Anti-interleukin 5 but not anti-IgE prevents airway inflammation and airway hyperresponsiveness.

The role of IL-5 and allergen-specific IgE in the development of eosinophilic airway inflammation and airway hyperresponsiveness (AHR) was investigated in a murine model. BALB/c mice were sensitized to ovalbumin (OVA) by intraperitoneal injection on Days 1 and 14, followed by airway challenge with OVA on Days 28 and 29. Anti-IL-5 (TRFK-5) or anti-IgE (antibody 1-5) was administered before each airway challenge. Sensitized and challenged mice developed increased OVA-specific IgE serum levels, Th2 cytokine production by peribronchial lymph node (PBLN) cells, increased numbers of eosinophils (predominantly located in the peribronchial regions of the lungs), and increased airway responsiveness to methacholine (MCh). Anti-IgE treatment significantly decreased serum anti-OVA IgE levels and prevented the development of anaphylaxis but failed to affect T cell function, eosinophil airway infiltration, and AHR in sensitized and challenged mice. In contrast, treatment with anti-IL-5 antibody did not affect B cell (Ig serum levels), T cell (cytokine production), or mast cell function (immediate cutaneous reactivity) but completely inhibited development of eosinophilic lung inflammation and AHR. These data identify IL-5-mediated eosinophilia as a major target for development of AHR in this model, with little effect resulting from neutralization of IgE.     

Inhibitory Effects of Anti-Immunoglobulin E Antibodies on Airway Remodeling in A Murine Model of Chronic Asthma

Background: Airway remodeling is one of the cardinal features of asthma and is thought to play a pivotal role in refractory or persistent asthma. Immunoglobulin E (IgE) has a major effect on the pathogenesis of asthma. The aim of this study was to investigate the effects of anti-IgE antibody not only on airway inflammation and bronchial hyperresponsiveness, but also on airway remodeling in a murine model of chronic asthma. Methods: The authors developed a mouse model of chronic asthma in which ovalbumin (OVA)-sensitized female BALB/c-mice were exposed to intranasal OVA administration twice a week for 3 months. Anti-IgE antibodies were administered intravenously starting on the 38th day and once a month thereafter for 3 months during the intranasal OVA challenge. Results: Mice that were chronically exposed to OVA developed sustained eosinophilic airway inflammation and airway hyperresponsiveness (AHR) to methacholine and showed increased levels of collagen, hydroxyproline, and α-smooth muscle actin, as compared with control mice. Treatment with anti-IgE antibody inhibited the development of AHR, eosinophilic inflammation, and airway remodeling. Moreover, anti-IgE antibody treatment reduced the levels of interleukin (IL)-5 and IL-13 in the bronchoalveolar lavage fluids, although it did not affect the levels of IL-10, transforming growth factor-β, and activin A. Conclusion: These results suggest that anti-IgE antibody treatment modulates the airway inflammation and remodeling associated with chronic allergen challenge. The inhibition of inflammation may be related to the regulation of Th2 cytokines. However, the mechanisms underlying the blocking of airway remodeling by anti-IgE antibody remain to be elucidated.     

Dual Role of Interleukin-23 in Epicutaneously-Sensitized Asthma in Mice

BackgroundInterleukin (IL)-23/Th17 axis plays an important role in the pathophysiology of asthma and eczema, however, there are some conflicting data about the effects of this system on allergic airway inflammation. In the present study, we aim to dissect the spatiotemporal differences in the roles of IL-23 in an epicutaneously-sensitized asthma model of mice.MethodsC57BL/6 mice were sensitized to ovalbumin (OVA) by patch application on the skin, followed by airway exposure to aerosolized OVA. During sensitization and/or challenge phase, either a specific neutralizing antibody (Ab) against IL-23 or control IgG was injected intraperitoneally. On days 1 and 8 after the final OVA exposure, airway inflammation and responsiveness to methacholine, immunoglobulin levels in serum, and cytokine release from splenocytes were evaluated. Skin Il23a mRNA levels were evaluated with quantitative RT-PCR.ResultsPatch application time-dependently increased the expression of Il23a mRNA expression in the skin. Treatment with the anti-IL-23 Ab during sensitization phase alone significantly reduced the number of eosinophils in bronchoalveolar lavage fluids and peribronchial spaces after allergen challenge compared with treatment with control IgG. Anti-IL-23 Ab also reduced serum levels of OVA-specific IgG1. In contrast, treatment with the anti-IL-23 Ab during the challenge phase alone rather exacerbated airway hyperresponsiveness to methacholine with little effects on airway eosinophilia or serum IgG₁ levels.ConclusionsIL-23 expressed in the skin during the sensitization phase plays an essential role in the development of allergic phenotypes, whereas IL-23 in the airways during the challenge phase suppresses airway hy- perresponsiveness.     

