Increased Airway Hyperresponsiveness Research Articles

Maternal diesel inhalation increases airway hyperreactivity in ozone-exposed offspring.

Air pollutant exposure is linked with childhood asthma incidence and exacerbations, and maternal exposure to airborne pollutants during pregnancy increases airway hyperreactivity (AHR) in offspring. To determine if exposure to diesel exhaust (DE) during pregnancy worsened postnatal ozone-induced AHR, timed pregnant C57BL/6 mice were exposed to DE (0.5 or 2.0 mg/m(3)) 4 hours daily from Gestation Day 9-17, or received twice-weekly oropharyngeal aspirations of the collected DE particles (DEPs). Placentas and fetal lungs were harvested on Gestation Day 18 for cytokine analysis. In other litters, pups born to dams exposed to air or DE, or to dams treated with aspirated diesel particles, were exposed to filtered air or 1 ppm ozone beginning the day after birth, for 3 hours per day, 3 days per week for 4 weeks. Additional pups were monitored after a 4-week recovery period. Diesel inhalation or aspiration during pregnancy increased levels of placental and fetal lung cytokines. There were no significant effects on airway leukocytes, but prenatal diesel augmented ozone-induced elevations of bronchoalveolar lavage cytokines at 4 weeks. Mice born to the high-concentration diesel-exposed dams had worse ozone-induced AHR, which persisted in the 4-week recovery animals. Prenatal diesel exposure combined with postnatal ozone exposure also worsened secondary alveolar crest development. We conclude that maternal inhalation of DE in pregnancy provokes a fetal inflammatory response that, combined with postnatal ozone exposure, impairs alveolar development, and causes a more severe and long-lasting AHR to ozone exposure.

Ozone inhalation promotes CX3CR1-dependent maturation of resident lung macrophages that limit oxidative stress and inflammation.

Inhalation of ambient ozone alters populations of lung macrophages. However, the impact of altered lung macrophage populations on the pathobiology of ozone is poorly understood. We hypothesized that subpopulations of macrophages modulate the response to ozone. We exposed C57BL/6 mice to ozone (2 ppm × 3 h) or filtered air. At 24 h after exposure, the lungs were harvested and digested and the cells underwent flow cytometry. Analysis revealed a novel macrophage subset present in ozone-exposed mice, which were distinct from resident alveolar macrophages and identified by enhanced Gr-1(+) expression [Gr-1 macrophages (Gr-1 Macs)]. Further analysis showed that Gr-1(+) Macs exhibited high expression of MARCO, CX3CR1, and NAD(P)H:quinone oxioreductase 1. Gr-1(+) Macs were present in the absence of CCR2, suggesting that they were not derived from a CCR2-dependent circulating intermediate. Using PKH26-PCL to label resident phagocytic cells, we demonstrated that Gr-1 Macs were derived from resident lung cells. This new subset was diminished in the absence of CX3CR1. Interestingly, CX3CR1-null mice exhibited enhanced responses to ozone, including increased airway hyperresponsiveness, exacerbated neutrophil influx, accumulation of 8-isoprostanes and protein carbonyls, and increased expression of cytokines (CXCL2, IL-1β, IL-6, CCL2, and TNF-α). Our results identify a novel subset of lung macrophages, which are derived from a resident intermediate, are dependent upon CX3CR1, and appear to protect the host from the biological response to ozone.

The protective role of TLR6 in a mouse model of asthma is mediated by IL-23 and IL-17A

TLRs are a family of receptors that mediate immune system pathogen recognition. In the respiratory system, TLR activation has both beneficial and deleterious effects in asthma. For example, clinical data indicate that TLR6 activation exerts protective effects in asthma. Here, we explored the mechanism or mechanisms through which TLR6 mediates this effect using mouse models of Aspergillus fumigatus-induced and house dust mite antigen-induced (HDM antigen-induced) chronic asthma. Tlr6-/- mice with fungal- or HDM antigen-induced asthma exhibited substantially increased airway hyperresponsiveness, inflammation, and remodeling compared with WT asthmatic groups. Surprisingly, whole-lung levels of IL-23 and IL-17 were markedly lower in Tlr6-/- versus WT asthmatic mice. Tlr6-/- DCs generated less IL-23 upon activation with lipopolysaccharide, zymosan, or curdlan. Impaired IL-23 generation in Tlr6-/- mice also corresponded with lower levels of expression of the pathogen-recognition receptor dectin-1 and expansion of Th17 cells both in vivo and in vitro. Exogenous IL-23 treatment of asthmatic Tlr6-/- mice restored IL-17A production and substantially reduced airway hyperresponsiveness, inflammation, and lung fungal burden compared with that in untreated asthmatic Tlr6-/- mice. Together, our data demonstrate that TLR6 activation is critical for IL-23 production and Th17 responses, which both regulate the allergic inflammatory response in chronic fungal-induced asthma. Thus, therapeutics targeting TLR6 activity might prove efficacious in the treatment of clinical asthma.

