Significant changes in the levels of secreted cytokines in brains of experimental antiphospholipid syndrome mice

Antiphospholipid syndrome (APS) is characterized by thromboses and neuropsychiatric manifestations possibly linked to brain inflammation. In order to examine the levels of proinflammatory and anti-inflammatory cytokines in experimental APS (eAPS) mice brains, we measured the levels of TNF-α, IFN-γ, and IL-10 in brain homogenates (cytosolic fractions) and in brain slices (secreted level) at 6, 15, and 24 weeks after immunization. We induced eAPS by immunization of Balb/c mice with β(2)-glycoprotein I (β(2)GPI), the major autoantigen in the disease and controls with adjuvant alone. We found increased levels of secreted TNF-α in eAPS mice for the entire experiment period. Cytosolic and secreted IL-10 and IFN-γ levels in eAPS mice were lower at 6 and 15 weeks and higher at 24 weeks after immunization. The results suggest that brain disease in APS is associated with significant and complex changes in proinflammatory and anti-inflammatory cytokines.

Role of C3a receptors, C5a receptors, and complement protein C6 deficiency in collagen antibody-induced arthritis in mice

The complement system, especially the alternative pathway, plays essential roles in the induction of injury in collagen Ab-induced arthritis (CAIA) in mice. The goal of the current study was to directly compare the roles of receptors for C3a and C5a, as well as the membrane attack complex, as effector mechanisms in the pathogenesis of CAIA. Clinical disease activity in C3aR(-/-), C5aR(-/-), and C6-deficient (C6-def) mice was decreased by 52, 94, and 65%, respectively, as compared with wild-type mice. Decreases in histopathologic injury as well as in IgG and C3 deposition paralleled the clinical disease activity. A decrease in the percentage of synovial neutrophils was observed in C3aR(-/-), C5aR(-/-), and C6-def mice, and a decrease in macrophages was observed in C3aR(-/-) and C5aR(-/-), but not in C6-def, mice. Synovial mRNA obtained by laser capture microdissection exhibited a decrease in TNF-α in C5aR(-/-) mice and in IL-1β in both C5aR(-/-) and C6-def mice, whereas C3aR(-/-) mice demonstrated no change in either cytokine. Our findings show that absent C3aR-, C5aR-, or membrane attack complex-initiated effector mechanisms each decrease susceptibility to CAIA, with clinical effects most pronounced in C5aR-deficient mice. Although the absence of C3aR, C5aR, or C6 led to differential deficiencies in effector mechanisms, decreased proximal joint IgG and C3 deposition was common to all three genotypes in comparison with wild-type mice. These data suggest the existence of positive-feedback amplification pathways downstream of all three effectors that promote additional IgG deposition and C3 activation in the joint.

Complement and the antiphospholipid syndrome

PURPOSE OF REVIEW

The antiphospholipid antibody syndrome (APS) is characterized by arterial or venous thrombosis or pregnancy morbidity in patients with persistent antiphospholipid antibodies (aPL). Experimental data supporting activation of the complement cascade has provided critical insight into the underlying pathophysiology of aPL-induced pregnancy loss and thrombosis.

RECENT FINDINGS

Although the mechanism by which pregnancy loss and thrombosis is incompletely elucidated, studies using mice deficient in complement components and specific inhibitors to complement have demonstrated that activation of complement contributes to fetal loss, growth restriction and thrombosis. Inhibition of complement activation can prevent these complications. Use of a specific complement inhibitor to C5 has been used successfully in a patient with catastrophic APS undergoing renal transplantation.

SUMMARY

Activation of complement plays an important role in the pathogenesis of aPL-induced pregnancy morbidity and thrombosis. This understanding has been advanced primarily using mouse models of APS and clinical studies in patients with APS are needed. Although there is currently no specific complement-targeted therapy approved for APS, developing and evaluating complement-targeted therapies in patients with APS are warranted. Complement inhibition may provide a novel upstream treatment option for patients with APS compared with the current standard treatment of anticoagulation.

[Immunological aspects of the antiphospholipid syndrome]

Antiphospholipid antibodies constitute a group of heterogeneous antibodies, which mainly recognize complexes made of proteins and anionic phospholipids. The nature of these complexes is currently better defined, as well as known, the structure of the antiphospholipid antibodies owing to the analysis of the monoclonal forms of these antibodies which were also studied both in terms of their precise specificities and cross-reactivity. However, the origin of these autoantibodies is not clearly understood, as well as the possible link between antiphospholipid antibodies present in healthy individuals, and those observed in autoimmune diseases. Only a fraction of antiphospholipid antibodies are pathogenic and directly responsible for the clinical manifestations of the antiphospholipid syndrome, but there is, to date, no biological test able to accurately detect pathogenic antiphospholipid antibodies. The diverse mechanisms which link these autoantibodies to the occurrence of symptoms, mainly during obstetrical complications, are better understood, and suggest new therapeutic avenues.

In vivo distribution of β2 glycoprotein I under various pathophysiologic conditions

In vitro studies have documented β2 glycoprotein I (β2GPI) binding to endothelial cells (ECs) and trophoblast using antiphospholipid antibodies. The in vivo binding of β2GPI to these cells and the conditions that favor their interaction have not been investigated. We analyzed the in vivo distribution of cyanine 5.5-labeled β2GPI in mice and evaluated the effect of pregnancy and circulating antibodies on its tissue localization. The signal was detected in the liver by whole body scan and ex vivo analysis. The β2GPI failed to bind to the vascular endothelium and reacted only with the ECs of uterine vessels. In pregnant mice the protein was localized on ECs and trophoblast at the embryo implantation sites. Immunized mice showed a similar β2GPI biodistribution to naive mice but the immunized pregnant animals exhibited a significant increase in fetal loss associated with C3 and C9 deposition at the implantation sites. Treatment of mice with LPS after β2GPI-Cy5.5 injection promoted protein localization on gut and brain ECs associated with IgG, C1q, and C9 deposition in immunized mice. These findings indicate that β2GPI binding to EC requires priming with pro-inflammatory factors which is not needed for uterine and placental localization probably dependent on hormonal changes.