Inhibition of phosphodiesterase 4 attenuates airway hyperresponsiveness and airway inflammation in a model of secondary allergen challenge

We compared for the first time the therapeutic potential of a specific phosphodiesterase 4 (PDE4) inhibitor, rolipram, with anti-VLA-4 and anti-IL-5 in a model of secondary allergen exposure of previously sensitized and challenged mice. To address these issues, mice were sensitized and challenged with ovalbumin (OVA) (primary challenge). Six weeks later, sensitized/challenged mice were reexposed to OVA (secondary challenge) and airway response (resistance [RL] and dynamic compliance [Cdyn]) to inhaled methacholine was monitored. After secondary OVA challenge, RL significantly increased as did the number of lung inflammatory cells and IL-4 and IL-5 production in bronchoalveolar lavage fluid (BALF). Administration of rolipram, in a dose-dependent manner, significantly prevented both changes in RL and Cdyn, as well as eosinophil, lymphocyte, and neutrophil accumulation in the BALF; IL-4 and IL-5 levels in BALF were also significantly reduced. In contrast, treatment with anti-VLA-4 and anti-IL-5 only prevented changes in RL and eosinophil numbers and IL-5 production in BALF. Further, goblet cell hyperplasia was suppressed only by treatment with rolipram. None of the treatments affected OVA-specific antibody levels. These studies confirm that IL-5 dependent eosinophilic inflammation plays an essential role in the development of certain aspects of airway function after rechallenge of sensitized mice and that lymphocytes and neutrophils are also important in the development of altered airway function. The use of agents that inhibit PDE4 may have an important role in the treatment of asthma in previously sensitized mice.     

Different IL-5 and IFN-γ Production from Peripheral Blood T-Cell Subsets in Atopic and Nonatopic Asthmatic Children

Defective Th1 and enhanced Th2-type cytokine responses have been implicated in the development of atopic disease. However, the immunopathology of nonatopic asthma, especially in children, remains unclear, and there have been few studies to compare the cytokine profile in peripheral blood T-cell subsets between atopic and nonatopic asthmatic children. To document whether atopic asthmatic children have a cytokine imbalance and to compare the cytokine profile between atopic and nonatopic asthmatic children, we investigated the interleukin (IL)-5-producing and interferon (IFN)-γ-producing T-cell subsets from peripheral blood mononuclear cells (PBMC). The percentages of IFN-γ-producing CD4⁺ and CD8⁺ T cells from atopic asthmatic children were decreased, but those in nonatopic asthmatic children were not decreased. In both groups of asthmatic children, the percentages of IFN-γ-producing CD4⁺ T cells were inversely correlated with the peripheral blood eosinophils and had a significant correlation with airway responsiveness (PC₂₀). Thus, we found that the mechanism underlying allergic inflammation of nonatopic asthma is not simple a Th1/Th2 cytokine imbalance. Considering the inverse relationship between IFN-γ-producing CD4⁺ T cells and eosinophilia or airway hyperresponsiveness, IFN-γ from CD4⁺ T cells may play an important role in allergic inflammation and airway hyperresponsiveness in asthmatic children.     

