Rationale: There is conflicting information about the development and resolution of airway inflammation and airway hyperresponsiveness (AHR) after repeated airway exposure to allergen in sensitized mice.
Methods: Sensitized BALB/c and C57BL/6 mice were exposed to repeated allergen challenge on 3, 7, or 11 occasions. Airway function in response to inhaled methacholine was monitored; bronchoalveolar lavage fluid inflammatory cells were counted; and goblet cell metaplasia, peribronchial fibrosis, and smooth muscle hypertrophy were quantitated on tissue sections. Bone marrow–derived dendritic cells were generated after differentiation of bone marrow cells in the presence of growth factors.
Results: Sensitization to ovalbumin (OVA) in alum, followed by three airway exposures to OVA, induced lung eosinophilia, goblet cell metaplasia, mild peribronchial fibrosis, and peribronchial smooth muscle hypertrophy; increased levels of interleukin (IL)-4, IL-5, IL-13, granulocyte-macrophage colony–stimulating factor, transforming growth factor-β1, eotaxin-1, RANTES (regulated on activation, normal T-cell expressed and secreted), and OVA-specific IgG1 and IgE; and resulted in AHR. After seven airway challenges, development of AHR was markedly decreased as was the production of IL-4, IL-5, and IL-13. Levels of IL-10 in both strains and the level of IL-12 in BALB/c mice increased. After 11 challenges, airway eosinophilia and peribronchial fibrosis further declined and the cytokine and chemokine profiles continued to change. At this time point, the number of myeloid dendritic cells and expression of CD80 and CD86 in lungs were decreased compared with three challenges. After 11 challenges, intratracheal instillation of bone marrow–derived dendritic cells restored AHR and airway eosinophilia.
Conclusions: These data suggest that repeated allergen exposure leads to progressive decreases in AHR and allergic inflammation, through decreases in myeloid dendritic cell numbers.
airway hyperresponsiveness; chronic asthma; cytokine; dendritic cells; eosinophil
Allergic sensitization to aeroallergens develops in response to mucosal exposure to these allergens. Allergic sensitization may lead to the development of asthma, which is characterized by chronic airway inflammation. The objective of this study is to describe in detail a model of mucosal exposure to cockroach allergens in the absence of an exogenous adjuvant.
Cockroach extract (CE) was administered to mice intranasally (i.n.) daily for 5 days, and 5 days later mice were challenged with CE for 4 consecutive days. A second group received CE i.n. for 3 weeks. Airway hyperresponsiveness (AHR) was assessed 24 h after the last allergen exposure. Allergic airway inflammation was assessed by BAL and lung histology 48 h after the last allergen exposure. Antigen-specific antibodies were assessed in serum. Lungs were excised from mice from measurement of cytokines and chemokines in whole lung lysate.
Mucosal exposure of Balb/c mice to cockroach extract induced airway eosinophilic inflammation, AHR and cockroach-specific IgG1; however, AHR to methacholine was absent in the long term group. Lung histology showed patchy, multicentric damage with inflammatory infiltrates at the airways in both groups. Lungs from mice from the short term group showed increased IL-4, CCL11, CXCL1 and CCL2 protein levels. IL4 and CXCL1 were also increased in the BAL of cockroach-sensitized mice in the short-term protocol.
Mucosal exposure to cockroach extract in the absence of adjuvant induces allergic airway sensitization characterized by AHR, the presence of Th2 cytokines in the lung and eosinophils in the airways.
Chronic asthma is often associated with neutrophilic infiltration in the airways. Neutrophils contain elastase, a potent secretagogue in the airways, nonetheless the role for neutrophil elastase as well as neutrophilic inflammation in allergen-induced airway responses is not well defined. In this study, we have investigated the impact of neutrophil elastase inhibition on the development of allergic airway inflammation and airway hyperresponsiveness (AHR) in previously sensitized and challenged mice.
BALB/c mice were sensitized and challenged (primary) with ovalbumin (OVA). Six weeks later, a single OVA aerosol (secondary challenge) was delivered and airway inflammation and airway responses were monitored 6 and 48 hrs later. An inhibitor of neutrophil elastase was administered prior to secondary challenge.
Mice developed a two-phase airway inflammatory response after secondary allergen challenge, one neutrophilic at 6 hr and the other eosinophilic, at 48 hr. PAR-2 expression in the lung tissues was enhanced following secondary challenge, and that PAR-2 intracellular expression on peribronchial lymph node (PBLN) T cells was also increased following allergen challenge of sensitized mice. Inhibition of neutrophil elastase significantly attenuated AHR, goblet cell metaplasia, and inflammatory cell accumulation in the airways following secondary OVA challenge. Levels of IL-4, IL-5 and IL-13, and eotaxin in BAL fluid 6 hr after secondary allergen challenge were significantly suppressed by the treatment. At 48 hr, treatment with the neutrophil elastase inhibitor significantly reduced the levels of IL-13 and TGF-β1 in the BAL fluid. In parallel, in vitro IL-13 production was significantly inhibited in spleen cells from sensitized mice.
These data indicate that neutrophil elastase plays an important role in the development of allergic airway inflammation and hyperresponsiveness, and would suggest that the neutrophil elastase inhibitor reduced AHR to inhaled methacholine indicating the potential for its use as a modulator of the immune/inflammatory response in both the neutrophil- and eosinophil-dominant phases of the response to secondary allergen challenge.
Neutrophil; Elastase; Airway; Hyperresponsiveness; Asthma
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 (Rn), 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 Rn 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 Rn, 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.
