Allergen-induced Airway Hyperresponsiveness Research Articles

Eosinophil activities modulate the immune/inflammatory character of allergic respiratory responses in mice

The importance and specific role(s) of eosinophils in modulating the immune/inflammatory phenotype of allergic pulmonary disease remain to be defined. Established animal models assessing the role(s) of eosinophils as contributors and/or causative agents of disease have relied on congenitally deficient mice where the developmental consequences of eosinophil depletion are unknown. We developed a novel conditional eosinophil-deficient strain of mice (iPHIL) through a gene knock-in strategy inserting the human diphtheria toxin (DT) receptor (DTR) into the endogenous eosinophil peroxidase genomic locus. Expression of DTR rendered resistant mouse eosinophil progenitors sensitive to DT without affecting any other cell types. The presence of eosinophils was shown to be unnecessary during the sensitization phase of either ovalbumin (OVA) or house dust mite (HDM) acute asthma models. However, eosinophil ablation during airway challenge led to a predominantly neutrophilic phenotype (>15% neutrophils) accompanied by allergen-induced histopathologies and airway hyper-responsiveness in response to methacholine indistinguishable from eosinophilic wild-type mice. Moreover, the iPHIL neutrophilic airway phenotype was shown to be a steroid-resistant allergic respiratory variant that was reversible upon the restoration of peripheral eosinophils. Eosinophil contributions to allergic immune/inflammatory responses appear to be limited to the airway challenge and not to the sensitization phase of allergen provocation models. The reversible steroid-resistant character of the iPHIL neutrophilic airway variant suggests underappreciated mechanisms by which eosinophils shape the character of allergic respiratory responses.

Astragalus Extract Attenuates Allergic Airway Inflammation and Inhibits Nuclear Factor κB Expression in Asthmatic Mice

BackgroundAstragalus membranaceus from traditional Chinese herbal medicines previously showed that it possesses a strong anti-inflammatory activity. The purpose of this study was to elucidate the effect of astragalus on allergen-induced airway inflammation and airway hyperresponsiveness and investigate its possible molecular mechanisms. MethodsFemale BALB/c mice sensitized and challenged with ovalbumin (OVA) developed airway inflammation. Bronchoalveolar lavage fluid was assessed for total and differential cell counts and cytokine and chemokine levels. In vivo airway responsiveness to increasing concentrations of methacholine was measured 24 hours after the last OVA challenge using whole-body plethysmography. The expression of inhibitory κB-α and p65 in lung tissues was measured by Western blotting. ResultsAstragalus extract attenuated lung inflammation, goblet cell hyperplasia and airway hyperresponsiveness in OVA-induced asthma and decreased eosinophils and lymphocytes in bronchoalveolar lavage fluid. In addition, astragalus extract treatment reduced expression of the key initiators of allergic Th2-associated cytokines (interleukin 4, interleukin 5) (P<0.05). Furthermore, astragalus extract could inhibit nuclear factor κB (NF-κB) expression and suppress NF-κB translocation from the cytoplasm to the nucleus in lung tissue samples. ConclusionsTaken together, our current study demonstrated a potential therapeutic value of astragalus extract in the treatment of asthma and it may act by inhibiting the expression of the NF-κB pathway.

Fish Oil Has Beneficial Effects on Allergen-Induced Airway Inflammation and Hyperreactivity in Mice

BackgroundFish oil (FO) is rich in n-3 polyunsaturated fatty acids (PUFA), which have been suggested to be anti-inflammatory and are associated with improvement of several inflammatory diseases. In this study, we investigated the influence of FO on allergen-induced lung inflammation and airway hyperreactivity in mice.MethodsMale A/J mice were fed either a standard-chow (SC) or a FO diet (FO) for 8 weeks. After 4 weeks, each group was further randomized for ovalbumin (SC-OVA and FO-OVA) or saline (SC-SAL and FO-SAL) challenge. Resistance and elastance were measured at baseline and after aerosolized methacholine, 24h after the last challenge. Bronchoalveolar lavage (BAL) was performed for leukocyte counts. Lung tissue mucus deposition, peribronchiolar matrix deposition and eosinophil infiltration were quantified. Serum immunoglobulin E (IgE) and IgG1 (ref 2.2), lung IL-4, IL-5, IL-10, IL-13, IL-17, INFγ and eotaxin-1 and 2 were detected by ELISA and nuclear factor kappa B (NFκB), GATA-3 and peroxisome proliferator-activated receptor gamma (PPARγ) expression was measured by Western blot.ResultsLevels of serum IgE and IgG1 were significantly higher in OVA sensitized mice. OVA challenge resulted in increased eosinophil infiltration, increased inflammatory cytokine production, peribronchiolar matrix and mucus deposition and airway hyperreactivity to aerosolized methacholine. Elevated lung NFκB and GATA-3 expression was noted in OVA-challenged mice. These changes were attenuated in mice fed with FO diet. Higher PPARγ expression was also detected in the lungs from the FO-fed groups.ConclusionOur results demonstrate that FO intake attenuated classical asthma features by suppressing the systemic sensitization, thus providing evidence that FO might be a prophylactic alternative for asthma prevention.

