Factor XII autoantibodies as a novel marker for thrombosis and adverse obstetric history in patients with systemic lupus erythematosus

Viewpoint: The value of non-criteria antiphospholipid antibodies

In 2006, at a meeting in Sydney, Australia, consensus was reached by an international group of specialists to establish a number of serological criteria that identify patients with a history of thrombosis or pregnancy complications as having antiphospholipid syndrome (APS). These criteria were originally formulated for research purposes and to compare clinical trials in different centres. However, these same criteria are now generally used and accepted for the diagnosis and treatment of patients. The practice of using these criteria for direct patient care requires that these criteria are based on sound scientific evidence. Indeed, for all the autoantibodies that are officially included in the serological criteria, it has been shown that they induce thrombosis and fetal loss when infused into mice. There are also a number of additional autoantibodies that have been identified in these patients but for these antibodies there was not enough evidence to meet the official APS criteria in 2006. Seventeen years have now passed since the consensus meeting, therefore, this review examines whether additional studies performed with these 'non-criteria' autoantibodies have provided sufficient results to suggest the inclusion of these autoantibodies in the official serological criteria of APS.

An Emerging Role for Type I Interferons as Critical Regulators of Blood Coagulation

Type I interferons (IFNs) are central mediators of anti-viral and anti-bacterial host defence. Detection of microbes by innate immune cells via pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and cGAS-STING, induces the expression of type I IFN-stimulated genes. Primarily comprising the cytokines IFN-α and IFN-β, type I IFNs act via the type I IFN receptor in an autocrine or exocrine manner to orchestrate rapid and diverse innate immune responses. Growing evidence pinpoints type I IFN signalling as a fulcrum that not only induces blood coagulation as a core feature of the inflammatory response but is also activated by components of the coagulation cascade. In this review, we describe in detail recent studies identifying the type I IFN pathway as a modulator of vascular function and thrombosis. In addition, we profile discoveries showing that thrombin signalling via protease-activated receptors (PARs), which can synergize with TLRs, regulates the host response to infection via induction of type I IFN signalling. Thus, type I IFNs can have both protective (via maintenance of haemostasis) and pathological (facilitating thrombosis) effects on inflammation and coagulation signalling. These can manifest as an increased risk of thrombotic complications in infection and in type I interferonopathies such as systemic lupus erythematosus (SLE) and STING-associated vasculopathy with onset in infancy (SAVI). We also consider the effects on coagulation of recombinant type I IFN therapies in the clinic and discuss pharmacological regulation of type I IFN signalling as a potential mechanism by which aberrant coagulation and thrombosis may be treated therapeutically.

Pathophysiology of the Antiphospholipid Antibody Syndrome

The antiphospholipid syndrome is characterized by antibodies directed against phospholipid-binding proteins and phospholipids attached to cell membrane receptors, mitochondria, oxidized lipoproteins, and activated complement components. When antibodies bind to these complex antigens, cells are activated and the coagulation and complement cascades are triggered, culminating in thrombotic events and pregnancy morbidity that further define the syndrome. The phospholipid-binding proteins most often involved are annexins II and V, β2-glycoprotein I, prothrombin, and cardiolipin. A distinguishing feature of the antiphospholipid syndrome is the "lupus anticoagulant". This is not a single entity but rather a family of antibodies directed against complex antigens consisting of β2-glycoprotein I and/or prothrombin bound to an anionic phospholipid. Although these antibodies prolong in vitro clotting times by competing with clotting factors for phospholipid binding sites, they are not associated with clinical bleeding. Rather, they are thrombogenic because they augment thrombin production in vivo by concentrating prothrombin on phospholipid surfaces. Other antiphospholipid antibodies decrease the clot-inhibitory properties of the endothelium and enhance platelet adherence and aggregation. Some are atherogenic because they increase lipid peroxidation by reducing paraoxonase activity, and others impair fetal nutrition by diminishing placental antithrombotic and fibrinolytic activity. This plethora of destructive autoantibodies is currently managed with immunomodulatory agents, but new approaches to treatment might include vaccines against specific autoantigens, blocking the antibodies generated by exposure to cytoplasmic DNA, and selective targeting of aberrant B-cells to reduce or eliminate autoantibody production.

Monitoring of Systemic Lupus Erythematosus Pregnancies: A Systematic Literature Review

OBJECTIVE

Few data exist to guide the frequency and type of monitoring in systemic lupus erythematosus (SLE) pregnancies. A systematic literature review was performed to address this gap in the literature.

METHODS

A systematic review of original articles (1975-2015) was performed using Medline, Embase, and Cochrane Library. We included search terms for SLE, pregnancy, and monitoring. We also hand-searched reference lists, review articles, and grey literature for additional relevant articles.

