Chronic inhaled ovalbumin exposure induces antigen-dependent but not antigen-specific inhalational tolerance in a murine model of allergic airway disease

Inhibition of Fatty Acid Amide Hydrolase (FAAH) Regulates NF-kb Pathways Reducing Bleomycin-Induced Chronic Lung Inflammation and Pulmonary Fibrosis

The deadly interstitial lung condition known as idiopathic pulmonary fibrosis (IPF) worsens over time and for no apparent reason. The traditional therapy approaches for IPF, which include corticosteroids and immunomodulatory drugs, are often ineffective and can have noticeable side effects. The endocannabinoids are hydrolyzed by a membrane protein called fatty acid amide hydrolase (FAAH). Increasing endogenous levels of endocannabinoid by pharmacologically inhibiting FAAH results in numerous analgesic advantages in a variety of experimental models for pre-clinical pain and inflammation. In our study, we mimicked IPF by administering intratracheal bleomycin, and we administered oral URB878 at a dose of 5 mg/kg. The histological changes, cell infiltration, pro-inflammatory cytokine production, inflammation, and nitrosative stress caused by bleomycin were all reduced by URB878. Our data clearly demonstrate for the first time that the inhibition of FAAH activity was able to counteract not only the histological alteration bleomycin-induced but also the cascade of related inflammatory events.

Differences in mouse strains determine the outcome of Der p 2 allergy induction protocols

In vivo animal models can provide worthy information on various aspects of asthma mechanism and pathogenesis. The genetic predisposition and phenotype of mice may affect the immune response itself. Here we compare the early immune response to Der p 2 or HDM allergen extract upon injection and inhalation in BALB/c and C57BL/6 mice. Female C57BL/6 and BALB/c mice were immunized with Der p 2 allergen subcutaneously followed by inhalation of Der p 2 or HDM extract. After challenge, the mice were euthanized; blood, bronchoalveolar lavage (BAL), spleens and lungs were collected. Cells from BAL were identified by May-Grünwald Giemsa staining and lung leukocyte populations were analyzed by flow cytometry. Serum antibody levels of Der p 2 specific IgE, IgG, IgG1 and IgG2a were assessed by ELISA, and cytokine secretion (IL-4, IFN-γ and IL-10) was evaluated upon stimulation with Der p 2 or HDM extract. The Th2 immune response was confirmed by elevated allergen-specific immunoglobulin E (IgE) and the allergic reaction was evidenced by infiltration of eosinophils and/or neutrophils into BAL. We found that BALB/c mice were inefficient in integrating local with systemic immune response, evidenced by almost no IgG or IgE production upon one subcutaneous injection and subsequent inhalation of Der p 2 allergen; also, the bronchoalveolar lavage infiltrate in these mice consisted of neutrophil infiltration, unlike C57BL/6 mice in which eosinophilic infiltrate predominated. The differences between BALB/c and C57BL/6 mice strains could be exploited for generating different types of responses to the Der p 2 allergen.

The effect of beetroot juice on airway inflammation in a murine model of asthma

The effects of beetroot juice on airways inflammation, cytokine levels, and oxidative stress biomarkers were evaluated using an allergen-induced murine model of asthma. Ovalbumin (OVA)-sensitized and challenged BALB/c mice were used as an asthma model. BALB/c mice were randomly assigned into four groups: control (Ova sensitization and normal saline challenge), control and beetroot (Ova sensitization and normal saline challenge plus beetroot juice), Ova S/C [Ova sensitization and challenge (Ova S/C)], Ova S/C and beetroot juice (Ova S/C plus beetroot juice). The bronchoalveolar lavage fluid (BALF) was analyzed for total and differential inflammatory cells count. The levels of cytokines [interleukin (IL)-10, IL-13, and IL-18], and oxidative stress biomarkers [glutathione peroxidase (GPx), catalase, and thiobarbituric acid reactive substances (TBARS)] were analyzed in the lung tissue. Simultaneous administration of beetroot juice and Ova S/C significantly increased the total inflammatory cells compared to the control (p = .0001) and Ova S/C (p = .013) groups and significantly increased the number of eosinophils (p ˂ .0001) and macrophages (p ˂ .0001) compared to the control. Moreover, the simultaneous administration of beetroot juice and Ova S/C did not affect the level of IL-10, IL-13, IL-18, GPx, or TBARS compared to the control (p > .05), but it significantly increased the level of catalase (p = .002). Results suggest that beetroot juice aggravates asthma by enhancing airway inflammation. However, it does not affect airway inflammation in healthy mice. PRACTICAL APPLICATIONS: Asthma is a chronic airway inflammatory disease that is characterized by variable degrees of airways inflammation and obstruction. Paradox data are reported in the literature regarding beetroot and asthma. The present study revealed that beetroot juice exacerbates asthma by enhancing airway inflammation. However, it is safe and has no effects on airway inflammation in healthy mice. Patients having asthma or a history of asthma are advised to avoid the consumption of beetroot.

Atrazine Inhalation Causes Neuroinflammation, Apoptosis and Accelerating Brain Aging

BACKGROUND

exposure to environmental contaminants has been linked to an increased risk of neurological diseases and poor outcomes. Chemical name of Atrazine (ATR) is 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine, and it is the most commonly used broad-spectrum herbicide in agricultural crops. Several studies have demonstrated that ATR has the potential to be harmful to the brain's neuronal circuits. Until today nobody has explored the effect of ATR inhalation on young and aged mice.

METHODS

young and aged mice were subject to 25 mg of ATR in a vehicle made with saline and 10% of Dimethyl sulfoxide (DMSO) every day for 28 days. At the end of experiment different behavioral test were made and brain was collected.

RESULTS

exposure to ATR induced the same response in terms of behavioral alterations and motor and memory impairment in mice but in aged group was more marked. Additionally, in both young and aged mice ATR inhalations induced oxidative stress with impairment in physiological antioxidant response, lipid peroxidation, nuclear factor kappa-light-chain-enhancer of activated B cells (nf-κb) pathways activation with consequences of pro-inflammatory cytokines release and apoptosis. However, the older group was shown to be more sensitive to ATR inhalation.

CONCLUSIONS

our results showed that aged mice were more susceptible compared to young mice to air pollutants exposure, put in place a minor physiologically response was seen when exposed to it.

Mimicking Antigen-Driven Asthma in Rodent Models-How Close Can We Get?

Asthma is a heterogeneous disease with increasing prevalence worldwide characterized by chronic airway inflammation, increased mucus secretion and bronchial hyperresponsiveness. The phenotypic heterogeneity among asthmatic patients is accompanied by different endotypes, mainly Type 2 or non-Type 2. To investigate the pathomechanism of this complex disease many animal models have been developed, each trying to mimic specific aspects of the human disease. Rodents have classically been employed in animal models of asthma. The present review provides an overview of currently used Type 2 vs. non-Type 2 rodent asthma models, both acute and chronic. It further assesses the methods used to simulate disease development and exacerbations as well as to quantify allergic airway inflammation, including lung physiologic, cellular and molecular immunologic responses. Furthermore, the employment of genetically modified animals, which provide an in-depth understanding of the role of a variety of molecules, signaling pathways and receptors implicated in the development of this disease as well as humanized models of allergic inflammation, which have been recently developed to overcome differences between the rodent and human immune systems, are discussed. Nevertheless, differences between mice and humans should be carefully considered and limits of extrapolation should be wisely taken into account when translating experimental results into clinical use.

Differential Influence on Regulatory B Cells by TH2 Cytokines Affects Protection in Allergic Airway Disease

The role of regulatory B cells (Bregs) in modulating immune responses and maintaining tolerance are well established. However, how cytokines present during immune responses affect Breg growth and function are not as well defined. Previously, our laboratory reported IL-5- and mCD40L-expressing fibroblast (mCD40L-Fb) stimulation induced IL-10 production from murine B cells. The current study investigated the phenotype and functional relevance of IL-10- producing B cells from this culture. We found IL-5/mCD40L-Fb stimulation induced IL-10 production exclusively from CD5⁺ splenic B cells of naive mice. After stimulation, the resulting IL-10⁺ B cells displayed markers of multiple reported Breg phenotypes. Interestingly, when investigating effects of IL-4 (a critical T_H2 cytokine) on IL-5/mCD40L-Fb-induced IL-10 production, we found IL-4 inhibited IL-10 production in a STAT6-dependent manner. Upon adoptive transfer, CD5⁺ B cells previously stimulated with IL-5/mCD40L-Fb were able to reduce development of OVA-induced allergic airway disease in mice. Using B cells from IL-10 mutant mice differentiated by IL-5/mCD40L-Fb, we found protection from allergic airway disease development was dependent on the IL-10 production from the transferred B cells. Bregs have been shown to play crucial roles in the immune tolerance network, and understanding stimuli that modulate their growth and function may be key in development of future treatments for diseases of immune dysregulation.

