Evidence for interleukin-10-mediated inhibition of cyclo- oxygenase-2 expression and prostaglandin production in preterm human placenta

Characterization of cytokine production by human term placenta macrophages in vitro

PROBLEM

Macrophages are apparently the only immune cells within placenta villi, yet functions of these cells remain obscure. It has been postulated that placental macrophages accomplish regulatory roles at the fetal-maternal interface by means of wide variety of secreted cytokines. We attempt to analyze the patterns of cytokine production in an isolated population of placental macrophages.

METHOD OF STUDY

Macrophages were obtained from term placentas in the absence of spontaneous labor. The basal and lipopolysaccharide (LPS)-stimulated levels of intracellular cytokines were detected by flow cytometry. The basal cytokine secretion was determined by BD Cytometry Bead Array (BD Biosciences, San Diego, CA, USA).

RESULTS

Intracellular IL-1alpha, IL-1beta, IL-6, and TNFalpha were detected in 31, 27, 4, and 3% CD68+ cells, respectively. Stimulation with LPS increased the proportions of cytokine-producing CD68+ cells to 48, 50, 28, and 49%, respectively. Under basal conditions, levels of released TNFalpha and IL-6, respectively, were 20- and 25-fold higher when compared with IL-1b while IL-10 was secreted in small but detectable amounts. When a secretory activity was estimated for cytokine-producing cells, the secretion rate for TNFalpha and IL-6 overwhelmingly surpassed that for IL-1beta (TNFalpha:IL-6:IL-1beta ratio was 192:145:1).

CONCLUSION

These results suggest functional heterogeneity of the placental macrophage population and contribute to the elucidation of regulatory roles of these cells in gestation.

IL-10 modulates placental responses to TLR ligands

PROBLEM

Intra-uterine infections increase production of pro-inflammatory cytokines. It is unclear whether different infectious agents determine the relative expression of pro-and anti-inflammatory cytokines.

METHODS OF STUDY

We compared the placental inflammatory response induced by bacterial lipopolysaccharide (LPS, endotoxin from Gram-negative bacteria) with those induced by lipoteichoic acid (LTA, a cell wall component of Gram-positive bacteria). Placental explants from term delivery were treated with either LPS or LTA, in the presence or absence of IL-10, for 24 hrs. Cytokines, prostaglandin E(2) (PGE(2)) production and cyclo-oxygenase-2 (COX-2) expression were quantified.

RESULTS

Both LTA and LPS significantly induced several cytokines with LPS eliciting more potent effects. IL-6 and IL-8 were induced to comparable levels in response to both LTA and LPS whereas monocyte chemotactic protein-1 (MCP-1) production was induced more by LTA, demonstrating a differential placental response to a specific toll-like receptor (TLR) ligand. IL-10 treatment significantly reduced most pro-inflammatory cytokines as well as PGE(2) induced by both LPS and LTA. Interestingly, IL-10 down-regulated LTA-mediated MCP1 induction, but not that mediated by LPS. Moreover, IL-10 was more effective in down-regulating PGE(2) after LPS- when compared with LTA stimulation.

CONCLUSIONS

Our results demonstrate that placental exposure to LTA and LPS appear to trigger distinct cytokine responses that can be modulated by IL-10.

Cervical insufficiency: re-evaluating the prophylactic cervical cerclage

Historically, placement of a cervical cerclage was based almost entirely on the obstetrical history. Over the past two decades however, we have recognised that history alone may not be the only indication for cerclage but rather, complementing the obstetrical history with ultrasonographic and biochemical findings may better identify those women who may benefit most from the placement of a cervical cerclage. Review of the literature appears to suggest that the best approach towards the management of a cervical insufficiency is to first categorise women as being either high risk of low risk-based on obstetrical history. Although women with an obstetrical history of at least three 2nd trimester losses are likely to benefit from a prophylactic cerclage than those without this history may better be managed with progesterone and serial cervical length measurements. This approach can in turn be used to identify those women with early cervical shortening that may require an emergency cerclage. Although randomised controlled trials are still lacking, recent studies suggests that this approach may be more effective especially when combined with markers of intra-amniotic inflammation. As for the prophylactic cerclage itself, with the abdominal cerclage being less invasive given the possibility of a laparoscopic placement, it may prove to be a more effective alternative to the conventionally placed McDonald cerclage. This however, remains to be evaluated more carefully.

