Requirements for Allergen-Induced Airway Hyperreactivity in T and B Cell-Deficient Mice

Survey the effect of drug treatment on modulation of cytokines gene expression in allergic rhinitis

Allergic rhinitis as common airway disease has high prevalence in all peoples worldwide. In allergic diseases, Th2 cells release type 2 cytokines that support the inflammation in airways. All the drugs used for allergic rhinitis do not cure completely, and the choice of drugs according to cost and efficacy is very important in all groups of atopic patients. Therefore, in this study, the effect of commercial drugs on cytokine gene expression has been studied. Male Balb/c mice were divided into six groups. Allergic rhinitis was induced in five of the six groups with ovalbumin, and four of these five groups were treated with salbutamol, budesonide, theophylline, and montelukast. The fifth group was used as positive control group and the sixth group as negative control group. For the survey, RNA was extracted, cDNA was synthesized, and quantitative real-time PCR was done for 21 genes. The four drugs had different effects on mRNA expression of cytokines (IL-1b, 2, 4, 5, 7, 8, 9, 11, 12, 13, 17, 18, 22, 25, 31, 33, 37, IFN-γ, TNF-α, TGF-β1, and eotaxin) in the allergic rhinitis groups. Salbutamol can be used during pregnancy and breastfeeding, but it has some side effects. Budesonide in the inhaled form is generally safe in pregnancy. Theophylline cannot control allergic attack in the long run. Montelukast is not useful in the treatment of acute allergic attacks. Immunomodulatory and anti-inflammatory effects of drugs in control of allergic rhinitis via Th2 cytokines can be new approaches in molecular medicine.

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.

Immunoglobulin E-Dependent Activation of Immune Cells in Rhinovirus-Induced Asthma Exacerbation

Acute exacerbation is the major cause of asthma morbidity, mortality, and health-care costs. Respiratory viral infections, particularly rhinovirus (RV) infections, are associated with the majority of asthma exacerbations. The risk for bronchoconstriction with RV is associated with allergic sensitization and type 2 airway inflammation. The efficacy of the humanized anti-IgE monoclonal antibody omalizumab in treating asthma and reducing the frequency and severity of RV-induced asthma exacerbation is well-known. Despite these clinical data, mechanistic details of omalizumab's effects on RV-induced asthma exacerbation have not been well-defined for years due to the lack of appropriate animal models. In this Perspective, we discuss potential IgE-dependent roles of mast cells and dendritic cells in asthma exacerbations.

The role of innate immunity in asthma development and protection: Lessons from the environment

Asthma, a complex, chronic disease characterized by airway inflammation, hyperresponsiveness and remodelling, affects over 300 million people worldwide. While the disease is typically associated with exaggerated allergen-induced type 2 immune responses, these responses are strongly influenced by environmental exposures that stimulate innate immune pathways capable of promoting or protecting from asthma. The dual role played by innate immunity in asthma pathogenesis offers multiple opportunities for both research and clinical interventions and is the subject of this review.

Bevacizumab regulates inflammatory cytokines and inhibits VEGFR2 signaling pathway in an ovalbumin-induced rat model of airway hypersensitivity

BACKGROUND

Bevacizumab with anti-angiogenesis properties reduces the vascular endothelial growth factor (VEGF) level and has widely been used to treat various diseases such as lung diseases and chronic obstructive pulmonary disease (COPD). This study, therefore, aimed to consider the effects of bevacizumab on VEGF receptor 2 (VEGFR2) and lung inflammation of the ovalbumin-induced rat model of airway hypersensitivity.

MATERIALS AND METHODS

Twenty-one male Wistar rats were randomly divided into 3 groups (n = 7 in each group): (1) control, (2) ovalbumin (OVA)-sensitized, and (3) OVA-sensitized with bevacizumab (OVA + Bmab). Groups 2 and 3 were sensitized with ovalbumin (OVA) and aluminum hydroxide on days 1, 8 and challenged with OVA on day 15 by atomization for 10 days (inhalation). After OVA sensitization, the OVA + Bmab was treated with bevacizumab for 2 weeks. VEGFR2 was semiquantitatively analyzed in the lungs by immunohistochemistry. VEGF was measured in the lung tissue by ELISA method. The mRNA of IL-10 and IL-6 lung tissue were measured by real-time PCR.

RESULTS

Ovalbumin exposure promoted the expression of VEGF and resulted in inflammatory factors overexpression (p ≤ 0.05). However, rats in OVA + Bmab group showed significantly a decrease in VEGFR2 and IL-1β, IL-6, TNFα, and an increase in IL-10 (p ≤ 0.05).

CONCLUSION

The results show that bevacizumab efficiently diminishes bronchial inflammation via reducing the expression of VEGFR2, and IL-6 genes and enhancing the expression of IL-10 gene. Hence, bevacizumab could be considered as a potential candidate drug to control pathological conditions relevant to airway hypersensitivity.

Innate Lymphoid Cells of the Lung

Although, as the major organ of gas exchange, the lung is considered a nonlymphoid organ, an interconnected network of lung-resident innate cells, including epithelial cells, dendritic cells, macrophages, and natural killer cells is crucial for its protection. These cells provide defense against a daily assault by airborne bacteria, viruses, and fungi, as well as prevent the development of cancer, allergy, and the outgrowth of commensals. Our understanding of this innate immune environment has recently changed with the discovery of a family of innate lymphoid cells (ILCs): ILC1s, ILC2s, and ILC3s. All lack adaptive antigen receptors but can provide a substantial and rapid source of IFN-γ, IL-5 and IL-13, and IL-17A or IL-22, respectively. Their ability to afford immediate protection to the lung and to influence subsequent adaptive immune responses highlights the importance of understanding ILC-regulated immunity for the design of future therapeutic interventions.

Prediction of response to biological treatment with monoclonal antibodies in severe asthma

In recent years, major developments have occurred in severe asthma management. Different asthma phenotypes and subgroups have been identified and new treatment options have become available. A total of five monoclonal antibodies are currently approved in severe asthma treatment: omalizumab, mepolizumab, reslizumab, benralizumab and dupilumab. These drugs have been shown to reduce exacerbations and to have an oral corticosteroid-sparing effect in many severe asthma patients. However, biological treatment is not successful in all patients and should be discontinued in non-responsive patients. Treating the right patient with the right biologic, and therefore biologic response prediction, has become a major point of interest in severe asthma management. A variety of response outcomes is utilized in the different clinical trials, as well as a huge range of potential predicting factors. Also, regarding the timing of the response evaluation, there are considerable differences between studies. This review summarizes the results from studies on predicting responses and responders to biological treatment in severe asthma, taking into account clinical, functional and inflammatory parameters assessed prior to the start of treatment as well as following a few months of therapy. In addition, future perspectives are discussed, highlighting the need for more research to improve patient identification and treatment responses in the field of biological treatment in severe asthma.

