Variable effects on murine pregnancy of immunoglobulin G fractions from women with antiphospholipid antibodies

TO SHOw how we have been ENgaged in the APS FiELD (What we learned on APS collaborating with Professor Yehuda Shoenfeld)

The present review reports the history of our scientific collaboration with Professor Shoenfeld's group. The collaboration started at the end of the 80s and was mainly focused on studies on the pathogenetic mechanisms of the anti-phospholipid syndrome (APS). Following the initial collaborative studies on antibodies against endothelium in systemic autoimmune vasculitis, we were able to use a similar strategy in APS. This line of research has resulted in the characterization of beta 2 glycoprotein I (β2GPI)-dependent anti-phospholipid antibodies (aPL) as mechanisms capable of mediating an endothelial perturbation crucial for the pathogenesis of APS. Thanks to these studies, the collaboration has led to the characterization of the membrane receptors for β2GPI and the cellular signaling resulting from antibody binding. This mechanism has also been shown to mediate the aPL effect on other cell types involved in APS pathogenesis. Finally, the exchange of information made it possible to replicate and extend the setting of animal models of the syndrome, which proved to be valuable tools for understanding the pathogenesis of the syndrome. It has been a long story recently refueled by common studies on the similarity of pro-inflammatory and pro-coagulant endotheliopathy in APS and in COVID-19.

Pregnancy in antiphospholipid syndrome: what should a rheumatologist know?

This review focuses on the management of reproductive issues in women who have antiphospholipid syndrome (APS) or are carriers of antiphospholipid antibodies (aPL). The importance of aPL detection during preconception counselling relies on their pathogenic potential for placental insufficiency and related obstetric complications. The risk of adverse pregnancy outcomes can be minimized by individualized risk stratification and tailored treatment aimed at preventing placental insufficiency. Combination therapy of low-dose acetylsalicylic acid and heparin is the mainstay of prophylaxis during pregnancy; immunomodulation, especially with hydroxychloroquine, should be considered in refractory cases. Supplementary ultrasound surveillance is useful to detect fetal growth restriction and correctly tailor the time of delivery. The individual aPL profile must be considered in the stratification of thrombotic risk, such as during assisted reproduction techniques requiring hormonal ovarian stimulation or during the follow-up after pregnancy in order to prevent the first vascular event.

Maternal autoimmune diseases and immunologically induced embryonic and fetoplacental damage

BACKGROUND

Autoimmune diseases are a group of illnesses in which autoantibodies are produced against various organs, presenting with a variety of clinical symptoms. In this review, we discuss the different aspects of autoimmune diseases in pregnancy. We also describe experimental models that help to understand the etiology and pathogenesis of the effects of this maternal disease on the developing embryo, fetus and placenta.

METHODS

The possible direct effects of sera or IgG obtained from women with systemic lupus erythematosus/antiphospholipid syndrome (SLE/APS) and recurrent pregnancy loss (RPL) were examined on cultured 10.5- and 11.5-day-old rat embryos and on cultured human placental explants, as compared to sera from healthy women or synthetic medium that were used as controls. In addition, we examined the effects of the sera obtained from these women after successful treatment that allowed the birth of normal infants.

RESULTS

We observed increased embryonic death and anomalies in embryos cultured on sera and IgG from SLE/APS women. Similarly, when human placental explants were cultured on these sera, trophoblastic cell growth was reduced and apoptotic rate was increased. Successful treatment also reduced the damage caused by the sera from these women in the cultured embryos and placentas.

CONCLUSIONS

Our results, and the cited studies, point to the important role of the placental damage in the etiology of RPL associated with SLE/APS. Animal models, both in vivo and in vitro, as well as cultured early human placental explants can be used successfully to understand some of the pathogenic aspects of SLE/APS and RPL.

