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.

Anti beta2-glycoprotein I antibodies: clinical significance

The introduction of anticardiolipin antibody (aCL) assay, described in 1983, was able to focus much attention on the study of patients suffering from thrombosis, repeated fetal loss and thrombocytopenia, and allowing the identification of the so called antiphospholipid syndrome (APS). The identification of beta2 glycoprotein I (beta2GPI) as an essential component of the antigenic complex recognized by aCL suggested that this molecule could be a direct target of the antibody response. Since then, different groups have described ELISAs for the detection of anti beta2GPI antibodies, applied to the clinical evaluation of patients with APS, and showing an overall better specificity. Recently, anti beta2GPI were also shown to bind apoptotic bodies resulting in an alteration of their physiological clearance with the triggering of TNFalpha release. This observation suggests that anti beta2GPI may also modify the immunogenicity of apoptotic bodies and of the autoantigens that they contain.

Diagnosis of the antiphospholipid syndrome: a proposal for use of laboratory tests

The presence of antiphospholipid (aPL) antibodies has been associated with thrombosis, pregnancy loss and thrombocytopenia in the antiphospholipid syndrome (APS). The anticardiolipin and the lupus anticoagulant tests are frequently used to detect aPL antibodies. The anticardiolipin ELISA utilizes cardiolipin coated on polystyrene plates as antigen and is a very sensitive test but lacks specificity, since it can be positive in a number of infectious (such as syphilis, HIV) and autoimmune diseases other than APS. In an effort to improve specificity, new ELISA techniques that employ alternative antigens (such as beta2-glycoprotein 1, particularly when coated onto oxidized microtiter plates or mixture of phospholipids) have been developed. Several investigators have reported that these new assays enable more specific determination of aPL antibodies and thus can be used more reliably for the diagnosis and confirmation of APS. This article examines the results of those studies, including data that shows correlations of these assays with clinical manifestations of APS, and proposes a new protocol for the use of laboratory tests in the diagnosis of APS.

Antiphospholipid antibodies and infertility: fact or fallacy

Some clinicians are convinced that antiphospholipid antibodies, including antibodies to any one of five-to-seven phospholipid antigens, are associated with infertility. Additionally, some clinicians recommend that infertile women who have antiphospholipid antibodies and are undergoing in-vitro fertilization should be treated with heparin to improve the rate of pregnancy. However, experts disagree regarding the relationship between antiphospholipid antibodies and infertility. There is also substantial evidence that treatment with heparin does not alter the rate of pregnancy following in-vitro fertilization. Why the confusion? Probable culprits include variation in study design and the selection of infertile patients. Another important problem is that assays for antiphospholipid antibodies other than anticardiolipin are not standardized. Before the real relationship between antiphospholipid antibodies and infertility is discovered, assays for antiphospholipid antibodies other than anticardiolipin must be standardized and properly designed studies conducted. Randomized, controlled trials must be done to determine if heparin should be recommended as an adjunctive treatment for in-vitro fertilization in women with antiphospholipid antibodies.

Methods for subtyping lupus anticoagulants

Two simple procedures were tested for their potential to identify beta2-glycoprotein 1 (beta2GP1) or prothrombin cofactor dependence among lupus anticoagulants (LA). The first comprised mixing test plasma 1:4 with beta2GP1-deficient plasma instead of with normal plasma. beta2GP1 deficiency decreased, but did not abolish most LA detectable in KCT, DRVVT and APTT clotting tests. Mixing 1:4 with bovine plasma was evaluated in a second test based on the KCT in the expectation that prothrombin-dependent LA would be preferentially shortened. Bovine plasma had a similar correcting effect on LA in all three tests considered here. Conversely, a prothrombin antibody was found to have similar prolonging effect on all three of these tests. LA patient plasmas displayed considerable heterogeneity when analysed using a combination of these two tests. The clinical significance of these tests remains uncertain. DRVVT and KCT tests do not appear to discriminate beta2GP1-dependent from prothrombin-dependent LA.

Many faces of lupus anticoagulants

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).