Evidence for heterogeneity of the obstetric antiphospholipid syndrome: thrombosis can be critical for antiphospholipid-induced pregnancy loss

BACKGROUND

Antiphospholipid antibodies are associated with thrombosis and repeated pregnancy losses during the antiphospholipid syndrome. Several experimental findings indicate that purified antiphospholipid antibodies are directly responsible for inflammation-induced pregnancy losses, or for disruption of the annexin A5 shield at the trophoblastic interface. We previously showed that passive transfer of CIC15, a monoclonal antiphospholipid antibody binding to cardiolipin and annexin A5 that was isolated from a patient with primary antiphospholipid syndrome, induces fetal resorption in pregnant mice.

OBJECTIVES

To investigate the mechanisms of CIC15-induced pregnancy loss.

METHODS/RESULTS

We show that CIC15 induces fetal loss through a new mechanism that is probably related to procoagulant activity. The time course is different from those of previously described models, and histologic analysis shows that the placentas are devoid of any sign of inflammation but display some signs of thrombotic events. Despite these differences, the CIC15 and 'inflammatory' models share some similarities: lack of FcγRI/III dependency, and the efficacy of heparin in preventing fetal losses. However, this latter observation is here mostly attributable to anticoagulation rather than complement inhibition, because fondaparinux sodium and hirudin show similar efficiency. In vitro, CIC15 enhances cardiolipin-induced thrombin generation. Finally, using a combination of surface-sensitive methods, we show that, although it binds complexes of cardiolipin-annexin A5, CIC15 is not able to disrupt the two-dimensional ordered arrays of annexin A5.

CONCLUSIONS

This human monoclonal antibody is responsible for pregnancy loss through a new mechanism involving thrombosis. This mechanism adds to the heterogeneity of the obstetric antiphospholipid syndrome.

Antiphospholipid syndrome: laboratory detection, mechanisms of action and treatment

The antiphospholipid syndrome (APS) identifies a condition at increased risk of vascular occlusion and/or pregnancy complications. Patients are defined as having APS if they have at least one clinical (vascular occlusion and/or pregnancy complications) and one laboratory criterion at the same time. The laboratory criteria that define APS are repeated positivity (confirmed 12 weeks apart) for lupus anticoagulants and/or antibodies targeted against cardiolipin or β(2) -glycoprotein I immobilized on solid surfaces. Over the years, APS has attracted the interest of many medical specialties. The aim of this review is to provide an update on (i) the laboratory criteria that determine the presence of APS, (ii) how the antibodies increase the risk of vascular occlusion and foetal loss and (iii) the treatment of the related clinical events.

[Pathogenic mechanisms of the anti-phospholipid antibodies]

The antiphospolipid syndrome (APS) is an autoimmune disease characterized by recurrent fetal loss, thrombotic events (arterial or venous) and hemocytopenic disorders associated to high titers of circulating aPL. Two variants of the APS have been described. Primary APS is a clinical entity without evidence of any other autoimmune disease and secondary APS is a clinical disorder mainly associated with Systemic Lupus Erithematosus (SLE). aPL are a widely group of immunoglobulins directed against different components or proteins factors. In 1990 three groups of researchers identified that β(2)GP-I is the mainly antigenic target of aPL in APS patients. There are evidences that show that more than one pathogenic mechanism is involved in the development of the APS. The best documented clinical manifestations associated with the APS are recurrent fetal loss and thrombotic disorders. The latter is based on observations in vivo in animal models and in vitro on the effects caused by aβ(2)GP-I antibodies from patients with APS or from animals which cause experimental APS. The objective of the present paper is to show the pathogenic mechanisms that participate in the development of the APS. We also presented evidence that shows that aβ(2)GP-I induces pro-inflammatory, pro-adhesive and pro-coagulant disorder.

β₂-glycoprotein I, the major target in antiphospholipid syndrome, is a special human complement regulator

The human plasma protein β(2)-glycoprotein I (β(2)-GPI) is the major target of autoantibodies associated with antiphospholipid syndrome. However, the biologic function of this abundant protein is still unclear. Here we identify β(2)-GPI as a complement regulator. β(2)-GPI circulates in the plasma in an inactive circular form. On surface binding, such as to apoptotic cells, β(2)-GPI changes conformation to an elongated form that acquires C3/C3b binding activities. β(2)-GPI apparently changes conformation of C3, so that the regulator factor H attaches and induces subsequent degradation by the protease factor I. β(2)-GPI also mediates further cleavage of C3/C3b compared with factor H alone. Our data provide important insights into innate immune regulation by plasma protein β(2)-GPI, which may be exploited in the prevention and therapy of autoimmune disease antiphospholipid syndrome.