Chorioamnionitis and increased galectin-1 expression in PPROM --an anti-inflammatory response in the fetal membranes?

PROBLEM

Galectin-1 can regulate immune responses upon infection and inflammation. We determined galectin-1 expression in the chorioamniotic membranes and its changes during histological chorioamnionitis.

METHOD OF STUDY

Chorioamniotic membranes were obtained from women with normal pregnancy (n = 5) and from patients with pre-term pre-labor rupture of the membranes (PPROM) with (n = 8) and without histological chorioamnionitis (n = 8). Galectin-1 mRNA and protein were localized by in situ hybridization and immunohistochemistry. Galectin-1 mRNA expression was also determined by quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Galectin-1 mRNA and protein were detected in the amniotic epithelium, chorioamniotic fibroblasts/myofibroblasts and macrophages, chorionic trophoblasts, and decidual stromal cells. In patients with PPROM, galectin-1 mRNA expression in the fetal membranes was higher (2.07-fold, P = 0.002) in those with chorioamnionitis than in those without. Moreover, chorioamionitis was associated with a strong galectin-1 immunostaining in amniotic epithelium, chorioamniotic mesodermal cells, and apoptotic bodies.

CONCLUSION

Chorioamnionitis is associated with an increased galectin-1 mRNA expression and strong immunoreactivity of the chorioamniotic membranes; thus, galectin-1 may be involved in the regulation of the inflammatory responses to chorioamniotic infection.

TLR9 activation coupled to IL-10 deficiency induces adverse pregnancy outcomes

Pregnancy outcome is severely compromised by intrauterine infections and inflammation. Although the pregnant uterine microenvironment is replete with innate immune cells and TLR expression, the mechanisms that facilitate adverse effects of their activation are largely unknown. In this study, we mimic the activation of TLR9 with its pathogenic ligand hypomethylated CpG and demonstrate that IL-10 proficiency protects against CpG-induced pregnancy complications. We show that fetal resorption and preterm birth are rapidly induced in IL-10(-/-) mice by low doses of CpG (approximately 25 microg/mouse) when injected i.p. on gestational day 6 or gestational day 14, respectively. In contrast, wild-type mice failed to experience such effects at comparable doses, but pups born at term displayed craniofacial/limb defects in response to higher doses (approximately 400 microg/mouse). Pregnancy complications in IL-10(-/-) mice were associated with unexpected and robust TLR9-triggered activation and amplification of uterine neutrophil and macrophage subpopulations followed by their migration to the placental zone. Furthermore, a dramatic increase in serum levels of mouse KC and TNF-alpha production by uterine F4/80(+) cells, but not uterine NK or Gr-1(+)CD11b(+) cells, was observed. Depletion of F4/80(+) macrophages or neutralization of TNF-alpha rescued pregnancy to term. Our results have important implications for IL-10-mediated "uterine tolerance" against CpG-driven innate immune activation.

Progesterone-induced blocking factor and cytokine profile in women with threatened pre-term delivery

PROBLEM

The objective of this study was to compare serum concentrations of progesterone-induced blocking factor (PIBF), anti-inflammatory (IL-10),and pro-inflammatory (IL-6, TNFa, and IFNc) cytokines of women with threatened pre-term delivery, with those of women with normal pregnancy and to evaluate the impact of PIBF on the outcome of pregnancy.

METHOD OF STUDY

A prospective study was conducted on a sample of 30 women with threatened pre-term delivery (study group) and 20 healthy pregnant women (control group) between the 24th and 37th gestational weeks. Serum PIBF, anti-inflammatory (IL-10), and pro-inflammatory (IL-6, TNFa, and IFNc) cytokine concentrations were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Thirteen of 30 patients (43.3%) with symptoms of threatened pre-term delivery, and one of 20 patients (5%) in the control group delivered before the 37th week of gestation. Mean PIBF concentrations in serum samples of patients with threatened pre-term delivery were significantly lower than in those of healthy pregnant women (171.12 +/-162.06 ng/mL versus 272.85 +/- 114.87 ng/mL; P < 0.05).Women with symptoms of threatened pre-term delivery had significantly lower serum levels of IL-10, and higher levels of IL-6 as well as IFNc compared with healthy controls.