The results of diagnostic studies for thrombophilia in a large group of patients with a personal or family history of thrombosis

The range of tests used in the evaluation of thrombophilia has been altered by the recent recognition of common genetic defects predisposing to thrombosis such as factor VLeiden (FVR506Q), enzyme deficiencies causing hyperhomocysteinemia, and improvement in the sensitivity and utilization of assays for antiphospholipid antibodies. In this study, the outcomes of laboratory evaluation of 402 patients with thrombophilia were reviewed and correlated with clinical data. A predisposing factor was present (positive diagnosis, group A) in 110 patients (27%), the test results of 111 patients (28%) could not be definitively interpreted (equivocal results, group B), and the test results of 181 (45%) were normal (group C). The median age of the group A patients was 48 years (range, 3.7-88 years), suggesting that evaluation of patients over the age of 50 is worthwhile. Of the 110 patients in group A, 84% had single defects and 16% had combined defects. The most common defect was factor VLeiden (44 patients). Equal numbers of patients presenting with arterial and venous thromboses were evaluated. Patients with arterial events were less likely to have a definable laboratory defect (33 of 132 [25%]) than were those with venous events (50 of 136 [37%]). Factor VLeiden was the most frequent finding in patients with venous events, and lupus anticoagulant or anticardiolipin antibodies were the most frequent findings in patients with arterial events. Positive diagnoses were made in patients on anticoagulants, indicating that this should not preclude investigation. Our study confirms the need for thorough evaluation to assess thrombotic risk, and it reflects the impact of newly identified thrombophilic disorders on the expected outcome of laboratory evaluation for thrombophilia.

Multiple antiphospholipid tests do not increase the diagnostic yield in antiphospholipid syndrome

The family of antiphospholipid antibodies (aPL) includes a heterogeneous population of autoantibodies whose specificity is directed against not only phospholipids, but their complex with plasma proteins. Anticardiolipin antibodies (aCL) and lupus anticoagulant (LA) tests are widely performed to screen the aPL family which is associated with thrombotic complications in patients with systemic lupus erythematosus (SLE) or antiphospholipid syndrome (APS). The clinical significance of other aPL tests, including antibodies against phosphatidylserine (aPS), phosphatidylinositol (aPI), phosphatidic acid (aPA), phosphatidylcholine (aPC) and phosphatidylethanolamine (aPE), has not been established. The purpose of this study was to evaluate whether multiple aPL tests have enhanced diagnostic value for APS. We tested IgG/M/A aPS, aPI, aPA, aPC and aPE by ELISA using 10% bovine serum as blocking and sample diluent in 26 SLE patients with clinical manifestations of APS, but negative for both aCL and LA (Group 1). The results were compared with 32 SLE patients without any features of APS (Group 2) and 24 SLE patients with APS (aCL and/or LA positive) (Group 3). In Group 1, 1/26 (4%) was positive for IgA aPE, less frequent than in other groups, and none of the patients had any other aPL. In Group 2, 1/32 (3%) was positive for aPS, two (6%) for aPI, one (3%) for aPA and four (12.5%) for aPE. None was positive for aPC. In the third group, 13/24 (54%) were positive for aPS, 11 (46%) for aPI, 15 (63%) for aPA, four (17%) for aPC and seven (29%) for aPE. Since aPE was found in some patients, we extended the study, including 207 SLE patients, and tested aPE. IgG/M/A aPE was found in six (3%), 10(5%) and 21 (10%), respectively, but no association was found between aPE and any clinical features of APS. This study suggests that screening by multiple aPL tests does not increase the diagnostic yield in APS.

Bleeding in a patient with lupus anticoagulant without associated hemostatic abnormalities

Bleeding is very rare in patients with lupus anticoagulants in the absence of associated hemostatic abnormalities. Few cases have been reported with attention given to work-up for other coagulation defects. We report a case of spontaneous hematoma in a patient with lupus anticoagulant, immunoglobulin (Ig)M anticardiolipin antibodies, and no other associated abnormalities.

Performance characteristics of a new synthetic APTT reagent

Performance characteristics of a totally synthetic activated partial thromboplastin time (APTT) reagent, recently available commercially, were evaluated and compared with a rabbit-brain extracted reagent. We found that the synthetic reagent, Synthasil, returned significantly higher normal APTT values than the brain-extracted reagent, Thrombosil. APTT ratios (APTT patients/normal mean APTT), yielded by Synthasil were higher in the majority of patients receiving heparin therapy. Synthasil also returned longer APTT values than did Thrombosil on normal plasma spiked with heparin. On patients with lupus anticoagulants, APTTs assayed with Synthasil were generally longer than with Thrombosil. However, the differences disappeared when APTT values were converted to ratios. Factors XII-, XI-, IX- and VIII-deficient plasmas supplemented with normal plasma to yield activities of 2-50%, generally gave longer APTTs with Synthasil than with Thrombosil. However, this was not always the case on plasmas from haemophilias A and B patients. No reduction in Synthasil activity was noted after the reagent had been left at 24 degrees C for 28 days.

[Ischemic stroke in young patients and/or livedo: is it important to look for anti-beta 2-glycoprotein I antibodies?]