Classical complement activation as a footprint for murine and human antiphospholipid antibody-induced fetal loss

Recurrent miscarriage, fetal growth restriction and intrauterine fetal death are frequently occurring complications of pregnancy in patients with systemic lupus erythaematosus (SLE) and antiphospholipid syndrome (APS). Murine models show that complement activation plays a pivotal role in antiphospholipid antibody-mediated pregnancy morbidity, but the exact pathways of complement activation and their potential role in human pregnancy are insufficiently understood. We hypothesized that the classical pathway would play a major role in inducing fetal loss. Pregnant C57BL/6 mice and mice deficient in C1q and factor D were injected with antiphospholipid antibodies or normal human IgG. Mouse placentas were subsequently stained with an anti-C4 antibody and anti-normal human IgG to determine the presence of classical complement activation and IgG binding. Findings in mice were validated in 88 human placentae from 83 women (SLE and APS cases versus controls), which were immunohistochemically stained for C4d, C1q, properdin and MBL. Staining patterns were compared to pregnancy outcome. In murine placentae of mice pretreated with antiphospholipid antibodies, increased C4 deposition was observed, which was associated with adverse fetal outcome but not with IgG binding. In humans, diffuse C4d staining at the feto-maternal interface was present almost exclusively in patients with SLE and/or APS (p < 0.001) and was related to intrauterine fetal death (p = 0.03). Our data show that presence of C4d in murine and human placentae is strongly related to adverse fetal outcome in the setting of SLE and APS. The excessive deposition of C4d supports the concept of severe autoantibody-mediated injury at the fetal-maternal interface. We suggest C4d as a potential biomarker of autoantibody-mediated fetal loss in SLE and APS.

Complement activation triggers metalloproteinases release inducing cervical remodeling and preterm birth in mice

Inflammation is frequently linked to preterm delivery (PTD). Here, we tested the hypothesis that complement activation plays a role in cervical remodeling and PTD. We studied two mouse models of inflammation-induced PTD. The first model was induced by vaginal administration of lipopolysaccharide (LPS) and the second one by administration of progesterone antagonist RU486. Increased cervical C3 deposition and macrophages infiltration and increased serum C3adesArg and C5adesArg levels were observed in both models when compared to gestational age matched controls. A significant increase in collagen degradation, matrix metalloproteinase 9 (MMP-9) activity and tissue distensibility was observed in the cervix in both models. Mice deficient in complement receptor C5a did not show increased MMP-9 activity and cervical remodeling and did not deliver preterm in response to LPS or RU486, suggesting a role for C5aR in the cervical changes that precede PTD. In vitro studies show that macrophages release MMP-9 in response to C5a. Progesterone diminished the amount of C5aR on the macrophages surface, inhibited the release of MMP-9 and prevented PTD. In addition, macrophages depletion also prevented cervical remodeling and PTD in LPS-treated mice. Our studies show that C5a-C5aR interaction is required for MMP-9 release from macrophages, and the cervical remodeling that leads to PTD. Complement inhibition and supplementation with progesterone may be good therapeutic options to prevent this serious pregnancy complication.

Risk factors for pregnancy failure in patients with anti-phospholipid syndrome treated with conventional therapies: a multicentre, case-control study

OBJECTIVE

To identify the risk factors associated with pregnancy failure in patients with APS treated with conventional therapy.

METHODS

A multicentre, case-control study was conducted to compare APS patients with successful and unsuccessful pregnancy outcomes. We retrospectively considered 410 pregnancies of women diagnosed with primary APS. The study focused on 57 unsuccessful pregnancies (considered the study population) and 57 successful pregnancies (considered the control population) matched for age and therapy. All the patients had been treated with conventional protocol treatments including low-dose aspirin and/or heparin. The clinical and laboratory features of the two groups of women diagnosed with APS were compared.

RESULTS

The independent risk factors for pregnancy failure were: (i) the presence of SLE or other autoimmune diseases [odds ratio (OR) 6.0; 95% CI 1.7, 20.8; P = 0.01]; (ii) history of both thrombosis and pregnancy morbidity (OR 12.1; 95% CI 1.3, 115.3; P = 0.03); and (iii) triple [Immunoglobulin (Ig) G/IgM aCLs plus IgG/IgM anti-β(2) glycoprotein I antibodies plus LA] aPL positivity (OR 4.1; 95% CI 1.0, 16.7; P = 0.05). APS patients diagnosed on the basis of a single positive test and/or history of pregnancy morbidity alone were generally found to have successful pregnancies.

CONCLUSION

It would seem from these findings that the risk of pregnancy failure in APS women planning to conceive can be stratified on the basis of some specific clinical and laboratory features.

Placental bed disorders in preterm labor, preterm PROM, spontaneous abortion and abruptio placentae

Failure of physiologic transformation of the spiral arteries has been studied using placental bed biopsies in several obstetrical syndromes. Contrary to what was originally believed, this lesion is not restricted to preeclampsia and/or intrauterine growth restriction. A review of published evidence indicates that failure of physiologic transformation can be observed in women with spontaneous second trimester abortions, preterm labor with intact membranes, preterm prelabor rupture of membranes and abruptio placentae. Therefore, disorders of deep placentation are present in a wide range of complications of pregnancy, emphasizing the importance of understanding the physiology and pathology of transformation of the spiral arteries. We propose that changes in the population and function of immunocytes at the maternal-fetal interface can be part of the mechanism of disease of obstetrical disorders, and this requires further investigation.

Role of tissue factor in pregnancy complications: crosstalk between coagulation and inflammation

Bad pregnancy outcomes have been associated with increased activation of the coagulation cascade and inflammation, in particular the activation of the complement cascade. Recent studies have suggested that inflammatory processes modulate thrombogenic pathways and vice versa. We studied the cross-talk between the coagulation and the complement cascade in the pathogenesis of recurrent miscarriages and preeclampsia in mice. We identified tissue factor (TF) as a crucial mediator of fetal and placental damage in mouse models of recurrent miscarriages and preeclampsia. Increased TF expression increases the release of reactive oxygen species and antiangiogenic molecules from inflammatory cells inducing trophoblast damage and bad pregnancy outcomes. We also demonstrated that pravastatin, by downregulating TF expression, prevents miscarriages and the onset of preeclampsia in mice.