T helper 1 cells stimulated with ovalbumin and IL-18 induce airway hyperresponsiveness and lung fibrosis by IFN-gamma and IL-13 production

We previously reported that ovalbumin (OVA) and IL-18 nasally administered act on memory type T helper (Th)1 cells to induce airway hyperresponsiveness (AHR) and inflammation, which is characterized by peribronchial infiltration with neutrophils and eosinophils. Here, we report this administration also induces lung fibrosis in an IL-13-dependent manner. Th1 cells secrete several cytokines, including IFN-gamma and bronchogenic cytokine IL-13, when stimulated with antigen (Ag) and IL-18. However, IL-13 blockade failed to attenuate AHR, although this treatment inhibited eosinophilic infiltration. To understand the mechanism by which Th1 cells induce AHR after Ag plus IL-18 challenge, we established "passive" and "active" Th1 mice by transferring OVA-specific Th1 cells into na?ve BALB/c mice or by immunizing na?ve BALB/c mice with OVA/complete Freund's adjuvant, respectively. Administration of Ag and IL-18 induced both types of Th1 mice to develop AHR, airway inflammation, and lung fibrosis. Furthermore, this treatment induced deposition of periostin, a novel component of lung fibrosis. Neutralization of IL-13 or IFN-gamma during Ag plus IL-18 challenges inhibited the combination of eosinophilic infiltration, lung fibrosis, and periostin deposition or the combination of neutrophilic infiltration and AHR, respectively. We also found that coadministration of OVA and LPS into Th1 mice induced AHR and airway inflammation via endogenous IL-18. Thus, IL-18 becomes a key target molecule for the development of a therapeutic regimen for the treatment of Th1-cell-induced bronchial asthma.     

Rat models of asthma and chronic obstructive lung disease

The rat has been extensively used to model asthma and somewhat less extensively to model chronic obstructive pulmonary disease (COPD). The features of asthma that have been successfully modeled include allergen-induced airway constriction, eosinophilic inflammation and allergen-induced airway hyperresponsiveness. T-cell involvement has been directly demonstrated using adoptive transfer techniques. Both CD4+ and CD8+ T cells are activated in response to allergen challenge in the sensitized rat and express Thelper2 cytokines (IL-4, IL-5 and IL-13). Repeated allergen exposure causes airway remodeling. Dry gas hyperpnea challenge also evokes increases in lung resistance, allowing exercise-induced asthma to be modeled. COPD is modeled using elastase-induced parenchymal injury to mimic emphysema. Cigarette smoke-induced airspace enlargement occurs but requires months of cigarette exposure. Inflammation and fibrosis of peripheral airways is an important aspect of COPD that is less well modeled. Novel approaches to the treatment of COPD have been reported including treatments aimed at parenchymal regeneration.     

Lipopolysaccharides promote a shift from Th2-derived airway eosinophilic inflammation to Th17-derived neutrophilic inflammation in an ovalbumin-sensitized murine asthma model

Introduction: The currently available treatments for severe asthma are insufficient. Infiltration of neutrophils rather than eosinophils into the airways is an important inflammatory characteristic of severe asthma. However, the mechanism of the phenotypic change from eosinophilic to neutrophilic inflammation has not yet been fully elucidated. Methods: In the current study, we examined the effect of lipopolysaccharides (LPS) on eosinophilic asthmatic mice sensitized with ovalbumin (OVA), as well as the roles of interleukin (IL)-17A/T helper (Th) 17 cells on the change in the airway inflammatory phenotype from eosinophilic to neutrophilic inflammation in asthmatic lungs of IL-17A-deficient mice. Results: Following exposure of OVA-induced asthmatic mice to LPS, neutrophil-predominant airway inflammation rather than eosinophil-predominant inflammation was observed, with increases in airway hyperresponsiveness (AHR), the IL-17A level in bronchoalveolar lavage fluid (BALF) and Th17 cells in the spleen and in the pulmonary hilar lymph nodes. Moreover, the neutrophilic asthmatic mice showed decreased mucus production and Th2 cytokine levels (IL-4 and IL-5). In contrast, IL-17A knockout (KO) mice exhibited eosinophil-predominant lung inflammation, decreased AHR, mucus overproduction and increased Th2 cytokine levels and Th2 cells. Conclusion: These findings suggest that the eosinophilic inflammatory phenotype of asthmatic lungs switches to the neutrophilic phenotype following exposure to LPS. The change in the inflammatory phenotype is strongly correlated with the increases in IL-17A and Th17 cells.     

