Accelerated thymic maturation and autoreactive T cells in bronchopulmonary dysplasia

Lower peripheral blood CD4+ lymphocyte ratio is associated with severe bronchopulmonary dysplasia

OBJECTIVE

To elucidate the characteristics of lymphocyte subsets in bronchopulmonary dysplasia (BPD) diagnosis following Jensen's criterion to understand the spectrum of lymphocytes in different degrees of BPD.

STUDY DESIGN

This single-center retrospective cohort study included 120 neonates admitted to the neonatal intensive care unit between 1 July 2014 and 30 June 2021, who had undergone peripheral blood lymphocyte subpopulation detection.

RESULTS

Thirty-one neonates were included in the control group, whereas 33 infants with BPD were included in the case group. In addition, we selected 56 infants with a gestational age (GA) <37 weeks without BPD who were receiving oxygen therapy. Among the three groups, the B cell and NK cell frequencies were significantly higher and the frequencies of T cells and CD4+ cells were significantly lower in the BPD group. In newborns without BPD, the distribution of T lymphocyte subsets was similar at different GAs. Comparing different degrees of BPD, the patients in the grades 2-3 BPD group had significantly lower percentages of T lymphocytes and CD4+ T cells than those in the other groups. Remarkably, the frequencies of NK cells were significantly higher in patients with grades 2-3 BPD, and the Treg cells slightly increased with BPD severity, although the differences were not significant.

CONCLUSION

Healthy neonates had similar ratios of lymphocyte subsets among different GAs; although as the GAs increased, the percentage of lymphocytes increased slightly. Severe BPD was associated with lower CD4+ T cells and higher NK cells. However, whether such changes were the cause or the consequence of BPD has not been determined.

Changes in Thymic Size and Immunity Are Associated with Bronchopulmonary Dysplasia

OBJECTIVE

Preterm infants with bronchopulmonary dysplasia (BPD) are at increased risk for dysfunctional immune responses in the postnatal period. This study aimed to verify the hypothesis that thymic function is altered in infants with BPD and changes in the expression of thymic function-related genes affect thymic development.

STUDY DESIGN

Included in the study were infants who had a gestational age ≤32 weeks and survived to a postmenstrual age of ≥36 weeks. The clinical features and thymic size were comparatively studied between infants with and without BPD. Thymic function and the expression of thymic function-related genes were determined in BPD infants at birth, week 2, and 4 of life. The thymic size was ultrasonographically assessed in terms of the thymic index (TI) and thymic weight index (TWI). T-cell receptor excision circles (TRECs) and gene expression were quantitatively determined by real-time quantitative reverse transcription polymerase chain reaction.

RESULTS

Compared to non-BPD infants, their BPD counterparts had a shorter GA, lower birth weight, lower Apgar scores at birth, and were more likely to be of the male gender. BPD infants had an elevated incidence of respiratory distress syndrome and sepsis. TI was 1.73 ± 0.68 versus 2.87 ± 0.70 cm3 and TWI was 1.38 ± 0.45 versus 1.72 ± 0.28 cm3/kg in the BPD group versus the non-BPD group (p < 0.05). In BPD infants, no significant changes were observed in thymic size, lymphocyte counts, and TREC copy numbers at the first 2 weeks (p > 0.05), but they all exhibited a significant increase at week 4 (p < 0.05). BPD infants presented a trend toward increased expression of transforming growth factor-β1 and decreased expression of forkhead box protein 3 (Foxp3) from birth to week 4 (p < 0.05). Nonetheless, no significant difference was found in IL-2 or IL-7 expression at all time points (p > 0.05).

CONCLUSION

For preterm infants with BPD, reduced thymic size at birth might be associated with impaired thymic function. Thymic function was developmentally regulated in the BPD process.

KEY POINTS

· For preterm infants with BPD, reduced thymic size at birth might be associated with impaired thymic.. · BPD infants had an elevated incidence of respiratory distress syndrome and sepsis.. · Thymic function was developmentally regulated in the BPD process..