Inhibiting the C5-C5a receptor axis

Activation of the complement system is a major pathogenic event that drives various inflammatory responses in numerous diseases. All pathways of complement activation lead to cleavage of the C5 molecule generating the anaphylatoxin C5a and, C5b that subsequently forms the terminal complement complex (C5b-9). C5a exerts a predominant pro-inflammatory activity through interactions with the classical G-protein coupled receptor C5aR (CD88) as well as with the non-G protein coupled receptor C5L2 (GPR77), expressed on various immune and non-immune cells. C5b-9 causes cytolysis through the formation of the membrane attack complex (MAC), and sub-lytic MAC and soluble C5b-9 also possess a multitude of non-cytolytic immune functions. These two complement effectors, C5a and C5b-9, generated from C5 cleavage, are key components of the complement system responsible for propagating and/or initiating pathology in different diseases, including paroxysmal nocturnal hemoglobinuria, rheumatoid arthritis, ischemia-reperfusion injuries and neurodegenerative diseases. Thus, the C5-C5a receptor axis represents an attractive target for drug development. This review provides a comprehensive analysis of different methods of inhibiting the generation of C5a and C5b-9 as well as the signalling cascade of C5a via its receptors. These include the inhibition of C5 cleavage through targeting of C5 convertases or via the C5 molecule itself, as well as blocking the activity of C5a by neutralizing antibodies and pharmacological inhibitors, or by targeting C5a receptors per se. Examples of drugs and naturally occurring compounds used are discussed in relation to disease models and clinical trials. To date, only one such compound has thus far made it to clinical medicine: the anti-C5 antibody eculizumab, for treating paroxysmal nocturnal hemoglobinuria. However, a number of drug candidates are rapidly emerging that are currently in early-phase clinical trials. The C5-C5a axis as a target for drug development is highly promising for the treatment of currently intractable major human diseases.

Pathophysiology of the antiphospholipid antibody syndrome

Antiphospholipid antibodies (aPL) are associated with the recurrent pregnancy loss and thrombosis that characterizes the antiphospholipid antibody syndrome (APS). Although the ontogeny of these pathogenic antibodies has not been fully elucidated, there is evidence that indicates the involvement of both genetic and environmental factors. The ability of aPL to induce a procoagulant phenotype in APS patients plays a central role in the development of arterial and venous thrombotic manifestations typical of the disease. Inflammation serves as a necessary link between this procoagulant phenotype and actual thrombus development and is an important mediator of the placental injury seen in APS patients with obstetric complications. Recent evidence has indicated a role for abnormal cellular proliferation and differentiation in the pathophysiology of APS, especially in those patients with pregnancy morbidity and other more atypical manifestations that have no identifiable thrombotic cause. The interplay of genetic and environmental factors responsible for aPL development and the mechanisms by which these antibodies produce disease in APS patients is the focus of this review.

The alternative pathway is required, but not alone sufficient, for retinal pathology in mouse laser-induced choroidal neovascularization

Human genetic studies have demonstrated that polymorphisms in different complement proteins can increase the risk for developing AMD. There are three pathways of complement activation, classical (CP), alternative (AP), and lectin (LP), which all activate a final common pathway. Proteins encoded by the AMD risk genes participate in the AP (CFB), CP/LP (C2), or in the AP and final common pathway (C3). Here we tested which pathway is essential in mouse laser-induced CNV. CNV was analyzed using single complement pathway knockouts (i.e., eliminating one complement pathway at a time), followed by a double knockout in which only the AP is present, and the CP and LP are disabled, using molecular, histological and electrophysiological outcomes. First, single-gene knockouts were analyzed and compared to wild type mice; C1q(-/-) (no CP), MBL(-/-) (no LP), and CFB(-/-) (no AP). Six days after the laser-induced lesion, mice without a functional AP had reduced CNV progression (P<0.001) and preserved ERG amplitudes, whereas those without a functional CP or LP were indistinguishable from the wild type controls (P>0.3). Second, AP-only mice (C1q(-/-)MBL(-/-)) were as protected from developing CNV as the CFB(-/-) mice. The degree of pathology in each strain correlated with protein levels of the angiogenic and anti-angiogenic protein VEGF and PEDF, respectively, as well as levels of terminal pathway activation product C5a, and C9. The analysis of complement activation pathways in mouse laser-induced CNV allows for the following conclusions. Comparing the single pathway knockouts with those having only a functional AP showed: (1) that AP activation is necessary, but not alone sufficient for injury; and (2) that initial complement activation proceeds via both the LP and CP. Thus, these data indicate an important role for the AP in the generation of complement-dependent injury in the RPE and choroid via amplification of CP- and LP-initiated complement activation. Improving our understanding of the local regulation of this pathway in the eye is essential for developing improved treatment approaches for AMD.

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.

Role of tissue factor in feto-maternal development: a xiphos

In this review, the dual role of tissue factor (TF) in pregnancy is described. On the one hand, TF is required for embryonic and placental development in a successful pregnancy, and on the other hand, pathologic expression of TF can lead to serious pregnancy complications in humans and mice. Human studies show increased TF levels in plasma, amniotic fluid and and/or placentas of abnormal pregnancies affected by miscarriages, preterm birth, or pre-eclampsia. Interestingly, using two mouse models, we found that blood-borne TF plays a crucial role in the pathogenesis of pregnancy complications. TF on neutrophils and monocytes is a critical mediator in trophoblast injury and embryo damage in pregnancy loss induced by antiphospholipid antibodies and in the antibody-independent CBA/J × DBA/2 model of miscarriages. Blockade of TF or genetic diminution prevented pregnancy complications, suggesting that TF may be a good target for therapy in patients with recurrent miscarriages, pregnancy loss, and pre-eclampsia. In addition, statins, which downregulate TF, may constitute a good therapeutic option for women with pregnancy complications. Clinical trials should be conducted to confirm these observations in women.

