Elevated complement factor C5a in maternal and umbilical cord plasma in preeclampsia

Systematic review of the complement components as potential biomarkers of pre-eclampsia: pitfalls and opportunities

The complement system (C) is a crucial component of the innate immune system. An increasing body of research has progressively shed light on the pivotal role of C in immunological tolerance at the feto-maternal interface. Excessive C activation or impaired C regulation may determine the onset of pregnancy-related pathological conditions, including pre-eclampsia (PE). Thus, several studies have investigated the presence of C components or split products in blood matrixes (i.e., plasma, serum), urine, and amniotic fluid in PE. In the current study, we systematically reviewed the currently available scientific literature reporting measurements of C components as circulating biomarkers in PE, based on a literature search using Pubmed, Scopus, and Embase databases. A total of 41 out of 456 studies were selected after full-text analysis. Fourteen studies (34.1%) were identified as measuring the blood concentrations of the classical pathway, 5 (12.1%) for the lectin pathway, 28 (68.3%) for the alternative pathway, 17 (41.5%) for the terminal pathway components, and 16 (39%) for C regulators. Retrieved results consistently reported C4, C3, and factor H reduction, and increased circulating levels of C4d, Bb, factor D, C3a, C5a, and C5b-9 in PE compared to normal pregnancies, depicting an overall scenario of excessive C activation and aberrant C regulation. With evidence of C activation and dysregulation, C-targeted therapy is an intriguing perspective in PE management. Moreover, we also discussed emerging pitfalls in C analysis, mainly due to a lack of experimental uniformity and biased cohort selection among different studies and laboratories, aiming to raise a more comprehensive awareness for future standardization.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024503070.

Pregnancy as a susceptible state for thrombotic microangiopathies

Pregnancy and the postpartum period represent phases of heightened vulnerability to thrombotic microangiopathies (TMAs), as evidenced by distinct patterns of pregnancy-specific TMAs (e.g., preeclampsia, HELLP syndrome), as well as a higher incidence of nonspecific TMAs, such as thrombotic thrombocytopenic purpura or hemolytic uremic syndrome, during pregnancy. Significant strides have been taken in understanding the underlying mechanisms of these disorders in the past 40 years. This progress has involved the identification of pivotal factors contributing to TMAs, such as the complement system, ADAMTS13, and the soluble VEGF receptor Flt1. Regardless of the specific causal factor (which is not generally unique in relation to the usual multifactorial origin of TMAs), the endothelial cell stands as a central player in the pathophysiology of TMAs. Pregnancy has a major impact on the physiology of the endothelium. Besides to the development of placenta and its vascular consequences, pregnancy modifies the characteristics of the women's microvascular endothelium and tends to render it more prone to thrombosis. This review aims to delineate the distinct features of pregnancy-related TMAs and explore the contributing mechanisms that lead to this increased susceptibility, particularly influenced by the "gravid endothelium." Furthermore, we will discuss the potential contribution of histopathological studies in facilitating the etiological diagnosis of pregnancy-related TMAs.

Deciphering the immunological interactions: targeting preeclampsia with Hydroxychloroquine's biological mechanisms

Preeclampsia (PE) is a complex pregnancy-related disorder characterized by hypertension, followed by organ dysfunction and uteroplacental abnormalities. It remains a major cause of maternal and neonatal morbidity and mortality worldwide. Although the pathophysiology of PE has not been fully elucidated, a two-stage model has been proposed. In this model, a poorly perfused placenta releases various factors into the maternal circulation during the first stage, including pro-inflammatory cytokines, anti-angiogenic factors, and damage-associated molecular patterns into the maternal circulation. In the second stage, these factors lead to a systemic vascular dysfunction with consecutive clinical maternal and/or fetal manifestations. Despite advances in feto-maternal management, effective prophylactic and therapeutic options for PE are still lacking. Since termination of pregnancy is the only curative therapy, regardless of gestational age, new treatment/prophylactic options are urgently needed. Hydroxychloroquine (HCQ) is mainly used to treat malaria as well as certain autoimmune conditions such as systemic lupus and rheumatoid arthritis. The exact mechanism of action of HCQ is not fully understood, but several mechanisms of action have been proposed based on its pharmacological properties. Interestingly, many of them might counteract the proposed processes involved in the development of PE. Therefore, based on a literature review, we aimed to investigate the interrelated biological processes of HCQ and PE and to identify potential molecular targets in these processes.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Pre-eclampsia is associated with complement pathway activation in the maternal and fetal circulation, and placental tissue

OBJECTIVES

Pre-eclampsia (PE) is a leading cause of obstetric morbidity, with no definitive therapy other than delivery. We aimed to compare complement markers in maternal and fetal circulation, and placental tissue, between women with PE and healthy pregnant controls.

STUDY DESIGN

Maternal and umbilical cord blood was tested for iC3b, C3, C4, properdin, Ba and C5b-9, and placental tissue for C3d, C4d, C9 and C1q, from women with PE (n = 34) and healthy pregnant controls (n = 33). Maternal properdin and Ba tests were repeated in a separate validation cohort (PE n = 35; healthy pregnant controls n = 35).

MAIN OUTCOME MEASURES

Complement concentrations in maternal and umbilical cord blood, and placental immunohistochemical complement deposition.

RESULTS

Women with PE had significantly lower concentrations of properdin (mean: 4828 vs 6877 ng/ml, p < 0.001) and C4 (mean: 0.20 vs 0.31 g/l, p < 0.001), and higher Ba (median: 150 vs 113 ng/ml, p = 0.012), compared to controls. After controlling for gestational age at blood draw, average properdin concentration was 1945 ng/ml lower in PE vs controls (95 % CI: 1487-2402, p < 0.001). Of the cord blood markers assessed, only Ba differed significantly between PE and controls (median: 337 vs 233 ng/ml, p = 0.004). C4d staining of the syncytiotrophoblast membrane was increased in PE vs controls (median immunoreactivity score 3 vs 0, p < 0.001). Maternal properdin and C4 were significantly negatively correlated with placental C4d staining.

