Lupus anticoagulants and antiphospholipid antibodies

Circulating microparticles in patients with antiphospholipid antibodies: characterization and associations

The antiphospholipid syndrome is characterized by venous or arterial thrombosis and/or recurrent fetal loss in the presence of circulating antiphospholipid antibodies. These antibodies cause activation of endothelial and other cell types leading to the release of microparticles with procoagulant and pro-inflammatory properties. The aims of this study were to characterize the levels of endothelial cell, monocyte or platelet derived, and tissue factor-bearing microparticles in patients with antiphospholipid antibodies, to determine the association of circulating microparticles with anticardiolipin and anti-β2-glycoprotein antibodies, and to define the cellular origin of microparticles that express tissue factor. Microparticle content within citrated blood from 47 patients with antiphospholipid antibodies and 144 healthy controls was analyzed within 2hours of venipuncture. Levels of Annexin-V, CD105 and CD144 (endothelial derived), CD41 (platelet derived) and tissue factor positive microparticles were significantly higher in patients than controls. Though levels of CD14 (monocyte-derived) microparticles in patient plasma were not significantly increased, increased levels of CD14 and tissue factor positive microparticles were observed in patients. Levels of microparticles that stained for CD105 and CD144 showed a positive correlation with IgG (R=0.60, p=0.006) and IgM anti-beta2-glycoprotein I antibodies (R=0.58, p=0.006). The elevation of endothelial and platelet derived microparticles in patients with antiphospholipid antibodies and their correlation with anti-β2-glycoprotein I antibodies suggests a chronic state of vascular cell activation in these individuals and an important role for β2-glycoprotein I in development of the pro-thrombotic state associated with antiphospholipid antibodies.

Lupus anticoagulant interference in activated protein C resistance testing: in vitro phenomenon or in vivo pathophysiologic effect?

Second-generation activated protein C resistance (APC-R) assay was developed to avert interferences from lupus anticoagulant (LA) and warfarin therapy by prediluting the patient sample with factor V (FV)-depleted plasma. We investigated the effect of LA on the second generation APC-R assay in 121 LA-positive patients. Twenty-five APC-R-positive patients were tested for the mutation in FV (Leiden, Hong Kong, and Cambridge). Eleven had FV Leiden and twelve were negative for any mutation (2 were not tested). Of 12, 8 had APC-R suggestive of heterozygous and 4 had APC-R suggestive of homozygous defects. These patients had strong LA activity, compared to those with concurrent FVL. This was associated with a trend toward increased thrombosis risk compared to those with normal APC-R. These findings suggest that LA causes acquired APC-R, reflecting an in vivo pathophysiologic effect of LA rather than merely an in vitro phenomenon even with the second generation APC-R assay.

IgA antiphospholipid antibodies are an independent risk factor for thromboses

Antiphospholipid antibodies (lupus anticoagulant, anti-cardiolipin and anti-β2-glycoprotein I antibodies, mostly IgG isotype) are strong risk factors for thrombosis. Because a paucity of information on IgA isotype exists in the literature, we retrospectively evaluated the thrombotic significance of IgA antiphospholipid antibodies. We included 472 patients with clinical information on thrombotic events and complete laboratory work-up for antiphospholipid antibodies syndrome. Odds ratios (OR) of various antiphospholipid antibodies for thrombosis were calculated by univariate and multivariate analyses. Lupus anticoagulant alone was detected in 57 (12%) patients, ELISA-based antibodies (IgG, IgM, IgA) against cardiolipin, phosphatidylserine or β2-glycoprotein-I alone were detected in 131 (28%) patients, whereas 80 (17%) patients had both. Antibody isotype distribution was IgG 32%, IgM 60% and IgA 56%. Univariate analysis showed a statistically significant risk of thrombosis in patients with elevated titres of IgA of any ELISA-based antiphospholipid antibodies (OR 1.77). Stepwise logistic regression (multivariate) analysis identified elevated titres of any ELISA-based IgA antiphospholipid antibodies as an independent risk factor for thrombosis (OR 1.6) in the entire cohort, and in the subgroup of patients without concurrent presence of lupus anticoagulant (OR 1.8). IgA antiphospholipid antibodies appear to be a significant independent risk factor for thrombosis, thereby meriting evaluation in patients with unexpected thrombosis.