Regulation of IgE activity in inhalational tolerance via formation of IgG anti-IgE/IgE immune complexes

Background

Allergic asthma is an inflammatory disorder of the airways that results from inappropriate production of IgE against harmless, environmental antigens. Sequestration of free IgE using humanized IgG anti-IgE is an effective therapy for asthma and other atopic disorders. However, the status of free IgE in subjects who have naturally developed immune tolerance to inhaled antigens has not been well studied.

Methods

C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) for 7 days to induce allergic airway disease (AAD) or 6 weeks to induce a state of local inhalational tolerance (LIT). Serum from AAD or LIT mice, diluted to achieve equivalent levels of total OVA-specific IgE, was used to sensitize rat basophil leukemia cells for allergen-mediated degranulation. Levels of degranulation were measured in relation to serum concentrations of free IgE and IgG anti-IgE/IgE immune complexes.

Results

Serum from AAD animals induced a greater degree of basophil degranulation than serum from LIT animals. These results correlated with higher levels of free IgE in AAD animals, whereas LIT mice demonstrated a significant increase in IgG anti-IgE/IgE immune complexes relative to their diseased counterparts.

Conclusions

Sequestration of free IgE by naturally occurring IgG anti-IgE may aid in the development of immune tolerance against inhaled allergens. The decrease in bioavailability of free IgE may, in turn, contribute to the overall reduction of asthma symptoms via a mechanism that mimics the therapeutic effects of humanized IgG anti-IgE.

Differential Expression and Function of PDE8 and PDE4 in Effector T cells: Implications for PDE8 as a Drug Target in Inflammation

Abolishing the inhibitory signal of intracellular cAMP is a prerequisite for effector T (Teff) cell function. The regulation of cAMP within leukocytes critically depends on its degradation by cyclic nucleotide phosphodiesterases (PDEs). We have previously shown that PDE8A, a PDE isoform with 40–100-fold greater affinity for cAMP than PDE4, is selectively expressed in Teff vs. regulatory T (Treg) cells and controls CD4⁺ Teff cell adhesion and chemotaxis. Here, we determined PDE8A expression and function in CD4⁺ Teff cell populations in vivo. Using magnetic bead separation to purify leukocyte populations from the lung draining hilar lymph node (HLN) in a mouse model of ovalbumin-induced allergic airway disease (AAD), we found by Western immunoblot and quantitative (q)RT-PCR that PDE8A protein and gene expression are enhanced in the CD4⁺ T cell fraction over the course of the acute inflammatory disease and recede at the late tolerant non-inflammatory stage. To evaluate PDE8A as a potential drug target, we compared the selective and combined effects of the recently characterized highly potent PDE8-selective inhibitor PF-04957325 with the PDE4-selective inhibitor piclamilast (PICL). As previously shown, PF-04957325 suppresses T cell adhesion to endothelial cells. In contrast, we found that PICL alone increased firm T cell adhesion to endothelial cells by ~20% and significantly abrogated the inhibitory effect of PF-04957325 on T cell adhesion by over 50% when cells were co-exposed to PICL and PF-04957325. Despite its robust effect on T cell adhesion, PF-04957325 was over two orders of magnitude less efficient than PICL in suppressing polyclonal Teff cell proliferation, and showed no effect on cytokine gene expression in these cells. More importantly, PDE8 inhibition did not suppress proliferation and cytokine production of myelin-antigen reactive proinflammatory Teff cells in vivo and in vitro. Thus, targeting PDE8 through PF-04957325 selectively regulates Teff cell interactions with endothelial cells without marked immunosuppression of proliferation, while PDE4 inhibition has partially opposing effects. Collectively, our data identify PF-04957325 as a novel function-specific tool for the suppression of Teff cell adhesion and indicate that PDE4 and PDE8 play unique and non-redundant roles in the control of Teff cell functions.

CD4⁺ and CD8⁺ T cells play a central role in a HDM driven model of allergic asthma

Background

The incidence of asthma is increasing at an alarming rate and while the current available therapies are effective in the majority of patients they fail to adequately control symptoms at the more severe end of the disease spectrum. In the search to understand disease pathogenesis and find effective therapies animal models are often employed. As exposure to house dust mite (HDM) has a causative link, it is thought of as the allergen of choice for modelling asthma.

The objective was to develop a HDM driven model of asthmatic sensitisation and characterise the role of key allergic effector cells/mediators.

Methods

Mice were sensitised with low doses of HDM and then subsequently challenged. Cellular inflammation, IgE and airway responsiveness (AHR) was assessed in wild type mice or CD4⁺/CD8⁺ T cells, B cells or IgE knock out mice.

Results

Only those mice sensitised with HDM responded to subsequent low dose topical challenge. Similar to the classical ovalbumin model, there was no requirement for systemic alum sensitisation. Characterisation of the role of effector cells demonstrated that the allergic cellular inflammation and AHR was dependent on CD4⁺ and CD8⁺ T cells but not B cells or IgE. Finally, we show that this model, unlike the classic OVA model, appears to be resistant to developing tolerance.

Conclusions

This CD4⁺/CD8⁺ T cell dependent, HDM driven model of allergic asthma exhibits key features of asthma. Furthermore, we suggest that the ability to repeat challenge with HDM means this model is amenable to studies exploring the effect of therapeutic dosing in chronic, established disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0359-y) contains supplementary material, which is available to authorized users.

Cbl-b Deficiency in Mice Results in Exacerbation of Acute and Chronic Stages of Allergic Asthma

Mice sensitized to ovalbumin (OVA) develop allergic airway disease (AAD) with short-term daily OVA aerosol challenge; inflammation resolves with long-term OVA aerosol exposure, resulting in local inhalational tolerance (LIT). Cbl-b is an E3 ubiquitin ligase involved with CD28 signaling; Cbl-b^−/− effector T cells are resistant to regulatory T cell-mediated suppression in vitro and in vivo. The present study utilized Cbl-b^−/− mice to investigate the role of Cbl-b in the development of AAD and LIT. Cbl-b^−/− mice exhibited increased airway inflammation during AAD, which failed to resolve with long-term OVA aerosol exposure. Exacerbation of inflammation in Cbl-b^−/− mice correlated with increased proinflammatory cytokine levels and expansion of effector T cells in the BAL during AAD, but did not result in either a modulation of lymphocyte subsets in systemic tissues or in OVA-specific IgE in serum. These results implicate a role for Cbl-b in the resolution of allergic airway inflammation.

The sickle cell mouse lung: proinflammatory and primed for allergic inflammation

Comorbid asthma in sickle cell disease (SCD) confers higher rates of vaso-occlusive pain and mortality, yet the physiological link between these two distinct diseases remains puzzling. We used a mouse model of SCD to study pulmonary immunology and physiology before and after the induction of allergic airway disease (AAD). SCD mice were sensitized with ovalbumin (OVA) and aluminum hydroxide by the intraperitoneal route followed by daily, nose-only OVA-aerosol challenge to induce AAD. The lungs of naive SCD mice showed signs of inflammatory and immune processes: (1) histologic and cytochemical evidence of airway inflammation compared with naive wild-type mice; (2) bronchoalveolar lavage (BAL) fluid contained increased total lymphocytes, %CD8+ T cells, granulocyte-colony stimulating factor, interleukin 5 (IL-5), IL-7, and chemokine (C-X-C motif) ligand (CXCL)1; and (3) lung tissue and hilar lymph node (HLN) had increased CD4+, CD8+, and regulatory T (Treg) cells. Furthermore, SCD mice at AAD demonstrated significant changes compared with the naive state: (1) BAL fluid with increased %CD4+ T cells and Treg cells, lower %CD8+ T cells, and decreased interferon gamma, CXCL10, chemokine (C-C motif) ligand 2, and IL-17; (2) serum with increased OVA-specific immunoglobulin E, IL-6, and IL-13, and decreased IL-1α and CXCL10; (3) no increase in Treg cells in the lung tissue or HLN; and (4) hyporesponsiveness to methacholine challenge. In conclusion, SCD mice have an altered immunologic pulmonary milieu and physiological responsiveness. These findings suggest that the clinical phenotype of AAD in SCD mice differs from that of wild-type mice and that individuals with SCD may also have a unique, divergent phenotype perhaps amenable to a different therapeutic approach.