KCa3.1 Channel-Blockade Attenuates Airway Pathophysiology in a Sheep Model of Chronic Asthma

BackgroundThe Ca2+-activated K+ channel KCa3.1 is expressed in several structural and inflammatory airway cell types and is proposed to play an important role in the pathophysiology of asthma. The aim of the current study was to determine whether inhibition of KCa3.1 modifies experimental asthma in sheep.Methodology and Principal FindingsAtopic sheep were administered either 30 mg/kg Senicapoc (ICA-17073), a selective inhibitor of the KCa3.1-channel, or vehicle alone (0.5% methylcellulose) twice daily (orally). Both groups received fortnightly aerosol challenges with house dust mite allergen for fourteen weeks. A separate sheep group received no allergen challenges or drug treatment. In the vehicle-control group, twelve weeks of allergen challenges resulted in a 60±19% increase in resting airway resistance, and this was completely attenuated by treatment with Senicapoc (0.25±12%; n = 10, P = 0.0147). The vehicle-control group had a peak-early phase increase in lung resistance of 82±21%, and this was reduced by 58% with Senicapoc treatment (24±14%; n = 10, P = 0.0288). Senicapoc-treated sheep also demonstrated reduced airway hyperresponsiveness, requiring a significantly higher dose of carbachol to increase resistance by 100% compared to allergen-challenged vehicle-control sheep (20±5 vs. 52±18 breath-units of carbachol; n = 10, P = 0.0340). Senicapoc also significantly reduced eosinophil numbers in bronchoalveolar lavage taken 48 hours post-allergen challenge, and reduced vascular remodelling.ConclusionsThese findings suggest that KCa3.1-activity contributes to allergen-induced airway responses, inflammation and vascular remodelling in a sheep model of asthma, and that inhibition of KCa3.1 may be an effective strategy for blocking allergen-induced airway inflammation and hyperresponsiveness in humans.

Laminin drives survival signals to promote a contractile smooth muscle phenotype and airway hyperreactivity

Increased airway smooth muscle (ASM) mass is believed to underlie the relatively fixed airway hyperresponsiveness (AHR) in asthma. Developments of therapeutic approaches to reverse airway remodeling are impeded by our lack of insight on the mechanisms behind the increase in mass of contractile ASM cells. Increased expression of laminin, an extracellular matrix protein, is associated with asthma. Our studies investigate the role of laminin-induced ASM survival signals in the development of increased ASM and AHR. Antagonizing laminin integrin binding using the laminin-selective competing peptide, YIGSR, and mimicking laminin with exogenous α2-chain laminin, we show that laminin is both necessary and sufficient to induce ASM cell survival, concomitant with the induction of ASM contractile phenotype. Using siRNA, we show that the laminin-binding integrin α7β1 mediates this process. Moreover, in laminin-211-deficient mice, allergen-induced AHR was not observed. Notably, ASM cells from asthmatic airways express a higher abundance of intracellular cell survival proteins, consistent with a role for reduced rates of cell apoptosis in development of ASM hyperplasia. Targeting the laminin-integrin α7β1 signaling pathway may offer new avenues for the development of therapies to reduce the increase in mass of contractile phenotype ASM cells that underlie AHR in asthma.

