Human bronchial epithelium controls TH2 responses by TH1-induced, nitric oxide-mediated STAT5 dephosphorylation: implications for the pathogenesis of asthma

STATs, promising targets for the treatment of autoimmune and inflammatory diseases

Cytokines play a crucial role in the pathophysiology of autoimmune and inflammatory diseases, with over 50 cytokines undergoing signal transduction through the Signal Transducers and Activators of Transcription (STAT) signaling pathway. Recent studies have solidly confirmed the pivotal role of STATs in autoimmune and inflammatory diseases. Therefore, this review provides a detailed summary of the immunological functions of STATs, focusing on exploring their mechanisms in various autoimmune and inflammatory diseases. Additionally, with the rapid advancement of structural biology in the field of drug discovery, many STAT inhibitors have been identified using structure-based drug design strategies. In this review, we also examine the structures of STAT proteins and compile the latest research on STAT inhibitors currently being tested in animal models and clinical trials for the treatment of immunological diseases, which emphasizes the feasibility of STATs as promising therapeutic targets and provides insights into the design of the next generation of STAT inhibitors.

Metabolomics combined with network pharmacology reveals anti-asthmatic effects of Nepeta bracteata on allergic asthma rats

Objective

To investigate the mechanisms that underlie the anti-asthmatic effects of Nepeta bracteata (DBJJ, Dabao Jingjie in Chinese) in rats by integrating metabolomics and network pharmacology.

Methods

In this study, the rat model of asthma was induced by ovalbumin (OVA), and the rats were treated with a decoction of N. bracteata. Pathological changes in lung tissue were observed, and the quantification of eosinophils (EOS) and white blood cells (WBC) in bronchoalveolar lavage fluid was performed. Furthermore, the serum levels of asthma-related factors induced by OVA were assessed. 1H NMR spectroscopy serum metabolomics method was utilized to identify differential metabolites and their associated metabolic pathways. UPLC-QE-MS/MS combined with network pharmacology was employed to predict the core targets and pathways of DBJJ in its action against asthma. The anti-asthmatic properties of DBJJ were investigated using an integrated approach of metabolomics and network pharmacology. The findings were validated through molecular docking and Western blotting analysis of the key targets.

Results

The administration of DBJJ effectively alleviated OVA-induced lung histopathological changes and decreased the number of EOS and WBC in BALF. Additionally, DBJJ inhibited the OVA-induced elevation of TNF-α, IL-18, Ig-E, EOS, IL-1β, MDA, VEGF-A, and TGF-β1. A total of 21 biomarkers and 10 pathways were found by metabolomics analysis. A total of 29 compounds were identified by UPLC-QE-MS/MS, in which 13 active components were screened by oral availability and Caco-2 cell permeability, the 120 targets and 173 KEGG pathways were predicted. The integration of metabolomics and network pharmacological analysis revealed that DBJJ's main constituents, including ferulic acid and ursolic acid, exerted their effects on four targets, namely DAO and NOS2, as well as their associated metabolites and pathways. The active constituents of DBJJ demonstrated a high binding affinity towards DAO and NOS2. Furthermore, DBJJ was observed to decrease the protein expression and phosphorylation levels of NOS2, MAPK, and STAT3.

Conclusion

The administration of DBJJ demonstrates notable anti-asthma properties in rats with allergic asthma. This effect can be attributed to the modulation of various targets, including NOS2, MAPK, and STAT3, by primary constituents such as ferulic acid and ursolic acid.

Nitric Oxide System and Bronchial Epithelium: More Than a Barrier

Airway epithelium forms a physical barrier that protects the lung from the entrance of inhaled allergens, irritants, or microorganisms. This epithelial structure is maintained by tight junctions, adherens junctions and desmosomes that prevent the diffusion of soluble mediators or proteins between apical and basolateral cell surfaces. This apical junctional complex also participates in several signaling pathways involved in gene expression, cell proliferation and cell differentiation. In addition, the airway epithelium can produce chemokines and cytokines that trigger the activation of the immune response. Disruption of this complex by some inflammatory, profibrotic, and carcinogens agents can provoke epithelial barrier dysfunction that not only contributes to an increase of viral and bacterial infection, but also alters the normal function of epithelial cells provoking several lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) or lung cancer, among others. While nitric oxide (NO) molecular pathway has been linked with endothelial function, less is known about the role of the NO system on the bronchial epithelium and airway epithelial cells function in physiological and different pathologic scenarios. Several data indicate that the fraction of exhaled nitric oxide (FENO) is altered in lung diseases such as asthma, COPD, lung fibrosis, and cancer among others, and that reactive oxygen species mediate uncoupling NO to promote the increase of peroxynitrite levels, thus inducing bronchial epithelial barrier dysfunction. Furthermore, iNOS and the intracellular pathway sGC-cGMP-PKG are dysregulated in bronchial epithelial cells from patients with lung inflammation, fibrosis, and malignancies which represents an attractive drug molecular target. In this review we describe in detail current knowledge of the effect of NOS-NO-GC-cGMP-PKG pathway activation and disruption in bronchial epithelial cells barrier integrity and its contribution in different lung diseases, focusing on bronchial epithelial cell permeability, inflammation, transformation, migration, apoptosis/necrosis, and proliferation, as well as the specific NO molecular pathways involved.