Th2 cells promote eosinophil-independent pathology in a murine model of allergic bronchopulmonary aspergillosis

Repeated inhalation of airborne conidia derived from the fungus Aspergillus fumigatus (Af) can lead to a severe eosinophil-dominated inflammatory condition of the lung termed allergic bronchopulmonary aspergillosis (ABPA). ABPA affects about 5 million individuals worldwide and the mechanisms regulating lung pathology in ABPA are poorly understood. Here, we used a mouse model of ABPA to investigate the role of eosinophils and T cell-derived IL-4/IL-13 for induction of allergic lung inflammation. Selective deletion of IL-4/IL-13 in T cells blunted the Af-induced lung eosinophilia and further resulted in lower expression of STAT6-regulated chemokines and effector proteins such as Arginase 1, Relm-α, Relm-β, and Muc5a/c. Eosinophil-deficient ΔdblGata mice showed lower IL-4 expression in the lung and the number of Th2 cells in the lung parenchyma was reduced. However, expression of the goblet cell markers Clca1 and Muc5a/c, abundance of mucin-positive cells, as well as weight gain of lungs were comparable between Af-challenged ΔdblGata and WT mice. Based on these results, we conclude that T cell-derived IL-4/IL-13 is essential for Af-induced lung eosinophilia and inflammation while eosinophils may play a more subtle immunomodulatory role and should not simply be regarded as pro-inflammatory effector cells in ABPA.

Fungi in Mucoobstructive Airway Diseases

Asthma, chronic rhinosinusitis, and related incurable allergic afflictions of the upper and lower airways are medically important because of their association with the disabling symptom of dyspnea and, at least for asthma, the potential to cause fatal asphyxiation. Extensive research over the past two decades has uncovered both the physiological basis of airway obstruction in asthma and key governing molecular pathways. Exaggerated airway constriction in response to diverse provocative stimuli, termed airway hyperresponsiveness, is mediated through the cytokines interleukin 4 (IL-4) and IL-13 and the transcription factor signal transducer and activator of transcription 6 (STAT6). Overproduction of mucus has long been known to be an essential second component of airway obstruction and is also mediated in part through the IL-4/IL-13/STAT6 pathway. In this review, we discuss a second major signaling pathway which underlies mucus production that is mediated through proteinase-cleaved fibrinogen signaling through Toll-like receptor 4. Unexpectedly, our analysis of human sputum and paranasal sinus fluid indicates that in most cases of severe allergic airway disease, a unique type of airway fungal infection, termed airway mycosis, is pathogenically linked to these conditions. We further discuss how fungal and endogenous proteinases mediate the fibrinogenolysis that is essential to both Toll-like receptor 4 signaling and fibrin deposition that, together with mucus, contribute to airway obstruction.

T cells and ILC2s are major effector cells in influenza-induced exacerbation of allergic airway inflammation in mice

Influenza virus infection is an important cause of severe asthma exacerbations, but it remains unclear how a Th1‐mediated antiviral response triggers a prototypical Th2 disease. We investigated CD4⁺ T cells and group 2 innate lymphoid cells (ILC2s) in influenza virus‐infected mice. We found that ILC2s accumulated in the lung rapidly after influenza virus infection, but the induction of IL‐5 and IL‐13 secretion was delayed and concomitant with T cell activation. In an influenza‐induced exacerbation of allergic airway inflammation model we noticed an initial reduction of ILC2 numbers and cytokine production in broncho‐alveolar lavage compared to chronic house dust mite (HDM)‐mediated airway inflammation alone. ILC2s phenotype was characterized by low T1/ST2, ICOS, KLRG1, and CD25 expression, resembling naïve ILC2s. The contribution of ILC2s to type 2 cytokine production in the early stage of the influenza‐induced exacerbation was limited. In contrast, T cells showed increased IL‐4 and IL‐5 production when exposed to both HDM and influenza virus. Upon virus clearance, ILC2s regained an activated T1/ST2^highICOS^highKLRG1^highCD25^high phenotype paired with cytokine production and were major contributors to the type 2 cytokine milieu. Collectively, our data indicate that both T cells and ILC2s contribute to influenza‐induced exacerbation of allergic airway inflammation, but with different kinetics.

Group 2 Innate Lymphoid Cells Exhibit a Dynamic Phenotype in Allergic Airway Inflammation

Group 2 innate lymphoid cells (ILC2) are implicated in allergic asthma as an early innate source of the type 2 cytokines IL-5 and IL-13. However, their induction in house dust mite (HDM)-mediated airway inflammation additionally requires T cell activation. It is currently unknown whether phenotypic differences exist between ILC2s that are activated in a T cell-dependent or T cell-independent fashion. Here, we compared ILC2s in IL-33- and HDM-driven airway inflammation. Using flow cytometry, we found that surface expression levels of various markers frequently used to identify ILC2s were dependent on their mode of activation, highly variable over time, and differed between tissue compartments, including bronchoalveolar lavage (BAL) fluid, lung, draining lymph nodes, and spleen. Whereas in vivo IL-33-activated BAL fluid ILC2s exhibited an almost uniform CD25⁺CD127⁺T1/ST2⁺ICOS⁺KLRG1⁺ phenotype, at a comparable time point after HDM exposure BAL fluid ILC2s had a very heterogeneous surface marker phenotype. A major fraction of HDM-activated ILC2s were CD25^lowCD127⁺T1/ST2^low ICOS^lowKLRG1^low, but nevertheless had the capacity to produce large amounts of type 2 cytokines. HDM-activated CD25^low ILC2s in BAL fluid and lung rapidly reverted to CD25^high ILC2s upon in vivo stimulation with IL-33. Genome-wide transcriptional profiling of BAL ILC2s revealed ~1,600 differentially expressed genes: HDM-stimulated ILC2s specifically expressed genes involved in the regulation of adaptive immunity through B and T cell interactions, whereas IL-33-stimulated ILC2s expressed high levels of proliferation-related and cytokine genes. In both airway inflammation models ILC2s were present in the lung submucosa close to epithelial cells, as identified by confocal microscopy. In chronic HDM-driven airway inflammation ILC2s were also found inside organized cellular infiltrates near T cells. Collectively, our findings show that ILC2s are phenotypically more heterogeneous than previously thought, whereby their surface marker and gene expression profile are highly dynamic.

House dust mite-driven asthma and allergen-specific T cells depend on B cells when the amount of inhaled allergen is limiting

BACKGROUND

Allergic asthma is a CD4 T_H2-lymphocyte driven disease characterized by airway hyperresponsiveness and eosinophilia. B cells can present antigens to CD4 T cells and produce IgE immunoglobulins that arm effector cells; however, mouse models are inconclusive on whether B cells are necessary for asthma development.

OBJECTIVES

We sought to address the role of B cells in a house dust mite (HDM)-driven T_H2-high asthma mouse model.

METHODS

Wild-type and B cell-deficient muMT mice were sensitized and challenged through the airways with HDM extracts. The antigen-presenting capacities of B cells were studied by using new T-cell receptor transgenic 1-DER mice specific for the Der p 1 allergen.

RESULTS

In vitro-activated B cells from HDM-exposed mice presented antigen to 1-DER T cells and induced a T_H2 phenotype. In vivo B cells were dispensable for activation of naive 1-DER T cells but necessary for full expansion of primed 1-DER T cells. At high HDM challenge doses, B cells were not required for development of pulmonary asthmatic features yet contributed to T_H2 expansion in the mediastinal lymph nodes but not in the lungs. When the amount of challenge allergen was decreased, muMT mice had reduced asthma features. Under these limiting conditions, B cells contributed also to expansion of T_H2 effector cells in the lungs and central memory T cells in the mediastinal lymph nodes.

CONCLUSION

B cells are a major part of the adaptive immune response to inhaled HDM allergen, particularly when the amount of inhaled allergen is low, by expanding allergen-specific T cells.