A subset of patients with stable asthma has prominent neutrophilic and reduced eosinophilic inflammation, which is associated with attenuated airways hyper-responsiveness (AHR). Haemophilus influenzae has been isolated from the airways of neutrophilic asthmatics; however, the nature of the association between infection and the development of neutrophilic asthma is not understood. Our aim was to investigate the effects of H. influenzae respiratory infection on the development of hallmark features of asthma in a mouse model of allergic airways disease (AAD). BALB/c mice were intraperitoneally sensitized to ovalbumin (OVA) and intranasally challenged with OVA 12–15 days later to induce AAD. Mice were infected with non-typeable H. influenzae during or 10 days after sensitization, and the effects of infection on the development of key features of AAD were assessed on day 16. T-helper 17 cells were enumerated by fluorescent-activated cell sorting and depleted with anti-IL-17 neutralizing antibody. We show that infection in AAD significantly reduced eosinophilic inflammation, OVA-induced IL-5, IL-13 and IFN-γ responses and AHR; however, infection increased airway neutrophil influx in response to OVA challenge. Augmented neutrophilic inflammation correlated with increased IL-17 responses and IL-17 expressing macrophages and neutrophils (early, innate) and T lymphocytes (late, adaptive) in the lung. Significantly, depletion of IL-17 completely abrogated infection-induced neutrophilic inflammation during AAD. In conclusion, H. influenzae infection synergizes with AAD to induce Th17 immune responses that drive the development of neutrophilic and suppress eosinophilic inflammation during AAD. This results in a phenotype that is similar to neutrophilic asthma. Infection-induced neutrophilic inflammation in AAD is mediated by IL-17 responses.
Approximately 50% of asthmatics have non-eosinophilic inflammation, and 20% of these patients have severe neutrophilic inflammation and increased IL-8 levels. These so-called neutrophilic asthmatics have persistent airway colonization with bacteria, and Haemophilus influenzae is one of the bacteria most commonly isolated. However, how H. influenzae is associated with the pathogenesis of neutrophilic asthma is unknown. In this study we used mouse models to investigate the relationship between H. influenzae infection and allergic airways disease (AAD). We showed that infection promoted the development of hallmark features of neutrophilic asthma. Infection suppressed Th2 cytokines, eosinophilic inflammation, and AHR in AAD, while increasing neutrophilic inflammation and IL-17 responses. Importantly, inhibition of IL-17 during AAD reduced airway neutrophils and neutrophil chemokines, suggesting that infection drives the development of neutrophilic inflammation through an IL-17-mediated mechanism. This provides novel insights into the mechanisms that may underpin infection-induced neutrophilic asthma. These data also suggest that treatments targeting infection may lead to improved management of neutrophilic asthma.
The effect of aging on several pathologic features of allergic-asthma (pulmonary inflammation, eosinophilia, mucus-hypersecretion), and their relationship with airway hyperresponsiveness (AHR) is not well characterized.
To evaluate lung inflammation, mucus-metaplasia and AHR in relationship to age in murine models of allergic-asthma comparing young and older mice.
Young (6-week) and older (6-, 12- 18-month) BALB/c mice were sensitized and challenged with ovalbumin (OVA). AHR and bronchoalveolar fluid (BALF) total inflammatory cell count and differential were measured. To evaluate mucus-metaplasia, quantitative PCR for the major airway mucin-associated gene, MUC-5AC, from lung tissue was measured, and lung tissue sections stained with periodic acid-Schiff (PAS) for goblet-cell enumeration. Lung tissue cytokine gene expression was determined by qPCR, and systemic cytokine protein levels by ELISA from spleen-cell cultures. Antigen-specific serum IgE was determined by ELISA.
AHR developed in both aged and young OVA-sensitized/challenged mice (OVA-mice), and was more significantly increased in young OVA-mice than in aged OVA-mice. However, BALF eosinophil numbers were significantly higher, and lung histology showed greater inflammation in aged OVA-mice than in young OVA-mice. MUC-5AC expression and numbers of PAS+ staining bronchial epithelial cells were significantly increased in the aged OVA-mice. All aged OVA-mice had increased IL-5 and IFN-γ mRNA expression in the lung and IL-5 and IFN-γ protein levels from spleen cell cultures compared to young OVA-mice. OVA-IgE was elevated to a greater extent in aged OVA-mice.
Although pulmonary inflammation and mucus-metaplasia after antigen sensitization/challenge occurred to a greater degree in older mice, the increase in AHR was significantly less compared with younger OVA-mice. Antigen treatment produced a unique cytokine profile in older mice (elevated IFN-γ and IL-5) compared with young mice (elevated IL-4 and IL-13). Thus, the airway response to inflammation is lessened in aging animals, and may represent age-associated events leading to different phenotypes in response to antigen provocation.