Nitric Oxide Signaling in T Cell-Mediated Immunity

Nitric oxide (NO) is a key messenger in the pathogenesis of inflammation, linking innate and adaptive immunity. By targeting signaling molecules, NO from inducible NO synthase (iNOS) and endothelial (e)NOS affects T helper cell differentiation and the effector functions of T lymphocytes, and is a potential target for therapeutic manipulation. In this review we discuss the regulatory actions exerted by NO on T cell functions, focusing on S-nitrosylation as an important post-translational modification by which NO acts as a signaling molecule during T cell-mediated immunity. We also present recent findings showing novel mechanisms through which NO regulates the activation of human T cells, and consider their potential in strategies to treat tumoral, allergic, and autoimmune diseases.

Role of transcription factors in the pathogenesis of asthma and COPD

Inflammation is a central feature of asthma and chronic obstructive pulmonary disease (COPD). Despite recent advances in the knowledge of the pathogenesis of asthma and COPD, much more research on the molecular mechanisms of asthma and COPD are needed to aid the logical development of new therapies for these common and important diseases, particularly in COPD where no effective treatments currently exist. In the future the role of the activation/repression of different transcription factors and the genetic regulation of their expression in asthma and COPD may be an increasingly important aspect of research, as this may be one of the critical mechanisms regulating the expression of different clinical phenotypes and their responsiveness to therapy, particularly to anti-inflammatory drugs.

Nitrosothiols in the immune system: signaling and protection

SIGNIFICANCE

In the immune system, nitric oxide (NO) has been mainly associated with antibacterial defenses exerted through oxidative, nitrosative, and nitrative stress and signal transduction through cyclic GMP-dependent mechanisms. However, S-nitrosylation is emerging as a post-translational modification (PTM) involved in NO-mediated cell signaling.

RECENT ADVANCES

Precise roles for S-nitrosylation in signaling pathways have been described both for innate and adaptive immunity. Denitrosylation may protect macrophages from their own S-nitrosylation, while maintaining nitrosative stress compartmentalized in the phagosomes. Nitrosothiols have also been shown to be beneficial in experimental models of autoimmune diseases, mainly through their role in modulating T-cell differentiation and function.

CRITICAL ISSUES

Relationship between S-nitrosylation, other thiol redox PTMs, and other NO-signaling pathways has not been always taken into account, particularly in the context of immune responses. Methods for assaying S-nitrosylation in individual proteins and proteomic approaches to study the S-nitrosoproteome are constantly being improved, which helps to move this field forward.

FUTURE DIRECTIONS

Integrated studies of signaling pathways in the immune system should consider whether S-nitrosylation/denitrosylation processes are among the PTMs influencing the activity of key signaling and adaptor proteins. Studies in pathophysiological scenarios will also be of interest to put these mechanisms into broader contexts. Interventions modulating nitrosothiol levels in autoimmune disease could be investigated with a view to developing new therapies.

Crosstalk between leptin and interleukin-1β abrogates negative inotropic effects in a model of chronic hyperleptinemia

Interleukin 1 beta (IL-1 β) is a proinflammatory cytokine with potent cardiosuppressive effects. Previous studies have shown that leptin blunts the negative inotropic effects of IL-1 β in isolated adult rat cardiac myocytes. However, the interactions between leptin and IL-1 β in the heart have not been examined on a background of chronic hyperleptinemia. To study this interaction, we have chosen the SHHF rat, a model of spontaneous hypertension that ultimately develops congestive heart failure. SHHF that are heterozygous for a null mutation of the leptin receptor (+/ fa cp, HET) are phenotypically lean but chronically hyperleptinemic and develop heart failure earlier than their normoleptinemic true lean (+/+, LN) littermates. Simultaneous cell shortening and calcium transients were measured in isolated ventricular cardiac myocytes from LN and HET SHHF in response to leptin, IL-1 β or IL-1 β following one hour pretreatment with leptin. Despite evidence of metabolic leptin resistance, HET myocytes were sensitive to the negative inotropic effect of leptin, similar to LN. Contractility returned to control levels in myocytes from HET that were pretreated with leptin prior to IL-1 β, while contractility remained depressed compared with control and similar to leptin alone in LN. Chronic hyperleptinemia resulted in altered JAK/STAT signaling in response to leptin and IL-1 β in isolated perfused hearts from HET compared with LN SHHF. Phosphorylated STAT3 (pSTAT3) and STAT5 (pSTAT5) decreased when HET hearts were treated with leptin followed by IL-1 β. While decreases in pSTAT3 and pSTAT5 may be associated with abrogation of the acute negative inotropic effects of IL-1 β in the presence of leptin in HET, long-term consequences remain to be explored. This study demonstrates that the heart remains sensitive to leptin in a hyperleptinemic state. Crosstalk between leptin and IL-1 β can influence cardiac function and cytokine signaling and these interactions are moderated by the presence of long-term hyperleptinemia.