CONCLUSION

Our results indicate that measuring PIBF and cytokine concentrations in serum during pregnancy is feasible and may be important for understanding immunological causes of pre-term delivery.

Resistance to lipopolysaccharide-induced preterm delivery mediated by regulatory T cell function in mice

Intrauterine or intraperitoneal administration of lipopolysaccharide (LPS) into normal mice at midgestation induces preterm delivery (PTD) within 24 h through a mechanism dependent on Toll-like receptor signaling and expression of inflammatory cytokines. The exact participants in the cellular network involved in PTD are not known. Although the activities of innate immune cells are thought to be important, the extent to which this process depends on T and B cells has yet to be examined. Mice deficient in T and B cells due to genetic deficiency in the recombination activating gene 1 (Rag1(-/-)) were given LPS intraperitoneally on Day 15 of gestation and found to be susceptible to LPS-induced PTD. This was found to involve many of the inflammatory mediators reported as important in normal mice. Moreover, at a low dose (3 microg), pregnant Rag1(-/-) mice were found to be more susceptible to PTD than a cohort of normal mice on the same genetic background. This increased susceptibility was partially reversed by transfer, on Day 10 of gestation, of whole lymphocytes or purified CD4(+) T cells. Transfer of purified CD4(+) T cells to Rag1(-/-) mice resulted in a uterine draining node population of FOXP3(+) cells, suggesting that these cells may contribute to resistance to LPS-induced PTD. Overall, the data suggest that, although T and B lymphocytes are not critical positive regulators of LPS-induced PTD, CD4(+) T cells play a protective and regulatory role, and thus could be a target for preventive or therapeutic manipulation.

The water channel aquaporin 1 is a novel molecular target of polychlorinated biphenyls for in utero anomalies

Despite serious health risks in humans and wild life, the underlying mechanisms that explain the gene-environment effects of chemical toxicants are largely unknown. Polychlorinated biphenyls (PCBs) are one of the most ubiquitous environmental toxicants worldwide, with reported epidemiological evidence for reproductive and neurocognitive anomalies in humans. Here, we show that Aroclor 1254, a mixture of structurally distinct PCBs, causes preterm birth in interleukin (IL)-10(-/-) mice at a dose that does not show any adverse effects in wild type mice, highlighting the significance of IL-10 as an anti-toxicant cytokine. Aroclor 1254-treated IL-10(-/-) mice demonstrated increased amniotic fluid, intrauterine growth restriction, and reduced litter size with postnatal neuromotor defects. Further, our results identify aquaporin 1 (AQP1), a potent effector of fluid volume regulation and angiogenic activity, as a novel placental target of PCBs. In vivo or in vitro exposure to Aroclor 1254 coupled with IL-10 deficiency significantly reduced the protein content of AQP1. Reduced uterine AQP1 levels were associated with defective spiral artery transformation. Importantly, recombinant IL-10 reversed PCB-induced in vivo and in vitro effects. These data demonstrate for the first time that the IL-10-AQP1 axis is a novel regulator of PCB-induced in utero effects.

Evidence for participation of uterine natural killer cells in the mechanisms responsible for spontaneous preterm labor and delivery

OBJECTIVE

The purpose of this study was to determine in a mouse model whether uterine natural killer (uNK) cell cytotoxic activation induces infection/inflammation-associated preterm labor and delivery.

STUDY DESIGN

Wild type or interleukin (IL)-10(-/-) mice were injected intraperitoneally with lipopolysaccharide on gestational day 14. Mice were either killed for collection of uteroplacental tissue, spleen, and serum or allowed to deliver. Uteroplacental tissue was used for histology and characterization of uNK cells.