Homocystéinémie et facteurs de thrombophilie dans des accidents de décompression immérités chez des plongeurs

INTRODUCTION

Decompression sickness with cerebral ischemic lesions occurs even in divers who have not committed any technical error. This study sought to determine whether an acquired or inborn thrombophilic factor might be involved.

METHODS

44 divers with ischemic medullar lesions (36 men, 8 women, mean age 39.9+/-4.7 yr) were compared with 44 controls (34 men, 10 women, mean age 38.2+/-5.1 yr). Coagulation screening included proteins S, C, and thrombin III and Factor VIII assays and circulating antibodies, Factor V Leiden, and mutation G20210A in Factor II gene research. Total plasma homocysteine (Hcy), an atherosclerosis factor (assayed by FPIA), folate and vitamin B12, (by microbiology), the cofactors of its metabolism, were assayed, and subjects were genotyped for mutation C677T on the MTHFR gene.

RESULTS

Coagulation screening--protein C, protein S, or antithrombin III deficit or mutation G20210A--was negative in all divers. 3/44 divers were heterozygous for Factor V Leiden, 1/44 had IgG antiphospholipid antibodies (9p.cent). While not found in controls, these percentages were not greater than those reported in the general population. 3/44 divers had elevated Factor VIII levels, but repeat assays on Day 2 were much lower. 11/44 divers had a moderate increase in Hcy value (20p.cent): in 7 divers, Hcy values were>15 micromol/L, and in 4 others>12, vs. 2.3p.cent of the controls; 2/11 had normal vitamin levels and 11 divers had folate or vitamin B12 deficiency or both, vs 2.3p.cent controls with a vitamin B12 deficit (percentage significantly different). 7/26 divers were homozygous for the C677T mutation, i.e. 27p.cent vs 12p.cent of 98 healthy controls (laboratory technicians).

CONCLUSIONS

A high percentage of unexplained diving accident victims had moderate HHC, a folate or vitamin B12 deficiency or both, that are easy to detect, plus a genetic predisposition to HHC or to coagulation abnormality. Easy-to-perform homocysteine, vitamin B12, and folate assays might prove helpful for primary prevention of diving accidents.

Antiphospholipid Syndrome With Anti-Prothrombin Autoantibodies in a Patient With an Axial-Flow Left Ventricular Assist Device

Autoantibodies to prothrombin, first described almost 50 years ago, are paradoxically associated with thrombosis. Described is an unusual case of fatal hypercoagulability in a patient with multiple arterial and venous thromboembolic complications despite intense anticoagulation while being bridged to transplantation with a left ventricular assist device. Serum analysis revealed the presence of prothrombin autoantibodies and high titers of anti-nuclear antibodies, and autopsy revealed pulmonary arteriolar vasculitis. These findings suggest an autoimmune basis for the presence of anti-prothrombin antibodies and the hypercoagulable state observed in the present case.

Is the determination of anti-beta2 glycoprotein I antibodies useful in patients with venous thromboembolism without the antiphospholipid syndrome?

