Elution of anticardiolipin antibodies and their cofactor beta 2-glycoprotein 1 from the placentae of patients with a poor obstetric history

The role of anti-phospholipid antibodies in autoimmune reproductive failure

Anti-phospholipid antibodies (aPL) are autoantibodies that are associated with thrombosis and a range of pregnancy complications including recurrent pregnancy loss and pre-eclampsia. The three clinically relevant, well-characterized aPL are anti-cardiolipin antibodies, lupus anticoagulant and anti-beta-2-glycoprotein I (β2GPI) antibodies. aPL do not bind directly to phospholipids but instead bind to a plasma-binding ‘cofactor’. The most extensively studied cofactor is β2GPI, whose role in pregnancy is not fully elucidated. Although the pathogenicity of aPL in recurrent pregnancy loss is well established in humans and animal models, the association of aPL with infertility does not appear to be causative. aPL may exert their detrimental effects during pregnancy by directly binding trophoblast cells of the placenta, altering trophoblast signalling, proliferation, invasion and secretion of hormones and cytokines, and by increasing apoptosis. Heparin is commonly used to treat pregnant women with aPL; however, as thrombotic events do not occur in the placentae of all women with aPL, it may exert a protective effect by preventing the binding of aPL to β2GPI or by acting through non-thrombotic pathways. The aim of this review is to present evidence summarizing the current understanding of this field.

Antiphospholipid antibodies and the placenta: a systematic review of their in vitro effects and modulation by treatment

BACKGROUND

Antiphospholipid antibodies (aPL) are a family of auto-antibodies that are associated with an increased risk of recurrent miscarriage, intrauterine growth restriction and preterm birth. The placenta is a major target of aPL and it is likely that these antibodies promote pregnancy morbidity by affecting trophoblast function. Numerous studies have investigated the effect of aPL on trophoblast function in vitro. However, different trophoblast models and a variety of culture conditions have been employed, resulting in a myriad of different reported findings. This review systematically summarized those published studies that have investigated the effect of aPL on trophoblast function in vitro. In addition, the reported effects of pharmacological treatment on trophoblast function in the presence of aPL were also systematically reviewed.

METHODS

PubMed, Scopus, Embase and Web of Science databases were searched using the keywords 'placenta OR trophoblast' AND 'antiphospholipid antibody OR antiphospholipid syndrome' up to 25 April 2014. Studies were excluded based on the absence of appropriate controls. The effects of aPL on trophoblast proliferation, death, syncytialization, invasion, hormone production, cytokine production, coagulation and complement activation were recorded. The effects of different treatments on the function of trophoblasts in the presence of aPL were also recorded.

RESULTS

A total of 1071 records were retrieved from the four databases. After removing duplicates, the titles and abstracts of 529 articles were reviewed. Of those, 48 articles were read and relevant experimental results were extracted from 47 articles.

CONCLUSIONS

This systematic review provides an overview of all the studies performed to date on the effects of aPL on trophoblast function in vitro. There is considerable support for aPL decreasing trophoblast viability, syncytialization and invasion in vitro. Some work has also suggested that aPL may affect the production of hormones and signalling molecules by trophoblasts, and may stimulate coagulation and complement activation in vitro. Current reports of the in vitro effects of therapeutic treatments on trophoblast function in the presence of aPL are inconclusive. This systematic review has highlighted many gaps in our knowledge of how aPL work and may direct future research in this area.

Antiphospholipid antibodies internalised by human syncytiotrophoblast cause aberrant cell death and the release of necrotic trophoblast debris

