Antibodies against domain I of β2-glycoprotein I: the one and only?

Specific domain V reduction of beta-2-glycoprotein I induces protein flexibility and alters pathogenic antibody binding

Beta-2-glycoprotein I (β2GPI) is a blood protein and the major antigen in the autoimmune disorder antiphospholipid syndrome (APS). β2GPI exists mainly in closed or open conformations and comprises of 11 disulfides distributed across five domains. The terminal Cys288/Cys326 disulfide bond at domain V has been associated with different cysteine redox states. The role of this disulfide bond in conformational dynamics of this protein has not been investigated so far. Here, we report on the enzymatic driven reduction by thioredoxin-1 (recycled by Tris(2-carboxyethyl)phosphine; TCEP) of β2GPI. Specific reduction was demonstrated by Western blot and mass spectrometry analyses confirming majority targeting to the fifth domain of β2GPI. Atomic force microscopy images suggested that reduced β2GPI shows a slightly higher proportion of open conformation and is more flexible compared to the untreated protein as confirmed by modelling studies. We have determined a strong increase in the binding of pathogenic APS autoantibodies to reduced β2GPI as demonstrated by ELISA. Our study is relevant for understanding the effect of β2GPI reduction on the protein structure and its implications for antibody binding in APS patients.

Non-criteria Antiphospholipid Antibodies: a narrative review

SUMMARY The 2006 Revised Sapporo Classification Criteria for Definite Antiphospholipid Syndrome included as laboratory criteria the tests for antiphospholipid antibodies whose accuracy was regarded as satisfactory according to the evidence available at that time. In practice, however, the sensitivity and specificity of these “criteria” of antiphospholipid antibodies are sometimes insufficient for identifying or ruling out antiphospholipid syndrome. It has been studied whether the accuracy of the laboratory diagnosis of the syndrome could be improved by testing for non-criteria antiphospholipid antibodies. In this work, we review evidence on the clinical associations and diagnostic value of the most commonly studied non-criteria antibodies, namely: antiphosphatidylethanolamine, anti-annexin A5, anti-prothrombin, anti-phosphatidylserine/prothrombin complex, IgA anticardiolipin, and IgG anti-domain I of the β2 glycoprotein antibodies.

Human Herpesvirus 6B Greatly Increases Risk of Depression by Activating Hypothalamic-Pituitary -Adrenal Axis during Latent Phase of Infection

Little is known about the effect of latent-phase herpesviruses on their host. Human herpesvirus 6B (HHV-6B) is one of the most ubiquitous herpesviruses, and olfactory astrocytes are one of the most important sites of its latency. Here, we identified SITH-1, an HHV-6B latent protein specifically expressed in astrocytes. Mice induced to produce SITH-1 in their olfactory astrocytes exhibited olfactory bulb apoptosis, a hyper-activated hypothalamic-pituitary-adrenal (HPA) axis and depressive symptoms. The binding of SITH-1 to the host protein calcium-modulating ligand (CAML) to form an activated complex promoted the influx of extracellular calcium. The serum antibody titers for depressive patients with respect to this activated complex were significantly higher than for normal controls (p = 1.78 × 10⁻¹⁵), when the antibody positive rates were 79.8% and 24.4%, respectively, and the odds ratio was 12.2. These results suggest that, in the latent phase, HHV-6B may be involved in the onset of depression.

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We identified SITH-1, a new protein specific to HHV-6B latent infection

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Mice expressing SITH-1 at HHV-6B latent infection site had depressive symptoms

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Depressive symptoms due to SITH-1 were associated with a hyper-activated HPA axis

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SITH-1-specific antibody detection significantly greater in depressive patients

Detection of anti-domain I antibodies by chemiluminescence enables the identification of high-risk antiphospholipid syndrome patients: A multicenter multiplatform study

BACKGROUND

Classification of the antiphospholipid syndrome (APS) relies predominantly on detecting antiphospholipid antibodies (aPLs). Antibodies against a domain I (DI) epitope of anti-β2glycoprotein I (β2GPI) proved to be pathogenic, but are not included in the current classification criteria.

OBJECTIVES

Investigate the clinical value of detecting anti-DI IgG in APS.

