REVIEW ARTICLE: Guilty As Charged: All Available Evidence Implicates Complement’s Role in Fetal Demise

Prevention of intrauterine fetal growth restriction by administrating C1q/TNF-related protein 6, a specific inhibitor of the alternative complement pathway

PURPOSE

The latest treatments do not sufficiently prevent miscarriage and fetal growth restriction (FGR) in pregnant women. Here, we assessed the effects of a human protein, CTRP6, that specifically inhibits the activation of the alternative complement pathway on miscarriage, fetal and placental development.

METHODS

Pregnant CBA/J mice mated with DBA/2 male mice as a model of spontaneous abortion and FGR were randomly divided into the control and CTRP6 groups. In the CTRP6 group, the mice were intravenously administered CTRP6 on days 4.5 and 6.5 post-conception (dpc). The abortion rate and fetal and placental weights on 14.5 dpc were examined. Remodeling of the spiral artery was also assessed.

RESULTS

The abortion rate in the CTRP6 group (13%) was reduced compared to the control group (21%), but there was no statistical difference. The placental and fetal weights in the CTRP6 group were also heavier than those in the control (P < 0.05). Moreover, the thickness of the blood vessel wall in the CTRP6 group was significantly thinner than that in the control (P < 0.05) and comparable to that in the non-abortion model (CBA/J x BALB). The ratio of the inner-per-the-outer diameter of the spiral artery increased more in the CTRP6 group than that in the control (P < 0.05). As well, the Th1/Th2 cytokine ratio was significantly reduced by CTRP6 treatment.

CONCLUSIONS

Taken together, the supplementation with a protein that regulates the alternative complement pathway in vivo improves FGR and promotes spiral artery remodeling in a mouse model of miscarriage and FGR.

Targeted therapy in antiphospholipid syndrome

PURPOSE OF REVIEW

To review novel therapeutic targets that are currently under investigation to develop safer, targeted therapies for antiphsopholipid antibody (aPL)-mediated clinical manifestations.

RECENT FINDINGS

Novel therapeutic options potentially available include anti-CD20 monoclonal antibodies and new-generation anticoagulants (such as direct thrombin and anti-Xa inhibitors). Research focusing on interfering with aPL-mediated cell activation, targeting complement components and the innovative concept of blocking the pathogenic subpopulation of aPL with tailored peptides are currently being explored.

SUMMARY

Antiphospholipid syndrome is an autoimmune disease characterized by thrombosis and pregnancy morbidity occurring in patients persistently positive for aPL. Current therapeutic options remain confined to long-term anticoagulation with vitamin K antagonists. The future holds much promise with the identification of novel potential targets, many of which are currently under investigation. The challenge will be to design prospective randomized controlled clinical trials to provide the evidence necessary to support integration of these therapies into clinical practice.

Neural tube defects, folate, and immune modulation

Periconceptional supplementation with folic acid has led to a significant worldwide reduction in the incidence of neural tube defects (NTDs). However, despite increasing awareness of the benefits of folic acid supplementation and the implementation of food fortification programs in many countries, NTDs continue to be a leading cause of perinatal morbidity and mortality worldwide. Furthermore, there exists a significant subgroup of women who appear to be resistant to the protective effects of folic acid supplementation. The following review addresses emerging clinical and experimental evidence for a role of the immune system in the etiopathogenesis of NTDs, with the aim of developing novel preventative strategies to further reduce the incidence of NTD-affected pregnancies. In particular, recent studies demonstrating novel roles and interactions between innate immune factors such as the complement cascade, neurulation, and folate metabolism are explored.

Placental malaria: from infection to malfunction

Malaria during pregnancy is a major factor in infant morbidity and mortality. In this issue of Cell Host and Microbe, Conroy et al. (2013) propose that C5a, a product of complement cascade activation, counteracts the placental vascular remodeling response induced by Plasmodium infection and contributes to fetal growth restriction.