Antiphospholipid antibodies (aPL) are the strongest maternal risk factor for pre-eclampsia, a hypertensive disease of human pregnancy. Pre-eclampsia is triggered by a toxic factor released from the placenta that activates the maternal endothelium. Antiphospholipid antibodies cause the release of necrotic trophoblast debris from the placental syncytiotrophoblast and this debris can activate endothelial cells. In this study, we investigated how aPL affects syncytiotrophoblast death and production of necrotic trophoblast debris by examining the interaction between aPL and human first trimester placental explants. Human polyclonal and murine monoclonal aPL, but not control antibodies, were rapidly internalised by the syncytiotrophoblast. Inhibitors of endocytosis or the low-density lipoprotein receptor (LDLR) family, but not toll-like receptors, decreased the internalisation of aPL and prevented the release of necrotic trophoblast debris from the syncytiotrophoblast. Once internalised, aPL increased inner mitochondrial membrane leak and Cytochrome c release while depressing oxidative flux through Complex IV of the electron transport system in syncytiotrophoblast mitochondria. These data suggest that the human syncytiotrophoblast internalises aPL by antigen-dependent endocytosis involving LDLR family members. Once internalised by the syncytiotrophoblast, aPL affects the death-regulating mitochondria, causing extrusion of necrotic trophoblast debris which can activate maternal endothelial cells thereby contributing to the pathogenesis of pre-eclampsia.

Autoimmune disease as a cause of reproductive failure

High-risk pregnancy is the most common clinical association with antiphospholipid antibodies; the principal manifestations are pregnancy loss and early preeclampsia. Membership in this family of antibodies is continually growing and includes antibodies against a variety of phospholipids, phospholipid-protein complexes, and phospholipid-binding proteins. The current information in the literature is inadequate to clearly implicate a subgroup of antiphospholipid antibodies or a particular pathophysiologic mechanism as being responsible for poor pregnancy outcomes. It is clear, however, that prevalent diagnostic tests for LA and aCL are extremely useful to identify many of these patients, but are inadequate for diagnosis of all patients with autoimmune pregnancy loss or to elucidate the pathophysiology. Many patients who present clinically with autoimmune-like pregnancy complications currently are negative in tests for LA or aCL, but have antibodies against annexin V, phosphatidylserine, or other relevant antigens. The greatest risk for a complicated pregnancy is conveyed by a subgroup of antibodies that affect the normal function of placental trophoblast. As clinical laboratory tests designed to detect more members of the antiphospholipid antibody family become available, understanding of this complicated disease (APS) will increase.

Antiphospholipid antibodies: biological basis and prospects for treatment

Antiphospholipid antibodies (aPL) are autoantibodies that are associated with recurrent reproductive failure and thrombotic disease. There are two well-characterised aPL, lupus anticoagulant and anticardiolipin antibodies. aPL were originally thought to bind to negatively-charged phospholipids but it is now clear that the title aPL is a misnomer and that the antigens for these autoantibodies are actually phospholipid-binding proteins. Chief amongst these phospholipid-binding proteins are prothrombin and beta(2) glycoprotein I. This review concentrates on the role of beta(2) glycoprotein I in the reproductive failure caused by aPL. Exactly how aPL cause reproductive failure remains unknown but there is emerging evidence that the antibodies may have several different adverse effects on trophoblasts. There is also evidence questioning the traditional hypothesis that fetal demise is secondary to thrombosis of the utero-placental circulation. Heparin is commonly used to treat pregnant women with aPL but if these antibodies do not cause fetal demise primarily by a thrombotic mechanism a question must be raised over the role of heparin. However, heparin binds to many proteins including beta(2) glycoprotein I and it is possible that the reported beneficial effects of heparin in aPL-affected pregnancies may be due to the ability of heparin to prevent the interaction of aPL and beta(2) glycoprotein I.

Which antiphospholipid antibody tests are most useful?

Despite an active international effort to improve diagnosis and treatment of the antiphospholipid syndrome (Hughes syndrome), there remain problems of lack of standardization and lack of prospective and multivariate epidemiologic analysis which restrict the diagnostic and predictive ability of commercially available tests. Nevertheless, current published series provide some data from which strategic approaches can be used to maximize the efficiency and usefulness of available tests. For further updates on new research and developments of interest to physicians and patients with this syndrome, the following web sites may prove helpful: www.slrapls.org, www.hematology.org, www.acforum.org, www.americanheart.org, www.rarediseases.org, www.aarda.org, and www.lupus.org.