RESULTS

Low-dose lipopolysaccharide treatment triggered preterm labor and delivery in IL-10(-/-), but not wild type mice, in a manner independent of progesterone levels. Preterm labor and delivery in IL-10(-/-) mice was associated with an increased number and placental infiltration of cytotoxic uNK cells and placental cell death. Depletion of NK cells or tumor necrosis factor (TNF)-alpha neutralization in these mice restored term delivery. Furthermore, TNF-alpha neutralization prevented uNK cell infiltration and placental cell apoptosis.

CONCLUSION

The uNK cell-TNF-alpha-IL-10 axis plays an important role in the genesis of infection/inflammation-induced preterm labor/delivery.

The anti-inflammatory limb of the immune response in preterm labor, intra-amniotic infection/inflammation, and spontaneous parturition at term: a role for interleukin-10

OBJECTIVE

The anti-inflammatory limb of the immune response is crucial for dampening inflammation. Spontaneous parturition at term and preterm labor (PTL) are mediated by inflammation in the cervix, membranes, and myometrium. This study focuses on the changes in the amniotic fluid concentrations of the anti-inflammatory cytokine interleukin (IL)- 10. The objectives of this study were to determine whether there is a relationship between amniotic fluid concentrations of IL-10 and gestational age, parturition (at term and preterm), and intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

A cross-sectional study was conducted including 301 pregnant women in the following groups: (1) mid-trimester of pregnancy who delivered at term (n = 112); (2) mid-trimester who delivered preterm neonates (n = 30); (3) term not in labor without IAI (n = 40); (4) term in labor without IAI (n = 24); (5) term in labor with IAI (n = 20); (6) PTL without IAI who delivered at term (n = 31); (7) PTL without IAI who delivered preterm (n = 30); (8) PTL with IAI who delivered preterm (n = 14). IL-10 concentrations in amniotic fluid were determined by a specific and sensitive immunoassay. Non-parametric statistics were used for analysis.

RESULTS

(1) IL-10 was detectable in amniotic fluid and its median concentration did not change with gestational age from mid-trimester to term. (2) Patients in labor at term had a significantly higher median amniotic fluid IL-10 concentration than that of patients at term not in labor (p = 0.04). (3) Women at term in labor with IAI had a significantly higher median amniotic fluid IL-10 concentration than that of patients at term in labor without IAI (p = 0.02). (4) Women with PTL and IAI who delivered preterm had a significantly higher median amniotic fluid concentration of IL-10 than those without IAI who delivered preterm and than those who delivered at term (p = 0.009 and p < 0.001, respectively). (5) Among patients with preterm labor without IAI, those who delivered preterm had a significantly higher median amniotic fluid IL-10 concentration than those who delivered at term (p = 0.03).

CONCLUSIONS

The anti-inflammatory cytokine IL-10 is detectable in the amniotic fluid of normal pregnant women. Spontaneous parturition at term and in preterm gestation is associated with increased amniotic fluid concentrations of IL-10. IAI (preterm and at term) is also associated with increased amniotic fluid concentrations of IL-10. We propose that IL-10 has a role in the regulation of the immune response in vivo by initiating actions that dampen inflammation.

Evolution of non-cytotoxic uterine natural killer cells

The immune tolerance and de novo vascularization are two highly intriguing processes at the maternal-fetal interface that appear to be central to normal pregnancy outcome. Immune tolerance occurs despite the local presence of an active maternal immune system including macrophages, dendritic cells and specialized CD56(bright)CD16(-) uterine natural killer (uNK) cells (65-70%). Recent observations indicate that the phenotypic and functional repertoire of uNK cells is distinct from peripheral blood NK and endometrial NK cells, challenging the understanding of their temporal occurrence and function. Origin and specialized programming of uNK cells continue to be debated. uNK cells, replete with an armamentarium to kill the foreign, tolerate the conceptus and facilitate pregnancy. Why do these uNK cells remain non-cytotoxic? Are these NK cells 'multitasking' in nature harboring beneficial and detrimental roles in pregnancy? Are there distinct subpopulations of NK cells that may populate the decidua? We propose that the endometrium/decidua functions as an 'inducible tertiary lymphoid tissue' that supports the recruitment and expansion of CD56(bright)CD16(-) NK cells and induces transcriptional up-regulation of angiogenic machinery in response to exposure to local hormonal factors, cytokine milieu and perhaps hypoxia. The angiogenic features of uNK cells could further result in a 'multitasking' phenotype that still remains to be characterized. This article discusses the factors and pathways that bridge the angiogenic and non-cytotoxic response machineries at the maternal-fetal interface.