The Protease Allergen Pen c 13 Induces Allergic Airway Inflammation and Changes in Epithelial Barrier Integrity and Function in a Murine Model

Fungal allergens are associated with the development of asthma, and some have been characterized as proteases. Here, we established an animal model of allergic airway inflammation in response to continuous exposure to proteolytically active Pen c 13, a major allergen secreted by Penicillium citrinum. In functional analyses, Pen c 13 exposure led to increased airway hyperresponsiveness, significant inflammatory cell infiltration, mucus overproduction, and collagen deposition in the lung, dramatically elevated serum levels of total IgE and Pen c 13-specific IgE and IgG1, and increased production of the Th2 cytokines IL-4, IL-5, and IL-13 by splenocytes stimulated in vitro with Pen c 13. To examine the mechanisms involved in the regulation of allergenicity by Pen c 13, we performed two-dimensional fluorescence difference gel electrophoresis analysis combined with nano-LC-MS/MS, followed by bioinformatics analysis to identify potential targets that associated with allergic inflammation, which suggested that galectin-3 and laminin might be involved in novel pathogenic mechanisms. Finally, we focused on junctional proteins between cells, because, in addition to opening of the epithelial barrier by environmental proteases possibly being the initial step in the development of asthma, these proteins are also associated with actin rearrangement. Taken together, our findings indicate that Pen c 13 exposure causes junctional structure alterations and actin cytoskeletal rearrangements, resulting in increased permeability and airway structural changes. These effects probably change the lung microenvironment and foster the development of allergic sensitization.

Playing a dirty trick on airway smooth muscle: house dust mite does it again

Increased airway smooth muscle (ASM) mass is a hallmark of asthma and is thought to be the main contributor to the increased airway hyperresponsiveness seen in asthmatics [1]. This increase is related to disease severity (reviewed in [2]) and caused by hyperplasia alone or in combination with hypertrophy, depending on the generation of airways [3, 4]. Why and how ASM mass is increased is incompletely understood, but in vitro studies have shown that ASM cells isolated from asthmatics proliferate faster in culture [5]. In addition, cultured patient cells produce more chemokines and an altered array of extracellular matrix proteins compared with those of healthy individuals [6, 7]. In vitro studies have shown that upon isolation, ASM cells display contractile function, but they rapidly change phenotype ( i.e. acquire proliferative and synthetic capacity) and become noncontractile during culture under serum-rich conditions [8]. When these synthetic–proliferative cells are serum-deprived for a prolonged period of time, a small population (so-called “hypercontractile” cells) starts re-expressing contractile protein genes, such as ACTA2 (encoding α-smooth muscle actin (α-SMA)) [9]. This dedifferentiation/modulation and differentiation/maturation of ASM cells is referred to as phenotype switching or phenotypic plasticity, and although this phenomenon clearly exists in vitro , we do not know whether this plays a role in thickening of the ASM layer. The increase in ASM proliferation in asthma is thought to be associated with decreased levels of CCAAT enhancer protein (c/EBP)α (encoded by the CEBPA gene), a crucial controller of cell cycle progression, differentiation and inflammation. The biological effects of this protein are exerted by the full-length (p42) isoform and counteracted by a shorter isoform (p30), which is formed after translation of the protein. Previously, it was shown that ASM from asthmatics has …

Utility of inhaled allergen challenge in clinical diagnosis and management of asthma: What never? Well, hardly ever!

Cite this as: D. S. Robinson, Clinical & Experimental Allergy, 2011 (41) 606–608.

