Douglas A. Kuperman

Direct effects of interleukin-13 on epithelial cells cause airway hyperreactivity and mucus overproduction in asthma

Asthma is an increasingly common disease that remains poorly understood and difficult to manage. This disease is characterized by airway hyperreactivity (AHR, defined by exaggerated airflow obstruction in response to bronchoconstrictors), mucus overproduction and chronic eosinophilic inflammation. AHR and mucus overproduction are consistently linked to asthma symptoms and morbidity. Asthma is mediated by Th2 lymphocytes, which produce a limited repertoire of cytokines, including interleukin-4 (IL-4), IL-5, IL-9 and IL-13. Although each of these cytokines has been implicated in asthma, IL-13 is now thought to be especially critical. In animal models of allergic asthma, blockade of IL-13 markedly inhibits allergen-induced AHR, mucus production and eosinophilia. Furthermore, IL-13 delivery to the airway causes all of these effects. IL-13 is thus both necessary and sufficient for experimental models of asthma. However, the IL-13-responsive cells causing these effects have not been identified. Here we show that mice lacking signal transducer and activator of transcription 6 (STAT6) were protected from all pulmonary effects of IL-13. Reconstitution of STAT6 only in epithelial cells was sufficient for IL-13-induced AHR and mucus production in the absence of inflammation, fibrosis or other lung pathology. These results demonstrate the importance of direct effects of IL-13 on epithelial cells in causing two central features of asthma.

Interleukin-4 interleukin-13, signal transducer and activator of transcription factor 6, and allergic asthma

Interleukin (IL)-4 and IL-13 share many biological activities. To some extent, this is because they both signal via a shared receptor, IL-4Ralpha. Ligation of IL-4Ralpha results in activation of Signal Transducer and Activator of Transcription factor 6 (STAT6) and Insulin Receptor Substrate (IRS) molecules. In T- and B-cells, IL-4Ralpha signaling contributes to cell-mediated and humoral aspects of allergic inflammation. It has recently become clear that IL-4 and IL-13 produced in inflamed tissues activate signaling in normally resident cells of the airway. The purpose of this review is to critically evaluate the contributions of IL-4- and IL-13-induced tissue responses, especially those mediated by STAT6, to some of the pathologic features of asthma including eosinophilic inflammation, airway hyperresponsiveness, subepithelial fibrosis and excessive mucus production. We also review the functions of some recently identified IL-4- and/or IL-13-induced mediators that provide some detail on molecular mechanisms and suggest an important contribution to host defense.

Epithelium, Inflammation, and Immunity in the Upper Airways of Humans: Studies in Chronic Rhinosinusitis

The purpose of this review is to discuss recent findings made during studies of the upper airways and sinuses of people with chronic rhinosinusitis (CRS) in the context of the literature. CRS is a chronic inflammatory disorder affecting nearly 30 million Americans and is generally resistant to therapy with antibiotics and glucocorticoids (Meltzer EO and coworkers, J Allergy Clin Immunol 2004;114:155-212). We have formed a collaboration that consists of otolaryngologists, allergists, and basic scientists to address the underlying immunologic and inflammatory processes that are occurring in, and possibly responsible for, this disease. The main emphasis of our work has been to focus on the roles that epithelium, in the sinuses and upper airways, plays as both a mediator and regulator of immune and inflammatory responses. It is not our intention here to provide a comprehensive review of the literature in this area, but we will try to put our work in the context of the findings of others (Kato A and Schleimer RP, Curr Opin Immunol 2007;19:711-720; Schleimer RP and coworkers, J Allergy Clin Immunol 2007;120:1279-1284). In particular, we discuss the evidence that epithelial cell responses are altered in CRS, including those relevant to regulation of dendritic cells, T cells, B cells, and barrier function.

CD11b+ Myeloid Cells Are the Key Mediators of Th2 Cell Homing into the Airway in Allergic Inflammation

STAT6-mediated chemokine production in the lung is required for Th2 lymphocyte and eosinophil homing into the airways in allergic pulmonary inflammation, and thus is a potential therapeutic target in asthma. However, the critical cellular source of STAT6-mediated chemokine production has not been defined. In this study, we demonstrate that STAT6 in bone marrow-derived myeloid cells was sufficient for the production of CCL17, CCL22, CCL11, and CCL24 and for Th2 lymphocyte and eosinophil recruitment into the allergic airway. In contrast, STAT6 in airway-lining cells did not mediate chemokine production or support cellular recruitment. Selective depletion of CD11b+ myeloid cells in the lung identified these cells as the critical cellular source for the chemokines CCL17 and CCL22. These data reveal that CD11b+ myeloid cells in the lung help orchestrate the adaptive immune response in asthma, in part, through the production of STAT6-inducible chemokines and the recruitment of Th2 lymphocytes into the airway.