CONCLUSIONS

Our data confirm excessive placental complement deposition associated with significant concurrent changes in maternal and fetal circulating complement biomarkers in PE. Inhibition of complement activation is a potential therapeutic target.

The role of immune cells and mediators in preeclampsia

Preeclampsia is a hypertensive disorder of major concern in pregnancy than can lead to intrauterine growth restriction, placental abruption and stillbirth. The pathophysiology of preeclampsia is multifactorial, including not only kidney dysfunction but also endothelial dysfunction, as the maternal endothelium becomes exposed to placental factors that are released into the circulation and increase systemic levels of vasoconstrictors, oxidative stress, anti-angiogenic factors and inflammatory mediators. Importantly, inflammation can lead to insufficient placental perfusion and low birthweight in offspring. Various innate and adaptive immune cells and mediators have been implicated in the development of preeclampsia, in which oxidative stress is associated with activation of the maternal inflammatory response. Immune cells such as regulatory T cells, macrophages, natural killer cells, and neutrophils are known to have major causative roles in the pathology of preeclampsia, but the contributions of additional immune cells such as B cells, inflammatory cytokines and anti-angiotensin II type 1 receptor autoantibodies are also now recognized. Immunological interventions, therefore, have therapeutic potential in this disease. Here, we provide an overview of the immune responses that are involved in the pathogenesis of preeclampsia, including the role of innate and adaptive immune cells and mediators.

Alternative pathway activation in pregnancy, a measured amount "complements" a successful pregnancy, too much results in adverse events

During pregnancy, the maternal host must adapt in order to enable growth of the fetus. These changes affect all organ systems and are designed both to protect the fetus and to minimize risk to the mother. One of the most prominent adaptations involves the immune system. The semi-allogenic fetoplacental unit has non-self components and must be protected against attack from the host. This requires both attenuation of adaptive immunity and protection from innate immune defense mechanisms. One of the key innate immune players is complement, and it is important that the fetoplacental unit is not identified as non-self and subjected to complement attack. Adaptation of the complement response must, however, be managed in such a way that maternal protection against infection is not compromised. As the complement system also plays a significant facilitating role in many of the stages of a normal pregnancy, it is also important that any necessary adaptation to accommodate the semi-allogenic aspects of the fetoplacental unit does not compromise this. In this review, both the physiological role of the alternative pathway of complement in facilitating a normal pregnancy, and its detrimental participation in pregnancy-specific disorders, are discussed.

Distinct Roles of Classical and Lectin Pathways of Complement in Preeclamptic Placentae

Pre-eclampsia is a pregnancy complication characterized by defective vascular remodeling in maternal decidua responsible for reduced blood flow leading to functional and structural alterations in the placenta. We have investigated the contribution of the complement system to decidual vascular changes and showed that trophoblasts surrounding unremodeled vessels prevalent in preeclamptic decidua fail to express C1q that are clearly detected in cells around remodeled vessels predominant in control placenta. The critical role of C1q is supported by the finding that decidual trophoblasts of female C1qa^-/- pregnant mice mated to C1qa^+/+ male mice surrounding remodeled vessels express C1q of paternal origin. Unlike C1qa^-/- pregnant mice, heterozygous C1qa^+/- and wild type pregnant mice share a high percentage of remodeled vessels. C1q was also found in decidual vessels and stroma of normal placentae and the staining was stronger in preeclamptic placentae. Failure to detect placental deposition of C1r and C1s associated with C1q rules out complement activation through the classical pathway. Conversely, the intense staining of decidual endothelial cells and villous trophoblast for ficolin-3, MASP-1 and MASP-2 supports the activation of the lectin pathway that proceeds with the cleavage of C4 and C3 and the assembly of the terminal complex. These data extend to humans our previous findings of complement activation through the lectin pathway in an animal model of pre-eclampsia and provide evidence for an important contribution of C1q in decidual vascular remodeling.

COVID-19, Pre-Eclampsia, and Complement System

COVID-19 is characterized by virus-induced injury leading to multi-organ failure, together with inflammatory reaction, endothelial cell (EC) injury, and prothrombotic coagulopathy with thrombotic events. Complement system (C) via its cross-talk with the contact and coagulation systems contributes significantly to the severity and pathological consequences due to SARS-CoV-2 infection. These immunopathological mechanisms overlap in COVID-19 and pre-eclampsia (PE). Thus, mothers contracting SARS-CoV-2 infection during pregnancy are more vulnerable to developing PE. SARS-CoV-2 infection of ECs, via its receptor ACE2 and co-receptor TMPRSS2, can provoke endothelial dysfunction and disruption of vascular integrity, causing hyperinflammation and hypercoagulability. This is aggravated by bradykinin increase due to inhibition of ACE2 activity by the virus. C is important for the progression of normal pregnancy, and its dysregulation can impact in the form of PE-like syndrome as a consequence of SARS-CoV-2 infection. Thus, there is also an overlap between treatment regimens of COVID-19 and PE. C inhibitors, especially those targeting C3 or MASP-2, are exciting options for treating COVID-19 and consequent PE. In this review, we examine the role of C, contact and coagulation systems as well as endothelial hyperactivation with respect to SARS-CoV-2 infection during pregnancy and likely development of PE.

Adipsin of the Alternative Complement Pathway Is a Potential Predictor for Preeclampsia in Early Pregnancy

Objective

The concentrations of complement proteins (adipsin, C3a, and C5a) and soluble endoglin (sENG) in the plasma were measured in this study, and their value as early-pregnancy predictors and potential diagnostic marker of preeclampsia was assessed, respectively.

Experimental Design

Plasma samples were obtained from healthy and preeclampsia pregnant women before delivery for a cross-sectional study. Plasma samples were collected from healthy and preeclampsia pregnant women throughout pregnancy and postpartum for a follow-up study. Enzyme-linked immunosorbent assays were used to detect plasma levels of several complement proteins (adipsin, C3a, and C5a) and sENG.

