The role of complement in pregnancy and fetal loss

In the United States, between 1 and 3% of women suffer recurrent miscarriages; 50-70% of all conceptions fail. Although in the majority of affected women the cause of recurrent miscarriages is unknown, an immune mechanism involving the inappropriate and subsequently injurious recognition of the conceptus by the mother's immune system has been proposed. Murine models have recently been developed that are relevant to this issue. We and others have identified a novel role for complement as an early effector in the pathway leading to pregnancy loss associated with placental inflammation. Indeed, it appears that inhibition of complement activation is an absolute requirement for normal pregnancy, and that in the antiphosphospholid syndrome overwhelming activation of complement triggered by antibodies (Ab) deposited in placenta leads to fetal injury. Identification of complement activation as a mediator of pregnancy loss and definition of the complement components necessary to trigger such injury is likely to lead to a better understanding of its pathogenesis and to new and improved treatments.     

Complement activation in animal and human pregnancies as a model for immunological recognition

Pregnancy is a most intriguing feature of biology, not at least because of the need to regulate the maternal immune response against fetal antigens. The mammalian embryo expresses paternal antigens foreign to the mother's immune system and thus elicits an immune response that can lead to fetal rejection and bad pregnancy outcomes such as recurrent miscarriages and preeclampsia. More effective strategies to prevent these pregnancy complications should be forthcoming once the underlying pathophysiological mechanisms that are involved in fetal rejection are completely understood. Our goal in writing this review is to discuss the crucial role of the complement system as an effector mechanism in placental and fetal damage that leads to bad pregnancy outcomes. Important information about the role of excessive complement activation and bad pregnancy outcomes was obtained from animal models. That uncontrolled complement activation puts at risk the survival of the fetus was reported in mouse models of recurrent miscarriages and preeclampsia. Interestingly, several observations described in the mouse models were confirmed in humans. Increased circulating levels of complement proteins, and their activation fragments were found in patients with preeclampsia, recurrent miscarriages and intrauterine growth restriction.Studies performed in animals and humans demonstrated the deleterious effect of complement activation on pregnancy outcomes. However, we also described in this article the strategic role of complement component C1q in normal placentation. C1q deserves special consideration for its role in promoting trophoblast invasion of deciduas, a crucial step in normal placental development.In conclusion, in this review we discussed all the available results of basic and clinical studies on the role of the complement system in pregnancy to expand the understanding of the pathophysiology of pregnancy complications.     

Complement Inhibition Keeps Mothers Calm and Avoids Fetal Rejection

The paternal antigens presented by the fetus could be considered foreign by the mother's immune system and elicit an immune response. Here we show that the complement system functions as an effector in fetal rejection in two different mouse models of pregnancy loss. In a mouse model of fetal loss and growth restriction (IUGR) induced by antiphospholipid antibodies (aPL), we found that complement activation is a crucial and early mediator of pregnancy loss. We demonstrated that C5a-C5aR interaction and neutrophils are key mediators of fetal injury. We identified tissue factor (TF) as a critical intermediate that, acting downstream of C5 activation, enhances neutrophil activity and trophoblast injury. In an antibody-independent mouse model of spontaneous miscarriage and IUGR (CBAxDBA) we also identified C5a as an essential mediator. Complement activation caused dysregulation of the angiogenic factors (deficiency of free vascular endothelial growth factor (VEGF) and elevated levels of soluble VEGF receptor 1) required for normal placental development. Inhibition of complement activation prevented angiogenesis failure and rescued pregnancies. Our studies in antibody-dependent and antibody-independent models of pregnancy complications identified complement activation as the crucial mediator of damage and will allow development of new interventions to prevent pregnancy loss and IUGR.     

