Degree of lung maturity determines the direction of the interleukin-1- induced effect on the expression of surfactant proteins

Lamellar body count: Marker for foetal lung maturation promoted by intra-amniotic infection and/or inflammation

OBJECTIVE

There is evidence indicating that the risk of respiratory distress syndrome is reduced in preterm neonates exposed to intra-amniotic infection and/or inflammation. We hypothesised that foetal lung maturation promoted by intra-amniotic infection and/or inflammation results in elevated lamellar body count (LBC) in amniotic fluid (AF). This study aimed to determine the relationship between LBC in AF and intra-amniotic infection and/or inflammation in patients with threatened preterm birth.

STUDY DESIGN

This was a retrospective cohort study of patients with threatened preterm birth. A total of 104 consecutive pregnant women underwent amniocentesis in the early preterm period [gestational age < 34 weeks] to evaluate intra-amniotic infection and/or inflammation and foetal lung maturity. Intra-amniotic infection was confirmed by positive AF culture results for aerobic/anaerobic bacteria, fungi, and genital mycoplasma. Intra-amniotic inflammation was defined as a positive AF matrix metalloproteinase-8 rapid test. Outcomes of the study population were compared according to LBC in AF using a cut-off of 15,000/mm³.

RESULTS

The rates of elevated LBC and intra-amniotic infection and/or inflammation were 23% (24/104) and 52% (54/104), respectively. The median LBC was significantly higher in patients with intra-amniotic infection and/or inflammation than in those without [median LBC, 9,000/mm³ (interquartile range, IQR: 3,000-39,000) vs. 3,000/mm³ (IQR: 2,750-5,000), p < 0.001]. Intra-amniotic infection and/or inflammation was observed in 96% (23/24) of patients with elevated LBC and 39% (31/80) of patients without elevated LBC (p < 0.001). On multivariable analysis, the presence of intra-amniotic infection and/or inflammation was significantly associated with elevated LBC with an odds ratio (OR) of 66.0 [95% confidence interval (CI) 6.6-664.4, p < 0.001], even after accounting for gestational age at amniocentesis being a significantly related factor for predicting elevated LBC with an OR of 1.5 (95% CI 1.1-2.0, p = 0.004).

CONCLUSION

LBC elevation was independently associated with the presence of intra-amniotic infection and/or inflammation in women with early threatened preterm birth (gestational age < 34 weeks). This finding may support the view that an intra-amniotic inflammatory response promotes foetal lung maturation that can be detected by elevated LBC in AF.

Pulmonary surfactant: a unique biomaterial with life-saving therapeutic applications

Pulmonary surfactant is a complex lipoprotein mixture secreted into the alveolar lumen by type 2 pneumocytes, which is composed by tens of different lipids (approximately 90% of its entire mass) and surfactant proteins (approximately 10% of the mass). It is crucially involved in maintaining lung homeostasis by reducing the values of alveolar liquid surface tension close to zero at end-expiration, thereby avoiding the alveolar collapse, and assembling a chemical and physical barrier against inhaled pathogens. A deficient amount of surfactant or its functional inactivation is directly linked to a wide range of lung pathologies, including the neonatal respiratory distress syndrome. This paper reviews the main biophysical concepts of surfactant activity and its inactivation mechanisms, and describes the past, present and future roles of surfactant replacement therapy, focusing on the exogenous surfactant preparations marketed worldwide and new formulations under development. The closing section describes the pulmonary surfactant in the context of drug delivery. Thanks to its peculiar composition, biocompatibility, and alveolar spreading capability, the surfactant may work not only as a shuttle to the branched anatomy of the lung for other drugs but also as a modulator for their release, opening to innovative therapeutic avenues for the treatment of several respiratory diseases.

Synthetic surfactant with a recombinant surfactant protein C analogue improves lung function and attenuates inflammation in a model of acute respiratory distress syndrome in adult rabbits

AIM

In acute respiratory distress syndrome (ARDS) damaged alveolar epithelium, leakage of plasma proteins into the alveolar space and inactivation of pulmonary surfactant lead to respiratory dysfunction. Lung function could potentially be restored with exogenous surfactant therapy, but clinical trials have so far been disappointing. These negative results may be explained by inactivation and/or too low doses of the administered surfactant. Surfactant based on a recombinant surfactant protein C analogue (rSP-C33Leu) is easy to produce and in this study we compared its effects on lung function and inflammation with a commercial surfactant preparation in an adult rabbit model of ARDS.

METHODS

ARDS was induced in adult New Zealand rabbits by mild lung-lavages followed by injurious ventilation (V_T 20 m/kg body weight) until P/F ratio < 26.7 kPa. The animals were treated with two intratracheal boluses of 2.5 mL/kg of 2% rSP-C33Leu in DPPC/egg PC/POPG, 50:40:10 or poractant alfa (Curosurf®), both surfactants containing 80 mg phospholipids/mL, or air as control. The animals were subsequently ventilated (V_T 8-9 m/kg body weight) for an additional 3 h and lung function parameters were recorded. Histological appearance of the lungs, degree of lung oedema and levels of the cytokines TNFα IL-6 and IL-8 in lung homogenates were evaluated.

RESULTS

Both surfactant preparations improved lung function vs. the control group and also reduced inflammation scores, production of pro-inflammatory cytokines, and formation of lung oedema to similar degrees. Poractant alfa improved compliance at 1 h, P/F ratio and PaO₂ at 1.5 h compared to rSP-C33Leu surfactant.

CONCLUSION

This study indicates that treatment of experimental ARDS with synthetic lung surfactant based on rSP-C33Leu improves lung function and attenuates inflammation.

Vulnerability of the developing airway

Longer term respiratory morbidity is a frequent concern for former preterm infants. Increased airway reactivity and wheezing disorders are extremely common in this population, both in infants who meet diagnostic criteria for bronchopulmonary dysplasia [BPD], and in the absence of this diagnosis. It is, therefore, imperative to gain a better understanding of normal and abnormal postnatal development of the immature airway. Airway hyperreactivity may be secondary to abnormal bronchoalveolar attachments in the face of parenchymal lung injury, or secondary to an imbalance between constrictor and dilator neural pathways. Finally, the airway itself may undergo functional and/or structural changes, including increased airway smooth muscle mass, and changes in airway extracellular matrix which may, in turn, modulate downstream signaling pathways to hyperoxia or pressure exposed vulnerable airways.

