Placental thrombosis and fetal loss after passive transfer of mouse lupus monoclonal or human polyclonal anti-cardiolipin antibodies in pregnant naive BALB/c mice

Antiphospholipid syndrome pathogenesis in 2023: an update of new mechanisms or just a reconsideration of the old ones?

Antibodies against phospholipid (aPL)-binding proteins, in particular, beta 2 glycoprotein I (β2GPI), are diagnostic/classification and pathogenic antibodies in antiphospholipid syndrome (APS). β2GPI-aPL recognize their target on endothelium and trigger a pro-thrombotic phenotype which is amplified by circulating monocytes, platelets and neutrophils. Complement activation is required as supported by the lack of aPL-mediated effects in animal models when the complement cascade is blocked. The final result is a localized clot. A strong generalized inflammatory response is associated with catastrophic APS, the clinical variant characterized by systemic thrombotic microangiopathy. A two-hit hypothesis was suggested to explain why persistent aPL are associated with acute events only when a second hit allows antibody/complement binding by modulating β2GPI tissue presentation. β2GPI/β2GPI-aPL are also responsible for obstetric APS, being the molecule physiologically present in placental/decidual tissues. Additional mechanisms mediated by aPL with different characteristics have been reported, but their diagnostic/prognostic value is still a matter of research.

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.

Placental damage in pregnancies with systemic lupus erythematosus: A narrative review

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease of unknown cause, which mainly affects women of childbearing age, especially between 15 and 55 years of age. During pregnancy, SLE is associated with a high risk of perinatal morbidity and mortality. Among the most frequent complications are spontaneous abortion, fetal death, prematurity, intrauterine Fetal growth restriction (FGR), and preeclampsia (PE). The pathophysiology underlying obstetric mortality and morbidity in SLE is still under investigation, but several studies in recent years have suggested that placental dysfunction may play a crucial role. Understanding this association will contribute to developing therapeutic options and improving patient management thus reducing the occurrence of adverse pregnancy outcomes in this group of women. In this review, we will focus on the relationship between SLE and placental insufficiency leading to adverse pregnancy outcomes.

Meant to B: B cells as a therapeutic target in systemic lupus erythematosus

B cells have a prominent role in the pathogenesis of systemic lupus erythematosus (SLE). They are mediators of inflammation through the production of pathogenic antibodies that augment inflammation and cause direct tissue and cell damage. Multiple therapeutic agents targeting B cells have been successfully used in mouse models of SLE; however, these preclinical studies have led to approval of only one new agent to treat patients with SLE: belimumab, a monoclonal antibody targeting B cell-activating factor (BAFF). Integrating the experience acquired from previous clinical trials with the knowledge generated by new studies about mechanisms of B cell contributions to SLE in specific groups of patients is critical to the development of new treatment strategies that will help to improve outcomes in patients with SLE. In particular, a sharper focus on B cell differentiation to plasma cells is warranted.

Pathogenic Role of Complement in Antiphospholipid Syndrome and Therapeutic Implications

Antiphospholipid syndrome (APS) is an acquired autoimmune disease characterized by thromboembolic events, pregnancy morbidity, and the presence of antiphospholipid (aPL) antibodies. There is sound evidence that aPL act as pathogenic autoantibodies being responsible for vascular clots and miscarriages. However, the exact mechanisms involved in the clinical manifestations of the syndrome are still a matter of investigation. In particular, while vascular thrombosis is apparently not associated with inflammation, the pathogenesis of miscarriages can be explained only in part by the aPL-mediated hypercoagulable state and additional non-thrombotic effects, including placental inflammation, have been described. Despite this difference, evidence obtained from animal models and studies in APS patients support the conclusion that complement activation is a common denominator in both vascular and obstetric APS. Tissue-bound aPL rather than circulating aPL-beta2 glycoprotein I immune complexes seem to be responsible for the activation of the classical and the alternative complement pathways. The critical role of complement is supported by the finding that complement-deficient animals are protected from the pathogenic effect of passively infused aPL and similar results have been obtained blocking complement activation. Moreover, elevated levels of complement activation products in the absence of abnormalities in regulatory molecules have been found in the plasma of APS patients, strongly suggesting that the activation of complement cascade is the result of aPL binding to the target antigen rather than of a defective regulation. Placental complement deposits represent a further marker of complement activation both in animals and in patients, and there is also some suggestive evidence that complement activation products are deposited in the affected vessels. The aim of this review is to analyze the state of the art of complement involvement in the pathogenesis of APS in order to provide insights into the role of this system as predictive biomarker for the clinical manifestations and as therapeutic target.

[Use of hydroxychloroquine and prednisone in the presence of serum autoimmunity in female infertility]

OBJECTIVE

Presence of non-specific autoimmunity (antinuclear antibodies without antigenic specificities and/or antiphospholipid antibodies without criteria of antiphospholipid syndrome) seems to be associated with unexplained female infertility. The objective is to study the characteristics of patients who undergone treatment for non-specific antibodies in Medically Assisted Procreation (MAP).

METHODS

Ten patients were prospectively followed at MAP center of Grenoble University Hospital. Patient characteristics were collected and evaluated. All patients had a consultation in internal medicine unit as well as an autoimmune assessment (antinuclear antibodies, APL especially) in search of defined autoimmune disease (exclusion criterion). The treatments undertaken were at clinician' discretion.

RESULTS

One patient received quadritherapy (heparin, platelet antiaggregant, prednisone and hydroxychloroquine), 5 received triple therapy, 3 had dual therapy, and one patient had prednisone only. The 10 patients had a pregnancy under treatment, 8 of which were completed without complications. The control of autoimmunity under treatment appears to show a decrease in serum antibody levels. Tolerance was good (delayed hypersensitivity to hydrochloroquine resulted in discontinuation of therapy in only one patient).

CONCLUSION

The presence of non-specific serum autoimmunity in a context of infertility appears to be pathogenic and immunomodulatory treatments are clinically and/or biologically effective. A prospective and interventional study with a larger number of patients is needed to assess the efficacy of such treatments in patients with unexplained infertility.