PURPOSE

This study was aimed at determining the prevalence of anti-beta 2glycoprotéine I antibodies (anti-beta 2-GPI antibodies) in young adult patients presenting with either livedo reticularis or ischemic stroke.

METHODS

Forty patients referred between February 1996 and February 1997 underwent clinical examination and laboratory tests with search for anticardiolipin antibodies (ACL antibodies), lupus anticoagulant (LA) and anti-beta 2GPI antibodies.

RESULTS

Twenty-one patients presented with ischemic stroke (one with ACL antibodies), 13 had livedo (six with ACL antibodies, two with LA) and six patients presented with Sneddon's syndrome (two with ACL antibodies, two with LA). Only one was positive for anti-beta 2-GPI antibodies.

CONCLUSION

beta 2-GPI is a cofactor that increases anticardiolipin antibody adhesion to cardiolipin. Our results suggest that the prevalence of anti-beta 2GPI antibodies is not high in young patients with either livedo reticularis or ischemic stroke. However, due to the small number of patients included in the study, definite conclusions may not be drawn out. Anti-beta 2-GPI antibodies assay is not justified in routine evaluation of patients with either livedo reticularis or ischemic stroke.

[Procainamide-induced lupus in a patient with bilateral pleural effusion]

A 70-year-old physician was admitted to our hospital because of bilateral pleural effusion and left-sided chest pain on deep inspiration. On admission, the APTT was prolonged and was not corrected with a 1:1 mixture of normal plasma. Results of serological examinations included a positive lupus-anticoagulant test and a positive ANA test at a titer of 1:1,280 in a homogeneous pattern. The patient's age, sex, symptoms, signs, and laboratory results all argued against the diagnosis of SLE except for ANA and lupus anticoagulant test. Because procainamide had been prescribed (250 mg every 6 h) for premature ventricular contractions for eight years before admission, procainamide-induced lupus was suspected. Procainamide was discontinued. Chest pain persisted and tests for c-reactive protein were positive. Prednisolone was administered. Procainamide induced lupus was diagnosed, because anti-histone H 2 A-H 2 B complex antibodies were high by enzyme-linked immunosorbent assay, and IgM-class anti-histone antibodies were found in response to H1, H 2 B and H 2 A-H 2 B complex (immunoblotting), which suggested the drug induced lupus. There are only a few reports of drug induced lupus in which the lupus-anticoagulant test was positive and prednisolone was indicated. The measurements of anti-histone antibodies and of expression of anti-histone antibodies were useful in distinguishing drug-induced lupus from SLE.

Activated protein C resistance assay as a screening test for thromboembolic disposition

An activated partial thromboplastin time (APTT) based method was developed to determine the anticoagulant response in patient plasma to added purified activated protein C (APC). On the other hand, Bertina et al. (1994) reported that one point mutation of amino acid 506 in the factor V was observed in such APC resistance patients. APC resistance for blood samples with known abnormal findings on the coagulation test also may be determined. Coagmaster II for the APTT assay system (Sankyo, Tokyo, Japan) was employed. The APC resistance assay system was a useful reagent as a screening test for lupus anticoagulant (LA), in addition to APC resistance.

Antiphospholipid antibody syndrome in a case with redo coronary artery bypass grafting under cardiopulmonary bypass

A patient who underwent redo coronary artery bypass grafting developed severe thrombocytopenia. A platelet transfusion caused recurrent hypotension and hypoxia. The patient status was complicated by a systemic thrombosis including coronary graft occlusion and central vein thrombosis. We found that the lupus anticoagulant, as well as other autoimmune antibodies, was positive only after the thrombotic episode developed. Even though the lupus anticoagulant returned to negative about 2 months after the episode of graft occlusion, the patient eventually died of heart failure.

Laboratory investigation of hypercoagulability

For many years, the laboratory investigation of patients with thrombophilia has lagged behind that of patients with bleeding diathesis. Improved understanding of the mechanisms that control and regulate coagulation, and the resultant recognition of new defects, have greatly stimulated clinical laboratory interest in this area. Assays to detect resistance to activated protein C; deficiencies of antithrombin, protein C, and protein S; and the presence of antiphospholipid antibodies are widely available and should form part of the investigation of patients that present with idiopathic thrombosis. Such a work-up will likely provide an explanation for thrombosis in 40 to 60% of patients. Abnormalities of fibrinogen and fibrinolysis may explain still more, although such defects are currently considered rare. In addition, presently unrecognized defects almost certainly exist, and the identification of such individuals will undoubtedly improve our understanding of the hemostatic mechanism. Laboratory tests to define the hypercoagulable state are continually being developed. They include whole blood coagulation and platelet function tests and novel activation markers. However, acceptance of these approaches by clinical laboratories has been slow.