The protective role of TLR6 during experimental fungal asthma is mediated by IL-23 and IL-17A. (103.6)

Abstract Toll-like receptors (TLRs) mediate pathogen recognition in the respiratory system, but TLR activation has both beneficial and deleterious effects during asthma. Clinical data demonstrates that TLR6 is an example of a pattern recognition receptor that exerts protective effects in clinical asthma. To explore the mechanism through which TLR6 expression by immune and inflammatory cells mediates this effect, we investigated its role in a murine model of Aspergillus fumigatus-induced chronic asthma. TLR6-/- mice with fungal asthma exhibited significantly increased airway hyperresponsiveness, inflammation, and remodeling compared with WT asthmatic groups. Surprisingly, whole lung levels of IL-23 and IL-17 were significantly lower in TLR6-/- versus WT asthmatic mice. TLR6-/- DCs generated significantly less IL-23 upon activation with either lipopolysaccharide or zymosan. Impaired IL-23 generation in TLR6-/- mice also corresponded with significantly lower dectin-1 expression and Th17 expansion both in vivo and in vitro. Exogenous IL-23 treatment of asthmatic TLR6-/- mice in vivo restored IL-17A production and significantly reduced airway hyperresponsiveness, inflammation, and lung fungal burden compared with untreated asthmatic TLR6-/- mice. Together, we demonstrate that TLR6 activation is critical for IL-23 and Th17, and both regulate the allergic inflammatory response during fungal asthma.

Elevated levels of NO are localized to distal airways in asthma

The contribution of nitric oxide (NO) to the pathophysiology of asthma remains incompletely defined despite its established pro- and anti-inflammatory effects. Induction of the inducible nitric oxide synthase (iNOS), arginase, and superoxide pathways is correlated with increased airway hyperresponsiveness in asthmatic subjects. To determine the contributions of these pathways in proximal and distal airways, we compared bronchial wash (BW) to traditional bronchoalveolar lavage (BAL) for measurements of reactive nitrogen/oxygen species, arginase activation, and cytokine/chemokine levels in asthmatic and normal subjects. Levels of NO were preferentially elevated in the BAL, demonstrating higher level NOS activation in the distal airway compartment of asthmatic subjects. In contrast, DHE+ cells, which have the potential to generate reactive oxygen species, were increased in both proximal and distal airway compartments of asthmatics compared to controls. Different patterns of cytokines and chemokines were observed, with a predominance of epithelial cell-associated mediators in the BW compared to macrophage/monocyte-derived mediators in the BAL of asthmatic subjects. Our study demonstrates differential production of reactive species and soluble mediators within the distal airways compared to the proximal airways in asthma. These results indicate that cellular mechanisms are activated in the distal airways of asthmatics and must be considered in the development of therapeutic strategies for this chronic inflammatory disorder.

D-4F, an apoA-1 mimetic, decreases airway hyperresponsiveness, inflammation, and oxidative stress in a murine model of asthma

Asthma is characterized by oxidative stress and inflammation of the airways. Although proinflammatory lipids are involved in asthma, therapies targeting them remain lacking. Ac-DWFKAFYDKVAEKFKEAFNH(2) (4F) is an apolipoprotein (apo)A-I mimetic that has been shown to preferentially bind oxidized lipids and improve HDL function. The objective of the present study was to determine the effects of 4F on oxidative stress, inflammation, and airway resistance in an established murine model of asthma. We show here that ovalbumin (OVA)-sensitization increased airway hyperresponsiveness, eosinophil recruitment, and collagen deposition in lungs of C57BL/6J mice by a mechanism that could be reduced by 4F. OVA sensitization induced marked increases in transforming growth factor (TGF)β-1, fibroblast specific protein (FSP)-1, anti-T15 autoantibody staining, and modest increases in 4-hydroxynonenal (4-HNE) Michael's adducts in lungs of OVA-sensitized mice. 4F decreased TGFβ-1, FSP-1, anti-T15 autoantibody, and 4-HNE adducts in the lungs of the OVA-sensitized mice. Eosinophil peroxidase (EPO) activity in bronchial alveolar lavage fluid (BALF), peripheral eosinophil counts, total IgE, and proinflammatory HDL (p-HDL) were all increased in OVA-sensitized mice. 4F decreased BALF EPO activity, eosinophil counts, total IgE, and p-HDL in these mice. These data indicate that 4F reduces pulmonary inflammation and airway resistance in an experimental murine model of asthma by decreasing oxidative stress.