Mesenchymal Stromal Cell-Derived Extracellular Vesicles Restore Thymic Architecture and T Cell Function Disrupted by Neonatal Hyperoxia

Treating premature infants with high oxygen is a routine intervention in the context of neonatal intensive care. Unfortunately, the increase in survival rates is associated with various detrimental sequalae of hyperoxia exposure, most notably bronchopulmonary dysplasia (BPD), a disease of disrupted lung development. The effects of high oxygen exposure on other developing organs of the infant, as well as the possible impact such disrupted development may have on later life remain poorly understood. Using a neonatal mouse model to investigate the effects of hyperoxia on the immature immune system we observed a dramatic involution of the thymic medulla, and this lesion was associated with disrupted FoxP3⁺ regulatory T cell generation and T cell autoreactivity. Significantly, administration of mesenchymal stromal cell-derived extracellular vesicles (MEx) restored thymic medullary architecture and physiological thymocyte profiles. Using single cell transcriptomics, we further demonstrated preferential impact of MEx treatment on the thymic medullary antigen presentation axis, as evidenced by enrichment of antigen presentation and antioxidative-stress related genes in dendritic cells (DCs) and medullary epithelial cells (mTECs). Our study demonstrates that MEx treatment represents a promising restorative therapeutic approach for oxygen-induced thymic injury, thus promoting normal development of both central tolerance and adaptive immunity.

T Lymphocytes, Multi-Omic Interactions and Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) remains a significant clinical challenge in neonatal medicine. BPD is clearly a multifactorial disease with numerous antenatal and postnatal components influencing lung development. Extremely immature infants are born in the late canalicular or early saccular stage and usually receive intensive care until the early alveolar stage of lung development, resulting in varying magnitudes of impairment of alveolar septation, lung fibrosis, and abnormal vascular development. The interactions between T lymphocytes, the genome and the epigenome, the microbiome and the metabolome, as well as nutrition and therapeutic interventions such as the exposure to oxygen, volutrauma, antibiotics, corticosteroids, caffeine and omeprazole, play an important role in pathogenesis and disease progression. While our general understanding of these interactions thanks to basic research is improving, this knowledge is yet to be translated into comprehensive prevention and clinical management strategies for the benefit of preterm infants developing BPD and later during infancy and childhood suffering from the disease itself and its sequelae. In this review, we summarise existing evidence on the interplay between T lymphocytes, lung multi-omics and currently used therapeutic interventions in BPD, and highlight avenues for potential future immunology related research in the field.

Pulmonary immune cell transcriptome changes in double-hit model of BPD induced by chorioamnionitis and postnatal hyperoxia

BACKGROUND

Preterm infants with bronchopulmonary dysplasia (BPD) have lifelong increased risk of respiratory morbidities associated with environmental pathogen exposure and underlying mechanisms are poorly understood. The resident immune cells of the lung play vital roles in host defense. However, the effect of perinatal events associated with BPD on pulmonary-specific immune cells is not well understood.

METHODS

We used a double-hit model of BPD induced by prenatal chorioamnionitis followed by postnatal hyperoxia, and performed a global transcriptome analysis of all resident pulmonary immune cells.

RESULTS

We show significant up-regulation of genes involved in chemokine-mediated signaling and immune cell chemotaxis, and down-regulation of genes involved in multiple T lymphocyte functions. Multiple genes involved in T cell receptor signaling are downregulated and Cd8a gene expression remains downregulated at 2 months of age in spite of recovery in normoxia for 6 weeks. Furthermore, the proportion of CD8a+CD3+ pulmonary immune cells is decreased.

CONCLUSIONS

Our study has highlighted that perinatal lung inflammation in a double-hit model of BPD results in short- and long-term dysregulation of genes associated with the pulmonary T cell receptor signaling pathway, which may contribute to increased environmental pathogen-associated respiratory morbidities seen in children and adults with BPD.

IMPACT

In a translationally relevant double-hit model of BPD induced by chorioamnionitis and postnatal hyperoxia, we identified pulmonary immune cell-specific transcriptomic changes and showed that T cell receptor signaling genes are downregulated in short term and long term. This is the first comprehensive report delineating transcriptomic changes in resident immune cells of the lung in a translationally relevant double-hit model of BPD. Our study identifies novel resident pulmonary immune cell-specific targets for potential therapeutic modulation to improve short- and long-term respiratory health of preterm infants with BPD.