Antiphospholipid antibodies as cause of pregnancy loss

Antiphospholipid antibodies detected by lupus anticoagulant, anticardiolipin or anti-beta2 glycoprotein I assays were associated with fetal loss. Rather than being diagnostic tools only, antiphospholipid antibodies are thought to be pathogenic. The strongest demonstration of their pathogenic role lies in the ability to induce fetal resorptions - the experimental equivalents of the human fetal losses - when passively infused in pregnant naive animals. However, still debated is how the antibodies might induce the obstetrical manifestations. Thrombotic events at the placental levels might be related to endothelial cell activation, inhibition of protein C/S system and fibrinolysis as well as to Annexin V displacement. However, the thrombophilic state apparently cannot explain all the miscarriages and a direct antibody-mediated damage on the trophoblast has been suggested. During differentiation to syncytium, trophoblasts express cell membrane anionic phospholipids that can bind beta2 glycoprotein I, the main cationic phospholipid binding protein recognized by the antiphospholipid antibodies. Adhered b2-glycoprotein I might be recognized by the antibodies that, once bound, strongly interfere with in vitro trophoblast cell maturation so resulting in a defective placentation. These mechanisms have been suggested to play a role in early fetal loss, while thrombotic events would be responsible for miscarriages late in the pregnancy.

Autoantibodies associated with reproductive failure

Autoimmune factors are involved in some of the cases of reproductive failure. These factors entail several autoantibodies, especially in patients having systemic lupus erythematosus (SLE) or the antiphospholipid syndrome (APS). These autoantibodies include mainly antibodies directed to phospholipid such as cardiolipin, phosphatidylserine, phosphatidylethanolamine or phospholipids binding glycoproteins such as b2glycoprotein-I, annexin V, prothrombin and protein-Z. There are also some other autoantibodies directed to laminin-I, thromboplastin, mitochondrial antibodies of the M5 type, corpus luteum, prolactin, poly (ADP-ribose), thyroglobulin and more, which were also found in SLE or APS patients with reproductive failure. Moreover, the presence of additional autoantibodies directed to actin, enolase, cubilin and others, needs further investigation to support a firm association to reproductive failure in women. Future studies are likely to help to determine and expand the number of autoantibodies screened in these patients, as well as by the use of proteomics technology, to determine peptides resembling the epitope specificities associated with the specific clinical manifestations.

Histopathology in the placentae of women with antiphospholipid antibodies: A systematic review of the literature

BACKGROUND

Antiphospholipid antibodies (aPLs) are a heterogenous group of autoantibodies associated with recurrent miscarriage, stillbirth, foetal growth restriction and premature birth. The cause of obstetric morbidity in women with aPLs is not completely understood. Workers have attempted to understand the role of aPLs in obstetric morbidity by investigating the histopathology of placentae from aPL-positive women. However, it is unclear from these diverse, and at times contradictory reports what histopathological lesions are common in the placentae of women with aPLs. This systematic review was undertaken to generate a complete picture of the placental features associated with aPLs in an attempt to understand the pathological processes that occur in pregnancies affected by aPLs.

METHODS

Pubmed, Scopus, Web of Science and Embase were searched on the 27th November 2014 using the keywords "placenta" OR "trophoblast" AND "antiphospholipid antibody" OR "antiphospholipid antibody syndrome". Records that were relevant and eligible were qualitatively assessed and given a score out of 24.

RESULTS

Of the 1112 records that were retrieved from the systematic search, 34 records were eligible for review, and were qualitatively scored. Of the 44 histopathological features that were reported in 580 placentae from aPL-positive women, six features appeared to be more common in the placentae of aPL-positive women compared to control women, including: placental infarction, impaired spiral artery remodelling, decidual inflammation, increased syncytial knots, decreased vasculosyncytial membranes and the deposition of complement split product C4d.

CONCLUSION

Based on the evidence in this systematic review, a human placental aPL fingerprint has been proposed. The diversity of the human placental aPL fingerprint suggests that multiple pathological processes may occur in pregnancies affected by aPL.

Complement activation and pregnancy failure

Pregnancy represents a physiologic condition where maternal immune system tolerates the semi-allogenic fetus. The fetal tissues are directly exposed to the maternal blood with potential attacks from maternal immune system, including the activation of complement cascade. Small amounts, of both early and late components, of complement are physiologically found in the placenta, maybe in relation to the vascular remodeling process. A significant increase of complement activation was associated with different pathologic pregnancy outcomes, namely pre-eclampsia, recurrent spontaneous abortions, intra-uterine growth retardation, and anti-phospholipid syndrome (APS). In some, but not in all, mice models of APS, complement activation plays a major role in pregnancy loss, with a massive accumulation of C3 in the placenta, while C3 deficient mice didn't show fetal resorption. Basing on these findings, anti-phospholipid antibodies and complement activation (via C3a, C5a, and MAC) may cooperate in triggering a local inflammatory process, eventually leading to placental thrombosis, hypoxia, and neutrophil infiltration. However, histological analysis of human placenta tissues from APS women shows small rather than widespread inflammation. In a similar manner, complement activation can be detected in human APS placentas but without any relationship with pregnancy outcome and therapy. Further studies are necessary to investigate whether complement activation and inflammatory processes found in animal models are really taking place in APS.

Antiphospholipid antibody-mediated reproductive failure in antiphospholipid syndrome

The association of elevated titers of circulating antiphospholipid (anti-PL) Abs in antiphospholipid syndrome (APS) and reproductive failure is well established in the literature. The clinical features include recurrent abortions at various stages, including implantation, placentation in the first trimester, miscarriages in the second and third trimesters, intrauterine growth retardation, preeclampsia with placental insufficiency and growth restrictions, arterial and venous thrombosis, and possibly also infertility. APS-mediated recurrent pregnancy loss and other features of reproductive failure might result from diverse autoimmune factors, inflammation, involving different mechanisms, which encompass pathogenic anti-PL Abs. Herein, we discuss the association of anti-PL Abs with reproductive failure with special emphasis on antiphospholipid autoantibodies characterizing APS. This association is evident from either human studies or murine models.