Inhibition of IκBβ/NFκB signaling prevents LPS-induced IL1β expression without increasing apoptosis in the developing mouse lung

BackgroundThe pro-inflammatory consequences of IL1β expression contribute to the pathogenesis of bronchopulmonary dysplasia. Selectively targeting Lipopolysaccharide (LPS)-induced IκBβ/NFκB signaling attenuates IL1β mRNA expression in macrophages. Whether targeting IκBβ/NFκB signaling affects the anti-apoptotic gene expression, a known consequence of global LPS-induced NFκB inhibition, is unknown.MethodsMacrophages (RAW 264.7, bone marrow-derived macrophage) were assessed for LPS-induced IL1β mRNA/protein expression, anti-apoptotic gene expression, cell viability (trypan blue exclusion), and activation of apoptosis (caspase-3 and PARP cleavage) following pharmacologic and genetic attenuation of IκBβ/NFκB signaling. Expressions of IL1β and anti-apoptotic genes were assessed in endotoxemic newborn mice (P0) with intact (WT), absent (IκBβ KO), and attenuated (IκBβ overexpressing) IκBβ/NFκB signaling.ResultsIn cultured macrophages, pharmacologic and genetic inhibition of LPS-induced IκBβ/NFκB signaling significantly attenuated IL1β mRNA and protein expression. Importantly, targeting IκBβ/NFκB signaling did not attenuate LPS-induced expression of anti-apoptotic genes or result in cell death. In endotoxemic neonatal mice, targeting LPS-induced IκBβ/NFκB signaling significantly attenuated pulmonary IL1β expression without affecting the anti-apoptotic gene expression.ConclusionTargeting IκBβ/NFκB signaling prevents LPS-induced IL1β expression without inducing apoptosis in cultured macrophages and in the lungs of endotoxemic newborn mice. Inhibiting this pathway may prevent inflammatory injury without affecting the protective role of NFκB activity in the developing lung.

Runt-Related Transcription Factor 1 Regulates LPS-Induced Acute Lung Injury via NF-κB Signaling

Runt-related transcription factor 1 (RUNX1), a transcription factor expressed in multiple organs, plays important roles in embryonic development and hematopoiesis. Although RUNX1 is highly expressed in pulmonary tissues, its roles in lung function and homeostasis are unknown. We sought to assess the role of RUNX1 in lung development and inflammation after LPS challenge. Expression of RUNX1 was assessed in the developing and postnatal lung. RUNX1 was conditionally deleted in pulmonary epithelial cells. Pulmonary maturation was evaluated in the developing and postnatal lung, and lung inflammation was investigated in adult mice after LPS challenge. Interactions between RUNX1 and inflammatory signaling via NF-κB-IkB kinase β were assessed in vitro. RUNX1 was expressed in both mesenchymal and epithelial compartments of the developing and postnatal lung. The RUNX1 gene was efficiently deleted from respiratory epithelial cells producing Runx1^∆/∆ mice. Although lung maturation was delayed, Runx1^∆/∆ mice survived postnatally and subsequent growth and maturation of the lung proceeded normally. Increased respiratory distress, inflammation, and proinflammatory cytokines were observed in the Runx1-deleted mice after pulmonary LPS exposure. RUNX1 deletion was associated with the activation of NF-κB in respiratory epithelial cells. RUNX1 was required for the suppression of NF-κB signaling pathway via inhibition of IkB kinase β in in vitro studies. RUNX1 plays a critical role in the lung inflammation after LPS-induced injury.

Meconium-induced inflammation and surfactant inactivation: specifics of molecular mechanisms

This review summarizes neonatal meconium aspiration syndrome in light of meconium-induced inflammation and inflammatory surfactant inactivation, related to both endogenous and therapeutic exogenous surfactant. The wide effect of meconium on surfactant properties is divided into three points. Direct effect of meconium on surfactant properties refers mainly to fragmentation of dipalmitoylphosphatidylcholine and other surfactant phospholipids together with cleavage of surfactant proteins. Initiation of inflammatory response due to activation of receptors by yet unspecified compounds involves complement and Toll-like receptor activation. A possible role of lung collectins, surfactant proteins A and D, which can exert both pro- and anti-inflammatory reactions, is discussed. Initiation of inflammatory response by specified compounds in meconium reflects inflammatory functioning of cytokines, bile acids, and phospholipases contained in meconium. Unifying sketch of many interconnections in all these actions aims at providing integrated picture of inflammatory surfactant inactivation.

miR-124 regulates fetal pulmonary epithelial cell maturation

MicroRNAs are a family of small noncoding RNAs that regulate the expression of their target proteins at the posttranscriptional level. Their functions cover almost every aspect of cell physiology. However, the roles of microRNAs in fetal lung development are not completely understood. The objective of this study is to investigate the regulation and molecular mechanisms of alveolar epithelial cell maturation during fetal lung development by miR-124. We discovered that miR-124 was downregulated during rat fetal lung development and predominantly expressed in the epithelial cells at late stage of the lung development. Overexpression of miR-124 with an adenovirus vector led to the inhibition of epithelial maturation in rat fetal lung organ cultures and fetal alveolar epithelial type II cells, as demonstrated by a decrease in the type II cell marker expression and an increase in glycogen content. We further demonstrated by luciferase reporter assays that miR-124 inhibited the NF-κB, cAMP/PKA, and MAPK/ERK pathways. In addition, nuclear factor I/B (NFIB), a critical protein in fetal lung maturation, was validated as a direct target of miR-124. Furthermore, miR-124 expression was induced by the Wnt/β-catenin signaling pathway through a direct interaction of LEF1 and the miR-124 promoter region. We concluded that miR-124 downregulation is critical to fetal lung epithelial maturation and miR-124 inhibits this maturation process at least partially through the inhibition of NFIB.

Thrown off balance: the effect of antenatal inflammation on the developing lung and immune system

In recent years, translational research with various animal models has been helpful to answer basic questions about the effect of antenatal inflammation on maturation and development of the fetal lung and immune system. The fetal lung and immune systems are very plastic and their development can be conditioned and influenced by both endogenous and/or exogenous factors. Antenatal inflammation can induce pulmonary inflammation, leading to lung injury and remodeling in the fetal lung. Exposure to antenatal inflammation can induce interleukin-1α production, which enhances surfactant protein and lipid synthesis thereby promoting lung maturation. Interleukin-1α is therefore a candidate for the link between lung inflammation and lung maturation, preventing respiratory distress syndrome in preterm infants. Antenatal inflammation can, however, cause structural changes in the fetal lung and affect the expression of growth factors, such as transforming growth factor-beta, connective tissue growth factor, fibroblast growth factor-10, or bone morphogenetic protein-4, which are essential for branching morphogenesis. These alterations cause alveolar and microvascular simplification resembling the histology of bronchopulmonary dysplasia. Antenatal inflammation may also affect neonatal outcome by modulating the responsiveness of the immune system. Lipopolysaccharide-tolerance (endotoxin hyporesponsiveness/immunoparalysis), induced by exposure to inflammation in utero, may prevent fetal lung damage, but increases susceptibility to postnatal infections. Moreover, prenatal exposure to inflammation appears to be a predisposition for the development of adverse neonatal outcomes, like bronchopulmonary dysplasia, if the preterm infant is exposed to a second postnatal hit, such as mechanical ventilation oxygen exposure, infections, or steroids.

Pilot trial of late booster doses of surfactant for ventilated premature infants

OBJECTIVE

Many premature infants at risk for bronchopulmonary dysplasia experience episodes of surfactant dysfunction with reduced surfactant protein B (SP-B). In this study, we investigated the safety and responses to booster doses of surfactant.

STUDY DESIGN

A total of 87 infants, 500 to 1250 g birth weight, who were ventilated at 7 to 10 days received 2 or 3 doses of Infasurf (Calfactant, Forest Pharmaceuticals, St Louis, MO, USA) within a 1-week period.