Pneumocystis Infection in an Immunocompetent Host Can Promote Collateral Sensitization to Respiratory Antigens

Infection with the opportunistic fungal pathogen Pneumocystis is assumed to pass without persistent pathology in immunocompetent hosts. However, when immunocompetent BALB/c mice were inoculated with Pneumocystis, a vigorous Th2-like pulmonary inflammation ensued and peaked at 14 days postinfection. This coincided with a 10-fold increase in the number of antigen-presenting cells (APCs) in the lung, and these cells were capable of presenting antigen in vitro, as well as greater uptake of antigen in vivo. When mice were presented with exogenous antigen at the 14-day time point of the infection, they developed respiratory sensitization to that antigen, in the form of increased airway hyperresponsiveness upon a later challenge, whereas mice not infected but presented with antigen did not. Like other forms of collateral sensitization, this response was dependent on interleukin-4 receptor signaling. This ability to facilitate sensitization to exogenous antigen has been previously reported for other infectious disease agents; however, Pneumocystis appears to be uniquely capable in this respect, as a single intranasal dose without added adjuvant, when it was administered at the appropriate time, was sufficient to initiate sensitization. Pneumocystis infection probably occurs in most humans during the first few years of life, and in the vast majority of cases, it fails to cause any overt direct pathology. However, as we show here, Pneumocystis can be an agent of comorbidity at this time by facilitating respiratory sensitization that may relate to the later development or exacerbation of obstructive airway disease.

Gp120 reduces AHR and airway inflammation in a humanized mouse model of allergic asthma through activation of regulatory T cells

Within this study we established a humanized mouse model of allergic asthma in immune deficient NOD-Scid gc–/– mice. For reconstitution of the animals we transferred 5 million peripheral blood mononuclear cells (PBMC) from allergic donors with sensitization against birch pollen intraperitoneally. The injection of PBMC together with birch and IL-4 followed by intranasal allergen challenge increased airway hyperresponsiveness (AHR) and airway inflammation after three weeks of engraftment. Recently it was shown that the HIV envelope protein gp120 functionally activates regulatory T cells (Tregs) through binding to the CD4 co-receptor that further leads to suppression of T effector cells (Blood 2009, 114 (6): 1263–69). To analyze the therapeutic effect of gp120 in our established humanized mouse model we treated the mice with gp120 on day 18. Administration of gp120 diminished AHR and influx of cells into the lung. To further analyze if Tregs are necessary for the occurring suppressive effects the CD25high expressing cells were removed from PBMC by depletion with dynabeads prior to engraftment. After depletion of Tregs treatment with gp120 no longer had any effect on airway inflammation in the humanized mouse model. These results confirm that gp120 promotes the tolerogenic function of Tregs and offer a new therapeutic strategy against atopic asthma.

Actual Control State of Intermittent Asthma Classified on the Basis of Subjective Symptoms

Many primary care physicians begin treatment of asthma patients on the basis of their subjective symptoms. We hypothesized that patients diagnosed as having intermittent asthma on the basis of subjective symptoms by a primary care physician may have their asthma severity underestimated. We investigated 293 patients who were in their 20s and diagnosed as having asthma. Two hundred and fifteen patients with intermittent asthma diagnosed on the basis of subjective symptoms were chosen. We evaluated their asthma severity using FEV(1) (% predicted), airway hyperresponsiveness to histamine dihydrochloride, and exhaled nitric oxide level as factors that determine asthma severity. Among these patients, 27.8% were determined to have moderate or severe asthma by the pulmonary function test. History of childhood asthma was the only significant risk factor for a low pulmonary function. Among the patients, 60.9% showed moderate or severe airway hyperresponsiveness. History of childhood asthma was the only significant risk factor for the increase in airway hyperresponsiveness. Moreover, 53.8% showed a high exhaled nitric oxide level. History of childhood asthma was associated with an increased risk of a high eNO level as determined by univariate analysis, but no significant difference was observed in the comparison by multiple logistic regression analysis. The percentage of subjects classified into the mild group by all of the results of the three tests was only 20.6%. We showed that asthma severity classified on the basis of only subjective symptoms may be underestimated in young adults. We showed that the diagnosis of mild intermittent asthma needs to be determined carefully.