Anti-beta2-glycoprotein I (beta2GPI) antibodies are frequently found in patients with lupus anticoagulant (LA). To investigate the prevalence of antibeta2GPI antibodies and their clinical impact in patients with a history of venous thromboembolism (VTE) without LA/anticardiolipin antibodies (ACA), we studied 503 patients [128 (36.2%) men, median age 41 years (interquartile range, IQR 28-54 years)] with previous thrombosis. A group of 113 individuals without VTE [43 (38.1%) men, age 46.7 years (IQR 38-52 years)] served as a control group. Among 418 patients without LA/ACA, anti-beta2GPI-IgG levels were elevated in seven (1.7%), -IgM in 15 (3.6%) and -IgA in 14 (3.3%) cases; in 58 patients with ACA, anti-beta2GPI-IgG levels were elevated in two (3.4%), six (10.3%) and three (5.2%), and in 27 with LA, they were elevated in 18 (66.7%), 19 (70.4%) and 10 (37%) respectively. Thus, the prevalence of elevated anti-beta2GPI antibodies was not increased in patients without LA/ACA but was strongly associated with LA. Patients without ACA/LA who had a recurrent event did not have higher prevalence of elevated anti-beta2GPI-IgG, -IgM or -IgA antibodies than those without a recurrent event. Thus, elevated antibeta2GPI antibodies are not likely to be a predictor of recurrent events in patients without LA. We conclude that determination of anti-beta2GPI antibodies does not improve the clinical management of patients with a history of VTE without LA/ACA.

Sulfatides: targets for anti-phospholipid antibodies

BACKGROUND

Sulfatides are sulfated glycosphingolipids expressed on the surface of erythrocytes, leukocytes, and platelets. Sulfatides interact with several cell adhesion molecules involved in hemostasis. Beta2-glycoprotein I is an anionic phospholipid-binding plasma protein, and the phospholipid-bound form is the target for most anti-phospholipid antibodies that are associated with recurrent thrombosis, miscarriages, and neurological symptoms. In this study, we examined whether beta2-glycoprotein I forms a complex with sulfatides and thereby becomes a target for anti-phospholipid antibodies.

METHODS AND RESULTS

Beta2-glycoprotein I binds to surface-bound sulfatides but not to other glycolipids, such as ceramide, cerebrosides, sphingomyelin, or ganglioside. At a sulfatide coating density of 1 microg/well, beta2-glycoprotein I reaches half-maximal binding at 2.5 microg/mL, and the binding is saturated at 10 microg/mL. The binding of beta2-glycoprotein I also depends on the coating density of sulfatides in the well. At a constant beta2-glycoprotein I concentration of 5 microg/mL, maximal binding of beta2-glycoprotein I is observed at a coating density of 1 mug/well. The serum from 14 patients with anti-cardiolipin antibodies, a subset of anti-phospholipid antibodies, bound to sulfatide-bound beta2-glycoprotein I and previous absorption on cardiolipin-coated surfaces decreased the immunoreactivity toward sulfatide-beta2-glycoprotein I complex by >50% in 12 of 14 patients. Furthermore, immunoaffinity-purified anti-cardiolipin antibodies from 4 of 5 patients reacted with sulfatide-bound beta2-glycoprotein I.

CONCLUSIONS

These results show that not only anionic phospholipids, as commonly known, but also sulfatides are targets for most anti-phospholipid antibodies. We therefore postulate that interactions of these antibodies with sulfatides may contribute to some of the clinical symptoms of the anti-phospholipid antibody syndrome.

Antiphospholipid antibodies: discovery, definitions, detection and disease

Antiphospholipid antibodies (aPL) are immunoglobulins of IgG, IgM and IgA isotypes that target phospholipid (PL) and/or PL-binding plasma proteins. Detection of aPL in the laboratory is done currently by both immunoassays and functional coagulation tests. Convention defines aPL specificity in immunoassays according to the particular PL substrate present, for example aPS represents antiphosphatidylserine antibodies. This may be technically incorrect inasmuch as a particular PL may be responsible for binding and highly concentrating a specific plasma protein, the latter then becomes the target for the aPL. The binding of beta(2)GP-I (apolipoprotein H) to the negatively charged PL, cardiolipin (CL) provides a good example of this circumstance. In contrast, aPL which specifically prolong coagulation times in in vitro are called lupus anticoagulants (LA). The precise PL target(s) of the aPL responsible for LA activities are unknown and often debated. The persistent finding of aPL in patients in association with abnormal blood clotting and a myriad of neurological, obstetrical and rheumatic disorders often compounded by autoimmune diseases has led to an established clinical diagnosis termed antiphospholipid syndrome (APS). The common denominator for these APS patients is the presence of circulating aPL on two or more occasions and the observation of events attributable to abnormal or accelerated blood clotting somewhere in vivo. The purpose of this review is to collect, collate, and consolidate information concerning aPL.