Blockade of JAK1/3 signaling with a selective inhibitor, R256, attenuates Th2 differentiation and development of allergen-induced airway hyperresponsiveness (AHR) and airway inflammation (P6047)

Abstract JAK are major downstream regulators of signaling through cytokine receptors, activating STAT. Effective targeting of the Th2-associated JAK-STAT pathway would represent a new therapeutic approach for the treatment of asthma. Here, we studied the effects of a novel selective JAK1/3 inhibitor, R256, on Th1, Th2, and Th17 differentiation in vitro and on the development of ovalubmin-induced AHR and airway inflammation in vivo in mice. R256 prevented only Th2 differentiation in vitro and was associated with the downregulation of STAT5 and STAT6 phosphorylation. In contrast, Th2 cells were unaffected by the inhibitor when added after polarization was complete. In vivo, R256 administered during the allergen sensitization phase prevented the development of AHR, airway eosinophilia, mucus hypersecretion, and Th2 cytokine production without altering Th1 and Th17 cytokine production, indicating that selective blockade of Th2 differentiation was critical. Inhibitor administration after allergen sensitization but during the challenge phase also suppressed AHR, airway eosinophilia, and mucus hypersecretion but no effect on Th2 cytokine levels in BAL could be detected, suggesting effects on downstream cytokine receptor signaling pathways. Thus, R256-mediated inhibition of JAK1/3 activation was effective when administered both prior to and after Th2 polarization to attenuate allergen-induced Th2 dominant airway inflammation and AHR.

Cannabinoid CB2 receptors as novel target for inhibiting house dust mite induced allergic airway inflammation (P6023)

Abstract Asthma is a chronic lung inflammatory disorder characterized by airflow obstruction, airway hyperreactivity (AHR) and bronchial inflammation in response to environmental stimuli including allergens. Allergic asthma is associated with the presence in the airways of CD4+ Th2 cells and eosinophils, together with goblet cell hyperplasia and epithelial desquamation. Recent studies have indicated that cannabis-derived compounds and cannabinoid receptor agonists have immunosuppressive and anti-inflammatory properties. In this study, we examined the effect of CB2 selective agonists on allergic airway inflammation using Derp house dust mite (HDM)-induced model of asthma. Our results revealed that the intranasal administration of nonpsychoactive CB2 agonists was highly effective at attenuating allergic airway inflammatory responses. Specifically, CB2 agonists caused a marked inhibition in the accumulation of CD4+ T cells and eosinophils into the airways and the level of Th2 cytokine production in the lungs of mice immunized and challenged with HDM. Moreover, treatment with CB2 agonists ameliorated HDM-induced AHR and mucus production. CB2 receptors were highly expressed by antigen-presenting cells in the airways during allergic inflammation. Collectively, these results demonstrate that CB2 activation leads to suppression of allergen-induced airway inflammation and AHR and may provide a novel approach for the treatment for lung inflammatory diseases such as asthma.

Nociceptin/orphanin FQ receptor activation decreases the airway hyperresponsiveness induced by allergen in sensitized mice

Several studies suggest that the N/OFQ (nociceptin/orphanin FQ)-NOP (N/OFQ peptide) receptor pathway is involved in airway physiology. We previously demonstrated a modulation of the endogenous N/OFQ levels in allergen-sensitized mice. Here, we investigated the effects of NOP receptor activation in allergen sensitization using a murine model of allergen-induced airway hyperresponsiveness (AHR). BALB/c mice were intraperitoneally treated with the NOP receptor agonist UFP-112, either during the sensitization phase (30 min before ovalbumin administration) or at the end of sensitization process (15 min before bronchopulmonary reactivity evaluation). At day 21 from the first allergen exposure, bronchopulmonary reactivity and total and differential cell count in bronchoalveolar lavage fluid were evaluated. In a separate set of experiments cell proliferation in lymphocytes, cytokine levels, IgE serum levels, and the effect of UFP-112 on IL-13-induced AHR were evaluated. Pretreatment with UFP-112, during the sensitization phase, caused a significant reduction in allergen-induced AHR and total cell lung infiltration. No effect on allergen-induced AHR was observed when the treatment was performed at the end of sensitization process, on tissues harvested from OVA-sensitized mice and on IL-13-induced AHR. The in vitro proliferative response of lymphocytes was significantly reduced by pretreatment during the sensitization phase with UFP-112. This effect was paralleled by a significant modulation of cytokine secretion in pulmonary tissues and lymphocytes. In conclusion, we demonstrated a role for the NOP receptor and N/OFQ pathway in the AHR induced by allergen, probably through a modulation of the immune response that triggers the development of AHR that involves pro- and anti-inflammatory cytokines.