A 24 kDa Excretory-Secretory Protein ofAnisakis simplexLarvae Could Elicit Allergic Airway Inflammation in Mice

We have reported that a 24 kDa protein (22U homologous; As22U) of Anisakis simplex larvae could elicit several Th2-related chemokine gene expressions in the intestinal epithelial cell line which means that As22U may play a role as an allergen. In order to determine the contribution of As22U to allergic reactions, we treated mice with 6 times intra-nasal application of recombinant As22U (rAs22U). In the group challenged with rAs22U and ovalbumin (OVA), the number of eosinophils in the bronchial alveolar lavage fluid (BALF) was significantly increased, as compared to the group receiving only OVA. In addition, mice treated with rAs22U and OVA showed significantly increased airway hyperresponsiveness. Thus, severe inflammation around the airway and immune cell recruitment was observed in mice treated with rAs22U plus OVA. The levels of IL-4, IL-5, and IL-13 cytokines in the BALF increased significantly after treatment with rAs22U and OVA. Similarly, the levels of anti-OVA specific IgE and IgG1 increased in mice treated with rAs22U and OVA, compared to those treated only with OVA. The Gro-α (CXCL1) gene expression in mouse lung epithelial cells increased instantly after treatment with rAs22U, and allergy-specific chemokines eotaxin (CCL11) and thymus-and-activation-regulated-chemokine (CCL17) gene expressions significantly increased at 6 hr after treatment. In conclusion, rAs22U may induce airway allergic inflammation, as the result of enhanced Th2 and Th17 responses.

Hyaluronan fragments contribute to the ozone-primed immune response to lipopolysaccharide.

Hyaluronan is a high-molecular mass component of pulmonary extracelluar matrix, and lung injury can generate a low-molecular mass hyaluronan (HA) fragment that functions as endogenous ligand to cell surface receptors CD44 and TLR4. This leads to activation of intracellular NF-κB signaling and proinflammatory cytokine production. Based on previous information that ozone exposure causes increased HA in bronchial alveolar lavage fluid and ozone pre-exposure primes immune response to inhaled LPS, we hypothesized that HA production during ozone exposure augments the inflammatory response to LPS. We demonstrate that acute ozone exposure at 1 part per million for 3 h primes the immune response to low-dose aerosolized LPS in C57BL/6J mice, resulting in increased neutrophil recruitment into the airspaces, increased levels of protein and proinflammatory cytokines in the bronchoalveolar lavage fluid, and increased airway hyperresponsiveness. Intratracheal instillation of endotoxin-free HA (25 μg) enhances the biological response to inhaled LPS in a manner similar to ozone pre-exposure. In vitro studies using bone marrow-derived macrophages indicate that HA enhances LPS responses measured by TNF-α production, while immunofluorescence staining of murine alveolar macrophages demonstrates that HA induces TLR4 peripheralization and lipid raft colocalization. Collectively, our observations support that ozone primes macrophage responsiveness to low-dose LPS, in part, due to HA-induced TLR4 peripheralization in lung macrophages.

Chronic OVA allergen challenged Siglec-F deficient mice have increased mucus, remodeling, and epithelial Siglec-F ligands which are up-regulated by IL-4 and IL-13

BackgroundIn this study we examined the role of Siglec-F, a receptor highly expressed on eosinophils, in contributing to mucus expression, airway remodeling, and Siglec-F ligand expression utilizing Siglec-F deficient mice exposed to chronic allergen challenge.MethodsWild type (WT) and Siglec-F deficient mice were sensitized and challenged chronically with OVA for one month. Levels of airway inflammation (eosinophils), Siglec-F ligand expresion and remodeling (mucus, fibrosis, smooth muscle thickness, extracellular matrix protein deposition) were assessed in lung sections by image analysis and immunohistology. Airway hyperreactivity to methacholine was assessed in intubated and ventilated mice.ResultsSiglec-F deficient mice challenged with OVA for one month had significantly increased numbers of BAL and peribronchial eosinophils compared to WT mice which was associated with a significant increase in mucus expression as assessed by the number of periodic acid Schiff positive airway epithelial cells. In addition, OVA challenged Siglec-F deficient mice had significantly increased levels of peribronchial fibrosis (total lung collagen, area of peribronchial trichrome staining), as well as increased numbers of peribronchial TGF-β1+ cells, and increased levels of expression of the extracellular matrix protein fibronectin compared to OVA challenged WT mice. Lung sections immunostained with a Siglec-Fc to detect Siglec-F ligand expression demonstrated higher levels of expression of the Siglec-F ligand in the peribronchial region in OVA challenged Siglec-F deficient mice compared to WT mice. WT and Siglec-F deficient mice challenged intranasally with IL-4 or IL-13 had significantly increased levels of airway epithelial Siglec-F ligand expression, whereas this was not observed in WT or Siglec-F deficient mice challenged with TNF-α. There was a significant increase in the thickness of the peribronchial smooth muscle layer in OVA challenged Siglec-F deficient mice, but this was not associated with significant increased airway hyperreactivity compared to WT mice.ConclusionsOverall, this study demonstrates an important role for Siglec-F in modulating levels of chronic eosinophilic airway inflammation, peribronchial fibrosis, thickness of the smooth muscle layer, mucus expression, fibronectin, and levels of peribronchial Siglec-F ligands suggesting that Siglec-F may normally function to limit levels of chronic eosinophilic inflammation and remodeling. In addition, IL-4 and IL-13 are important regulators of Siglec-F ligand expression by airway epithelium.