Expansion of CD4(+) CD25(+) and CD25(-) T-Bet, GATA-3, Foxp3 and RORγt cells in allergic inflammation, local lung distribution and chemokine gene expression

Allergic asthma is associated with airway eosinophilia, which is regulated by different T-effector cells. T cells express transcription factors T-bet, GATA-3, RORγt and Foxp3, representing Th1, Th2, Th17 and Treg cells respectively. No study has directly determined the relative presence of each of these T cell subsets concomitantly in a model of allergic airway inflammation. In this study we determined the degree of expansion of these T cell subsets, in the lungs of allergen challenged mice. Cell proliferation was determined by incorporation of 5-bromo-2'-deoxyuridine (BrdU) together with 7-aminoactnomycin (7-AAD). The immunohistochemical localisation of T cells in the lung microenvironments was also quantified. Local expression of cytokines, chemokines and receptor genes was measured using real-time RT-PCR array analysis in tissue sections isolated by laser microdissection and pressure catapulting technology. Allergen exposure increased the numbers of T-bet(+), GATA-3(+), RORγt(+) and Foxp3(+) cells in CD4(+)CD25(+) and CD4(+)CD25(-) T cells, with the greatest expansion of GATA-3(+) cells. The majority of CD4(+)CD25(+) T-bet(+), GATA-3(+), RORγt(+) and Foxp3(+) cells had incorporated BrdU and underwent proliferation during allergen exposure. Allergen exposure led to the accumulation of T-bet(+), GATA-3(+) and Foxp3(+) cells in peribronchial and alveolar tissue, GATA-3(+) and Foxp3(+) cells in perivascular tissue, and RORγt(+) cells in alveolar tissue. A total of 28 cytokines, chemokines and receptor genes were altered more than 3 fold upon allergen exposure, with expression of half of the genes claimed in all three microenvironments. Our study shows that allergen exposure affects all T effector cells in lung, with a dominant of Th2 cells, but with different local cell distribution, probably due to a distinguished local inflammatory milieu.

Regulation of lymphocytes by nitric oxide

Shortly after the identification of nitric oxide (NO) as a product of macrophages, it was discovered that NO generated by inducible NO synthase (iNOS) inhibits the proliferation of T lymphocytes. Since then, it has become clear that iNOS activity also regulates the development, differentiation, and/or function of various types of T cells and B cells and also affects NK cells. The three key mechanisms underlying the iNOS-dependent immunoregulation are (a) the modulation of signaling processes by NO, (b) the depletion of arginine, and (c) the alteration of accessory cell functions. This chapter highlights important principles of iNOS-dependent immunoregulation of lymphocytes and also reviews more recent evidence for an effect of endothelial or neuronal NO synthase in lymphocytes.

Cancer-associated myeloproliferation: old association, new therapeutic target

The association between malignancy and development of a paraneoplastic leukocytosis, the so-called leukemoid reaction, has long been appreciated. Although a leukemoid reaction has conventionally been defined as a peripheral blood leukocytosis composed of both mature and immature granulocytes that exceeds 50,000/microL, a less profound leukocytosis may be appreciated in many patients harboring a malignant disease. More recent insights have shed new light on this long-recognized association, because research performed in both murine models and cancer patients has uncovered multiple mechanisms by which tumors both drive myelopoiesis, sometimes leading to a clinically apparent leukocytosis, and inhibit the differentiation of myeloid cells, resulting in a qualitative change in myelopoiesis. This qualitative change leads to the accumulation of immature myeloid cells, which due to their immune suppressive effects have been collectively called myeloid-derived suppressor cells. More recently, myeloid cells have been shown to promote tumor angiogenesis. Cancer-associated myeloproliferation is not merely a paraneoplastic phenomenon of questionable importance but leads to the suppression of host immunity and promotion of tumor angiogenesis, both of which play an integral part in tumorigenesis and metastasis. Therefore, cancer-associated myeloproliferation represents a novel therapeutic target in cancer that, decades after its recognition, is only now being translated into clinical practice.