Aging; murine; asthma; airway hyperresponsiveness; eosinophil; inflammation
In this investigation we have used a mouse model containing certain phenotypic characteristics consistent with asthma and IL-4- and CD40-deficient mice to establish the role of this cytokine and allergen-specific immunoglobulins in the initiation of airways hyperreactivity and morphological changes to the airways in responses to aeroallergen challenge. Sensitization and aerosol challenge of mice with ovalbumin resulted in a severe airways inflammatory response which directly correlated with the induction of extensive airways damage and airways hyperreactivity to beta-methacholine. Inflammatory infiltrates were primarily characterized by the presence of CD4+ T cells and eosinophils. In IL-4-deficient mice, the recruitment of airways eosinophils was impaired, but not abolished in response to aeroallergen. Moreover, the characteristic airways damage and hyperreactivity normally resulting from allergen inhalation were not attenuated. Induction of these structural and functional changes to the airways occurred in the absence of ovalbumin-specific IgE and IgG1, but IgG2a and IgG3 were detected in the sera of IL-4-deficient mice. CD4+ T cells isolated from both wild-type and IL-4-deficient mice given ovalbumin produced significant levels of IL-5 after in vitro stimulation. Treatment of IL-4-deficient mice with anti-IL-5 mAb before aeroallergen challenge abolished blood and airways eosinophilia, lung damage, and airways hyperreactivity. These results indicate that IL-4 is not essential for the development of IL-5-producing CD4+ T cells or for the induction of eosinophilic inflammation and airways damage and hyperreactivity. In response to sensitization and aerosol challenge, CD40-deficient mice did not produce ovalbumin-specific IgE, IgG isotypes, or IgA, and airways inflammation and hyperreactivity were not attenuated. Our results suggest that allergic airways disease can occur via pathways which operate independently of IL-4 and allergen-specific immunoglobulins. Activation of these pathways is intimately associated with IL-5 and eosinophilic inflammation. Such pathways may play a substantive role in the etiology of asthma.
Airway hyperresponsiveness (AHR) is one of the most prominent features of asthma, however, precise mechanisms for its induction have not been fully elucidated. We previously reported that systemic antigen sensitization alone directly induces AHR before development of eosinophilic airway inflammation in a mouse model of allergic airway inflammation, which suggests a critical role of antigen-specific systemic immune response itself in the induction of AHR. In the present study, we examined this possibility by cell transfer experiment, and then analyzed which cell source was essential for this process.
BALB/c mice were immunized with ovalbumin (OVA) twice. Spleen cells were obtained from the mice and were transferred in naive mice. Four days later, AHR was assessed. We carried out bronchoalveolar lavage (BAL) to analyze inflammation and cytokine production in the lung. Fluorescence and immunohistochemical studies were performed to identify T cells recruiting and proliferating in the lung or in the gut of the recipient. To determine the essential phenotype, spleen cells were column purified by antibody-coated microbeads with negative or positive selection, and transferred. Then, AHR was assessed.
Transfer of spleen cells obtained from OVA-sensitized mice induced a moderate, but significant, AHR without airway antigen challenge in naive mice without airway eosinophilia. Immunization with T helper (Th) 1 elicited antigen (OVA with complete Freund's adjuvant) did not induce the AHR. Transferred cells distributed among organs, and the cells proliferated in an antigen free setting for at least three days in the lung. This transfer-induced AHR persisted for one week. Interleukin-4 and 5 in the BAL fluid increased in the transferred mice. Immunoglobulin E was not involved in this transfer-induced AHR. Transfer of in vitro polarized CD4+ Th2 cells, but not Th1 cells, induced AHR. We finally clarified that CD4+CD62Llow memory/effector T cells recruited in the lung and proliferated, thus induced AHR.
These results suggest that antigen-sensitized memory/effector Th2 cells themselves play an important role for induction of basal AHR in an antigen free, eosinophil-independent setting. Therefore, regulation of CD4+ T cell-mediated immune response itself could be a critical therapeutic target for allergic asthma.
Rationale: In humans, immune responses to inhaled aeroallergens develop in the lung and draining lymph nodes. Many animal models of asthma bypass this route and instead use intraperitoneal injections of allergen using aluminum hydroxide as an adjuvant.
Objectives: We investigated whether allergic sensitization through the airway elicits immune responses qualitatively different than those arising in the peritoneum.
Methods: Mice were sensitized to allergen through the airway using low-dose LPS as an adjuvant, or through the peritoneum using aluminum hydroxide as an adjuvant. After a single allergen challenge, ELISA and flow cytometry were used to measure cytokines and leukocyte subsets. Invasive measurements of airway resistance were used to measure allergen-induced airway hyperreactivity (AHR).
Measurements and Main Results: Sensitization through the peritoneum primed strong Th2 responses and eosinophilia, but not AHR, after a single allergen challenge. By contrast, allergic sensitization through the airway primed only modest Th2 responses, but strong Th17 responses. Th17 cells homed to the lung and released IL-17 into the airway on subsequent encounter with inhaled allergen. As a result, these mice developed IL-17–dependent airway neutrophilia and AHR. This AHR was neutrophil-dependent because it was abrogated in CXCR2-deficient mice and also in wild-type mice receiving a neutrophil-depleting antibody. Individually, neither IL-17 nor ongoing Th2 responses were sufficient to confer AHR, but together they acted synergistically to promote neutrophil recruitment, eosinophil recruitment and AHR.
Conclusions: Allergic sensitization through the airway primes modest Th2 responses but strong Th17 responses that promote airway neutrophilia and acute AHR. These findings support a causal role for neutrophils in severe asthma.
asthma; lung; immunity
Chronic allergic asthma is the result of a Th2- biased immune status. Current asthma therapies control symptoms in some patients, but a long lasting therapy has not been established. ASHMI™, a Chinese herbal formula improved symptoms and lung function, and reduced Th2 responses in a controlled trial of patients with persistent moderate to severe asthma.