Anticardiolipin antibody associated arterial thrombosis following fibula fracture

A case is described of a 20-year-old college student in whom open reduction and internal fixation of a Weber B fibula fracture was complicated by arterial thrombosis and gangrene of the foot. The patient subsequently required a below-knee amputation. A hypercoagulability workup revealed the presence of an anticardiolipin antibody. Although this is an extremely unusual complication, young female patients with a positive personal or family history of early thrombotic events, such as DVT, multiple pregnancy loss, or early myocardial infarction, should be viewed as being at increased risk. Additional risk factors such as oral contraceptive use, should be sought during the initial history.

Antiphospholipid antibodies before and after liver transplantation

OBJECTIVE

The aim of this study was to determine whether liver transplantation of patients with antiphospholipid antibodies (APA) is 1) adversely affected with vascular thrombosis and 2) whether such antibodies persist post transplantation.

METHODS

Twelve patients with APA awaiting transplant were identified and characterized biochemically and immunologically. Each had the level of APA determined using commercially available enzyme-linked immunoassay kits before, during, and after liver transplantation.

RESULTS

No patient in this series experienced a transplant-related vascular thrombosis. The titer of APA fell to levels at or below those present in normals and remained low in two of 12 or undetectable in 10 of 12 patients 1 yr after liver transplantation.

CONCLUSIONS

We reached the following conclusions: 1) Antiphospholipid positivity does not identify patients at high risk for post-transplant vascular thrombosis. 2) The levels of antiphospholipid present in sera pretransplant fell during transplantation and remained low or undetectable 1 month and 1 yr post transplantation.

Anticardiolipin antibodies as a risk factor for venous thromboembolism in a population-based prospective study

Anticardiolipin antibodies, one of the family of 'antiphospholipid' antibodies, increase the risk of venous thromboembolism in the presence of autoimmune disease. Our objective was to determine prospectively whether there is a positive association between anticardiolipin antibodies and venous thromboembolism in ostensibly healthy adults. We conducted a nested case-control study (n = 317 patients and n = 655 control subjects) in a longitudinal study of over 20 000 participants. Baseline (prediagnosis) anticardiolipin IgG and IgM antibodies were assessed by enzyme-linked immunoassays. Venous thromboembolism was validated using standardized criteria for venous thrombosis and pulmonary embolism. There was no association between anticardiolipin antibodies and subsequent venous thromboembolism occurrence, overall or in any subgroup. For example, the multivariate-adjusted relative risk was 0.88 (95% confidence interval, 0.43, 1.78) for greater than versus less than the 95th percentile of anticardiolipin IgG. In conclusion, in this general population sample, an elevated anticardiolipin antibody level was not a risk factor for venous thromboembolism.

Longitudinal myelitis associated with systemic lupus erythematosus: clinical features and magnetic resonance imaging of six cases