Role of Tissue Factor in the Maternal Immunological Attack of the Embryo in the Antiphospholipid Syndrome

Recurrent fetal loss affects 1–5% of women of childbearing age. Immunological mechanisms may account for 40% of recurrent miscarriages, and in particular, the antiphospholipid syndrome (APS) appears to be implicated in 7–25% of the cases. Because antiphospholipid (aPL) antibodies have thrombogenic properties, fetal loss in patients with APS has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically activation of complement with generation of the anaphylotoxin C5a, is an essential trigger of fetal injury. Thrombosis and inflammation are linked in many clinical conditions. Tissue factor (TF), the major cellular initiator of the coagulation protease cascade, plays important roles in both thrombosis and inflammation, and its expression is increased in patients with APS. Here we describe how TF, acting as a proinflammatory molecule, induces trophoblast injury and fetal death in a mouse model of APS. Importantly, we will discuss how TF contributes to C5a-induced oxidative burst in neutrophils leading to trophoblasts and fetal injury in APS. The finding that TF is an important effector in aPL-induced inflammation may allow the development of new therapies to abrogate the inflammatory loop caused by tissue factor and improve pregnancy outcomes in patients with aPL antibodies. Statins downregulate TF-induced inflammation and rescued the pregnancies in aPL-treated mice, suggesting they may be a good treatment for women with aPL-induced pregnancy complications.     

Analysis of genes coding for CD46, CD55, and C4b‐binding protein in patients with idiopathic,recurrent, spontaneous pregnancy loss

Since a tightly regulated complement system is needed for a successful pregnancy, we hypothesized that alterations in complement inhibitors may be associated with idiopathic, recurrent miscarriage. We sequenced all exons coding for three complement inhibitors: C4b‐binding protein (C4BP), CD46, and CD55 in 384 childless women with at least two miscarriages that could not be explained by known risk factors. Several alterations were found in C4BPA, of which the R120H, I126T, and the G423T mutations affected the expression level and/or the ability of recombinant C4BP to serve as cofactor for factor I. The only variant in C4BPB was located in the C‐terminal part, and did not impair the polymerization of the molecule. Our results identify for the first time alterations in C4BP in women experiencing recurrent miscarriages. We also found four CD46 alterations in individual patients that were not found in healthy controls. One of the rare variants, P324L, showed decreased expression, whereas N213I resulted in deficient protein processing as well as an impaired cofactor activity in the degradation of both C4b and C3b. The identified alterations may result in in vivo consequences and contribute to the disorder but the degree of association must be evaluated in larger cohorts.     

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.     

Prevalence of circulating procoagulant microparticles in women with recurrent miscarriage: a case-controlled study

BACKGROUND: Circulating microparticles are markers of cell activation associated with various prothrombotic states. As hypoxia due to uteroplacental thrombosis is considered to be one of the causes of pregnancy loss, microparticles may be associated with pregnancy loss, in addition to, or as part of, other procoagulant states such as antiphospholipid syndrome or hereditary thrombophilias. The objective of this study was to examine the prevalence of circulating microparticles in women with recurrent pregnancy loss. METHODS: A total of 96 women with recurrent pregnancy losses were enrolled in a case-control study and compared with 90 parous women. Microparticles were measured by flow cytometry using fluorescent anti-CD51/CD31 antibodies. RESULTS: Microparticle levels >2 SD above the mean of controls (57,700/ml) were detected in 12 out of 96 women with recurrent miscarriages (12.5%), compared with two of the 90 control women (2.2%), P<0.008. The titre of microparticles did not correlate with age, number of pregnancy losses, primary secondary or tertiary aborters status, or with pregnancy losses in the 1st or 2nd trimesters. CONCLUSIONS: A proportion of women with pregnancy loss have elevated endothelial microparticles suggesting that endothelial damage or activation might be associated with the pathogenesis of pregnancy loss.     