Fetal cord blood and tissue immune responses to chronic placental inflammation and chorioamnionitis

Background

Chorioamnionitis is a risk factor for future asthma development. Animal models of chorioamnionitis demonstrate increased T_H17-to-T_reg ratios associated with proinflammatory cytokine elevations. The association of chorioamnionitis on human neonatal immune cells systemically and within tissues is not known.

Methods

We enrolled two cohorts to evaluate T_H17 and regulatory T cell (T_reg) phenotypic markers in chorioamnionitis. From a cohort of 19 live birth infants, we collected cord blood and placenta samples to evaluate for signs of acute and chronic histologic inflammation and cell phenotype characterization. We analyzed a second cohort of stillborn infants with and without chorioamnionitis to classify and enumerate cell infiltrate phenotypes in the spleen, thymus, and lung. We used linear regression analysis determine the association of retinoic acid-related orphan receptor gamma t positive (RORγt⁺) and T_reg cell frequency with different types of inflammation seen in the live cohort subjects. Using linear mixed models, we evaluated for any associations between chorioamnionitis and T- and B-cell with a logarithmic scale for level of expression of cellular markers. We then performed Wilcoxon rank sum tests to assess the associations between cell count and chorioamnionitis.

Results

In the live birth subjects with chronic placental inflammation we observed an increased proportion of RORγt⁺ cells in Foxp3⁺ cells, regardless of the presence of acute inflammation, compared to subjects with neither acute nor chronic inflammation. We also found an increased proportion of RORγt⁺ cells within Foxp3⁺ cells in subjects with acute high stage fetal and maternal inflammation compared to those without acute or chronic inflammation. In the stillborn subjects with chorioamnionitis, we observed a decrease in splenic Foxp3⁺ cells and an increase in lung CD3⁺ cells compared with subjects that did not have chorioamnionitis.

Conclusion

Exposure to chorioamnionitis in utero may affect immune activation in neonates with an increased frequency of RORγt⁺ cells systemically as well as lymphocytic infiltrate in the lung. Our findings suggest an increase in RORγt⁺ cells during chorioamnionitis and thus may support the known associations between chorioamnionitis with asthma.

Altered thymocyte and T cell development in neonatal mice with hyperoxia-induced lung injury

BACKGROUND

The adaptive immune system of neonates is relatively underdeveloped. The thymus is an essential organ for adaptive T cell development and might be affected during the natural course of oxygen induced lung injury. The effect of prolonged hyperoxia on the thymus, thymocyte and T cell development, and its proliferation has not been studied extensively.

METHODS

Neonatal mice were exposed to 85% oxygen (hyperoxia) or room air (normoxia) up to 28 days. Flow cytometry using surface markers were used to assay for thymocyte development and proliferation.

RESULTS

Mice exposed to prolonged hyperoxia had evidence of lung injury associated alveolar simplification, a significantly lower mean weight, smaller thymic size, lower mean thymocyte count and higher percentage of apoptotic thymocytes. T cells subpopulation in the thymus showed a significant reduction in the count and proliferation of double positive and double negative T cells. There was a significant reduction in the count and proliferation of single positive CD4+ and CD8+ T cells.

CONCLUSIONS

Prolonged hyperoxia in neonatal mice adversely affected thymic size, thymocyte count and altered the distribution of T cells sub-populations. These results are consistent with the hypothesis that prolonged hyperoxia causes defective development of T cells in the thymus.