Urinary nitric oxide excretion in infants with eczema

Eczema is characterized by inflammation of the skin and is commonly associated with food allergy. It has been suggested that nitric oxide (NO) is an important player in eczema, food allergy and intestinal inflammation. The aim of this study was to assess the levels of urinary NO breakdown products in infants with eczema and the effect of eczema treatment on NO levels. Ninety-four infants with eczema, 58 boys and 36 girls, with a mean age of 7.5 ± 5.2 months (mean ± s.d.) at inclusion were examined twice with an interval of 6 wk. The sum of nitrite and nitrate was measured colorimetrically in urinary samples from both visits and compared with clinical data concerning eczema severity, nutrition, gastrointestinal symptoms, asthma and skin prick positivity. The levels of NO products increased significantly from the first to the second visit: 289; 374 μm (median; IQR) vs. 457; 678 μm (median; IQR) (p < 0.001) in parallel with a significant improvement of the eczema. After eczema treatment consisting of skin care and elimination diet during the 6-wk interval between evaluations, the NO levels approached the values previously found in healthy children. The results support previous studies indicating that the homeostasis of nitrogen radicals is disturbed in childhood eczema.

Elucidation of asthma phenotypes in atopic teenagers through parallel immunophenotypic and clinical profiling

BACKGROUND

Current treatment strategies for asthma in teenagers derive primarily from information on chronic disease in adults. More detailed understanding of risk factors related to teenage asthma might aid in the development of improved preventive and treatment strategies for this age group.

OBJECTIVE

We sought to identify biomarkers associated with asthma phenotypes in teenagers, particularly atopic asthma, and to identify markers that aid in discriminating between atopic subjects at high versus low risk of asthma.

METHODS

We studied 1380 unselected 14-year-olds and collected data on clinical history, allergic sensitization, and respiratory and immunoinflammatory function. The latter comprised measurements of circulating inflammatory markers and in vitro innate and adaptive immune functions, including house dust mite T-cell responses. We integrated the data into regression models to identify variables most strongly associated with asthma risk and severity among atopic subjects.

RESULTS

Eight hundred twenty-seven subjects were atopic, 140 subjects were asthmatic, and 81% of asthmatic subjects were also atopic. We identified asthma risk variables related to atopy intensity, including specific IgE and eosinophil levels, plus an additional series external to the T(H)2 cascade but that modified risk only in atopic subjects, including IFN-gamma, IL-10, and IL-12 responses and neutrophil numbers in blood. Moreover, bronchial hyperresponsiveness was associated strongly with atopic but not nonatopic asthma, and the bronchial hyperresponsiveness risk profile was itself dominated by atopy-associated variables.

CONCLUSIONS

Asthma in teenagers is predominantly driven by atopy acting in concert with a second tier of T(H)2-independent immunoinflammatory mechanisms, which contribute to pathogenesis only against the background of pre-existing inhalant allergy.

Biomarkers in asthma

PURPOSE OF REVIEW

The purpose of this review is to highlight seminal and current literature that informs our understanding of the clinical and investigative utility of biomarkers in asthma. Biomarkers derive from a variety of sources [bronchiolar lavage (BAL), sputum, exhaled breath, and blood], and have widely variant performance characteristics, and applicability.

RECENT FINDINGS

Increasing attention is given to biomarkers in exhaled breath, both gaseous (exhaled nitric oxide) and higher molecular weight moieties [in exhaled breath condensate (EBC)]. Current research in EBC analysis has focused on validation, standardization, and technical considerations, whereas research on exhaled nitric oxide (ENO) has moved to testing its predictive value in clinical situations. The use of advanced biostatistical techniques, and combinatorial analyses has led to additional advances in the utility of biomarkers.

SUMMARY

To date, the best validated, and best performing biomarkers for clinical asthma appear to be measures of inflammation in induced sputum, and measures of ENO. Some trials using ENO appear particularly promising for early clinical use. EBC metrics are at present too inchoate for clinical purposes. However, not all important clinical and research questions can be addressed with sputum, EBC, or ENO metrics, leaving an important place for BAL, bronchial biopsy, and perhaps EBC measurements in the research arena.

Nitric oxide gas phase release in human small airway epithelial cells

Background

Asthma is a chronic airway inflammatory disease characterized by an imbalance in both Th1 and Th2 cytokines. Exhaled nitric oxide (NO) is elevated in asthma, and is a potentially useful non-invasive marker of airway inflammation. However, the origin and underlying mechanisms of intersubject variability of exhaled NO are not yet fully understood. We have previously described NO gas phase release from normal human bronchial epithelial cells (NHBEs, tracheal origin). However, smaller airways are the major site of morbidity in asthma. We hypothesized that IL-13 or cytomix (IL-1β, TNF-α, and IFN-γ) stimulation of differentiated small airway epithelial cells (SAECs, generation 10–12) and A549 cells (model cell line of alveolar type II cells) in culture would enhance NO gas phase release.