Complement activation and kidney transplantation; a complex relationship

Although kidney transplantation is the best treatment for end stage kidney disease, the benefits are limited by factors such as the short fall in donor numbers, the burden of immunosuppression and graft failure. Although there have been improvements in one-year outcomes, the annual rate of graft loss beyond the first year has not significantly improved, despite better therapies to control the alloimmune response. There is therefore a need to develop alternative strategies to limit kidney injury at all stages along the transplant pathway and so improve graft survival. Complement is primarily part of the innate immune system, but is also known to enhance the adaptive immune response. There is increasing evidence that complement activation occurs at many stages during transplantation and can have deleterious effects on graft outcome. Complement activation begins in the donor and occurs again on reperfusion following a period of ischemia. Complement can contribute to the development of the alloimmune response and may directly contribute to graft injury during acute and chronic allograft rejection. The complexity of the relationship between complement activation and allograft outcome is further increased by the capacity of the allograft to synthesise complement proteins, the contribution complement makes to interstitial fibrosis and complement’s role in the development of recurrent disease. The better we understand the role played by complement in kidney transplant pathology the better placed we will be to intervene. This is particularly relevant with the rapid development of complement therapeutics which can now target different the different pathways of the complement system. Combining our basic understanding of complement biology with preclinical and observational data will allow the development and delivery of clinical trials which have best chance to identify any benefit of complement inhibition.     

Short-term therapy for recurrent abortion using intravenous immunoglobulins: results of a double-blind placebo-controlled Italian study

It is still unclear whether i.v. immunoglobulins (Ig) can facilitate the reproductive prognosis of women who have suffered recurrent pregnancy loss. We report the results of a multicentre placebo- controlled study on the effect of Ig administration on pregnancy outcome in 46 women who had suffered at least three recurrent miscarriages. All were screened to exclude chromosomal or Mullerian abnormalities, the presence of antinuclear antibodies, lupus anticoagulant (LA) or elevated titres of anticardiolipin antibodies which may have revealed an underlying autoimmune problem. To avoid a selection bias towards ongoing pregnancies, i.v. Ig or placebo were administered between weeks 5 and 7 of gestation for 2 consecutive days as soon as each woman knew she was pregnant and before embryonic heart activity could be detected. A further infusion was administered at week 8 when ultrasonography confirmed an ongoing embryonic development. In all, 68% of the women who received Ig went to term versus 79% of those who received a placebo (not significant), with no significant differences in the pregnancy course or the perinatal outcome. These results suggest either that women with recurrent miscarriages who have no recognized cause of pregnancy loss have a good reproductive prognosis without any treatment or that the emotional care associated with the administration of a placebo can indirectly facilitate the progression of pregnancy.      

1141174724Complement activation induces dysregulation of angiogenic factors and causes fetal loss

Complement is an important effector in pregnancy loss in the antiphospholipid syndrome. We now test the hypothesis that complement activation is a necessary intermediary event in the pathogenesis of recurrent spontaneous miscarriage in DBA/2-mated female CBA/J mice (CBAxDBA), a well-studied model of autoantibody-independent pregnancy failure. Blockade of C3 activation with Crry-Ig completely rescued pregnancies in CBAxDBA mice (Crry-Ig vs untreated 8.5 ± 6.3% fetal resorptions vs 28.0 ± 7.2%, P <  0.01). Inhibition of C5 cleavage with anti-C5 mAb and blockade of C5a receptors with a peptide antagonist also prevented pregnancy loss (8.6 ± 4.4% and 8.0 ± 5.9% resorptions, respectively, P <  0.01 versus control). Inhibition of the alternative pathway resulted in pregnancy outcomes similar to controls (8.4 ± 6.6% versus 9.2 ± 3.2% resorptions). In CBAxDBA matings, we observed elevated plasma levels of soluble VEGF receptor-1 (sVEGFR-1; a potent anti-angiogenic molecule), increased placental inflammatory infiltrates and defective development of placenta. Our complement inhibitory strategies blocked the increase in sVEGFR-1, prevented functional deficiency of VEGF and rescued pregnancies. We confirmed the importance of complement as a proximal effector in in vitro studies; monocytes stimulated with C5a released sVEGFR-1 which sequesters VEGF required for normal placental development. Our data indicate that complement activation leads to recruitment of inflammatory cells and production of inhibitors of angiogenesis (sVEGFR-1) which cause placental dysfunction and fetal injury. These studies identify key innate immune effectors that mediate poor pregnancy outcomes and provide novel and important targets for prevention of recurrent pregnancy loss in patients.     