We evaluated the persistence of ASHMI™ beneficial effects following therapy in a murine model of persistent asthma and the immunological mechanisms underlying such effects. BALB/c mice sensitized intraperitoneally with ovalbumin (OVA) received 3 weekly intratracheal OVA challenges to induce airway hyperreactivity (AHR) and inflammation (OVA mice). Additional OVA mice were treated with ASHMI™ (OVA/ASHMI™) or water (OVA/Sham) for 4 weeks, and then challenged immediately and eight weeks post-therapy. In other experiments OVA mice received ASHMI™ treatment with concomitant neutralization of IFN-γ or TGF-β. Effects on airway responses, cytokine and OVA-specific IgE levels were determined 8 weeks post-therapy.
Prior to treatment, OVA mice exhibited AHR and pulmonary eosinophilic inflammation following OVA challenge, which was almost completely resolved immediately after completing treatment with ASHMI™ and did not re-occur following OVA re-challenge up to 8 wks post-therapy. Reduced allergen-specific IgE and Th2 cytokine levels, and increased IFN-γ levels also persisted at least 8 wks post-therapy. ASHMI™ effects were eliminated by neutralization of IFN-γ, but not TGF-β, during therapy.
ASHMI™ induced long-lasting post-therapy tolerance to antigen-induced inflammation and AHR. IFN-γ is a critical factor in ASHMI™ effects.
Allergic asthma; Mice; Traditional Chinese Medicine; Th-2 cytokines; Interferon-γ; IgE
Asthma leads to structural changes in the airways, including the modification of extracellular matrix proteins such as tenascin-C. The role of tenascin-C is unclear, but it might act as an early initiator of airway wall remodelling, as its expression is increased in the mouse and human airways during allergic inflammation. In this study, we examined whether Th1 or Th2 cells are important regulators of tenascin-C in experimental allergic asthma utilizing mice with impaired Th1 (STAT4-/-) or Th2 (STAT6-/-) immunity.
Balb/c wildtype (WT), STAT4-/- and STAT6-/- mice were sensitized with intraperitoneally injected ovalbumin (OVA) followed by OVA or PBS airway challenge. Airway hyperreactivity (AHR) was measured and samples were collected. Real time PCR and immunohistochemistry were used to study cytokines and differences in the expression of tenascin-C. Tenascin-C expression was measured in human fibroblasts after treatment with TNF-α and IFN-γ in vitro.
OVA-challenged WT mice showed allergic inflammation and AHR in the airways along with increased expression of TNF-α, IFN-γ, IL-4 and tenascin-C in the lungs. OVA-challenged STAT4-/- mice exhibited elevated AHR and pulmonary eosinophilia. The mRNA expression of TNF-α and IFN-γ was low, but the expression of IL-4 was significantly elevated in these mice. OVA-challenged STAT6-/- mice had neither AHR nor pulmonary eosinophilia, but had increased expression of mRNA for TNF-α, IFN-γ and IL-4. The expression of tenascin-C in the lungs of OVA-challenged STAT4-/- mice was weaker than in those of OVA-challenged WT and STAT6-/- mice suggesting that TNF-α and IFN-γ may regulate tenascin-C expression in vivo. The stimulation of human fibroblasts with TNF-α and IFN-γ induced the expression of tenascin-C confirming our in vivo findings.
Expression of tenascin-C is significantly attenuated in the airways of STAT4-/- mice, which may be due to the impaired secretion of TNF-α and IFN-γ in these mice.
Asthmatic responses involve a systemic component where activation of the bone marrow leads to mobilization and lung-homing of progenitor cells. This traffic may be driven by stromal cell derived factor-1 (SDF-1), a potent progenitor chemoattractant. We have previously shown that airway angiogenesis, an early remodeling event, can be inhibited by preventing the migration of endothelial progenitor cells (EPC) to the lungs. Given intranasally, AMD3100, a CXCR4 antagonist that inhibits SDF-1 mediated effects, attenuated allergen-induced lung-homing of EPC, vascularization of pulmonary tissue, airway eosinophilia and development of airway hyperresponsiveness. Since SDF-1 is also an eosinophil chemoattractant, we investigated, using a transgenic eosinophil deficient mouse strain (PHIL) whether EPC lung accumulation and lung vascularization in allergic airway responses is dependent on eosinophilic inflammation.
Wild-type (WT) BALB/c and eosinophil deficient (PHIL) mice were sensitized to house dust mite (HDM) using a chronic exposure protocol and treated with AMD3100 to modulate SDF-1 stimulated progenitor traffic. Following HDM challenge, lung-extracted EPCs were enumerated along with airway inflammation, microvessel density (MVD) and airway methacholine responsiveness (AHR).
Following Ag sensitization, both WT and PHIL mice exhibited HDM-induced increase in airway inflammation, EPC lung-accumulation, lung angiogenesis and AHR. Treatment with AMD3100 significantly attenuated outcome measures in both groups of mice. Significantly lower levels of EPC and a trend for lower vascularization were detected in PHIL versus WT mice.
This study shows that while allergen-induced lung-homing of endothelial progenitor cells, increased tissue vascularization and development lung dysfunction can occur in the absence of eosinophils, the presence of these cells worsens the pathology of the allergic response.