Affinity purified human antiphospholipid antibodies bind normal term placenta

Antiphospholipid antibodies (aPL) are associated with an increased incidence of fetal loss, but the pathophysiology remains unclear. One mechanism may involve the binding of aPL directly to the placenta where they may initiate placental thrombosis and infarction. We have developed an immunofluorescent technique to detect human aPL binding to human placenta. Endogenous immunoglobulins were eluted by extensive washing and residual staining was prevented by incorporating multiple blocking steps. APL were affinity purified on both cardiolipin and phosphatidylserine liposomes from the sera of six patients with aPL (five antiphospholipid syndrome (APS) patients and one post bone marrow transplant patient). Heterogeneous binding to normal term placenta, involving either the trophoblast microvillous surface, stromal and peri-vascular regions was demonstrated by affinity purified aPL from five of six patients. Preliminary sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting studies have demonstrated that aPL bind a number of placental proteins. beta2GPI was not the predominant protein bound by aPL using this technique. This study provides further evidence for the involvement of aPL in mediating placental damage.

Current insights into the "antiphospholipid" syndrome: clinical, immunological, and molecular aspects

Advances in defining the target antigen(s) for the autoantibodies in the APS highlight the inadequacies of the current classification of these autoantibodies into anticardiolipin and LA antibodies. The discovery that beta 2GPI is the target antigen for the autoantibodies detected in solid-phase immunoassays has opened a number of areas of research linking these autoantibodies to atherogenesis and thrombus formation. Although the role of beta 2GPI in the regulation of blood coagulation in unclear, current evidence suggests that anti-beta 2GPI antibodies interfere with its "normal" role and appear to promote a procoagulant tendency. The expansion of research in this area and the diversity of the clinical manifestations of patients with APS have resulted in the inclusion of molecular biologists and pharmaceutical companies joining immunologists, hematologists, rheumatologists, obstetricians, neurologists, vascular surgeons, and protein and lipid biochemists in attempting to understand the pathophysiology of this condition. Although the published literature may result in conflicting results and introduce new controversies, developing standardized laboratory methods and extrapolation of in vitro experimental results to the vivo situation will advance our understanding of the regulation of the immune system and its interaction with normal hemostatic mechanisms. Since the authors' last review in 1991, the study and understanding of the pathophysiology of APS have evolved from lipid biochemistry to molecular techniques that may eventually provide specific therapies for the clinical manifestations of this condition. Although current treatment has improved the morbidity associated with this condition, especially in improving pregnancy outcomes, future therapies, as outlined in this review, may specifically address the biological abnormalities and have fewer side effects. Better diagnostic tools, such as magnetic resonance imaging with perfusion studies, will allow the study of the true incidence and prevalence of vascular flow changes/tissue ischemia and infarction associated with aPL antibodies and help determine treatment and prophylaxis for APS patients. APS is still the only hypercoagulable condition where both arterial and venous beds can be affected independently or in the same individual.

Placental pathology in systemic lupus erythematosus: a prospective study

OBJECTIVES

Systemic lupus erythematosus and antiphospholipid antibody, often identified in patients with systemic lupus erythematosus, are associated with poor pregnancy outcome. This study distinguishes between the effect of each of these factors on gestational outcome and placental pathologic conditions in pregnant patients with systemic lupus erythematosus.

STUDY DESIGN

Thirty-seven pregnancies and 40 placentas from 33 women with systemic lupus erythematosus were studied prospectively.

RESULTS

Systemic lupus erythematosus alone, but not systemic lupus erythematosus activity, was associated with increased spontaneous abortions, preterm gestations, and fetal growth restriction. Placental correlates were ischemic-hypoxic change, decidual vasculopathy, decidual and fetal thrombi, chronic villitis, and decreased placental weight. Extensive infarction and fetal death were important antiphospholipid antibody-related findings.

CONCLUSIONS

Decidual vasculopathy/coagulopathy appears to mediate the antiphospholipid antibody-related and much of the systemic lupus erythematosus-related deleterious effect on the placenta and gestational outcome. The presence of antiphospholipid antibody largely, but not invariably, predicts fetal death. Antiphospholipid antibody-independent chronic villitis may represent a second mechanism of systemic lupus erythematosus-related change.