A novel peptide ADAM8 inhibitor attenuates bronchial hyperresponsiveness and Th2 cytokine mediated inflammation of murine asthmatic models

A disintegrin and metalloproteinase 8 (ADAM8) has been identified as a signature gene associated with moderate and severe asthma. Studies in mice have demonstrated that the severity of asthma can be reduced by either transgenic knock-out or by antibodies blocking ADAM8 function, highlighting ADAM8 as potential drug target for asthma therapy. Here, we examined the therapeutic effect of an ADAM8 inhibitor peptide (BK-1361) that specifically blocks cellular ADAM8 activity in ovalbumin-sensitized and challenged Balb/c mice. We found that BK-1361 (25 μg/g body weight) attenuated airway responsiveness to methacholine stimulation by up to 42%, concomitantly reduced tissue remodeling by 50%, and decreased inflammatory cells (e.g. eosinophils down by 54%)/inflammatory factors (e.g. sCD23 down by 50%)/TH2 cytokines (e.g. IL-5 down by 70%)/ADAM8-positive eosinophils (down by 60%) in the lung. We further verified that BK-1361 specifically targets ADAM8 in vivo as the peptide caused significantly reduced levels of soluble CD23 in wild-type but not in ADAM8-deficient mice. These findings suggest that BK-1361 blocks ADAM8-dependent asthma effects in vivo by inhibiting infiltration of eosinophils and TH2 lymphocytes, thus leading to reduction of TH2-mediated inflammation, tissue remodeling and bronchial hyperresponsiveness. Taken together, pharmacological ADAM8 inhibition appears as promising novel therapeutic strategy for the treatment of asthma.

The adaptor protein insulin receptor substrate 2 inhibits alternative macrophage activation and allergic lung inflammation

Insulin receptor substrate 2 (IRS2) is an adaptor protein that becomes tyrosine-phosphorylated in response to the cytokines interleukin-4 (IL-4) and IL-13, which results in activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. IL-4 and IL-13 contribute to allergic lung inflammation. To examine the role of IRS2 in allergic disease, we evaluated the responses of IRS2-deficient (IRS2(-/-)) mice. Unexpectedly, loss of IRS2 resulted in a substantial increase in the expression of a subset of genes associated with the generation of alternatively activated macrophages (AAMs) in response to IL-4 or IL-13 in vitro. AAMs secrete factors that enhance allergic responses and promote airway remodeling. Moreover, compared to IRS2(+/+) mice, IRS2(+/-) and IRS2(-/-) mice developed enhanced pulmonary inflammation, accumulated eosinophils and AAMs, and exhibited airway and vascular remodeling upon allergen stimulation, responses that partially depended on macrophage-intrinsic IRS2 signaling. Both in unstimulated and IL-4-stimulated macrophages, lack of IRS2 enhanced phosphorylation of Akt and ribosomal S6 protein. Thus, we identified a critical inhibitory loop downstream of IRS2, demonstrating an unanticipated and previously unrecognized role for IRS2 in suppressing allergic lung inflammation and remodeling.

T cells are necessary for ILC2 activation in house dust mite-induced allergic airway inflammation in mice

Allergic asthma is a chronic inflammation of the airways mediated by an adaptive type 2 immune response. Upon allergen exposure, group 2 innate lymphoid cells (ILC2s) can be rapidly activated and represent an early innate source of IL-5 and IL-13. Here, we used a house dust mite (HDM)-driven asthma mouse model to study the induction of ILC2s in allergic airway inflammation. In BALF, lungs, and lymph nodes, ILC2 activation is critically dependent on prior sensitization with HDM. Importantly, T cells are required for ILC2 induction, whereby T-cell activation precedes ILC2 induction. During HDM-driven allergic airway inflammation the accumulation of ILC2s in BALF is IL-33 independent, although infiltrating ILC2s produce less cytokines in Il33(-/-) mice. Transfer of in vitro polarized OVA-specific OT-II Th2 cells alone or in combination with Th17 cells followed by OVA and HDM challenge is not sufficient to induce ILC2, despite significant eosinophilic inflammation and T-cell activation. In this asthma model, ILC2s are therefore not an early source of Th2 cytokines, but rather contribute to type 2 inflammation in which Th2 cells play a key role. Taken together, ILC2 induction in HDM-mediated allergic airway inflammation in mice critically depends on activation of T cells.

Challenges and Current Efforts in the Development of Biomarkers for Chronic Inflammatory and Remodeling Conditions of the Lungs

This review discusses biomarkers that are being researched for their usefulness to phenotype chronic inflammatory lung diseases that cause remodeling of the lung's architecture. The review focuses on asthma, chronic obstructive pulmonary disease (COPD), and pulmonary hypertension. Bio-markers of environmental exposure and specific classes of biomarkers (noncoding RNA, metabolism, vitamin, coagulation, and microbiome related) are also discussed. Examples of biomarkers that are in clinical use, biomarkers that are under development, and biomarkers that are still in the research phase are discussed. We chose to present examples of the research in biomarker development by diseases, because asthma, COPD, and pulmonary hypertension are distinct entities, although they clearly share processes of inflammation and remodeling.

Long-Acting Beta Agonists Enhance Allergic Airway Disease

Asthma is one of the most common of medical illnesses and is treated in part by drugs that activate the beta-2-adrenoceptor (β₂-AR) to dilate obstructed airways. Such drugs include long acting beta agonists (LABAs) that are paradoxically linked to excess asthma-related mortality. Here we show that LABAs such as salmeterol and structurally related β₂-AR drugs such as formoterol and carvedilol, but not short-acting agonists (SABAs) such as albuterol, promote exaggerated asthma-like allergic airway disease and enhanced airway constriction in mice. We demonstrate that salmeterol aberrantly promotes activation of the allergic disease-related transcription factor signal transducer and activator of transcription 6 (STAT6) in multiple mouse and human cells. A novel inhibitor of STAT6, PM-242H, inhibited initiation of allergic disease induced by airway fungal challenge, reversed established allergic airway disease in mice, and blocked salmeterol-dependent enhanced allergic airway disease. Thus, structurally related β₂-AR ligands aberrantly activate STAT6 and promote allergic airway disease. This untoward pharmacological property likely explains adverse outcomes observed with LABAs, which may be overcome by agents that antagonize STAT6.

Airway fibrinogenolysis and the initiation of allergic inflammation

The past 15 years of allergic disease research have produced extraordinary improvements in our understanding of the pathogenesis of airway allergic diseases such as asthma. Whereas it was previously viewed as largely an immunoglobulin E-mediated process, the gradual recognition that T cells, especially Type 2 T helper (Th2) cells and Th17 cells, play a major role in asthma and related afflictions has inspired clinical trials targeting cytokine-based inflammatory pathways that show great promise. What has yet to be clarified about the pathogenesis of allergic inflammatory disorders, however, are the fundamental initiating factors, both exogenous and endogenous, that drive and sustain B- and T-cell responses that underlie the expression of chronic disease. Here we review how proteinases derived from diverse sources drive allergic responses. A central discovery supporting the proteinase hypothesis of allergic disease pathophysiology is the role played by airway fibrinogen, which in part appears to serve as a sensor of unregulated proteinase activity and which, when cleaved, both participates in a novel allergic signaling pathway through Toll-like receptor 4 and forms fibrin clots that contribute to airway obstruction. Unresolved at present is the ultimate source of airway allergenic proteinases. From among many potential candidates, perhaps the most intriguing is the possibility such enzymes derive from airway fungi. Together, these new findings expand both our knowledge of allergic disease pathophysiology and options for therapeutic intervention.