Myelopathy is a rare central nervous system (CNS) complication associated with systemic lupus erythematosus (SLE). Acute transverse myelitis (ATM) is the most frequent form of SLE-related myelopathy. Magnetic resonance imaging (MRI) typically shows increased signal intensity in T2-weighted images and cord swelling. In the present paper, we describe six cases of SLE-related myelopathy with multiple increased signals in the T2-weighted images involving continuous levels of the cervical and thoracic spinal cord, a distinctive feature recently named 'longitudinal myelitis'. The clinical and laboratory findings are similar to those presented by ATM patients, including paraparesis, sensory level and sphincter disturbances. Four patients had positive antiphospholipid antibodies (aPL) suggesting that this could be a characteristic of longitudinal myelitis. Treatment in all cases included high doses of corticosteroids and immunosuppressive agents (intravenous (i.v.) cyclophosphamide). Anticoagulation therapy was given to one patient and two others received low doses of aspirin. The outcome was mainly unfavorable with slow improvement in only one case, no improvement in two and relapse of the myelopathy in the remaining three. In conclusion, longitudinal myelitis is an unusual form of SLE-related myelopathy, it might be associated with aPL and it has a poor prognosis.

Low levels of activated protein C in patients with systemic lupus erythematosus do not relate to lupus anticoagulants but to low levels of factor II

The presence of lupus anticoagulants (LAC) in plasma is a major risk factor for thrombosis. An attractive hypothesis to explain a LAC-mediated thrombotic tendency is that LAC interfere with activation of protein C, a natural antithrombotic in plasma. We investigated the relationship between LAC and protein C activation in vivo. We selected 20 patients with systemic lupus erythematosus (SLE) with LAC (and not using oral anticoagulants), 36 patients with SLE without LAC and 25 healthy volunteers. In these, we measured circulating levels of activated protein C (APC), prothrombin (FII), free protein S, C4BP, protein C, and antibodies to protein C, protein S, FII and beta2-glycoprotein I (beta2GPI). In SLE patients (n = 56), mean levels of APC, FII and free protein S were significantly (P < 0.001) lower than those in healthy volunteers (respectively 13%, 17% and 14%). Mean protein C levels and C4BP levels were similar for SLE patients and healthy volunteers. In contrast to the above hypothesis, the decreased levels of APC could not be attributed to the presence of LAC. Levels of APC were correlated with both FII levels and protein C levels. Decreased levels of APC, FII, protein C and free protein S were related to the presence of anti-FII antibodies. None of the patients had antibodies against protein C or protein S. In conclusion, although the mean levels of APC, FII and free protein S were significantly decreased in SLE patients, no correlation with LAC was found. However, anti-FII antibodies were related to decreased levels of APC, FII, protein C, free protein S and C4BP. As FII levels, and not protein C levels, were decreased in SLE patients and correlated with APC levels, we conclude that the decreased FII levels are responsible for the low levels of APC.

Diabetic thigh muscle infarction in association with antiphospholipid antibodies

BACKGROUND

Diabetic muscle infarction (DMI) is a rare complication of type 1 diabetes mellitus. DMI has a stereotyped clinical presentation and characteristic, though nonspecific, magnetic resonance imaging (MRI) and histologic findings. The etiology, however, remains controversial.

OBJECTIVES

To present the first reported cases of DMI in association with positive antiphospholipid (aPL) antibody titers and to discuss the etiologic and pathogenic significance of the association between type 1 diabetes and aPL antibodies.

METHODS

Descriptive case reports of 2 patients with DMI and positive aPL antibodies and a review of the relevant literature.

RESULTS

Our 2 patients with DMI are female type-1 diabetics with end-organ microvascular complications who presented with an abrupt, painful swelling or mass of the thigh musculature. The diagnosis of DMI was based on the clinical picture and the findings on T2-weighted MRI and histologic evaluation. The first patient had a long history of known aPL antibodies in the setting of systemic lupus erythematosus. The second patient was only determined to be aPL positive after her recurrent episodes of DMI. The first patient was treated with anticoagulation and corticosteroids with relatively rapid resolution of symptoms. The second patient was treated with local débridement and supportive care with a resulting course of prolonged symptoms and recurrences. There are no controlled trials of the treatment of DMI. In the literature there is evidence for an increased prevalence of aPL antibodies in type 1 diabetic patients. The pathogenesis of DMI is poorly understood, but the hypercoagulable state often associated with aPL antibodies may play an important role.