RESULTS

The search yielded a total of 1106 articles. After removing 117 duplicates, 929 articles that were evidently unrelated to our topic based on title and/or abstract, and 7 that were in a language other than English or French, 53 articles were included for full-text review. Following a more in-depth review, 15 were excluded: 6 did not use any measure of SLE activity and 6 did not specifically address SLE monitoring in pregnancy; 1 case series, 1 review, and 1 metaanalysis were removed. Among the 38 included studies, presence of active disease, antiphospholipid (aPL) antibodies positivity, and abnormal uterine and umbilical artery Doppler studies predicted poor pregnancy outcomes. No studies evaluated an evidence-based approach to the frequency of monitoring.

CONCLUSION

Few existing studies address monitoring for optimal care during SLE pregnancies. The available data imply roles for aPL antibodies measurement (prior to pregnancy and/or during the first trimester), uterine and umbilical artery Doppler studies in the second trimester, and following disease activity. Optimal frequency of monitoring is not addressed in the existing literature.

Contact activation products are new potential biomarkers to evaluate the risk of thrombotic events in systemic lupus erythematosus

Introduction

Patients with systemic lupus erythematosus (SLE) have persistent platelet activation and an increased risk of thrombotic events, which cannot be accounted for by traditional cardiovascular risk factors. Factor (F)XII has a potentially important role in thrombus formation and is triggered by activated platelets. We therefore asked whether the contact system is involved in inflammation and vascular disease (VD) in SLE.

Methods

Fibrin clots were incubated with purified FXII or whole blood, and the activation and regulation of FXII were studied. Plasma from SLE patients with (n = 31) or without (n = 38) previous VD and from matched healthy controls (n = 68) were analyzed for the presence of complexes formed between contact system enzymes and antithrombin (AT) or C1 inhibitor (C1INH) and evaluated with regard to clinical data and laboratory parameters.

Results

Fibrin clots elicited FXII activation and acted as co-factors for AT. In clotting plasma, the levels of FXIIa-AT increased, and FXIIa-C1INH decreased. A similar reciprocal relationship existed in SLE patients. FXIIa-AT was elevated in the SLE patients with a history of VD, while the corresponding levels of factor FXIIa-C1INH were significantly decreased. FXIIa-AT correlated strongly with platelet parameters. The odds ratio for VD among the SLE patients was 8.9 if they had low levels of FXIIa-C1INH, 6.1 for those with high levels of FXIIa-AT, and increased to 23.4 for those with both decreased levels of FXIIa-C1INH and increased levels of FXIIa-AT.

Conclusions

Activation of FXII is elicited by fibrin during thrombotic reactions in vitro and in vivo, and fibrin acts as a heparin-like co-factor and regulates AT. Patients with SLE had altered levels of FXIIa-serpin complexes, supporting that the contact system is involved in this disease. FXIIa-serpin complexes are strongly associated with previous VD in SLE patients, suggesting that these complexes are potential biomarkers for monitoring and assessing the risk of thrombotic events in SLE.

Factors associated with arterial vascular events in PROFILE: a Multiethnic Lupus Cohort

The objective of this study was to determine the factors associated with the occurrence of arterial vascular events in a multiethnic systemic lupus erythematosus (SLE) cohort. The PROFILE cohort, comprised SLE patients (n = 1333) of defined ethnicity from five different US institutions, was studied to determine demographic, clinical and biological variables associated with vascular events. An arterial vascular event (first episode) was either a myocardial infarction, angina pectoris and/or a vascular procedure for myocardial infarction, stroke, claudication and/or evidence of gangrene. Patient characteristics were analyzed by univariable and multivariable Cox proportional hazards regression analyses. One-hundred twenty-three (9.8%) patients had at least one incident arterial event. Age at cohort enrollment (HR = 1.04, 95% CI 1.03-1.06), smoking (HR = 2.20, 95% CI 1.40-3.46) and the CRP2* C alleles (HR = 1.91, 95% CI 1.04-3.49) were associated with a shorter time-to-the occurrence of arterial vascular events. Some clinical manifestations of disease activity were associated with a shorter time-to-occurrence [psychosis (HR = 2.21, 95% CI 1.10-4.44), seizures (HR = 1.85, 95% CI 1.00-3.24) and anaemia (HR = 1.83, 95% CI 1.02-3.31)], but others were not [arthritis (HR = 0.32, 95% CI 0.18-0.58)]. In conclusion, older patients, especially in the context of a predisposing environmental factor (smoking) and severe clinical manifestations, are at higher risk of having arterial vascular events. The genetic contribution of the variation at the CRP locus was not obscured by demographic or clinical variables. Awareness of these factors should lead to more effective management strategies of patients at risk for arterial vascular events.

European attempts for the standardisation of the antiphospholipid antibodies

According to the Sydney criteria, antiphospholipid syndrome (APS) diagnosis is closely related to the demonstration of antiphospholipid antibodies (aPL) in patients sera. For this purpose, three different assays are conventionally accepted: lupus anticoagulant (LA), anticardiolipin (aCL) and anti-β2 glycoprotein I (β2GPI) antibodies. LA, described in the 1950s is a coagulation-based functional assay, which indirectly detects the presence of aPL. The aCL ELISA was developed in 1985; the identification of β2GPI as a major target of aPL, allowed the introduction of anti-β2GPI ELISA. Even if the diagnostic criteria for APS have been well defined, the laboratory detection of aPL is not always reproducible for many reasons. To achieve a univocal diagnostic definition of APS, efforts were made to reduce the inter- and/or intra-laboratory variability of the diagnostic tests. In this article, we analyse the studies performed to standardise aPL assays that were developed within the European Forum on Antiphospholipid Antibodies.