B cells play key roles in th2-type airway immune responses in mice exposed to natural airborne allergens

Humans are frequently exposed to various airborne allergens. In addition to producing antibodies, B cells participate in immune responses via various mechanisms. The roles of B cells in allergic airway inflammation and asthma have been controversial. We examined the functional importance of B cells in a mouse model of asthma, in which mice were exposed repeatedly to common airborne allergens. Naïve wild-type BALB/c mice or B cell-deficient JH^−/− mice were exposed intranasally to a cocktail of allergen extracts, including Alternaria, Aspergillus, and house dust mite, every other day for two weeks. Ovalbumin was included in the cocktail to monitor the T cell immune response. Airway inflammation, lung pathology, and airway reactivity were analyzed. The airway exposure of naïve wild type mice to airborne allergens induced robust eosinophilic airway inflammation, increased the levels of Th2 cytokines and chemokines in the lung, and increased the reactivity to inhaled methacholine. These pathological changes and immune responses were attenuated in B cell-deficient JH^−/− mice. The allergen-induced expansion of CD4⁺ T cells was impaired in the lungs and draining lymph nodes of JH^−/− mice. Furthermore, lymphocytes from JH^−/− mice failed to produce Th2 cytokines in response to ovalbumin re-stimulation in vitro. Our results suggest that B cells are required for the optimal development of Th2-type immune responses and airway inflammation when exposed to common airborne allergens. The therapeutic targeting of B cells may be beneficial to treat asthma in certain patients.

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.

ADAM8 in asthma. Friend or foe to airway inflammation?

Airway inflammation has been suggested as the pathological basis in asthma pathogenesis. Recruitment of leukocytes from the vasculature into airway sites is essential for induction of airway inflammation, a process thought to be mediated by a disintegrin and metalloprotease 8 (ADAM8). However, there is an apparent controversy about whether ADAM8 helps or hampers transmigration of leukocytes through endothelium in airway inflammation of asthma. This review outlines the current contradictory concepts concerning the role of ADAM8 in airway inflammation, particularly focusing on the recruitment of leukocytes during asthma, and attempts to bridge the existing experimental data on the basis of the functional analysis of different domains of ADAM8 and their endogenous processing in vivo. We suggest a possible hypothesis for the specific mechanism by which ADAM8 regulates the transmigration of leukocytes to explain the disparity existing in current studies, and we also raise some questions that require future investigations.

Reduction of eotaxin production and eosinophil recruitment by pulmonary autologous macrophage transfer in a cockroach allergen-induced asthma model

We sought to investigate the effects of cockroach allergen (CRA) exposure on the lung macrophage population to determine how different macrophage phenotypes influence exacerbation of disease. CRA exposure caused significantly reduced expression of CD86 on lung macrophages. These effects were not systemic, as peritoneal macrophage CD86 expression was not altered. To investigate whether naïve macrophages could reduce asthma-like pulmonary inflammation, autologous peritoneal macrophages were instilled into the airways 24 h before the final CRA challenge. Pulmonary inflammation was assessed by measurement of airway hyperresponsiveness, mucin production, inflammatory cell recruitment, and cytokine production. Cell transfer did not have significant effects in control mice, nor did it affect pulmonary mucin production or airway hyperresponsiveness in control or CRA-exposed mice. However, there was significant reduction in the number of eosinophils recovered in the bronchoalveolar lavage (BAL) (5.8 × 10⁵ vs. 0.88 × 10⁵), and total cell recruitment to the airways of CRA-exposed mice was markedly reduced (1.1 × 10⁶ vs. 0.57 × 10⁶). The reduced eosinophil recruitment was reflected by substantially lower levels of eosinophil peroxidase in the lung and significantly lower concentrations of eotaxins in BAL (eotaxin 1: 3 pg/ml vs. undetectable; eotaxin 2: 2,383 vs. 131 pg/ml) and lung homogenate (eotaxin 1: 1,043 vs. 218 pg/ml; eotaxin 2: 10 vs. 1.5 ng/ml). We conclude that CRA decreases lung macrophage CD86 expression. Furthermore, supplementation of the lung cell population with peritoneal macrophages inhibits eosinophil recruitment, achieved through reduction of eotaxin production. These data demonstrate that transfer of naïve macrophages will reduce some aspects of asthma-like pulmonary inflammation in response to CRA.

Overexpression of methyl-CpG binding protein 2 impairs T(H)1 responses

The DNA binding protein methyl-CpG binding protein 2 (MeCP2) critically influences neuronal and brain function by modulating gene expression, and children with overexpression of the MECP2 gene exhibit postnatal neurological syndromes. We demonstrate that some children with MECP2 duplication also display variable immunological abnormalities that include reductions in memory T and B cells and natural killer cells and immunoglobulin assay responses. Moreover, whereas mice with MeCP2 overexpression were unable to control infection with the intra-macrophage parasite Leishmania major and secrete interferon-γ (IFN-γ) from involved lymph nodes, they were able to control airway fungal infection by Aspergillus niger and mount protective T helper cell type 2 (T(H)2)-dependent allergic responses. Relative to normal T cells, T(H) cells from children and mice with MECP2 duplication displayed similar impairments in IFN-γ secretion and T(H)1 responses that were due to both MeCP2-dependent suppression of IFN-γ transcription and sequestration of the IFN-γ locus as assessed by chromatin immunoprecipitation assay. Thus, overexpressed MeCP2 aberrantly suppresses IFN-γ secretion from T(H) cells, potentially leading to a partially immunodeficient state. Our findings establish a rational basis for identifying, treating, and preventing infectious complications potentially affecting children with MECP2 duplication.

Insights into mast cell functions in asthma using mouse models

Therapeutics targeting specific mechanisms of asthma have shown promising results in mouse models of asthma. However, these successes have not transferred well to the clinic or to the treatment of asthma sufferers. We suggest a reason for this incongruity is that mast cell-dependent responses, which may play an important role in the pathogenesis of both atopic and non-atopic asthma, are not a key component in most of the current asthma mouse models. Two reasons for this are that wild type mice have, in contrast to humans, a negligible number of mast cells localized in the smaller airways and in the parenchyma, and that only specific protocols show mast cell-dependent reactions. The development of mast cell-deficient mice and the reconstitution of mast cells within these mice have opened up the possibility to generate mouse models of asthma with a marked role of mast cells. In addition, mast cell-deficient mice engrafted with mast cells have a distribution of mast cells more similar to humans. In this article we review and highlight the mast cell-dependent and -independent responses with respect to airway hyperresponsiveness and inflammation in asthma models using mast cell-deficient and mast cell-engrafted mice.

Mouse models to evaluate the function of genes associated with allergic airway disease

PURPOSE OF REVIEW

In recent years, considerable effort has been invested in developing mouse models of allergic airway disease, as a means of evaluating the role of select genes in its pathophysiology. Here, we review the principal models used in this field, including models of allergic asthma and hypersensitivity pneumonitis. As an example of how these models can reveal novel functional roles for genes, we review our work showing a role for the stem-cell-associated gene, Cd34. Through this example, we illustrate the genetic and immunological strategies available in the field to better understand allergic airway inflammation.