Antiphospholipid antibodies or not? The role of beta 2 glycoprotein 1 in autoantibody-mediated pregnancy loss

Antiphospholipid antibodies are a family of autoantibodies including lupus anticoagulant and anticardiolipin antibodies that appear to react with negatively charged phospholipids. These antibodies induce thrombosis and pregnancy complications including recurrent stillbirth, recurrent miscarriage, pre-eclampsia and intra-uterine growth retardation. Recent evidence indicates that antiphospholipid antibodies do not bind directly to phospholipid but rather to phospholipid-binding proteins or to a combination of phospholipid and phospholipid-binding proteins. This opens the possibility that antiphospholipid antibodies may be pathogenic by disrupting the function of phospholipid-binding proteins rather than membrane phospholipid. The antigenic role of one phospholipid-binding protein, beta 2 glycoprotein, has been studied in the greatest detail and is reviewed. Despite being highly conserved and expressed at high levels, the physiological function of beta 2 glycoprotein 1 remains unknown. However, a number of putative roles have been proposed which allow speculation as to the mechanism by which antiphospholipid antibodies may disrupt haemostasis and pregnancy.

Synthesis of beta2 glycoprotein 1 by the human placenta

Autoantibodies to negatively charged phospholipids (aPL) can cause fetal loss, including recurrent miscarriage and stillbirth. The immunopathogenic mechanism by which this occurs is unknown, but these antibodies are known to bind phospholipid via a protein cofactor, beta2 glycoprotein 1. This protein is localized on placental syncytiotrophoblast and enables the binding of aPL from maternal blood. In this study, reverse transcription and the polymerase chain reaction (RT-PCR) was used on mRNA isolated from normal human placental villous tissue and from human choriocarcinoma cell lines (Jeg-3, BeWo and JAr) to demonstrate that placental cells themselves synthesize beta2 glycoprotein 1 transcripts. Protein production was confirmed by immunoblotting experiments. Previous immunohistochemical studies were extended to demonstrate that beta2 GP1 is localized to extravillous cytotrophoblast in addition to syncytiotrophoblast. Production of beta2 glycoprotein 1 by fetal trophoblast indicates this protein is likely to have a physiological function in the placenta, and hence aPL may induce their pathological effect in pregnancy by inhibiting the function of placental beta2 glycoprotein 1.

Anti-phospholipid antibodies in preeclampsia and their binding ability for placental villous lipid fractions

OBJECTIVE

In order to investigate the significance of the anti-phospholipid antibodies (APAs) in preeclampsia, 3 kinds of APAs-namely, the anti-cardiolipin antibody (ACA), the anti-phosphatidylserine antibody (APSA), and the anti-phosphatidylcholine antibody (APCA)-were measured, and the APA-binding ability for placental villi using villous lipid fractions was studied.

METHODS

Serum samples were taken from 70 cases of preeclampsia, including 42 cases of the severe type, and from 45 normal pregnant women. The APAs were measured by an enzyme linked immunoabsorbent assay (ELISA). Placental villous membranes (PVMs) from normal placenta were purified and the lipid fractions were extracted from PVMs. The antibody-binding ability for PVM lipid fractions was evaluated by the ELISA method.

RESULTS

In IgG-antibody measurements, the rate of ACA-positive, APSA-positive and APCA-positive cases were 10.0%, 18.1%, and 7.1%, respectively. The presence of APAs was revealed in preeclampsia. Using thin-layer chromatography, negatively charged phospholipids were found in the lipid fractions obtained from PVMs. Antibody binding for the lipid fractions of PVMs was detected in 9 of 12 APA-positive cases in preeclampsia.

CONCLUSION

The results suggest that one cause of preeclampsia is the production of antiphospholipid antibodies that bind to placental villous membrane antigens.

The lupus anticoagulant/antiphospholipid syndrome

Lupus anticoagulants and anticardiolipin antibodies have been strongly associated with the risk of thrombosis, recurrent fetal loss, thrombocytopenia, and a number of other clinical manifestations that together have been referred to as the antiphospholipid syndrome. Despite growing evidence of the significance of this relationship, the pathogenetic mechanisms involved are largely unknown. Recent data suggest strongly that lupus anticoagulants (LACs) and anticardiolipin antibodies (ACAs) are antibodies to protein-phospholipid complexes rather than to phospholipids, as had originally been thought, and that other protein-phospholipid complexes, not recognized by standard assays for LACs or ACAs, may also exist in patients with the antiphospholipid syndrome. Although very recent experimental data may lead to new therapeutic approaches in this syndrome, at present we can only deal with the thrombotic risk by the use of long-term anticoagulation. This chapter reviews current methods of diagnosis, concepts of pathogenesis, and the basis for an approach to anticoagulation in patients at risk for thrombosis or other manifestations of the antiphospholipid syndrome.