Methods

Confluent monolayers of SAECs and A549 cells were cultured in Transwell plates and SAECs were allowed to differentiate into ciliated and mucus producing cells at an air-liquid interface. The cells were then stimulated with IL-13 (10 ng/mL) or cytomix (10 ng/mL for each cytokine). Gas phase NO release in the headspace air over the cells was measured for 48 hours using a chemiluminescence analyzer.

Results

In contrast to our previous result in NHBE, baseline NO release from SAECs and A549 is negligible. However, NO release is significantly increased by cytomix (0.51 ± 0.18 and 0.29 ± 0.20 pl^.s^-1.cm^-2, respectively) reaching a peak at approximately 10 hours. iNOS protein expression increases in a consistent pattern both temporally and in magnitude. In contrast, IL-13 only modestly increases NO release in SAECs reaching a peak (0.06 ± 0.03 pl^.s^-1.cm^-2) more slowly (30 to 48 hours), and does not alter NO release in A549 cells.

Conclusion

We conclude that the airway epithelium is a probable source of NO in the exhaled breath, and intersubject variability may be due, in part, to variability in the type (Th1 vs Th2) and location (large vs small airway) of inflammation.

Respiratory Homeostasis and Exploitation of the Immune System for Lung Cancer Vaccines

Lung cancer is the leading cause of all cancer deaths in the US. The international scientific and clinical community has made significant advances toward understanding specific molecular mechanisms underlying lung carcinogenesis; however, despite these insights and advances in surgery and chemoradiotherapy, the prognosis for non-small-cell lung cancer (NSCLC) remains poor. Nonetheless, significant effort is being focused on advancing translational research evaluating the efficacy of novel targeted therapeutic strategies for lung cancer. Illustrative examples of this include antagonists of the epidermal growth factor receptor (EGFR), tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib, and a diverse assortment of anti-angiogenic compounds targeting growth factors and/or their receptors that regulate tumor-associated angiogenic programs. In addition, with the increased awareness of the significant role chronically activated leukocytes play as potentiators of solid-tumor development, the role of innate and adaptive immune cells as regulators of lung carcinogenesis is being examined. While some of these studies are examining how novel therapeutic strategies may enhance the efficacy of lung cancer vaccines, others are evaluating the intrinsic characteristics of the immune response to lung cancer in order to identify rate-limiting molecular and/or cellular programs to target with novel anticancer therapeutics. In this article, we explore important aspects of the immune system and its role in regulating normal respiratory homeostasis compared with the immune response accompanying development of lung cancer. These hallmarks are then discussed in the context of recent efforts to develop lung cancer vaccines, where we have highlighted important concepts that must be taken into consideration for future development of novel therapeutic strategies and clinical trials assessing their efficacy.

Prominin-1+/CD133+ bone marrow-derived heart-resident cells suppress experimental autoimmune myocarditis

AIMS

Experimental autoimmune myocarditis (EAM) is a CD4(+) T cell-mediated mouse model of inflammatory heart disease. Tissue-resident bone marrow-derived cells adopt different cellular phenotypes depending on the local milieu. We expanded a specific population of bone marrow-derived prominin-1-expressing progenitor cells (PPC) from healthy heart tissue, analysed their plasticity, and evaluated their capacity to protect mice from EAM and heart failure.

METHODS AND RESULTS

PPC were expanded from healthy mouse hearts. Analysis of CD45.1/CD45.2 chimera mice confirmed bone marrow origin of PPC. Depending on in vitro culture conditions, PPC differentiated into macrophages, dendritic cells, or cardiomyocyte-like cells. In vivo, PPC acquired a cardiac phenotype after direct injection into healthy hearts. Intravenous injection of PPC into myosin alpha heavy chain/complete Freund's adjuvant (MyHC-alpha/CFA)-immunized BALB/c mice resulted in heart-specific homing and differentiation into the macrophage phenotype. Histology revealed reduced severity scores for PPC-treated mice compared with control animals [treated with phosphate-buffered saline (PBS) or crude bone marrow at day 21 after MyHC-alpha/CFA immunization]. Echocardiography showed preserved fractional shortening and velocity of circumferential shortening in PPC but not PBS-treated MyHC-alpha/CFA-immunized mice. In vitro and in vivo data suggested that interferon-gamma signalling on PPC was critical for nitric oxide-mediated suppression of heart-specific CD4(+) T cells. Accordingly, PPC from interferon-gamma receptor-deficient mice failed to protect MyHC-alpha/CFA-immunized mice from EAM.

CONCLUSION

Prominin-1-expressing, heart-resident, bone marrow-derived cells combine high plasticity, T cell-suppressing capacity, and anti-inflammatory in vivo effects.