Postpartum Thyroiditis

Post partum thyroiditis occurs in 50% of TPO AB+ve women and is characterised by transient hyperthyroidism followed by transient hypothyroidism during the first six months, post partum. A third of the latter group develop permanent hypothyroidism. The syndrome is seen in 5-9% of women and post partum thyroid dysfunction (PPTD) reoccurs in 75% of women in a subsequent pregnancy. An increase in depressive symptomatology is seen in women with PPTD as well as in ante TPO Ab+ve women without PPTD. The immunology of PPT is associated with the presence of TPO antiboides with those IgG subclasses best able to activate the complement cascade. The HLA-DR frequencies seen in PPT suggest that PPT may be related to Hashimoto's thyroiditis. TPO Ab driven complement fixation is seen in PPT and complement activation relates to the extent and progression of thyroid damage. Recent studies have shown an increase in both Th2 and Th1 cytokine release from lymphocytes in ante partum women destined to develop PPTD. More data are required on the cellular immune changes both ante partum and post partum in PPT.     

Hysteroscopy may be justified after two miscarriages

BACKGROUND: Recurrent pregnancy loss is traditionally investigated after three or more consecutive pregnancy losses. Although there is a trend to start investigation after two miscarriages, data are not available to date to justify this approach. We sought to compare the frequency of uterine anomalies between women referred to hysteroscopy for repeated miscarriages after two, and three or more, miscarriages respectively. METHODS: A retrospective analysis of acquired and congenital uterine anomalies in all patients undergoing hysteroscopy for repeated pregnancy loss at an academic and referral medical centre. RESULTS: Hysteroscopy was performed on 165 women referred for recurrent pregnancy loss: 67 after two and 98 after three or more consecutive miscarriages. The rate of uterine anomalies did not differ significantly and was 32 versus 28% respectively. CONCLUSIONS: Hysteroscopy may be justified following two spontaneous pregnancy losses.     

Prevalence of hypothyroidism in recurrent pregnancy loss in first trimester

Aim: To determine the frequency of hypothyroidism in women with recurrent pregnancy loss in first trimester in the Indian population. Settings and Design: The study included 163 non-pregnant women with recurrent pregnancy loss in a gestational age up to 相似文献   

Complement inhibition keeps mothers calm and avoids fetal rejection

The paternal antigens presented by the fetus could be considered foreign by the mother's immune system and elicit an immune response. Here we show that the complement system functions as an effector in fetal rejection in two different mouse models of pregnancy loss. In a mouse model of fetal loss and growth restriction (IUGR) induced by antiphospholipid antibodies (aPL), we found that complement activation is a crucial and early mediator of pregnancy loss. We demonstrated that C5a-C5aR interaction and neutrophils are key mediators of fetal injury. We identified tissue factor (TF) as a critical intermediate that, acting downstream of C5 activation, enhances neutrophil activity and trophoblast injury. In an antibody-independent mouse model of spontaneous miscarriage and IUGR (CBAxDBA) we also identified C5a as an essential mediator. Complement activation caused dysregulation of the angiogenic factors (deficiency of free vascular endothelial growth factor (VEGF) and elevated levels of soluble VEGF receptor 1) required for normal placental development. Inhibition of complement activation prevented angiogenesis failure and rescued pregnancies. Our studies in antibody-dependent and antibody-independent models of pregnancy complications identified complement activation as the crucial mediator of damage and will allow development of new interventions to prevent pregnancy loss and IUGR.     

A longitudinal study of pregnancy outcome following idiopathic recurrent miscarriage.