Serum complement activation on heterologous platelets is associated with arterial thrombosis in patients with systemic lupus erythematosus and antiphospholipid antibodies

Complement plays a major role in inflammation and thrombosis associated with systemic lupus erythematosus (SLE) and the antiphospholipid syndrome (APS). A cross-sectional retrospective analysis was performed to evaluate serum complement fixation on platelets and thrombotic incidence using banked sera and clinical data from patients with SLE (n = 91), SLE with antiphospholipid antibodies (aPL) or APS (n = 78) and primary aPL (n = 57) or APS (n = 96). In-situ complement fixation was measured as C1q and C4d deposition on heterologous platelets using an enzyme-linked immunosorbent assay approach. Platelet activation by patient serum in the fluid phase was assessed via serotonin release assay. Enhanced in-situ complement fixation was associated with the presence of IgG aPL and IgG anti-beta2 glycoprotein 1 antibodies (P < 0.05) and increased platelet activation (P < 0.005). Moreover, enhanced complement fixation, especially C4d deposition on heterologous platelets, was positively associated with arterial thrombotic events in patients with SLE and aPL (P = 0.039). Sera from patients with aPL possess an enhanced capacity for in-situ complement fixation on platelets. This capacity may influence arterial thrombosis risk in patients with SLE.

Murine monoclonal antibody 26 raised against tetanus toxoid cross-reacts with beta2-glycoprotein I: its characteristics and role in molecular mimicry

PROBLEM

Studies on experimental antiphospholipid syndrome (APS) models proved that molecular mimicry between plasma protein beta(2)-glycoprotein I (beta(2)GPI) and structure within micro-organisms or their products, might be a cause for experimental APS. Considering the heterogeneity of polyclonal antiphospholipid antibodies (aPLs), it is important to define the precise characteristics of pathogenic aPLs. To avoid the influence of polyclonality and to further analyse the connection between molecular mimicry and APS, we produced monoclonal antibodies (MAbs) against tetanus toxoid (TTd) and tested their reactivity against beta(2)GPI.

METHOD OF STUDY

In this report, we analysed the characteristics of MAb26 raised against TTd and cross-reactive with beta(2)GPI: its binding properties in various in vitro immunoassays, its specific interactions with surface epitopes expressed on apoptotic cells and its role in vivo.

RESULTS

We have demonstrated that MAb26: (i) binds beta(2)GPI being immobilized on an appropriate surface: irradiated polystyrene plates, non-irradiated plates pre-coated with anionic phospholipids and polyvinylidene fluoride membrane; (ii) binds specifically to apoptotic but not to viable cells and the binding is beta(2)GPI-dependent; and (iii) induces a pathologic pregnancy outcome when passively injected into BALB/c mice.

CONCLUSION

This study concluded that certain subpopulations of antibodies raised against TTd and cross-reactive with beta(2)GPI, because of the molecular mimicry mechanism, could have pathologic potential.

The monoclonal antibody 26 raised against tetanus toxoid also recognizes tetanus toxin and β2-glycoprotein I - its binding properties in vitro and potential applications

A murine monoclonal IgG1 antibody, marked as MAb26, specific for tetanus toxoid has been immunochemically characterized. By performing enzyme-linked immunosorbent assays (ELISAs) and western blot analyses, it was demonstrated that MAb26 reacted with tetanus toxoid, tetanus toxin and ?2-glycoprotein I (?2GPI). According to the results, MAb26 recognized the sequential epitope on the tetanus heavy chain. The affinity constant, calculated from Scatchard plots of MAb26 binding to tetanus toxoid, was 1.145?108 M-1 and the measurement of the relative affinity of MAb26 by ELISA using thiocyanate elution showed a significantly higher affinity of MAb26 to the toxoid (p = 0.0012) in comparison to the toxin. Additionally, the reactivity of MAb26 toward the toxoid forms increased when the tetanus toxin was detoxified using 8 mM and higher formaldehyde concentrations. The similarity of the tetanus toxoid to several sera proteins, either at the level of its conformation (IL-1?) or at the level of peptide sequences (?2GPI, laminin) favors its role in autoimmunity by the mechanism of molecular mimicry. As the induction of an autoimmune disease is dependent on the breakdown of tolerance, which could be the result of an overt hyperstimulation, the control of the presence and concentration of self-reactive epitopes in vaccine preparations is a prerequisite. In this study, it was shown that MAb26 can: 1) discriminate between the tetanus toxin and different toxoid forms, which makes it a good candidate for antibody control during vaccine preparation; 2) due to its cross-reactivity with ?2GPI, it could provide information on the presence of a potentially dangerous sequential epitope expressed at the protein surface.

Pathomorphologic and immunohistochemical study on the devastation of rat embryos by antiphospholipid antibody positive serum

PROBLEM

While relying on previous publications, our aim was to examine the morphologic changes, induced in early rat embryos by intra-uterine exposure to the low-molecular weight fraction of boiled human serum containing antiphospholipid antibodies (APLA) that had been obtained from women with antiphospholipid syndrome (APS).

METHOD OF STUDY

Human APLA-positive sera were pooled, boiled, centrifuged and separated by ultrafiltration. The molecular weight fraction lower than 30 kDa was used for the experiments. One hundred and fifty microlitres was injected into one uterine horn of 12 pregnant rats, 5 or 6 days after fertilization, while similarly prepared normal human serum or saline were injected into the contralateral horn. The rats were subsequently sacrificed. Serial sections, obtained from all uterine horns, were stained histologically and immunohistochemically. Normal embryos developed in the control uterine horns, while embryos in the experimental horns were destroyed rapidly.

RESULTS

Signs of apoptosis appeared 2 hr following the injection, and 4 hr later all the embryonic cells were apoptotically destroyed. There was only partial damage to cytotrophoblasts and intermediate trophoblasts.

CONCLUSION

These findings support the existence of a novel factor in the APLA-positive serum, causing a detrimental effect to the conceptus, without any relation to the antiphospholipid antibodies.

Updating on the pathogenic mechanisms 5 of the antiphospholipid antibodies-associated pregnancy loss

Anti-phospholipid antibodies (aPL) are risk factor for recurrent pregnancy loss and obstetrical complications. The mechanisms of aPL-mediated pregnancy failure are still a matter of research. Although aPL are associated with thrombosis, thrombotic events cannot explain all the miscarriages. There is evidence for a direct in vitro aPL effect on the trophoblast as shown by their binding; reduction of proliferation, human chorionic gonadotrophin release, in vitro invasiveness, adhesion molecule expression; and increased apoptosis. Such a direct reactivity is supported by the expression of beta2 glycoprotein (beta 2GP) I on trophoblast cell membranes. aPL/anti-beta 2GPI antibodies also bind to human decidual/endometrial cells in vitro and induce a pro-inflammatory phenotype. APL-mediated inflammatory processes at the placental level are apparently responsible for fetal loss at least in animal models. Both complement activation and pro-inflammatory cytokine/chemokine secretion have been shown to play a role. More recently, complement-induced tissue factor expression on infiltrating neutrophils was described as an additional pathogenic mechanisms mediated by aPL. As a whole, these findings do suggest that aPL may induce a defective placentation by acting at different levels without involving necessarily thrombotic events.