Results

The plasma levels of adipsin, C5a, and sENG were significantly increased before delivery in pregnant women with preeclampsia. During pregnancy, the plasma adipsin, C5a, and sENG levels were increased from the third trimester in healthy pregnant women; plasma adipsin levels remained stable after delivery, while C3a levels increased in the second trimester and remained stable afterward. Furthermore, levels of adipsin, C5a, and sENG were higher in preeclampsia patients at different stages of pregnancy; the C3a level presents a similar change and no difference was found in the third trimester. In the first trimester, receiver-operating curve (ROC) curve analysis showed that adipsin (AUC, 0.83 ± 0.06, P=0.001) and sENG (AUC, 0.74 ± 0.09, P=0.021) presented high value as predictors of early pregnancy.

Conclusions

Adipsin is likely a novel plasma biomarker to monitor the increased risk of preeclampsia in early pregnancy. Moreover, the increased plasma levels of adipsin, C5a, and sENG before delivery may be associated with preeclampsia.

Complement activation by an angiogenic imbalance leads to systemic vascular endothelial dysfunction: A new proposal for the pathophysiology of preeclampsia

The underlying mechanism of preeclampsia by which an angiogenic imbalance results in systemic vascular endothelial dysfunction remains unclear. Complement activation directly induces endothelial dysfunction and is known to be involved in preeclampsia; nevertheless, the association between complement activation and angiogenic imbalance has not been established. This study aimed to evaluate whether angiogenic imbalance affects the expression and secretion of inhibitory complement factor H (CFH) in endothelial cells, resulting in complement activation and systemic vascular endothelial dysfunction. Viability of human umbilical vein endothelial cells (HUVECs) was assessed upon CFH knockdown by targeted-siRNA, and were incubated with complement factors. HUVECs were also treated with placental growth factor (PlGF) and/or soluble fms-like tyrosine kinase 1 (sFlt1), and CFH expression and secretion were measured. These cells were evaluated by cell viability assay and cell surface complement activation was quantified by immunocytochemical assessment of C5b-9 deposition. HUVECs transfected with CFH-siRNA had significantly lower viability than that of control cells. Moreover, the expression and secretion of CFH were significantly increased upon PlGF treatment compared with PlGF + sFlt1 combo. HUVECs treated with PlGF had less C5b-9 deposition and higher viability than HUVECs treated with PlGF + sFlt1. In summary, CFH was found to be essential for endothelial cell survival by inhibiting complement activation. An angiogenic imbalance, including decreased PlGF and increased sFlt1, suppresses CFH expression and secretion, resulting in complement activation on the surface of endothelial cells and systemic vascular endothelial dysfunction.

The Complement System in the Pathophysiology of Pregnancy and in Systemic Autoimmune Rheumatic Diseases During Pregnancy

The complement system plays a double role in pregnancy exerting both protective and damaging effects at placental level. Complement activation at fetal-maternal interface participates in protection against infectious agents and helps remove apoptotic and necrotic cells. Locally synthesized C1q contributes to the physiologic vascular remodeling of spiral arteries characterized by loss of smooth muscle cells and transformation into large dilated vessels. Complement activation triggered by the inflammatory process induced by embryo implantation can damage trophoblast and other decidual cells that may lead to pregnancy complications if the cells are not protected by the complement regulators CD55, CD46, and CD59 expressed on cell surface. However, uncontrolled complement activation induces placental alterations resulting in adverse pregnancy outcomes. This may occur in pathological conditions characterized by placental localization of complement fixing antibodies directed against beta2-glycoprotein 1, as in patients with anti-phospholipid syndrome, or circulating immune complexes deposited in placenta, as in patients with systemic lupus erythematosus. In other diseases, such as preeclampsia, the mechanism of complement activation responsible for complement deposits in placenta is unclear. Conflicting results have been reported on the relevance of complement assays as diagnostic and prognostic tools to assess complement involvement in pregnant patients with these disorders.

Complement inhibitor Crry expression in mouse placenta is essential for maintaining normal blood pressure and fetal growth

Many circumstantial evidences from human and animal studies suggest that complement cascade dysregulation may play an important role in pregnancy associated complications including preeclampsia. Deletion of rodent specific complement inhibitor gene, Complement Receptor 1-related Gene/Protein y (Crry) produces embryonic lethal phenotype due to complement activation. It is not clear if decreased expression of Crry during pregnancy produces hypertensive phenotype. We downregulated Crry in placenta by injecting inducible lentivialshRNA vectors into uterine horn of pregnant C57BL/6 mice at the time of blastocyst hatching. Placenta specific downregulation of Crry without significant loss of embryos was achieved upon induction of shRNA using an optimal doxycycline dose at mid gestation. Crry downregulation resulted in placental complement deposition. Late-gestation measurements showed that fetal weights were reduced and blood pressure increased in pregnant mice upon downregulation of Crry suggesting a critical role for Crry in fetal growth and blood pressure regulation.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Pathophysiology of the Venous Thromboembolism Risk in Preeclampsia

Preeclampsia complicates up to 8% of pregnancies and is a leading cause of fetomaternal morbidity andmortality. Treatment options are limited, with supportive care and delivery of the placenta representing the cornerstone of current management strategies. Derangements in blood coagulation are wellrecognised in this disorder and appear to favour an increased risk of venous thromboembolism among affected women. This risk appears to be most significant in the postpartum period. The mechanisms underlying this increased thrombosis risk remain to be fully elucidated although increased expression of procoagulant factors, endothelial dysfunction, attenuation of endogenous anticoagulant activity and increased platelet activity have been implicated in the prothrombotic tendency. Preeclampsia is also occasionally complicated by life-threatening haemorrhagic events and current evidence suggests that in some severe manifestations of this disease a coagulopathy with a clinical bleeding tendency may be the predominant haemostatic abnormality. Identifying affected women at significant risk of thrombosis and managing the competing thrombotic and haemorrhagic risks continue to be a significant clinical challenge. Derangements in blood coagulation are also implicated in the pathogenesis of preeclampsia; however, the role of antiplatelet or anticoagulant drugs in the prevention and treatment of this disorder remains a source of considerable debate. In addition, the potential role of specific haemostatic markers as diagnostic or screening tools for preeclampsia has also yet to be determined. Further characterisation of the underlying molecular mechanisms would likely be of major translational relevance and could provide insights into the pathogenesis of this disease as well as the associated haemostatic dysfunction.