RESULT

For 184 doses, occurrence rates of transient bradycardia (13) and plugged endotracheal tube (5) were low, and no other adverse effects were noted. Treatment transiently improved the respiratory severity score (FiO(2) × mean airway pressure), SP-B content (+75%) and surface properties of isolated surfactant. Levels of eight proinflammatory cytokines in tracheal aspirate were interrelated and unchanged from baseline after surfactant treatment.

CONCLUSION

Booster doses of surfactant for premature infants with lung disease are safe and transiently improve respiratory status as well as composition and function of endogenous surfactant.

Complement component C4A and apolipoprotein A-I in plasmas as biomarkers of the severe, early-onset preeclampsia

Preeclampsia is a common pregnancy complication that is associated with maternal perinatal morbidity and mortality. Because of its early onset (before 34 weeks) and the potential for serious outcomes, severe, early-onset preeclampsia (sePE) should be regarded as a different form of preeclampsia. It is an important cause of preterm birth and fetal growth restriction and adverse maternal and neonatal outcomes. As there is no diagnostic test yet available for this disease, we used a proteomic approach to identify novel plasma biomarkers for developing severe, early-onset preeclampsia. We conducted case-control studies comparing nulliparous women with severe preeclampsia requiring delivery prior to 34 weeks of gestation with healthy nulliparous women matched by gestational age at sampling. Plasma was depleted of albumin and IgG and analyzed by two-dimensional gel electrophoresis (2DE). Seven specific plasma proteins for early-onset preeclampsia were detected by mass spectrometry had statistically significant expression differences when compared to controls. The expression of complement component C4A and apolipoprotein A-I were validated by immunoblotting. The complement component C4A in the plasmas of sePE women is lower than the severe, late-onset PE (slPE) women [mean ± SD; 3.05 ± 0.14 times reference level (normal/sePE) in sePE women vs. 2.73 ± 0.10 times reference level (normal/slPE) in slPE women, P < 0.05]. Apolipoprotein A-I is higher in sePE women than slPE women [mean ± SD; 1.58 ± 0.14 times reference level (sePE/normal) in sePE women vs. 1.04 ± 0.16 times reference level (slPE/normal) in slPE women, P < 0.05]. Furthermore, C4A can accurately distinguish severe PE (sePE and slPE) from mild PE (mePE and mlPE) and was proved by the results of ELISA. Further studies have been done to determine the relation between PE and hypoxia. JAR cells were cultured under hypoxia for 72 h. Total cellular proteins were gathered and lysed. Lower C4A and higher apolipoprotein A-I had been observed in JAR of hypoxia conditions than normoxia conditions through western blotting. The result proved that PE is correlated with hypoxia. In summary, C4A and apolipoprotein A-I are able to function as markers to distinguish ePE women from lPE women, and severe PE from mild PE, or perhaps even as disease predictors that might become relevant for diagnostics.

Intra-amniotic infection increases amniotic lamellar body count before 34 weeks of gestation

OBJECTIVE

To examine the lamellar body count (LBC) value in intra-amniotic infection cases and evaluate its association with the incidence of respiratory distress syndrome (RDS).

METHODS

Three hundred sixty-five amniotic fluid (AF) samples were obtained at caesarean section from 27 to 38 weeks of gestation. LBC and glucose concentrations in AF were measured with no centrifugation. We defined AF glucose concentrations<0.8 mmol/L and positive C-reactive protein (CRP) of the neonates as intra-amniotic infection.

RESULTS

An LBC cutoff value of 29,500/μL resulted in 94.0% sensitivity, 82.4% specificity, and 99.1% negative predictive value (NPV) for RDS. Neonates with glucose concentrations<0.8 mmol/L in AF and positive CRP had no RDS and significantly higher LBC values than controls before 34 weeks of gestation (17.0 vs. 4.3, p<0.05 and 25.5 vs. 5.0, p<0.05, respectively), but there were no significant differences after 34 weeks of gestation.

CONCLUSIONS

LBC is an accurate predictor of foetal lung maturity and our LBC cutoff value had a high NPV for predicting RDS. We showed that intra-amniotic infection was associated with significantly higher LBC values than the value in controls before 34 weeks of gestation, which correlated with a low incidence of RDS.

Prenatal inflammation and lung development

Prenatal exposure of very low birth weight infants to chronic indolent chorioamnionitis with organisms such as mycoplasma and ureaplasma is frequent. Chorioamnionitis is inconsistently associated with changed risks of respiratory distress syndrome (RDS) or bronchopulmonary dysplasia (BPD), probably because the diagnosis of chorioamnionitis does not quantify the extent or duration of the fetal exposures to infection and inflammation. The correlations between prenatal exposures and postnatal lung disease also are confounded by the imprecision of the diagnoses of RDS and BPD. In animal models, chorioamnionitis caused by pro-inflammatory mediators or live ureaplasma induces lung maturation, but also causes alveolar simplification and vascular injury. Intra-amniotic endotoxin administration also modulates the fetal innate immune system, resulting in maturation of monocytes to alveolar macrophages and the induction or paralysis of inflammatory responses depending on exposure history. Prenatal inflammation can have profound effects on the fetal lung and subsequent immune responses.

Amniotic fluid concentration of surfactant proteins in intra-amniotic infection

OBJECTIVE

Pulmonary surfactant is a complex molecule of lipids and proteins synthesized and secreted by type II alveolar cells into the alveolar epithelial lining. Both lipid and protein components are essential for lung function in postnatal life. Infection is a well-established cause of preterm delivery, and several inflammatory cytokines play a role in the mechanisms of preterm parturition. An increased concentration of inflammatory cytokines in amniotic fluid or fetal plasma has been linked to the onset of preterm parturition and fetal/neonatal injury, including cerebral palsy and chronic lung disease. Experimental evidence indicates that inflammatory mediators also regulate surfactant protein synthesis, and histologic chorioamnionitis is associated with a decreased incidence of hyaline membrane disease in neonates. This study was conducted to determine if amniotic fluid concentrations of surfactant protein (SP)-A, SP-B, and SP-D change in patients with and without intra-amniotic infection (IAI).

MATERIALS AND METHODS

A case-control study was conducted to determine amniotic fluid concentrations of SP-A, SP-B, SP-D, and total protein in patients who had an amniocentesis performed between 18 and 34 weeks of gestation for the detection of IAI in patients with spontaneous preterm labor with intact membranes (n = 42) and cervical insufficiency prior to the application of cerclage (n = 6). Amniotic fluid samples were selected from a bank of biological specimens and included patients with (n = 16) and without (n = 32) IAI matched for gestational age at amniocentesis. Intra-amniotic infection was defined as a positive amniotic fluid culture for microorganisms. Each group was further subdivided according to a history of corticosteroid administration within 7 days prior to amniocentesis into the following subgroups: (1) patients without IAI who had received antenatal corticosteroids (n = 21), (2) patients with IAI who had received antenatal corticosteroids (n = 9), (3) patients without IAI who had not received antenatal corticosteroids (n = 11), and (4) patients with IAI who had not received antenatal corticosteroids (n = 7). Amniotic fluid was obtained by transabdominal amniocentesis. SP-A, SP-B, and SP-D concentrations in amniotic fluid were determined by enzyme-linked immunosorbent assay (ELISA). Non-parametric statistics were used for analysis.