Antiphospholipid antibodies: laboratory and pathogenetic aspects

Antiphospholipid antibodies (aPL) constitute a heterogeneous group of autoantibodies that share the ability to bind phospholipids (PL) alone, protein-PL complexes, or PL-binding proteins. They have been detected in isolation, in association with autoimmune diseases such as systemic lupus erythematosus (SLE), and during the course of different infections. aPL have been associated with an array of clinical manifestations in virtually every organ, although deep vein and arterial thrombosis as well as pregnancy morbidity are predominant. The co-occurrence of these clinical findings with aPL constitutes the so-called antiphospholipid syndrome (APS). aPL can be detected by immunological methods [e.g., anticardiolipin antibodies (aCL)] or by functional methods that exploit the effect of aPL on blood coagulation [lupus anticoagulant (LA)]. Since aPL are heterogeneous, numerous immunological and coagulation assays have been developed. These assays have not been fully standardized, and, therefore, problems such as high interlaboratory variation are relatively frequent. Recently, recommendations have been published regarding LA and aCL testing. Not all aPL are pathogenic. However, when they are not associated with infections, they have a role in the pathogenesis of APS. Clinical and experimental data have shown that aPL exert their pathogenic activity by interfering with the function of coagulation factors, such as thrombin and factors X, XI and XII, and with the function of anticoagulant proteins of the protein C system. In addition, aPL interaction with platelets and endothelial cells induces a pro-adhesive activated phenotype.

Role of complement in antiphospholipid antibody-mediated thrombosis

The mechanisms by which an antibody that reacts with phospholipids (universal components of mammalian membranes) causes thrombosis are not immediately obvious. The development of an animal model of antiphospholipid antibody syndrome has moved the field forward in dissecting the pathogenesis of antiphospholipid antibody syndrome and has implicated the complement system in the mechanism of disease. Understanding complement's role in promoting thrombosis will be important in designing safer, more effective approaches to the treatment of patients with antiphospholipid antibodies, and may shed light on which patients are at greatest risk for thrombosis, perhaps permitting primary prophylaxis before irreversible tissue and organ damage occur.

Placental thrombosis in experimental anticardiolipin antibodies-mediated intrauterine fetal death

PROBLEM

Anticardiolipin (aCL) antibodies are associated with stillbirths, recurrent miscarriages and recurrent in vitro fertilization implantation failure in women. Previous animal studies have demonstrated that these antibodies can cause early fetal demise and implantation failure in mice, but most previous studies have not allowed the immunized mice to proceed to the full term of gestation.

METHOD OF STUDY

Mice were immunized with either cardiolipin alone or cardiolipin in combination with beta2-glycoprotein I (beta2GPI) and have studied the effects of these antibodies on pregnancies which were allowed to progress to term.

RESULTS

Immunization with cardiolipin alone induced significant levels of anticardiolipin antibodies in mice, but immunization with a combination of cardiolipin and beta2GPI produced even higher levels of antibodies. Mice with elevated levels of anticardiolipin antibodies had poor pregnancy outcomes. This study confirms previous results that anticardiolipin antibodies cause early pregnancy losses and also demonstrates that these antibodies cause stillbirth-like late fetal demise. This study further demonstrated that very high levels of anticardiolipin antibodies cause intrauterine death by facilitating the thrombotic episode in placenta.

CONCLUSIONS

The present study concludes that the possible mechanism involves in stillbirth of aCL is possibly because of the thrombotic events of placenta.

Complement activation in anti-phospholipid syndrome: A clue for an inflammatory process?

Anti-phospholipid syndrome (APS) is defined by recurrent arterial/venous thrombosis and/or fetal losses in the persistent presence of anti-phospholipid antibodies (aPL). In in vivo experimental models aPL thrombogenic activity is associated with a pro-inflammatory endothelial phenotype (increased adhesion molecule [ADM] expression and leukocyte adhesion) in addition to a pro-coagulant one (tissue factor [TF] expression). This is in line with the in vitro aPL ability to trigger intracellular signalling and to up-regulate ADM, TF and pro-inflammatory cytokine/chemokine expression at the mRNA and protein level in endothelial cells. Comparable effects were also reported in monocytes in vitro. In addition, complement activation is required by aPL to display their thrombogenic activity in in vivo models. Interestingly, complement activation blocking as well as Tumor Necrosis Factor alpha neutralization protect animals from aPL-induced fetal losses. Altogether these findings speak in favour for a role of inflammation in APS in spite of the absence of a clear inflammatory signature in the patients. We could not find any complement (C3c and C4d) deposition in the placentas from 2 late abortions (20 weeks of gestation) in APS women. Further studies are necessary to investigate whether complement activation and inflammatory processes found in animal models are taking place in APS patients.

Protection against inflammation- and autoantibody-caused fetal loss by the chemokine decoy receptor D6

Fetal loss in animals and humans is frequently associated with inflammatory conditions. D6 is a promiscuous chemokine receptor with decoy function, expressed in lymphatic endothelium, that recognizes and targets to degradation most inflammatory CC chemokines. Here, we report that D6 is expressed in placenta on invading extravillous trophoblasts and on the apical side of syncytiotrophoblast cells, at the very interface between maternal blood and fetus. Exposure of D6-/- pregnant mice to LPS or antiphospholipid autoantibodies results in higher levels of inflammatory CC chemokines and increased leukocyte infiltrate in placenta, causing an increased rate of fetal loss, which is prevented by blocking inflammatory chemokines. Thus, the promiscuous decoy receptor for inflammatory CC chemokines D6 plays a nonredundant role in the protection against fetal loss caused by systemic inflammation and antiphospholipid antibodies.

Excessive complement activation is associated with placental injury in patients with antiphospholipid antibodies

OBJECTIVE

Studies that use a murine model of antiphospholipid syndrome have demonstrated a critical role for complement activation that leads to fetal and placental injury in the presence of antiphospholipid antibodies (APAs). We examined the placentas of patients with APAs to demonstrate a similar association with tissue injury in humans.

STUDY DESIGN

Immunohistochemical analyses with the use of antibodies to the complement products C4d, C3b, and C5b-9 were performed on paraffin-embedded tissue sections of placentas from 47 patients with APAs and 23 normal control patients.