Dysregulation of complement system during pregnancy in patients with preeclampsia: A prospective study

Recent studies have shown that aberrant activation of the complement system plays an important role in the pathogenesis of preeclampsia. There is evidence to suggest that aberrant activation of the complement system may already be present during the first trimester. Here, we performed a prospective study in which peripheral blood samples were collected from 500 women during pregnancy. Twenty-one patients (41 specimens) suffering from preeclampsia later in pregnancy were classified into the study group, and sixty-three gravidas with normal pregnancies (136 specimens) were selected as the control group. The plasma concentrations of complement factor B (CFB), C1q, complement factor H (CFH), C3c, C4, C3a, C5a and soluble C5b-9 (sC5b-9) were measured. The levels of CFB (P = 0.004), CFH (P = 0.002), C1q (P = 0.044), C3c (P = 0.032) and C4 (P = 0.015) were significantly higher in preeclampsia than in normal pregnancy during the first trimester, and these levels became similar to those in normal pregnancy thereafter. Before the onset of preeclampsia, the levels of C3a, C5a and sC5b-9 in the preeclampsia group were similar to those in control group even in late pregnancy. C3a levels showed a significant positive correlation with C5a in normal pregnancy (r=0.658, P<0.01) but not in preeclampsia (r = 0.001, P = 1).Thus, we found that aberrant activation of the complement system in patients with preeclampsia was initiated during the first trimester but returned to normal pregnancy levels in the second trimester. At the same time, there is aberrant regulation of complement activation at the C3a-C5a level in preeclampsia during pregnancy.

Normal range of complement components during pregnancy: A prospective study

PROBLEM

The complement system plays a key role in normal placentation, and delicate regulation of complement system activation is critical for successful pregnancy. Therefore, establishing a normal range of complement components during pregnancy is important for clinical evaluation and research.

METHODS

We performed a prospective study to investigate the normal range of complement components in circulation during different stages of pregnancy. Plasma concentrations of complement factor B (CFB), C1q, complement factor H (CFH), C3, C3c, and C4 were measured using an immunoturbidimetric assay; mannan-binding lectin (MBL), C3a, C5a, and soluble C5b-9 (sC5b-9) levels at different time points of pregnancy were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 733 plasma samples were collected from 362 women with a normal pregnancy and 65 samples from non-pregnant women. In the first trimester of pregnancy, the levels of CFB, CFH, MBL, C3c, C4, and C3a were 414.5 ± 85.9 mg/L (95% CI for mean: 402.4-426.6 mg/L), 381.0 ± 89.0 mg/L (95% CI for mean: 368.5-393.6 mg/L), 4274.5 ± 2752 ng/mL (95% CI for mean: 3881.1-4656.4 ng/mL), 1346.9 ± 419.8 mg/L (95% CI for mean: 1287.7-1406.0 mg/L), 357.4 ± 101.8 mg/L (95% CI for mean: 343.0-371.7 mg/L), and 182.5 ± 150.0 ng/mL (95% CI for mean: 186.9-229.1 ng/mL), respectively. The levels of C3 and C4 increased gradually throughout pregnancy. The levels of C1q, C5a, and sC5b-9 in the first and second trimesters were nearly the same as those in non-pregnant women.

CONCLUSION

The results of this study show that pregnancy itself may influence the plasma levels of complement system components.

The role of the complement system in HIV infection and preeclampsia

BACKGROUND

The complement system is a key component of the innate immune system that plays a vital role in host defense, maintains homeostasis and acts as a mediator of the adaptive immune response. The complement system could possibly play a role in the pathogenesis of HIV infection and preeclampsia (PE), both of which represent major causes of maternal death in South Africa.

RECENT FINDINGS

The relationship between PE and HIV infection is unclear as PE represents an exaggerated immune response, while HIV infection is associated with a decline in immune activity. Although the complement system works to clear and neutralize HIV, it could also enhance the infectivity of HIV by various other mechanisms. It has been suggested that the dysregulation of the complement system is associated with the development of PE.

CONCLUSION

There is currently a paucity of information on the combined effect of the complement system in HIV-associated PE. This review highlights the role of the complement system in the duality of HIV infection and PE and provides new insights into this relationship whilst also elucidating potential therapeutic targets.

Pathogenic roles of anti-C1q antibodies in recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is often considered idiopathic, however excessive complement activation has been observed in pregnancy related manifestations. Anti-C1q antibodies (anti-C1q) are associated with the activation of complement pathway in lupus patients, while it remains unclear in RPL. Firstly, we showed that both the prevalence and titre of anti-C1q were significantly higher in unexplained RPL than in healthy parous individuals. Secondly, we established the murine model of anti-C1q induced pregnancy loss using a monoclonal anti-mouse C1q antibody, JL-1. In mice treated with JL-1, high ratio of pregnancy loss and fetal growth restriction were frequently observed and complement activation occurred. C5a receptor (C5aR) blockade cancelled these pathogenic changes in mice treated with JL-1. In conclusion, our study reveals an association between the prevalence of anti-C1q and RPL. Additionally, our murine model has indicated that anti-C1q can induce reproductive failure, which might be ameliorated by therapy targeting the C5-C5aR axis.

Complement in stem cells and development

From its discovery in the late nineteenth century, as a 'complement' to the cellular immune response, the complement system has been widely affirmed as a powerful controller of innate and adaptive immune responses. In recent decades however, new roles for complement have been discovered, with multiple complement proteins now known to function in a broad array of non-immune systems. This includes during development, where complement exerts control over stem cell populations from fertilization and implantation throughout embryogenesis and beyond post-natal development. It is involved in processes as diverse as cell localisation, tissue morphogenesis, and the growth and refinement of the brain. Such physiological actions of complement have also been described in adult stem cell populations, with roles in proliferation, differentiation, survival, and regeneration. With such a broad range of complement functions now described, it is likely that current research only describes a fraction of the full reach of complement proteins. Here, we review how complement control of physiological cell processes has been harnessed in stem cell populations throughout both development and in adult physiology.

