Elevated IL-6 in midtrimester amniotic fluid is involved with the onset of preeclampsia

Respiratory syncytial virus exhibits differential tropism for distinct human placental cell types with Hofbauer cells acting as a permissive reservoir for infection

BACKGROUND

Respiratory syncytial virus (RSV) is capable of transient viremia and extrapulmonary dissemination. Recently, this virus has been identified in fetal cord blood, suggesting the possibility of in utero acquisition in humans. Here, we assess permissivity and kinetics of RSV replication in primary human placental cells, examine their potential to transfer this infection to neighboring cells, and measure the inflammatory response evoked by the virus.

METHODS AND FINDINGS

Human placental villus tissue was collected immediately upon delivery and processed for isolation of placental cytotrophoblast, fibroblast, and macrophage (Hofbauer) cells. Isolated cells were infected with a recombinant RSV-A2 strain (rrRSV) expressing red fluorescent protein (RFP) and analyzed by fluorescence microscopy, Western blot, and quantitative PCR (qPCR). Based on RFP expression, rrRSV exhibited differential tropism for the three major placental cell types. Placental fibroblasts and Hofbauer cells were permissive and supported productive rrRSV replication. While infected cytotrophoblast cells expressed viral glycoprotein (G protein), only limited RSV replication was detected. Importantly, qPCR and fluorescence-focused unit assay revealed that the viral progeny remains trapped within infected Hofbauer cells for up to 30 days, with no release into surrounding media. Yet, Hofbauer cells passed the infection onto overlaid naïve 16HBE cells, suggesting contact-dependent trans-infection. Lastly, a significant increase in proinflammatory cytokines, particularly IL-6, TNF-alpha, and IFN-gamma was measured in the supernatant of infected Hofbauer cells by multiplex cytokine assay and conventional ELISA.

CONCLUSIONS

This study demonstrates that RSV can replicate in human placenta, exhibits differential tropism for distinct placental cell types, can be stored and transferred to neighboring cells by Hofbauer cells, and elicits an inflammatory response. It also supports the hypothesis that this respiratory virus can be vertically transferred to the fetus and potentially affect its development and the outcome of pregnancies.

Cytokines as key players in the pathophysiology of preeclampsia

Preeclampsia (PE) is an important, common, and dangerous complication of pregnancy; it causes maternal and perinatal illness and is responsible for a high proportion of maternal and infant deaths. PE is associated with increased blood pressure and proteinuria, with a whole host of other potentially serious complications in the mother and fetus. The maternal syndrome in PE is primarily that of generalized dysfunction of the maternal endothelium, and this generalized endothelial dysfunction appears to be part of an exaggerated systemic inflammatory response that involves maternal leukocytes and proinflammatory cytokines. This review examines evidence that points to a significant role for the maternal immune system; inadequate trophoblast invasion of spiral arteries initiates ischemia and hypoxia in the placenta, resulting in an increased release of proinflammatory cytokines in the placenta. Placental ischemia and hypoxia also cause the enhanced release of trophoblast microparticles into the maternal circulation which stimulates increased induction of proinflammatory cytokines and the activation of maternal endothelial cells. This activation results in a systemic, diffuse endothelial cell dysfunction which is the fundamental pathophysiological feature of this syndrome. Recent evidence also supports important roles for proinflammatory cytokines in hypertension, proteinuria, and edema which are characteristic features of PE.

Interleukin-6 in pregnancy and gestational disorders

IL6 is a multifunctional cytokine with pivotal roles in the inflammatory response and in directing T cell differentiation in adaptive immunity. IL6 is widely expressed in the female reproductive tract and gestational tissues, and exerts regulatory functions in embryo implantation and placental development, as well as the immune adaptations required to tolerate pregnancy. Here, we summarise the current understanding of how membrane-bound and soluble receptors mediate IL6 signalling to regulate leukocytes and non-haemopoietic cells. We review the published literature regarding the expression and actions of IL6 in the uterus, decidua and placenta, and studies implicating this cytokine in pregnancy disorders. Elevated IL6 is frequently evident in the altered cytokine profiles characteristic of unexplained infertility, recurrent miscarriage, preeclampsia and preterm delivery. Notably, there is compelling evidence indicating altered systemic IL6 trans-signalling in women prone to recurrent miscarriage, with excessive IL6 bioavailability potentially inhibiting generation of CD4+ T regulatory cells required for pregnancy tolerance. Insufficient local IL6 may also contribute to fetal loss, since IL6 expression is reduced in the endometrium of women with recurrent miscarriage, and in the fetal-placental tissue of CBA×DBA/2 mice. Consistent with the role of IL6 in key reproductive events, Il6 null mutant mice exhibit elevated fetal resorption and delayed parturition. Investigation of the association between IL6 signalling components and T cell responses in pregnant women, as well as detailed analysis of the maternal immune response in IL6-deficient mice, is now required to define the mechanisms by which this cytokine exerts influence on reproductive success.