T cell developmental arrest in former premature infants increases risk of respiratory morbidity later in infancy

The inverse relationship between gestational age at birth and postviral respiratory morbidity suggests that infants born preterm (PT) may miss a critical developmental window of T cell maturation. Despite a continued increase in younger PT survivors with respiratory complications, we have limited understanding of normal human fetal T cell maturation, how ex utero development in premature infants may interrupt normal T cell development, and whether T cell development has an effect on infant outcomes. In our longitudinal cohort of 157 infants born between 23 and 42 weeks of gestation, we identified differences in T cells present at birth that were dependent on gestational age and differences in postnatal T cell development that predicted respiratory outcome at 1 year of age. We show that naive CD4+ T cells shift from a CD31-TNF-α+ bias in mid gestation to a CD31+IL-8+ predominance by term gestation. Former PT infants discharged with CD31+IL8+CD4+ T cells below a range similar to that of full-term born infants were at an over 3.5-fold higher risk for respiratory complications after NICU discharge. This study is the first to our knowledge to identify a pattern of normal functional T cell development in later gestation and to associate abnormal T cell development with health outcomes in infants.

Cellular and humoral biomarkers of Bronchopulmonary Dysplasia

The pathogenesis of Bronchopulmonary Dysplasia (BPD) is multifactorial and the clinical phenotype of BPD is extremely variable. Predicting BPD is difficult, as it is a disease with a clinical operational definition but many clinical phenotypes and endotypes. Most biomarkers studied over the years have low predictive accuracy, and none are currently used in routine clinical care or shown to be useful for predicting longer-term respiratory outcome. Targeted cellular and humoral biomarkers and novel systems biology 'omic' based approaches including genomic and microbiomic analyses are described in this review.

Postnatal Infections and Immunology Affecting Chronic Lung Disease of Prematurity

Premature infants suffer significant respiratory morbidity during infancy with long-term negative consequences on health, quality of life, and health care costs. Enhanced susceptibility to a variety of infections and inflammation play a large role in early and prolonged lung disease following premature birth, although the mechanisms of susceptibility and immune dysregulation are active areas of research. This article reviews aspects of host-pathogen interactions and immune responses that are altered by preterm birth and that impact chronic respiratory morbidity in these children.

Developmentally determined reduction in CD31 during gestation is associated with CD8+ T cell effector differentiation in preterm infants

Homeostatic T cell proliferation is more robust during human fetal development. In order to understand the relative effect of normal fetal homeostasis and perinatal exposures on CD8+ T cell behavior in PT infants, we characterized umbilical cord blood CD8+ T cells from infants born between 23-42weeks gestation. Subjects were recruited as part of the NHLBI-sponsored Prematurity and Respiratory Outcomes Program. Cord blood from PT infants had fewer naïve CD8+ T cells and lower regulatory CD31 expression on both naïve and effector, independent of prenatal exposures. CD8+ T cell in vitro effector function was greater at younger gestational ages, an effect that was exaggerated in infants with prior inflammatory exposures. These results suggest that CD8+ T cells earlier in gestation have loss of regulatory co-receptor CD31 and greater effector differentiation, which may place PT neonates at unique risk for CD8+ T cell-mediated inflammation and impaired T cell memory formation.

Effects of Intrauterine Growth Restriction During Late Pregnancy on the Development of the Ovine Fetal Thymus and the T-Lymphocyte Subpopulation

PROBLEM

The retarded development of fetal thymus in intrauterine growth restriction (IUGR) from maternal undernutrition during late pregnancy destroys the tridimensional structure and modifies the development of fetal T lymphocytes. The mechanisms, however, remain unclear. The objective of this study was to investigate the effect of IUGR during late pregnancy on the development of the ovine fetal thymus and the T-lymphocyte subpopulation.

METHOD OF STUDY

Eighteen time-mated ewes with singleton fetuses were allocated to three groups at day 90 of pregnancy: restricted group 1 (RG1, 0.18 MJ ME/BW(0.75) /day, n = 6), restricted group 2 (RG2, 0.33 MJ ME/BW(0.75) /day, n = 6) and a control group (CG, ad libitum, 0.67 MJ ME/BW(0.75) /day, n = 6). Fetuses were recovered at slaughter on day 140.