Immunological Tolerance, Pregnancy, and Preeclampsia: The Roles of Semen Microbes and the Father

Although it is widely considered, in many cases, to involve two separable stages (poor placentation followed by oxidative stress/inflammation), the precise originating causes of preeclampsia (PE) remain elusive. We have previously brought together some of the considerable evidence that a (dormant) microbial component is commonly a significant part of its etiology. However, apart from recognizing, consistent with this view, that the many inflammatory markers of PE are also increased in infection, we had little to say about immunity, whether innate or adaptive. In addition, we focused on the gut, oral and female urinary tract microbiomes as the main sources of the infection. We here marshall further evidence for an infectious component in PE, focusing on the immunological tolerance characteristic of pregnancy, and the well-established fact that increased exposure to the father's semen assists this immunological tolerance. As well as these benefits, however, semen is not sterile, microbial tolerance mechanisms may exist, and we also review the evidence that semen may be responsible for inoculating the developing conceptus (and maybe the placenta) with microbes, not all of which are benign. It is suggested that when they are not, this may be a significant cause of PE. A variety of epidemiological and other evidence is entirely consistent with this, not least correlations between semen infection, infertility and PE. Our view also leads to a series of other, testable predictions. Overall, we argue for a significant paternal role in the development of PE through microbial infection of the mother via insemination.

Complement 5a-mediated trophoblasts dysfunction is involved in the development of pre-eclampsia

Pre‐eclampsia (PE) is a life‐threatening multisystem disorder leading to maternal and neonatal mortality and morbidity. Emerging evidence showed that activation of the complement system is implicated in the pathological processes of PE. However, little is known about the detailed cellular and molecular mechanism of complement activation in the development of PE. In this study, we reported that complement 5a (C5a) plays a pivotal role in aberrant placentation, which is essential for the onset of PE. We detected an elevated C5a deposition in macrophages and C5a receptor (C5aR) expression in trophoblasts of pre‐eclamptic placentas. Further study showed that C5a stimulated trophoblasts towards an anti‐angiogenic phenotype by mediating the imbalance of angiogenic factors such as soluble fms‐like tyrosine kinase 1 (sFlt1) and placental growth factor (PIGF). Additionally, C5a inhibited the migration and tube formation of trophoblasts, while, C5aR knockdown with siRNA rescued migration and tube formation abilities. We also found that maternal C5a serum level was increased in women with PE and was positively correlated with maternal blood pressure and arterial stiffness. These results demonstrated that the placental C5a/C5aR pathway contributed to the development of PE by regulating placental trophoblasts dysfunctions, suggesting that C5a may be a novel therapeutic possibility for the disease.

Cadmium Handling, Toxicity and Molecular Targets Involved during Pregnancy: Lessons from Experimental Models

Even decades after the discovery of Cadmium (Cd) toxicity, research on this heavy metal is still a hot topic in scientific literature: as we wrote this review, more than 1440 scientific articles had been published and listed by the PubMed.gov website during 2017. Cadmium is one of the most common and harmful heavy metals present in our environment. Since pregnancy is a very particular physiological condition that could impact and modify essential pathways involved in the handling of Cd, the prenatal life is a critical stage for exposure to this non-essential element. To give the reader an overview of the possible mechanisms involved in the multiple organ toxic effects in fetuses after the exposure to Cd during pregnancy, we decided to compile some of the most relevant experimental studies performed in experimental models and to summarize the advances in this field such as the Cd distribution and the factors that could alter it (diet, binding-proteins and membrane transporters), the Cd-induced toxicity in dams (preeclampsia, fertility, kidney injury, alteration in essential element homeostasis and bone mineralization), in placenta and in fetus (teratogenicity, central nervous system, liver and kidney).

Complement component C1q as potential diagnostic but not predictive marker of preeclampsia

PROBLEM

We have previously found that C1q is constitutively expressed by invading trophoblast and endothelial cells of decidua and contributes to vascular and tissue remodeling. Based on these findings, we sought to determine whether there were changes in the circulating level of C1q that may be used as a diagnostic and predictive marker of preeclampsia.

METHOD OF STUDY

We measured the levels of C1q, C4, and complement activation products in serum or plasma of normal pregnant women and preeclamptic patients from different cohorts.

RESULTS

We observed a marked decrease in the concentration of C1q associated with a reduced level of C4 in preeclamptic patients as compared to matched healthy pregnant woman but no significant difference in the circulating level of the activating products C5a and the soluble terminal complement complex sC5b-9. Analysis of serum samples collected at early phase of pregnancy from women who later developed preeclampsia failed to show a decrease in C1q level.

CONCLUSION

The results of the present investigation demonstrate that low levels of C1q and C4 are associated with preeclampsia but cannot be used as predictive markers.

Expression of the complement system's activation factors in plasma of patients with early/late-onset severe pre-eclampsia

PROBLEM

To investigate the expression of complement activation factors in plasma of patients with early/late-onset severe pre-eclampsia.

METHODS

A case-control study was performed. The study group consisted of 30 cases of early-onset severe pre-eclampsia (EOSPE) and 30 cases of late-onset severe pre-eclampsia (LOSPE). Thirty cases were selected as the early-onset control group (E-control) and 30 as the late-onset control group (L-control). ELISA was used to test C1q, C4d, MBL, Bb, C3a, C5a, and MAC in the maternal peripheral circulation.

RESULTS

The complement activation factors Bb, C3a, C5a, and MAC were increased significantly in EOSPE (all P<.01) and LOSPE (P value: .027, <.001, .001, and <.001, respectively) compared with E/L-control. C1q and C4d were increased significantly in LOSPE (P value: .003 and .014, respectively) compared with L-control.

CONCLUSION

Abnormal activation of the complement system exists in the maternal circulation of patients with early- and late-onset severe pre-eclampsia. In patients complicated with LOSPE, the complement system was activated through both the classical and alternative pathways, while in EOSPE, the complement system was activated mainly through the alternative pathway.

