Regnase-1 degradation is crucial for IL-33- and IL-25-mediated ILC2 activation.

Group 2 innate lymphoid cells (ILC2s) are a critical innate source of type 2 cytokines in allergic inflammation. Although ILC2s are recognized as a critical cell population in the allergic inflammation, the regulatory mechanism(s) of ILC2s are less well understood. Here, we show that Regnase-1, an immune regulatory RNAse that degrades inflammatory mRNAs, negatively regulates ILC2 function and that IκB kinase (IKK) complex-mediated Regnase-1 degradation is essential for IL-33- and IL-25-induced ILC2 activation. ILC2s from Regnase-1AA/AA mice expressing a Regnase-1 S435A/S439A mutant resistant to IKK complex-mediated degradation accumulated Regnase-1 protein in response to IL-33 and IL-25. IL-33- and IL-25-stimulated Regnase-1AA/AA ILC2s showed reduced cell proliferation and type 2 cytokine (IL-5, IL-9, and IL-13) production and increased cell death. In addition, Il2ra and Il1rl1, but not Il5, Il9, or Il13, mRNAs were destabilized in IL-33-stimulated Regnase-1AA/AA ILC2s. In vivo, Regnase-1AA/AA mice showed attenuated acute type 2 pulmonary inflammation induced by the instillation of IL-33, IL-25, or papain. Furthermore, the expulsion of Nippostrongylus brasiliensis was significantly delayed in Regnase-1AA/AA mice. These results demonstrate that IKK complex-mediated Regnase-1 degradation is essential for ILC2-mediated type 2 responses both in vitro and in vivo. Therefore, controlling Regnase-1 degradation is a potential therapeutic target for ILC2-contributed allergic disorders.

Activation of group 2 innate lymphoid cells exacerbates and confers corticosteroid resistance to mouse nasal type 2 inflammation.

Both Th2 cells and group 2 innate lymphoid cells (ILC2s) contribute to allergic diseases. However, their exact role and relationship in nasal allergic disorders are unclear. In this study, we investigated the cooperation of Th2 cells and ILC2s in a mouse model of nasal allergic disorder. To differentially activate Th2 cells and/or ILC2s in nasal mucosa, mice were intra-nasally administered ovalbumin (OVA) antigen, papain, an ILC2-activator, or both for 2 weeks. Epithelial thickness and number of eosinophils in the nasal mucosa were evaluated at 24 h after the final challenge. Intra-nasal administration of OVA and papain preferentially activated Th2 cells and ILC2s, respectively, in the nose. Both OVA and papain increased the nasal epithelial thickness and number of eosinophils, and their coadministration significantly enhanced the symptoms. Although T-/B-cell-deficient mice showed severely decreased nasal symptoms induced by OVA or OVA-plus-papain, the mice still showed slight papain-induced nasal symptoms. In ILC2-deficient mice, OVA-plus-papain-induced nasal symptoms were suppressed to the same level as OVA-alone. Similarly, IL-33- and ST2-deficient mice showed decreased OVA-plus-papain-induced nasal symptoms. IL-5 induced eosinophilia only, but IL-13 contributed to both nasal epithelial thickening and eosinophilia induced by OVA-plus-papain. Dexamethasone ameliorated OVA-alone-induced nasal epithelial thickening. However, OVA-plus-papain-induced nasal epithelial thickening was only partially controlled by dexamethasone. These results demonstrate that IL-33/ST2-pathway-mediated ILC2 activation exacerbated Th2-cell-induced nasal inflammation by producing IL-13. Although Th2-cell-alone-induced nasal inflammation was controlled by corticosteroid treatment, the activation of ILC2s conferred treatment resistance. Therefore, ILC2s and their activators could be therapeutic targets for treatment-refractory nasal allergic disorders.

Allergen endotoxins induce T-cell-dependent and non-IgE-mediated nasal hypersensitivity in mice.

BACKGROUND: Allergen-mediated cross-linking of IgE on mast cells/basophils is a well-recognized trigger for type 1 allergic diseases such as allergic rhinitis (AR). However, allergens may not be the sole trigger for AR, and several allergic-like reactions are induced by non-IgE-mediated mechanisms. OBJECTIVE: We sought to describe a novel non-IgE-mediated, endotoxin-triggered nasal type-1-hypersensitivity-like reaction in mice. METHODS: To investigate whether endotoxin affects sneezing responses, mice were intraperitoneally immunized with ovalbumin (OVA), then nasally challenged with endotoxin-free or endotoxin-containing OVA. To investigate the role of T cells and mechanisms of the endotoxin-induced response, mice were adoptively transferred with in vitro-differentiated OVA-specific TH2 cells, then nasally challenged with endotoxin-free or endotoxin-containing OVA. RESULTS: Endotoxin-containing, but not endotoxin-free, OVA elicited sneezing responses in mice independent from IgE-mediated signaling. OVA-specific TH2 cell adoptive transfer to mice demonstrated that local activation of antigen-specific TH2 cells was required for the response. The Toll-like receptor 4-myeloid differentiation factor 88 signaling pathway was indispensable for endotoxin-containing OVA-elicited rhinitis. In addition, LPS directly triggered sneezing responses in OVA-specific TH2-transferred and nasally endotoxin-free OVA-primed mice. Although antihistamines suppressed sneezing responses, mast-cell/basophil-depleted mice had normal sneezing responses to endotoxin-containing OVA. Clodronate treatment abrogated endotoxin-containing OVA-elicited rhinitis, suggesting the involvement of monocytes/macrophages in this response. CONCLUSIONS: Antigen-specific nasal activation of CD4+ T cells followed by endotoxin exposure induces mast cell/basophil-independent histamine release in the nose that elicits sneezing responses. Thus, environmental or nasal residential bacteria may exacerbate AR symptoms. In addition, this novel phenomenon might explain currently unknown mechanisms in allergic(-like) disorders.