RECENT FINDINGS

CD34 was found to play an important role in the development of two different models of allergic disease, that is, Th2-driven allergic asthma and Th17-driven hypersensitivity pneumonitis. Using a combination of genetically modified mice as well as cell transfers and chimeric mice, we showed that CD34 is important for the efficient trafficking of hematopoietic subsets into and out of the lung, including mast cells, eosinophils and dendritic cells.

SUMMARY

The currently available array of mutant mice and animal models of allergic disease now offers an opportunity to make profound insights into these diseases and provide preclinical models for the development of therapeutics.

Tracheobronchial mycosis in a retrospective case-series study of five status asthmaticus patients

The etiology of status asthmaticus (SA), a complication of severe asthma, is unknown. Fungal exposure, as measured by fungal atopy, is a major risk factor for developing asthma, but the relationship of fungi in SA per se has not previously been reported. In this five patient retrospective case series study, lower respiratory tract cultures were performed on bronchoalveolar lavage or tracheal aspirate fluid, comparing standard clinical laboratory cultures with a specialized technique in which respiratory mucus was removed prior to culture. We show that mucolytic treatment allows an increased detection of fungal growth, especially yeast, from the lower airways of all SA patients. We also demonstrate that inhalation of the yeast Candida albicans readily induces asthma-like disease in mice. Our observations suggest that SA may represent a fungal infectious process, and support additional prospective studies utilizing anti-fungal therapy to supplement conventional therapy, broad-spectrum antibiotics and high-dose glucocorticoids, which can promote fungal overgrowth.

The AGC kinase inhibitor H89 attenuates airway inflammation in mouse models of asthma

BACKGROUND

H89 is a potent inhibitor of Protein Kinase A (PKA) and Mitogen- and Stress-Activated protein Kinase 1 (MSK1) with some inhibitory activity on other members of the AGC kinase family. H89 has been extensively used in vitro but its anti-inflammatory potential in vivo has not been reported to date. To assess the anti-inflammatory properties of H89 in mouse models of asthma.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were sensitized intraperitoneally (i.p.) to ovalbumin (OVA) with or without alum, and challenged intranasally with OVA. H89 (10 mg/kg) or vehicle was given i.p. two hours before each OVA challenge. Airway hyperresponsiveness (AHR) was assessed by whole-body barometric plethysmography. Inflammation was assessed by the total and differential cell counts and IL-4 and IL-5 levels in bronchoalveolar lavage (BAL) fluid. Lung inflammation, mucus production and mast cell numbers were analyzed after histochemistry. We show that treatment with H89 reduces AHR, lung inflammation, mast cell numbers and mucus production. H89 also inhibits IL-4 and IL-5 production and infiltration of eosinophils, neutrophils and lymphocytes in BAL fluid.

CONCLUSIONS/SIGNIFICANCE

Taken together, our findings implicate that blockade of AGC kinases may have therapeutic potential for the treatment of allergic airway inflammation.

Immune response to n-terminal and c-terminal deletion mutants of Aspergillus fumigatus major allergen ASP F 3

The ubiquitous fungus Aspergillus fumigatus causes allergic rhinitis, asthma, sinusitis and allergic bronchopulmonary aspergillosis. A number of major allergens from A. fumigatus are purified, but their structure-function role in the pathogenesis of disease is not known. Such information is essential for devising alternative therapy of fungal allergic diseases. In the present study, N-terminal and C-terminal deletion mutants ofAsp f 3 were constructed and their immunopathological responses studied in a mice model of allergy. Three mutants viz,Asp f 3 (aa 33-168), (aa 1-142), and (aa 23-142) were made by deleting certain amino acids from epitopic regions of full lengthAsp f 3, a major allergen of A. furnigatus. TheAsp f 3 and three mutated proteins were expressed in pET vector. The C-terminal deletion mutantAsp f 3 (aa 1-142) induced elevated IFN-γ but low levels of IL-4 by spleen cells. This mutant also showed significant downregulation of peripheral blood eosinophils and lung inflammation in immunized mice. The N-terminal deletion mutantAsp f 3 (aa 33-168) also exhibited an immuno-suppressive effect in terms of IgE production and induction of Th2 cytokine. The results indicate thatrAsp f 3 and its deletion mutants induced distinct immune-inflammatory responses in mice on challenge with these proteins. The non-IgE binding deletion mutants ofAsp f 3 (aa 1-142 and aa 33-168) could deviate Th2 immune response with a concomitant reduction in airway inflammation and infiltration of inflammatory cells.

Mast cell engraftment of the peripheral lung enhances airway hyperresponsiveness in a mouse asthma model

Allergic asthma is a chronic inflammatory disease, characterized by airway hyperresponsiveness (AHR), inflammation, and tissue remodeling, in which mast cells play a central role. In the present study, we analyzed how mast cell numbers and localization influence the AHR in a chronic murine model of asthma. C57BL/6 (wild-type) and mast cell-deficient B6.Cg-Kit(W-sh) mice without (Wsh) and with (Wsh+MC) mast cell engraftment were sensitized to and subsequently challenged with ovalbumin for a 91-day period. In wild-type mice, pulmonary mast cells were localized in the submucosa of the central airways, whereas the more abundant mast cells in Wsh+MC mice were found mainly in the alveolar parenchyma. In Wsh+MC, ovalbumin challenge induced a relocation of mast cells from the perivascular space and central airways to the parenchyma. Allergen challenge caused a similar AHR in wild-type and Wsh mice in the resistance of the airways and the pulmonary tissue. In Wsh+MC mice the AHR was more pronounced. The elevated functional responses were partly related to the numbers and localization of connective tissue-type mast cells in the peripheral pulmonary compartments. A mast cell-dependent increase in IgE and IL-33 together with impairment of the IL-23/IL-17 axis was evoked in Wsh and Wsh+MC mice by allergen challenge. This study shows that within the same chronic murine asthma model the development of AHR can be both dependent and independent of mast cells. Moreover, the spatial distribution and number of pulmonary mast cells determine severity and localization of the AHR.

Mucin production and mucous cell metaplasia in otitis media

Otitis media (OM) with mucoid effusion, characterized by mucous cell metaplasia/hyperplasia in the middle ear cleft and thick fluid accumulation in the middle ear cavity, is a subtype of OM which frequently leads to chronic OM in young children. Multiple factors are involved in the developmental process of OM with mucoid effusion, especially disorders of mucin production resulting from middle ear bacterial infection and Eustachian tube dysfunction. In this review, we will focus on several aspects of this disorder by analyzing the cellular and molecular events such as mucin production and mucous cell differentiation in the middle ear mucosa with OM. In addition, infectious agents, mucin production triggers, and relevant signaling pathways will be discussed.

Airway epithelial regulation of allergic sensitization in asthma

While many of the contributing cell types and mediators of allergic asthma are known, less well understood are the factors that influence the development of allergic responses that lead to the development of allergic asthma. As the first airway cell type to respond to inhaled factors, the epithelium orchestrates downstream interactions between dendritic cells (DCs) and CD4⁺ T cells that quantitatively and qualitatively dictate the degree and type of the allergic asthma phenotype, making the epithelium of critical importance for the genesis of allergies that later manifest in allergic asthma. Amongst the molecular processes of critical importance in airway epithelium is the transcription factor, nuclear factor-kappaB (NF-κB). This review will focus primarily on the genesis of pulmonary allergies and the participation of airway epithelial NF-κB activation therein, using examples from our own work on nitrogen dioxide (NO₂) exposure and genetic modulation of airway epithelial NF-κB activation. In addition, the mechanisms through which Serum Amyloid A (SAA), an NF-κB-regulated, epithelial-derived mediator, influences allergic sensitization and asthma severity will be presented. Knowledge of the molecular and cellular processes regulating allergic sensitization in the airways has the potential to provide powerful insight into the pathogenesis of allergy, as well as targets for the prevention and treatment of asthma.