Optimized Treatment of Heparinized Blood Fractions to Make Them Suitable for Analysis

BACKGROUND

It has been known for decades that many cytokines, such as IL-2, IL-6, and IL-12, bind to heparin. Even though some enzyme-linked immunosorbent assays (ELISA) use antibody-recognizing epitopes not affected by this binding, ELISA manufacturers often warn that heparinized plasma or serum fractions containing more than 3 IU (international units)/mL of heparin should not be used in assays so as to prevent heparin interference in the reaction. In addition, enzyme-based nucleic acid amplifications from heparinized samples have been shown defective by several research groups. The aim of this study was to determine optimal degradation and/or removal of heparin from heparinized blood samples to best turn them into fractions for appropriate ELISA and RT-PCR analysis.

METHODS AND RESULTS

A colorimetric reporter assay based on the metachromatic effect of the binding of heparin to toluidine blue was shown to be a low-cost effective method to discriminate assay compatible blood fractions with heparin levels below 3 IU/mL. Heparin removal from human blood fractions was best achieved by treatment with either Bacteroides Heparinase II or the less expensive Heparinase I at a final concentration of 0.1 U/μL and incubations at 30°C for a period between 30 min and 4 h, or by adsorption to Ecteola slurries at a concentration of 20 mg/mL for 20 min at room temperature (RT). The fact that both enzymatic and resin-based optimized treatments allowed for replication of the readings obtained with heparin-free equivalent fractions in both ELISA and RT-PCR assays indicates they should be appropriate for quantitative studies such as expression profiling at both the protein and nucleic acid level.

CONCLUSIONS

The cost-effective protocols developed in this study could make heparinized, otherwise unusable, blood-derived collections suitable for analysis by ELISA and RT-PCR amplifications, among other analyses, enhancing the possibilities for studying valuable bio-banked heparinized human samples.

Complement Activation in Placental Malaria

Sixty percent of all pregnancies worldwide occur in malaria endemic regions. Pregnant women are at greater risk of malaria infection than their non-pregnant counterparts and have a higher risk of adverse birth outcomes including low birth weight resulting from intrauterine growth restriction and/or preterm birth. The complement system plays an essential role in placental and fetal development as well as the host innate immune response to malaria infection. Excessive or dysregulated complement activation has been associated with the pathobiology of severe malaria and with poor pregnancy outcomes, dependent and independent of infection. Here we review the role of complement in malaria and pregnancy and discuss its part in mediating altered placental angiogenesis, malaria-induced adverse birth outcomes, and disruptions to the in utero environment with possible consequences on fetal neurodevelopment. A detailed understanding of the mechanisms underlying adverse birth outcomes, and the impact of maternal malaria infection on fetal neurodevelopment, may lead to biomarkers to identify at-risk pregnancies and novel therapeutic interventions to prevent these complications.

The Relationship of Longitudinal Levels of Complement Bb During Pregnancy with Preeclampsia

PROBLEM

To determine the understudied relationship between complement Bb during pregnancy in subjects with preeclampsia compared with normotensive controls.

METHOD OF STUDY

Nested case-control study.

RESULTS

Average Bb levels significantly decreased over time in pregnancy [weekly slope (S.E.): -0.0094 (0.0005), P < 0.01]. Cross-sectionally, at less than 10 weeks, Bb levels decreased with increasing gestational age in women who remained normotensive [weekly slope (S.E.): -0.007 (0.02) and for women who developed preeclampsia (weekly slope (S.E.): -0.059 (0.03) P = 0.12]. Among women who developed preeclampsia, Bb levels were greatest when samples were drawn in the gestational window of 15-20 weeks [(weekly slope (S.E.): 0.06 (0.02)], while levels among normotensive women were inversely related with gestational age [weekly slope (S.E.): -0.02 (0.01)]. The differences in slopes between cases and controls between 10 and 21 weeks' gestation were statistically significant (P = 0.003).

CONCLUSIONS

We suggest dysregulation of Bb activation between 10 and 20 weeks' gestation in women who develop preeclampsia.

Complement Split Products C3a/C5a and Receptors: Are They Regulated by Circulating Angiotensin II Type 1 Receptor Autoantibody in Severe Preeclampsia?

BACKGROUND

This study measured the serum levels of complement component (C)3a and C5a and the placental expressions of C3a receptor (R) and C5aR to determine a potential correlation with circulating angiotensin II type 1 (AT1) receptor agonistic autoantibody (AT1-AA) in severe pre-eclampsia.

METHODS

A total of 118 women were recruited and divided into 2 groups: the control group (normotensive preterm pregnancies, n = 66) and severe pre-eclampsia group (n = 52). Levels of C3a, C5a and AT1-AA in serum were measured by enzyme-linked immunosorbent assay and C3aR and C5aR in placenta by Western blotting.

RESULTS

Levels of C3a, C5a and AT1-AA in serum from the severe pre-eclampsia group were significantly higher than in controls (p < 0.05). Placental expression of C3aR and C5aR in the pre-eclampsia group was lower than that in controls (p < 0.05). There were significant positive correlations between levels of C3a, C5a and AT1-AA in serum from the pre-eclampsia group (p < 0.05). In contrast, there was no correlation between C3aR and C5aR in the placenta and AT1-AA in serum in the pre-eclampsia group (p > 0.05).

CONCLUSION

Increased C3a, C5a and AT1-AA in the serum provide indirect evidence that AT1-AA-mediated activation contributes to activate complement, which is a key mechanism underlying the pathogenesis of severe pre-eclampsia.

Complement Split Products in Amniotic Fluid in Pregnancies Subsequently Developing Early-Onset Preeclampsia

Objective. To determine the second-trimester amniotic fluid concentrations of complement split products in pregnancies subsequently affected by early-onset preeclampsia. Study Design. Cohort of 731 women with singleton pregnancies undergoing second-trimester genetic amniocentesis followed up to delivery and analyzed as a nested case-control study. Cases of preeclampsia developing before 34 weeks' gestation (n = 15) were compared with 47 uncomplicated term controls. Amniotic fluid collected at amniocentesis was tested for complement split products Bb, C4a, C3a, and C5a. Results. Women who developed early-onset preeclampsia as compared with the term pregnant controls had significantly higher (P = 0.04) median amniotic fluid C3a levels (318.7 ng/mL versus 254.5 ng/mL). Median amniotic fluid Bb levels were also significantly higher (P = 0.03) in preeclamptic women than in normal pregnant women (1127 ng/mL versus 749 ng/mL). Median levels of C4a and C5a were not significantly different between the groups. Conclusion. Our data suggest that complement activation in early pregnancy is associated with early-onset preeclampsia. We believe this to be the first prospective study to link complement activation in amniotic fluid in early pregnancy and later development of preeclampsia. Our findings provide evidence that immune dysregulation may precede the clinical manifestations of preeclampsia and that the alternative complement pathway is principally involved.