PATIENTS/METHODS

From eight European centers 1005 patients were enrolled. Anti-cardiolipin (CL) and anti-β2GPI were detected by four commercially available solid phase assays; anti-DI IgG by the QUANTA Flash® β2GPI domain I assay.

RESULTS

Odds ratios (ORs) of anti-DI IgG for thrombosis and pregnancy morbidity proved to be higher than those of the conventional assays. Upon restriction to patients positive for anti-β2GPI IgG, anti-DI IgG positivity still resulted in significant ORs. When anti-DI IgG was added to the criteria aPLs or used as a substitute for anti-β2GPI IgG/anti-CL IgG, ORs for clinical symptoms hardly improved. Upon removing anti-DI positive patients, lupus anticoagulant remained significantly correlated with clinical complications. Anti-DI IgG are mainly present in high-risk triple positive patients, showing higher levels. Combined anti-DI and triple positivity confers a higher risk for clinical symptoms compared to only triple positivity.

CONCLUSIONS

Detection of anti-DI IgG resulted in higher ORs for clinical manifestations than the current APS classification criteria. Regardless of the platform used to detect anti-β2GPI/anti-CL, addition of anti-DI IgG measured by QUANTA Flash® did not improve the clinical associations, possibly due to reduced exposure of the pathogenic epitope of DI. Our results demonstrate that anti-DI IgG potentially helps in identifying high-risk patients.

The role of beta-2-glycoprotein I in health and disease associating structure with function: More than just APS

Beta-2-Glycoprotein I (β2GPI) plays a number of essential roles throughout the body. β2GPI, C-reactive protein and thrombomodulin are the only three proteins that possess the dual capability to up and down regulate the complement and coagulation systems depending upon external stimulus. Clinically, β2GPI is the primary antigen in the autoimmune condition antiphospholipid syndrome (APS), which is typically characterised by pregnancy morbidity and vascular thrombosis. This protein is also capable of adopting at least two distinct structural forms, but it has been argued that several other intermediate forms may exist. Thus, β2GPI is a unique protein with a key role in haemostasis, homeostasis and immunity. In this review, we examine the genetics, structure and function of β2GPI in the body and how these factors may influence its contribution to disease pathogenesis. We also consider the clinical implications of β2GPI in the diagnosis of APS and as a potentially novel therapeutic target.

Lysine residues control the conformational dynamics of beta 2-glycoprotein I

One of the major problems in the study of the dynamics of proteins is the visualization of changing conformations that are important for processes ranging from enzyme catalysis to signaling. A protein exhibiting conformational dynamics is the soluble blood protein beta 2-glycoprotein I (beta2GPI), which exists in two conformations: the closed (circular) form and the open (linear) form. It is hypothesized that an increased proportion of the open conformation leads to the autoimmune disease antiphospholipid syndrome (APS). A characteristic feature of beta2GPI is the high content of lysine residues. However, the potential role of lysine in the conformational dynamics of beta2GPI has been poorly investigated. Here, we report on a strategy to permanently open up the closed protein conformation by chemical acetylation of lysine residues using acetic acid N-hydroxysuccinimide ester (NHS-Ac). Specific and complete acetylation was demonstrated by the quantification of primary amino groups with fluoraldehyde o-phthalaldehyde (OPA) reagent, as well as western blot analysis with an anti-acetylated lysine antibody. Our results demonstrate that acetylated beta2GPI preserves its secondary and tertiary structures, as shown by circular dichroism spectroscopy. We found that after lysine acetylation, the majority of proteins are in the open conformation as revealed by atomic force microscopy high-resolution images. Using this strategy, we proved that the electrostatic interaction of lysine residues plays a major role in stabilizing the beta2GPI closed conformation, as confirmed by lysine charge distribution calculations. We foresee that our approach will be applied to other lysine-rich proteins (e.g. histones) undergoing conformational transitions. For instance, conformational dynamics can be triggered by environmental conditions (e.g. pH, ion concentration, post-translational modifications, and binding of ligands). Therefore, our study may be relevant for investigating the equilibrium of protein conformations causing diseases.