Dendritic cells (DCs) are considered to be the most efficient antigen-presenting cells. Intratracheal administration of allergen-pulsed bone marrow–derived dendritic cells (BMDCs) before allergen challenge induces airway hyperresponsiveness (AHR) and inflammation. Ovalbumin (OVA)-pulsed BMDCs from wild-type (WT) mice were transferred into naive WT, CD4−/−, CD8−/−, or IL-13−/− mice. Two days (short protocol) or 10 days (long protocol) after BMDC transfer, mice were challenged with 1% OVA for 3 days and assayed 2 days later. Transfer of OVA-primed BMDCs into BALB/c or C57BL/6 mice elicited AHR in both protocols. Airway eosinophilia, Th2 cytokines, or goblet cell metaplasia were increased in the long but not short protocol. Lung T cells from both protocols produced Th2 cytokines in response to OVA in vitro. Carboxyfluorescein diacetate succinimidylester–labeled BMDCs were observed in bronchoalveolar lavage (BAL) fluid and lung parenchyma at early time points, and were detected in draining lymph nodes 48 hours after transfer. CD8−/− mice developed AHR comparable to WT mice in the short protocol, but decreased levels of AHR, airway eosinophilia, Th2 cytokines in BAL fluid, and goblet cell metaplasia compared with WT mice in the long protocol. CD4−/− or IL-13−/− mice did not develop AHR or airway inflammation in either protocol. These data suggest that allergen-pulsed BMDCs initiate development of AHR that is dependent initially on CD4+ T cells, and at later time periods on CD8+ T cells and IL-13. Thus, the timing of allergen challenge after transfer of allergen-pulsed BMDC affects the development of AHR and airway inflammation.
dendritic cells; CD8+ T cells; airway hyperresponsiveness
Allergic asthma is characterized by airway hyperresponsiveness (AHR) and allergic inflammation of the airways, driven by allergen-specific Th2 cells. The asthma phenotypes and especially AHR are sensitive to the presence and activity of regulatory T (Treg) cells in the lung. Glucocorticoid-induced tumor necrosis factor receptor (GITR) is known to have a co-stimulatory function on effector CD4+ T cells, rendering these cells insensitive to Treg suppression. However, the effects of GITR signaling on polarized Th1 and Th2 cell effector functions are not well-established. We sought to evaluate the effect of GITR signaling on fully differentiated Th1 and Th2 cells and to determine the effects of GITR activation at the time of allergen provocation on AHR and airway inflammation in a Th2-driven mouse model of asthma.
CD4+CD25- cells were polarized in vitro into Th1 and Th2 effector cells, and re-stimulated in the presence of GITR agonistic antibodies to assess the effect on IFNγ and IL-4 production. To evaluate the effects of GITR stimulation on AHR and allergic inflammation in a mouse asthma model, BALB/c mice were sensitized to OVA followed by airway challenges in the presence or absence of GITR agonist antibodies.
GITR engagement potentiated cytokine release from CD3/CD28-stimulated Th2 but not Th1 cells in vitro. In the mouse asthma model, GITR triggering at the time of challenge induced enhanced airway hyperresponsiveness, serum IgE and ex vivo Th2 cytokine release, but did not increase BAL eosinophilia.
GITR exerts a differential effect on cytokine release of fully differentiated Th1 and Th2 cells in vitro, potentiating Th2 but not Th1 cytokine production. This effect on Th2 effector functions was also observed in vivo in our mouse model of asthma, resulting in enhanced AHR, serum IgE responses and Th2 cytokine production. This is the first report showing the effects of GITR activation on cytokine production by polarized primary Th1 and Th2 populations and the relevance of this pathway for AHR in mouse models for asthma. Our data provides crucial information on the mode of action of the GITR signaling, a pathway which is currently being considered for therapeutic intervention.
NF-κB activation within the epithelium has been implicated in the pathogenesis of asthma, yet the exact role of epithelial NF-κB in allergen-induced inflammation and airway remodeling remains unclear. In the present study, we utilized an intranasal House Dust Mite (HDM) extract exposure regimen time course in BALB/c mice to evaluate inflammation, NF-κB activation, airway hyperresponsiveness (AHR), and airway remodeling. We utilized CC10-IκBαSR transgenic mice to evaluate the functional importance of epithelial NF-κB in response to HDM. After a single exposure of HDM, mRNA expression of pro-inflammatory mediators was significantly elevated in lung tissue of WT mice, in association with increases in nuclear RelA and RelB, components of the classical and alternative NF-κB pathway, respectively, in the bronchiolar epithelium. In contrast, CC10-IκBαSR mice displayed marked decreases in nuclear RelA and RelB and mRNA expression of pro-inflammatory mediators compared to WT mice. After 15 challenges with HDM, WT mice exhibited increases in inflammation, airway hyperresponsiveness, mucus metaplasia and peri-bronchiolar fibrosis. CC10-IκBαSR transgenic mice displayed marked decreases in neutrophilic infiltration, tissue damping, and elastance parameters, in association will less peri-bronchiolar fibrosis and decreases in nuclear RelB in lung tissue. However, central airway resistance and mucus metaplasia remained elevated in CC10-IκBαSR transgenic mice, in association with continued presence of lymphocytes, and partial decreases in eosinophils and IL-13. The current study demonstrates that following airway exposure with an asthma-relevant allergen, activation of classical and alternative NF-κB pathways occur within the airway epithelium and may coordinately contribute to allergic inflammation, AHR and fibrotic airway remodeling.