Inflammation in pregnancy: its roles in reproductive physiology, obstetrical complications, and fetal injury

Fetal development and growth occur in a sterile amniotic cavity while first exposure to microorganisms happens at birth. However, at least 25% of all preterm births, the leading cause of perinatal morbidity and mortality worldwide, occur in mothers with microbial invasion of the amniotic cavity. Microbial attack of the fetus takes place in approximately 10% of pregnancies with intra-amniotic infection, and the human fetus is capable of deploying an inflammatory response (cellular and humoral) in the mid-trimester of pregnancy. The onset of premature labor in the context of infection is mediated by pro-inflammatory cytokines, such as interleukin (IL)-1beta and tumor necrosis factor alpha (TNF-alpha), as these cytokines are produced by intrauterine tissues in response to microbial products, can stimulate prostaglandin production, and induce labor in animals. Moreover, knockout experiments suggest that infection is less likely to lead to premature labor when the IL-1 and TNF signaling pathways are disrupted. A fetal inflammatory systemic response occurs in a fraction of fetuses exposed to microorganisms in utero, and is associated with the impending onset of labor as well as multisystem organ involvement. Neonates born with funisitis, the histologic marker of such inflammation, are at increased risk for neurologic handicap and cerebral palsy. Evidence has begun to accumulate that gene-environment interactions determine the likelihood of preterm labor and delivery and, probably, the risk of fetal injury. Fetal inflammation has emerged as a major mechanism of disease responsible for complications in the perinatal period (in utero and in the first 28 days of life), as well as in infancy. Moreover, reprogramming of the fetal immune response may predispose to diseases in adulthood.

Interleukin-10 protects cultured fetal rat type II epithelial cells from injury induced by mechanical stretch

Mechanical ventilation plays a central role in the pathogenesis of bronchopulmonary dysplasia. However, the mechanisms by which excessive stretch of fetal or neonatal type II epithelial cells contributes to lung injury are not well defined. In these investigations, isolated embryonic day 19 fetal rat type II epithelial cells were cultured on substrates coated with fibronectin and exposed to 5% or 20% cyclic stretch to simulate mechanical forces during lung development or lung injury, respectively. Twenty percent stretch of fetal type II epithelial cells increased necrosis, apoptosis, and proliferation compared with control, unstretched samples. By ELISA and real-time PCR (qRT-PCR), 20% stretch increased secretion of IL-8 into the media and IL-8 gene expression and inhibited IL-10 release. Interestingly, administration of recombinant IL-10 before 20% stretch did not affect cell lysis but significantly reduced apoptosis and IL-8 release compared with stretched samples without IL-10. Collectively, our studies suggest that IL-10 may play an important role in protection of fetal type II epithelial cells from injury secondary to stretch.

Visfatin/Pre-B cell colony-enhancing factor in amniotic fluid in normal pregnancy, spontaneous labor at term, preterm labor and prelabor rupture of membranes: an association with subclinical intrauterine infection in preterm parturition

OBJECTIVE

Visfatin, a novel adipokine originally discovered as a pre-B-cell colony enhancing factor, is expressed by amniotic epithelium, cytotrophoblast, and decidua and is over-expressed when fetal membranes are exposed to mechanical stress and/or pro-inflammatory stimuli. Visfatin expression by fetal membranes is dramatically up-regulated after normal spontaneous labor. The aims of this study were to determine if visfatin is detectable in amniotic fluid (AF) and whether its concentration changes with gestational age, spontaneous labor, preterm prelabor rupture of membranes (preterm PROM) and in the presence of microbial invasion of the amniotic cavity (MIAC).