The antiphospholipid-protein syndrome

The pathogenesis of the antiphospholipid syndrome remains uncertain. Antibodies that react with phospholipids may not be directly responsible for cellular injury, but may be part of the immune network through which autoantibodies with pathogenic potential are generated. The latter may recognize proteins such as beta 2-glycoprotein I that form complexes with phospholipids, proteins whose functions depend upon interaction with phospholipids such as protein C and its cofactors, altered lipoproteins such as oxidized low-density lipoproteins, or other molecules that share only antigenic similarity. Thus, a spectrum of autoantibodies that recognize different lipid-protein complexes may develop in these patients and contribute to the observed clinical heterogeneity of the syndrome. Current techniques do not permit identification of the subset of patients with antiphospholipid antibodies at risk for thrombosis or abortion and there are no prospective, controlled trials addressing the prophylaxis or treatment of affected individuals. Identification of the cellular targets of antibodies to lipid-protein moieties is needed to identify patients at risk for these complications and as a means to monitor therapy.

Anticardiolipin antibodies in patients with pregnancy loss induce factor Xa production in the presence of beta 2-glycoprotein I

PROBLEM

Anticardiolipin antibodies (aCL) are commonly associated with recurrent pregnancy loss, though the mechanism is uncertain. Some investigators have indicated that aCL may be directed at a complex made up of cardiolipin and a blood anticoagulant, beta 2-glycoprotein I (beta 2GPI). We therefore investigated the effects of beta 2GPI-dependent aCL IgG enriched fractions, isolated from sera of patients with pregnancy losses, on blood coagulation.

METHOD

beta 2GPI-dependent aCL were prepared from sera of three women with second trimester pregnancy losses, by cardiolipin affinity column chromography, following by anti-beta 2GPI affinity column chromatography. The effects of beta 2GPI and beta 2GPI-dependent aCL on the activation of factor X in vitro were examined.

RESULTS

beta 2GPI inhibited the activation of factor X and beta 2GPI-dependent aCL blocked this inhibitory effect in a dose dependent manner.

CONCLUSION

These results imply the possibility of beta 2GPI-dependent aCL induce hypercoagulation or thrombus by blocking the inhibitory effect of beta 2GPI on activation of factor X, which may result in pregnancy loss.

Specific antiphospholipid antibodies (aPL) eluted from placentae of pregnant women with aPL-positive sera

The mechanism by which antiphospholipid antibodies (aPL) cause recurrent pregnancy loss remains unclear. It has however been reported that aPL may affect cytotrophoblasts in vitro and thus direct placental damage might occur. Therefore, we investigated whether aPL are bound directly to placental tissues in patients with immunoglobulin G (IgG)-aPL positive sera. The material investigated comprised the placentae of six patients with a history of recurrent pregnancy loss and subclinical autoimmune disorder and one with systemic lupus erythematosus, who were treated with a combination of prednisolone and aspirin. Normal controls consisted of placentae derived from six women, negative for serum aPL, with no medical or obstetrical complication during their pregnancy. Five kinds of IgG- and IgM-antiphospholipid (anti-PS, PI, PA, PG and CL) antibodies were eluted from the placentae of both patients and controls, which were measured by enzyme-linked immunosorbent assay. IgG-aPL were detected in the placental eluates of four of seven (57%) patients, whereas IgM-aPL were not found in any. With respect to the pregnancy outcome of the four patients with IgG-aPL-positive placental eluates, one experienced intrauterine fetal death (IUFD) at 23 weeks of gestation and three demonstrated intrauterine growth retardation (IUGR). In contrast, the remaining three patients, evaluated negative for IgG-aPL in placental eluates, gave birth to one baby with IUGR and two appropriate-for-date babies. The placentae of the four mothers with IgG-aPL-positive placental eluates pathologically showed severe thrombotic findings. These results suggest that IgG-aPL can directly bind to placental tissue and might cause pathologic damage resulting in IUFD or IUGR.