Sputum eosinophil apoptotic rate is positively correlated to exhaled nitric oxide in children

RATIONALE FOR STUDY

Exhaled nitric oxide (FE(NO)), a potential biomarker for asthma, is positively correlated with eosinophilic airway inflammation. Eosinophil apoptotic rate (AR) may be increased by NO but the relationship between eosinophil AR and NO has not been studied in vivo. This study tested the hypothesis that eosinophil AR will be positively related to FE(NO).

METHODS

Children with and without asthma were recruited and participated in an assessment that included FE(NO) measurement, skin prick reactivity, spirometry, and sputum induction. The absolute sputum eosinophil count and eosinophil AR were determined by morphology under light microscope after staining.

RESULTS

There were 31 children recruited, mean age 11 years, 21 were asthmatic and 19 were boys. The median FE(NO) (range) was 15.6 parts per billion (3.1-102.6), 17 were atopic and the mean (SD)% FEV(1) was 85 (10)%. Sputum eosinophil AR was determined in 19 children (16 asthmatics), mean (SD) value 0.49 (0.13). There were positive relationships between eosinophil AR and FE(NO) (Spearman rho = 0.46, P = 0.046), eosinophil AR and % eosinophil count (Spearman rho = 0.45, P = 0.050) and also FE(NO) and % eosinophil count (Spearman rho = 0.49, P = 0.024).

CONCLUSION

There is a positive relationship between FE(NO) and eosinophil AR. Nitric oxide may be involved in regulation of eosinophil AR in the airways.

Manipulation of acute inflammatory lung disease

Inflammatory lung disease to innocuous antigens or infectious pathogens is a common occurrence and in some cases, life threatening. Often, the inflammatory infiltrate that accompanies these events contributes to pathology by deleterious effects on otherwise healthy tissue and by compromising lung function by consolidating (blocking) the airspaces. A fine balance, therefore, exists between a lung immune response and immune-mediated damage, and in some the "threshold of ignorance" may be set too low. In most cases, the contributing, potentially offending, cell population or immune pathway is known, as are factors that regulate them. Why then are targeted therapeutic strategies to manipulate them not more commonplace in clinical medicine? This review highlights immune homeostasis in the lung, how and why this is lost during acute lung infection, and strategies showing promise as future immune therapeutics.

Inflammatory levels of nitric oxide inhibit airway epithelial cell migration by inhibition of the kinase ERK1/2 and activation of hypoxia-inducible factor-1 alpha

Increased synthesis of NO during airway inflammation, caused by induction of nitric-oxide synthase 2 in several lung cell types, may contribute to epithelial injury and permeability. To investigate the consequence of elevated NO production on epithelial function, we exposed cultured monolayers of human bronchial epithelial cells to the NO donor diethylenetriaamine NONOate. At concentrations generating high nanomolar levels of NO, representative of inflammatory conditions, diethylenetriaamine NONOate markedly reduced wound closure in an in vitro scratch injury model, primarily by inhibiting epithelial cell migration. Analysis of signaling pathways and gene expression profiles indicated a rapid induction of the mitogen-activated protein kinase phosphatase (MPK)-1 and decrease in extracellular signal-regulated kinase (ERK)1/2 activation, as well as marked stabilization of hypoxia-inducible factor (HIF)-1alpha and activation of hypoxia-responsive genes, under these conditions. Inhibition of ERK1/2 signaling using U0126 enhanced HIF-1alpha stabilization, implicating ERK1/2 dephosphorylation as a contributing mechanism in NO-mediated HIF-1alpha activation. Activation of HIF-1alpha by the hypoxia mimic cobalt chloride, or cell transfection with a degradation-resistant HIF-1alpha mutant construct inhibited epithelial wound repair, implicating HIF-1alpha in NO-mediated inhibition of cell migration. Conversely, NO-mediated inhibition of epithelial wound closure was largely prevented after small interfering RNA suppression of HIF-1alpha. Finally, NO-mediated inhibition of cell migration was associated with HIF-1alpha-dependent induction of PAI-1 and activation of p53, both negative regulators of epithelial cell migration. Collectively, our results demonstrate that inflammatory levels of NO inhibit epithelial cell migration, because of suppression of ERK1/2 signaling, and activation of HIF-1alpha and p53, with potential consequences for epithelial repair and remodeling during airway inflammation.