RESULTS

Fetuses in RG1 exhibited decreased (P < 0.05) thymic weight, cortical thickness, cortical:medullary, DNA content, total antioxidant capacity, and superoxide dismutase; intermediate changes were found in RG2 fetuses, including decreased thymic weight, cortical thickness, and DNA content (P < 0.05). The reductions (P < 0.05) of CD4(+) CD8(+) T cells, relative mRNA expression of keratin 8, recombination activating gene 1 (RAG1), and B-cell lymphoma 2 (Bcl-2) were found in both restricted groups. In addition, there was reduced mRNA expression (P < 0.05) of T-cell receptor, apoptosis antigen 1 ligand, and RAG2 in the RG1 group. In contrast, increases in glutathione peroxidase, malondialdehyde, caspase-3, Cytochrome c, and CD4(+) T cells were observed (P < 0.05), and higher mRNA expressions (P < 0.05) of protein 53, Bcl-2 associated X protein (Bax), and apoptosis antigen 1 (Fas) were found in RG1 fetuses; and thymuses of RG2 fetuses had increased caspase-3, and expression of Fas and Bax (P < 0.05), relative to control fetuses.

CONCLUSION

These results indicate that reduced cell proliferation, oxidative stress, and increased cell apoptosis were the potential mechanisms for impaired development and microenvironment of IUGR fetal thymus, and for modifying the maturation of CD4(+) CD8(+) thymocytes underlying their reduced numbers .

Responses of the spleen to intraamniotic lipopolysaccharide exposure in fetal sheep

BACKGROUND

Intrauterine inflammation activates the fetal immune system and can result in organ injury and postnatal complications in preterm infants. As the spleen is an important site for peripheral immune activation, we asked how the fetal spleen would respond to intrauterine inflammation over time. We hypothesized that intraamniotic lipopolysaccharide (IA LPS) exposure induces acute and persistent changes in the splenic cytokine profile and T-cell composition that may contribute to the sustained fetal inflammatory response after chorioamnionitis.

METHODS

Fetal sheep were exposed to IA LPS 5, 12, and 24 h and 2, 4, 8, or 15 d before delivery at 125 d of gestational age (term = 150 d). Splenic cytokine mRNA levels and cleaved caspase-3, CD3, and Foxp3 expression were evaluated.

RESULTS

IA LPS increased interleukin (IL)1, IL4, IL5, and IL10 mRNA by twofold 24 h after injection. Interferon gamma increased by fivefold, whereas IL23 decreased 15 d post-LPS exposure. Cleaved caspase-3-positive cells increased 2 and 8 d after LPS exposure. CD3 immunoreactivity increased within 5 h with increased Foxp3-positive cells at 12 h.

CONCLUSION

Intrauterine inflammation induced a rapid and sustained splenic immune response with persistent changes in the cytokine profile. This altered immune status may drive sustained inflammation and injury in other fetal organs.

Chronic lung disease in the preterm infant. Lessons learned from animal models

Neonatal chronic lung disease, also known as bronchopulmonary dysplasia (BPD), is the most common complication of premature birth, affecting up to 30% of very low birth weight infants. Improved medical care has allowed for the survival of the most premature infants and has significantly changed the pathology of BPD from a disease marked by severe lung injury to the "new" form characterized by alveolar hypoplasia and impaired vascular development. However, increased patient survival has led to a paucity of pathologic specimens available from infants with BPD. This, combined with the lack of a system to model alveolarization in vitro, has resulted in a great need for animal models that mimic key features of the disease. To this end, a number of animal models have been created by exposing the immature lung to injuries induced by hyperoxia, mechanical stretch, and inflammation and most recently by the genetic modification of mice. These animal studies have 1) allowed insight into the mechanisms that determine alveolar growth, 2) delineated factors central to the pathogenesis of neonatal chronic lung disease, and 3) informed the development of new therapies. In this review, we summarize the key findings and limitations of the most common animal models of BPD and discuss how knowledge obtained from these studies has informed clinical care. Future studies should aim to provide a more complete understanding of the pathways that preserve and repair alveolar growth during injury, which might be translated into novel strategies to treat lung diseases in infants and adults.

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.

Intraamniotic lipopolysaccharide exposure changes cell populations and structure of the ovine fetal thymus

RATIONALE

Chorioamnionitis induces preterm delivery and acute involution of the fetal thymus which is associated with postnatal inflammatory disorders. We studied the immune response, cell composition, and architecture of the fetal thymus following intraamniotic lipopolysaccharide (LPS) exposure.