Recurrent miscarriage is a difficult clinical problem occurring in approximately 1-2% of fertile women. Following investigation, most cases fail to reveal an identifiable cause and are therefore classified as idiopathic. The aim of this study was to identify important gestational milestones for pregnancy success prediction in women following idiopathic recurrent miscarriage. A total of 325 consecutive patients with idiopathic recurrent miscarriage was involved in a prospective longitudinal observational study. Patients were identified from a miscarriage database of 716 patients. Preconceptual presentation and investigation excluded patients from the study sample with known associations of recurrent pregnancy loss, such as antiphosholipid syndrome, oligomenorrhoea, mid-trimester loss and other rare causes, e.g. abnormal parental karyotype. Following early presentation in a subsequent pregnancy, all patients followed a standard clinic protocol including fetal viability ultrasonography on a fortnightly basis throughout the first trimester. Kaplan-Meier curves were constructed for pregnancy outcome. Out of 325 idiopathic cases, 70% (n = 226) conceived, with a 75% success rate. Of 55 miscarriages, longitudinal assessment showed that six losses occurred following detection of fetal cardiac activity (3%). Data from this large study group have enabled accurate prediction of future pregnancy success and have established important gestational milestones for women with idiopathic recurrent miscarriage.     

Complement therapeutic strategies in trauma,hemorrhagic shock and systemic inflammation – closing Pandora’s box?

After severe trauma, the immune system is challenged with a multitude of endogenous and exogenous danger molecules. The recognition of released danger patterns is one of the prime tasks of the innate immune system. In the last two decades, numerous studies have established the complement cascade as a major effector system that detects and processes such danger signals. Animal models with engineered deficiencies in certain complement proteins have demonstrated that widespread complement activation after severe injury culminates in complement dysregulation and excessive generation of complement activation fragments. Such exuberant pro-inflammatory signaling evokes systemic inflammation, causes increased susceptibility to infections and is associated with a detrimental course of the disease after injury. We discuss the underlying processes of such complementopathy and recapitulate different intervention strategies within the complement cascade. So far, several orthogonal anti-complement approaches have been tested with varying success in a large number of rodent, in several porcine and few simian studies. We illustrate the different features among those intervention strategies and highlight those that hold the greatest promise to become potential therapeutic options for the intricate disease of traumatic injury.     

Recurrent miscarriage--an aspirin a day?

Recurrent miscarriage and later pregnancy complications are in some cases associated with placental thrombosis and infarction. The aim of this study was to assess the value of low dose aspirin (75 mg daily) in improving the subsequent livebirth rate amongst women with either unexplained recurrent early miscarriage (<13 weeks gestation; n = 805) or unexplained late pregnancy loss (n = 250). Amongst women with recurrent early miscarriages, there was no significant difference in the livebirth rate between those who took aspirin (251/367; 68.4%) compared with those who did not take aspirin [278/438; 63.5%; odds ratio (OR) 1.24; 95% confidence interval (CI) 0.93-1.67]. This relationship was independent of the number of previous early miscarriages. In contrast, women with a previous late miscarriage who took aspirin had a significantly higher livebirth rate (122/189; 64.6%) compared with those who did not take aspirin (30/61; 49.2%: OR 1.88; 95% CI 1.04-3.37). The empirical use of low dose aspirin amongst women with unexplained recurrent early miscarriage is not justified. We are currently investigating the role of incremental doses of aspirin in the treatment of women both with early miscarriages associated with thrombophilic abnormalities and in those with late pregnancy losses.     