CD11b+ monocytes abrogate Th17 CD4+ T cell-mediated experimental autoimmune myocarditis

Experimental autoimmune myocarditis (EAM) represents a Th17 T cell-mediated mouse model of postinflammatory heart disease. In BALB/c wild-type mice, EAM is a self-limiting disease, peaking 21 days after alpha-myosin H chain peptide (MyHC-alpha)/CFA immunization and largely resolving thereafter. In IFN-gammaR(-/-) mice, however, EAM is exacerbated and shows a chronic progressive disease course. We found that this progressive disease course paralleled persistently elevated IL-17 release from T cells infiltrating the hearts of IFN-gammaR(-/-) mice 30 days after immunization. In fact, IL-17 promoted the recruitment of CD11b(+) monocytes, the major heart-infiltrating cells in EAM. In turn, CD11b(+) monocytes suppressed MyHC-alpha-specific Th17 T cell responses IFN-gamma-dependently in vitro. In vivo, injection of IFN-gammaR(+/+)CD11b(+), but not IFN-gammaR(-/-)CD11b(+), monocytes, suppressed MyHC-alpha-specific T cells, and abrogated the progressive disease course in IFN-gammaR(-/-) mice. Finally, coinjection of MyHC-alpha-specific, but not OVA-transgenic, IFN-gamma-releasing CD4(+) Th1 T cell lines, together with MyHC-alpha-specific Th17 T cells protected RAG2(-/-) mice from EAM. In conclusion, CD11b(+) monocytes play a dual role in EAM: as a major cellular substrate of IL-17-induced inflammation and as mediators of an IFN-gamma-dependent negative feedback loop confining disease progression.

Animal models of asthma

Animal models of asthma are a tool that allows studies to be conducted in the setting of an intact immune and respiratory system. These models have highlighted the importance of T-helper type 2 driven allergic responses in the progression of asthma and have been useful in the identification of potential drug targets for interventions involving allergic pathways. However, a number of drugs that have been shown to have some efficacy in animal models of asthma have shown little clinical benefit in human asthmatics. This may be due to a number of factors including the species of animal chosen and the methods used to induce an asthmatic phenotype in animals that do not normally develop a disease that could be characterized as asthma. The range of animal models available is vast, with the most popular models being rodents (inbred mice and rats) and guinea-pigs, which have the benefit of being easy to handle and being relatively cost effective compared with other models that are available. The recent advances in transgenic technology and the development of species-specific probes, particularly in mice, have allowed detailed mechanistic studies to be conducted. Despite these advances in technology, there are a number of issues with current animal models of asthma that must be recognized including the disparity in immunology and anatomy between these species and humans, the requirement for adjuvant during senitization in most models, the acute nature of the allergic response that is induced and the use of adult animals as the primary disease model. Some larger animal models using sheep and dogs have been developed that may address some of these issues but they also have different biology from humans in many ways and are extremely costly, with very few probes available for characterizing allergic responses in the airway in these species. As research in this area continues to expand, the relative merits and limitations of each model must be defined and understood in order to evaluate the information that is obtained from these models and to extrapolate these findings to humans so that effective drug therapies can be developed. Despite these issues, animal models have been, and will continue to be, vital in understanding the mechanisms that are involved in the development and progression of asthma.

A NOS1 gene polymorphism associated with asthma and specific immunoglobulin E response to mite allergens in a Colombian population

BACKGROUND

Nitric oxide (NO) is involved in asthma pathogenesis and is synthesized by three isoforms of NO synthase, one of them encoded by NOS1 gene. The CA-repeat and the C5266T SNP in NOS1 exon 29 have been associated with asthma and IgE levels. We thought to test the association of asthma and asthma-related phenotypes with the exon 29 CA-repeat and the C5266T SNP in a Colombian population sample.

METHODS

The CA-repeat and the C5266T SNP were genotyped in 167 asthmatics and 166 controls using PCR-based fragment length polymorphism and TaqMan assay. We also determined total and mite-specific IgE against Blomia tropicalis and Dermatophagoides pteronyssinus.

RESULTS

Three new CA-repeat alleles, 14, 23 and 24 repeats were detected. Allele comprising 16 repeats was associated with asthma (OR: 1.90 (CI 1.22-2.97, p(c) = 0.028) and low total (p(c) = 0.02) and specific IgE to B. tropicalis (p(c) < 0.0001) and D. pteronyssinus (p(c) < 0.0001). We found no association of the C5266T SNP and asthma or IgE levels.

CONCLUSION

NOS1 exon 29 CA-repeat may be a risk factor for asthma susceptibility and mite specific IgE response in a Colombian population.