High prevalence of thrombocytopenia in SLE patients with a high level of anticardiolipin antibodies combined with lupus anticoagulant

The relationship between thrombocytopenia and the level of anticardiolipin antibodies (aCL) and/or the existence of lupus anticoagulant (LA) ware studied in 146 patients with systemic lupus erythematosus (SLE). These patients were divided into six groups: A, those LA positive with a high level of aCL (>10 U/ml) (10 cases); B, those LA positive with a low level of aCL (3-10 U/ml) (15 cases); C, those LA positive but aCL negative (<3 U/ml) (12 cases); D, LA negatives with a high level of aCL (12 cases); E, LA negatives with a low level of aCL (16 cases); and F, aCL and LA double negatives (81 cases). The prevalence of thrombocytopenia (platelet count < or = 100 x 10(9)L) was by far the highest in group A (9/10 cases, 90.0%, P < 0.005, Fisher's exact probability test) as compared with group B (4/15 cases, 26.7%), group C (4/12 cases, 33.3%), group D (1/12 cases, 8.3%), group E (4/16 cases, 25.5%), and group F (9/81 cases, 11.1%). When the relationship between moderate thrombocytopenia and arterial or venous thrombosis was studied in these patients with SLE, thrombocytopenia was detected in 10 (83.3%, P < 0.005, Fisher's exact probability test) of 12 patients with arterial thrombosis; however, it was present in only 4 (23.5%) of 17 patients with venous thrombosis and in 14 (12.3%) of 114 patients without thrombosis. These findings suggest that a high aCL activity combined with LA positively reflects a high risk for both thrombocytopenia and arterial thrombosis.

Cerebral magnetic resonance imaging in patients with or without antiphospholipid antibodies

OBJECTIVE

To determine in patients with systemic lupus erythematosus (SLE) or with primary antiphospholipid syndrome (PAPS) the prevalence of cerebral magnetic resonance imaging changes (MRI) and the relationship with antiphospholipid antibodies.

METHODS

Twenty-nine consecutive SLE patients, 24 PAPS patients and 31 healthy controls were prospectively included in the study and underwent MRI Scan over a 1-year period. MRI scans were analyzed separately by a neuroradiologist for white matter changes [periventricular hyperintensity (PVH) (0-6 scale), deep white matter hyperintensity (WMH) (0-24 scale)], and one neurologist for cerebral atrophy (0-39 scale) and stroke subtypes. Statistical assessment consisted of a discriminant analysis performed with SAS-package with MRI data as dependent variables and, as independent variables, age, sex, arterial hypertension, diabetes mellitus, cardiopathy, migraine, neurological symptoms, antiphospholipid antibodies, SLE, steroid treatment.

RESULTS

The prevalence of cerebral atrophy was increased in both SLE and PAPS groups relative to controls. PVH and WMH scores were significantly higher in SLE and PAPS than in controls. Focal infarct did not differ in the SLE group when compared with PAPS. PVH and WMH scores were significantly higher in patients with neurological symptoms. Using a correlation test we found a weak significant correlation between cerebral atrophy and lupus anticoagulant. The multivariate analysis found only three independent variables related to PVH and WMH: age, the diagnosis of SLE and cerebral atrophy.

CONCLUSIONS

Age, presence of SLE and presence of neurological symptoms were independently related with WMH and PVH, but not antiphospholipid antibodies.

[Antiphospholipid syndrome]

Antiphospholipid antibodies (aPL) are a family of autoantibodies with specificity for negatively charged phospholipids, or more accurately for their complex to phospholipid binding proteins. Their presence is associated with arterial/venous thrombosis and recurrent pregnancy loss. These clinical manifestations with the persistence of aPL are recognized as antiphospholipid syndrome(APS), one of the most common acquired thrombophilia. beta 2-glycoprotein I(beta 2GPI) bears the epitope(s) for anticardiolipin antibodies (aCL) on its molecule, and lupus anticoagulant activity depends on the presence of beta 2GPI or prothrombin. Thus phospholipid binding proteins may have some crucial roles in the pathophysiology of thrombotic events in APS. It has been hypothesized that aPL bind to cells and induce procoagulant activity via phospholipid binding proteins.