The Use of Intravenous Immunoglobulin in Recurrent Pregnancy Loss Associated With Combined Alloimmune and Autoimmune Abnormalities

PROBLEM: Several studies have evaluated the effect of intravenous gammaglobulin (IVIG) in women with unexplained recurrent spontaneous abortions (RSA). Data regarding the underlying immunologic abnormalities in these patients is scant. This study reports the pregnancy outcome and immunologic changes observed in a large group of women with RSA associated with well-defined alloimmune and autoimmune abnormalities treated with IVIG. METHODS: Thirty-five patients with three or more recurrent miscarriages were studied. None of the patients had identifiable alloimmune response to paternal lymphocytes. Twenty-four patients had anti-thyroid antibodies, ten patients had high levels of circulating immune complexes, and six patients had anti-cardiolipin antibodies. Five patients had Hashimoto's disease, one had immune thrombocytopenic purpura, and one had Crohn's disease. Twenty-three patients had more than one autoimmune abnormality. All patients received IVIG infusions (200–250 mg/kg) every 3 weeks during the first 8 months of pregnancy. RESULTS: Twenty-eight patients (80%) had a successful pregnancy. Decrease of the level of autoantibodies and circulating immune complexes was observed in all patients who had a successful pregnancy. Only three of these patients developed measurable alloimmune response to paternal antigens. CONCLUSIONS: This preliminary study suggests that IVIG may be of benefit to patients with recurrent pregnancy loss associated with combined alloimmune and autoimmune abnormalities. This benefit was seen in spite of lack of detectable correction of the alloimmune abnormality in the majority of patients.     

Complement receptors and the shaping of the natural antibody repertoire

Complement and complement receptors have been known for several decades to play important roles in immune effector mechanisms related to pathogen elimination and tissue inflammation. In addition, studies over the last 10 years have clearly demonstrated a key role for the complement C3d activation fragment receptor designated CR2 (complement receptor type 2) in the switched-isotype, high-affinity and memory humoral immune responses to T-dependent foreign antigens. More recent studies have extended those observations to include a key role for CR2 and C3d in the humoral immune response to T-independent foreign antigens. Conversely, as these studies have proceeded, a parallel series of analyses have linked defects in expression or function of complement C4 and other classical pathway activation pathway proteins, as well as CR2 and the closely related CR1, to the loss of self tolerance to nuclear antigens such as double-stranded DNA and chromatin in systemic lupus erythematosus. With regard to the topic of this issue, it is now becoming increasingly clear that CR2 also plays a major role in the development of the natural antibody repertoire. Specifically, in the absence of this receptor natural IgM and IgG develop in the naïve animal that demonstrate clearly altered recognition patterns for specific natural antibody targets. This repertoire change is important physiologically in at least one setting because these CR2-dependent natural antibodies are necessary for the recognition of ischemic self tissues. In addition, it is possible that certain of the phenotypes manifest by CR2-deficient mice may be strongly influenced not only by effects on later stages of B cell activation and maturation, as commonly thought, but also by alterations in the pre-existing pool of natural antibodies that are influenced by this receptor. This review will examine the evidence that has accumulated over the last few years supporting these hypotheses.     

Review of the immune mechanisms of preeclampsia and the potential of immune modulating therapy

Successful pregnancy relies on maternal immunologic tolerance mechanisms limit maladaptive immune responses against the semi-allogeneic fetus and placenta and support fetal growth. Preeclampsia is a common disorder of pregnancy that affects 4–10% of pregnancies and is a leading cause of maternal and neonatal morbidity and mortality. Preeclampsia clinically manifests as maternal hypertension, proteinuria, and progressive multi-organ injury likely triggered by hypoxic injury to the placenta, resulting in local and systemic anti-angiogenic and inflammatory factor production. Despite the steady rising rates of preeclampsia in the United States, effective treatment options are limited to delivery, which improves maternal status often at the cost of prematurity in the newborn. Preeclampsia also increases the lifelong risk of cardiovascular disease for both mother and infant. Thus, identifying new therapeutic targets is a high priority area to improve maternal, fetal, and infant health outcomes. Immune abnormalities in the placenta and in the maternal circulation have been reported to precede the clinical onset of disease. In particular, excessive systemic and placental complement activation and impaired adaptive T cell tolerance with Th1/Th2/Th17/Treg imbalance has been reported in humans and in animal models of preeclampsia. In this review, we focus on the evidence for the immune origins of preeclampsia, discuss the promise of immune modulating therapy for prevention or treatment, and highlight key areas for future research.