Magnesium sulfate normalizes placental interleukin-6 secretion in preeclampsia

Interleukin-6 (IL-6) is one of the main proinflammatory mediators of hypertension and endothelial dysfunction in preeclampsia. In this study, we investigated the capacity of the preeclamptic placenta to secrete IL-6 and the effect of magnesium sulfate (MgSO(4)) on it. Placentas from normotensive (37-40 weeks) and preeclamptic (36-40 weeks) pregnancies were dually perfused for 6 h in the absence [normotensive (n = 3); preeclamptic (n = 4)] and presence [normotensive (n = 3); preeclamptic (n = 4)] of MgSO(4). Perfusate samples from the maternal and the fetal circulations were collected at each 30 min throughout the perfusion period and examined for IL-6 by enzyme-linked immunoassay. Statistical analysis was performed using the 2-way analysis of variance. In the absence of MgSO(4), IL-6 levels in the maternal and the fetal circulations of preeclamptic placentas (4.2 ± 1.3 and 0.9 ± 0.5 pg/mL/g cotyledon; respectively) were significantly higher, when compared with normotensive placentas (1.9 ± 0.5 and 0.2 ± 0.2 pg/mL/g cotyledon; respectively) (P < 0.05). Addition of MgSO(4) to the perfusate of normotensive placentas did not affect IL-6 secretion. However, exposure of preeclamptic placentas to MgSO(4) resulted in decreased IL-6 levels in the maternal circulations (1.7 ± 0.3 pg/mL/g cotyledon), when compared with the control group (P < 0.05). In the fetal circulation, the addition of MgSO(4) resulted only in a nonstatistical significant tendency toward decreased IL-6 levels, when compared with the control group. Our findings indicate that the perfused preeclamptic placenta secretes increased levels of IL-6 into the fetal and the maternal circulations and that MgSO(4) may normalize these increased secreted IL-6 levels.

Autoantibody-mediated IL-6-dependent endothelin-1 elevation underlies pathogenesis in a mouse model of preeclampsia

Preeclampsia (PE) is a life-threatening hypertensive disorder of pregnancy. Elevated circulating endothelin-1 (ET-1) is associated with the disease. However the molecular basis of increased ET-1 production and its role in PE are unknown. This study aimed to investigate the causative factors, pathological role of elevated ET-1 production in PE, and the underlying mechanisms. In this study, we found that IgG from women with PE, in contrast to IgG from normotensive pregnant women, induced preproET-1 mRNA expression via angiotensin II type 1 receptor activation in kidneys and placentas in pregnant mice. The ET-A receptor-specific antagonist BQ123 significantly attenuated autoantibody-induced hypertension, proteinuria, and renal damage in pregnant mice, demonstrating that autoantibody-induced ET-1 production contributes to pathophysiology. Mechanistically, we discovered that IL-6 functioned downstream of TNF-α signaling, contributing to increased ET-1 production in pregnant mice. IL-6 blockade inhibited preeclamptic features in autoantibody-injected pregnant mice. Extending the data to human studies, we found that IL-6 was a key cytokine underlying ET-1 induction mediated by IgG from women with PE in human placental villous explants and that endothelial cells are a key source of ET-1. Overall, we provide human and mouse studies showing that angiotensin II type I receptor-agonistic autoantibody is a novel causative factor responsible for elevated ET-1 production and that increased TNF-α/IL-6 signaling is a key mechanism underlying increased ET-1 production and subsequent maternal features. Significantly, our findings revealed novel factors and signaling cascades involved in ET-1 production, subsequent disease symptom development, and possible therapeutic intervention in the management of PE.