RESULTS

Women with IAI had a higher median amniotic fluid concentration of SP-B and of SP-B/total protein, but not other SPs, than those without IAI (both p = 0.03). Among patients who had received antenatal corticosteroids, the median amniotic fluid concentration of SP-B and of SP-B/total protein was significantly higher in patients with IAI than in those without IAI (SP-B, IAI: median 148 ng/mL, range 37.3-809 ng/mL vs. without IAI: median 7.2 ng/mL, range 0-1035 ng/mL; p = 0.005 and SP-B/total protein, IAI: median 14.1 ng/mg, range 4.3-237.5 ng/mg vs. without IAI: median 1.45 ng/mg, range 0-79.5 ng/mg; p = 0.003). Among women who had not received antenatal corticosteroids, the median amniotic fluid concentrations of SP-B and of SP-B/total protein were not significantly different between patients with and without IAI (SP-B, IAI: median 4 ng/mL, range 0-31.4 ng/mL vs. without IAI: median 3.4 ng/mL, range 0-37 ng/mL; p = 0.8 and SP-B/total protein, IAI: median 0.55 ng/mg, range 0-6.96 ng/mg vs. without IAI: median 0.59 ng/mg, range 0-3.28 ng/mg; p = 0.9). The median amniotic fluid concentrations of SP-A, SP-A/total protein, SP-D, and SP-D/total protein were not significantly different between patients with and without IAI whether they received antenatal corticosteroids or not (all p > 0.05).

CONCLUSIONS

IAI was associated with an increased amniotic fluid concentration of SP-B in patients who received antenatal corticosteroids within 7 days prior to amniocentesis.

Cord immunoproteins as predictors of respiratory outcome in preterm infants

OBJECTIVE

The purpose of this study was to evaluate the role of cord blood proteins and antenatal factors in the prediction of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD).

STUDY DESIGN

The prospectively collected cohort included 163 infants. All infants were born between 1998-2002 in a single regional hospital before 32 weeks of gestation and survived the first hospitalization. Altogether, 107 cord blood proteins were analyzed. Twenty-two antenatal clinical factors were included in the data mining and logistic regression analyses.

RESULTS

The incidence of RDS was 64% and of BPD was 25%. Histologic chorioamnionitis protected from RDS (odds ratio [OR], 0.24; 95% confidence interval [CI], 0.11-0.53; P < .001). Besides the length of gestation, other clinical factors poorly predicted the outcomes. Matrix metalloproteinase-9 independently predicted RDS (OR, 8.3; 95% CI, 3.0-23.1; P < .001). Soluble glycoprotein 130 independently predicted BPD (OR, 6.07; 95%CI, 2.20-16.7; P < .001).

CONCLUSION

Specific antenatal immunologic activation predicts either acute or chronic respiratory disease in very preterm infants.

Identification of proteomic biomarkers of preeclampsia in amniotic fluid using SELDI-TOF mass spectrometry

OBJECTIVE

To identify proteomic biomarkers in amniotic fluid (AF) that can distinguish preeclampsia (PE) from chronic hypertension (CHTN) and normotensive controls (CTR).

METHODS

AF from women with PE, CHTN, and CTR were subjected to proteomic analysis by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry.

RESULTS

Proteomic profiling of AF identified 2 biomarkers: peak X (17399.11 Da), which distinguished PE from CTR, and peak Y (28023.34 Da), which distinguished PE and CHTN from CTR. High performance liquid chromatography fractions containing the biomarkers were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in-gel tryptic digestion. The biomarkers were matched to proapolipoprotein A-I (peak Y) and a functionally obscure peptide, SBBI42 (peak X). Western blot analysis confirmed that AF from PE and CHTN had higher proapolipoprotein A-I levels than CTR.

CONCLUSION

Proteomic analysis of AF can distinguish PE from CHTN and CTR. The discriminatory proteins were identified as proapolipoprotein A-I and SBBI42.

Cytokine gene polymorphisms in Italian preterm infants: association between interleukin-10 -1082 G/A polymorphism and respiratory distress syndrome

In this study, we determined the genotype frequencies of polymorphisms of cytokine genes and investigated their association with the risk of respiratory distress syndrome (RDS) in preterm infants. Genetic polymorphisms in the cytokines interleukin (IL)-10, IL-8, and tumor necrosis factor (TNF) alpha, were studied in 342 white Italian newborns (112 without RDS, 66 prematurely born with RDS, and 164 infants born at term who were included as healthy controls). The polymorphisms were analyzed by polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP). The IL-10 mRNA levels were analyzed according to genotype by quantitative real-time PCR (QRT-PCR) in Epstein-Barr virus-transformed lymphoblastoid cell lines (EBV-LCLs) of 42 full-term healthy infants. Logistic regression analysis demonstrated the risk of RDS to be significantly lower in preterm infants with an IL-10 -1082 GG/GA genotype than in those with an AA genotype [odds ratio (OR) = 0.48, 95% confidence interval (CI): 0.24-0.95, p = 0.03]. QRT-PCR analyses showed that the IL-10 mRNA levels were significantly higher in 27 IL-10 -1082 GG/GA carriers compared with 15 IL-10 -1082 AA carriers (p = 0.03). We conclude that the IL-10 -1082 GG/GA polymorphism may have a role in RDS development in premature infants.

Respiratory mechanics in brain-damaged patients

OBJECTIVE

To assess respiratory mechanics on the 1st and 5th days of mechanical ventilation in a cohort of brain-damaged patients on positive end-expiratory pressure (PEEP) of 8 cmH(2)O or zero PEEP (ZEEP).

DESIGN AND SETTING

Physiological study with randomized control trial design in a multidisciplinary intensive care unit of a university hospital.

PATIENTS AND MEASUREMENTS

Twenty-one consecutive mechanically ventilated patients with severe brain damage and no acute lung injury were randomly assigned to be ventilated with ZEEP (n = 10) or with 8 cmH(2)O of PEEP (n = 11). Respiratory mechanics and arterial blood gases were assessed on days 1 and day 5 of mechanical ventilation.

RESULTS

In the ZEEP group on day 1 static elastance and minimal resistance were above normal limits (18.9 +/- 3.8 cmH(2)O/l and 5.6 +/- 2.2 cmH(2)O/l per second, respectively); on day 5 static elastance and iso-CO(2) minimal resistance values were higher than on day 1 (21.2 +/- 4.1 cmH(2)O/l; 7.0 +/- 1.9 cmH(2)O/l per second, respectively). In the PEEP group these parameters did not change significantly. One of the ten patients on ZEEP developed acute lung injury. On day 5 there was a significant decrease in PaO(2)/FIO(2) in both groups.

CONCLUSIONS

On day 1 of mechanical ventilation patients with brain damage exhibit abnormal respiratory mechanics. After 5 days of mechanical ventilation on ZEEP static elastance and minimal resistance increased significantly, perhaps reflecting "low lung volume" injury. Both could be prevented by administration of moderate levels of PEEP.