Innate IL-13-producing nuocytes arise during allergic lung inflammation and contribute to airways hyperreactivity

BACKGROUND

IL-4, IL-5, and IL-13 are thought to be central to the allergic asthmatic response. Previous work supposed that the essential source of these cytokines was CD4(+) T(H)2 cells. However, more recent studies have suggested that other innate production of type 2 cytokines might be as important.

OBJECTIVES

Nuocytes are a novel population of IL-13-producing innate cells, which are critical for protective immunity in Nippostrongylus brasiliensis infection. Given this, we investigated the potential existence and functional importance of nuocytes in experimental allergic asthma.

METHODS

We generated Il4(+/eGFP)Il13(+/Tomato) dual-reporter mice to study cytokine-producing cells during allergic inflammation. We adoptively transferred innate IL-13-producing cells to investigate their role in airways hyperreactivity (AHR).

RESULTS

We show that allergen-induced nuocytes infiltrate the lung and are a major innate source of IL-13. CD4(+) T cells in the lung almost exclusively express only IL-13, whereas IL-4-producing T cells were restricted to the draining lymph nodes. Intranasal administration of IL-25 or IL-33 induced IL-13-producing nuocytes in the BAL fluid. Strikingly, adoptive transfer of wild-type nuocytes, but not Il13(-/-) nuocytes, into Il13(-/-) mice, which are normally resistant to IL-25-induced AHR, restored airways resistance and lung cell infiltration.

CONCLUSIONS

These findings identify nuocytes as a novel cell type in allergic lung inflammation and an innate source of IL-13 that can directly induce AHR in the absence of IL-13-producing CD4(+) T cells. These data highlight nuocytes as an important new consideration in the development of future allergic asthma therapy.

Necessary and sufficient role for T helper cells to prevent fungal dissemination in allergic lung disease

Mucosal immune responses to fungal infection range from T helper type 2 (Th2) cell-directed allergic inflammation to Th1-predominant neutrophilic inflammation, but the mechanisms directing these divergent mucosal immune outcomes and the role of T cells in host defense against mucosal fungal infections are not known. Here we examined the mouse mucosal immune responses to 12 filamentous environmental fungal species over a broad range of exposure doses and determined the requirement of T cells for host defense. For all tested fungi, low-grade conidium exposures induced Th2- and eosinophil-predominant allergic lung disease, whereas higher exposures led to rapid conversion to neutrophil- and Th1 cell-predominant inflammation, a phenomenon we term immune phenotype switching. All fungal exposure doses were further linked to the secretion of interleukin-17A (IL-17A). Fungal infections with Curvularia lunata and Aspergillus fumigatus were typically confined to the airway during allergic inflammation but became locally invasive and disseminated to the brain at higher conidium challenge doses, in association with predominant Th1 responses. Fungal dissemination occurred at relatively low challenge doses with the conidia of Aspergillus fumigatus administered to recombinase activating gene 1 (Rag-1)-deficient mice, which lack B and T cells, but B cell-deficient μMT mice and T helper cell-reconstituted Rag-1-deficient mice were comparable to wild-type mice in preventing fungal dissemination. Our findings demonstrate that Th2 cell-predominant allergic responses followed by immune phenotype switching and fungal dissemination are highly predictable outcomes with progressive fungal infectious burdens and that T helper cell responses are protective against lethal fungal dissemination.

Proteinases as molecular adjuvants in allergic airway disease

BACKGROUND

Asthma and related respiratory tract allergic diseases are among the most common chronic diseases of adults and children. Despite their importance, disease course cannot be predicted and treatment remains non-specific and potentially hazardous, with no means for cure. Improved clinical management of asthma will require an improved understanding of the fundamental factors that initiate allergic inflammation, especially T helper type 2 (T(H)2) cell induction.

SCOPE OF REVIEW

In this review, we explore the Proteinase Hypothesis of allergic airway disease, considering specifically how organismal proteinases contribute to the expression of allergic disease and potentially important proteinase signaling pathways.

MAJOR CONCLUSIONS

Proteinases from diverse sources (bacteria, fungi, plants) may cause occupational asthma by acting as immune adjuvant factors that specifically elicit T(H)2 cell-dependent allergic inflammation. However, more conventional allergic airway diseases (asthma, allergic sinusitis) are more likely to arise from contained fungal or viral infections of the airway in which proteinases are produced and serve as major virulence factors. Proteinases may elicit allergic disease by disrupting numerous cellular proteins, potentially including Toll like receptor (TLR) 4, but critical proteinase-activated signaling pathways remain largely unknown.

GENERAL SIGNIFICANCE

Clarification of how proteinases cause allergic disease, specifically confirming an infectious basis for airway proteinase exposure, will likely radically advance how asthma and related respiratory tract disorders are diagnosed and treated. This article is part of a Special Issue entitled Biochemistry of Asthma.

Triggering receptor expressed on myeloid cells-1 (TREM-1) modulates immune responses to Aspergillus fumigatus during fungal asthma in mice

Triggering receptor expressed on myeloid cells-1 (TREM-1) expression is increased during pulmonary fungal infection suggesting that this receptor might be involved in anti-fungal immune responses. To address the role of TREM-1 in a murine model of fungal allergic airway disease, A. fumigatus-sensitized CBA/J mice received by intratracheal injection a mixture of live A. fumigatus conidia and one of a control adenovirus vector (Ad70), an adenovirus containing a gene encoding for the extracellular domain of mouse TREM-1 and the F(c) portion of human IgG (AdTREM-1Ig; a soluble inhibitor of TREM-1 function), or an adenovirus containing mouse DAP12 (AdDAP12; DAP12 is an intracellular adaptor protein required for TREM-1 signaling), and examined at various days after challenge. Whole lung TREM-1 levels peaked at day 3 whereas circulating TREM-1 levels peaked at day 30 in this fungal asthma model. AdTREM-1Ig-treated mice exhibited significantly higher airway hyperresponsiveness following methacholine challenge compared with Ad70- and AdDAP12-treated mice. Whole lung analysis of AdTREM-1Ig treated mice revealed markedly higher amounts of fungal material compared with the other groups. ELISA analysis of whole lung and bronchoalveolar lavage samples indicated that several pro-allergic cytokine and chemokines including CCL17 and CCL22 were significantly increased in the AdTREM-1Ig group compared with the other groups. Finally, Pam3Cys and soluble Aspergillus antigens induced TREM-1 transcript expression in macrophages in a TLR2 dependent manner. In conclusion, TREM-1 modulates the immune response directed against A. fumigatus during experimental fungal asthma.

Epithelial, dendritic, and CD4(+) T cell regulation of and by reactive oxygen and nitrogen species in allergic sensitization

BACKGROUND

While many of the contributing cell types and mediators of allergic asthma are known, less well understood are the factors that induce allergy in the first place. Amongst the mediators speculated to affect initial allergen sensitization and the development of pathogenic allergic responses to innocuous inhaled antigens and allergens are exogenously or endogenously generated reactive oxygen species (ROS) and reactive nitrogen species (RNS).

