The mechanisms underlying airway hyperresponsiveness remain unclear, although airway inflammation and remodeling are likely important contributing factors. We hypothesized that airway physiology would differ between mice subjected to brief or chronic allergen exposure, and that these differences would be associated with characteristic inflammatory markers and indices of airway remodeling. BALB/c mice were sensitized to ovalbumin and studied at several time points following brief or chronic allergen challenge protocols. By measuring airway responses to methacholine, we demonstrated increases in maximal inducible bronchoconstriction that persisted for 8 wk following either brief or chronic allergen challenge; we also observed increases in airway reactivity, although it was only in chronically challenged mice that these changes persisted beyond the resolution of allergen-induced inflammation. Using airway morphometry, we further demonstrated that increases in maximal bronchoconstriction were associated with increases in airway contractile tissue in both models, and that chronic, but not brief, allergen challenge resulted in subepithelial fibrosis. Our observations that different aspects of sustained airway dysfunction and remodeling persist beyond the resolution of acute inflammatory events support the concept that remodeling occurs as a consequence of allergic airway inflammation, and that these structural changes contribute independently to the persistence of airway hyperresponsiveness.

It is now well established that passive exposure to inhaled OVA leads to a state of immunological tolerance. Therefore, to elicit allergic sensitization, researchers have been compelled to devise alternative strategies, such as the systemic delivery of OVA in the context of powerful adjuvants, which are alien to the way humans are exposed and sensitized to allergens. The objectives of these studies were to investigate immune-inflammatory responses to intranasal delivery of a purified house dust mite (HDM) extract and to evaluate the role of GM-CSF in this process. HDM was delivered to BALB/c mice daily for 10 days. After the last exposure, mice were killed, bronchoalveolar lavage was performed, and samples were obtained. Expression/production of Th2-associated molecules in the lymph nodes, lung, and spleen were evaluated by real-time quantitative PCR and ELISA, respectively. Using this exposure protocol, exposure to HDM alone generated Th2 sensitization based on the expression/production of Th2 effector molecules and airway eosinophilic inflammation. Flow cytometric analysis demonstrated expansion and activation of APCs in the lung and an influx of activated Th2 effector cells. Moreover, this inflammation was accompanied by airways hyper-responsiveness and a robust memory-driven immune response. Finally, administration of anti-GM-CSF-neutralizing Abs markedly reduced immune-inflammatory responses in both lung and spleen. Thus, intranasal delivery of HDM results in Th2 sensitization and airway eosinophilic inflammation that appear to be mediated, at least in part, by endogenous GM-CSF production.

No abstract

Increases in bone-marrow (BM) inflammatory cell progenitors are associated with allergen-induced airway hyperresponsiveness and inflammation in asthmatics and dogs. Here, for the first time, we compare the time course of airway hyperresponsiveness, inflammation, and marrow progenitor responses in a mouse model of airway allergen challenge. Sensitized BALB/c mice were studied at 2, 12, 24, 48, and 72 h after intranasal ovalbumin or saline challenges. Outcome measurements included airway responsiveness, airway inflammation as assessed via bronchoalveolar lavage (BAL) and lung tissue sections, and BM eosinophil colony-forming units (Eo-CFU) as enumerated using a semisolid culture assay with optimal concentrations of interleukin-5. We observed significant increases in BAL fluid eosinophils, neutrophils, lymphocytes, and macrophages by 2 h after the second of two intranasal allergen challenges (P < 0.05). Significant increases in airway responsiveness or BM Eo-CFU were observed at 24 h and persisted until 48 h after the second challenge (P < 0.05). Airway inflammation, including eosinophils, persisted until at least 72 h (P < 0.05). We observed that allergen-induced airway eosinophilia is accompanied by increases in BM eosinophil progenitors, indicating that in this model, increased eosinophil production involves an expansion of the relevant stem-cell population. These findings support the use of this model to explore the mechanisms of increased eosinopoiesis observed in human asthma.