Endotoxin-induced nitric oxide production rescues airway growth and maturation in atrophic fetal rat lung explants

Inflammation induces premature maturation of the fetal lung but the signals causing this effect remain unclear. We determined if nitric oxide (NO) synthesis, evoked by Escherichia coli lipopolysaccharide (LPS, 2 microg ml-1), participated in this process. Fetal rat lung airway surface complexity rose 2.5-fold over 96h in response to LPS and was associated with increased iNOS protein expression and activity. iNOS inhibition by N6-(1-iminoethyl)-L-lysine-2HCl (L-NIL) abolished this and induced airway atrophy similar to untreated explants. Surfactant protein-C (SP-C) expression was also induced by LPS and abolished by L-NIL. As TGFbeta suppresses iNOS activity, we determined if feedback regulation modulated NO-dependent maturation. LPS induced TGFbeta1 release and SMAD4 nuclear translocation 96 h after treatment. Treatment of explants with a blocking antibody against TGFbeta1 sustained NO production and airway morphogenesis whereas recombinant TGFbeta1 antagonized these effects. Feedback regulation of NO synthesis by TGFbeta may, thus, modulate airway branching and maturation of the fetal lung.

Micelles of pulmonary surfactant in human amniotic fluid at term

Studies using in vitro analysis have shown that the interaction between pulmonary surfactant and vernix caseosa could explain the appearance of amniotic fluid turbidity. That phenomenon is interpreted based on the "roll-up" hypothesis. We tested the roll-up hypothesis by examining the presence of micelles of pulmonary surfactant in human amniotic fluid at term. Amniotic fluid samples were collected from each of six healthy pregnant women at term and at 16 wk of gestation. These samples were stained negatively and analyzed using an electron microscope. Ultrastructures present in amniotic fluid were compared with the structure of micelles derived from suspended surfactant TA isolated from bovine lung. Surfactant TA formed spheroidal and rod-shaped micelles 10-70 nm in diameter above the critical micelle concentration. Identical micelle particles were described in human amniotic fluid at term. In addition, surfactant protein B was identified in the micelle fraction of amniotic fluid. However, no micelles were found in human amniotic fluid taken at 16 wk of gestation. Our results support the view that pulmonary surfactant could induce the detachment of vernix caseosa and increase the turbidity of the amniotic fluid.

Neonatal lung remodeling: structural, inflammatory, and ventilator-induced injury

The developing lung is subject to events, both prenatal and postnatal, that alter the normal developmental process. The degree of insult or injury affects how the lung functions at birth and then responds to the insult throughout childhood. In this article, only 3 of the influences are examined: structural, inflammatory, and mechanical. It is recognized that there is a plethora of other factors that influence lung remodeling.

Transcription Factors NF-κB and C/EBPδ and IL-1-Induced Expression of Surfactant Protein A in Lung Explants during the Perinatal Period

Interleukin-1 (IL-1) increases the expression of surfactant protein A (SP-A) in rabbit, lamb and human fetal lung. The upregulation disappears towards term. Among the transcription factors, IL-1 activates nuclear factor kappaB (NF-kappaB) and CCAAT/enhancer-binding protein delta (C/EBPdelta). NF-kappaB presumably has a role in IL-1-induced upregulation of SP-A. Also, C/EBPdelta may regulate SP-A expression. The aim was to study the role of these transcription factors in the induced effect of IL-1 on SP-A expression. Explants from fetal and neonatal rabbit lung were cultured in vitro followed by studies using immunohistochemistry, electrophoretic mobility shift assay and Northern analysis. We found gestation-dependent changes in IL-1-induced immunoreactivities of NF-kappaB and C/EBPdelta in the nuclei of alveolar cells. This increase in nuclear transcription factors correlated with IL-1-induced SP-A expression levels. As studied in the explants from fetal and newborn lung, the SP-A mRNA expression additionally associated with C/EBPdelta mRNA and with the binding of nuclear extracts from the lung explants to the C/EBP consensus probe. On the basis of the present and previous studies, we propose that NF-kappaB and C/EBPdelta have potential mediator roles in IL-1-induced upregulation of SP-A in immature lung.

Fetal and neonatal inflammatory response and adverse outcome

This article will define the concept of fetal/neonatal inflammatory response, and examine the complex interaction between inflammation and neurotoxicity. There appear to be important interactions between infection/inflammation and hypoxia-ischaemia leading to cytokine release and subsequent brain injury. This article will also define adverse outcome and summarize the complexities inherent to neurodevelopmental assessment. Finally, this article will investigate the currently available evidence suggesting a link between inflammatory response and adverse neurodevelopmental outcome, and focus on those variables that need further study: timing and nature of the infectious/inflammatory process; established and new anti-insult strategies; morbidity in organs other than the brain; genetic influences; and environmental factors.

Lipopolysaccharide increases alveolar type II cell number in fetal mouse lungs through Toll-like receptor 4 and NF-κB

Chorioamnionitis is a major cause of preterm delivery. Infants exposed to inflammation in utero and then born preterm may have improved lung function in the immediate postnatal period. We developed a mouse model of chorioamnionitis to study the inflammatory signaling mechanisms that might influence fetal lung maturation. With this in vivo model, we found that Escherichia coli lipopolysaccharide (LPS) increased the number of alveolar type II cells in the fetal mouse lung. LPS also increased type II cell number in cultured fetal lung explants, suggesting that LPS could directly signal the fetal lung in the absence of maternal influences. Using immunostaining, we localized cells within the fetal mouse lung expressing the LPS receptor molecule Toll-like receptor 4 (TLR4). Similar to the signaling pathways in inflammatory cells, LPS activated NF-κB in fetal lung explants. Activation of the TLR4/NF-κB pathway appeared to be required, as LPS did not increase the number of type II cells in C.C3H- Tlr4 Lps-d mice, a congenic strain containing a loss of function mutation in tlr4. In addition, the sesquiterpene lactone parthenolide inhibited NF-κB activation following LPS exposure and blocked the LPS-induced increase in type II cells. On the basis of these data from our mouse model of chorioamnionitis, it appears that LPS specifically activated the TLR4/NF-κB pathway, leading to increased type II cell maturation. These data implicate an important signaling mechanism in chorioamnionitis and suggest the TLR4/NF-κB pathway can influence lung development.

The pulmonary paradox in premature infants: in-utero infected lungs do better than those with accelerated maturation

AIMS

To document, and explain, the pulmonary paradox whereby despite relative lung immaturity, preterm infants exposed to amniotic infection (AI) have better postnatal pulmonary function than those exposed to preeclampsia (PE).

METHODS

Lung maturation was characterized in 65 preterm perinatal deaths [AI (n=40) and PE (n=25)] and postnatal respiratory function in 100 preterm survivors [AI (n=50) and PE (n=50)].

RESULTS

At autopsy, lung architecture was in advance of gestational age in 5% of AI infants versus 40% of PE infants (P<0.001). In survivors, the groups were similar in age and Apgar scores. At birth, 40% of the AI group required continuous positive airway pressure or mechanical ventilation versus 24% of the PE group (NS). However, 24 hours later, only 1 AI infant had deteriorated compared to 40% of PE infants (P<0.05).