ATP-binding cassette transporter expression in human placenta as a function of pregnancy condition

Fetal drug exposure is determined by the type and concentration of placental transporters, and their regulation is central to the development of new treatments and delivery strategies for pregnant women and their fetuses. We tested the expression of several clinically important transporters in the human placenta associated with various pregnancy conditions (i.e., labor, preeclampsia, and preterm labor-inflammation). Placentas were obtained from five groups of women at the time of primary cesarean section: 1) term no labor; 2) term labor; 3) preterm no labor (delivered for severe preeclampsia); 4) preterm labor without inflammation (PTLNI); and 5) preterm labor with inflammation (PTLI). Samples were analyzed by Western blot and immunohistochemistry to identify changes in protein expression. Relative mRNA expression was determined by quantitative real-time polymerase chain reaction. A functional genomic approach was used to identify placental gene expression and elucidate molecular events that underlie the given condition. Placental expression of ATP-binding cassette transporters from women in labor and women with preeclampsia was unaltered. Multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) and mRNA expression increased in placentas of women with preterm labor with inflammation. Molecular pathways of genes up-regulated in PTLI samples included cytokine-cytokine receptor interactions and inflammatory response compared with those in the PTLNI group. The mRNA expression of MDR1 and BCRP was correlated with that of interleukin-8, which also increased significantly in PTLI samples. These data suggest that the transfer of drugs across the placenta may be altered in preterm pregnancy conditions associated with inflammation through changes in MDR1 and BCRP.

Elevated maternal soluble Gp130 and IL-6 levels and reduced Gp130 and SOCS-3 expressions in women complicated with preeclampsia

Increased inflammatory response plays a significant role in the vascular pathophysiology in preeclampsia. However, the mechanism for increased inflammatory response in preeclampsia is largely unknown. Interleukin (IL)-6 levels are elevated in women with preeclampsia. IL-6 and its receptors, IL-6R and glycoprotein (gp)130, play a critical role in mediating antiinflammatory response via induction of SOCS-3 (suppressor of cytokine signaling-3). However, IL-6 receptor levels and expressions have not been studied in preeclampsia. In this study, we measured IL-6 and its 2 soluble receptors, soluble IL-6R and soluble gp130, in maternal plasma from normal and preeclamptic pregnant women and found that not only IL-6 but also soluble gp130 levels were significantly higher in preeclamptic women than in normotensive pregnant controls. We further examined IL-6R, gp130, and SOCS-3 expressions in maternal vessels and leukocytes and found that gp130 and SOCS-3 expressions were downregulated in both vessel endothelium and leukocytes from preeclampsia. Different patterns for IL-6R and gp130 expressions were found. IL-6R expression was also downregulated in leukocytes from preeclampsia. Our results suggest that increased plasma soluble gp130/soluble IL-6R/IL-6 ratio and reduced membrane transsignaling gp130 expression could contribute to decreased SOCS-3 expression and subsequent reduction in SOCS-3 antiinflammatory activity in women with preeclampsia. Thus, reduced gp130 and SOCS-3 expressions may offer, at least in part, a plausible explanation of reduced antiinflammatory protection in the maternal vascular system in preeclampsia.

Differences in amniotic fluid and maternal serum cytokine levels in early midtrimester women without evidence of infection