Anti-Inflammatory Effects of the Neurotransmitter Agonist Honokiol in a Mouse Model of Allergic Asthma

Chronic airway inflammation is a hallmark of asthma, an immune-based disease with great societal impact. Honokiol (HNK), a phenolic neurotransmitter receptor (γ-aminobutyric acid type A) agonist purified from magnolia, has anti-inflammatory properties, including stabilization of inflammation in experimentally induced arthritis. The present study tested the prediction that HNK could inhibit the chronic inflammatory component of allergic asthma. C57BL/6 mice sensitized to and challenged with OVA had increased airway hyperresponsiveness to methacholine challenge and eosinophilia compared with naive controls. HNK-treated mice showed a reduction in airway hyperresponsiveness as well as a significant decrease in lung eosinophilia. Histopathology studies revealed a marked drop in lung inflammation, goblet cell hyperplasia, and collagen deposition with HNK treatment. Ag recall responses from HNK-treated mice showed decreased proinflammatory cytokines in response to OVA, including TNF-α-, IL-6-, Th1-, and Th17-type cytokines, despite an increase in Th2-type cytokines. Regulatory cytokines IL-10 and TGF-β were also increased. Assessment of lung homogenates revealed a similar pattern of cytokines, with a noted increase in the number of FoxP3(+) cells in the lung. HNK was able to alter B and T lymphocyte cytokine secretion in a γ-aminobutyric acid type A-dependent manner. These results indicate that symptoms and pathology of asthma can be alleviated even in the presence of increased Th2 cytokines and that neurotransmitter agonists such as HNK have promise as a novel class of anti-inflammatory agents in the treatment of chronic asthma.

Mepacrine treatment attenuates allergic airway remodeling segregated from airway inflammation in mice

Asthma is a chronic airway disease characterized by increased airway hyperresponsiveness, airway inflammation, and airway remodeling including collagen deposition in subepithelial regions. We have shown earlier that mepacrine has anti-inflammatory activity and decreased the features of airway remodeling in a subacute model of asthma, when administered during the inflammatory phase. But it was not clear whether the reduction of airway remodeling by mepacrine was a direct effect or indirectly related to the reduction in the airway inflammation. In this study, we determined the effect of mepacrine on airway remodeling and airway hyperresponsiveness (AHR) in a chronic model of asthma which showed the features of airway inflammation in the initial stage (inflammation predominant stage) and airway remodeling with mild airway inflammation in a later stage (remodeling predominant stage). Mepacrine was administered only in the later stage that more accurately simulates human asthma, where airway remodeling already exists at the time of diagnosis. The remodeling predominant stage was associated with high levels of Th2 cytokines like IL-4 and IL-13, increase in the levels of profibrotic mediators such as arginase and TGF-β, and increased collagen deposition. These were efficiently attenuated by mepacrine treatment and led to a significant reduction in AHR. Thus, we conclude from this study that mepacrine has direct effects on established airway remodeling independent of its anti-inflammatory effects.