RESULTS

We found evidence of increased complement deposition in the trophoblast cytoplasm (C4d and C3b), trophoblastic cell and basement membrane (C4d), and extravillous trophoblasts (C4d) of patients with APAs, compared with control patients. We report a correlation between placental pathologic features and complement deposition (C4d) in the trophoblastic cytoplasm, cell membrane, and basement membrane.

CONCLUSION

These findings are consistent with murine studies that implicate complement as a critical factor in the fetal tissue injury observed in antiphospholipid syndrome.

The role of TLR2 in the inflammatory activation of mouse fibroblasts by human antiphospholipid antibodies

Antiphospholipid antibodies (APLAs) promote inflammatory and procoagulant responses in endothelial cells and monocytes. Previous studies have shown that MyD88, TRAF6, and NF-kappaB mediate cell activation by APLAs. These intermediates are also used by toll-like receptors (TLRs). We investigated the role of TLRs in the cellular response to APLAs. IgGs were isolated from the plasma of 5 patients with antiphospholipid syndrome along with immunopurified anti-beta2-glycoprotein 1 IgG from a sixth patient. Control IgG was obtained from a pool of healthy donor plasmas negative for APLAs. Wild-type mouse embryonic fibroblasts (EFs) and EFs deficient in TLR1, TLR2, TLR4, or TLR6 were incubated with APLAs, anti-beta2-glycoprotein 1 IgG, or control IgG. On incubation with the patient IgG, but not control IgG, a significant increase in mRNA levels of the inflammatory marker proteins MCP-1, ICAM-1, and IL-6 as well as IL-6 secretion was observed in wild-type EFs, whereas TLR2-deficient EFs did not respond. Responses in TLR1- and TLR6-deficient EFs were decreased and those in TLR4-deficient EFs comparable to those in wild-type EFs. Overexpression of human TLR2 in the TLR2-deficient EFs restituted the response to patient IgG. Our results imply that TLR2 plays a role in mouse fibroblast activation by APLAs.

Anti-beta-2 glycoprotein I antibodies affect Bcl-2 and Bax trophoblast expression without evidence of apoptosis

Antiphospholipid antibodies (aPLs) reacting with beta-2 glycoprotein I (beta2GPI) have been associated with recurrent fetal loss and pregnancy complications. The aim of the study was to investigate whether aPLs with anti-beta2GPI specificity induce apoptosis of human trophoblasts in vitro. To this end, human anti-beta2GPI monoclonal IgM derived from a patient with antiphospholipid syndrome and a human irrelevant monoclonal IgM were incubated with human trophoblast cell cultures for 24, 48, and 72 h. In all the cultures we evaluated: (i) Bcl-2 and Bax mRNA and protein expression by Western blot and reverse transcription polymerase chain reaction (RT-PCR), respectively; (ii) DNA fragmentation by a commercial ELISA kit and by agarose gel electrophoresis; and (iii) the percentage of cells reactive with the monoclonal antibody (MAb) M30 by indirect immunofluorescence. The results were: Bcl-2/Bax ratio increased in untreated trophoblast cells during the time of culture, showing the highest values detectable after 72 h (2.68 and 2.28 at protein and mRNA levels, respectively). Cell incubation with anti-beta2GPI MAbs induced a significant Bcl-2/Bax ratio reduction in comparison with untreated cells (1.22 and 1.28 at protein and mRNA levels, respectively, after 72 h incubation). No significant difference was detected after cell exposure to irrelevant MAbs. However, neither DNA fragmentation nor increase in cells positive for the caspase-cleaved epitope of cytokeratin 18 cytoskeletal protein (M30) was found. In Conclusion, anti-beta2GPI antibodies react with trophoblast cells and reduce the Bcl-2/Bax ratio, but without any clear apoptotic effect.

Platelet C4d is highly specific for systemic lupus erythematosus

OBJECTIVE

Complement-activation product C4d is deposited on normal erythrocytes, while abnormal levels have been observed on the surface of erythrocytes of patients with systemic lupus erythematosus (SLE). This study examines whether C4d also deposits on human platelet surfaces, and whether platelet-bound C4d may provide a biomarker for SLE.

METHODS

We conducted a cross-sectional study of 105 patients with SLE, 115 patients with other diseases, and 100 healthy controls. Levels of C4d on the surface of platelets were examined by flow cytometry and scanning confocal microscopy. Statistical analyses were performed to determine the clinical variables associated with platelet C4d.

RESULTS

Abnormal levels of platelet C4d were found to be highly specific for SLE. Platelet C4d was detected in 18% of patients with SLE, being 100% specific for a diagnosis of SLE compared with healthy controls and 98% specific for SLE compared with patients with other diseases (P < 0.0001). In addition, platelet C4d was significantly associated with positivity for lupus anticoagulant (P < 0.0001) and anticardiolipin antibodies of the IgG (P = 0.035) or the IgM (P = 0.016) isotype. Platelet C4d was also significantly associated with SLE disease activity according to the SLE Disease Activity Index (P = 0.039), low serum C4 (P = 0.046), an elevated erythrocyte sedimentation rate (P = 0.006), and abnormal levels of C4d on erythrocytes (P < 0.0001).

CONCLUSION

This observation suggests that platelet-bound C4d may be a useful biomarker for SLE and may be a clue to the pathogenic mechanisms responsible for the myriad thrombotic and vascular complications of lupus associated with antiphospholipid antibodies.

A Prospective Study of 1038 Pregnancies on the Predictive Value of Anti-Annexin V Antibodies for Fetal Loss

Retrospective studies have demonstrated that anti-annexin V (anti-AnxV) antibodies are linked to miscarriage. Their predictive value is, however, unknown. We have carried out a prospective study to evaluate the relationship between anti-AnxV antibodies and the pregnancy outcome. A serum sample was taken from 1038 consecutive healthy women at the beginning of pregnancy. IgG and IgM anti-AnxV antibodies were measured by an ELISA method. The cutoff value was set at 5 units for both IgG and IgM. Out of 1038 women, 116 (11.4%) had a miscarriage by the 22nd week; 10 were lost to follow-up, 10 had an induced abortion, 6 had a preterm delivery, and 896 carried their pregnancy through to term. An adverse outcome of the pregnancy proved to be directly related to the number of previous miscarriages (P = .008) and the age of the woman (P = .002). IgG and IgM anti-AnxV were present in 25% and 27% of the women who miscarried, and in 23% and 28% of those who gave birth (mean antibody concentration IgG, 4.2 vs. 4.4 U/mL; IgM, 3.7 vs. 3.5 U/mL). IgG and IgM anticardiolipin and anti-beta(2)GPI, together with antinuclear, antithyroperoxidase, and antithyroglobulin antibodies, were also measured in the 116 sera of the women with miscarriage and in an equal number of women who gave birth. Their positivity or level proved not to be useful in discriminating between the risk of miscarriage and term delivery. This large-scale prospective study demonstrates that the presence of IgG and IgM anti-AnxV antibodies, when measured in healthy women, does not give a positive predictive lead towards the possibility of a miscarriage, and it is not useful in evaluating the risk of miscarriage at the beginning of pregnancy.