The amniotic fluid cytokine profile has been shown to be indicative of various disease states, and changes may be associated with preterm labor or infection. Anti-inflammatory cytokine profiles may be essential for successful normal pregnancy. However, there are currently few normative data on the concentration of cytokines in amniotic fluids during pregnancy. The aim of this study was to provide new amniotic fluid cytokine data for future comparative studies in disease states, notably in utero viral infections, and to compare these with maternal serum levels. Amniotic fluid was obtained from 100 pregnant women undergoing elective amniocentesis at the Royal Hospital for Women, Randwick. Concentrations of 27 cytokines were simultaneously measured in amniotic fluid and a subset of matching maternal sera (n=33) using a multiplex bead-based immunoassay system (Bio-Plex, Bio-Rad). To exclude infection, nested multiplex PCR targeting 17 known congenital infectious agents were performed on all amniotic fluid and maternal serum samples, and serological testing was also performed against some of these agents. Maternal serum concentration was positively correlated with amniotic fluid levels for MIP-1beta (r=0.39, P=0.027). IL-1ra was positively correlated to maternal age (r=0.210, P=0.036), and mean IL-5 levels were significantly higher in amniotic fluids from pregnancies with male fetuses than those with female fetuses (P=0.036). Normal amniotic fluid concentrations for five cytokines (IL-6, IL-8, IP-10, MCP-1, IL-1ra) were found to be significantly elevated over maternal serum concentrations in matched pairs (P<0.05). Concentrations of 12 cytokines (eotaxin, IFN-gamma, IL-9, IL-12, IL-15, IL-17, MIP-1alpha, MIP-1beta, RANTES, TNF-alpha, VEGF, PDGF bb) were significantly elevated in maternal serum compared to paired amniotic fluid at midtrimester (P<0.05). Amniotic fluid may be more representative of the fetal cytokine profile than cytokine analysis on antenatal sera as it represents predominantly fetal urinary and respiratory secretions. This study provides new normative data for multiple cytokine levels in amniotic fluid and maternal sera at 14-16 weeks gestation, and is a valuable tool for future diagnostic and comparative studies.

Immunological analogy between allograft rejection, recurrent abortion and pre-eclampsia - the same basic mechanism?

There are still controversies concerning the role of immunological mechanisms engaged both in recurrent abortions (RA) and pre-eclampsia (PE). According to some opinions, recurrent miscarriage is comparable to organ-specific autoimmune disease. Analysis of immune reactions shows that graft rejection shares many similar mechanisms with RA and PE. This fact allows us to conclude that rejection of transplanted alloantigenic organs and pregnancy loss have probably the same evolutionary origin. Subsets and functions of immunocompetent cells (T CD4, suppressor gammadeltaT, cytotoxic T CD8, Treg, Tr1, uterine NK cells), over-activation of innate immunity (activation of NK cytotoxic cells, macrophages, neutrophils and complement), changes of Th1/Th2 cytokine balance (IL-2, IL-12, IL-15, IL-18, IFNgamma, TNFalpha vs. IL-4, IL-10, TGFbeta), importance of HLA-G molecule, CD200/CD200R interaction, over-expression of adhesion molecules, fgl2 prothrombinase activation and stimulation of IDO and HO expression, all suggest that RA and PE are syndromes of fetal allograft rejection, and not organ-specific autoimmune diseases. According to that supposition, an analogy might exist between acute graft rejection and recurrent abortion, and between chronic graft rejection and pre-eclampsia.

Maternal Cytokine Production Patterns in Women with Pre-eclampsia

PROBLEM

To determine the levels of cytokines produced upon mitogenic or antigenic stimulation of maternal peripheral blood mononuclear cells (PBMC) from women with pre-eclampsia.

METHOD OF STUDY

PBMC from 54 women with a history of successful pregnancy and 32 women undergoing pre-eclamptic delivery were stimulated with a mitogen or with autologous placental cells or with trophoblast antigens, and the levels of cytokines released into the culture supernatants then assessed by enzyme-linked immunosorbent assay.

RESULTS

Significantly higher levels of the Th1 cytokines, interferon-gamma, and tumor necrosis factor-alpha were produced by the pre-eclamptic group than by the normal pregnancy group, which on the contrary showed significantly greater production of the Th2 cytokines, interleukin (IL)-4, IL-5, IL-6 and IL-10. A comparison of the ratios of Th2 to Th1 cytokines indicates a higher Th1 cytokine bias in pre-eclampsia as compared with normal pregnancy.

CONCLUSIONS

These data are suggestive of a maternal pro-inflammatory cytokine bias in pre-eclampsia.