HIF‐1α inhibition ameliorates an allergic airway disease via VEGF suppression in bronchial epithelium

Hypoxia-inducible factor-1α (HIF-1α) plays a critical role in immune and inflammatory responses. One of the HIF-1α target genes is vascular endothelial growth factor (VEGF), which is a potent stimulator of inflammation, airway remodeling, and physiologic dysregulation in allergic airway diseases. Using OVA-treated mice and murine tracheal epithelial cells, the signaling networks involved in HIF-1α activation and the role of HIF-1α in the pathogenesis of allergic airway disease were investigated. Transfection of airway epithelial cells with HIF-1α siRNA suppressed VEGF expression. In addition, the increased levels of HIF-1α and VEGF in lung tissues after OVA inhalation were substantially decreased by an HIF-1α inhibitor, 2-methoxyestradiol. Our data also show that the increased numbers of inflammatory cells, increased airway hyperresponsiveness, levels of IL-4, IL-5, IL-13, and vascular permeability in the lungs after OVA inhalation were significantly reduced by 2-methoxyestradiol or a VEGF inhibitor, CBO-P11. Moreover, we found that inhibition of the PI3K p110δ isoform (PI3K-δ) or HIF-1α reduced OVA-induced HIF-1α activation in airway epithelial cells. These findings indicate that HIF-1α inhibition may attenuate antigen-induced airway inflammation and hyperresponsiveness through the modulation of vascular leakage mediated by VEGF, and that PI3K-δ signaling may be involved in the allergen-induced HIF-1α activation.

Genetic deletion of apolipoprotein A-I increases airway hyperresponsiveness, inflammation, and collagen deposition in the lung

The relationship between high-density lipoprotein and pulmonary function is unclear. To determine mechanistic relationships we investigated the effects of genetic deletion of apolipoprotein A-I (apoA-I) on plasma lipids, paraoxonase (PON1), pro-inflammatory HDL (p-HDL), vasodilatation, airway hyperresponsiveness and pulmonary oxidative stress, and inflammation. ApoA-I null (apoA-I(-/-)) mice had reduced total and HDL cholesterol but increased pro-inflammatory HDL compared with C57BL/6J mice. Although PON1 protein was increased in apoA-I(-/-) mice, PON1 activity was decreased. ApoA-I deficiency did not alter vasodilatation of facialis arteries, but it did alter relaxation responses of pulmonary arteries. Central airway resistance was unaltered. However, airway resistance mediated by tissue dampening and elastance were increased in apoA-I(-/-) mice, a finding also confirmed by positive end-expiratory pressure (PEEP) studies. Inflammatory cells, collagen deposition, 3-nitrotyrosine, and 4-hydroxy-2-nonenal were increased in apoA-I(-/-) lungs but not oxidized phospholipids. Colocalization of 4-hydroxy-2-nonenal with transforming growth factor beta-1 (TGFbeta-1 was increased in apoA-I(-/-) lungs. Xanthine oxidase, myeloperoxidase and endothelial nitric oxide synthase were increased in apoA-I(-/-) lungs. Dichlorodihydrofluorescein-detectable oxidants were increased in bronchoalveolar lavage fluid (BALF) in apoA-I(-/-) mice. In contrast, BALF nitrite+nitrate levels were decreased in apoA-I(-/-) mice. These data demonstrate that apoA-I plays important roles in limiting pulmonary inflammation and oxidative stress, which if not prevented, will decrease pulmonary artery vasodilatation and increase airway hyperresponsiveness.

CD27 costimulation is not critical for the development of asthma and respiratory tolerance in a murine model

CD27 is a costimulatory molecule of the TNFR family strongly expressed on activated CD4 + and CD8 + T lymphocytes. Binding with its ligand CD70, present on lymphocytes and DCs, leads to enhanced T cell activation and proliferation. Several other costimulatory molecules of the TNFR family like CD30, CD134 (OX40) or CD137 (4-1BB) have been shown to be critically involved in the development of asthma and/or respiratory tolerance. However, the role of CD27/CD70 signalling in these disease models has not been studied intensively. The aim of this study was to directly investigate the role of CD27 for the development of asthma and respiratory tolerance by comparative analysis of wild type (WT) and CD27 −/− mice in the corresponding murine models. Ovalbumin (OVA)-sensitized and challenged CD27 −/− mice developed comparably increased airway hyperreactivity (AHR), eosinophilic airway inflammation, mucus hypersecretion and elevated OVA-specific serum IgE levels in response to OVA sensitization as WT mice. In addition, Th2 cytokine production in spleen cell culture supernatants and proliferation of splenocytes after in vitro OVA restimulation was equally enhanced when derived from WT and CD27 −/− mice. Furthermore, the absence of CD27 had no decisive impact on tolerance induction, so that WT and CD27 −/− mice were comparably protected from asthma development by mucosal antigen application before sensitization. Our results suggest that CD27 costimulation is dispensable for a Th2 cell mediated allergic asthma response and respiratory tolerance induction in murine models.