Current debates in antiphospholipid syndrome: the acquired antibody-mediated thrombophilia

Antiphospholipid (APL) syndrome is the most common form of acquired thrombophilia. It can cause significant morbidity and even mortality. The term "APL antibodies" represents a heterogeneous group of antibodies associated with this disorder. Currently no single assay can identify every APL antibody. Clinically relevant APL antibodies are mainly anticardiolipin antibodies (ACA) detected by solid phase enzyme-linked immunosorbent assay (ELISA) and lupus anticoagulants (LA) demonstrated by in vitro coagulation assay. However, there are some other antibodies associated with the APL syndrome (i.e., subgroup APL antibodies). ACAs, LAs, and subgroup APL antibodies represent intersecting, but non-identical, subsets of autoantibodies. Thus, those autoantibodies may coexist or may occur independently. Any organ system and any size of vessel can be affected during the clinical course of the disease. Therefore, the APL syndrome can manifest itself in a wide variety of clinical thrombotic features. Fetal loss and pregnancy morbidity represent a specific challenge. Despite tremendous advances in the understanding of the pathogenesis of APL syndrome during the past decade, the mainstay of management is still anticoagulation. However, there is no general agreement regarding the duration and intensity of anti-coagulant therapy. In this review, we focused on the current dilemmas and their present clarifications in the wide clinicopathologic spectrum of APL syndrome and APL antibody-related distinct pathologic conditions.

Heparin prevents antiphospholipid antibody-induced fetal loss by inhibiting complement activation

The antiphospholipid syndrome (APS) is defined by thrombosis and recurrent pregnancy loss in the presence of antiphospholipid (aPL) antibodies and is generally treated with anticoagulation therapy. Because complement activation is essential and causative in aPL antibody-induced fetal injury, we hypothesized that heparin protects pregnant APS patients from complications through inhibition of complement. Treatment with heparin (unfractionated or low molecular weight) prevented complement activation in vivo and in vitro and protected mice from pregnancy complications induced by aPL antibodies. Neither fondaparinux nor hirudin, other anticoagulants, inhibited the generation of complement split products or prevented pregnancy loss, demonstrating that anticoagulation therapy is insufficient protection against APS-associated miscarriage. Our data indicate that heparins prevent obstetrical complications in women with APS because they block activation of complement induced by aPL antibodies targeted to decidual tissues, rather than by their anticoagulant effects.

Complement system on the attack in autoimmunity

The antiphospholipid syndrome is characterized clinically by fetal loss and thrombosis and serologically by the presence of autoantibodies to lipid-binding proteins. In a model of this procoagulant condition in which these antibodies are injected into pregnant mice, fetal loss was prevented by blocking of complement activation. Specifically, interaction of complement component 5a (C5a) with its receptor is necessary for thrombosis of placental vasculature. Inhibition of complement activation may have a therapeutic role in this disease.

Complement C5a receptors and neutrophils mediate fetal injury in the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is defined by recurrent pregnancy loss and thrombosis in the presence of antiphospholipid (aPL) Ab's. Currently, therapy for pregnant women with APS is focused on preventing thrombosis, but anticoagulation is only partially successful in averting miscarriage. We hypothesized that complement activation is a central mechanism of pregnancy loss in APS and tested this in a model in which pregnant mice receive human IgG containing aPL Ab's. Here we identify complement component C5 (and particularly its cleavage product C5a) and neutrophils as key mediators of fetal injury, and we show that Ab's or peptides that block C5a-C5a receptor interactions prevent pregnancy complications. The fact that F(ab)'2 fragments of aPL Ab's do not mediate fetal injury and that C4-deficient mice are protected from fetal injury suggests that activation of the complement cascade is initiated via the classical pathway. Studies in factor B-deficient mice, however, indicate that alternative pathway activation is required and amplifies complement activation. In contrast, activating Fc gamma Rs do not play an important role in mediating aPL Ab-induced fetal injury. Our findings identify the key innate immune effectors engaged by pathogenic autoantibodies that mediate poor pregnancy outcomes in APS and provide novel and important targets for prevention of pregnancy loss in APS.

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: 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.

Molecular and genetic characterizations of five pathogenic and two non-pathogenic monoclonal antiphospholipid antibodies

Antiphospholipid syndrome (APS) is an autoimmune disease that is characterized by thrombosis, recurrent fetal loss and thrombocytopenia. Antiphospholipid antibodies, detected by enzyme-linked immunoabsorbent assays (aCL) and/or in vitro blood clotting assays (LAC) are strongly associated with APS. Both the molecular structures used by pathogenic antiphospholipid antibodies and the genetic mechanisms leading to their production are unknown. We describe here the variable region genes of seven IgG antiphospholipid antibodies derived from two APS patients. Of these, five are pathogenic as defined in a mouse model of thrombosis and two are not. Analyses of the expressed variable region genes show no preferential V gene usage. However, similar to anti-DNA antibodies, pathogenic antiphospholipid antibodies contain an increased number of arginine residues in the third complimentarity-determining region (CDR3) of their H chains. The increased accumulation of arginine residues in the V(H) CDR3 may act to enhance antigen binding, promote disease and point to the importance of the H chain in the pathogenic potential of certain antiphospholipid antibodies.