Fragment Bb: evidence for activation of the alternative pathway of the complement system in pregnant women with acute pyelonephritis

OBJECTIVE

Pyelonephritis during pregnancy is associated with a more severe course than in the non-pregnant state. This has been attributed to an increased susceptibility of pregnant women to microbial products. The complement system is part of innate immunity and its alternative pathway is activated mainly by microorganisms. The purpose of this study was to determine if activation of the alternative pathway of the complement system (determined by maternal fragment Bb concentrations) occurs in pregnant women with acute pyelonephritis.

METHODS

This cross-sectional study included the following groups: (1) normal pregnant women (n=62) and (2) pregnant women with pyelonephritis (n=38). Maternal plasma fragment Bb concentrations were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

(1) Pregnant women with pyelonephritis had a higher median plasma concentration of fragment Bb than those with a normal pregnancy (1.3 μg/ml, IQR: 1.1-1.9 vs. 0.8 μg/ml, IQR: 0.7-0.9; p<0.001); (2) No significant differences were observed in the median maternal plasma concentration of fragment Bb between pregnant women with pyelonephritis who had a positive blood culture and those with a negative blood culture (1.4 μg/ml, IQR: 1.1-3.5 vs. 1.3 μg/ml, IQR: 1.1-1.9; p=0.2).

CONCLUSIONS

Pregnant women with acute pyelonephritis have evidence of activation of the alternative pathway of the complement system, regardless of the presence or absence of a positive blood culture.

Antiphospholipid antibodies promote leukocyte-endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via β2GPI and apoER2

In antiphospholipid syndrome (APS), antiphospholipid antibodies (aPL) binding to β2 glycoprotein I (β2GPI) induce endothelial cell-leukocyte adhesion and thrombus formation via unknown mechanisms. Here we show that in mice both of these processes are caused by the inhibition of eNOS. In studies of cultured human, bovine, and mouse endothelial cells, the promotion of monocyte adhesion by aPL entailed decreased bioavailable NO, and aPL fully antagonized eNOS activation by diverse agonists. Similarly, NO-dependent, acetylcholine-induced increases in carotid vascular conductance were impaired in aPL-treated mice. The inhibition of eNOS was caused by antibody recognition of domain I of β2GPI and β2GPI dimerization, and it was due to attenuated eNOS S1179 phosphorylation mediated by protein phosphatase 2A (PP2A). Furthermore, LDL receptor family member antagonism with receptor-associated protein (RAP) prevented aPL inhibition of eNOS in cell culture, and ApoER2-/- mice were protected from aPL inhibition of eNOS in vivo. Moreover, both aPL-induced increases in leukocyte-endothelial cell adhesion and thrombus formation were absent in eNOS-/- and in ApoER2-/- mice. Thus, aPL-induced leukocyte-endothelial cell adhesion and thrombosis are caused by eNOS antagonism, which is due to impaired S1179 phosphorylation mediated by β2GPI, apoER2, and PP2A. Our results suggest that novel therapies for APS can now be developed targeting these mechanisms.

Apolipoprotein E receptor 2 is involved in the thrombotic complications in a murine model of the antiphospholipid syndrome

Antiphospholipid (aPL)/anti-β(2) glycoprotein I (anti-β(2)GPI) antibodies stimulates tissue factor (TF) expression within vasculature and in blood cells, thereby leading to increased thrombosis. Several cellular receptors have been proposed to mediate these effects, but no convincing evidence for the involvement of a specific one has been provided. We investigated the role of Apolipoprotein E receptor 2 (ApoER2') on the pathogenic effects of a patient-derived polyclonal aPL IgG preparation (IgG-APS), a murine anti-β(2)GPI monoclonal antibody (E7) and of a constructed dimeric β(2)GPI I (dimer), which in vitro mimics β(2)GPI-antibody immune complexes, using an animal model of thrombosis, and ApoER2-deficient (-/-) mice. In wild type mice, IgG-APS, E7 and the dimer increased thrombus formation, carotid artery TF activity as well as peritoneal macrophage TF activity/expression. Those pathogenic effects were significantly reduced in ApoER2 (-/-) mice. In addition, those effects induced by the IgG-APS, by E7 and by the dimer were inhibited by treatment of wild-type mice with soluble binding domain 1 of ApoER2 (sBD1). Altogether these data show that ApoER2 is involved in pathogenesis of antiphospholipids antibodies.

Antiphospholipid syndrome: a challenging hypercoagulable state with systemic manifestations

Antiphospholipid syndrome (APS) is a systemic disease that causes venous and arterial thrombosis in virtually any organ and is responsible for fetal losses and pregnancy disorders. Previously, APS was thought to be present mainly in patients with systemic lupus erythematosus. The spectrum of clinical manifestations is wide, because the thrombotic process may involve arterial and venous vessels of any size in any organ. At present, there is no evidence to support or refute specific treatment strategies for primary prophylaxis of thrombosis.

New therapeutic targets for the antiphospholipid syndrome

IMPORTANCE OF THE FIELD

The antiphospholipid syndrome (APS) is an autoimmune condition whereby pathogenic antiphospholipid antibodies (aPL) cause vascular thrombosis and/or recurrent miscarriage, and carries a high burden of morbidity and mortality. Currently the only proven treatment is long-term anticoagulation, which is not effective in all patients and carries risk of haemorrhage.