Antiphospholipid antibodies may impair factor XIIa-dependent activation of fibrinolysis in pregnancy: in vitro evidence with human endothelial cells in culture and monoclonal anticardiolipin antibodies

OBJECTIVE

The purpose of this study was to analyze the in vitro activation of the contact complex with the use of human umbilical vein endothelial cells (HUVEC) in culture and monoclonal anticardiolipin antibodies (MaCL).

STUDY DESIGN

Cultured HUVECs were incubated with pooled plasma from third-trimester pregnant women with the addition (20 mg/mL) of MaCL with anti-beta-2 glycoprotein I activity that was obtained from patients with antiphospholipid syndrome (APS), MaCL from an individual without APS, or from a control patient with immunoglobulin M without aCL activity. Supernatants were evaluated. Activated factors XII and VII, prothrombin-fragment 1 + 2, urokinase-type plasminogen activator (UPA), and differentiating 2 chain UPA were determined.

RESULTS

In the cultured HUVEC supernatants, the addition of MaCL increased activated factor VII and prothrombin-fragment 1 + 2, did not modify UPA, and decreased activated factor XII and differentiating 2 chain UPA, in comparison with samples with control immunoglobulin M added. The MaCL without APS activity did not change any parameter that was evaluated.

CONCLUSION

MaCL with anti-beta-2 activity that was obtained from patients with APS may interfere in the activation of the contact complex during pregnancy.

Examining the non-linear relationship between monoclonal antiphospholipid antibody sequence, structure and function

In the antiphospholipid syndrome (APS), pathogenic antiphospholipid antibodies (aPL) that cause thrombosis or pregnancy morbidity are characterized by binding to anionic phospholipids (PL) and β2-glycoprotein I (β2GPI). Sequence analysis of human monoclonal aPL has shown that high affinity for these antigens is associated with the presence of three particular amino acids: arginine (Arg), asparagine and lysine in the complementarity determining regions (CDRs) of their heavy and light chains. In vitro expression systems have been used to create variants of the antibodies in which these amino acids have been altered. In general, removal of Arg residues reduces affinity for anionic PL and β2GPI. Arg at different positions in the sequence, however, have different effects on binding affinity and effects on binding are not always mirrored by effects on pathogenicity. This review will focus upon the sequence motifs that have been found to distinguish pathogenic from non-pathogenic aPL, and whether these or other properties may help to identify distinct pathogenic subsets of aPL. In particular, we will focus on our recent work in which we are trying to develop a better understanding of the molecular mechanisms involved in activation of target cells by pathogenic aPL. These studies, together with molecular models of antigen/antibody complexes, help us to understand exactly how pathogenic antibodies interact with antigens. Ultimately, this understanding may aid the design of more powerful diagnostic/prognostic assays and targeted therapeutic agents to block the pathogenic effects of these antibodies.

Autoantibody explosion in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis and pregnancy loss in the presence of antiphospholipid antibodies (aPL), mainly anticardiolipin, anti-beta2-glycoprotein I and lupus anticoagulant. However, similar to systemic lupus erythematosus, APS is also characterized by multiple other autoantibodies including 'non-classical' aPL, as well as other antibodies. Herein we describe the autoantigen properties, prevalence and clinical importance of 30 different antibodies in APS. Among the other antibodies characterizing APS are autoantibodies directed to platelets, glycoproteins, various coagulation factors, lamins, mitochondrial antigens and cell surface markers. Few of these autoantibodies are correlated with the presence of other antibodies, and some may have an additive role in the pro-thrombotic tendency of the syndrome. This autoantibody explosion might be important in early identification of the syndrome and its manifestations.

Current insight into diagnostics and pathophysiology of the antiphospolipid syndrome

The diagnosis of the antiphospholipid syndrome, a non-inflammatory autoimmune disease characterized by thrombosis or pregnancy morbidity in the presence of antiphospholipid antibodies, depends greatly upon laboratory diagnostics. The diagnostic value of all available assays to detect antiphospholipid antibodies and the anticardiolipin assay in particular, is a matter of ongoing debate. Although the presence of lupus anticoagulant correlates best with thrombosis, accurate determination is not always possible due to anticoagulant treatment. Data on the predictive value of alternatives such as the anti-beta2-glycoprotein I and the anti-prothrombin antibody assay are insufficient and prospective cohort studies are needed. Determining antiphospholipid antibody profiles seems to increase diagnostic specificity. Substantial progress has been made in unravelling the pathophysiological mechanisms underlying the antiphospholipid syndrome. Several cellular receptors for antibody-beta2-glycoprotein I complexes have been identified and their roles in cellular activation are being investigated. In vivo data should provide more insight into the importance of the interaction with individual receptors.