Prevention of IL-6 signaling ameliorates toluene diisocyanate-induced steroid-resistant asthma

BackgroundAccumulating evidence indicated the crucial role for interleukin 6 (IL-6) signaling in the development of allergic asthma. Yet, the role of IL-6 signaling in toluene diisocyanate (TDI)-induced mixed granulocytic airway inflammation still remains unclear. Thus, the aims of this study were to dissect the role of IL-6 signaling and to evaluate the effect of tocilizumab on TDI-induced steroid-resistant asthma.MethodsTDI-induced asthma model was prepared and asthmatic mice were respectively given IL-6 monoclonal antibody, IL-6R monoclonal antibody (tocilizumab, 5 mg/kg, i.p. after each challenge) for therapeutic purposes or isotype IgG as control.ResultsTDI exposure just elevated IL-6R expression in the infiltrated inflammatory cells around the airway, but increased glycoprotein 130 expression in the whole lung, especially in bronchial epithelium. Moreover, TDI inhalation increased airway hyperresponsiveness (AHR) to methacholine, coupled with mixed granulocytic inflammation, exaggerated epithelial denudation, airway smooth muscle thickening, goblet cell metaplasia, extensive submucosal collagen deposition, dysregulated Th2/Th17 responses, as well as innate immune responses and raised serum IgE. And almost all these responses except for raised serum IgE were markedly ameliorated by the administration of IL-6 neutralizing antibody or tocilizumab, but exhibited poor response to systemic steroid treatment. Also, TDI challenge induced nucleocytoplasm translocation of HMGB1 and promoted its release in the BALF, as well as elevated lung level of STAT3 phosphorylation, which were inhibited by anti-IL-6 and anti-IL-6R treatment.ConclusionsOur data suggested that IL-6 monoclonal antibody and tocilizumab might effectively abrogate TDI-induced airway inflammation and remodeling, which could be used as a clinical potential therapy for patients with severe asthma.     

Beneficial effect of anti-interleukin-33 on the murine model of allergic inflammation of the lower airway

Objective. Interleukin (IL)-33, which mediates the T(h)2 allergic pathway, may play a key role in allergic airway inflammation. This study was conducted to evaluate the therapeutic potential of anti-IL-33 antibody for treatment of allergic inflammation of the lower airway in a murine model. Methods. Twenty-four BALB/c mice were used in this study. Saline was used for sensitization and challenge of mice in Group A (control group, n?=?6). Mice in Group B (ovalbumin (OVA) group, n?=?6) received intraperitoneal (ip) and intranasal OVA challenge. In Group C (control IgG group, n?=?6), mice received ip injection with control IgG prior to OVA challenge. Mice in Group D (anti-IL-33 group, n?=?6) received an ip injection of anti-IL-33 prior to challenge. Measurements of serum total and OVA-specific IgE and the number of eosinophils, neutrophils, and lymphocytes in bronchoalveolar lavage (BAL) fluid were performed. We performed histopathologic examination to evaluate the degree of eosinophilic infiltration in lung tissue. Airway hyperreactivity was measured according to change of enhanced pause (Penh). Results. A significant decrease in serum total and OVA-specific IgE and the number of eosinophils and neutrophils in BAL fluid was observed in Group D, compared with Group B or Group C (p?相似文献   

Requirement for leukotriene B4 receptor 1 in allergen-induced airway hyperresponsiveness

RATIONALE: Leukotriene B4 (LTB4) is a rapidly synthesized, early leukocyte chemoattractant that signals via its cell surface receptor, leukotriene B4 receptor 1 (BLT1), to attract and activate leukocytes during inflammation. A role for the LTB4-BLT1 pathway in allergen-induced airway hyperresponsiveness and inflammation is not well defined. OBJECTIVES: To define the role of the LTB4 receptor (BLT1) in the development of airway inflammation and altered airway function. METHODS: BLT1-deficient (BLT1 -/-) mice and wild-type mice were sensitized to ovalbumin by intraperitoneal injection and then challenged with ovalbumin via the airways. Airway responsiveness to inhaled methacholine, bronchoalveolar lavage fluid cell composition and cytokine levels, and lung inflammation and goblet cell hyperplasia were assessed. RESULTS: Compared with wild-type mice, BLT1 -/- mice developed significantly lower airway responsiveness to inhaled methacholine, lower goblet cell hyperplasia in the airways, and decreased interleukin (IL)-13 production both in vivo, in the bronchoalveolar lavage fluid, and in vitro, after antigen stimulation of lung cells in culture. Intracellular cytokine staining of lung cells revealed that bronchoalveolar lavage IL-13 levels and numbers of IL-13(+)/CD4+ and IL-13(+)/CD8+ T cells were also reduced in BLT1 -/- mice. Reconstitution of sensitized and challenged BLT1 -/- mice with allergen-sensitized BLT1 +/+ T cells fully restored the development of airway hyperresponsiveness. In contrast, transfer of naive T cells failed to do so. CONCLUSION: These data suggest that BLT1 expression on primed T cells is required for the full development of airway hyperresponsiveness, which appears to be associated with IL-13 production in these cells.     