The clinical value of assays detecting antibodies against domain I of β2-glycoprotein I in the antiphospholipid syndrome

As the clinical symptoms of the antiphospholipid syndrome (APS) frequently occur irrespective of the syndrome, diagnosis predominantly depends on the laboratory assays measuring the level or function of antiphospholipid antibodies (aPLs). β2-glycoprotein I (β2GPI) is increasingly accepted as the most important target of aPLs. Anti-β2GPI antibodies constitute a heterogeneous population, but current in vivo and in vitro evidence show that especially the first domain (DI) of β2GPI contains an important pathogenic epitope. This epitope containing Glycine40-Arginine43 (G40-R43) has proven to be cryptic and only exposed when β2GPI is in its open conformation. A previous study demonstrated a highly variable exposure of the cryptic epitope in commercial anti-β2GPI assays, with implications on correct patient classification. Unexpectedly, recent unpublished data revealed impaired exposure of the pathogenic epitope in the commercially available anti-DI chemiluminescence immunoassay (CIA) assay detecting specific antibodies directed to DI. In this review we summarize the laboratory and clinical performance characteristics of the different anti-DI assays in published data and conclude with inconsistent results for both the correlation of anti-DI antibodies with clinical symptoms and the added value of anti-DI antibodies in the classification criteria of APS. Additionally, we hypothesize on possible explanations for the observed discrepancies. Finally, we highly advise manufacturers to use normal pooled plasma spiked with the monoclonal anti-DI antibodies to verify correct exposure of the cryptic epitope.

Thrombophilia Caused by Beta2-Glycoprotein I Deficiency: In Vitro Study of a Rare Mutation in APOH Gene

This study aimed to explore the mechanism of a novel mutation (p.Lys38Glu) in apolipoprotein H (APOH) gene causing hereditary beta2-glycoprotein I (β2GPI) deficiency and thrombosis in a proband with thrombophilia. The plasma level of β2GPI was measured by ELISA and Western blotting, and anti-β2GPI antibody by ELISA. Lupus anticoagulant (LA) was assayed using the dilute Russell viper venom time. Deficiency of the major natural anticoagulants including protein C (PC), protein S (PS), antithrombin (AT) and thrombomodulin (TM) was excluded from the proband. A mutation analysis was performed by amplification and sequencing of the APOH gene. Wild type and mutant (c.112A>G) APOH expression plasmids were constructed and transfected into HEK293T cells. The results showed that the thrombin generation capacity of the proband was higher than that of the other family members. Missense mutation p.Lys38Glu in APOH gene and LA coexisted in the proband. The mutation led to β2GPI deficiency and thrombosis by impairing the protein production and inhibiting the platelet aggregation. It was concluded that the recurrent thrombosis of the proband is associated with the coexistence of p.Lys38Glu mutation in APOH gene and LA in plasma.

Effects of Toll-like receptor 4 on β2-glycoprotein I-induced splenic T cell subsets differentiation

Our previous study demonstrated that beta 2-glycoprotein I (β2GPI) stimulation promotes bone marrow derived dendritic cells (BMDCs) maturation and T cell proliferation in a Toll-like receptor 4 (TLR4) dependent manner. However, β2GPI induced T cell differentiation and the role of TLR4 in this process have rarely been reported. In the present study, we focused on the differentiation of splenic T cells in β2GPI immunized Balb/c, C3H/HeN and C3H/HeJ mice. According to our results, Th2 dominated differentiation was observed in β2GPI immunized Balb/c and C3H/HeN mice than in those treated with normal saline (NS), namely the up-regulated levels of Th2 markers GATA3 and IL-4 (p < 0.05). Meanwhile, reduced Th1 markers T-bet and IFN-γ, and Treg marker Foxp3 were observed in β2GPI immunized mice (p < 0.05). C3H/HeJ mice have the same gene background with C3H/HeN mice except a functional mutant in TLR4 gene. However, the described Th2 differentiation was not detected in these TLR4 deficient mice, indicating the importance of TLR4 in immune response against β2GPI. In addition, we found that β2GPI-induced Th2 differentiation could be strengthened by cytokines secreted by dendritic cells (DCs) and DCs-T cells interaction. However, DCs-T cells contact was indispensable during this process because of its unique role in suppressing Th1 function. Furthermore, this Th2 biased differentiation pattern was more noticeable in mice received 4 times β2GPI immunization than those received 2 times, suggesting the amplifying effects of anti-β2GPI Ab on β2GPI induced Th2 response. These findings may partly explain the immune imbalance in APS patient through the view angle of T cell differentiation and anti-β2GPI antibody production.