AREAS COVERED IN THIS REVIEW

Novel therapeutic targets that are currently being explored for APS in order to address the unmet needs of better, safer and ideally targeted therapy. These include B cell depletion, new-generation anticoagulants, interfering with aPL cell-mediated activation of endothelial cells and platelets both at the cell surface level and intracellularly, targeting components of the complement system and the novel concept of using decoy peptides to target only the pathogenic sub-population of aPL.

WHAT THE READER WILL GAIN

An overview of the potential targets and rationale underpinning them.

TAKE HOME MESSAGE

Though current options remain limited for the treatment of APS, the future holds much promise with the identification of multiple targets, many of which are currently being explored. The challenge will be to undertake carefully designed prospective multi-centre trials to generate the evidence necessary to support integration of such candidates into clinical practice.

An allelic variant of Crry in the murine Sle1c lupus susceptibility interval is not impaired in its ability to regulate complement activation

The Sle1c subinterval on distal murine chromosome 1 confers loss of tolerance to chromatin. Cr2, which encodes complement receptors 1 and 2 (CR1/CR2; CD35/CD21), is a strong candidate gene for lupus susceptibility within this interval based on structural and functional alterations in its protein products. CR1-related protein/gene Y (Crry) lies 10 kb from Cr2 and encodes a ubiquitously expressed complement regulatory protein that could also play a role in the pathogenesis of systemic lupus erythematosus. Crry derived from B6.Sle1c congenic mice migrated at a higher m.w. by SDS-PAGE compared with B6 Crry, as a result of differential glycosylation. A single-nucleotide polymorphism in the first short consensus repeat of Sle1c Crry introduced a novel N-linked glycosylation site likely responsible for this structural alteration. Five additional single-nucleotide polymorphisms in the signal peptide and short consensus repeat 1 of Sle1c Crry were identified. However, the cellular expression of B6 and B6.Sle1c Crry and their ability to regulate the classical pathway of complement were not significantly different. Although soluble Sle1c Crry regulated the alternative pathway of complement more efficiently than B6 Crry, as a membrane protein, it regulated the alternative pathway equivalently to B6 Crry. These data fail to provide evidence for a functional effect of the structural alterations in Sle1c Crry and suggest that the role of Cr2 in the Sle1c autoimmune phenotypes can be isolated in recombinant congenic mice containing both genes.

High-dose unfractionated heparin therapy in a pregnant patient with antiphospolipid syndrome: a case report

A case of a 37-year-old pregnant patient with antiphospholipid syndrome (APS), who has a medical history of both thrombosis and recurrent fetal loss, is presented. She was treated with predonisolone and fixed-dose unfractionated heparin (UFH) infusion, followed by plasmaphereses and fixed-dose low-molecular-weight heparin infusion during her fourth pregnancy. Unfortunately, this treatment did not have beneficial effects, resulting in intrauterine growth restriction and finally neonatal death. Continuous intravenous UFH infusion and low-dose aspirin were administrated under the monitoring of the activated partial thromboplastin time to achieve a target level of 120 s during her fifth pregnancy. A healthy baby weighing 1818 g at birth was delivered by Cesarean section at the 34th week of pregnancy. High-dose UFH infusion may be considered to be one of the preferable options to manage pregnant patients with refractory APS.

Preeclampsia and pregnancies with small-for-gestational age neonates have different profiles of complement split products

OBJECTIVE

The activation of the complement system results in the generation of split products with pro-inflammatory properties. The objective of this study was to determine whether preeclampsia and small-for-gestational age (SGA) are associated with changes in the maternal plasma concentrations of anaphylatoxins C3a, C4a and C5a.

METHODS

A cross-sectional study was conducted in the following groups: (a) normal pregnant women (n = 134); (b) women who delivered an SGA neonate (n = 53); (c) preeclampsia with (n = 52) and without SGA (n = 54). Maternal plasma anaphylatoxin concentrations were determined by enzyme-linked immunoassay.

RESULTS

(1) Women with preeclampsia with or without SGA had a significantly higher median plasma C5a concentration than that of normal pregnant women and those with SGA alone (all P < 0.01); (2) women with SGA alone did not have an increase in plasma C5a concentration; (3) in contrast, the median maternal plasma concentration of C4a was lower in women with preeclampsia and SGA than that of those with a normal pregnancy (P = 0.001); (4) no changes in C3a were observed among the study groups.

CONCLUSION

Preeclampsia is associated with increased plasma concentration of C5a, regardless of the presence or absence of an SGA fetus. In contrast, there was no difference in the plasma C3a, C4a and C5a concentration in patients with SGA.

Role of tissue factor in thrombosis in antiphospholipid antibody syndrome

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder defined by the presence of an antiphospholipid antibody (aPL) and the occurrence of at least one associated clinical condition that includes venous thrombosis, arterial thrombosis or pregnancy morbidity. The aPL detected in APS have long been thought to have a direct prothrombotic effect in vivo. However, the pathophysiology underlying their coagulopathic effect has not been defined. Emerging data suggest a role for the procoagulant protein tissue factor (TF). In this review we provide an overview of TF, describe mouse models used in the evaluation of the role of TF in thrombosis, as well as summarize recent work on TF and APS.