Prevalence and clinical usefulness of antiphospholipid and anticofactor antibodies in different Spanish preeclampsia subsets

Objective: To study the prevalence and clinical usefulness of antiphospholipid antibodies in different preeclampsia subsets. Design: Observational cross-sectional study. Setting: Tertiary teaching hospital. Patients: Ninety-nine women with preeclampsia versus 83 healthy pregnant women as controls. Interventions: We analysed anticardiolipin IgG/IgM, anti-ß2glycoprotein IgG/IgM, antiphosphatidylserine IgG/IgM, antiAnnexin-A5 IgG/IgM, and lupus anticoagulant. Main outcome measure: Comparison of antiphospholipid antibody positivity between groups. Results: Antiphospholipid antibody prevalence was 14.14% in the study group vs. 7.23% in controls. Excluding antiAnnexin-A5-positive women, overall antiphospholipid prevalence was 13.19% vs. 3.61% ( p = 0.034). Only IgM-anticardiolipin positivity showed significant differences between preeclampsia group and controls (8.1% vs. 1.20%, p = 0.041). Comparing a severe preeclampsia subset vs. controls, we obtained these significant results: for two or more positive antiphospholipid tests: 9.09% vs. 1.20 ( p = 0.037); IgM-anticardiolipin 10.91% vs. 1.20% ( p = 0.016); IgG/IgM-anti-ß2glycoprotein-I 10.91% vs. 1.90% ( p = 0.016), IgM-anti-ß2glycoprotein-I 9.09% vs.1.20 ( p = 0.037). When comparing early-onset preeclampsia vs. controls we found IgM-anticardiolipin 11.11% vs. 1.20% ( p = 0.029). Conclusions: Prevalence of antiphospholipid antibodies in preeclampsia patients is twice that in healthy pregnant women. Multipositive aPL test, IgM-anticardiolipin and IgM-anti-ß2glycoprotein-I isotypes showed an association with severe and early-onset preeclampsia. Larger studies are needed to establish the usefulness of antiphospholipid tests as risk markers for severe and early onset preeclampsia.

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.

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.

Low-molecular-weight heparin inhibition in classical complement activation pathway during pregnancy

INTRODUCTION

Low-molecular-weight heparin is used clinically for the prevention of pregnancy complications associated with prothrombotic disorders, particularly anti-phospholipid syndrome. Nevertheless, recent studies have suggested that heparin may exert direct effects on the placental trophoblast, independently of its anticoagulant activity. In addition, heparin prevents complement activation in vivo and protects mice from pregnancy complications.

MATERIALS AND METHODS

The inhibition of the classical complement activation pathway by heparin was analyzed by means of in vitro assays and in pregnant women receiving prophylaxis with therapeutic doses (40 mg/day) of subcutaneous low molecular weight heparin by haemolysis of antibody-sensitized sheep erythrocytes (CH(50) assay).

RESULTS

The specific interaction between low-molecular-weight heparin and the C1q subunit of the C1 complex of the complement cascade allowed the isolation of a small subpopulation of heparin ( 8.03+/-1.20 microg %), with an anti-activated factor X activity more than four times greater than the starting material. This subpopulation could be responsible for the in vitro inhibition of the classical complement activation pathway evaluated by the total haemolysis of antibody-sensitized sheep erythrocytes. About 60 microg/ml of low molecular weight heparin was needed to achieve 50% of haemolysis. The detection of the classical complement pathway inhibition in pregnant women treated with heparin required a first activation with aggregated human IgG.

CONCLUSIONS

We concluded that the interaction between low-molecular-weight heparin and C1q could be relevant not only in the complement-dependent, but also in the complement-independent inflammation mechanisms responsible for the prevention of pregnancy loss.

Anti-phospholipid antibodies and other immunological causes of recurrent foetal loss--a review of literature of various therapeutic protocols

PROBLEM

An immune-based aetiology is one of the several accepted causes for recurrent foetal loss (RFL). However, most of the immunological theories have not fulfilled the criteria for causality. This is a review of the various immunological causes of RFL and the outcome of different treatment protocols.