Effects of treatment with anti-immunoglobulin E antibody omalizumab on airway inflammation in allergic asthma

IgE plays an important role in allergic asthma. We hypothesized that reducing IgE in the airway mucosa would reduce airway inflammation. Forty-five patients with mild to moderate persistent asthma with sputum eosinophilia of 2% or more were treated with humanized monoclonal antibody against IgE (omalizumab) (n = 22) or placebo (n = 23) for 16 weeks. Outcomes included inflammatory cells in induced sputum and bronchial biopsies, and methacholine responsiveness. Treatment with omalizumab resulted in marked reduction of serum IgE and a reduction of IgE+ cells in the airway mucosa. The mean percentage sputum eosinophil count decreased significantly (p < 0.001) from 6.6 to 1.7% in the omalizumab group, a reduction significantly (p = 0.05) greater than with placebo (8.5 to 7.0%). This was associated with a significant reduction in tissue eosinophils; cells positive for the high-affinity Fc receptor for IgE; CD3+, CD4+, and CD8+ T lymphocytes; B lymphocytes; and cells staining for interleukin-4, but not with improvement in airway hyperresponsiveness to methacholine. This study shows antiinflammatory effects of omalizumab treatment and provides clues for mechanisms whereby omalizumab reduces asthma exacerbations and other asthma outcomes in more severe asthma. The lack of effect of omalizumab on methacholine responsiveness suggests that IgE or eosinophils may not be causally linked to airway hyperresponsiveness to methacholine in mild to moderate asthma.     

不同内型哮喘小鼠模型中的小气道功能研究及其机制初探

目的 探讨不同内型哮喘小鼠模型中,小气道功能是否存在异常及其相关机制.方法 卵清蛋白(OVA)致敏、激发建立T2型哮喘模型,OVA联合臭氧暴露(OVA+ozone)建立非T2型哮喘模型.模拟强迫振荡系统检测小鼠小气道功能,激发试验检测气道反应性.酶联免疫吸附试验法检测支气管肺泡灌洗液(BALF)中的细胞因子;苏木精-伊...     

Effects and Mechanism of Arsenic Trioxide on Reversing the Asthma Pathologies Including Th17-IL-17 Axis in a Mouse Model

In traditional Chinese medicine, arsenous compounds, including arsenic trioxide (ATO), are often used to treat many diseases, which are safe and effective. Recently, studies have indicated that Th17- IL-17 involved in the pathogenesis and development of asthma. The goal of this study was to investigate the effect and mechanism of ATO on asthma, especially the Th17- IL-17 axis.We used oval bumin (OVA)-immunized mice as a model for asthma and treated mice with ATO or dexamethasone. The mice were then monitored airway responsiveness, airway inflammation, mucus production, IL-17 levels in BALF and the positive rate of Th17 cells. In vitro, CD4+ T cells from splenic cell suspensions were separated and purified. We measured the expression of IL-17 and caspase-12 protein in purified CD4+ T cells, and detected IL-17 levels in CD4+ T lymphocyte culture solution with or without ATO. Moreover, apoptosis, mitochondrial membrane potential, cytosolic calcium were analyzed. We found that ATO could reduce airway responsiveness, airway inflammation, mucus hyperplasia, the expression of IL-17 in BALF and the positive rate of Th17 cells at a level comparable to treatment with DXM. In vitro data suggested that ATO can induce CD4+ T cells apoptosis, cause mitochondrial dysfunction, Ca2+ overload and promote caspase-12 activation. Our study suggested that ATO had potential medical value for the treatment of human asthma..     