CONCLUSIONS

Accelerated morphologic lung maturation in preterm PE infants does not translate into improved postnatal respiratory function. Most likely, this is due to a relative lack of surfactant, ascribable to low stimulant cytokine and high TNF-alpha levels. An intrauterine history supplemented by an antenatal cytokine profile could identify an increased exogeneous surfactant need in preterm infants exposed to PE.

Lung inflammatory responses to intratracheal interleukin-1alpha in ventilated preterm lambs

Interleukin-1alpha is an early response proinflammatory cytokine that has been associated with chorioamnionitis and preterm labor, brain injury, and bronchopulmonary dysplasia. However, IL-1alpha also can increase expression of surfactant proteins and induce lung maturation in the preterm fetus. We measured the effects of IL-1alpha given by intratracheal instillation (IT) and compared the responses with injection of i.v. IL-1alpha in surfactant-treated and ventilated premature lambs. IT recombinant ovine IL-1alpha at doses of 5 and 50 microg/kg caused a similar large recruitment of neutrophils into the bronchoalveolar lavage fluid. The neutrophils expressed CD11b, CD14, and CD44, but did not produce increased amounts of H(2)O(2). Cells from the bronchoalveolar lavage fluid had increased expression of proinflammatory cytokines, which also were increased in mRNA from lung tissue. The IT IL-1alpha also suppressed the expression of surfactant protein-C mRNA. Systemic effects were decreased neutrophils in blood, decreased lung function, increased heart rate, and hypotension or death in the 50 microg/kg IL-1alpha IT group and only decreased neutrophils in the blood in the 5 microg/kg IL-1alpha IT group. The i.v. IL-1alpha caused no lung inflammation or injury but did result in severe neutropenia and hypotension leading to early death. IT IL-1alpha can cause intense lung inflammation and systemic shock in ventilated preterm lungs.

Inflammatory and anti-inflammatory responsiveness of surfactant proteins in fetal and neonatal rabbit lung

Spontaneous preterm birth due to intrauterine infection is associated with increased concentrations of cytokines in amniotic fluid and in the airways at birth. Intra-amniotic IL-1 induces fetal lung maturity, consistent with the decrease in the incidence of respiratory distress syndrome (RDS) in intrauterine inflammation. On the other hand, antenatal corticosteroid decreases the incidence of RDS in infants born prematurely. The aim of the present study was to investigate the interaction between IL-1 and glucocorticoid in the expression of the surfactant proteins SP-A, -B, and -C. Lung explants from rabbit fetuses at 22 (immature), 27 (transitional), and 30 (mature) d of gestation (term, 30-31 d) and on d 1 after term birth were cultured with dexamethasone (Dx), IL-1alpha, or vehicle in the presence or absence of actinomycin D. According to the present results, IL-1alpha and Dx additively increased the expression of SP-A and SP-B on d 22. Later in gestation, SP-B and SP-C were suppressed by IL-1, whereas glucocorticoid tended to increase the expression of SP-B and SP-C and prevented the IL-1-induced suppression of SP. IL-1alpha and steroid interactively increased the stability of SP mRNA compared with the single agonist, possibly explaining the additive effects on the SP mRNA levels. The present results reveal beneficial additive effects of glucocorticoid and cytokine on lung surfactant. They may explain some of the acute beneficial effects of glucocorticoid therapy in chorioamnionitis before premature birth and in inflammatory lung disease after birth.

Surfactant protein A and B genetic variants in respiratory distress syndrome in singletons and twins

Interactive genetic and environmental factors may influence the differentiation of surfactant and the risk of respiratory distress syndrome (RDS). DNA samples from 441 premature singleton infants and 480 twin or multiple infants were genotyped for surfactant-specific protein (SP)-A1, SP-A2, and SP-B exon 4 polymorphisms and intron 4 size variants in a homogeneous white population. Distributions of the SP-A and SP-B gene variants between RDS and no-RDS infants were determined alone and in combination. SP-A1 allele 6A2 (p = 0.009) and the homozygous genotype 6A2/6A2 (p = 0.003) were overrepresented in RDS of singletons when the SP-B exon 4 genotype was Thr/Thr, and underrepresented in RDS of multiples when the SP-B genotype was Ile/Thr (p = 0.012 for 6A2 and p = 0.03 for 6A2/6A2) or Thr/Thr (p = 0.12 for 6A2 and p = 0.018 for 6A2/6A2, respectively). The SP-A 6A2 allele in the SP-B Thr131 background predisposed the smallest singleton infants to RDS, whereas near-term multiples were protected from RDS. There was a continuous association between fetal mass and risk of RDS, defined by the SP-A and SP-B variants. Labeled lung explants with the Thr/Thr genotype showed proSP-B amino-terminal glycosylation, which was absent in Ile/Ile samples. Genetic and environmental variation may influence intracellular processing of surfactant complex and the susceptibility to RDS.

Minimal lung and systemic responses to TNF-alpha in preterm sheep

TNF-alpha has been associated with chorioamnionitis and the subsequent development of bronchopulmonary dysplasia in preterm infants. We asked whether bioactive recombinant ovine TNF-alpha could induce chorioamnionitis, lung inflammation, lung maturation, and systemic effects in fetal sheep. We compared the responses to IL-1alpha, a cytokine known to induce these responses in preterm sheep. Intra-amniotic TNF-alpha caused no chorioamnionitis, no lung maturation, and a very small increase in inflammatory cells in the fetal lung after 5 h, 2 days (d), and 7 d. In contrast, IL-1alpha induced inflammation and lung maturation. TNF-alpha given into the airways at birth increased granulocytes in the bronchoalveolar lavage fluid of ventilated preterm lungs and decreased the mRNA for surfactant protein C but did not adversely effect postnatal lung function. An intravascular injection of IL-1alpha caused a systemic inflammatory response in fetal sheep, whereas there was no fetal response to intravascular TNF-alpha. Fetal and newborn preterm sheep are minimally responsive to TNF-alpha. Therefore, the presence of a mediator such as TNF-alpha in a developing animal does not necessarily mean that it is causing the responses anticipated from previous results in adult animals.

Pulmonary surfactant for neonatal respiratory disorders

Surfactant therapy has revolutionized neonatal care and is used routinely for preterm infants with respiratory distress syndrome. Recent investigation has further elucidated the function of surfactant-associated proteins and their contribution toward surfactant and lung immune defense functions. As the field of neonatology moves away from intubation and mechanical ventilation of preterm infants at birth toward more aggressive use of nasal continuous positive airway pressure, the optimal timing of exogenous surfactant therapy remains unclear. Evidence suggests that preterm neonates with bronchopulmonary dysplasia and prolonged mechanical ventilation also experience surfactant dysfunction; however, exogenous surfactant therapy beyond the first week of life has not been well studied. Surfactant replacement therapy has been studied for use in other respiratory disorders, including meconium aspiration syndrome and pneumonia. Commercial surfactant preparations currently available are not optimal, given the variability of surfactant protein content and their susceptibility to inhibition. Further progress in the treatment of neonatal respiratory disorders may include the development of "designer" surfactant preparations.