IL-4 Receptor Signaling in Clara Cells Is Required for Allergen-Induced Mucus Production

Excessive mucus production is an important pathological feature of asthma. The Th2 cytokines IL-4 and IL-13 have both been implicated in allergen-induced mucus production, inflammation, and airway hyperreactivity. Both of these cytokines use receptors that contain the IL-4Rα subunit, and these receptors are expressed on many cell types in the lung. It has been difficult to determine whether allergen-induced mucus production is strictly dependent on direct effects of IL-4 and IL-13 on epithelial cells or whether other independent mechanisms exist. To address this question, we used a cell type-specific inducible gene-targeting strategy to selectively disrupt the IL-4Rα gene in Clara cells, an airway epithelial cell population that gives rise to mucus-producing goblet cells. Clara cell-specific IL-4Rα-deficient mice and control mice developed similar elevations in serum IgE levels, airway inflammatory cell numbers, Th2 cytokine production, and airway reactivity following OVA sensitization and challenge. However, compared with control mice, Clara cell-specific IL-4Rα-deficient mice were nearly completely protected from allergen-induced mucus production. Because only IL-13 and IL-4 are thought to signal via IL-4Rα, we conclude that direct effects of IL-4 and/or IL-13 on Clara cells are required for allergen-induced mucus production in the airway epithelium.

The Epithelial Anion Transporter Pendrin Is Induced by Allergy and Rhinovirus Infection, Regulates Airway Surface Liquid, and Increases Airway Reactivity and Inflammation in an Asthma Model

Asthma exacerbations can be triggered by viral infections or allergens. The Th2 cytokines IL-13 and IL-4 are produced during allergic responses and cause increases in airway epithelial cell mucus and electrolyte and water secretion into the airway surface liquid (ASL). Since ASL dehydration can cause airway inflammation and obstruction, ion transporters could play a role in pathogenesis of asthma exacerbations. We previously reported that expression of the epithelial cell anion transporter pendrin is markedly increased in response to IL-13. Herein we show that pendrin plays a role in allergic airway disease and in regulation of ASL thickness. Pendrin-deficient mice had less allergen-induced airway hyperreactivity and inflammation than did control mice, although other aspects of the Th2 response were preserved. In cultures of IL-13-stimulated mouse tracheal epithelial cells, pendrin deficiency caused an increase in ASL thickness, suggesting that reductions in allergen-induced hyperreactivity and inflammation in pendrin-deficient mice result from improved ASL hydration. To determine whether pendrin might also play a role in virus-induced exacerbations of asthma, we measured pendrin mRNA expression in human subjects with naturally occurring common colds caused by rhinovirus and found a 4.9-fold increase in mean expression during colds. Studies of cultured human bronchial epithelial cells indicated that this increase could be explained by the combined effects of rhinovirus and IFN-γ, a Th1 cytokine induced during virus infection. We conclude that pendrin regulates ASL thickness and may be an important contributor to asthma exacerbations induced by viral infections or allergens.

12/15-Lipoxygenase deficiency protects mice from allergic airways inflammation and increases secretory IgA levels.

BACKGROUND Induction of 15-lipoxygenase-1 (15-LO-1) has been observed in the airways of subjects with asthma, although its physiologic role in the airways has remained largely undefined. OBJECTIVES We sought to test the hypothesis that the mouse 15-LO-1 ortholog 12/15-LO contributes to the development of allergic airways inflammation. METHODS Two models were used to evaluate wild-type and 12/15-LO-deficient mice. The systemic model involved intraperitoneal injections of allergen, and the mucosal model involved allergen exposures occurring exclusively in the airways. The systemic and mucosal-specific contributions of 12/15-LO to allergic sensitization and airways inflammation were determined by comparing the results obtained in the 2 models. RESULTS In the mucosal model 12/15-LO knockout mice were protected from the development of allergic sensitization and airways inflammation, as evidenced by circulating levels of allergen-specific IgE, IgG1, and IgG2a; the profile of inflammatory cells in bronchoalveolar lavage fluid; and the expression of cytokines and mediators in lung tissue. In the systemic model 12/15-LO knockout mice were not protected. This suggested the presence of a lung-restricted protective role for 12/15-LO deficiency that was potentially accounted for by increased activation of mucosal B cells and increased production of the known mucosal-specific protective mediator secretory IgA. CONCLUSIONS Induction of 15-LO-1 in asthma might contribute to allergic sensitization and airways inflammation, potentially by causing suppression of secretory IgA.