Cytokines of the placenta and extra-placental membranes: roles and regulation during human pregnancy and parturition

Summary In an earlier, companion, review, we concluded that cytokines produced by the placenta and associated membranes are likely to be involved in control of the processes of implantation and placental development (Bowen et al., 2002). In this review, we discuss evidence that cytokines continue to be part of a paracrine/autocrine regulatory network in the placenta and membranes throughout the mid and late stages of gestation. Cytokines are involved in regulation of placental growth during these later stages of pregnancy and also function to protect the fetus from pathological organisms. The evidence, while not entirely consistent, suggests that production of certain cytokines within the extraplacental membranes is altered during normal term parturition, whereas in the villous placenta evidence of labour-associated changes is much more equivocal. Roles for cytokines have been postulated in many facets of parturition, including expulsion of the fetus by uterine contractions, membrane rupture, and dilation of the cervix. Imbalances and disruptions to the cytokine milieu have been implicated in a number of diseases of pregnancy involving abnormalities of both placental growth/establishment and initiation of parturition. Cytokine secretion induced by intrauterine infection is associated with increased occurrence or severity of some neonatal diseases. This wealth of data supports the view that cytokines are an integral part of a functional regulatory/communication network operating within the placental-maternal unit during normal gestation.

Aberrations in placental cytokine mRNA related to intrauterine growth retardation

During normal pregnancy, a predominance of Th2 type cytokines prevails and is considered to protect the fetus. Animal experiments suggest that an increase of Th1 type cytokines may instead have deleterious effects. We have studied with the reverse transcription PCR technique mRNA for IL-1alpha, IL-1beta, IL-6, IL-8, IL-10, transforming growth factor-beta, tumor necrosis factor-alpha, and interferon-gamma in placentas from full-term appropriately grown newborns, newborns with intrauterine growth retardation (IUGR) and newborns who were only small for gestational age. The mRNA for IL-10 was significantly reduced in the IUGR placentas (p < 0.05), whereas the mRNA for IL-8 was significantly higher (p < 0.05) for the IUGR cases compared with the full-term neonates. It might be that reduced IL-10 in the placenta is involved in the pathogenesis of IUGR.

Cytokine levels in midtrimester amniotic fluid in normal pregnancy and in the prediction of pre-eclampsia

Midtrimester amniotic fluid cytokines may reflect the function of the maternal immune system in the maternal-fetal interface and thus be predictive of pre-eclampsia. We determined the concentrations of interleukin (IL)-6, IL-8, IL-10, IL-11, IL-12, IL-15, tumour necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta in amniotic fluid at 14-16 weeks of gestation from women with normal pregnancies and from those who subsequently developed severe pre-eclampsia. The concentrations of the cytokines in amniotic fluid did not significantly differ between patients and normal controls. The median concentration of IL-6 was 950 pg/ml in normal pregnant women and 578 pg/ml in the patient group. The median concentration of IL-8 was 606 pg/ml in normal controls and 294 pg/ml in the patient group. The levels of IL-6, IL-8 and TGF-beta correlated positively with each other. TNF-alpha concentrations were low and similar in both groups. IL-10 and IL-12 were detected at very low levels in 37 and 7% of the samples, respectively. No difference was found in IL-15 concentrations between the groups. IL-11 was found only at low levels in both groups. Although none of the cytokines measured was predictive of pre-eclampsia, this study provides information of cytokines in amniotic fluid during the period when the spiral arteries are remodelled.

Advances in perinatal medical care--from our experience

In the last 30 years, maternal and perinatal mortality rates have markedly improved in Japan. These results are supported by the advanced technologies and newly developed treatments in obstetric and neonatal medicine, the evidence of which will be described through the authors' experiences. Ultrasound-guided treatments for fetuses and pediatric surgery for extremely tiny infants have been performed with cooperation among cardiac surgeons, anesthesiologists and perinatologists. The remarkable achievements in neonatal medicine are surfactant replacement therapy, application of high frequency oscillation (HFO) respirator, nitric oxide and extracorporeal membrane oxygenation (ECMO) systems and transcutaneous blood gas monitoring. The possibility to have a safe pregnancy and delivery arose for women with severe medical complications such as diabetes mellitus (DM), heart diseases, and hemo-dialysis, factors formerly regarded as contraindications to pregnancy. The accumulative data of these high-risk pregnancies treated in our center are introduced. It is noted that molecular mechanisms in fetal growth have been elucidated to some extent. The insulin-like growth factor I (IGF-I) and IGF-binding protein 1 (IGFBP1) system, and cytokines, are involved in the fetal growth. Newly developed treatments such as urinary trypsin inhibitor (Urinastatin) for prevention of preterm delivery and amnioinfusion to cases of preterm premature rupture of the membrane are summarized. Finally, the reference to advanced medicine and its side effects lead to broad discussions regarding the future development of perinatal medicine.