Smooth muscle CaMKIIδ promotes allergen-induced airway hyperresponsiveness and inflammation

Airway smooth muscle (ASM) is a key target cell in allergen-induced asthma known to contribute to airway hyperresponsiveness (AHR) and chronic airway remodeling. Changes in ASM calcium homeostasis have been shown to contribute to AHR although the mechanisms and Ca(2+) signal effectors are incompletely understood. In the present study, we tested the function of ASM multifunctional protein kinase Ca(2+)/calmodulin-dependent kinase II (CaMKII) isoforms CaMKIIδ and CaMKIIγ in allergen-induced AHR and airway remodeling in vivo. Using a murine model of atopic asthma, we demonstrate that CaMKIIδ protein is upregulated in ASM derived from ovalbumin (OVA)-treated animals compared to controls. A genetic approach to conditionally knock out smooth muscle CaMKIIδ and CaMKIIγ in separate Cre-loxp systems was validated, and using this loss-of-function approach, the function of these CaMKII isoforms was tested in ovalbumin (OVA)-induced airway remodeling and AHR. OVA treatment in control mice had no effect on ASM remodeling in this model of AHR, and CaMKIIδ knockouts had no independent effects on ASM content. However, at 1 day post-final OVA challenge, OVA-induced AHR was eliminated in the CaMKIIδ knockouts. OVA-induced peribronchial inflammation and bronchoalveolar lavage fluid (BALF) levels of the Th2 cytokine IL-13 were significantly decreased in the CaMKIIδ knockouts. Unexpectedly, we found increased peribronchial eosinophils in the smooth muscle CaMKIIδ knockouts compared to control animals at 1 day post-final challenge, suggesting that lack of ASM CaMKIIδ delays the progression of AHR rather than inhibiting it. Indeed, when AHR was determined at 7 days post-final OVA challenge, CaMKIIδ knockouts showed robust AHR while AHR was fully resolved in OVA-challenged control mice. These in vivo studies demonstrate a role for smooth muscle CaMKIIδ in promoting airway inflammation and AHR and suggest a complex signaling role for CaMKIIδ in regulating ASM function. These studies confirm the diverse roles of ASM cells as immune effectors that control AHR and call for further studies into CaMKIIδ-mediated signaling in ASM cells during disease.

Long-Term Exposure to House Dust Mite Leads to the Suppression of Allergic Airway Disease Despite Persistent Lung Inflammation

BACKGROUND

Allergic asthma is a major cause of worldwide morbidity and results from inadequate immune regulation in response to innocuous, environmental antigens. The need exists to understand the mechanisms that promote nonreactivity to human-relevant allergens such as house dust mite (HDM) in order to develop curative therapies for asthma. The aim of our study was to compare the effects of short-, intermediate- and long-term HDM administration in a murine asthma model and determine the ability of long-term HDM exposure to suppress allergic inflammation.

METHODS

C57BL/6 mice were intranasally instilled with HDM for short-term (2 weeks), intermediate-term (5 weeks) and long-term (11 weeks) periods to induce allergic airway disease (AAD). The severity of AAD was compared across all stages of the model via both immunological and pulmonary parameters.

RESULTS

Short- and intermediate-term HDM exposure stimulated the development of AAD that included eosinophilia in the bronchoalveolar lavage fluid (BALF), pronounced airway hyperreactivity (AHR) and evidence of lung inflammation. Long-term HDM exposure promoted the suppression of AAD, with a loss of BALF eosinophilia and AHR despite persistent mononuclear inflammation in the lungs. Suppression of AAD with long-term HDM exposure was associated with an increase in both Foxp3+ regulatory T cells and IL-10-positive alveolar macrophages at the site of inflammation.

CONCLUSIONS

This model recapitulates the key features of human asthma and may facilitate investigation into the mechanisms that promote immunological tolerance against clinically relevant aeroallergens.

Regulatory B cells in allergic airways disease and asthma

B cells have long been known to participate in both innate and adaptive immune responses by contributing to antigen presentation and by producing antigen-specific antibodies. Recent evidence shows that certain B-cell subsets can also inhibit T-cell immune responses. Like regulatory T cells (Treg), these regulatory B cells (Breg) appear to comprise several subpopulations. How Breg cells are generated and how they control immune responses in vivo are just beginning to be elucidated. Here, we provide detailed instructions for the identification, isolation, and functional characterization of Breg cells in a murine model of allergic airway disease.

Persistence of asthma requires multiple feedback circuits involving type 2 innate lymphoid cells and IL-33

BACKGROUND

Asthma in a mouse model spontaneously resolves after cessation of allergen exposure. We developed a mouse model in which asthma features persisted for 6 months after cessation of allergen exposure.

OBJECTIVE

We sought to elucidate factors contributing to the persistence of asthma.

METHODS

We used a combination of immunologic, genetic, microarray, and pharmacologic approaches to dissect the mechanism of asthma persistence.

RESULTS

Elimination of T cells though antibody-mediated depletion or lethal irradiation and transplantation of recombination-activating gene (Rag1)(-/-) bone marrow in mice with chronic asthma resulted in resolution of airway inflammation but not airway hyperreactivity or remodeling. Elimination of T cells and type 2 innate lymphoid cells (ILC2s) through lethal irradiation and transplantation of Rag2(-/-)γc(-/-) bone marrow or blockade of IL-33 resulted in resolution of airway inflammation and hyperreactivity. Persistence of asthma required multiple interconnected feedback and feed-forward circuits between ILC2s and epithelial cells. Epithelial IL-33 induced ILC2s, a rich source of IL-13. The latter directly induced epithelial IL-33, establishing a positive feedback circuit. IL-33 autoinduced, generating another feedback circuit. IL-13 upregulated IL-33 receptors and facilitated IL-33 autoinduction, thus establishing a feed-forward circuit. Elimination of any component of these circuits resulted in resolution of chronic asthma. In agreement with the foregoing, IL-33 and ILC2 levels were increased in the airways of asthmatic patients. IL-33 levels correlated with disease severity.

CONCLUSIONS

We present a critical network of feedback and feed-forward interactions between epithelial cells and ILC2s involved in maintaining chronic asthma. Although T cells contributed to the severity of chronic asthma, they were redundant in maintaining airway hyperreactivity and remodeling.

Intestinal helminths regulate lethal acute graft-versus-host disease and preserve the graft-versus-tumor effect in mice

Donor T lymphocyte transfer with hematopoietic stem cells suppresses residual tumor growth (graft-versus-tumor [GVT]) in cancer patients undergoing bone marrow transplantation (BMT). However, donor T cell reactivity to host organs causes severe and potentially lethal inflammation called graft-versus-host disease (GVHD). High-dose steroids or other immunosuppressive drugs are used to treat GVHD that have limited ability to control the inflammation while incurring long-term toxicity. Novel strategies are needed to modulate GVHD, preserve GVT, and improve the outcome of BMT. Regulatory T cells (Tregs) control alloantigen-sensitized inflammation of GVHD, sustain GVT, and prevent mortality in BMT. Helminths colonizing the alimentary tract dramatically increase the Treg activity, thereby modulating intestinal or systemic inflammatory responses. These observations led us to hypothesize that helminths can regulate GVHD and maintain GVT in mice. Acute GVHD was induced in helminth (Heligmosomoides polygyrus)-infected or uninfected BALB/c recipients of C57BL/6 donor grafts. Helminth infection suppressed donor T cell inflammatory cytokine generation and reduced GVHD-related mortality, but maintained GVT. H. polygyrus colonization promoted the survival of TGF-β-generating recipient Tregs after a conditioning regimen with total body irradiation and led to a TGF-β-dependent in vivo expansion/maturation of donor Tregs after BMT. Helminths did not control GVHD when T cells unresponsive to TGF-β-mediated immune regulation were used as donor T lymphocytes. These results suggest that helminths suppress acute GVHD using Tregs and TGF-β-dependent pathways in mice. Helminthic regulation of GVHD and GVT through intestinal immune conditioning may improve the outcome of BMT.