Complement C3 activation is required for antiphospholipid antibody-induced fetal loss

The antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, vascular thrombosis, and thrombocytopenia occurring in the presence of antiphospholipid (aPL) antibodies. The pathogenesis of fetal loss and tissue injury in APS is incompletely understood, but is thought to involve platelet and endothelial cell activation as well as procoagulant effects of aPL antibodies acting directly on clotting pathway components. Recent studies have shown that uncontrolled complement activation in the placenta leads to fetal death in utero. We hypothesized that aPL antibodies activate complement in the placenta, generating split products that mediate placental injury and lead to fetal loss and growth retardation. To test this hypothesis, we used a murine model of APS in which pregnant mice are injected with human IgG containing aPL antibodies. We found that inhibition of the complement cascade in vivo, using the C3 convertase inhibitor complement receptor 1-related gene/protein y (Crry)-Ig, blocks fetal loss and growth retardation. Furthermore, mice deficient in complement C3 were resistant to fetal injury induced by aPL antibodies. While antigenic epitopes recognized by aPL antibodies are important in the pathogenesis of APS, our data show that in vivo complement activation is required for aPL antibody-induced fetal loss and growth retardation.

The effects of a human IgM monoclonal anticardiolipin antibody on pregnancy in a transgenic mouse model

The clinical features of antiphospholipid (or Hughes') syndrome (APS) are most commonly seen in individuals who have raised levels of IgG anticardiolipin antibodies. Most murine models of the syndrome have involved the administration of such antibodies to normal mice. However, APS can occur in the presence of raised levels of serum IgM anticardiolipin antibodies alone. The present study was designed to see if an IgM monoclonal antibody can induce changes in mice similar to those seen in human APS. This antibody, BH1, has previously been derived from a patient with primary APS. In its ligand-binding and idiotypic characteristics it is representative of antiphospholipid antibodies (aPL) found in the serum of patients with APS. In order to minimise the immune response to human IgM, we used transgenic mice (F15) which express, and are predicted to be tolerant of, human immunoglobulin mu chains. The features of APS may develop more readily in individuals who have an existing autoimmune disorder, such as systemic lupus erythematosus (SLE). We therefore crossed these transgenic mice with New Zealand Black (NZB, SLE-prone) mice, and used the progeny (F15 x NZB/F1) in our experiments. Twenty-four F15 x NZB/F1 mice were given BH1, or a control IgM antibody, (A5566) immediately preceding and then three times during pregnancy. There was a reduction in the mean number of foetuses in animals given BH1 compared with those given A5566 (8.6 vs 11.0; P < 0.05), and a similar reduction in mean total foetal weight per pregnancy (9.05 vs 12.73 g; P < 0.05). Two mice showed a marked reduction in platelet count. No evidence of thrombosis was detected macroscopically or histologically. Our results show a lower incidence of APS-type features compared to previous studies in which mice have been administered aPL. This may be because BH1 is an IgM antibody. Nevertheless, the data support the concept that IgM aPL of particular ligand-binding specificities may have a direct pathogenetic role in certain cases of human APS.

Induction and treatment of the antiphospholipid syndrome--lessons from animal models

The diagnosis of antiphospholipid syndrome (APS) is based on a combination of clinical and serological criteria. This review summarizes the literature regarding animal models of APS. Animal models of this syndrome help to elucidate pathogenic roles of the characteristic antiphospholipid antibodies in pregnancy morbidity, vascular thrombosis, neurologic disease and atherosclerosis. Furthermore, these models also provide measures to evaluate novel therapies for APS. These include bone-marrow transplantation, intravenous immunoglobulin, anticoagulation, interleukin-3, in addition to other therapies. Experimental induction and treatment of APS largely contributes to our understanding of the disease and to better management of its clinical characteristics.

Antiphospholipid antibodies affect trophoblast gonadotropin secretion and invasiveness by binding directly and through adhered beta2-glycoprotein I

OBJECTIVE

To investigate the in vitro ability of antiphospholipid antibodies (aPL) to bind human trophoblast cells and to affect gonadotropin secretion and invasiveness.

METHODS

Antiphospholipid antibody IgG from women with recurrent miscarriages, beta2-glycoprotein I (beta2GPI)-independent IgG aPL human monoclonal antibody (mAb) (519), and IgM anti-beta2GPI human mAb (TMIG2) were investigated for their binding to trophoblasts cultured for various amounts of time, their ability to affect invasiveness of Matrigel-coated filters, and their release of human chorionic gonadotropin (hCG).

RESULTS

Polyclonal IgG aPL, as well as mAb 519 and TMIG2, bound to trophoblasts, the highest binding being found when cells displayed the greatest amount of syncytium formation. TM1G2 binding was found to be betaGPI dependent. Both polyclonal and monoclonal aPL, but not the controls, significantly reduced hCG release and Matrigel invasiveness.

CONCLUSION

These findings suggest that aPL recognition of both anionic PL and adhered beta2GPI on trophoblast cell structures might represent a potential pathogenetic mechanism for defective placentation in women with the antiphospholipid syndrome.

Annexin V is critical in the maintenance of murine placental integrity

OBJECTIVES

Recurrent fetal loss can be a consequence of placental thrombosis, frequently occurring in autoimmune disorders such as antiphospholipid syndrome. A potent anticoagulant, annexin V, is abundant in placental tissues. We investigated the role of annexin V in maintaining fetal viability.

STUDY DESIGN

Sites of annexin V activity in placenta were found and neutralized, and the physiologic consequences on fetal development were evaluated. To find extracellular binding sites for annexin V on placental membrane, 2 approaches were taken. An epitope-tagged recombinant annexin V was infused into pregnant BALB/c mice. Endogenous annexin V was evaluated by immunohistochemical techniques. To define a role for annexin V during pregnancy, annexin V was neutralized by tail-vein infusion of affinity-purified anti-annexin V antibodies immediately before mating, 16 hours before the vaginal plugs were observed. Fetal viability, number, and size were evaluated at days 11 or 15 after conception.

RESULTS

Endogenous annexin V is enriched along the apical surfaces of trophoblasts. Animals infused with epitope-tagged annexin V had confirmed presence of extracellular binding sites for annexin V exclusively along these surfaces. In mice infused with anti-annexin V antibodies, various degrees of fetal absorption were observed. Thrombosis and necrosis were present in the fetal component of placentas from partially absorbed embryos. Focal necrosis and fibrosis were present in the decidua of placentas from embryos that were significantly smaller than the normal embryos in the same uterus.