METHODS

Time-mated ewes received an intraamniotic injection of LPS 5, 12, or 24 hours or 2, 4, 8, or 15 days before delivery at 125 days gestational age (term = 150 days).

RESULTS

The LPS exposure resulted in decreased blood lymphocytes within 5 hours and decreased thymic corticomedullary ratio within 24 hours. Thymic interleukin 6 (IL6) and IL17 messenger RNA (mRNA) increased 5-fold 24 hours post-LPS exposure. Increased toll-like receptor 4 (TLR4) mRNA and nuclear factor κB positive cells at 24 hours after LPS delivery demonstrated acute thymic activation. Both TLR4 and IL1 mRNA increased by 5-fold and the number of Foxp3-positive cells (Foxp3+ cells) decreased 15 days after exposure.

CONCLUSION

Intraamniotic LPS exposure caused a proinflammatory response, involution, and a persistent depletion of thymic Foxp3+ cells indicating disturbance of the fetal immune homeostasis.

Ovine fetal thymus response to lipopolysaccharide-induced chorioamnionitis and antenatal corticosteroids

Rationale

Chorioamnionitis is associated with preterm delivery and involution of the fetal thymus. Women at risk of preterm delivery receive antenatal corticosteroids which accelerate fetal lung maturation and improve neonatal outcome. However, the effects of antenatal corticosteroids on the fetal thymus in the settings of chorioamnionitis are largely unknown. We hypothesized that intra-amniotic exposure to lipopolysaccharide (LPS) causes involution of the fetal thymus resulting in persistent effects on thymic structure and cell populations. We also hypothesized that antenatal corticosteroids may modulate the effects of LPS on thymic development.

Methods

Time-mated ewes with singleton fetuses received an intra-amniotic injection of LPS 7 or 14 days before preterm delivery at 120 days gestational age (term = 150 days). LPS and corticosteroid treatment groups received intra-amniotic LPS either preceding or following maternal intra-muscular betamethasone. Gestation matched controls received intra-amniotic and maternal intra-muscular saline. The fetal intra-thoracic thymus was evaluated.

Results

Intra-amniotic LPS decreased the cortico-medullary (C/M) ratio of the thymus and increased Toll-like receptor (TLR) 4 mRNA and CD3 expression indicating involution and activation of the fetal thymus. Increased TLR4 and CD3 expression persisted for 14 days but Foxp3 expression decreased suggesting a change in regulatory T-cells. Sonic hedgehog and bone morphogenetic protein 4 mRNA, which are negative regulators of T-cell development, decreased in response to intra-amniotic LPS. Betamethasone treatment before LPS exposure attenuated some of the LPS-induced thymic responses but increased cleaved caspase-3 expression and decreased the C/M ratio. Betamethasone treatment after LPS exposure did not prevent the LPS-induced thymic changes.

Conclusion

Intra-amniotic exposure to LPS activated the fetal thymus which was accompanied by structural changes. Treatment with antenatal corticosteroids before LPS partially attenuated the LPS-induced effects but increased apoptosis in the fetal thymus. Corticosteroid administration after the inflammatory stimulus did not inhibit the LPS effects on the fetal thymus.

Maternal dietary DHA supplementation to improve inflammatory outcomes in the preterm infant

Dietary DHA (22:6n-3) is a long-chain PUFA that has provocative effects on inflammatory signal events that could potentially affect preterm infant health. It is well known that the essential fatty acid of the (n-3) series; α-linolenic acid (18:3n:3) can be desaturated and elongated in the liver endoplasmic reticulum and peroxisome to produce the 22-carbon DHA. Nevertheless, concern exists as to the efficiency of this mechanism in providing the preterm infant with adequate DHA. Activity of the δ-6-desaturase and the δ-5-desaturase necessary for DHA synthesis is decreased by protein deprivation. The combined effects of suboptimal intake of both DHA and protein in the preterm infants could have substantial clinical consequences.