METHODS

In this cross-sectional study, visfatin concentration in AF was determined in patients in the following groups: 1) mid-trimester (n=75); 2) term not in labor (n=27); 3) term in spontaneous labor (n=51); 4) patients with preterm labor with intact membranes (PTL) without MIAC who delivered at term (n=35); 5) patients with PTL without MIAC who delivered preterm (n=52); 6) patients with PTL with MIAC (n=25); 7) women with preterm PROM without MIAC (n=26); and 8) women with preterm PROM with MIAC (n=26). Non-parametric statistics were used for analysis.

RESULTS

1) The median AF concentration of visfatin was significantly higher in patients at term than in mid-trimester; 2) Among women with PTL who delivered preterm, the median visfatin concentration was significantly higher in patients with MIAC than those without MIAC; 3) Similarly, patients with PTL and MIAC had a higher median AF visfatin concentration than those with PTL who delivered at term; 4) Among women with preterm PROM, the median AF visfatin concentration was significantly higher in patients with MIAC than those without MIAC.

CONCLUSIONS

1) Visfatin is a physiologic constituent of AF; 2) The concentration of AF visfatin increases with advancing gestational age; 3) AF visfatin concentration is elevated in patients with MIAC, regardless of the membrane status, suggesting that visfatin participates in the host response against infection.

Premature labor: a state of platelet activation?

OBJECTIVE

This study was undertaken to determine whether premature labor is associated with changes in the maternal plasma concentration of soluble CD40 ligand (sCD40L), a marker of platelet activation.

METHODS

A cross-sectional study included patients in the following groups: 1) non-pregnant (n=21); 2) normal pregnancy (n=71); 3) normal pregnancy at term with (n=67) and without labor (n=88); 4) preterm labor (PTL) with intact membranes (n=136) that was divided into the following sub-groups: 4a) PTL who delivered at term (n=49); 4b) PTL without intra-amniotic infection and/or inflammation (IAI) who delivered preterm (n=54); and 4c) PTL with IAI who delivered preterm (n=33). sCD40L concentrations were measured by ELISA.

RESULTS

The median maternal plasma sCD40L concentration was higher in pregnant than non-pregnant women (P=0.017). Patients with PTL had a higher median maternal plasma sCD40L concentration than women with normal pregnancies, regardless of the presence or absence of IAI and gestational age at delivery (P<0.001 for all comparisons). IAI was not associated with a higher median maternal plasma concentration of sCD40L.

CONCLUSIONS

Normal pregnancy is a state in which there is a physiologic increase of sCD40L. PTL was associated with an increased median maternal plasma sCD40L concentration that could not be accounted for by IAI. Thus, our findings suggest that platelet activation occurs during an episode of preterm labor.

Nutritionally essential fatty acids and biologically indispensable cyclooxygenases

The study of cyclooxygenases (COXs), targets of aspirin and related drugs, is rooted in the discovery of essential fatty acids (EFAs). There are two COXs that convert EFAs, primarily arachidonic acid, to prostaglandins. Each COX is involved with distinct biologies. COX-1 expression is constitutive while COX-2 is inducible. The two COXs might have evolved partly to permit prostaglandin formation at different tissue sites. However, COX-2 is sometimes induced in cells already expressing COX-1, and in these instances, COX-2 functions while COX-1 is latent. This can occur because of unique biochemical properties of COX-2 that enable cells to form prostaglandins when arachidonic acid comprises a small fraction of available fatty acids and the concentrations of peroxides that are necessary for COX to function are low.

Variations in cervical IL-10 and IL-8 concentrations throughout gestation in normal pregnancies

PROBLEM

Data regarding cervical interleukin 18 (IL-8) and IL-10 concentrations during pregnancy is limited.

METHOD OF STUDY

This was a cross sectional study of healthy pregnant women. Specimens were collected from the cervical os secretions. IL-8 and IL-10 levels were measured by using enzyme-linked immunosorbent assay. Median (range) cytokine concentrations were derived for each trimester and compared across trimesters. The relationship between gestational age and cytokine levels was assessed by regression analysis. The mean of the ratios of IL-8 to IL-10 was compared in each trimester using anova.

