samples from healthy controls and patients (with or without antiplasminogen antibodies or thrombosis). Anti-prothrombin antibodies and antiplasminogen antibodies occur frequently in patients with systemic autoimmune disease. Anti-prothrombin antibodies, but not antiplasminogen antibodies are a risk factor for thrombosis. Anti-plasminogen are in most cases unrelated to antiprothrombin antibodies.

Immunologic and hematologic properties of antibodies to prothrombin and plasminogen in a mouse model

Antibodies to prothrombin have been associated with venous and arterial thrombosis, and they cross-react with a structurally closely related protein plasminogen. We immunised 16 mice with human prothrombin and 15 mice with human plasminogen. Mice immunised with prothrombin developed cross-reactive antibodies to plasminogen (12/16), beta2-glycoprotein I (4/16), tissue-type plasminogen activator (6/16) and cardiolipin (11/16). Mice immunised with plasminogen developed cross-reactive antibodies to prothrombin (8/15), tissue-type plasminogen activator (2/12) and cardiolipin (5/12). Functional effects of antibodies were examined. Immunisation with prothrombin induced lupus anticoagulant activity in 9/14 mice. In mice immunised with plasminogen, radial fibrinolysis was inhibited in 8/10 and plasminogen activation in the chromogenic assay was inhibited in 9/11. No cross-functionality was observed. In conclusion, antibodies to prothrombin and plasminogen cross-react in vivo. Antibodies to prothrombin and plasminogen have different functional profiles, immunisation with prothrombin leads to prolonged blood clotting time, and immunisation with plasminogen induces antibodies interfering with fibrinolysis.

Autoantibodies to modified LDLs and other phospholipid-protein complexes as markers of cardiovascular diseases

Recent studies have suggested that antiphospholipid antibodies contribute to the development of atherothrombosis by enhancing atherogenesis and/or by interfering with blood coagulation. The antigenic targets of antiphospholipid antibodies are cardiolipin, oxidized LDL, beta2-glycoprotein I, or prothrombin. Oxidized LDL and beta2-glycoprotein I are found in the atherosclerotic plaque and antibodies to these proteins enhance in vitro the accumulation of modified LDL into macrophages. Autoantibodies binding to modified LDL, cardiolipin and prothrombin have been associated with atherosclerosis and its thrombotic complications in sero-epidemiological studies. These autoantibodies can be used as markers of atherosclerosis but their possible pathogenic role in the athero- and thrombogenesis needs further studies.

Acquired autoantibodies to coagulation factors

Acquired coagulation factor antibodies are either alloantibodies or autoantibodies. Alloantibodies are formed when the body reacts to an external antigen. Commonly, alloantibodies arise when a patient who has a congenital clotting factor deficiency is infused with a blood product. Alternately, patients exposed to a coagulation protein from a different species may develop alloantibodies to the animal protein that cross-reacts with their own protein. On the other hand, autoantibodies develop spontaneously in people without pre-existing factor deficiencies and without exposure to an external antigen. These antibodies may neutralize function of a clotting factor, promote rapid clearance of a clotting factor from the blood, or alter the clotting factor in such a way that the protein-antibody complex acquires a unique function. This review focuses on recent reports of autoantibodies directed against fibrinogen, prothrombin, factor V, factor VII, factor X, and von Willebrand factor, in which these various activities of autoantibodies are illustrated.

Anti-prothrombin antibodies and their relation with thrombosis and lupus anticoagulant

Antiphospholipid antibodies are a heterogeneous group of antibodies, comprising antibodies with different antigen specificity. Prothrombin is one of the antigens which can be detected by antiphospholipid antibodies and therefore anti-prothrombin antibodies belong to the antiphospholipid antibody family. The presence of antiphospholipid antibodies correlates strongly with thromboembolic complications; however a mechanism by which these autoantibodies induce a thrombotic complication in vivo is not understood. The classic assays for the detection of antiphospholipid antibodies (LAC and anticardiolipin ELISAs) aim to measure all the antiphospholipid antibodies present in the samples without making a distinction between the different subspecificities of the antibodies present in one single sample. Moreover, most of the in-vitro studies performed were carried out with total IgGs, which contain a mixture of antibodies. The absence of an accurate characterization of the plasma samples and the lack of specificity of the IgGs used in in-vitro tests makes it difficult to determine the contribution of antiprothrombin antibodies to the thrombotic complications. Here we review and critically analyse the literature regarding the clinical relevance of the presence of antiprothrombin antibodies and the possible participation of these antibodies in the pathogenesis of the thrombotic complications.

Antiphospholipid antibodies and myocardial infarction

In prospective studies, increased levels of cardiolipin-biding antibodies and autoantibodies to oxidized low-density lipoprotein (LDL) have been observed in patients with myocardial infarction (MI). These findings suggest that antiphospholipid antibodies may contribute to the development of MI. The 'oxidative-modification hypothesis' in the pathogenesis of atherosclerotic heart disease is based on the oxidation of LDL, its accumulation into arterial wall, and the development of chronic inflammation in the atheroma. Evidence of enhanced lipid peroxidation and its association with antiphospholipid antibodies has been recently reported in SLE patients. There is also epidemiological data showing a remarkably increased risk of MI in SLE. In this review, the role of different types of antiphospholipid antibodies in the development of atherosclerotic heart disease is evaluated with particular attention to their potential pathogenic mechanisms and the possibilities in the prevention of MI associated with antiphospholipid antibodies.