Airway hyperreactivity (AHR), lung inflammation, and atopy are clinical signs of allergic asthma. Gestational exposure to cigarette smoke (CS) markedly increases the risk for childhood allergic asthma. Muscarinic receptors regulate airway smooth muscle tone, and asthmatics exhibit increased AHR to muscarinic agonists. We have previously reported that in a murine model of bronchopulmonary aspergillosis maternal exposure to mainstream CS increases AHR after acute intratracheal administration of Aspergillus fumigatus extract (Af). However, the mechanism by which gestational CS induces allergic asthma is unclear. We now show for the first time that, compared to controls, mice exposed prenatally to secondhand CS exhibit increased lung inflammation (predominant infiltration by eosinophils and polymorphs), atopy, and airway resistance, and produce proinflammatory cytokines (IL-4, IL-5, IL-6, and IL-13, but not IL-2 or IFN-γ). These changes, which occur only after an allergen (Af) treatment, are correlated with marked upregulated lung expression of M1, M2, and M3 muscarinic receptors and phosphodiesterase-4D5 (PDE4D5) isozyme. Interestingly, the PDE4-selective inhibitor rolipram attenuates the increase in AHR, muscarinic receptors, and PDE4D5, but fails to downregulate lung inflammation, Th2 cytokines, or serum IgE levels. Thus, the fetus is extraordinarily sensitive to CS, inducing allergic asthma after postnatal exposure to allergens. While the increased AHR might reflect increased PDE4D5 and muscarinic receptor expression, the mechanisms underlying atopy and lung inflammation are unrelated to the PDE4 activity. Thus, PDE4 inhibitors might ease AHR, but are unlikely to attenuate lung inflammation and atopy associated with childhood allergic asthma.
Early-life respiratory viral infections, notably with respiratory syncytial virus (RSV), increase the risk of subsequent development of childhood asthma. The purpose of this study was to assess whether early-life infection with a species-specific model of RSV and subsequent allergen exposure predisposed to the development of features of asthma.
We employed a unique combination of animal models in which BALB/c mice were neonatally infected with pneumonia virus of mice (PVM, which replicates severe RSV disease in human infants) and following recovery, were intranasally sensitised with ovalbumin. Animals received low-level challenge with aerosolised antigen for 4 weeks to elicit changes of chronic asthma, followed by a single moderate-level challenge to induce an exacerbation of inflammation. We then assessed airway inflammation, epithelial changes characteristic of remodelling, airway hyperresponsiveness (AHR) and host immunological responses.
Allergic airway inflammation, including recruitment of eosinophils, was prominent only in animals that had recovered from neonatal infection with PVM and then been sensitised and chronically challenged with antigen. Furthermore, only these mice exhibited an augmented Th2-biased immune response, including elevated serum levels of anti-ovalbumin IgE and IgG1 as well as increased relative expression of Th2-associated cytokines IL-4, IL-5 and IL-13. By comparison, development of AHR and mucous cell change were associated with recovery from PVM infection, regardless of subsequent allergen challenge. Increased expression of IL-25, which could contribute to induction of a Th2 response, was demonstrable in the lung following PVM infection. Signalling via the IL-4 receptor α chain was crucial to the development of allergic inflammation, mucous cell change and AHR, because all of these were absent in receptor-deficient mice. In contrast, changes of remodelling were evident in mice that received chronic allergen challenge, regardless of neonatal PVM infection, and were not dependent on signalling via the IL-4 receptor.
In this mouse model, interaction between early-life viral infection and allergen sensitisation/challenge is essential for development of the characteristic features of childhood asthma, including allergic inflammation and a Th2-biased immune response.
As passive environmental tobacco smoke (ETS) exposure in nonsmokers can increase both asthma symptoms and the frequency of asthma exacerbations, we utilized a mouse model, in which ovalbumin (OVA) + ETS induce significantly increased levels of eosinophilic airway inflammation and remodeling compared to either stimulus alone, to determine whether a Toll-like receptor-9 (TLR-9) agonist could reduce levels of airway inflammation, airway remodeling and airway hyperreactivity (AHR).
Mice treated with or without a TLR-9 agonist were sensitized to OVA and challenged with OVA + ETS for 1 month. AHR to methacholine was assessed in intubated and ventilated mice. Lung Th2 cytokines and TGF-β1 were measured by ELISA. Lungs were processed for histology and immunohistology to quantify eosinophils, mucus, peribronchial fibrosis and smooth muscle changes using image analysis.
Administration of a TLR-9 agonist to mice coexposed to chronic ETS and chronic OVA allergen significantly reduced levels of eosinophilic airway inflammation, mucus production, peribronchial fibrosis, the thickness of the peribronchial smooth muscle layer, and AHR. The reduced airway remodeling in mice treated with the TLR-9 agonist was associated with significantly reduced numbers of peribronchial MBP+ and peribronchial TGF-β1+ cells, and with significantly reduced levels of lung Th2 cytokines [interleukin-5 and interleukin-13] and TGF-β1.
These studies demonstrate that TLR-9-based therapies inhibit airway inflammation, remodeling and AHR in mice coexposed to ETS and allergen who exhibit enhanced airway inflammation and remodeling.
Toll-like receptor-9; Airway hyperreactivity; Airway inflammation; Airway remodeling; Eosinophils
Recent evidence suggests that IL-17 contributes to airway hyperresponsiveness (AHR); however, the mechanisms that suppress the production of this cytokine remain poorly defined.
We sought to understand the cellular and molecular basis for suppression of established, IL-17-dependent allergic airways disease.
Mice were sensitized by airway instillations of ovalbumin (OVA) together with low levels of lipopolysaccharide. Leukocyte recruitment to the lung and AHR were assessed following daily challenges with aerosolized OVA. Flow cytometry and gene targeted mice were used to identify naturally-arising subsets of regulatory T cells (Tregs) and their cytokines required for the suppression of established allergic airway disease.