RESULTS

The median (range) IL-8 concentrations in cervical secretions were in pg/mL: 1562 (1210-4100), 2460 (1047-4688), 3660 (1451-4748) (P < 0.0021); the median (range) IL-10 concentrations in cervical secretions were in pg/mL: 38.3 (6.8-227.9), 10.9 (0-263.3), 9.5 (0-35.6); the mean IL10/IL-8 x 100 (+/- standard deviation) concentrations were: 3.33 +/- 0.65, 1.47 +/- 0.41, 0.38 +/- 0.52 (P = 0.0035) during the first, second and third trimesters, respectively.

CONCLUSION

The patterns of cervical IL-8 concentration is inversely related to gestational age, and the ratio of IL-10/IL-8 decreases with advancing gestation.

Influence of labor on neonatal neutrophil apoptosis, and inflammatory activity

Neutrophil apoptosis is impaired in neonates, and this contributes to prolonged inflammation and tissue injury in infants after infection or trauma. In the present studies, we investigated whether labor generates mediators that further suppress apoptosis. We found that neutrophil apoptosis was reduced in neonates exposed to labor, when compared with infants delivered by cesarean section before labor. This was not due to alterations in caspase-3 or inhibitor of apoptosis protein-2 (IAP-2). In contrast, labor primed neutrophils to express tumor necrosis factor alpha (TNF-alpha), suggesting that proinflammatory mediators contribute to reduced apoptosis after labor. Eicosanoids generated via cyclooxygenase-2 (Cox-2) and lipoxygenase (Lox) also regulate neutrophil apoptosis. 15-Lox, which generates proapoptotic lipoxins, but not Cox-2, was greater in neutrophils before labor, relative to cells exposed to labor. Anti-inflammatory eicosanoids exert their effects in part via peroxisome proliferator-activated receptor gamma (PPAR-gamma). Expression of gelatinase-associated lipocalin and catalase, two markers of PPAR-gamma activity, were increased in neonatal neutrophils before labor, relative to cells exposed to labor. These findings suggest that the anti-inflammatory environment is maintained before labor, in part, by eicosanoids. Although increased neutrophil longevity after labor is important for host defense in the immediate newborn period, it may contribute to inflammatory or oxidative injury in susceptible infants.

The role of inflammation and infection in preterm birth

Inflammation has been implicated in the mechanisms responsible for preterm and term parturition, as well as fetal injury. Out of all of the suspected causes of preterm labor and delivery, infection and/or inflammation is the only pathological process for which both a firm causal link with preterm birth has been established and a molecular pathophysiology defined. Inflammation has also been implicated in the mechanism of spontaneous parturition at term. Most cases of histopathological inflammation and histological chorioamnionitis, both in preterm and term labor, are sub-clinical in nature. The isolation of bacteria in the amniotic fluid, known as microbial invasion of the amniotic cavity, is a pathological finding; the frequency of which is dependent upon the clinical presentation and gestational age. This article reviews the role of inflammation in preterm and term parturition.

The preterm parturition syndrome

The implicit paradigm that has governed the study and clinical management of preterm labour is that term and preterm parturition are the same processes, except for the gestational age at which they occur. Indeed, both share a common pathway composed of uterine contractility, cervical dilatation and activation of the membranes/decidua. This review explores the concept that while term labour results from physiological activation of the components of the common pathway, preterm labour arises from pathological signalling and activation of one or more components of the common pathway of parturition. The term "great obstetrical syndromes" has been coined to reframe the concept of obstetrical disease. Such syndromes are characterised by: (1) multiple aetiology; (2) long preclinical stage; (3) frequent fetal involvement; (4) clinical manifestations that are often adaptive in nature; and (5) gene-environment interactions that may predispose to the syndromes. This article reviews the evidence indicating that the pathological processes implicated in the preterm parturition syndrome include: (1) intrauterine infection/inflammation; (2) uterine ischaemia; (3) uterine overdistension; (4) abnormal allograft reaction; (5) allergy; (6) cervical insufficiency; and (7) hormonal disorders (progesterone related and corticotrophin-releasing factor related). The implications of this conceptual framework for the prevention, diagnosis, and treatment of preterm labour are discussed.