Beta 2 glycoprotein I-function in health and disease

Beta-2 glycoprotein I (beta2GPI) is the principal target of autoantibodies in the antiphospholipid syndrome (APS). It is abundant in human plasma and shares high homology between different mammalian species. Although the exact physiological function of beta2GPI has not been fully elucidated, several interactions have been described with other proteins and with negatively charged surfaces, such as anionic phospholipids, dextran and heparin. beta2GPI is involved in the coagulation pathway, exerting both procoagulant and anticoagulant activities. Plasma from beta2GPI-deficient mice exhibits impaired thrombin generation in vitro. Recently, it has been demonstrated that beta2GPI binds factor (F) XI in vitro at concentrations lower than those of the protein in human plasma, and this binding inhibits FXI activation to FXIa by thrombin and FXIIa. Proteolytic cleavage of the fifth domain of beta2GPI abolishes its inhibition of FXI activation and results in reduced ability of the cleaved beta2GPI to bind phospholipids. It retains its ability to bind FXI. In vivo activation of FXI by thrombin is thought to be an important mechanism by which coagulation is accelerated via components of the contact activation pathway. Thus beta2GPI may attenuate the contact activation pathway by inhibiting activation of FXI by thrombin. Moreover, because beta2GPI is the dominant autoantigen in patients with APS, dysregulation of this pathway by autoantibodies may be an important mechanism for thrombosis in patients with APS.

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.

Autoreactive CD4(+) T-cell clones to beta2-glycoprotein I in patients with antiphospholipid syndrome: preferential recognition of the major phospholipid-binding site

Autoreactive CD4(+) T cells to beta2-glycoprotein I (beta2GPI) that promote antiphospholipid antibody production were recently identified in patients with antiphospholipid syndrome (APS). To further examine antigen recognition profiles and T-cell helper activity in beta2GPI-reactive T cells, 14 CD4(+) T-cell clones specific to beta2GPI were generated from 3 patients with APS by repeated stimulation of peripheral blood T cells with recombinant beta2GPI. At least 4 distinct T-cell epitopes were identified, but the majority of the beta2GPI-specific T-cell clones responded to a peptide encompassing amino acid residues 276 to 290 of beta2GPI (KVSFFCKNKEKKCSY; single-letter amino acid codes) that contains the major phospholipid-binding site in the context of the DRB4*0103 allele. Ten of 12 beta2GPI-specific T-cell clones were able to stimulate autologous peripheral blood B cells to promote anti-beta2GPI antibody production in the presence of recombinant beta2GPI. T-cell helper activity was exclusively found in T-cell clones capable of producing interleukin 6 (IL-6). In vitro anti-beta2GPI antibody production induced by T-cell clones was inhibited by anti-IL-6 or anti-CD40 ligand monoclonal antibody. In addition, exogenous IL-6 augmented anti-beta2GPI antibody production in cultures of the T-cell clone lacking IL-6 expression. These results indicate that beta2GPI-specific CD4(+) T cells in patients with APS preferentially recognize the antigenic peptide containing the major phospholipid-binding site and have the capacity to stimulate B cells to produce anti-beta2GPI antibodies through IL-6 expression and CD40-CD40 ligand engagement. These findings are potentially useful for clarifying the pathogenesis of APS and for developing therapeutic strategies that suppress pathogenic antiphospholipid antibody production in these patients.

Management of pregnancy in antiphospholipid syndrome

Pregnant women with APS are at high risk of maternal and fetal pregnancy complications. Multidisciplinary teams expert in this condition should coordinate management. Even with current management strategies, the risk of maternal thrombosis, fetal loss, or other adverse obstetric outcomes remains. Close monitoring of the various aspects of this condition may reduce maternal morbidity and improve fetal outcome. The pathogenesis of the adverse pregnancy outcome in APS has not yet been fully elucidated, although active research in this field continues. Until this is ascertained, we must accept that many aspects of management are purely empiric, and it is our duty to counsel patients thoroughly so that they understand the risks and benefits of the treatment options they are offered.

Obstetric management of antiphospholipid syndrome

The obstetric management of women with antiphospholipid (aPL) syndrome remains controversial. Despite recent advances, the controversies have been fueled by our limited understanding of the multi-factorial causes of aPL-associated pregnancy loss and the lack of data from randomized studies. We have escaped from the narrow confines of the concept of aPL pregnancy loss being purely thrombotic in aetiology and attention is now focused on the adverse effects of aPL on embryonic implantation and trophoblast invasion. Combined treatment with aspirin and heparin has been demonstrated in two randomized studies to lead to a high live birth rate in aPL pregnancies. However, successful pregnancies are characterized by a high rate of perinatal complications and some women are refractory to this treatment combination. In addition to addressing these issues, multi-centre studies, which should perhaps be internet based, are needed to identify those aPL that are causative of pregnancy complications and those that are not, the role of IVIG and the long-term follow-up of both mothers with aPL and their babies.

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.