Allergic sensitization through the airway primed both effector and regulatory responses. Effector responses were initially dominant and led to airway inflammation and IL-17-dependent AHR. However, after multiple daily allergen challenges, IL-17 production and AHR declined, even though pulmonary levels of Th17 cells remained high. This loss of AHR was reversible and required the expansion of a Treg subset expressing both Foxp3 and inducible co-stimulator (ICOS). These Tregs also expressed the regulatory cytokines, IL-10, TGF-beta and IL-35. Whereas IL-10 and TGF-beta were dispensable for suppression of airway hyperresponsiveness, IL-35 was required. Analysis of human ICOS+ Tregs revealed that they also selectively expressed IL-35.
IL-35 production by ICOS+ Tregs can suppress IL-17 production and thereby reverse established, IL-17-dependent AHR in mice. The production of IL-35 by human ICOS+ Tregs suggests that targeting this pathway might be of therapeutic value for treating allergic asthma in humans.
Asthma; airway hyperresponsiveness; AHR; IL-17; Th17; Th2; IL-35; ICOS; ovalbumin
The mammalian target of rapamycin (mTOR) signaling pathway integrates environmental cues, promotes cell growth / differentiation and regulates immune responses. While inhibition of mTOR with rapamycin has potent immunosuppressive activity, mixed effects have been reported in ovalbumin-induced models of allergic asthma. We investigated the impact of two different rapamycin treatment protocols on the major characteristics of allergic asthma induced by the clinically relevant allergen, house dust mite (HDM). In protocol 1, Balb/c mice were exposed to 10 intranasal HDM doses over a period of 24 days and treated with rapamycin simultaneously during the sensitization/exposure period. In protocol 2, rapamycin was administered after the mice had been sensitized to HDM (I.P. injection) and prior to initiation of two intranasal HDM challenges over 4 days. Airway hyperreactivity (AHR), IgE, inflammatory cells, cytokines, leukotrienes, goblet cells, and activated T cells were assessed. In protocol 1, rapamycin blocked HDM-induced increases in AHR, inflammatory cell counts, IgE, and attenuated goblet cell metaplasia. In protocol 2, rapamycin blocked increases in AHR, IgE, T cell activation, and reduced goblet cell metaplasia, but had no effect on inflammatory cell counts. Increases in IL-13 and leukotrienes were also blocked by rapamycin, although increases in IL-4 were unaffected. These data demonstrate that rapamycin can inhibit cardinal features of allergic asthma including increases in AHR, IgE, and goblet cells most likely due to its ability to reduce the production of two key mediators of asthma, IL-13 and leukotrienes. These findings highlight the importance of the mTOR pathway in allergic airway disease.
Th2 immune responses are linked primarily to mild and moderate asthma, while Th17 cells, Interleukin-17A (IL-17) and neutrophilia have been implicated in more severe forms of disease. How Th2-dependent allergic reactions are influenced by Th17 and IL-17-γδ T cells is poorly understood. In murine models, under some conditions, IL-17 promotes Th2-biased airway inflammatory responses. However, IL-17-γδ T cells have been implicated in the inhibition and resolution of allergic airway inflammation and hyperresponsiveness (AHR).
We compared airway responses in Balb/c mice sensitized to OVA with (and without) a Th2-skewing aluminum-based adjuvant and the IL-17 skewing, complete Freund’s adjuvant (CFA). AHR was measured invasively by flexiVent, while serum OVA-IgE was quantified by an enzyme immunoassay. Airway inflammatory and cytokine profiles, and cellular sources of IL-17 were assessed from bronchoalveolar lavage and/or lungs. The role of γδ T cells in these responses was addressed in OVA/CFA sensitized mice using a γδ T cell antibody.
Following OVA challenge, all mice exhibited mixed eosinophilic/neutrophilic airway inflammatory profiles and elevated serum OVA-IgE. Whereas OVA/alum sensitized mice had moderate inflammation and AHR, OVA/CFA sensitized mice had significantly greater inflammation but lacked AHR. This correlated with a shift in IL-17 production from CD4+ to γδ T cells. Additionally, OVA/CFA sensitized mice, given a γδ TCR stimulatory antibody, showed increased frequencies of IL-17-γδ T cells and diminished airway reactivity and eosinophilia.
Thus, the conditions of antigen sensitization influence the profile of cells that produce IL-17, the balance of which may then modulate the airway inflammatory responses, including AHR. The possibility for IL-17-γδ T cells to reduce AHR and robust eosinophilic inflammation provides evidence that therapeutic approaches focused on stimulating and increasing airway IL-17-γδ T cells may be an effective alternative in treating steroid resistant, severe asthma.
Electronic supplementary material
The online version of this article (doi:10.1186/s12931-014-0090-5) contains supplementary material, which is available to authorized users.
Asthma; Interleukin-17; γδ T cell; Adjuvant; Complete Freund’s adjuvant
Asthma frequently commences in early life during airway and immune development and exposure to new environmental challenges. Endobronchial biopsies from children with asthma are abnormal, and lung function is maximally reduced by 6 years of age. As longitudinal biopsy studies are unethical in children, the relationship between development of pathology and reduced lung function is unknown. We aimed to establish a novel neonatal mouse model of allergic airways disease to investigate the developmental sequence of the pathophysiologic features of asthma. Neonatal Balb/c mice were challenged three times weekly from Day 3 of life using intranasal house dust mite (HDM) or saline for up to 12 weeks. Weekly assessments of airway inflammation and remodeling were made. Airway hyperresponsiveness (AHR) to methacholine was assessed from Week 2 onward. Total and eosinophilic inflammation was significantly increased in the lungs of HDM-exposed neonates from Week 2 onwards, and a peak was seen at 3 weeks. Goblet cells and peribronchiolar reticulin deposition were significantly increased in HDM-exposed neonates from Week 3, and peribronchiolar collagen was significantly greater from Week 4. HDM-exposed neonates had increased AHR from Week 2 onward. Although inflammation and AHR had subsided after 4 weeks without allergen challenge, the increased reticulin and collagen deposition persisted in HDM-exposed mice. Neonatal mice exposed to intranasal HDM developed eosinophilic inflammation, airway remodeling, and AHR as reported in pediatric asthma. Importantly, all abnormalities developed in parallel, not sequentially, between 2 and 3 weeks of age.