Type V Collagen–induced Tolerance Prevents Airway Hyperresponsiveness

Type V Collagen–induced Tolerance Prevents Airway Hyperresponsiveness

The Inhibitory Role of Hydrogen Sulfide in Airway Hyperresponsiveness and Inflammation in a Mouse Model of Asthma

Cystathionine γ-lyase (CSE) is one of the major enzymes producing hydrogen sulfide (H2S) in lungs, participating in the regulation of respiratory functions. The role of CSE-derived H2S in eosinophil-dominant inflammation in allergic diseases has been unclear. The objective of this study was to explore the protective role of H2S against allergen-induced airway hyperresponsiveness (AHR) and inflammation. CSE expression and H2S production rate were assessed in mouse lung tissues with ovalbumin (OVA)-induced acute asthma. AHR, airway inflammation, and Th2 response in wild-type (WT) mice were compared with those in CSE gene knockout (KO) mice. The effect of NaHS, an exogenous H2S donor, was also evaluated on these parameters. CSE expression was absent and H2S production rate was significantly lower in the lungs of CSE KO mice when compared with WT littermates. OVA challenge decreased lung CSE expression and H2S production in WT mice. CSE deficiency resulted in aggravated AHR, increased airway inflammation, and elevated levels of Th2 cytokines such as IL-5, IL-13, and eotaxin-1 in bronchoalveolar lavage fluid after OVA challenge. The aforementioned alterations were reversed by exogenous H2S treatment. More importantly, NaHS supplement rescued CSE KO mice from the aggravated pathological process of asthma. The CSE/H2S system plays a critical protective role in the development of asthma. A new therapeutic potential for asthma via targeting CSE/H2S metabolism is indicated.

Modified Foxp3 mRNA protects against asthma through an IL-10–dependent mechanism

Chemically modified mRNA is capable of inducing therapeutic levels of protein expression while circumventing the threat of genomic integration often associated with viral vectors. We utilized this novel therapeutic tool to express the regulatory T cell transcription factor, FOXP3, in a time- and site-specific fashion in murine lung, in order to prevent allergic asthma in vivo. We show that modified Foxp3 mRNA rebalanced pulmonary T helper cell responses and protected from allergen-induced tissue inflammation, airway hyperresponsiveness, and goblet cell metaplasia in 2 asthma models. This protection was conferred following delivery of modified mRNA either before or after the onset of allergen challenge, demonstrating its potential as both a preventive and a therapeutic agent. Mechanistically, FOXP3 induction controlled Th2 and Th17 inflammation by regulating innate immune cell recruitment through an IL-10-dependent pathway. The protective effects of FOXP3 could be reversed by depletion of IL-10 or administration of recombinant IL-17A or IL-23. Delivery of Foxp3 mRNA to sites of inflammation may offer a novel, safe therapeutic tool for the treatment of allergic asthma and other diseases driven by an imbalance in helper T cell responses.

IL-4Rα Expression by Airway Epithelial Cells Promotes Allergen-Induced Airway Hyperresponsiveness

IL-4Rα Expression by Airway Epithelial Cells Promotes Allergen-Induced Airway Hyperresponsiveness

The Steroidogenic Enzyme Cyp11a1 Is Essential for CD8+ Tc2 Conversion to Enhance Allergen-Induced Airway Hyperresponsiveness and Inflammation

The Steroidogenic Enzyme Cyp11a1 Is Essential for CD8+ Tc2 Conversion to Enhance Allergen-Induced Airway Hyperresponsiveness and Inflammation

PD-L2 modulates asthma severity by directly decreasing dendritic cell IL-12 production.

Studies examining the role of PD-L2/PD-1 in asthma have yielded conflicting results. To clarify its role, we examined PD-L2 expression in biopsies from human asthmatics and lungs of aeroallergen-treated mice. PD-L2 expression in bronchial biopsies correlated with the severity of asthma. In mice, allergen exposure increased PD-L2 expression on pulmonary myeloid dendritic cells, and PD-L2 blockade diminished allergen-induced airway hyperresponsiveness (AHR). In contrast, PD-1 blockade had no impact, suggesting that PD-L2 promotes AHR in a PD-1-independent manner. Decreased AHR was associated with enhanced serum IL-12 p40 and in vitro stimulation of DCs with allergen and PD-L2-Fc reduced IL-12 p70 production, suggesting that PD-L2 inhibits allergen-driven IL-12 production. In our model, IL-12 did not diminish Th2 responses, but rather directly antagonized IL-13-inducible gene expression, highlighting a novel role for IL-12 in regulation of IL-13 signaling. Thus, allergen-driven enhancement of PD-L2 signaling through a PD-1-independent mechanism limits IL-12 secretion, exacerbating AHR.