The treatment of anti-phospholipid syndrome: A comprehensive clinical approach

Anti-phospholipid syndrome (APS) is an acquired pro-thrombotic autoimmune disease that predisposes to thrombotic events and/or obstetric complications, in the persistent presence of anti-phospholipid antibodies (aPL). Life long moderate-intensity anticoagulation is the option of choice for aPL-positive patients with a previous thrombosis; critical issues concern the management of those with a history of arterial event due to the high rate of recurrence. Alternatives comprise anti-platelet agents and high-intensity anticoagulation. Low dose aspirin (LDASA) and low molecular weight heparin provide the mainstay of the treatment of obstetric APS, allowing a birth rate in 70% of cases. The management of refractory APS, thrombotic as well as obstetric, is highly debated, but an increasing burden of evidence points towards the beneficial effects of multiple treatments. Similarly, a management envisaging multiple drugs (anticoagulation, steroids, plasma exchange and/or intravenous immunoglobulins) is the most effective approach in catastrophic APS. Asymptomatic aPL carriers are at higher risk of thrombotic and obstetric complications compared to the general population, thus potentially benefitting of a pharmacological intervention. LDASA and hydroxychloroquine can be considered as options, in particular in case of high risk aPL profile, concomitant cardiovascular risk factors or associated autoimmune disease. APS is apparently a simple condition, but its multifaceted nature requires a complex and tailored treatment.

Coexistence of anti-β2-glycoprotein I domain I and anti-phosphatidylserine/prothrombin antibodies suggests strong thrombotic risk

BACKGROUND

Highly specific assays for measuring antiphospholipid antibodies (aPLs) are required for accurate assessment of thrombotic risk. aPLs against β2-glycoprotein I domain I (anti-β2GPIdI) and against prothrombin complexed with phosphatidylserine (anti-PS/PT) have been recently identified as being associated with a hypercoagulable state. This study evaluated the synergism between anti-β2GPIdI and anti-PS/PT for predicting thrombotic events.

METHODS

A total of 180 patients with clinical suspicion of hypercoagulability were evaluated. The plasma levels of lupus anticoagulant (LA) and antibodies against anticardiolipin (anti-CL) (IgG and IgM), β2GPI (IgG and IgM), PS/PT (IgG and IgM), and β2GPI dI (IgG) were measured.

RESULTS

IgG anti-β2GPIdI and LA were highly associated with thrombosis. Mean values and positivity rates of IgG anti-β2GPI dI and IgG anti-PS/PT were significantly higher in the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+) than in the other groups. Interestingly, the thrombotic risk [odds ratio (OR) 24.400, 95% confidence interval (CI) 1.976-63.273, p<0.001] of the newly defined triple positive group (LA+, IgG anti-CL+, IgG anti-β2GPIdI+; OR 11.182, 95% CI 1.976-63.273, p=0.006) was more than twice that of the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+). Double positivity for IgG anti-PS/PT and IgG anti-β2GPI also indicated significant thrombotic risk (OR 7.467, 95% CI 2.350-23.729, p=0.001). Furthermore, the thrombotic risk associated with double positivity for IgG anti-PS/PT and IgG anti-β2GPIdI was markedly elevated (OR 33.654, 95% CI 6.322-179.141, p<0.001).

CONCLUSIONS

Our data suggest that simultaneous measurement of IgG anti-β2GPIdI and IgG anti-PS/PT may improve clinical decision-making for aPL-positive patients.

Distribution of antiphospholipid antibodies in a large population-based German cohort

BACKGROUND

Antiphospholipid syndrome (APS) is the most common acquired thrombophilia. Diagnosis is based on clinical criteria and the presence of antiphospholipid antibodies (aPLs) above the 99th percentile of a reference group. Data on the distribution of aPL in the population are limited. The distribution of aPL including diagnostic cutoffs should be determined in a population-based cohort.

METHODS

The Gutenberg Health Study (GHS) is a population-based cohort aged 35-74 years. We determined the presence of antibodies against cardiolipin (aCL, IgG, and IgM), β2-glycoprotein I (anti-β2GPI, IgG, and IgM), and domain 1 of β2-glycoprotein I (anti-domain 1, IgG) in a sample of 4979 participants.