Gastrin-releasing peptide blockade as a broad-spectrum anti-inflammatory therapy for asthma

Gastrin-releasing peptide (GRP) is synthesized by pulmonary neuroendocrine cells in inflammatory lung diseases, such as bronchopulmonary dysplasia (BPD). Many BPD infants develop asthma, a serious disorder of intermittent airway obstruction. Despite extensive research, early mechanisms of asthma remain controversial. The incidence of asthma is growing, now affecting >300 million people worldwide. To test the hypothesis that GRP mediates asthma, we used two murine models: ozone exposure for air pollution-induced airway hyperreactivity (AHR), and ovalbumin (OVA)-induced allergic airway disease. BALB/c mice were given small molecule GRP blocking agent 77427, or GRP blocking antibody 2A11, before exposure to ozone or OVA challenge. In both models, GRP blockade abrogated AHR and bronchoalveolar lavage (BAL) macrophages and granulocytes, and decreased BAL cytokines implicated in asthma, including those typically derived from Th1 (e.g., IL-2, TNFα), Th2 (e.g., IL-5, IL-13), Th17 (IL-17), macrophages (e.g., MCP-1, IL-1), and neutrophils (KC = IL-8). Dexamethasone generally had smaller effects on all parameters. Macrophages, T cells, and neutrophils express GRP receptor (GRPR). GRP blockade diminished serine phosphorylation of GRPR with ozone or OVA. Thus, GRP mediates AHR and airway inflammation in mice, suggesting that GRP blockade is promising as a broad-spectrum therapeutic approach to treat and/or prevent asthma in humans.

Thymic changes after chorioamnionitis induced by intraamniotic lipopolysaccharide in fetal sheep

OBJECTIVE

Regulatory T lymphocytes mediate homeostasis of the immune system and differentiate under the control of the transcription factor FoxP3 in the fetal thymus. We asked whether fetal inflammation caused by chorioamnionitis would modulate thymus development.

STUDY DESIGN

Fetal sheep were exposed to an intraamniotic injection of 10 mg lipopolysaccharide at 5 hours, 1 day, 2 days, or 5 days before delivery at 123 gestation days. Cord blood lymphocytes, plasma cortisol, and thymus weight were measured. Glucocorticoid receptor-, activated caspase-3-, Ki-67-, proliferating cell nuclear antigen-, nuclear factor-kappaB-, and FoxP3-positive cells were immunohistochemically evaluated in thymus.

RESULTS

Intraamniotic lipopolysaccharide exposure decreased the number of circulating lymphocytes by 40% after 1 day. Thymus-to-body weight ratios were reduced in all lipopolysaccharide groups by a maximum of 40% at 5 days. Lipopolysaccharide exposure modestly increased plasma cortisol concentration, increased nuclear factor-kappaB immunostaining in fetal thymus and reduced the number of FoxP3-positive cells by 40% at 1 day.

CONCLUSION

Intraamniotic exposure to lipopolysaccharide induced thymic changes and influenced thymic FoxP3 expression.

Modulation of fetal inflammatory response on exposure to lipopolysaccharide by chorioamnion, lung, or gut in sheep

OBJECTIVE

We hypothesized that fetal lipopolysaccharide exposures to the chorioamnion, lung, or gut would induce distinct systemic inflammatory responses.

STUDY DESIGN

Groups of 5-7 time-mated ewes were used to surgically isolate the fetal respiratory and the gastrointestinal systems from the amniotic compartment. Outcomes were assessed at 124 days gestational age, 2 days and 7 days after lipopolysaccharide (10 mg, Escherichia coli 055:B5) or saline solution infusions into the fetal airways or amniotic fluid.

RESULTS

Lipopolysaccharide induced systemic inflammatory changes in all groups in the blood, lung, liver, and thymic lymphocytes. Changes in lymphocytes in the posterior mediastinal lymph node draining lung and gut, occurred only after direct contact of lipopolysaccharide with the fetal lung or gut.

CONCLUSION

Fetal systemic inflammatory responses occurred after chorioamnion, lung, or gut exposures to lipopolysaccharide. The organ responses differed based on route of the fetal exposure.