Tumor necrosis factor-related apoptosis-inducing ligand mediates the resolution of allergic airway inflammation induced by chronic allergen inhalation

Allergic asthma can vanish over time either spontaneously or induced by allergen-specific immunotherapy. In mice with established airway allergic inflammation, chronic intranasal (IN) allergen challenges decreases progressively airway allergic inflammation. Here we compared the contribution of different regulatory pathways that could be associated with this phenomenon, known as local inhalational tolerance. We found that inhalational tolerance was not associated with increased number of regulatory T cells or suppressive cytokines. Instead, it was associated with increased apoptosis of airway inflammatory leukocytes revealed by annexin-V staining and the expression of apical caspase 8 and effector caspase 3. Also, the transition from acute to chronic phase was associated with a shift in the expression of pro-allergic to pro-apoptotic molecules. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was found to be a key molecule in mediating resolution of allergic inflammation because anti-TRAIL treatment blocked apoptosis and increased the infiltration of T helper type 2 (Th2) cells and eosinophils. Notably, repeated IN treatment with recombinant TRAIL in established airway allergic inflammation augmented leukocyte apoptosis and decreased the frequency of interleukin-5-producing Th2 cells and eosinophils to airways. Our data indicate that TRAIL signaling is sufficient for downmodulation of allergic airway disease, suggesting a potential therapeutic use of TRAIL for asthma treatment.

Regulatory B cells from hilar lymph nodes of tolerant mice in a murine model of allergic airway disease are CD5+, express TGF-β, and co-localize with CD4+Foxp3+ T cells

In a biphasic, ovalbumin (OVA)-induced murine asthma model where allergic airway disease is followed by resolution and the development of local inhalational tolerance (LIT), transforming growth factor (TGF)-β-expressing CD5(+) B cells were selectively expanded locally in hilar lymph nodes (HLN) of LIT mice. LIT HLN CD5(+) B cells, but not LIT HLN CD5(-) B cells, induced expression of Foxp3 in CD4(+)CD25(-) T cells in vitro. These CD5(+) regulatory B cells (Breg) and CD4(+)Foxp3(+) T cells demonstrated similar increases in expression of chemokine receptors (CXCR4 and CXCR5) and co-localized in HLN B cell zones of LIT mice. The adoptive transfer of LIT HLN CD5(+) B cells, but not LIT HLN CD5(-) B cells, increased the number of CD4(+)Foxp3(+) T cells in the lung and inhibited airway eosinophilia in this OVA model. Thus, Breg in HLNs of LIT mice reside in a CD5(+) TGF-β-producing subpopulation and co-localize with CD4(+)Foxp3(+) T cells.

Phenotypic changes to the endogenous antigen-specific CD8+ T cell response correlates with the development and resolution of allergic airway disease

The role of CD8(+) T cells in the pathogenesis of asthma remains controversial, as both pro- and anti-inflammatory functions have been suggested. This study was designed to examine the endogenous CD8(+) T cell response in a biphasic ovalbumin (OVA)-induced model of allergic airway disease (AAD) and its subsequent resolution with the development of local inhalational tolerance (LIT). We observed increases in OVA-specific CD8(+) T cell numbers in the local lung compartments (bronchoalveolar lavage, lung tissue, hilar lymph node) at AAD and LIT; systemic compartments (spleen, inguinal lymph node) displayed no such increases in CD8(+) T cell numbers. OVA-specific CD8(+) T cells appeared to exhibit plasticity both phenotypically and functionally. They possessed pro-inflammatory characteristics at AAD, with high phenotypic expression of CD11a and increased functional expression of granzyme B and interferon-γ. In contrast, at LIT they showed increased phenotypic expression of the inhibitory marker NKG2A and functionally did not produce granzyme B or interferon-γ. In addition, in a discontinuous model the OVA-specific CD8(+) T cells could be recalled on re-exposure to OVA, demonstrating memory. Finally, confocal microscopy results showed that OVA-specific CD8(+) T cells at AAD are associated with B cell aggregates in lung tissue. These B cell aggregates resembled tertiary ectopic lymphoid tissue and may thus provide a local environment for the salient cellular interactions that contribute to the development of LIT.

The Temporal Evolution of Airways Hyperresponsiveness and Inflammation

Airways hyperresponsiveness (AHR) is usually produced within days of first antigen exposure in mouse models of asthma. Furthermore, continual antigen challenge eventually results in the resolution of the AHR phenotype. Human asthma also waxes and wanes with time, suggesting that studying the time course of AHR in the allergic mouse would offer insights into the variation in symptoms seen in asthmatics. Mice were sensitized with ovalbumin (OVA) on days 0 and 14. As assessed by airway resistance (R_n ), lung elastance (H) and tissue damping (G), AHR was measured post an OVA inhalation on day 21 (Short Challenge group), after three days of OVA inhalation on day 25 (Standard Challenge group) and following an OVA inhalation on day 55 in mice previously challenged on days 21-23 (Recall Challenge group). Bronchoalveolar lavage was analyzed for inflammatory cells, cytokines and protein. AHR in the Short Challenge group was characterized by an increase in R_n and neutrophil accumulation in the lavage. AHR in the Standard Challenge group was characterized by increases in H and G but by only a modest response in R_n , while inflammation was eosinophilic. In the Standard Challenge protocol, mice lacking fibrinogen were no different from control in their AHR response. AHR in the Recall Challenge group was characterized by increases only in G and H and elevated numbers of both neutrophils and eosinophils. Lavage cytokines were only elevated in the Recall Challenge group. Lavage protein was significantly elevated in all groups. The phenotype in allergically inflamed mice evolves distinctly over time, both in terms of the nature of the inflammation and the location of the AHR response. The study of mouse models of AHR might be better served by focusing on this variation rather than simply on a single time point at which AHR is maximal.

Models and approaches to understand the role of airway remodelling in disease

Airway remodelling is a collective term for changes in the amount or organisation of the cellular and molecular constituents of the airway wall. Remodelling occurs in and is associated with the pathophysiology of airways diseases including asthma and chronic obstructive pulmonary disease. The remodelling that occurs in these diseases exhibits both shared and distinct features. Remodelling is generally considered to be deleterious to airway function but recent studies also indicate potential protective effects. However, the true impact of different aspects of the remodelling process on lung function, both negative and positive, is poorly understood. In addition, the genetic susceptibility and processes by which environmental insults drive the cell and molecular events which result in airway remodelling and the potential for therapeutic reversibility are also incompletely understood. The last 10-15 years has seen the development of animal models of airway remodelling which have been refined and modified as new factors such as exacerbations and early life influences have been recognised as being of importance. In addition, invertebrate models have been put forward and complex in vitro culture systems and lung slice preparations developed. In parallel, imaging technology has developed to an extent where it is feasible using a combination of techniques to image structural components, cells and proteins in the airway wall as well as to analyse biological processes, cell and receptor activation non-invasively over time. The integration of data from in vivo and in vitro models together with use of imaging techniques in man and animals should allow validation of models, further our understanding of the pathophysiology of airway remodelling and potentially improve predictive accuracy for the translation of novel therapeutic agents into the clinic.

Persistent activation of dendritic cells after resolution of allergic airway inflammation breaks tolerance to inhaled allergens in mice

RATIONALE

Polysensitization of patients who are allergic is a common feature. The underlying immunologic mechanism is not clear. The maturation status of dendritic cells (DCs) is considered to be important for priming naive T cells in the draining lymph nodes. We hypothesized that chronic airway inflammation can induce an enhanced maturation of airway DCs and facilitate subsequent priming to neoallergens.

OBJECTIVES

To investigate whether chronic airway inflammation could induce an altered activation of airway DCs in mice and whether this influences the development of allergic sensitization.

METHODS

Balb/c mice were repeatedly challenged with DCs to induce a chronic airway inflammation. We evaluated (1) the induction of the main characteristic features of human asthma including persistent remodeling, (2) the maturation status of airway DCs 1 month after inflammation resolved, (3) whether this influences tolerance to inhaled neoallergen, and (4) what type of T helper response would be induced by DCs.

MEASUREMENTS AND MAIN RESULTS

Airway DCs displayed a mature phenotype after complete resolution of airway eosinophilia. Inhalation of a neoallergen without any adjuvant was able to induce airway inflammation in postinflammation lungs but not in control lungs. One month after inflammation, airway DCs were able to induce Th2 polarization in naive T cells consistent with the up-regulation of the Th2 skewing molecules Ym1/2 and OX-40L compared with DCs of control airways.

CONCLUSIONS

This study provides evidence that sustained maturation of DCs after resolution of Th2-mediated inflammation can contribute to polysensitization.