RESULTS

aPL titers were similar in the whole sample and in an apparently healthy subgroup of 1049 individuals. There was a strong age-dependent increase of both aCL and anti-β2GPI IgM, while aPL IgG titers were stable or tended to decrease with age. A relevant decrease was observed for aCL IgG in women and anti-domain 1 IgG in both sexes. There was no association of aPL titers with a history of venous thromboembolism (VTE).

CONCLUSIONS

Our data show that for IgM aPL, age-dependent reference ranges should be used. In fact, the controversy regarding the clinical utility of IgM aPL might be related to the use of inappropriate reference ranges among other causes. In our population, aPLs were not associated with a history of VTE.

Role of anti-domain 1-β2 glycoprotein I antibodies in the diagnosis and risk stratification of antiphospholipid syndrome

Essentials Antibodies to domain 1 of β2 glycoprotein I (aD1) are a subset of antiphospholipid antibodies. We evaluated the added diagnostic value of an automated aD1 assay in antiphospholipid syndrome. AD1 IgG correctly classifies patients at risk for thrombosis. Agreement between aD1 and aβ2GPI IgG is high, limiting the added value of aD1 in our setting. Click to hear Professor de Groot's perspective on new mechanistic understanding in antiphospholipid syndrome

SUMMARY

Background Laboratory diagnosis of antiphospholipid syndrome (APS) includes lupus anticoagulant (LAC), anticardiolipin (aCL) or anti-β2 glycoprotein I (aβ2 GPI) antibodies. Antibodies targeting domain 1 of β2 GPI (aD1) constitute a pathogenic subset of autoantibodies. Objectives In this cohort study, we determined the clinical performance characteristics, additional diagnostic value and the contribution to APS risk stratification of an automated aD1 assay. Patients/Methods LAC, aCL, aβ2 GPI and aD1 IgG were measured in 101 APS patients, 123 patients with autoimmune disorders, 82 diseased controls and 120 healthy controls. aD1 antibodies were detected by QUANTA Flash(®) Beta2GPI-Domain 1 chemiluminescence immunoassay. Results With a cut-off value of 20.0 CU, the aD1 IgG assay identifies APS patients in a clinically affected patient cohort with a sensitivity of 53.5% and specificity of 98.8%. It implied a high odds ratio (OR) for clinical events (OR, 17.0; 95% confidence interval [CI], 7.1-40.5). aD1 IgG did not add diagnostic value to the formal aPL panel because aβ2 GPI IgG was nearly as specific but more sensitive for APS (sensitivity 56.4%) with a higher OR for clinical events (36.2; 95% CI, 11.1-117.9). High aD1 titers identify triple-positive patients and patients with thrombosis in a β2 GPI-dependent LAC-positive population. Agreement between aD1 IgG and aβ2 GPI IgG was high (positive and negative agreement 91.7% and 98.4%, respectively). Conclusion Detection of aD1 IgG correctly classifies patients at risk of thrombosis. However, the contribution of aD1 IgG to APS diagnosis and risk stratification depends upon the solid phase assays used for aCL and aβ2 GPI detection.

IgG/IgM antiphospholipid antibodies present in the classification criteria for the antiphospholipid syndrome: a critical review of their association with thrombosis

Essentials The clinical value of IgM antibodies in thrombotic antiphospholipid syndrome (APS) is debated. By review of literature, we reconsidered the clinical value of IgM antibodies in thrombotic APS. More significant correlations with thrombosis were found for the IgG compared to IgM isotype. Unavailability of paired IgG/IgM results hampers evaluating the added value of IgM positivity. Click to hear Dr de Groot's perspective on antiphospholipid syndrome