pediatric; remodeling; asthma pathophysiology; mouse model; allergic airways disease
IL-4 and IL-13 are closely related cytokines that are produced by Th2 cells. However, IL-4 and IL-13 have different effects on the development of asthma phenotypes. Here, we evaluated downstream molecular mechanisms involved in the development of Th2 type asthma phenotypes. A murine model of Th2 asthma was used that involved intraperitoneal sensitization with an allergen (ovalbumin) plus alum and then challenge with ovalbumin alone. Asthma phenotypes, including airway-hyperresponsiveness (AHR), lung inflammation, and immunologic parameters were evaluated after allergen challenge in mice deficient in candidate genes. The present study showed that methacholine AHR and lung inflammation developed in allergen-challenged IL-4-deficient mice but not in allergen-challenged IL-13-deficient mice. In addition, the production of OVA-specific IgG2a and IFN-γ-inducible protein (IP)-10 was also impaired in the absence of IL-13, but not of IL-4. Lung-targeted IFN-γ over-expression in the airways enhanced methacholine AHR and non-eosinophilic inflammation; in addition, these asthma phenotypes were impaired in allergen-challenged IFN-γ-deficient mice. Moreover, AHR, non-eosinophilic inflammation, and IFN-γ expression were impaired in allergen-challenged IL-12Rβ2- and STAT4-deficient mice; however, AHR and non-eosinophilic inflammation were not impaired in allergen-challenged IL-4Rα-deficient mice, and these phenomena were accompanied by the enhanced expression of IL-12 and IFN-γ. The present data suggest that IL-13-mediated asthma phenotypes, such as AHR and non-eosinophilic inflammation, in the Th2 type asthma are dependent on the IL-12-STAT4-IFN-γ axis, and that these asthma phenotypes are independent of IL-4Ralpha-mediated signaling.
asthma; interferon-γ; interleukin-12; interleukin-13; respiratory hypersensitivity; Th2 cells
Existing asthma models develop tolerance when chronically exposed to the same allergen.
To establish a chronic model that sustains features of asthma long after discontinuation of allergen exposure.
We immunized and exposed mice to a combination of single, double or triple allergens (dust-mite, ragweed, and Aspergillus) intranasally for 8 weeks. Airway hyperreactivity and morphological features of asthma were studied 3 weeks after the allergen exposure. Signaling effects of the allergens were studied on dendritic cells.
Sensitization and repeated exposure to a single allergen induced tolerance. Sensitization to double, and especially triple allergens broke through tolerance and established AHR, eosinophilic inflammation, mast cell and smooth muscle hyperplasia, mucus production and airway remodeling that persisted at least 3 weeks after allergen exposure. Mucosal exposure to triple allergens in the absence of an adjuvant was sufficient to induce chronic airway inflammation. Anti-IL5 and -IL13 antibodies inhibited inflammation and AHR in the acute asthma model but not in the chronic triple allergen model. Multiple allergens produce a synergy in p38 MAPK signaling and maturation of dendritic cells, which provides a heightened T cell co-stimulation at a level that cannot be achieved with a single allergen.
Sensitivity to multiple allergens leads to chronic asthma in mice. Multiple allergens synergize in dendritic cell signaling and T cell stimulation that allows escape from the single allergen-associated tolerance development.
We have developed a model of chronic asthma that allows for the study and treatment of long-lasting features of asthma obviating the need for acute de novo allergen challenges.
chronic asthma; mouse; inflammation; airway hyperreactivity; tolerance; dendritic cells
Deficient suppression of T cell responses to allergen by CD4+CD25+ regulatory T cells has been observed in patients with allergic disease. Our current experiments used a mouse model of airway inflammation to examine the suppressive activity of allergen-specific CD4+CD25+ T cells in vivo. Transfer of ovalbumin (OVA) peptide-specific CD4+CD25+ T cells to OVA-sensitized mice reduced airway hyperreactivity (AHR), recruitment of eosinophils, and T helper type 2 (Th2) cytokine expression in the lung after allergen challenge. This suppression was dependent on interleukin (IL) 10 because increased lung expression of IL-10 was detected after transfer of CD4+CD25+ T cells, and regulation was reversed by anti-IL-10R antibody. However, suppression of AHR, airway inflammation, and increased expression of IL-10 were still observed when CD4+CD25+ T cells from IL-10 gene-deficient mice were transferred. Intracellular cytokine staining confirmed that transfer of CD4+CD25+ T cells induced IL-10 expression in recipient CD4+ T cells, but no increase in IL-10 expression was detected in airway macrophages, dendritic cells, or B cells. These data suggest that CD4+CD25+ T cells can suppress the Th2 cell-driven response to allergen in vivo by an IL-10-dependent mechanism but that IL-10 production by the regulatory T cells themselves is not required for such suppression.