Murine allergic rhinitis and nasal Th2 activation are mediated via TSLP- and IL-33-signaling pathways.

Thymic stromal lymphopoietin (TSLP) and IL-33 are epithelium-derived proallergic cytokines that contribute to allergic diseases. Although the involvement of TSLP in allergic rhinitis (AR) is suggested, the exact role of TSLP in AR is poorly understood. Furthermore, the relative contribution of TSLP and IL-33 in nasal allergic responses has not been described. In this study, we examined the roles of TSLP and IL-33 in AR by analyzing acute and chronic AR models. Acute AR mice were intraperitoneally immunized with ragweed, then intranasally challenged with ragweed pollen for four consecutive days. Chronic AR mice were nasally administrated ragweed pollen on consecutive days for 3 weeks. In both models, TSLP receptor (TSLPR)-deficient mice showed defective sneezing responses and reduced serum ragweed-specific IgE levels compared with wild-type (WT) mice. Analyses of bone-marrow chimeric mice demonstrated that hematopoietic cells were responsible for defective sneezing in TSLPR-deficient mice. In addition, FcεRI(+)-cell-specific TSLPR-deficient mice showed partial but significant reduction in sneezing responses. Of note, Th2 activation and nasal eosinophilia were comparable between WT and TSLPR-deficient mice. ST2- and IL-33-deficient mice showed defective Th2 activation and nasal eosinophilia to acute, but not chronic, ragweed exposure. TSLPR and ST2 double-deficient mice showed defective Th2 activation and nasal eosinophilia even after chronic ragweed exposure. These results demonstrate that TSLPR signaling is critical for the early phase response of AR by controlling the IgE-mast-cell/basophil pathway. The IL-33/ST2 pathway is central to nasal Th2 activation during acute allergen exposure, but both TSLPR and ST2 contribute to Th2 responses in chronically allergen-exposed mice.

Proallergic cytokines and group 2 innate lymphoid cells in allergic nasal diseases.

Recent advances in our understanding of proallergic cytokines and group 2 innate lymphoid cells (ILC2s) indicate their critical roles in type 2 immunity-mediated disorders. Proallergic cytokines, interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin, are released from epithelial cells in inflamed tissues and drive type 2 inflammation by acting on innate and acquired immune systems. ILC2s are an innate immune population that responds to proallergic cytokines by producing type 2 cytokines. In line with allergic disorders in the lung, skin, and intestine, emerging evidence suggests the involvement of proallergic cytokines and ILC2s in allergic nasal diseases such as chronic rhinosinusitis with polyps (CRSwNP), allergic fungal rhinosinusitis, and allergic rhinitis (AR). In CRSwNP patients, both proallergic cytokine levels and ILC2s frequency are increased in the nasal mucosa. Increased proallergic cytokine levels correlate with poorer disease outcomes in CRSwNP. Levels of nasal proallergic cytokines are also elevated in AR patients. In addition, animal studies demonstrate that cytokines are essential for the development of AR. It is becoming clear that the proallergic cytokine/ILC2s axis participates in allergic diseases by multiple mechanisms dependent upon the inflammatory context. Thus, a thorough understanding of these cytokines and ILC2s including their tissue- and disease-specific roles is essential for targeting the pathways to achieve therapeutic applications.

Nasal sensitization with ragweed pollen induces local-allergic-rhinitis-like symptoms in mice.

Recently, the concept of local allergic rhinitis (LAR) was established, namely rhinitis symptoms with local IgE production and negative serum antigen-specific IgE. However, the natural course of LAR development and the disease pathogenesis is poorly understood. This study investigated the pathophysiology of mice with allergic rhinitis that initially sensitized with ragweed pollen through the nasal route. Mice were nasally administrated ragweed pollen over consecutive days without prior systemic immunization of the allergen. Serial nasal sensitization of ragweed pollen induced an allergen-specific increase in sneezing, eosinophilic infiltration, and the production of local IgE by day 7, but serum antigen-specific IgE was not detected. Th2 cells accumulated in nose and cervical lymph nodes as early as day 3. These symptoms are characteristic of human LAR. Continual nasal exposure of ragweed pollen for 3 weeks resulted in the onset of classical AR with systemic atopy and adversely affected lung inflammation when the allergen was instilled into the lung. Fcer1a(-/-) mice were defective in sneezing but developed normal eosinophilic infiltration. Contrary, Rag2(-/-) mice were defective in both sneezing and eosinophilic infiltration, suggesting that T cells play a central role in the pathogenesis of the disease. These observations demonstrate nasal allergen sensitization to non-atopic individuals can induce LAR. Because local Th2 cell accumulation is the first sign and Th2 cells have a central role in the disease, a T-cell-based approach may aid the diagnosis and treatment of LAR.