Suppression of Th2-driven airway inflammation by allergen immunotherapy is independent of B cell and Ig responses in mice

Allergen-specific immunotherapy (IT) uniquely renders long-term relief from allergic symptoms and is associated with elevated serum levels of allergen-specific IgG and IgA. The allergen-specific IgG response induced by IT treatment was shown to be critical for suppression of the immediate phase of the allergic response in mice, and this suppression was partially dependent on signaling through FcγRIIB. To investigate the relevance of the allergen-specific IgG responses for suppression of the Th2-driven late-phase allergic response, we performed IT in a mouse model of allergic asthma in the absence of FcγRIIB or FcγRI/FcγRIII signaling. We found that suppression of Th2 cell activity, allergic inflammation, and allergen-specific IgE responses is independent of FcγRIIB and FcγRI/FcγRIII signaling. Moreover, we show that the IT-induced allergen-specific systemic IgG or IgA responses and B cell function are dispensable for suppression of the late-phase allergic response by IT treatment. Finally, we found that the secretory mucosal IgA response also is not required for suppression of the Th2-driven allergic inflammation by IT. These data are in contrast to the suppression of the immediate phase of the allergic response, which is critically dependent on the induced allergen-specific serum IgG response. Hence, IT-induced suppression of the immediate and late phases of the allergic response is governed by divergent and independent mechanisms. Our data show that the IT-induced suppression of the Th2 cell-dependent late-phase allergic response is independent of the allergen-specific IgG and IgA responses that are associated with IT treatment.

Modeling susceptibility versus resistance in allergic airway disease reveals regulation by Tec kinase Itk

Murine models of allergic asthma have been used to understand the mechanisms of development and pathology in this disease. In addition, knockout mice have contributed significantly to our understanding of the roles of specific molecules and cytokines in these models. However, results can vary significantly depending on the mouse strain used in the model, and in particularly in understanding the effect of specific knockouts. For example, it can be equivocal as to whether specific gene knockouts affect the susceptibility of the mice to developing the disease, or lead to resistance. Here we used a house dust mite model of allergic airway inflammation to examine the response of two strains of mice (C57BL/6 and BALB/c) which differ in their responses in allergic airway inflammation. We demonstrate an algorithm that can facilitate the understanding of the behavior of these models with regards to susceptibility (to allergic airway inflammation) (S(aai)) or resistance (R(aai)) in this model. We verify that both C57BL/6 and BALB/c develop disease, but BALB/c mice have higher S(aai) for development. We then use this approach to show that the absence of the Tec family kinase Itk, which regulates the production of Th2 cytokines, leads to R(aai) in the C57BL/6 background, but decreases S(aai) on the BALB/c background. We suggest that the use of such approaches could clarify the behavior of various knockout mice in modeling allergic asthma.

Preventive and curative glycoside kaempferol treatments attenuate the TH2-driven allergic airway disease

Asthma is a chronic respiratory disease characterized by airway inflammation and airway hyperresponsiveness (AHR). One strategy to treat allergic diseases is the development of new drugs. Flavonoids are compounds derived from plants and are known to have antiallergic, anti-inflammatory, and antioxidant properties. To investigate whether the flavonoid kaempferol glycoside 3-O-[beta-d-glycopiranosil-(1-->6)-alpha-l-ramnopiranosil]-7-O-alpha-l-ramnopiranosil-kaempferol (GRRK) would be capable of modulating allergic airway disease (AAD) either as a preventive (GRRK P) or curative (GRRK C) treatment in an experimental model of asthma. At weekly intervals, BALB/c mice were subcutaneously (sc) sensitized twice with ovalbumin (OVA)/alum and challenged twice with OVA administered intranasally. To evaluate any preventive effect, GRRK was administered 1h (hour) before each OVA-sensitization and challenge, while to analyze the curative effect, mice were first sensitized with OVA, followed by GRRK given at day 18 through 21. The onset of AAD was evaluated 24h after the last OVA challenge. Both treatments resulted in a dose-dependent reduction in total leukocyte and eosinophil counts in the bronchoalveolar lavage fluid (BAL). GRRK also decreased CD4(+), B220(+), MHC class II and CD40 molecule expressions in BAL cells. Histology and lung mechanic showed that GRRK suppressed mucus production and ameliorated the AHR induced by OVA challenge. Furthermore, GRRK impaired Th2 cytokine production (IL-5 and IL-13) and did not induce a Th1 pattern of inflammation. These findings demonstrate that GRRK treatment before or after established allergic lung disease down-regulates key asthmatic features. Therefore, GRRK has a potential clinical use for the treatment of allergic asthma.

Breastmilk from allergic mothers can protect offspring from allergic airway inflammation

OBJECTIVE

Breastfeeding is associated with a reduced risk of developing asthma in children. Using a murine model we previously demonstrated that mothers with Th1-type immunity to ovalbumin (OVA) transfer antigen-specific protection from OVA-induced allergic airway disease (AAD) to their offspring. The aim of this study was to evaluate the contribution of breastmilk and maternal B cell immunity from allergic mothers in the vertical transmission of protection from AAD.

METHODS

This was investigated using an adoptive nursing strategy. Naive offspring were nursed by allergic wild-type or B cell-deficient foster mothers with histories of Th2-type immunity to OVA. Following weaning, offspring were immunized with OVA-Al(OH)(3) and challenged with aerosolized OVA to induce AAD.

RESULTS

Offspring nursed by wild-type OVA-immune foster mothers demonstrated lower levels of OVA-specific immunoglobulin E, interleukin-5, and airway eosinophilia than progeny nursed by naive control mothers. In contrast, offspring nursed by B cell-deficient OVA-immune foster mothers had similar parameters of OVA-induced AAD as progeny nursed by naive control mothers.

CONCLUSIONS

These data demonstrate the ability of breastmilk from allergic mothers to protect offspring from AAD was dependent on intact maternal B cell immunity. Nursing alone, when done by wild-type mothers with AAD, was sufficient for offspring to acquire the antigen-specific protective factor(s) from breastmilk.

High levels of grass pollen inside European dairy farms: a role for the allergy-protective effects of environment?

BACKGROUND

There is evidence of an allergy protective effect in children raised on farm. It has been assumed that microbial exposure may confer this protection. However in farm, little attention has been given to the pollen level and to concomitant microbiological exposure, and indoor pollen concentrations have never been precisely quantified.

METHODS

The kinetics of pollen in dairy farms have been studied in a pilot study (n = 9), and exposure in a sub-sample of the ongoing European birth cohort PASTURE (n = 106). Measurements of viable microorganisms and pollen were performed in air samples. To identify factors that modulate the pollen concentration multivariate regression analyses were run.

RESULTS

Indoor pollen (95% of Poaceae fragments and grains) were significantly higher in winter than in summer (P = 0.001) and ranged between 858 to 11 265 counts/m(3) during feeding in winter, thus exceeding typical outdoor levels during the pollen season. Geometric mean in French farms was significantly higher than in German and Swiss farms (7 534, 992 and 1 079 count/m(3), respectively). The presence of a ventilation system and loose housing systems significantly reduced indoor pollen levels. This pollen concentration rise after feeding was accompanied by an increase in fungal and actinomycetal levels, whereas the concentration of bacteria was not associated with feeding.

CONCLUSIONS

Farmers and their children who attend cowsheds during the feeding sessions are exposed perennially to high pollen concentrations. It might be speculated that the combined permanent exposure to microbes from livestock and grass pollen may initiate tolerance in children living on a farm.

Multiple challenges in a mouse model of chemical-induced asthma lead to tolerance: ventilatory and inflammatory responses are blunted, immunologic humoral responses are not

To improve our mouse model of chemical-induced asthma we compared a single with a multiple intranasal challenge protocol. BALB/c mice received toluene diisocyanate (TDI) or vehicle on each ear (days 1 and 8) with the first challenge by intranasal instillation given on day 15. In a "long" protocol, the mice received 1 to 6 intranasal instillations, with 1-week interval. In a "short" protocol, the mice received 6 intranasal challenges over a period of 10 days. The "early" ventilatory response and methacholine reactivity were measured. Broncho-alveolar-lavage (BAL), total serum immunoglobulins and draining lymph nodes were analyzed. After 1, 2 or 3 TDI challenges, a significant increase in airway reactivity, total cell count and neutrophils (15-20%) was found in TDI-treated mice. This response diminished with increasing numbers of challenges in both models. The percentage CD4(+) and CD8(+) cells decreased and the percentage CD19(+) cells increased in the lymph nodes, but these returned to control values with multiple challenges. IL-4 secretion increased in cervical lymph node cells in vitro. Total serum IgE levels were persistently increased in TDI-treated mice. Although humoral signs of allergy remain increased after multiple challenges, diminishing ventilatory and inflammatory responses are indicative of the induction of tolerance.