CONCLUSIONS/RELEVANCE

aPL antibodies may be involved in the pathogenesis of diabetic muscle infarction and could serve as an important target of therapeutic intervention, namely with anticoagulation.

Primary antiphospholipid antibody syndrome with mutations in the phospholipid binding domain of beta(2)-glycoprotein I

beta(2)-Glycoprotein I, an anionic phospholipid-binding 50-kDa plasma protein, circulates in the plasma at a concentration of 30-200 microg/ml. Its physiological role remains uncertain, but an important clue to this role is suggested by the finding that antibodies to this protein are frequently found in patients with antiphospholipid antibodies and thrombosis. beta(2)-Glycoprotein I belongs to the complement control protein (CCP) superfamily with five CCP domains. The fifth CCP domain of beta(2)-glycoprotein I has a unique structure and contains a stretch of positively charged amino acids that mediates the binding to phospholipids. This interaction may mediate the clearance of anionic phospholipid-containing surfaces from the circulation. Mutations in this domain affect its binding to phospholipids. We have identified a patient with primary antiphospholipid syndrome who is a compound heterozygous for two mutations in the fifth CCP. One mutation is located in exon 7 (codon 306), and the second mutation is in exon 8 (codon 316). The mutant beta(2)-glycoprotein I was present in normal quantities in his plasma but did not bind to cardiolipin. He had recurrent deep vein thrombosis and pulmonary embolism at age 28 and a thrombotic stroke at age 35, with no other identifiable risk factor for a hypercoagulable state. This report offers some insight into the mechanism of formation of antiphospholipid antibodies and suggests the possible role of the deficiency of beta(2)-glycoprotein I in the pathogenesis of thrombosis.

Antiphospholipid antibodies and the protein C pathway

Among the mechanisms suggested for the prothrombotic activity of lupus anticoagulant and antiphospholipid antibodies is the direct inhibition of the anticoagulant activated protein C (APC) pathway. Although some pathological antibodies may be directed towards the proteins involved, we hypothesize that populations exist which selectively inhibit the APC complex as a result of differences in the phospholipid requirements of this complex as compared to those of the procoagulant complexes. The most prominent feature is the requirement for the presence of phosphatidylethanolamine in the membrane for APC anticoagulant function. This mimics the requirements for inhibitory activity of at least a subset of autoantibodies associated with thrombosis. The role of oxidation of the phospholipid in APC function and antibody reactivity is also discussed.

Recent insights into antiphospholipid antibody-mediated thrombosis

The clinically relevant antiphospholipid antibodies (APA) include anticardiolipin antibodies and lupus anticoagulant. Most autoimmune APA require the presence of a cofactor for phospholipid binding, and the growing list of candidate cofactors has prompted redefinition of APA to 'antiphospholipid protein antibodies'. Current evidence favours beta2-glycoprotein I (beta2GPI) and prothrombin as the primary antigens for anticardiolipin antibodies and lupus anticoagulant respectively. Patients with APA show a predisposition for venous and arterial thromboembolism, recurrent fetal loss, thrombocytopenia and a number of neurological syndromes and miscellaneous conditions. The association between APA and thrombosis has been well documented, but a definite mechanism remains to be clarified. Proposed mechanisms have included disruption of endothelial regulatory processes, impairment of fibrinolysis, augmented platelet activation and/or adhesion, inhibition of antithrombin activity and negation of the anticoagulant effects of beta2GPI and annexin V. In this review we describe recent insights into the role of beta2GPI as a natural anticoagulant, the procoagulant effects of APA on the Protein C system, the interactions between APA and prothrombin resulting in augmentation of thrombin generation, and cellular expression of Tissue Factor in patients with APA. Cellular immunity to beta2GPI is also discussed. Elucidation of these pathophysiological mechanisms may shed further light on the association between APA and thrombosis.