While type 2 immune responses to environmental antigens are thought to play pivotal roles in asthma and allergic airway diseases, the immunological mechanisms that initiate the responses are largely unknown. Many allergens have biologic activities, including enzymatic activities and abilities to engage innate pattern-recognition receptors such as TLR4. Here we report that IL-33 and thymic stromal lymphopoietin (TSLP) were produced quickly in the lungs of naïve mice exposed to cysteine proteases, such as bromelain and papain, as a model for allergens. IL-33 and TSLP sensitized naïve animals to an innocuous airway antigen OVA, which resulted in production of type 2 cytokines and IgE antibody and eosinophilic airway inflammation when mice were challenged with the same antigen. Importantly, upon exposure to proteases, uric acid (UA) was rapidly released into the airway lumen, and removal of this endogenous UA by uricase prevented type 2 immune responses. UA promoted secretion of IL-33 by airway epithelial cells in vitro, and administration of UA into the airways of naïve animals induced extracellular release of IL-33, followed by both innate and adaptive type 2 immune responses in vivo. Finally, a potent UA synthesis inhibitor, febuxostat, mitigated asthma phenotypes that were caused by repeated exposure to natural airborne allergens. These findings provide mechanistic insights into the development of type 2 immunity to airborne allergens and recognize airway UA as a key player that regulates the process in respiratory mucosa.

The results of this study showed that there is increased activation of the coagulation system in the nasal mucosa of CRS patients and that thrombin may play a role in nasal polyp formation by stimulating VEGF production from airway epithelial cells.

Epithelial cells at mucosal surfaces are integral components of innate and adaptive immunity. IL-25 is reportedly produced by epithelial cells and likely plays vital roles in regulating type-2 immune responses. However, little is known regarding the mechanisms that control production and extracellular releases of IL-25. We hypothesized that proteases from the multiple allergens may induce IL-25 production in airway epithelial cells. In this study, we found that IL-25 is constitutively produced and detectable in cytoplasm of resting normal human bronchial epithelial (NHBE) cells. When exposed to airborne allergens such as house dust mite (HDM), stored IL-25 was released rapidly to the extracellular space. IL-25 release was not accompanied by cell death, suggesting involvement of active secretory mechanism(s). HDM also enhanced IL-25 mRNA transcription, which was dependent on their protease activities. Furthermore, activation of NHBE cells with authentic proteases, such as trypsin and papain, or with a peptide agonist for protease-activated receptor 2 was sufficient to enhance IL-25 mRNA transcription and protein. Protease-driven increase in mRNA transcription and allergen-driven extracellular release of IL-25 protein was also observed in primary nasal epithelial cells from healthy individuals. These findings suggest that IL-25 production by airway epithelial cells is regulated by the transcription and protein release levels and that allergen proteases likely play pivotal roles in both biological processes.Keywords: airway epithelial cells; allergen; PAR-2; protease; In addition to being a physical barrier between the airway and the immune system, epithelial cells are now thought to play vital roles in innate and adaptive immune responses (1). Epithelial cells produce chemokines and cytokines that recruit and enhance survival of dendritic cells and interact directly with dendritic cells through membrane-associated chemokines (2-4). Epithelial cells also express soluble and cell-surface molecules that regulate recruitment, differentiation, proliferation, and function of T and B cells (2, 5). In particular, newly discovered epithelial-derived cytokines, such as thymic stromal lymphopoietin, IL-25, and IL-33, may play key roles in the development and regulation of T helper 2 (Th2) cytokine-dependent immune responses (6).There is increasing evidence to suggest the roles for IL-25 in the type-2 immune response and in the pathogenesis of asthma and allergic diseases. IL-25 (also known as IL-17E) is a member of a family of six structurally related but functionally distinct proteins. IL-17A and IL-17F appear to play important roles in neutrophilic inflammation and autoimmunity. In contrast, IL-25 is exceptional in promoting eosinophilic inflammation and a type-2 immune response (7). This has been well demonstrated in mouse models: exogenous administration of IL-25 (8, 9) or transgenic expression (10, 11) induces Th2-type inflammation. IL-25 is increased in animal bronchial challenge models (12), and its inhibition reduce...

Background: Group 2 innate lymphoid cells (ILC2s) play important roles in allergic inflammation. However, their roles in the pathophysiology of allergic rhinitis (AR) are poorly understood. Objective: Prevalence of ILC2s in the inferior nasal turbinate (INT) tissues and the activating mechanisms of ILC2s were examined in patients with house dust mite (HDM)-induced AR. Methods: Eighteen patients with HDM-induced AR and 13 control subjects were recruited. Fresh INT tissues and peripheral blood mononuclear cells (PBMCs) were analysed using flow cytometry. Nasal lavage fluids (NLF) were collected at 10 minutes after the nasal provocation test (NPT) with HDM disc, and released mediators were measured by ELISA. Sorted ILC2s were cultured and stimulated with mediators associated with AR. Results: The prevalence of ILC2s was significantly increased in nasal mucosa of patients with HDM-induced AR, and it was positively correlated with the number of infiltrating eosinophils. ILC2s in the INT tissues expressed a prostaglandin D 2 (PGD 2 )receptor, chemoattractant receptor-homologous molecule-expressed TH2 cells (CRTH2) and a cysteinyl leukotriene (cysLTs) receptor, CysLT1. After NPT, the number of eosinophils and concentrations of PGD 2 and cysLTs were significantly increased in the NLF from AR patients. PGD 2 and cysLTs significantly induced IL-5 production from cultured PBMC-derived ILC2s dose-dependently. PGD 2 -induced and cysLTs-induced productions of IL-5 and IL-13 from ILC2s were completely inhibited by ramatroban, a dual CRTH2 and thromboxane receptor antagonist, and montelukast, a CysLT1 antagonist, respectively.Conclusions: PGD 2 -CRTH2 and cysLTs-CysLT1 axes may activate tissue-resident ILC2s to produce Th2 cytokines, IL-5 and IL-13, leading to the development of allergic inflammation in AR.

The results of this study indicate that eosinophil-epithelial cell interactions are important in the pathogenesis of tissue remodeling of eosinophil-predominant airway inflammation such as occurs in nasal polyposis and bronchial asthma.