SCOPE OF REVIEW

The interactions between ROS/RNS, dendritic cells (DCs), and CD4(+) T cells, as well as their modulation by lung epithelium, are of critical importance for the genesis of allergies that later manifest in allergic asthma. Therefore, this review will primarily focus on the initiation of pulmonary allergies and the role that ROS/RNS may play in the steps therein, using examples from our own work on the roles of NO(2) exposure and airway epithelial NF-κB activation.

MAJOR CONCLUSIONS

Endogenously generated ROS/RNS and those encountered from environmental sources interact with epithelium, DCs, and CD4(+) T cells to orchestrate allergic sensitization through modulation of the activities of each of these cell types, which quantitiatively and qualitatively dictate the degree and type of the allergic asthma phenotype.

GENERAL SIGNIFICANCE

Knowledge of the effects of ROS/RNS at the molecular and cellular levels has the potential to provide powerful insight into the balance between inhalational tolerance (the typical immunologic response to an innocuous inhaled antigen) and allergy, as well as to potentially provide mechanistic targets for the prevention and treatment of asthma.

Seeking common pathophysiology in asthma, atopy and sinusitis

Asthma and chronic sinusitis are inexplicably common airway diseases that are linked to atopy and allergic inflammation. T helper type 2 (Th2) cells and the associated cytokines are believed to play crucial pathogenic roles in asthma, but the environmental factors that instigate allergic airway disease remain poorly understood. Environmental proteinases are highly allergenic and are candidate inducers of airway Th2 responses. Determining the proteinases and their sources that are relevant to airway disease, however, remains challenging. In this Opinion, we summarize the evidence that implicates fungi as both a relevant source of allergenic proteinases and a potential cause of asthma, atopy and chronic sinusitis through airway infection. Clarification of the extrinsic causes of these processes will markedly improve diagnosis, prognosis and therapy.

NO2 inhalation induces maturation of pulmonary CD11c+ cells that promote antigenspecific CD4+ T cell polarization

Background

Nitrogen dioxide (NO₂) is an air pollutant associated with poor respiratory health, asthma exacerbation, and an increased likelihood of inhalational allergies. NO₂ is also produced endogenously in the lung during acute inflammatory responses. NO₂ can function as an adjuvant, allowing for allergic sensitization to an innocuous inhaled antigen and the generation of an antigen-specific Th2 immune response manifesting in an allergic asthma phenotype. As CD11c⁺ antigen presenting cells are considered critical for naïve T cell activation, we investigated the role of CD11c⁺ cells in NO₂-promoted allergic sensitization.

Methods

We systemically depleted CD11c⁺ cells from transgenic mice expressing a simian diphtheria toxin (DT) receptor under of control of the CD11c promoter by administration of DT. Mice were then exposed to 15 ppm NO₂ followed by aerosolized ovalbumin to promote allergic sensitization to ovalbumin and were studied after subsequent inhaled ovalbumin challenges for manifestation of allergic airway disease. In addition, pulmonary CD11c⁺ cells from wildtype mice were studied after exposure to NO₂ and ovalbumin for cellular phenotype by flow cytometry and in vitro cytokine production.

Results

Transient depletion of CD11c⁺ cells during sensitization attenuated airway eosinophilia during allergen challenge and reduced Th2 and Th17 cytokine production. Lung CD11c⁺ cells from wildtype mice exhibited a significant increase in MHCII, CD40, and OX40L expression 2 hours following NO₂ exposure. By 48 hours, CD11c⁺MHCII⁺ DCs within the mediastinal lymph node (MLN) expressed maturation markers, including CD80, CD86, and OX40L. CD11c⁺CD11b^- and CD11c⁺CD11b⁺ pulmonary cells exposed to NO₂ in vivo increased uptake of antigen 2 hours post exposure, with increased ova-Alexa 647⁺ CD11c⁺MHCII⁺ DCs present in MLN from NO₂-exposed mice by 48 hours. Co-cultures of ova-specific CD4⁺ T cells from naïve mice and CD11c⁺ pulmonary cells from NO₂-exposed mice produced IL-1, IL-12p70, and IL-6 in vitro and augmented antigen-induced IL-5 production.

Conclusions

CD11c⁺ cells are critical for NO₂-promoted allergic sensitization. NO₂ exposure causes pulmonary CD11c⁺ cells to acquire a phenotype capable of increased antigen uptake, migration to the draining lymph node, expression of MHCII and co-stimulatory molecules required to activate naïve T cells, and secretion of polarizing cytokines to shape a Th2/Th17 response.

Pathogens and immunologic memory in asthma: what have we learned?

Animal models and clinical studies of asthma have generated important insights into the first effector phase leading to the development of allergic airway disease and bronchial hyper-reactivity. In contrast, mechanisms related to asthma chronicity or persistence are less well understood. The CD4(+) T-helper 2 lymphocytes are known initiators of the inflammatory response associated with asthma. There is now increasing evidence that memory T-cells, sensitized against allergenic, occupational or viral antigens, are also involved in the persistence of asthma. Additionally, the role of pathogens in asthma has been linked to both the initial susceptibility to and flares of this disease. This review will discuss the potential links between infection and asthma, the role of the memory T-cells in asthma, and the potential mechanisms by which these factors interact to lead to the development and/or persistence of asthma.

Particulate matter-induced airway hyperresponsiveness is lymphocyte dependent

BACKGROUND

Exposure to airborne particulate matter (PM), a major component of air pollution, has been associated with increases in both exacerbations of and hospitalizations for asthma. We have previously shown that exposure to ambient PM collected in urban Baltimore (AUB) induces airway hyperresponsiveness (AHR), eosinophilic and neutrophilic inflammation, and the recruitment of T cells. However, the mechanism(s) by which it induces these features of asthma remains unknown.

OBJECTIVE

We investigated whether T lymphocytes play a role in AUB-induced AHR.

METHODS

We compared the effects of AUB exposure on the allergic phenotype in wild-type (WT) BALB/c mice and in mice deficient in recombinase-activating gene-1 (Rag1-/-) that lack mature lymphocytes.

RESULTS

We found that exposure of WT mice to AUB induced AHR concomitant with increases in the numbers of bronchoalveolar lavage (BAL) fluid lymphocytes, eosinophils, neutrophils, and mucus-containing cells in the lungs of WT mice. Interestingly, we show for the first time that these effects were associated with significant elevations in interleukin (IL)-17A, IL-17F, and T-helper 2 cell (TH2) (IL-13, IL-5) cytokine levels in lung cells, as well as reductions in the levels of the suppressive cytokine IL-10. Interestingly, Rag1-/- mice failed to develop AUB-induced AHR; however, AUB-induced BAL fluid cellularity, and mucus cell changes were only partially inhibited in Rag1-/- mice.

CONCLUSIONS

Taken together, our results suggest that AUB exposure increases the pathophysiological features of asthma via activation of lymphocyte-dependent pathways. These results provide a plausible biological mechanism for the strong association between PM exposure and the increased severity of asthma.