SUMMARY

Background Despite the update of the classification criteria for the antiphospholipid syndrome (APS), difficulties persist in the identification of patients at risk for thrombosis. Current guidelines include assays detecting IgG/IgM anti-β2 -glycoprotein I and anti-cardiolipin antibodies, although the relevance of IgM antibodies has been debated. Objectives Through a review of the literature from 2001 to 2014, we aimed to formally establish the thrombotic risk stratification potential of IgM as compared with IgG anti-phospholipid antibodies (aPLs). Patients/methods One thousand two hundred and twenty-eight articles were selected by a computer-assisted search of the literature. Of the 177 studies that met our inclusion criteria, the clinical value of IgG/IgM aPLs was established through analysis of odds ratios for thrombosis or percentage of positives in the thrombotic population. Results/conclusions We clearly found more significant correlations with thrombosis for the IgG than for the IgM isotype. Nonetheless, in a minority of studies, significant associations with thrombosis were found for IgM but not IgG antibodies. The unavailability of paired results of IgG and IgM for each separate patient hampers evaluation of the added value of isolated IgM positivity. To fully take advantage of results obtained by future studies, we strongly encourage scientists to provide all studied information per patient. We planned a large multicenter study to investigate clinical associations of isolated/combined positivity for criteria/non-criteria aPLs. Importantly, because of the presence of non-pathogenic aPLs, quantitative assays are characterized by a high false-positivity rate. Optimization of functional assays, such as thrombin generation measuring the whole scheme of coagulation, may help to reduce APS-related morbidity and mortality.

β2GP1, Anti-β2GP1 Antibodies and Platelets: Key Players in the Antiphospholipid Syndrome

Anti-beta 2 glycoprotein 1 (anti-β2GP1) antibodies are commonly found in patients with autoimmune diseases such as the antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). Their presence is highly associated with increased risk of vascular thrombosis and/or recurrent pregnancy-related complications. Although they are a subtype of anti-phospholipid (APL) antibody, anti-β2GP1 antibodies form complexes with β2GP1 before binding to different receptors associated with anionic phospholipids on structures such as platelets and endothelial cells. β2GP1 consists of five short consensus repeat termed "sushi" domains. It has three interchangeable conformations with a cryptic epitope at domain 1 within the molecule. Anti-β2GP1 antibodies against this cryptic epitope are referred to as 'type A' antibodies, and have been suggested to be more strongly associated with both vascular and obstetric complications. In contrast, 'type B' antibodies, directed against other domains of β2GP1, are more likely to be benign antibodies found in asymptomatic patients and healthy individuals. Although the interactions between anti-β2GP1 antibodies, β2GP1, and platelets have been investigated, the actual targeted metabolic pathway(s) and/or receptor(s) involved remain to be clearly elucidated. This review will discuss the current understanding of the interaction between anti-β2GP1 antibodies and β2GP1, with platelet receptors and associated signalling pathways.

Cofactor-independent human antiphospholipid antibodies induce venous thrombosis in mice

Essentials Cofactor-independent antiphospholipid antibodies (CI-aPL) are generally considered non-pathogenic. We analyzed the effects of human monoclonal CI-aPL in a mouse model of venous thrombosis. As shown in vitro, CI-aPL induce a procoagulant state in vivo by activation of endosomal NADPH-oxidase. Contrary to common belief, CI-aPL induce venous thrombosis in vivo.

SUMMARY

Background There is general consensus that the antiphospholipid syndrome (APS) is caused by antiphospholipid antibodies (aPL) with antibodies against β2-glycoprotein-I being the most relevant. aPL that bind phospholipids in the absence of protein cofactors are generally considered pathogenetically irrelevant. We showed that cofactor-independent human monoclonal aPL isolated from APS patients induce proinflammatory and procoagulant cellular responses by activating endosomal NADPH-oxidase 2 (NOX2). Similar aPL were detected in all IgG fractions from APS patients analyzed. Objectives We aimed to clarify if cofactor-independent aPL can be thrombogenic in vivo and, if so, whether these effects are mediated via activation of NOX2. Methods Two cofactor-independent human monoclonal aPL, HL5B and RR7F, were tested in a mouse model of venous thrombosis. Genetically modified mice and in vitro assays were used to delineate the mechanisms underlying thrombus induction. Results HL5B and RR7F dramatically accelerate thrombus formation in this mouse model. Thrombus formation depends on tissue factor activation. It cannot be induced in NOX2-deficient mice. Bone marrow chimeras of C57BL/6J mice reconstituted with NOX2-deficient bone marrow showed that leukocyte activation plays a major role in thrombus formation. Neither TLR4 signaling nor platelet activation by our aPL is required for venous thrombus formation. Conclusions Cofactor-independent aPL can induce thrombosis in vivo. This effect is mainly mediated by leukocyte activation, which depends on the previously described signal transduction via endosomal NOX2. Because most APS patients have been shown to harbor aPL with similar activity, our data are of general relevance for the APS.