Experimental Malaria in Pregnancy Induces Neurocognitive Injury in Uninfected Offspring via a C5a-C5a Receptor Dependent Pathway

The in utero environment profoundly impacts childhood neurodevelopment and behaviour. A substantial proportion of pregnancies in Africa are at risk of malaria in pregnancy (MIP) however the impact of in utero exposure to MIP on fetal neurodevelopment is unknown. Complement activation, in particular C5a, may contribute to neuropathology and adverse outcomes during MIP. We used an experimental model of MIP and standardized neurocognitive testing, MRI, micro-CT and HPLC analysis of neurotransmitter levels, to test the hypothesis that in utero exposure to malaria alters neurodevelopment through a C5a-C5aR dependent pathway. We show that malaria-exposed offspring have persistent neurocognitive deficits in memory and affective-like behaviour compared to unexposed controls. These deficits were associated with reduced regional brain levels of major biogenic amines and BDNF that were rescued by disruption of C5a-C5aR signaling using genetic and functional approaches. Our results demonstrate that experimental MIP induces neurocognitive deficits in offspring and suggest novel targets for intervention.

A growing body of evidence has established the importance of the in utero environment on neurodevelopment and long-term cognitive and behavioral outcomes. These data suggest factors that disrupt the tightly regulated in utero environment can modify normal neurodevelopmental processes. Approximately 125 million pregnancies worldwide are at risk of malaria infection every year. However the impact of in utero exposure to MIP on fetal neurodevelopment is unknown. Here we use a mouse model of malaria in pregnancy to examine the impact of maternal malaria exposure on neurocognitive outcomes in offspring. We observed impaired learning and memory and depressive-like behavior in malaria-exposed offspring that were neither congenitally infected nor low birth weight. These neurocognitive impairments were associated with decreased tissue levels of neurotransmitters in regions of the brain linked to the observed deficits. Disruption of maternal C5a complement receptor signaling restored the levels of neurotransmitters and rescued the associated cognitive phenotype observed in malaria-exposed offspring. This study provides the first evidence implicating a causal link between pre-natal exposure to malaria, complement signaling and subsequent neurocognitive impairment in offspring.

Time-course analysis of C3a and C5a quantifies the coupling between the upper and terminal Complement pathways in vitro

An in vitro zymosan-activation of the Complement system, through the lectin and alternative pathways, was performed in pooled human serum over a 24h time-course. Activation was quantitatively monitored by measuring the concentration of the upper Complement pathway fragment, C3a and the terminal pathway fragment, C5a. Upper Complement showed a maximum activation of 39% and the time-to-maximum activation reduced 8-fold, as a highly non-linear function of the zymosan dose. The C3a:C5a molar ratio rose to a maximum of 1100:1, before terminal pathway activation was initiated; indicating a flux threshold. This threshold appears to be exceeded once more than 31% of C3 molecules are activated. Above this threshold, significant activation of terminal pathway was observed; reducing the molar ratio to 17:1. The C5a/C3a molar ratio was used to determine the terminal pathway activation relative to total Complement activation and ranged from 0.1-0.8%. This depicts upper Complement activation to be 49-fold larger than terminal activation, a figure consistent with the observed density of the membrane attack complex in the membrane of cells. Our results thus indicate that the relative activity of opsonisation is ~50-fold greater than membrane attack complex formation, in vitro, in the pooled serum phenotype. The results suggest a potential clinical application, where an in vitro analysis of a patient on admission, or prior to a surgical procedure, would indicate their upper Complement activation capacity, with activation of C3 measured thereafter, or post-operatively. A patient with an exhausted upper Complement capacity may be vulnerable to infections and complications, such as sepsis.

The Role of C5a Receptor Signaling in Endotoxin-Induced Miscarriage and Preterm Birth

PROBLEM

Complement factor 5a (C5a), a potent pro-inflammatory mediator of the complement system, has been implicated in fetal rejection throughout gestation, from miscarriage to preterm birth. This study aimed to investigate the role of the principal C5a receptor, C5aR1 (CD88), in both miscarriage and preterm birth, in a bacterial endotoxin (lipopolysaccharide; LPS) murine model.

METHOD OF STUDY

Wild-type and C5ar1 knockout mice were administered LPS at 9.5 or 15.5 days post-conception to induce miscarriage or preterm birth, respectively.

RESULTS

C5ar1 knockout mice were protected against miscarriage in response to administration of LPS in early gestation. However, the absence of C5aR1 had no effect on the rates of preterm birth when LPS was administered in late gestation.

CONCLUSION

There may be a gestational window in which excessive activation of C5a can exert deleterious effects in pregnancy. Future strategies targeting the C5a-C5aR1 signaling axis should be considered to ameliorate miscarriages in patients with recurrent pregnancy loss.

Elevation of the terminal complement activation products C5a and C5b-9 in ALS patient blood

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterized by the progressive loss of motor neurons within the central nervous system. Neural degeneration and inflammatory processes, including activation of the complement system are hallmarks of this pathology. Our past work in ALS animal models (hSOD1 G93A rodents) has revealed that blockade of the receptor for complement activation fragment C5a (C5aR), improves ALS-like symptoms and extends survival. We now show that the levels of C5a and C5b-9, but not C3a nor C4a, are significantly elevated in plasma from ALS patients compared to healthy controls. C5a was also elevated within leukocytes from ALS patients suggesting heightened C5a receptor interaction. Overall, these findings indicate that there is enhanced peripheral immune complement terminal pathway activation in ALS, which may have relevance in the disease process.