Gastrin-releasing peptide, immune responses, and lung disease

Gastrin-releasing peptide (GRP) is produced by pulmonary neuroendocrine cells (PNECs), with highest numbers of GRP-positive cells present in fetal lung. Normally GRP-positive PNECs are relatively infrequent after birth, but PNEC hyperplasia is frequently associated with chronic lung diseases. To address the hypothesis that GRP mediates chronic lung injury, we present the cumulative evidence implicating GRP in bronchopulmonary dysplasia (BPD), the chronic lung disease of premature infants who survive acute respiratory distress syndrome. The availability of well-characterized animal models of BPD was a critical tool for demonstrating that GRP plays a direct role in the early pathogenesis of this disease. Potential mechanisms by which GRP contributes to injury are analyzed, with the main focus on innate immunity. Autoreactive T cells may contribute to lung injury late in the course of disease. A working model is proposed with GRP triggering multiple cell types in both the innate and adaptive immune systems, promoting cascades culminating in chronic lung disease. These observations represent a paradigm shift in the understanding of the early pathogenesis of BPD, and suggest that GRP blockade could be a novel treatment to prevent this lung disease in premature infants.

Regulation and signaling of human bombesin receptors and their biological effects

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of molecular mechanisms by which mammalian bombesin receptors are regulated and which intracellular signaling pathways have been characterized to mediate agonist-dependent receptor biological effects.

RECENT FINDINGS

Mammalian bombesin receptors have been demonstrated to be involved in a larger array of physiological and pathophysiological conditions than previously reported. Pharmacological experiments in vitro and in vivo as well as utilization of animals genetically deficient of the gastrin-releasing peptide receptor demonstrated roles in memory and fear behavior, lung development and injury, small intestinal cell repair, autocrine tumor growth, and mediating signals for pruritus and penile reflexes. Intracellular signaling studies predominantly of the gastrin-releasing peptide receptor owing to its frequent overexpression in some human malignancies showed that PI3 kinase activation is an important mechanism of cell proliferation. Tumor cell treatment including gastrin-releasing peptide receptor antagonists combined with inhibition of epidermal growth factor receptor resulted in an additive effect on blocking cell proliferation. Novel molecular mechanisms of the orphan bombesin receptor subtype-3 and gastrin-releasing peptide receptor gene regulation have been elucidated.

SUMMARY

Inhibition of gastrin-releasing peptide receptor signaling in human malignancies represents an attractive target for pharmacological treatment. Novel functions of bombesin related peptides have been identified including processes in the central nervous system, lung and intestinal tract.

Early interstitial lung disease in familial pulmonary fibrosis

RATIONALE

Identification of early, asymptomatic interstitial lung disease (ILD) in populations at risk of developing idiopathic pulmonary fibrosis (IPF) may improve the understanding of the natural history of IPF.

OBJECTIVES

To determine clinical, radiographic, physiologic, and pathologic features of asymptomatic ILD in family members of patients with familial IPF.

METHODS

One hundred sixty-four subjects from 18 kindreds affected with familial IPF were evaluated for ILD. Bronchoalveolar lavage fluid cells were analyzed using flow cytometry. Lung biopsies were performed in six subjects with asymptomatic ILD.

MEASUREMENTS AND MAIN RESULTS

High-resolution computed tomography abnormalities suggesting ILD were identified in 31 (22%) of 143 asymptomatic subjects. Subjects with asymptomatic ILD were significantly younger than subjects with known familial IPF (P < 0.001) and significantly older than related subjects without lung disease (P < 0.001). A history of smoking was identified in 45% of subjects with asymptomatic ILD and in 67% of subjects with familial IPF; these percentages were significantly higher than that of related subjects without lung disease (23%) (P = 0.02 and P < 0.001, respectively). Percentages of activated CD4(+) lymphocytes were significantly higher in bronchoalveolar lavage fluid cells from subjects with asymptomatic ILD compared with related subjects without lung disease (P < 0.001). Lung biopsies performed in subjects with asymptomatic ILD revealed diverse histologic subtypes.

CONCLUSIONS

Asymptomatic ILD in individuals at risk of developing familial IPF can be identified using high-resolution computed tomography scan of the chest, especially in those with a history of smoking. Lung biopsies from individuals in this cohort with early asymptomatic lung disease demonstrate various histologic subtypes of ILD.