METHOD OF STUDY

Both auto- and alloimmune maternal immunological abnormalities have been proposed to account for foetal loss. Among the autoimmune factors, anti-phospholipid antibodies (APAs) have been demonstrated to be the strongest risk factors for foetal loss, the prevalence of which is as high as 40% in women with RFL. Other autoimmune antibodies implicated in RFL are anti-nuclear antibodies (ANAs), anti-thyroid antibodies and anti-endothelial cell antibodies. The alloimmune factors implicated in pregnancy loss of unknown aetiology include abnormal natural killer (NK) cell activity, alteration in T helper 1 (Th1) and T helper 2 (Th2) ratios, presence of alloimmune antibodies like anti-paternal cytotoxic antibodies, anti-idiotypic antibodies, mixed lymphocyte reaction blocking antibodies and abnormal expression of HLA-G molecules. Management of patients with RFL is mainly based on immunomodulatory (prednisolone, intravenous immunoglobulins, plasma exchange, paternal lymphocyte therapy), anti-aggregation (aspirin) or anti-coagulation (unfractionated or low molecular weight heparin) agents.

RESULTS

Low-molecular-weight heparin with low-dose aspirin has been found to be the most effective treatment for women with APAs and RFL. Differences in dosage, timing of treatment, inclusion criteria, outcome assessment parameters etc. are some of the factors which have resulted in discrepancies in various reports.

CONCLUSION

Identification of the immunological mechanisms involved in pregnancy loss and the action of different therapeutic reagents is important so that effective therapies can be designed and investigated.

Pravastatin prevents miscarriages in mice: role of tissue factor in placental and fetal injury

Pregnancy loss and intrauterine growth restriction (IUGR) are serious pregnancy complications, and the triggers and mediators of placental and fetal damage are not completely understood. Using a mouse model of recurrent spontaneous miscarriages (DBA/2-mated CBA/J mice) that shares features with human recurrent miscarriage and fetal growth restriction, we identified tissue factor (TF) as an essential participating factor in placental and fetal injury. We have previously shown that C5a releases antiangiogenic molecule sFlt-1 in monocytes that causes defective placental development and fetal death in DBA/2-mated CBA/J mice. In this study, we found that TF not only activates the coagulation pathway, but it also mediates sFlt-1 release in monocytes causing defective placental development and fetal death. Blockade of TF with a monoclonal antibody inhibited sFlt-1 release, prevented the pathological activation of the coagulation pathway, restored placental blood flow, prevented placental oxidative stress, and rescued pregnancies. We also demonstrated that pravastatin, by down-regulating TF expression on monocytes and trophoblasts, prevented placental damage and protected pregnancies in DBA/2-mated CBA/J mice. These studies indicate that TF is an important mediator in fetal death and growth restriction and that statins may be a good treatment for women with recurrent miscarriages and IUGR.

Syngeneic immune-dependent abortions in mice suggest paternal alloantigen-independent mechanisms

PROBLEM

Recurrent immune-associated miscarriages in humans are thought to result from maternal immune responses to paternal alloantigens. We investigated the role of paternal alloantigens in a mouse model of immune-dependent abortion.

METHOD OF STUDY

Sib-crosses of C57Bl/6J (haplotype b/b) mice heterozygous for a targeted hypomorphic allele of the tbp gene (tbp(deltaN/+)) resulted in selective mid-gestational abortion of 88% of the tbp(deltaN/deltaN) fetuses. In dams lacking mature lymphocytes (rag1-/-), nearly all tbp(deltaN/deltaN) fetuses survived to birth, indicating abortions were immune-dependent. Allogeneic pregnancies bearing tbp(deltaN/deltaN) fetuses were established by either hybridizing the paternal lineage to BALB/cJ (haplotype d/d) and mating hybrid tbp(deltaN/+) sires to haplotype b/b tbp(deltaN/+) C57Bl/6J dams, or by transfer of haplotype b/b zygotes from tbp(deltaN/+)x tbp(deltaN/+) matings into pseudopregnant wild-type CByD2F1/J dams (haplotype d/d).

RESULTS

Neither hemizygous paternal allogeneic loci nor homozygous allogeneic loci, including a haplotype-mismatched major histocompatibility complex (MHC), increased abortion frequencies.

CONCLUSION

Results suggested that mechanisms for maternal tolerance of paternal alloantigens, including mismatched MHC antigens, were intact in these pregnancies, yet maternal immune-dependent paternal antigen-independent abortion of mutants occurred. These data indicate that, in some cases of immune-mediated abortions, the presence of paternal alloantigens can be coincidental and superfluous to the compromising rejection response.