Induced apoptosis of Th2 lymphocytes and inhibition of airway hyperresponsiveness and inflammation by combined lactic acid bacteria treatment

Several lactic acid bacteria (LAB) demonstrably regulate the immune system and inhibit allergic disease. This study examined whether oral feeding of either Lactobacillus paracasei (L. paracasei) BB5 and/or Lactobacillus rhamnosus (L. rhamnosus) BB1 suppresses ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) and inflammation in a murine model. OVA-specific immune responses, cell profile of bronchoalveolar lavage fluid (BALF), and airway AHR were assessed following OVA and methacholine challenge. We investigated whether LAB can enhance CD4+FoxP3+ and CD8+FoxP3+ regulatory T (Treg) cells in splenic cells and apoptosis of CD4+IL-4+ T cells. Results found oral administration of combined LAB better than single L. paracasei or L. rhamnosus strain, improving Penh ratio after challenge with methacholine. High-dose combined LAB starkly decreased synthesis of OVA-specific IgE and IgG2a levels, as well as eosinophils infiltration in BALF. In addition, CD4+IL-4+ T cells decreased while CD4+FoxP3+ and CD8+FoxP3+ Treg cells increased significantly in splenic mononuclear cells of high-dose combined LAB group. Findings indicate allergen-induced AHR and airway allergic inflammation suppressed by enhances CD4+FoxP3+ and CD8+FoxP3+ Treg populations as well as Th1 cell response after treating with combined LAB. This study may provide a basis for developing a novel therapeutic or protective method for airway allergic disease.

The pharmacological modulation of allergen-induced asthma

Aeroallergens are the most common triggers for the development of asthma. Recent birth cohort studies have identified viral infections occurring against a background of aeroallergen sensitization as a potent risk factor for initiation of asthma. Viral infection enhances immunopathogenic potential of pre-existing inhalant allergy via modulating airway mucosal dendritic cells. By using an allergen inhalation challenge clinical model, studies have shown that the late asthma response (LAR) is associated with more pronounced allergen-induced airway inflammation and airway hyperresponsiveness. The degree of airway eosinophilia, regulated by bone marrow progenitor cells and interleukin-5 level, correlates with the magnitude of the LAR and the increase in hyperresponsiveness. Both myeloid and plasmacytoid dendritic cell subsets have been involved in the pathogenesis of allergen-induced LAR. Myeloid dendritic cells are responsible for the allergen presentation and induction of inflammation and plasmacytoid dendritic cells play a role in the resolution of allergen-induced inflammation. A variety of potential new classes of asthma medication has also been evaluated with the allergen inhalation challenge in mild asthmatic subjects. Examples are TPI ASM8, an inhaled anti-sense oligonucleotide drug product, which attenuated both early and LARs via inhibition of the target gene mRNA of chemokine receptor 3, and the common β chain of interleukin-3, interleukin-5 and granulocyte-macrophage colony-stimulating factor receptor. Anti-human antibody interleukin-13 (IM-638) significantly attenuated both early and late allergen-induced asthma response. Pitrakinra, which targets both interleukin-4 and interleukin-13, substantially diminishes allergen-induced airway responses. Allergen-induced airway responses are a valuable way to evaluate the activity of possible new therapies in asthmatic airways.

Microbial Heat Shock Protein 65 Attenuates Airway Hyperresponsiveness and Inflammation by Modulating the Function of Dendritic Cells

Heat shock proteins (HSPs), produced in response to stress, are suppressive in disease models. We previously showed that Mycobacterium leprae HSP65 prevented development of airway hyperresponsiveness and inflammation in mice. Our goal in this study was to define the mechanism responsible for the suppressive effects of HSP. In one in vivo approach, BALB/c mice were sensitized to OVA, followed by primary OVA challenges. Several weeks later, HSP65 was administered prior to a single, provocative secondary challenge. In a second in vivo approach, the secondary challenge was replaced by intratracheal instillation of allergen-pulsed bone marrow-derived dendritic cells (BMDCs). The in vitro effects of HSP65 on BMDCs were examined in coculture experiments with CD4(+) T cells. In vivo, HSP65 prevented the development of airway hyperresponsiveness and inflammation. Additionally, Th1 cytokine levels in bronchoalveolar lavage fluid were increased. In vitro, HSP65 induced Notch receptor ligand Delta1 expression on BMDCs, and HSP65-treated BMDCs skewed CD4(+) T cells to Th1 cytokine production. Thus, HSP65-induced effects on allergen-induced airway hyperresponsiveness and inflammation were associated with increased Delta1 expression on dendritic cells, modulation of dendritic cell function, and CD4(+) Th1 cytokine production.

Iron supplementation decreases severity of allergic inflammation in murine lung.