Lupus anticoagulants: pathogenesis and laboratory diagnosis

The pathogenesis of the lupus anticoagulant (LA) has been the focus of much research over the past decade, and a plethora of laboratory tests have been developed to detect it. This essay reviews the nature of LA and its pathogenesis, and a number of approaches employed in its diagnosis. These range from well established tests such as the kaolin clotting time (KCT), activated partial thromboplastin time (APTT) and tissue thromboplastin inhibition test (TTI), to the 'newer' tests such as the dilute Russell's viper venom time (DRVVT) and more recent snake venom tests such as the textarin/ecarin ratio and Taipan snake venom time (TSVT). The criteria for diagnosis are discussed, including pre-analytical variables such as sample preparation, and the effects of therapeutic anticoagulants used to treat thrombotic manifestations of the syndrome or an underlying disease process.

[Recurrent acute transverse myelopathy: an 83-year-old man with antiphospholipid syndrome]

We reported here an 83-year-old man with recurrent acute transverse myelopathy probably due to antiphospholipid syndrome (APS). The patient was admitted to a local hospital on May 8, 1996, because of hypoesthesia and muscle weakness of both legs, accompanied by dysuria. T2-weighted magnetic resonance image (MRI) showed significant swelling and increased intensity of the thoracic spinal cord between Th3 and Th7 without enhancement by contrast medium. After the treatment with steroid, both clinical symptoms and abnormal findings on MR imaging disappeared. On 24 June, however, motor paralysis of both legs and sensory loss below the chest relapsed. The lesion in the thoracic spinal cord between Th4 and Th8 reappeared on T2-weighted MRI. Blood examination disclosed the presence of a lupus anticoagulant. Repeated examinations of CSF revealed the continuous elevation of IgG. Clinical and laboratory findings indicated that immunological mechanisms related with APS might be responsible for the transverse myelopathy in this patient.

[Etiological analysis of thrombophilia]

We have established a system for etiological analysis of thrombophilia which includes assays of antithrombin III, protein C, protein S, plasminogen, fibrinogen, heparin cofactor II and lupus anticoagulants as well as gene analysis. The analysis conducted on 115 patients with venous thrombosis, arterial thrombosis and small vessel thrombosis revealed that forty-one patients(36% of the examined patients) were accompanied with decreased activities of protein S, protein C, antithrombin III and plasminogen. Eleven candidate causal mutations were found by gene analysis. These studies indicate that a comprehensive examination is instrumental in identifying and confirming the etiology in patients with thrombophilia.

Pulmonary hypertension as presenting feature of childhood SLE: association with lupus anticoagulant

This is an unusual case of childhood SLE with pulmonary hypertension. A ten year old girl had an illness of brief duration without clinically overt involvement of any organ system other than pulmonary vasculature. Pulmonary hypertension as an isolated presenting manifestation of SLE is extremely rare in childhood.

Thrombin generation measured ex vivo following microvascular injury is increased in SLE patients with antiphospholipid-protein antibodies

Antiphospholipid-protein antibodies (APA) include lupus-type anticoagulant (LA) and antibodies recognizing complexes of anionic phospholipids (e.g. cardiolipin) and proteins (e.g. prothrombin and beta2-glycoprotein I). The presence of APA is associated with an increased risk of both arterial and venous thrombosis. However, the pathogenic mechanism leading to thrombosis in patients with APA remains unclear. We studied 32 patients with systemic lupus erythematosus (SLE) who were divided into two groups depending on the presence (n = 19) or absence (n = 13) of APA. Healthy volunteers (n = 12) matched by age and sex served as controls. In all subjects LA and IgG class anticardiolipin antibodies (ACA) were determined. Thrombin generation was monitored ex vivo measuring fibrinopeptide A (FPA) and prothrombin fragment F1 + 2 (F1 + 2) in blood emerging from a skin microvasculature injury, collected at 30 second intervals. In subjects with antiphospholipid antibodies mean FPA and F1 + 2 concentrations were significantly higher at most blood sampling times than in controls. In some SLE patients with APA the process of thrombin generation was clearly disturbed and very high concentrations of fibrinopeptide A were detected already in the first samples collected. Two minutes after skin incision SLE patients without APA produced slightly more FPA, but not F1 + 2, as compared to healthy subjects. Mathematical model applied to analyze the thrombin generation kinetics revealed that APA patients generated significantly greater amounts of thrombin than healthy controls (p = 0.02 for either marker). In contrast, in the same patients generation of thrombin in recalcified plasma in vitro was delayed pointing to the role of endothelium in the phenomenon studied. In summary, these data show for the first time that in SLE patients with antiphospholipid-protein antibodies thrombin generation after small blood vessel injury is markedly increased. Enhanced thrombin generation might explain thrombotic tendency observed in these patients.