Nitric oxide promotes airway epithelial wound repair through enhanced activation of MMP-9

The airway epithelium provides a protective barrier against inhaled environmental toxins and microorganisms, and epithelial injury initiates a number of processes to restore its barrier integrity, including activation of matrix metalloproteinases such as MMP-9 (92-kD gelatinase B). Airway epithelial cells continuously produce nitric oxide (NO), which has been linked to cell migration and MMP-9 regulation in several cell types, but the importance of epithelial NO in mediating airway epithelial repair or MMP-9 activation is unknown. Using primary or immortalized human bronchial epithelial cells, we demonstrate that low concentrations of NO promote epithelial cell migration and wound repair in an in vitro wound assay, which was associated with increased localized expression and activation of MMP-9. In addition, in HBE1 cells that were stably transfected with inducible NOS (NOS2), to mimic constitutive epithelial NOS2 expression in vivo, NOS inhibition decreased epithelial wound repair and MMP-9 expression. The stimulatory effects of NO on epithelial wound repair and MMP-9 expression were dependent on cGMP-mediated pathways and were inhibited by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase. Inhibition of cGMP-dependent protein kinase (PKG) attenuated NO-mediated epithelial wound closure, but did not affect MMP-9 expression. However, pharmacologic MMP inhibition and siRNA knockdown of MMP-9 expression demonstrated the contribution of MMP-9 to NO-mediated wound closure. Overall, our results demonstrate that NOS2-derived NO contributes to airway epithelial repair by both PKG-dependent and -independent mechanisms, and involves NO-dependent expression and activation of MMP-9.

Regulatory role of pro-Th1 and pro-Th2 cytokines in modulating the activity of Th1 and Th2 cells when B cell and macrophages are used as antigen presenting cells

BACKGROUND

Presence of antigen presenting cells, expression of costimulatory molecules, the strength of first signal and cytokine milieu are quite important in influencing the reactivation of differentiated Th1 and Th2 cells.

RESULTS

In the present study, we have analyzed the concerted action of pro-Th1 and pro-Th2 cytokines in the presence of B cells, peritoneal and splenic macrophages as antigen presenting cells and varied concentration of first (anti-CD3 Ab) and second (B7-1 transfectant) signals on the proliferation and cytokine secretion by Th1 and Th2 cells. Interesting observations were made that IFN-gamma significantly augmented the secretion of IL-4 by Th2 cells when either B cells or splenic or peritoneal macrophages were used as APC. Further, IFN-gamma significantly inhibited the proliferation of Th1 cells only in the presence of peritoneal macrophages. We have also observed that B cells could significantly respond to cytokines to further enhance the proliferation and cytokine release by Th1 and Th2 cells. But not much effect on addition of exogenous cytokines IL-1, IL-4, IL-5, IL-12 was observed on the proliferation of Th1 and Th2 cells in the presence of macrophages. In contrast, both IFN-gamma and IL-2 significantly enhanced the production of IL-4 and IL-5 respectively, by Th2 cells in presence of B cells, splenic and peritoneal macrophages. Another important observation was that the addition of B7-1 transfectants in the cultures, which were stimulated with low dose of anti-CD3 Ab significantly, enhanced the proliferation and cytokine secretion.

CONCLUSION

This study indicates involvement of different type of APCs, cytokine milieu, dose of first and second signals in a concerted manner in the outcome of the immune response. The significance of this study is that the immunization with antigen along with costimulatory molecules may significantly reduce the dose of antigen and can generate better immune response than antigen alone.

RUTI: a new chance to shorten the treatment of latent tuberculosis infection

Treatment of latent tuberculosis infection (LTBI) requires a long period of chemotherapy (9 months), which makes treatment-compliance extremely difficult. Current knowledge of latent bacilli and of the lesions with which they are associated suggests that these bacilli survive in granulomas with a central necrotic core and an outermost layer of foamy macrophages (FM) that represent an important immunosuppressive barrier. The presence of FM, which is especially strong in mice, explains not only the kinetics of the drainage of dead bacilli, debris and surfactant, but also how latent bacilli can escape from the granuloma and re-grow in the periphery, particularly in the alveolar spaces where they can disseminate easily. RUTI, a therapeutic vaccine made of detoxified, fragmented Mycobacterium tuberculosis cells, delivered in liposomes, was used to assess its effectiveness in a short period of chemotherapy (1 month). The rationale of this therapy was first to take advantage of the bactericidal properties of chemotherapy to kill active growing bacilli, eliminate the outermost layer of FM and reduce local inflammatory responses so as to avoid the predictable Koch phenomenon caused by M. tuberculosis antigens when given therapeutically. After chemotherapy, RUTI can be inoculated to reduce the probability of regrowth of the remaining latent bacilli. RUTI has already demonstrated its efficacy in controlling LTBI in experimental models of mice and guinea-pigs after a short period of chemotherapy; these experiments in animals showed the induction of a mixed Th1/Th2/Th3, polyantigenic response with no local or systemic toxicity. Local accumulation of specific CD8 T cells and a strong humoral response are characteristic features of RUTI that explain its protective properties; these are particular improvements when compared with BCG, although the regulatory response to RUTI may also be an important advantage. Further experiments using bigger animals (goats and mini-pigs) will provide more data on the efficacy of RUTI before starting phase I clinical trials.