Antenatal factors and the development of bronchopulmonary dysplasia

The lung of the preterm fetus is often exposed to antenatal glucocorticoids, and histologic chorioamnionitis is frequent. Clinically and experimentally, antenatal glucocorticoids and/or chorioamnionitis are associated with early lung maturation, but in experimental models, both glucocorticoids and intra-uterine inflammation decrease alveolarization. Experimental chorioamnionitis also can amplify the inflammatory response of the preterm lung to mechanical ventilation. In this article, the hypothesis developed is that bronchopulmonary dysplasia occurs because of repetitive adverse lung exposures, or hits, and that the initial hits may be antenatal glucocorticoid exposure and/or antenatal inflammation.

Differentiation of human pulmonary type II cells in vitro by glucocorticoid plus cAMP

Mature alveolar type II cells that produce pulmonary surfactant are essential for adaptation to extrauterine life and prevention of infant respiratory distress syndrome. We have developed a new in vitro model to further investigate regulation of type II cell differentiation. Epithelial cells isolated from human fetal lung were cultured in serum-free medium on plastic. Cells treated with dexamethasone + cAMP analog and isobutylmethylxanthine for 4 days exhibited increased phosphatidylcholine synthesis and content of disaturated phosphatidylcholine species, manyfold increases in all surfactant proteins with processing to mature forms, and abundant lamellar bodies. DNA microarray analysis identified approximately 3,100 expressed genes, including subsets of genes induced 2- to >100-fold (approximately 2.5%) or repressed 2- to 18-fold (approximately 1.2%) by hormone treatment. Of the highly regulated genes, most were coregulated in an additive or synergistic manner by dexamethasone and cAMP agents. Approximately 90% of the regulated genes identified by this initial microarray analysis have not been previously recognized as hormone responsive. One newly identified hormone-induced gene is Nkx2.1 (thyroid transcription factor-1), which has a critical role in surfactant protein gene expression. Our findings indicate that glucocorticoid + cAMP is sufficient and necessary for precocious induction of functional type II cells in this in vitro system and that these hormones act primarily in combination to regulate expression of a subset of specific genes.

Sequelae of chorioamnionitis

Chorioamnionitis correlates to preterm delivery prior to 30 weeks of gestation. In most studies, proxies of intrauterine infection (clinical chorioamnionitis, histological chorioamnionitis, intra-amniotic increase in cytokines) are associated with acute neonatal morbidity and mortality and, at least to some degree, with neurological impairments (periventricular leukomalacia, intraventricular hemorrhage, cerebral palsy, polymicrogyria), chronic lung disease, and involution of the thymus in the preterm infant. The connection to visual impairment and cognitive deficits is uncertain or unknown. Full-term babies exposed to intrauterine infection often present with depressed Apgar scores and neonatal encephalopathy, and are at markedly increased risk of developing cerebral palsy. The infectious/inflammatory mechanisms involved are incompletely understood, and the types of microbes, as well as the genetic characteristics of the host adaptive and innate immune response, need to be better characterized.

Regulation of surfactant proteins by LPS and proinflammatory cytokines in fetal and newborn lung

Intra-amniotic lipopolysaccharide (LPS) and cytokines may decrease respiratory distress syndrome (RDS) and increase chronic lung disease in the newborn. The aim was to identify the primary inflammatory mediators regulating the expression of surfactant proteins (SP) in explants from immature (22-day-old fetus) and mature (30-day term fetus and 2-day-old newborn) rabbits. In immature lung, interleukin (IL)-1alpha and IL-1beta upregulated the expression of SP-A and SP-B. These effects of IL-1 were diminished, and SP-C mRNA was suppressed additively in the presence of tumor necrosis factor (TNF)-alpha and either LPS or interferon (IFN)-gamma. LPS, TNF-alpha, or IFN-gamma had no effect alone. In explants from the term fetus and the newborn, LPS, IL-1alpha, and TNF-alpha additively suppressed the SPs. LPS acutely induced IL-1alpha in alveolar macrophages in mature lung but not in the immature lung. IFN-gamma that generally has low expression in intrauterine infection decreased the age dependence of the other agonists' effects on SPs. The present study serves to explain the variation of the pulmonary outcome after an inflammatory insult. We propose that IL-1 from extrapulmonary sources induces the SPs in premature lung and is responsible for the decreased risk of RDS in intra-amniotic infection.

Early gestational intra-amniotic endotoxin: lung function, surfactant, and morphometry

We determined the effects in preterm lambs of endotoxin-induced inflammation at early gestational ages on lung function and structure and on the surfactant system. Pregnant ewes were randomized to one of five intra-amniotic endotoxin (Escherichia coli 055:B5) groups: 1 mg injected at 60 days of gestation, 1 mg at 80 days, 1 mg at 100 days, 1 mg at 60 days plus 100 days, or 0.6 mg/ day infused from Day 80 to Day 108. Control lambs received saline treatments. At 125 days, lung function was improved in all endotoxin groups. Marked increases in saturated phosphatidylcholine in lung tissue but not alveolar lavage samples were seen in all endotoxin groups except the 60- plus 100-day group. Surfactant protein mRNA and protein pool sizes were affected differently according to the timing of endotoxin treatment, but a large increase in the amount of mature surfactant protein B in alveolar lavage samples was observed in all endotoxin groups. Lung-to-body weight ratio, alveolar number, total surface area, and alveolar wall thickness were reduced by 80- to 108-day endotoxin. Intra-amniotic inflammatory stimuli in early gestation can alter pulmonary development, with the net effect of improving preterm lung function, despite changes in surfactant and lung growth that are similar to changes in the lungs of ventilated animals developing bronchopulmonary dysplasia.

Intra-amniotic injection of IL-1 induces inflammation and maturation in fetal sheep lung

Antenatal inflammation may be an important triggering event in the pathogenesis of bronchopulmonary dysplasia but may also accelerate fetal lung maturation. We examined the effects of intra-amniotic (IA) interleukin (IL)-1 alpha and IL-1 beta on maturation of the fetal sheep lung. These cytokine effects were compared with IA endotoxin, a potent proinflammatory stimulus that accelerated lung maturation. Date-bred ewes received 15 or 150 microg recombinant ovine IL-1 alpha or IL-1 beta or 10 mg Escherichia coli endotoxin by IA injection at 118 days gestation (term = 150 days), and fetuses were delivered at 125 days. IL-1 alpha and IL-1 beta improved lung function and increased alveolar saturated phosphatidylcholine (Sat PC) and surfactant protein mRNA expression at the higher dose. The maturation response to IL-1 alpha was greater than that to IL-1 beta, which was similar to endotoxin response. Inflammation was also more pronounced after IL-1 alpha treatment. Only endotoxin animals had residual inflammation of the fetal membranes at 7 days. Lung compliance, lung volume, and alveolar Sat PC were positively correlated with residual alveolar wash leukocyte numbers 7 days after IL-1 treatment, suggesting a link between lung inflammation and maturation.

Antenatal infection/inflammation and postnatal lung maturation and injury

Chorioamnionitis is frequently associated with preterm deliveries before 30 weeks gestation. Chorioamnionitis correlates both with an increased risk of bronchopulmonary dysplasia and with a decreased risk of respiratory distress syndrome. Both interleukin-1alpha and endotoxin can induce inflammation in the fetal lungs and lung maturation after preterm birth when given by intra-amniotic injection. Inflammation can also result in an arrest of alveolarization, and this lung developmental abnormality is prominent in the lungs of preterm infants that die of bronchopulmonary dysplasia. The mechanisms by which infection/inflammation can have both beneficial and injurious effects on the preterm lung remain to be characterized.