IL-12p40 is essential for the down-regulation of airway hyperresponsiveness in a mouse model of bronchial asthma with prolonged antigen exposure

BACKGROUND

We previously reported a mouse model of bronchial asthma showing eosinophilic inflammation, but not airway hyperresponsiveness (AHR), after prolonged antigen exposure. This model showed an increase of IL-12 in the lung.

OBJECTIVE

The aim of this study was to investigate the role of IL-12p40 in a murine asthma model with prolonged antigen exposures.

METHODS

An ovalbumin (OVA)-induced asthma model was first established in wild-type (WT) and IL-12p40-deficient (IL-12p40(-/-)) mice. Both strains of mice were further exposed to either OVA (prolonged exposure group) or phosphate-buffered saline (positive control group) 3 days per week for 3 weeks. During week 4, both groups of mice were given a final challenge with OVA.

RESULTS

Prolonged antigen exposures resulted in marked suppression of airway eosinophilia in both WT and IL-12p40(-/-) mice. However, AHR persisted in IL-12p40(-/-) but not in WT mice. There were no significant differences of IL-5, IL-13 or IFN-gamma levels in bronchoalveolar lavage fluid between WT and IL-12p40(-/-) mice. The hydroxyproline content of the lung and peribronchial fibrosis were, however, significantly increased in IL-12p40(-/-) mice.

CONCLUSION

The results suggest that endogenous IL-12p40 is essential for inhibition of AHR and peribronchial fibrosis, but not eosinophilic inflammation, in a murine asthma model with prolonged antigen exposures.

Severe vitamin E deficiency modulates airway allergic inflammatory responses in the murine asthma model

Allergic asthma is a complex immunologically mediated disease associated with increased oxidative stress and altered antioxidant defenses. It was hypothesized that alpha-tocopherol (alpha-T) decreases oxidative stress and therefore its absence may influence allergic inflammatory process, a pathobiology known to be accompanied by oxidative stress. Therefore, selected parameters of allergic asthma sensitization and inflammation were evaluated following ovalbumin sensitization and re-challenge of alpha-T transfer protein (TTP) knock-out mice (TTP(-/-)) that have greatly reduced lung alpha-T levels (e.g.<5%) compared to their litter mate controls (TTP(+/+)). Results showed that severe alpha-T deficiency result in a blunted lung expression of IL-5 mRNA and IL-5 protein and plasma IgE levels compared with TTP(+/+) mice following immune sensitization and rechallenge, although lung lavage eosinophil levels were comparable in both genomic strains. It is concluded that the initial stimulation of immune responses by the TTP(-/-) mice were generally blunted compared to the TTP(+/+) mice, thus diminishing some aspects of subsequent allergic inflammatory processes.

Regulatory role of B cells in a murine model of allergic airway disease

Mice sensitized to OVA and subjected to acute OVA aerosol exposures develop allergic airway disease (AAD). However, chronic continuous Ag exposure results in resolution of AAD and the development of local inhalational tolerance (LIT). Because we have previously observed the persistence of B cells in the bronchoalveolar lavage (BAL) and hilar lymph nodes (HLN) at the resolution stage of this model, we investigated the role of B cells in the modulation of AAD. Although B cell-deficient mice developed LIT, adoptive transfer of HLN B cells from LIT mice to OVA-sensitized recipients resulted in attenuated AAD following subsequent OVA aerosol exposure, as determined by reduced BAL leukocytosis and eosinophilia, decreased tissue inflammation, and absent methacholine hyper-responsiveness. In similar adoptive transfer studies, HLN B cells from AAD mice were without effect. The protection transferred by LIT HLN B cells was Ag specific and was associated with accumulation of Foxp3(+) T regulatory cells regionally in BAL and HLN, but not systemically in the spleen. Fluorescent labeling of LIT HLN B cells before adoptive transfer demonstrated that these cells had the capacity to migrate to local inflammatory sites. In vitro assessment demonstrated that the LIT HLN B cells exerted this regulatory effect via TGF-beta induced conversion of CD4(+)CD25(-) T effector cells into functionally suppressive CD4(+)CD25(+)Foxp3(+) T regulatory cells. These findings illustrated a novel regulatory role for regional B cells in AAD and suggested a possible contributory role of B cells, along with other cell types, in the establishment of LIT.

Acute exercise decreases airway inflammation, but not responsiveness, in an allergic asthma model

Previous studies have suggested that the asthmatic responses of airway inflammation, remodeling, and hyperresponsiveness (AHR) are interrelated; in this study, we used exercise to examine the nature of this interrelationship. Mice were sensitized and challenged with ovalbumin (OVA); mice were then exercised via running on a motorized treadmill at a moderate intensity. Data indicate that, within the lungs of OVA-treated mice, exercise attenuated the production of inflammatory mediators, including chemokines KC, RANTES, and MCP-1 and IL-12p40/p80. Coordinately, OVA-treated and exercised mice displayed decreases in leukocyte infiltration, including eosinophils, as compared with sedentary controls. Results also show that a single bout of exercise significantly decreased phosphorylation of the NFkappaB p65 subunit, which regulates the gene expression of a wide variety of inflammatory mediators. In addition, OVA-treated and exercised mice exhibited decreases in the levels of Th2-derived cytokines IL-5 and IL-13 and the prostaglandin PGE(2), as compared with sedentary controls. In contrast, results show that a single bout of exercise had no effect on AHR in OVA-treated mice challenged with increasing doses of aerosolized methacholine (0-50 mg/ml) as compared with sedentary mice. Exercise also had no effect on epithelial cell hypertrophy, mucus production, or airway wall thickening in OVA-treated mice as compared with sedentary controls. These findings suggest that a single bout of aerobic exercise at a moderate intensity attenuates airway inflammation but not AHR or airway remodeling in OVA-treated mice. The implication of these findings for the interrelationship between airway inflammation, airway remodeling, and AHR is discussed.

Cigarette smoke enhances Th-2 driven airway inflammation and delays inhalational tolerance

BACKGROUND

Active smoking increases asthma severity and is related to diminished treatment efficacy. Animal models in which inhalation of both allergen and mainstream cigarette smoke are combined can help us to understand the complex interaction between both agents. We have recently shown that, in allergic mice, the airway inflammation can be cleared by repeated allergen challenge, resulting in the establishment of a state of inhalational tolerance.

METHODS

In this study, we assessed in vivo the impact of cigarette smoke on the efficacy and time course of this form of tolerance induction. We exposed sensitized mice to concurrent mainstream cigarette smoke and allergen (Ovalbumin- OVA) and measured the airway inflammation at different time points.

RESULTS

We first confirmed that aerosolized OVA administered for a prolonged time period (4-8 weeks) resulted in the establishment of tolerance. Concurrent OVA and smoke exposure for 2 weeks showed that tobacco smoke enhanced the Th-2 driven airway inflammation in the acute phase. In addition, the induction of the tolerance by repeated inhalational OVA challenge was delayed significantly by the tobacco smoke, since 4 weeks of concurrent exposure resulted in a more persistent eosinophilic airway inflammation, paralleled by a more mature dendritic cell phenotype. However, smoke exposure could not prevent the establishment of tolerance after 8 weeks of antigen exposure as shown by both histopathology (disappearance of the Th-2 driven inflammation) and by in vivo functional experiments. In these tolerized mice, some of the inflammatory responses to the smoke were even attenuated.

CONCLUSION

Cigarette smoke enhances acute allergic inflammation and delays, but does not abrogate the development of tolerance due to prolonged challenge with inhaled antigen in experimental asthma.

Subcutaneous late phase responses are augmented during local inhalational tolerance in a murine asthma model

Acute exposure of sensitized mice to antigen elicits allergic airway disease (AAD) characterized by Th2 cytokine-dependent pulmonary eosinophilia, methacholine hyperresponsiveness and antigen-specific IgE elevation. However, chronic exposure induces a local inhalational tolerance (LIT), with resolution of the airway responses but persistent systemic IgE production. To further determine if systemic immunologic responses were maintained during LIT, we assessed subcutaneous late phase responses to ovalbumin in this model. Sensitized and AAD mice developed small subcutaneous responses to ovalbumin, with footpad thickness increasing to 113.7 and 113.6% of baseline, respectively. In comparison, LIT mice developed marked foot swelling (141.6%). Histologic examination confirmed increased inflammation in the chronic animals, with a significant contribution by eosinophils. Thus, the resolution of airway inflammatory responses with chronic antigen inhalation is a localized response, not associated with loss of systemic responses to antigen.