Complement factor B activation in patients with preeclampsia

Preeclampsia is a leading cause of maternal and fetal morbidity and mortality. Bb, the active fragment of complement factor B (fB), has been reported to be a predictor of preeclampsia. However, conflicting results have been found by some investigators. We hypothesized that the disagreement in findings may be due to the racial/ethnic differences among various study groups, and that fB activation is significant in women of an ethnic minority with preeclampsia. We investigated the maternal and fetal levels of Bb (the activated fB fragment) in pregnant women of an ethnic minority with or without preeclampsia. We enrolled 291 pregnant women (96% of an ethnic minority, including 78% African-American). Thirteen percent of these were diagnosed with preeclampsia. Maternal venous blood was collected from all participants together with fetal umbilical cord blood samples from 154 deliveries in the 291 women. The results were analyzed using the Mann-Whitney U test and multivariate analyses. Maternal Bb levels were significantly higher in the preeclamptic group than in the nonpreeclamptic group. Levels of Bb in fetal cord blood were similar in both groups. Subgroup analyses of African-American patients' results confirmed the study hypothesis that there would be a significant increase in Bb in the maternal blood of the preeclamptic group and no increase in Bb in the fetal cord blood of this group. These results suggest that a maternal immune response through complement fB might play a role in the development of preeclampsia, particularly in African-American patients.

An AGM model for changes in complement during pregnancy: neutralization of influenza virus by serum is diminished in late third trimester

Pregnant women in the third trimester are at increased risk of severe influenza disease relative to the general population, though mechanisms behind this are not completely understood. The immune response to influenza infection employs both complement (C') and antibody (Ab). The relative contributions of these components to the anti-viral response are difficult to dissect because most humans have pre-existing influenza-specific Abs. We developed the African green monkey (AGM) as a tractable nonhuman primate model to study changes in systemic innate immunity to influenza during pregnancy. Because the AGMs were influenza-naïve, we were able to examine the role of C' in influenza virus neutralization using serum from non-pregnant animals before and after influenza infection. We determined that serum from naïve AGMs neutralized influenza via C', while post-infection neutralization did not require C', suggesting an Ab-mediated mechanism. The latter mimicked neutralization using human serum. Further, we found that ex vivo neutralization of influenza with both naïve and influenza-immune AGM serum occurred by virus particle aggregation and lysis, with immune serum lysing virus at a much higher rate than naïve serum. We hypothesized that the anti-influenza C' response would diminish late in AGM pregnancy, corresponding with the time when pregnant women suffer increased influenza severity. We found that influenza neutralization capacity is significantly diminished in serum collected late in the third trimester. Strikingly, we found that circulating levels of C3, C3a, and C4 are diminished late in gestation relative to nonpregnant animals, and while neutralization capacity and serum C3a return to normal shortly after parturition, C3 and C4 levels do not. This AGM model system will enable further studies of the role of physiologic and hormonal changes in downregulating C'-mediated anti-viral immunity during pregnancy, and it will permit the identification of therapeutic targets to improve outcomes of influenza virus infection in pregnant women.

Evaluation of current and new biomarkers in severe preeclampsia: a microarray approach reveals the VSIG4 gene as a potential blood biomarker

Preeclampsia is a placental disease characterized by hypertension and proteinuria in pregnant women, and it is associated with a high maternal and neonatal morbidity. However, circulating biomarkers that are able to predict the prognosis of preeclampsia are lacking. Thirty-eight women were included in the current study. They consisted of 19 patients with preeclampsia (13 with severe preeclampsia and 6 with non-severe preeclampsia) and 19 gestational age-matched women with normal pregnancies as controls. We measured circulating factors that are associated with the coagulation pathway (including fibrinogen, fibronectin, factor VIII, antithrombin, protein S and protein C), endothelial activation (such as soluble endoglin and CD146), and the release of total and platelet-derived microparticles. These markers enabled us to discriminate the preeclampsia condition from a normal pregnancy but were not sufficient to distinguish severe from non-severe preeclampsia. We then used a microarray to study the transcriptional signature of blood samples. Preeclampsia patients exhibited a specific transcriptional program distinct from that of the control group of women. Interestingly, we also identified a severity-related transcriptional signature. Functional annotation of the upmodulated signature in severe preeclampsia highlighted two main functions related to “ribosome” and “complement”. Finally, we identified 8 genes that were specifically upmodulated in severe preeclampsia compared with non-severe preeclampsia and the normotensive controls. Among these genes, we identified VSIG4 as a potential diagnostic marker of severe preeclampsia. The determination of this gene may improve the prognostic assessment of severe preeclampsia.

Urinary excretion of C5b-9 in severe preeclampsia: tipping the balance of complement activation in pregnancy

The complement cascade is activated in normal pregnancy, and excessive complement activation propagates the systemic inflammatory response in severe preeclampsia. Consequently, biomarkers of complement dysregulation may be useful for prediction or treatment of disease. Because renal damage with proteinuria is a characteristic pathological feature of preeclampsia, we hypothesized that complement markers in urine, rather than plasma, could better reflect complement dysregulation in disease. To investigate this, we performed a case-control study of pregnant women, enrolling 25 cases with severe preeclampsia, 25 controls with chronic hypertension, and 25 healthy controls without hypertension matched by gestational age and parity. Subjects were recruited from the Brigham and Women's Hospital from March 2012 to March 2013. Urine and blood samples were collected on the day of enrollment, with complement activation (C3a, C5a, and C5b-9) measured by ELISA. Severe preeclampsia was associated with marked elevations in urinary C5b-9 (median [interquartile range], 4.3 [1.2-15.1] ng/mL) relative to subjects with chronic hypertension (0 [0-0]) and healthy controls (0 [0-0]; P<0.0001). Urinary excretion of C5b-9 was detected in 96% of cases with severe preeclampsia, 12% of controls with chronic hypertension, and 8% of healthy controls. Cases were also notable for significantly greater urinary excretion of C3a and C5a. Plasma levels of C5a and C5b-9, but not C3a, were increased in the cases with severe preeclampsia compared with healthy controls; however, they did not distinguish preeclampsia from chronic hypertension, supporting our hypothesis that complement markers in urine, rather than plasma, better reflect complement dysregulation. Complement inhibition is an intriguing treatment option for patients with severe preeclampsia.