Aspirin-triggered lipoxin prevents antiphospholipid antibody effects on human trophoblast migration and endothelial cell interactions

OBJECTIVE

Antiphospholipid antibodies (aPL) interfere with several physiologic functions of human trophoblasts, including reducing their ability to migrate, decreasing their production of angiogenic factors, and inducing an inflammatory response. This may provide the underlying mechanism by which aPL responses lead to recurrent pregnancy loss or preeclampsia in women with obstetric antiphospholipid syndrome (APS). Although treatment with heparin may reduce the rate of recurrent pregnancy loss, the risk of preeclampsia remains high. Therefore, alternative treatments are needed for the management of pregnant patients with APS. Since aspirin-triggered lipoxins (ATLs) have immune and angiogenic modulatory properties, the objective of this study was to determine the effects of the ATL 15-epi-lipoxin A4 on the function of aPL-altered human trophoblasts in the first trimester of pregnancy.

METHODS

A first-trimester human trophoblast cell line (HTR8) was treated with mouse anti-human β2 -glycoprotein I monoclonal antibodies (aPL) in the presence or absence of the ATL 15-epi-lipoxin A4 . Trophoblast migration and interactions with endometrial endothelial cells were measured using Transwell and coculture assays. Trophoblast secretion of cytokines and angiogenic factors was measured by enzyme-linked immunosorbent assay.

RESULTS

Treatment of HTR8 cells with ATL reversed the aPL-induced decrease in trophoblast migration, an effect that appeared to be regulated through restoration of interleukin-6 production. Using a model of spiral artery transformation, aPL and sera from APS patients with pregnancy morbidity disrupted trophoblast-endothelial cell interactions, and treatment with ATL restored the stability of the cocultures. In contrast, ATL treatment did not resolve the proinflammatory and antiangiogenic responses of trophoblasts induced by aPL.

CONCLUSION

These findings indicate that ATLs may have some benefits in terms of preventing the effects of aPL on trophoblast function, which raises the possibility of the use of ATLs as an adjuvant therapy in women with aPL.

Management of women with recurrent pregnancy losses and antiphospholipid antibody syndrome

Antiphospholipid antibodies (aPL) have been associated with recurrent pregnancy losses (RPL) and other obstetrical complications. The diagnostic criteria for the classical antiphospholipid antibody syndrome (APS) have been utilized for the detection of obstetrical APS in women with RPL. However, laboratory findings and immunopathology of obstetrical APS are significantly different from those of classical APS. In addition, many women with RPL who have positive aPL do not have symptoms consistent with the current APS criteria. The induction of a proinflammatory immune response from trophoblasts and complement activation by aPL rather than thromboembolic changes has been reported as a major immunopathological feature of obstetrical APS. Heparin treatment has been reported to be effective in prevention of early pregnancy loss with APS but not for the late pregnancy loss or complications. The complex effects of heparin may explain the limited efficacy of heparin treatment in RPL. New diagnostic criteria for obstetrical APS are needed urgently, and new therapeutic approaches should be explored further.

Conformation of beta2glycoprotein I and its effect on coagulation

β(2)glycoprotein I (β(2)GPI) is the major antigen in the antiphospholipid syndrome. It has been shown that β(2)GPI can adapt to different conformations, a circular, a S-shaped and a J-shaped conformation. In literature anticoagulant properties of β(2)GPI have been indicated, though there is no consensus on how β(2)GPI exerts a certain action. This article will first review existing data on the conformation of β(2)GPI. In addition, we will investigate whether the conformation of β(2)GPI plays a role in in the proposed anticoagulant activity of β(2)GPI. We investigated the effect of native β(2)GPI and phospholipid-bound β(2)GPI on thrombin generation (TG). Native β(2)GPI was found to have no significant effect on the TG regardless of the concentration of tissue factor. On the contrary, β(2)GPI preincubated with phospholipids significantly inhibited TG triggered with low TF concentration, suggesting an effect on the intrinsic pathway. This indicates that native β(2)GPI in circulation obtains its anticoagulant activity in the presence of anionic phospholipids such as activated blood cells thereby serving as an inhibitory modulator in hemostasis.