Toll-like receptors as sensors of pathogens

Initial recognition of microbes, as they enter the body, is based on germ line-encoded pattern recognition receptors that selectively bind to essential components of pathogens. This allows the body to respond immediately to the microbial invasion before the development of active immunity. The signal-transducing receptors that trigger the acute inflammatory cascade have been elusive until very recently. On the basis of their genetic similarity to the Toll signaling pathway in Drosophila, mammalian Toll-like receptors (TLRs) have been identified. By now, nine transmembrane proteins in the TLR family have been described. Mammalian TLR4 is the signal-transducing receptor activated by the bacterial lipopolysaccharide. The activation of TLR4 leads to DNA binding of the transcription factor NF-kappaB, resulting in activation of the inflammatory cascade. Activation of other TLRs is likely to have similar consequences. TLR2 mediates the host response to Gram-positive bacteria and yeast. TLR1 and TLR6 may participate in the activation of macrophages by Gram-positive bacteria, whereas TLR9 appears to respond to a specific sequence of bacterial DNA. The TLRs that control the onset of an acute inflammatory response are critical antecedents for the development of adaptive acquired immunity. Genetic and developmental variation in the expression of microbial pattern recognition receptors may affect the individual's predisposition to infections in childhood and may contribute to susceptibility to severe neonatal inflammatory diseases, allergies, and autoimmune diseases.

Glucocorticoids, inflammation and the perinatal lung

Many women delivering preterm infants at less than 30 weeks gestation have subclinical chorioamnionitis. Based on current guidelines, maternal glucocorticoid treatment is given to induce lung maturation. Fetal exposure to proinflammation can cause acute and chronic injury, but inflammation also can induce fetal lung maturation. Both antenatal glucocorticoids and inflammation modulate lung development, by inducing the surfactant system, inducing structural maturation, and inhibiting alveolarization. The opportunities for the future are to develop new safer strategies to mature the preterm foetus, and the risks are potential adverse interactions of repetitive glucocorticoid exposures and unrecognized fetal exposure to inflammation.

GM-CSF mediates alveolar macrophage proliferation and type II cell hypertrophy in SP-D gene-targeted mice

Mice deficient in surfactant protein (SP) D develop increased surfactant pool sizes and dramatic changes in alveolar macrophages and type II cells. To test the hypothesis that granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates alveolar macrophage proliferation and activation and the type II cell hypertrophy seen in SP-D null mice, we bred SP-D and GM-CSF gene-targeted mice to obtain littermate double null, single null, and wild-type mice. Bronchoalveolar lavage levels of phospholipid, protein, SP-D, SP-A, and GM-CSF were measured from 1 to 4 mo. There was an approximately additive accumulation of phospholipid, total protein, and SP-A at each time point. Microscopy showed normal macrophage number and morphology in GM-CSF null mice, numerous giant foamy macrophages and hypertrophic type II cells in SP-D null mice, and large but not foamy macrophages and mostly normal type II cells in double null mice. These results suggest that the mechanisms underlying the alveolar surfactant accumulation in the SP-D-deficient and GM-CSF-deficient mice are different and that GM-CSF mediates some of the macrophage and type II cell changes seen in SP-D null mice.

Surfactant in respiratory distress syndrome and lung injury

A deficiency in alveolar surfactant due to immaturity of alveolar type II epithelial cells causes respiratory distress syndrome (RDS). In contrast to animals, the fetal maturation of surfactant in human lungs takes place before term, exceptionally large quantities of surfactant accumulating in the amniotic fluid. The antenatal development of surfactant secretion is very variable but corresponds closely to the risk of RDS. The variation in SP-A and SP-B genes, race, sex and perinatal complications influence susceptibility to RDS. Surfactant therapy has improved the prognosis of RDS remarkably. Abnormalities in alveolar or airway surfactant characterize many lung and airway diseases. In the acute respiratory distress syndrome, deficiencies in surfactant components (phospholipids, SP-B, SP-A) are evident, and may be caused by pro-inflammatory cytokines (IL-1, TNF) that decrease surfactant components. The resultant atelectasis localizes the disease, possibly allowing healing (regeneration, increase in surfactant). In the immature fetus, cytokines accelerate the differentiation of surfactant, preventing RDS. After birth, however, persistent inflammation is associated with low SP-A and chronic lung disease. A future challenge is to understand how to inhibit or redirect the inflammatory response from tissue destruction and poor growth towards normal lung development and regeneration.

Intra-amniotic endotoxin: chorioamnionitis precedes lung maturation in preterm lambs

The inflammatory and lung maturational effects of intra-amniotic exposure to endotoxin were assessed in fetal lambs. Five hours to 25 days after intra-amniotic injection of endotoxin, preterm lambs were delivered at 119-125 days gestation. Intra-amniotic endotoxin caused an inflammatory cell infiltration in amnion/chorion at 5 h, which persisted for 25 days. At 5-15 h after endotoxin, amnion/chorion cytokine mRNAs increased [12- to 26-fold for interleukin (IL)-1beta, IL-6, and IL-8 mRNA and 3-fold for tumor necrosis factor-alpha mRNA]. At 1-2 days after endotoxin, lung cytokine mRNAs increased 6- to 49-fold. Endotoxin caused modest changes in peripheral white blood cell counts and no significant cytokine mRNA responses in fetal liver, placenta, or jejunum. Lung maturation, as characterized by increased lung volumes and alveolar saturated phosphatidylcholine, occurred at 7 days and persisted for 25 days after endotoxin. We conclude that exposure to a single dose of intra-amniotic endotoxin causes inflammation and increases in cytokine mRNA in amnion/chorion and the fetal lung before lung maturation, consistent with the hypothesis that proinflammatory cytokines signal lung maturation.

Intra-amniotic endotoxin increases pulmonary surfactant proteins and induces SP-B processing in fetal sheep

Intra-amniotic (IA) endotoxin induces lung maturation within 6 days in fetal sheep of 125 days gestational age. To determine the early fetal lung response to IA endotoxin, the timing and characteristics of changes in surfactant components were evaluated. Fetal sheep were exposed to 20 mg of Escherichia coli 055:B5 endotoxin by IA injection from 1 to 15 days before preterm delivery at 125 days gestational age. Surfactant protein (SP) A, SP-B, and SP-C mRNAs were maximally induced at 2 days. SP-D mRNA was increased fourfold at 1 day and remained at peak levels for up to 7 days. Bronchoalveolar lavage fluid from control animals contained very little SP-B protein, 75% of which was a partially processed intermediate. The alveolar pool of SP-B was significantly increased between 4 and 7 days in conjunction with conversion to the fully processed active airway peptide. All SPs were significantly elevated in the bronchoalveolar lavage fluid by 7 days. IA endotoxin caused rapid and sustained increases in SP mRNAs that preceded the increase in alveolar saturated phosphatidylcholine processing of SP-B and improved lung compliance in prematurely delivered lambs.