The mechanisms underlying airway hyperresponsiveness remain unclear, although airway inflammation and remodeling likely play important roles. We have observed sustained airway hyperreactivity and airway remodeling occurring in mice after chronic allergen exposure and persisting beyond resolution of allergen-induced inflammation. The aim of this study was to delineate mechanisms involved in allergen-induced airway hyperreactivity and airway remodeling and to examine evidence for a causal association between airway remodeling and sustained airway hyperreactivity. Wild-type (WT) and interleukin (IL)-4-, IL-5-, and IL-13-deficient (-/-) mice were sensitized and studied 4 weeks after chronic allergen exposure. By measuring airway responsiveness and airway morphometry, we demonstrated that WT mice developed sustained airway hyperreactivity and aspects of airway remodeling after chronic allergen exposure. Both IL-4(-/-) and IL-13(-/-) mice were protected from developing sustained airway hyperreactivity and aspects of airway remodeling. In contrast, IL-5(-/-) mice developed sustained airway hyperreactivity and aspects of airway remodeling similar to that seen in WT mice. Our results confirm that IL-4 and IL-13, but not IL-5, are critical for the development of sustained airway hyperreactivity and airway remodeling after allergen exposure.

SUMMARYThe role of in¯ammatory effector cells in the pathogenesis of airway allergy has been the subject of much investigation. However, whether systemic factors are involved in the development of local responses in both upper and lower airways has not been fully clari®ed. The present study was performed to investigate aspects of the pathogenesis of isolated allergic rhinitis in a murine model sensitized to ovalbumin (OVA). Both upper-and lower-airway physiological responsiveness and in¯ammatory changes were assessed, as well as bone marrow progenitor responses, by culture and immunohistological methods. Signi®cant nasal symptoms and hyper-responsiveness appeared after intranasal OVA challenge (P<0 . 0001 and P<0 . 01, respectively), accompanied with signi®-cant nasal mucosal changes in CD4+ cells (P<0 . 001), interleukin (IL)-4 + cells (P<0 . 01), IL-5 + cells (P<0 . 01), basophilic cells (P<0 . 02) and eosinophils (P<0 . 001), in the complete absence of hyper-responsiveness or in¯ammatory changes in the lower airway. In the bone marrow, there were signi®cant increases in CD34 + cells, as well as in eosinophils and basophilic cells. In the presence in vitro of mouse recombinant IL-5, IL-3 or granulocyte±macrophage colony-stimulating factor (GM-CSF), the level of bone marrow eosinophil/basophil (Eo/Baso) colony-forming cells increased signi®cantly in the OVA-sensitized group. We conclude that, in this murine model of allergic rhinitis, haemopoietic progenitors are upregulated, which is consistent with the involvement of bone marrow in the pathogenesis of nasal mucosal in¯ammation. Both local and systemic events, initiated in response to allergen provocation, may be required for the pathogenesis of allergic rhinitis. Understanding these events and their regulation could provide new therapeutic targets for rhinitis and asthma.

No abstract

Airway remodeling, including subepithelial fibrosis, is a characteristic feature of asthma and likely contributes to the pathogenesis of airway hyperresponsiveness. We examined expression of genes related to airway wall fibrosis in a model of chronic allergen-induced airway dysfunction using laser capture microdissection and quantitative real-time PCR. BALB/c mice were sensitized and subjected to chronic ovalbumin exposure over a 12-wk period, after which they were rested and then harvested 2 and 8 wk after the last exposure. Chronic allergen-exposed mice had significantly increased indices of airway remodeling and airway hyperreactivity at all time points, although no difference in expression of fibrosis-related genes was found when mRNA extracted from whole lung was examined. In contrast, fibrosis-related gene expression was significantly upregulated in mRNA obtained from microdissected bronchial wall at 2 wk after chronic allergen exposure. In addition, when bronchial wall epithelium and smooth muscle were separately microdissected, gene expression of transforming growth factor-beta1 and plasminogen activating inhibitor-1 were significantly upregulated only in the airway epithelium. These data suggest that transforming growth factor-beta1 and other profibrotic mediators produced by airway wall, and specifically, airway epithelium, play an important role in the pathophysiology of airway remodeling.