Antiphospholipid syndrome: critical analysis of the diagnostic path

Antiphospholipid syndrome (APS) is diagnosed in the presence of vascular thrombosis or pregnancy morbidity occurring in patients with circulating antiphospholipid antibodies (lupus anticoagulant [LA] and/or IgG/IgM anticardiolipin [aCL] and/or IgG/IgM anti-beta2glycoprotein I [abeta2GPI] antibodies). Each test may identify different autoantibodies; a single test makes the diagnosis possible when positive on two or more occasions at least 12 weeks apart. However, single test positivity may be unrelated to pathogenic antibodies, which are now considered to be a subclass of abeta2GPI antibodies directed against the domain I of this protein. Conversely, all three positive tests identify a single class of abeta2GPI antibodies, thus identifying high-risk patients with APS.

Fetal rejection: infertility and immunity

Defective reaction toward fetal alloantigens could result in both recurrent spontaneous abortions (RSAs) and recurrent early pregnancy failures (REPFs), the latter existing in couples with unexplained infertility and multiple failures of implantation after in vitro fertilization embryo transfer. Immunological mechanisms leading to RSA and REPF seem to be different, although both syndromes probably have a genetic background that has not been identified so far. Despite the fact that antiphospholipid syndrome is a well-established cause of repeated pregnancy loss, the role of different autoantibodies existing in RSA and REPF patients needs to be elucidated. Immunotherapy is believed to correct the detrimental immune reactions; however, its real effectiveness and safety for the treatment of distinct forms of pregnancy loss need to be reconsidered.

Effects of polyclonal IgG derived from patients with different clinical types of the antiphospholipid syndrome on monocyte signaling pathways

A major mechanism of hypercoagulability in the antiphospholipid syndrome (APS) is antiphospholipid Ab-mediated upregulation of tissue factor (TF) on monocytes via activation of TLRs, p38 MAPK, and NF-kappaB pathways. We examined whether monocyte signaling pathways are differentially activated by IgG from patients with vascular thrombosis (VT) alone compared with IgG from patients with pregnancy morbidity (PM) alone. We purified IgG from 49 subjects. A human monocyte cell line and ex vivo healthy monocytes were treated with 100 microg/ml IgG for 6 h, and cell extracts were examined by immunoblot using Abs to p38 MAPK and NF-kappaB. To further investigate intracellular signaling pathways induced by these IgGs, specific inhibitors of p38 MAPK, NF-kappaB, TLR4, and TLR2 were used to determine their effect on TF activity. Only IgG from patients with VT but no PM (VT+/PM-) caused phosphorylation of NF-kappaBand p38 MAPK and upregulation of TF activity in monocytes. These effects were not seen with IgG from patients with PM alone (VT-/PM+), anti-phospholipid Ab-positive patients without APS, or healthy controls. TF upregulation caused by the VT+/PM- samples was reduced by inhibitors of p38 MAPK, NF-kappaB, and TLR4. The effects of VT+/PM- IgG on signaling and TF upregulation were concentrated in the fraction that bound beta-2-glycoprotein I. Our findings demonstrate that IgGs from patients with diverse clinical manifestations of APS have differential effects upon phosphorylation of NF-kappaB and p38 MAPK and TF activity that may be mediated by differential activation of TLR4.

Cognitive dysfunction and white matter abnormalities in antiphospholipid syndrome

Diagnosis of the antiphospholipid syndrome (APS) requires that a patient have both a clinical event (thrombosis or pregnancy loss) and persistently positive antiphospholipid antibodies (aPL). Although stroke and transient ischemic attack are the most common neurologic manifestations of APS, both cognitive dysfunction and magnetic resonance imaging (MRI) white matter hyperintensities can occur in aPL-positive patients (with or without APS). Relatively little is known about the cognitive pattern in aPL-positive patients; MRI white matter hyperintensities may be related to underlying attentional and executive cognitive impairment. Studies with sophisticated neuroimaging techniques aimed to better understand MRI white matter hyperintensities may eventually facilitate our understanding of cognitive dysfunction in aPL-positive patients.

Antiphospholipid syndrome: pathogenesis and a window of treatment opportunities in the future

BACKGROUND

Antiphospholipid syndrome (APS) is a systemic autoimmune vascular disease characterized by recurrent thrombotic episodes and/or obstetric complications. Management of this disease has been restricted mainly to anticoagulation; however, in recent years, significant advancement has been made in elucidating the pathophysiology of the disease including antiphospholipid antibody (aPL)-induced activation of the platelets, endothelial cells, monocytes, complement and coagulation cascade. Stemming from these advances, potential targeted therapeutic approaches have been proposed.

MATERIALS AND METHODS

We utilized a computer-assisted search of the literature (MEDLINE, National Library of Medicine, Bethesda, MD, USA) up until September 2009 using the keywords: antiphospholipid syndrome, antiphospholipid antibodies, anticardiolipin antibodies, lupus anticoagulant, anti beta-2 glycoprotein antibodies, complement system, tissue factor, p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor kappa B, toll-like receptors, annexin, Rituximab, statins and tumour necrosis factor.

RESULTS

Several study groups have separately demonstrated the importance of inflammatory mediators in the pathogenesis of APS. It was also established that tissue factor, MAPK, nuclear factors kappa B, and the complement system are integral to the disease process. Toll-like receptors and annexin have as well been associated with the disease pathophysiology. Some study groups proposed new targeted therapeutic strategies some of which have shown promising results in preclinical studies. These include Rituximab, complement inhibition, anti-cytokine therapy, p38 MAPK inhibitors, nuclear factor inhibitors and tissue factor inhibitors.

CONCLUSION

As more insight is being gained into the pathophysiology of APS, newer therapeutic strategies are being proposed that might lead to safer and more efficacious treatment modalities in the future.