Immunomodulatory effects of CpG oligodeoxynucleotides on house dust mite-induced airway inflammation in mice

BACKGROUND

CpG oligodeoxynucleotides (CpG ODNs) are reported to protect against airway eosinophilia and hyperresponsiveness in animal models of asthma. However, little is known about the effects of CpG ODNs on house dust mites, one of the most common environmental allergens, causing allergic asthma. In the present study, we evaluated the immunomodulatory effects of CpG ODNs on the development of house dust mite-induced airway inflammation and remodeling in mice.

METHODS

Mice were instilled with Dermatophagoides farinae (Der f) into the trachea 8 times without any additional adjuvants. 48 h after the final allergen instillation, the airway responsiveness to acetylcholine (Ach) was measured, and bronchoalveolar lavage (BAL) and histopathological examination were carried out. CpG ODNs were instilled into the trachea mixed with Der f at the first allergen instillation.

RESULTS

Repeated instillation of Der f induced increases in airway responsiveness to Ach, the numbers of inflammatory cells, the levels of T-helper type 2 cytokines and transforming growth factor-beta(1) in the BAL fluid. Furthermore, goblet cell hyperplasia, the thickness of the epithelium and subepithelial fibrosis were observed. The simultaneous instillation of CpG ODNs with Der f at the first allergen instillation showed significant inhibition of these parameters dose dependently.

CONCLUSIONS

Our results demonstrate that CpG ODNs have inhibitory effects on Der f-induced airway hyperresponsiveness and eosinophilia, as well as airway remodeling, and that CpG ODNs can be a therapeutic approach for the treatment of house dust mite-induced asthma.

Pin1 regulates TGF-beta1 production by activated human and murine eosinophils and contributes to allergic lung fibrosis

Eosinophilic inflammation is a cornerstone of chronic asthma that often culminates in subepithelial fibrosis with variable airway obstruction. Pulmonary eosinophils (Eos) are a predominant source of TGF-beta1, which drives fibroblast proliferation and extracellular matrix deposition. We investigated the regulation of TGF-beta1 and show here that the peptidyl-prolyl isomerase (PPIase) Pin1 promoted the stability of TGF-beta1 mRNA in human Eos. In addition, Pin1 regulated cytokine production by both in vitro and in vivo activated human Eos. We found that Pin1 interacted with both PKC-alpha and protein phosphatase 2A, which together control Pin1 isomerase activity. Pharmacologic blockade of Pin1 in a rat asthma model selectively reduced eosinophilic pulmonary inflammation, TGF-beta1 and collagen expression, and airway remodeling. Furthermore, chronically challenged Pin1(-/-) mice showed reduced peribronchiolar collagen deposition compared with wild-type controls. These data suggest that pharmacologic suppression of Pin1 may be a novel therapeutic option to prevent airway fibrosis in individuals with chronic asthma.

Accumulation of regulatory T cells in local draining lymph nodes of the lung correlates with spontaneous resolution of chronic asthma in a murine model

BACKGROUND

Mice sensitized to ovalbumin develop allergic airway disease (AAD) with short-term aerosol challenge; however, airway inflammation resolves with long-term aerosol challenge, referred to as local inhalational tolerance (LIT).

METHODS

We sought to determine if resolution of airway inflammation correlated with increases in lymphocyte subsets in local lung compartments, including putative regulatory T cells.

RESULTS

At the AAD stage, total numbers of T and B lymphocytes in bronchoalveolar lavage (BAL) were significantly increased above controls; however, at LIT, T and B lymphocytes were significantly reduced compared to AAD. In the lung tissue, the only alteration was a significant increase in CD4+ CD25+ T cells at AAD. In the hilar lymph node (HLN), CD4+ and CD4+ CD25+ T cells were significantly increased at AAD and LIT. In addition, CD8+ T cells were significantly elevated in the HLN at LIT, and CD19+ B cells were significantly increased at AAD. Adoptive transfer of HLN lymphocytes to lymphopenic mice confirmed that AAD lymphocytes could induce airway inflammation in response to aerosol challenge, whereas LIT lymphocytes were unable to do so. Depletion of CD4+ CD25+ T cells in vivo resulted in exacerbation of inflammation at AAD and LIT. CD4+ CD25+ T cells in the HLN also displayed suppressive activity in vitro. Additionally, T cells expressing Foxp3 were increased in the BAL and HLN during LIT.

CONCLUSIONS

These results indicate that lymphocytes with regulatory functions are increased and sustained in local lung compartments at LIT and that their appearance correlates with the resolution of lung inflammation.

Maternal transmission of resistance to development of allergic airway disease

Parental phenotype is known to influence the inheritance of atopic diseases, such as allergic asthma, with a maternal history being a more significant risk factor for progeny than paternal history. We hypothesized that recall Th1- or Th2-type immune responses during pregnancy would result in transfer of maternal factors that would differentially impact development of immune responsiveness in offspring. Following weaning, susceptibility and severity of allergic airway disease (a murine model of human asthma) was evaluated in progeny, disease being elicited by immunization with OVA-Al(OH)(3) and challenge with aerosolized OVA. We found that progeny of mothers with Th1-biased immunity to OVA subjected to recall aerosol challenge during pregnancy had reduced levels of Ag-specific IgE and airway eosinophilia compared with progeny of mothers with Th2-biased immunity to OVA or naive mothers. Interestingly, progeny of mothers with Th1-type immunity to a heterologous albumin, BSA, were not protected from developing OVA-induced allergic airway disease. These findings demonstrated that maternal transfer of protection from development of allergic airway disease to offspring in this model of maternal Th1-type immunity was Ag specific.

A novel pathway that regulates inflammatory disease in the respiratory tract

In animals with acute airway inflammation followed by repeated exposure to inhaled Ag, inflammation wanes over time and thus limits the study of chronic airway inflammatory diseases such as asthma. We developed a model of airway inflammation and inhalational exposure to investigate regulatory pathways in the respiratory tract. We show that Th1- and Th2-induced airway inflammation followed by repeated exposure to inhaled Ag leads to a state of immunosuppression. Challenge of these animals with a marked population of TCR transgenic effector Th1 or Th2 cells results in a striking inhibition of inflammation and effector Th cells. In Th2 models, airway hyperresponsiveness, mucus, and eosinophilia are reduced. The inhibitory effects observed are Ag nonspecific, can be induced in lymphocyte-deficient mice, and are associated with a population of TGF-beta1-expressing macrophages. Induction of this pathway may offer potent localized treatment of chronic T cell-mediated respiratory illnesses and provide insights into the development of such diseases.

Age-related difference in the persistency of allergic airway inflammation and bronchial hyperresponsiveness in a murine model of asthma

AIM

Asthmatic children are more likely to outgrow their symptoms than adult patients. Thus, we wanted to know whether there were any age-related differences in the time course of the allergic airway inflammation.

METHODS

BALB/C mice at different ages (young: 3 days after birth, and mature: 8 weeks of age) were sensitized with ovalbumin (OVA). Subsequently, animals were challenged with aerosolized OVA during 1, 2, 4 or 8 consecutive weeks. Bronchial hyperresponsiveness (BHR), serum IgE levels, the degrees of inflammatory cell infiltration (ICI) and goblet cell metaplasia (GCM) in the airways, and the number of eosinophils and cytokine levels in bronchoalveolar lavage fluid (BALF) were examined.

RESULTS

At 1 week, airway inflammation and BHR occurred similarly between young and mature mice. However, BHR disappeared at 4 weeks in young, whereas it persisted even at 8 weeks in mature mice. GCM, ICI and eosinophilia in BALF attenuated with time, with more remarkable reduction in young mice. The BALF IL-4 level was high during the first 2 weeks in both groups, while the IL-2 level was significantly increased at 2 weeks solely in young mice.

CONCLUSION

Different time courses in airway inflammation and in BHR may relate to the different prognoses between childhood and adult asthma. The understanding of the mechanisms underlying this age-related differences may be helpful to induce remission in asthmatic patients.