The incidence and severity of allergic asthma have increased over the last century, particularly in the United States and other developed countries. This time frame was characterized by marked environmental changes, including enhanced hygiene, decreased pathogen exposure, increased exposure to inhaled pollutants, and changes in diet. Although iron is well-known to participate in critical biologic processes such as oxygen transport, energy generation, and host defense, iron deficiency remains common in the United States and world-wide. The purpose of these studies was to determine how dietary iron supplementation affected the severity of allergic inflammation in the lungs, using a classic model of IgE-mediated allergy in mice. Results showed that mice fed an iron-supplemented diet had markedly decreased allergen-induced airway hyperreactivity, eosinophil infiltration, and production of pro-inflammatory cytokines, compared with control mice on an unsupplemented diet that generated mild iron deficiency but not anemia. In vitro, iron supplementation decreased mast cell granule content, IgE-triggered degranulation, and production of pro-inflammatory cytokines post-degranulation. Taken together, these studies show that iron supplementation can decrease the severity of allergic inflammation in the lung, potentially via multiple mechanisms that affect mast cell activity. Further studies are indicated to determine the potential of iron supplementation to modulate the clinical severity of allergic diseases in humans.

Nebulized Anti–IL-13 Monoclonal Antibody Fab′ Fragment Reduces Allergen-Induced Asthma

IL-13 is a prototypic T helper type 2 cytokine and a central mediator of the complex cascade of events leading to asthmatic phenotype. Indeed, IL-13 plays key roles in IgE synthesis, bronchial hyperresponsiveness, mucus hypersecretion, subepithelial fibrosis, and eosinophil infiltration. We assessed the potential efficacy of inhaled anti-IL-13 monoclonal antibody Fab' fragment on allergen-induced airway inflammation, hyperresponsiveness, and remodeling in an experimental model of allergic asthma. Anti-IL-13 Fab' was administered to mice as a liquid aerosol generated by inExpose inhalation system in a tower allowing a nose-only exposure. BALB/c mice were treated by PBS, anti-IL-13 Fab', or A33 Fab' fragment and subjected to ovalbumin exposure for 1 and 5 weeks (short-term and long-term protocols). Our data demonstrate a significant antiasthma effect after nebulization of anti-IL-13 Fab' in a model of asthma driven by allergen exposure as compared with saline and nonimmune Fab fragments. In short- and long-term protocols, administration of the anti-IL-13 Fab' by inhalation significantly decreased bronchial responsiveness to methacholine, bronchoalveolar lavage fluid eosinophilia, inflammatory cell infiltration in lung tissue, and many features of airway remodeling. Levels of proinflammatory mediators and matrix metalloprotease were significantly lower in lung parenchyma of mice treated with anti-IL-13 Fab'. These data demonstrate that an inhaled anti-IL-13 Fab' significantly reduces airway inflammation, hyperresponsiveness, and remodeling. Specific neutralization of IL-13 in the lungs using an inhaled anti-IL-13 Fab' could represent a novel and effective therapy for the treatment of asthma.

Effect of oral feeding with Clostridium leptum on regulatory T-cell responses and allergic airway inflammation in mice

BackgroundAllergic lung inflammation is mediated by allergen-specific T responses, which are negatively regulated by regulatory T cells (Tregs). Previous studies have reported that inoculation of indigenous Clostridium species in the early lives of mice can induce Tregs that colonize the colon. However, whether inoculation of C leptum alone in adult mice could induce systemic Treg responses and inhibit allergic airway inflammation remains unclear. ObjectiveTo investigate the effect of oral administration of C leptum on systemic Treg responses and allergic airway inflammation in a mouse model of asthma. MethodsAdult BABL/c mice were injected with ovalbumin to induce asthma and treated orally with C leptum or vehicle daily for 2 weeks. The numbers of Foxp3+CD4+CD25+ Tregs in both the spleen and mediastinal lymph nodes were examined by flow cytometry. After allergen challenge, the airway hyperresponsiveness of individual mice was measured, and the numbers of inflammatory infiltrates and the levels of cytokines in bronchoalveolar lavage fluids ere determined. ResultsOral feeding with C leptum increased the percentage and total number of Tregs in the spleens and mediastinal lymph nodes at 14 days after inoculation and attenuated allergen-induced airway hyperresponsiveness and inflammation by inhibiting inflammatory cytokine production but enhancing interleukin 10 and transforming growth factor β1 production in the lungs. ConclusionOral treatment with C leptum can attenuate induced allergic airway inflammation in adult mice.