Dysregulated complement activation as a common pathway of injury in preeclampsia and other pregnancy complications

The complement system protects the host against invading organisms, initiates inflammation and dispose of immune complexes and the products of inflammatory injury. The complement system provides an important link between the innate and adaptive immune systems. Experimental observations suggest that increased complement activation causes and/or perpetuates inflammation during pregnancy. Recent studies suggest a link between complement activation and preeclampsia. Excessive activation or insufficient regulation of complement recruits leukocytes and unleashes potent inflammatory and anti-angiogenic mediators associated with placental insufficiency and maternal endothelial dysfunction characteristic of preeclampsia. We review the animal and human studies that link complement activation and pathogenic events in preeclampsia, present evidence that activation of the complement system is associated with the development of preeclampsia and provides new targets to prevent its complications.

Neutrophils in a mouse model of autoantibody-mediated arthritis: critical producers of Fc receptor gamma, the receptor for C5a, and lymphocyte function-associated antigen 1

OBJECTIVE

Neutrophils represent a prominent component of inflammatory joint effusions and are required for synovial inflammation in mouse models, but the mechanisms are poorly understood. In this study, we developed a system with which to test the importance of the production of specific factors by neutrophils in a mouse model of arthritis.

METHODS

Neutrophil-deficient Gfi-1(-/-) mice were administered sublethal doses of radiation and were then engrafted with donor bone marrow cells (BMCs), which resulted in the production of mature neutrophils within 2 weeks. By reconstituting with BMCs from mice lacking selected proinflammatory factors, we generated mice that specifically lacked these factors on their neutrophils. Arthritis was initiated by transfer of K/BxN serum to identify the role of defined neutrophil factors on the incidence and severity of arthritis.

RESULTS

Neutrophils lacking the signaling chain of stimulatory Fc receptors (FcRgamma(-/-)) were unable to elicit arthritis, but neutrophils lacking FcgammaRIII still did so. Neutrophils lacking the chemotactic or adhesion receptor C5a receptor (C5aR) or CD11a/lymphocyte function-associated antigen 1 (LFA-1) also failed to initiate arthritis but could enter joints in which inflammation had been initiated by wild-type neutrophils. Neutrophils unable to produce interleukin-1alpha (IL-1alpha) and IL-1beta (IL-1alpha/beta(-/-)) or leukotrienes (5-lipoxygenase [5-LOX(-/-)]) produced arthritis of intermediate severity. The inability of neutrophils to make tumor necrosis factor or to express receptors for tumor necrosis factor or IL-1 had no effect on arthritis.

CONCLUSION

A novel transfer system was developed to identify neutrophil production of FcRgamma, C5aR, and CD11a/LFA-1 as critical components of autoantibody-mediated arthritis. Neutrophil production of IL-1 and leukotriene B(4) likely contributes to inflammation but is not essential. Molecular requirements for neutrophil influx into joints become more permissive after inflammation is initiated.

Uterine disorders and pregnancy complications: insights from mouse models

Much of our knowledge of human uterine physiology and pathology has been extrapolated from the study of diverse animal models, as there is no ideal system for studying human uterine biology in vitro. Although it remains debatable whether mouse models are the most suitable system for investigating human uterine function(s), gene-manipulated mice are considered by many the most useful tool for mechanistic analysis, and numerous studies have identified many similarities in female reproduction between the two species. This Review brings together information from studies using animal models, in particular mouse models, that shed light on normal and pathologic aspects of uterine biology and pregnancy complications.

Activation of the alternative pathway of complement is a feature of pre-term parturition but not of spontaneous labor at term

PROBLEM

Plasma concentrations of fragment Bb (FBb) are a marker for activation of the alternative pathway of the complement system. High concentrations of FBb in maternal blood, as early as the first trimester, are associated with subsequent spontaneous pre-term delivery <34 weeks of gestation. The aim of this study was to determine whether spontaneous pre-term labor (PTL) with intact membranes, intra-amniotic infection/inflammation (IAI) or labor at term are associated with alterations in circulating maternal FBb concentrations.

METHOD OF STUDY

This cross-sectional study included women in the following groups: (i) non-pregnant (n = 40); (ii) normal pregnancy (gestational age range 20-36, 6/7 weeks, n = 63); (iii) women at term not in labor (n = 70); (iv) women at term in spontaneous labor (n = 59); (v) patients with an episode of PTL who delivered at term (n = 62); (vi) PTL without IAI who delivered pre-term (n = 30); and (vii) PTL with IAI who delivered pre-term (n = 67). Maternal plasma FBb concentrations were determined by ELISA.

RESULTS

(i) Among patients with PTL, those who had a pre-term delivery either with IAI (1.21 microg/mL, IQR 0.77-2.16) or without IAI (1.13 microg/mL, IQR 0.92-2.08) had a higher median maternal plasma FBb concentration than those who delivered at term (0.86 microg/mL, IQR 0.64-1.57; P = 0.007 and P = 0.026, respectively); (ii) there was no difference in the median plasma FBb concentration between patients with and without IAI who delivered pre-term (P = 0.9); (iii) in contrast, spontaneous labor at term was not associated with a significant change in the maternal plasma FBb concentration (P = 0.8); (iv) maternal plasma concentration of FBb did not differ significantly between normal pregnant women and the non-pregnant controls (P = 0.8) and were not correlated with advancing gestational age (r = -0.28, P = 0.8).

CONCLUSION

(i) Pre-term parturition is associated with activation of the alternative complement pathway in maternal circulation; (ii) such activation is not detectable in spontaneous labor at term; (iii) IAI does not explain the activation of the alternative pathway of complement in PTL. Collectively, these observations suggest that pre-term and term labors have fundamental differences in the regulation of innate immunity.