Prolonged inhaled allergen exposure can induce persistent tolerance

Murine asthma models suggest that failure of immune tolerance rather than a defective T helper cell type 1 (Th1) immunity underlies the immune biology of Th2-driven allergen-induced airway disease. Intriguingly, prolonged exposures can result in a full waning of inflammation. The mechanisms underlying this observation are not understood. We hypothesized that the fading of inflammation is the result of regulatory processes, characterized by altered dendritic cell (DC)-T cell interactions. First, we implemented a model in which mice developed Th2-driven airway disease. When we subjected these mice to prolonged antigen ovalbumin (OVA) exposures (8 wk), all inflammation disappeared. Re-immunization and re-challenge showed an inability to mount Th2-skewed immune responses, with absence of airway eosinophils, IgE, and Th2 cytokines. Besides specific immune tolerance, bystander protection was observed. A decrease in CD4+CD25+Foxp3+ T-regulatory cells, PD-1, and IL-10 expression was discerned as compared with acute inflammation. In addition, suppression of ICOS and CD28 was found, along with inhibited DC maturation. This process of disease inhibition surprisingly had a long-lasting memory and was not caused by endotoxin signaling through TLR-4. In summary, our results indicate that the disappearance of Th2-driven airway disease upon persistent antigen exposure is associated with the induction of immune tolerance. The tolerant state is antigen-dependent, and extends to bystander antigens. Moreover, this tolerance is characterized by an altered DC-T cell communication and is long-lasting. Our data further suggest that the mechanism of the disease inhibition after allergic airway inflammation differs from the anti-inflammatory mechanisms observed during acute eosinophilic airway inflammation.

Lung inflammation and vascular remodeling after repeated allergen challenge detected noninvasively by MRI

Magnetic resonance imaging (MRI) has been used previously to follow noninvasively inflammatory processes in rat acute models of lung inflammation. Here the technique was applied to a model involving repeated intratracheal administration of ovalbumin (OA). Anatomical MRI was performed at different time points with respect to a single or multiple OA challenges in Brown Norway rats actively sensitized to the allergen. Vascular permeability was assessed using dynamic contrast-enhanced MRI (DCE-MRI). Bronchoalveolar lavage (BAL) fluid analysis and histology were performed to validate the MRI data. The time course of MRI signals after a single OA challenge reached a maximum at 48 h and decreased significantly at 96 h. After the second and subsequent challenges, the maximum signal occurred at 6 h with a time-dependent decline over the remainder of the time course. A reduction of the inflammatory response following repeated administration of OA was also detected by BAL fluid analysis. The decrease in vascular permeability assessed by DCE-MRI in repeatedly OA-challenged rats was consistent with the thickening of the vascular wall for vessels of diameter up to 300 microm revealed by histology. Angiogenesis of vessels smaller than 30 microm was also detected histologically. These results suggest that MRI can be used to detect the inflammatory response and vascular remodeling associated with chronic airway inflammation in rat models involving repeated administration of allergen. As the contrast agent used in the DCE-MRI experiments is approved for clinical use, there is potential to translate the approach to patients.

Needleless intranasal administration of HVJ-E containing allergen attenuates experimental allergic rhinitis

Allergic rhinitis (AR) is one of the most common chronic diseases. Although current medications are highly effective in controlling its symptoms, they do not reverse the allergen-specific hypersensitivities that underlie the disease. Immunoglobulin E is a key mediator of AR, and preventing its production is clinically important. In this study, we developed an efficient needleless intranasal protein delivery system using the hemagglutinating virus of Japan envelope vector (HVJ-E). Intranasal delivery of ovalbumin (OVA) once a week for 3 weeks using this system enhanced OVA-induced interferon-gamma production by murine splenocytes. This treatment also attenuated the OVA-induced release interleukin-4 (IL-4) and IL-5 from splenocytes and the production of plasma OVA-specific immunoglobulin E in OVA-sensitive AR model mice. Thus, allergen-containing HVJ-E may be useful for noninvasive treatment of AR.

The cytochromes P450 (CYP) response to allergic inflammation of the lung

The expression of the mouse Cyp family and key inflammatory mediators were examined in a model of ovalbumin (OVA)-induced allergic airway disease. The expression of IL-4, IL-13 and Ccl11 increased during the acute phase of allergic inflammation and decreased with its resolution. Interestingly, the expression of Ccl20 was increased during the resolution phase. The response of the Cyp gene family to the development of allergic inflammation was differential and correlated with the evolution of the inflammatory response. During the acute inflammatory phase the mRNA levels of Cyp2e1, Cyp2f2, Cyp2j6, Cyp4b1, Cyp8a1 and Cypor were decreased while the mRNA levels of Cyp4f18, Cyp5a1 and Cyp7b1 were elevated. With resolution of the inflammation the expression patterns returned to normal. These changes suggest that the Cyp family may play a role in the allergic inflammation by modulating the metabolism of xenobiotics and endogenous compounds such as LTB4, TXA1, PGI2 and native anti-glucocorticoids.

Prolonged ovalbumin exposure attenuates airway hyperresponsiveness and T cell function in mice

BACKGROUND

Continuous exposure of sensitized mice to an innocuous antigen, such as OVA, does not lead to chronic airway eosinophilia, but induces antigen unresponsiveness and resolution of the inflammatory response. In this study we explored mechanisms underlying attenuation of the airway inflammatory response, assessed whether the phenomenon is strain-specific, and determined its consequences to airway physiology.

METHODS

Mice were sensitized and exposed to OVA for two and four weeks. Analysis involved BAL, flow cytometry, adoptive transfer of OVA specific CD4 T cells, ex vivo cytokine expression and response to methacholine challenge.

RESULTS

Chronic exposure to antigen resulted in decreased eosinophilia in 5 different mouse strains. Likewise, numbers of lung CD4 T cells expressing activation and Th2 markers sharply declined following continuous OVA exposure. Transfer studies using OVA TcR transgenic cells revealed that the contraction of lung T cells included antigen-specific cells. Systemically, we observed a loss of Th2 memory effector function. Finally, we observed significantly attenuated airway hyper-responsiveness (AHR) in chronically exposed animals.

CONCLUSIONS

Attenuation of airway eosinophilia in response to chronic OVA exposure is independent of genetic background. Airway eosinophilia, but not systemic responses, correlates with and is predictive for airway hyperresponsiveness. Our study contributes to the understanding of immune regulatory processes controlling antigen-driven airway inflammatory responses.

Loss of pro-apoptotic Bim promotes accumulation of pulmonary T lymphocytes and enhances allergen-induced goblet cell metaplasia

Immunological tolerance during prolonged exposure to allergen is accompanied by a shift in the lymphocyte content and a reduction of goblet cell metaplasia (GCM). Bim initiates negative selection of autoreactive T and B cells and shut down of T cell immune responses in vivo. The present study investigated whether Bim plays a role in the resolution of GCM during prolonged exposure to allergen. Loss of Bim increased T lymphocyte numbers in the bronchoalveolar lavage at 4 and 15 days of allergen exposure. The numbers of pulmonary CD4(+)8(-), CD4(-)8(+), and gammadelta T cells were significantly higher in naive and allergen-challenged bim(-/-) mice compared with wild-type (WT) littermates. When activated, pulmonary bim(-/-) T cells produced increased levels of IFNgamma compared with bim(+/+) T cells. No differences were noted in the total numbers of epithelial cells per millimeter of basal lamina between bim(+/+) and bim(-/-) mice, and the rate of resolution over 15 days of exposure was similar in both groups of mice. However, GCM was significantly enhanced and expression of IL-13Ralpha2 was reduced in bim(-/-) mice compared with WT mice at 4 days. Furthermore, treatment of bronchiolar explant cultures with increasing IFNgamma levels reduced immunostaining for IL-13Ralpha2. Collectively, these studies suggest that, during prolonged exposure to allergen, Bim plays no role in the resolution of GCM, but increased IFNgamma levels in bim(-/-) mice may be responsible for reduced expression of IL-13Ralpha2 and enhanced GCM despite similar levels of IL-13 in bim(+/+) and bim(-/-) mice.

Animal models of allergen-induced tolerance in asthma: are T-regulatory-1 cells (Tr-1) the solution for T-helper-2 cells (Th-2) in asthma?

Non-specific anti-inflammatory medication is actually the treatment of choice for controlling the T-helper type 2 (Th-2) cell-driven airway inflammation in asthma. The induction of counterbalancing Th-1 cell clones, long considered a promising approach for immunotherapy, has failed to fulfil its promise because of potentially detrimental side-effects. This is therefore probably not a valid option for the treatment of asthma. With the increasing awareness that active immune mechanisms exist to control inflammatory responses, interest rises to investigate whether these can be exploited to control allergen-induced airway disease. The induction of antigen-specific T cells with suppressive characteristics (regulatory T cells) is therefore a potentially interesting approach. These regulatory T cells mediate tolerance in healthy, non-atopic individuals and have the potential of becoming an effective means of preventing allergen-induced airway inflammation and possibly of suppressing ongoing allergic immune responses. Here we review the available knowledge about allergen-induced suppressive immunity obtained from animal models taking into account the different developmental stages of allergic airway disease.