CONCLUSIONS

Apical surfaces of syncytiotrophoblasts in the placenta possess annexin V binding sites. The binding of annexin V to these coagulation-promoting surfaces is crucial for the maintenance of blood flow through the placenta and consequently for fetal viability. Infusion of anti-annexin V antibodies decreased the availability of annexin V to bind to the trophoblast surfaces and caused placental thrombosis, necrosis, and fetal loss. Our study suggests that anti-annexin V autoantibodies may contribute to recurrent pregnancy failure resulting from placental thrombosis, as found in patients with certain autoimmune diseases.

Pregnancy loss and antiphospholipid antibodies

With the use of low-dose heparin, fetal survival of aPL pregnancies is 70-80%, but prematurity and intrauterine growth restriction are common. It is likely, but not proven, that dysregulated placental coagulation and resultant vasculopathy are the cause of fetal loss. Details of dysregulated coagulation remain to be described. Opportunities remain to determine the role of coagulopathy in repeated pregnancy loss, identify a critical event or window to which intervention might be directed, identify maternal (and fetal) characteristics other than aPL that determine fetal loss, describe toxicity profiles of current treatments, develop more specific, less toxic therapies, and describe long-term fetal and maternal outcomes.

A chemically defined, toleragen-based approach for targeting anti-beta2-glycoprotein I antibodies

Antiphospholipid syndrome is characterized by a prothrombotic state and the presence of beta2-glycoprotein I (beta2-GPI)-dependent antiphospholipid antibodies. The feasibility of a B cell tolerance-based approach for specific reduction of anti-beta2-GPI antibodies was investigated. Anti-beta2-GPI antibodies isolated from a patient with antiphospholipid syndrome were used to screen peptide libraries expressed in phage, resulting in the identification of a phage that specifically bound anti-beta2-GPI antibodies. The phage-displayed peptide was identified and chemically optimized to generate a synthetic 14-mer peptide with an internal thioether linkage (LJP 685) that retained the binding profile of the original phage. LJP 685 was conjugated to a defined, non-immunogenic organic platform to generate a tetravalent presentation of LJP 685 for use as a toleragen. Tetravalent LJP 685 induced a dose-dependent reduction in antibody levels in mice previously immunized and boosted with LJP 685 coupled to the carrier keyhole limpet hemocyanin. These experiments support the technical feasibility of a tolerance-based approach for reducing anti-beta2-GPI antibodies in vivo.

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.

Human anticardiolipin monoclonal autoantibodies cause placental necrosis and fetal loss in BALB/c mice

OBJECTIVE

To analyze the structure, specificity, and in vivo pathogenetic potential of 2 human anticardiolipin (aCL) monoclonal antibodies (MAb).

METHODS

Human aCL IgG MAb were generated from hybridized Epstein-Barr virus-induced B cell lines from a healthy subject (MAb 519) and from a patient with primary antiphospholipid syndrome (MAb 516). Studies of antigen-binding specificity and analysis of Ig V-gene mutations were carried out. The MAb were independently injected into mated female BALB/c mice, and their effect on pregnancy outcome was compared with that of MAb 57, a highly mutated and antigen-selected human IgG1lambda rabies virus antibody.

RESULTS

Both MAb 519 and MAb 516 utilized minimally mutated V(H)DJ(H) and VkappaJkappa gene segments and bound cardiolipin and other anionic phospholipids in the absence of beta2-glycoprotein I (beta2-GPI). The mice injected with aCL MAb displayed a significantly higher rate of fetal resorption and a significant reduction in fetal and placental weight as compared with those injected with MAb 57. These findings were accompanied by a finding of placental human IgG deposition and necrosis in the aCL MAb-treated animals.

CONCLUSION

The results of this study indicate that human aCL IgG that are beta2-GPI independent can induce pathology.

Placental pathology in systemic lupus erythematosus and phospholipid antibody syndrome

Fetal loss is increased in women who meet the Arthritis and Rheumatism Association criteria for systemic lupus erythematosus (SLE) and in women who have phospholipid antibody syndrome (APS). There are multiple causes for this fetal loss, and in patients with SLE, disease activity appears to be an important contributing factor. In APS patients, it appears that some individuals will experience recurrent fetal loss and will continuously fail to complete pregnancy naturally. Placental examination has helped to elucidate some of the pathology that may be contribute to this fetal loss and our studies have shown that the same pathology is repeated in subsequent pregnancies. Placental examination in SLE or APS patients with recurrent fetal loss is vital if we are going to be able to determine appropriate therapy to prevent fetal loss.

Thrombogenic properties of murine anti-cardiolipin antibodies induced by beta 2 glycoprotein 1 and human immunoglobulin G antiphospholipid antibodies

BACKGROUND

Recurrent arterial thrombosis and venous thrombosis are frequent complications of the antiphospholipid syndrome (APS). Patients produce anti-cardiolipin antibodies, but the role of these antibodies in thrombus formation is uncertain. This study used a unique CD-1 mouse model of thrombosis to determine whether anti-cardiolipin and anti-beta 2 glycoprotein 1 (beta 2 GP1) antibodies induced immunologically in these animals are thrombogenic.

METHODS AND RESULTS

The CD-1 mouse model enables measurement of the kinetics of a thrombus induced in the femoral vein of the animal. Animals are first anesthetized, then one femoral vein is exposed and subjected to a standardized, nonpenetrating "pinch" injury that induces a thrombus. The vein is trans-illuminated, and the growing thrombus is visualized on a television screen. The rate of formation and disappearance of the thrombus as well as its area can be measured by a computer attached to the television. Three groups of CD-1 mice (each group comprising seven animals) were studied. Group 1 mice were actively immunized with beta 2GP1, resulting in production of anti-beta 2GP1 and anti-cardiolipin antibodies. Group 2 mice were actively immunized with human immunoglobulin G (IgG) anti-cardiolipin antibodies and produced anti-human IgG as well as anti-cardiolipin antibodies (the latter by an idiotype-anti-idiotype reaction). These animals did not produce anti-beta 2GP1 antibodies. Group 3 mice were immunized with human serum albumin (HSA) and produced anti-HSA but not anti-cardiolipin antibodies. The kinetics of thrombus formation induced in the femoral veins of the experimental mice were compared. Results showed that the mean thrombus area as well as mean time during which thrombi persisted were significantly greater in group 1 and group 2 mice compared with group 3. There was no statistical difference between group 1 or group 2.

CONCLUSIONS

Demonstration of a thrombogenic effect of murine anti-cardiolipin antibodies suggests that these antibodies may be pathogenic in humans with APS.