Asthma: Pathophysiology and Diagnosis

Although asthma is a common disorder affecting approximately 7.8% of the United States population (Schiller et al. 2006) or 23 million Americans, the pathogenesis of this disease remains to be fully elucidated. Extensive research over the last few decades has yielded a better understanding of asthma. We know that the basic features of asthma include episodic airways inflammation, airways hyperresponsiveness, and mucous hypersecretion. Although we understand the basic clinical features of asthma, the links between symptoms, physical signs, and underlying pathophysiological mechanisms are still being delineated. Asthma is a heterogeneous disease process with varying phenotypes and presentations. In this chapter, we will briefly explore some major theories of asthma pathogenesis, both new and old. We will also explore how understanding the pathophysiology of asthma can help us to understand the symptoms and presentation of asthma, as well as the best strategies for diagnosing this disease.

Eosinophils and allergic airway disease: there is more to the story

The eosinophil has been perceived as a terminal effector cell in allergic airway diseases. However, recent work has shown that this multifunctional cell could be more involved in the initial stages of allergic disease development than was previously thought, particularly with regard to the ability of the eosinophil to modulate T-cell responses. In this review, we discuss recent advances that suggest that eosinophils can present antigen to naïve as well as to antigen-experienced T cells, induce T helper 2 cell development, cytokine production or both, and affect T-cell migration to sites of inflammation. These findings are changing the way that eosinophil function in disease is perceived, and represent a shift in the dogma of allergic disease development.

Link between allergic asthma and airway mucosal infection suggested by proteinase-secreting household fungi

Active fungal proteinases are powerful allergens that induce experimental allergic lung disease strongly resembling atopic asthma, but the precise relationship between proteinases and asthma remains unknown. Here, we analyzed dust collected from the homes of asthmatic children for the presence and sources of active proteinases to further explore the relationship between active proteinases, atopy, and asthma. Active proteinases were present in all houses and many were derived from fungi, especially Aspergillus niger. Proteinase-active dust extracts were alone insufficient to initiate asthma-like disease in mice, but conidia of A. niger readily established a contained airway mucosal infection, allergic lung disease, and atopy to an innocuous bystander antigen. Proteinase produced by A. niger enhanced fungal clearance from lung and was required for robust allergic disease. Interleukin 13 (IL-13) and IL-5 were required for optimal clearance of lung fungal infection and eosinophils showed potent anti-fungal activity in vitro. Thus, asthma and atopy may both represent a protective response against contained airway infection due to ubiquitous proteinase-producing fungi.

Extravascular inflammation does not increase atherosclerosis in apoE-deficient mice

There is much speculation whether extravascular inflammation accelerates atherosclerosis. We tested this hypothesis in apoE(-/-) mice using three well-characterized models of non-autoimmune chronic inflammation: croton oil-induced skin inflammation, Aspergillus fumigatus antigen-induced allergic lung disease, and A. fumigatus antigen-induced peritonitis. The croton oil model produced recurrent inflammatory skin ulceration, and marked increases in plasma levels of IL-6 and serum amyloid A (SAA). The allergic lung disease model showed strong local inflammation with eosinophilic infiltration and serum IgE induction. The recurrent peritonitis model was accompanied by mild elevation in plasma SAA levels. Aortic atherosclerosis was quantified by computer-assisted morphometry of en face arteries in apoE(-/-) mice at 34 weeks for the croton oil model, 26 and 42 weeks for the allergic lung disease model, and 26 weeks for the peritonitis model. We found that all three forms of chronic extravascular inflammation had no effect on the rate of atherosclerosis development.

Divergent functions for airway epithelial matrix metalloproteinase 7 and retinoic acid in experimental asthma

The innate immune response of airway epithelial cells to aeroallergen initiates the development of T cell responses that are central to allergic inflammation. Although proteinase allergens induce the expression of interleukin 25 we show that epithelial matrix metalloproteinase 7 (MMP7) was expressed in asthma and was required for maximal activity of IL-25 in promoting T helper type 2 cell differentiation. Allergen-challenged Mmp7^−/− mice showed reduced airway hyperreactivity, allergic inflammatory cytokine production and increased expression of retinal dehydrogenase (RALDH)-1. Inhibition of RALDH-1 restored the asthma phenotype in Mmp7^−/− mice and inhibited lung T regulatory cell responses while exogenous administration of retinoic acid attenuated the asthma phenotype. Thus, MMP7 coordinates allergic lung inflammation by activating IL-25 while simultaneously inhibiting retinoid-dependent T regulatory cell development.

Chronic intranasal administration of Aspergillus fumigatus spores leads to aggravation of airway inflammation and remodelling in asthmatic rats

BACKGROUND AND OBJECTIVE

Epidemiological evidence indicates a close link between exposure to fungi and deterioration of asthma. However, the role of fungi as an exogenous precipitant for initiation and progression of asthma has been incompletely explored. In this study, the effects of Aspergillus fumigatus exposure on airway inflammation and remodelling in a rat model of chronic asthma were investigated.

METHODS

The rat model of chronic asthma was established by systemic sensitization and repeated challenge with ovalbumin (OVA). The asthmatic rats were exposed to chronic intranasal inhalation of A. fumigatus spores. Changes in airway inflammation, remodelling and BHR were measured after exposure to the fungus.

RESULTS

Chronic inhalation of A. fumigatus spores elevated the production of T helper 2 (Th2) cytokines, increased the concentration of total serum IgE, and resulted in the recruitment of eosinophils and lymphocyte infiltration into the airways of asthmatic rats. Goblet cell hyperplasia, mucus hyperproduction and subepithelial collagen deposition were also induced by inhalation of the fungus. The remodelling changes induced by inhalation of the fungus paralleled the changes in BHR in this rat model of asthma.

CONCLUSIONS

Chronic exposure to A. fumigatus aggravated Th2 airway inflammation, promoted airway remodelling and increased BHR in OVA-sensitized and -challenged rats.

A new mechanism regulating the initiation of allergic airway inflammation

BACKGROUND

The earliest immune events induced by allergens are poorly understood, yet are likely essential to understanding how allergic inflammation is established.

OBJECTIVE

We sought to describe the earliest signaling events activated by allergen and determine their significance to allergic inflammation.

METHODS

A fungal-associated allergenic proteinase (FAP) or ovalbumin was administered once intranasally to wild-type mice to determine their ability to induce allergy-associated genes and initiate allergic lung inflammation. Mice deficient in recombinase activating gene 1, C3a, the C3a anaphylatoxin receptor, and MyD88 were challenged similarly to understand the requirement of these molecules and T and B cells for allergic inflammation. Adoptive T-cell transfer experiments were further performed to determine whether signal transducer and activator of transcription 6 (STAT6) was required for cell recruitment and allergic inflammation.

RESULTS

FAP, but not ovalbumin, induced eosinophilic airway inflammation and lung IL-4 production in the absence of adaptive immune cells after the transcriptional induction of allergy-specific airway chemokines. Allergen-mediated chemokine secretion and innate allergic lung inflammation occurred in the absence of STAT6, recombinase activating gene 1, C3a, C3a anaphylatoxin receptor, Toll-like receptor 4, and MyD88 but required intact proteinase activity. Furthermore, FAP induced recruitment of T(H)2 cells and eosinophils to lungs independently of STAT6, which was previously thought to be required for T(H)2 cell homing.

CONCLUSION

FAP induces allergic lung inflammation through a previously unrecognized innate immune signaling mechanism.

CLINICAL IMPLICATIONS

These findings reveal a new paradigm for understanding how allergic inflammation begins and suggest novel possibilities for the prevention and treatment of allergic diseases, such as asthma.