CD+4CD+25 T淋巴细胞对支气管哮喘小鼠气道炎症的影响及作用机制

目的探讨CD+4 CD+25 T淋巴细胞(Treg细胞)对支气管哮喘(简称哮喘)小鼠气道炎症的影响及作用机制.方法 60只小鼠按随机数字表法分为3组,每组20只.哮喘组(A组)小鼠于第1、13天以鸡卵白蛋白(OVA)0.1 ml腹腔注射致敏,第21～29天雾化吸入2% OVA生理盐水溶液10 ml激发 30 min后建立小鼠哮喘模型.生理盐水对照组(B组)以生理盐水10 ml替代OVA处理.去除T淋巴细胞哮喘组(C组)去除小鼠体内CD+25 T淋巴细胞后再按A组方法复制小鼠哮喘模型(用药剂量和方法同A组).分离A、B、C 3组小鼠脾脏淋巴细胞,用流式细胞仪(FACS)检测Treg细胞数量,计算其占CD+4 T淋巴细胞的百分比;分离CD+4 T淋巴细胞,用逆转录-聚合酶链反应(RT-PCR)法检测白细胞介素10(IL-10)、转化生长因子β1(TGF-β1)和细胞毒性T淋巴细胞抗原4 mRNA(CTLA-4 mRNA)的表达;同时对肺组织行苏木精-伊红 (HE)染色,观察小鼠肺组织的炎症改变. 结果经过OVA反复激发,A组小鼠脾脏Treg细胞占CD+4 T淋巴细胞的百分比为(3.10±0.03)%,B组为(9.60±0.04)%,A、B两组间及C组分别与A、B组比较差异均有统计学意义(P均<0.01); IL-10、TGF-β1和CTLA-4 mRNA的表达A组分别为0.250±0.040、0.29±0.03、0.28±0.06, B组分别为0.480±0.080、0.47±0.05、0.50±0.03、C组分别为0.080±0.020、0.11±0.04、0.12±0.05,A、B两组及C组分别与A、B组比较差异均有统计学意义(P均<0.01).与B组比较,A组肺部以嗜酸粒细胞浸润为主要表现的炎症改变明显增强,C组则较A、B组显著增强.结论 Treg细胞的数量减少和(或)功能障碍可能是哮喘气道炎症发生发展的重要机制.     

Adoptive transfer of T-helper cell type 1 clones attenuates an asthmatic phenotype in mice.

T-helper cell type 1 (Th1) cells have been postulated to have a significant role in protective immunity against allergic diseases. However, recent studies using polarised Th1 cells showed conflicting effects on both airway responsiveness and eosinophilic inflammation in a mouse asthma model. The current study explored the effects of adoptive transfer of established Th1 clones on a murine model of atopic asthma. Mice (BALB/c) were sensitised with ovalbumin (OVA) and challenged with aerosolised OVA (5%, 20 min) for 5 days. Just before starting the first challenge, Th1 clones (5x10(6) x body(-1)) or PBS alone were injected via the tail vein. After assessment of airway responsiveness to methacholine, bronchoalveolar lavage fluid (BALF) was obtained. Histological examination, including morphometric analysis, measurement of cytokines in the BALF and Northern blotting of lung chemokines, was also performed. Adoptive transfer of Th1 clones showed a significantly increased total number of cells, whereas significantly decreased eosinophils were found in the BALF, when compared with mice with injection of vehicle alone or splenic mononuclear cells. Administration of Th1 clones significantly decreased the infiltration of eosinophils but increased mononuclear cells in the peribronchial area. Goblet cell hyperplasia and peribronchial fibrosis were also suppressed by Th1 clones. The transfer of Th1 cells significantly decreased airway responsiveness. Th1 injection significantly increased interferon gamma in the BALF, but significantly decreased interleukin (IL)-5 and IL-13. Eotaxin mRNA was predominantly expressed in the lungs of asthma model mice, whereas RANTES (regulated on activation, normal T-cell expressed and secreted) predominates in such mice with Th1 transfer. In conclusion, results suggest that the adoptive transfer of T-helper cell type 1 clones can suppress both lung eosinophilia and airway responsiveness, but increase noneosinophilic inflammation in a mouse model of asthma.     

Importance of myeloid dendritic cells in persistent airway disease after repeated allergen exposure

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-beta(1), 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.