Dendritic cells and alveolar macrophages mediate IL-13–induced airway inflammation and chemokine production

BACKGROUND IL-13 in the airway induces pathologies that are highly characteristic of asthma, including mucus metaplasia, airway hyperreactivity (AHR), and airway inflammation. As such, it is important to identify the IL-13-responding cell types that mediate each of the above pathologies. For example, IL-13s effects on epithelium contribute to mucus metaplasia and AHR. IL-13s effects on smooth muscle also contribute to AHR. However, it has been difficult to identify the cell types that mediate IL-13-induced airway inflammation. OBJECTIVE We sought to determine which cell types mediate IL-13-induced airway inflammation. METHODS We treated the airways of mice with IL-13 alone or in combination with IFN-γ. We associated the inhibitory effect of IFN-γ on IL-13-induced airway inflammation and chemokine production with cell types in the lung that coexpress IL-13 and IFN-γ receptors. We then evaluated IL-13-induced responses in CD11c promoter-directed diphtheria toxin receptor-expressing mice that were depleted of both dendritic cells and alveolar macrophages and in CD11b promoter-directed diphtheria toxin receptor-expressing mice that were depleted of dendritic cells. RESULTS Dendritic cell and alveolar macrophage depletion protected mice from IL-13-induced airway inflammation and CCL11, CCL24, CCL22, and CCL17 chemokine production. Preferential depletion of dendritic cells protected mice from IL-13-induced airway inflammation and CCL22 and CCL17 chemokine production but not from IL-13-induced CCL11 and CCL24 chemokine production. In either case mice were not protected from IL-13-induced AHR and mucus metaplasia. CONCLUSIONS Pulmonary dendritic cells and alveolar macrophages mediate IL-13-induced airway inflammation and chemokine production.

Expression of IL-4 receptor α on smooth muscle cells is not necessary for development of experimental allergic asthma

BACKGROUND Airflow in the lungs of patients with allergic asthma is impaired by excessive mucus production and airway smooth muscle contractions. Elevated levels of the cytokines IL-4 and IL-13 are associated with this pathology. In vitro studies have suggested that IL-4 receptor alpha (IL-4Ralpha) signaling on smooth muscle cells is critical for airway inflammation and airway hyperresponsiveness. OBJECTIVE To define the contribution of IL-4 and IL-13 to the onset of asthmatic pathology, the role of their key receptor IL-4Ralpha in smooth muscle cells was examined in vivo. METHODS By using transgenic smooth muscle myosin heavy chain(cre)IL-4Ralpha(-/lox) mice deficient in IL-4Ralpha in smooth muscle cells, in vivo effects of impaired IL-4Ralpha signaling in smooth muscle cells on the outcome of asthmatic disease were investigated for the first time. Allergic asthma was introduced in mice by repeated sensitization with ovalbumin/aluminum hydroxide on days 0, 7, and 14, followed by intranasal allergen challenge on days 21 to 23. Mice were investigated for the presence of airway hyperresponsiveness, airway inflammation, allergen-specific antibody production, T(h)2-type cytokine responses, and lung pathology. RESULTS Airway hyperresponsiveness, airway inflammation, mucus production, T(h)2 cytokine production, and specific antibody responses were unaffected in smooth muscle myosin heavy chain(cre)IL-4Ralpha(-/lox) mice compared with control animals. CONCLUSION The impairment of IL-4Ralpha on smooth muscle cells had no effect on major etiologic markers of allergic asthma. These findings suggest that IL-4Ralpha responsiveness in airway smooth muscle cells during the early phase of allergic asthma is not, as suggested, necessary for the outcome of the disease.

12/15-lipoxygenase is an interleukin-13 and interferon-γ counterregulated-mediator of allergic airway inflammation.

Interleukin-13 and interferon-γ are important effectors of T-helper cells. Interleukin-13 increases expression of the arachidonic acid-metabolizing enzyme, 15-lipoxygenase-1, in a variety of cell types. 15-lipoxygenase-1 is dramatically elevated in the airways of subjects with asthma. Studies in animals indicate that 15-lipoxygenase-1 contributes to the development of allergic airway inflammation but is protective in some other forms of inflammation. We tested the hypothesis that the ability of interleukin-13 and interferon-γ to counterregulate allergic airway inflammation was potentially mediated by counterregulation of 12/15-lipoxygenase, the mouse ortholog of 15-lipoxygenase-1. The airways of mice were treated with interleukin-13 or interferon-γ one day prior to each of the four allergen exposures. Interleukin-13 augmented and interferon-γ inhibited allergic airway inflammation independently of systemic IgE and mucosal IgA responses but in association with counterregulation of 12/15-lipoxygenase. Interleukin-13 and interferon-γ counterregulate 12/15-lipoxygenase potentially contributing to the effects of these cytokines on allergic airway inflammation.