An Interleukin-33-Mast Cell-Interleukin-2 Axis Suppresses Papain-Induced Allergic Inflammation by Promoting Regulatory T Cell Numbers.

House dust mite-derived proteases contribute to allergic disorders in part by disrupting epithelial barrier function. Interleukin-33 (IL-33), produced by lung cells after exposure to protease allergens, can induce innate-type airway eosinophilia by activating natural helper (NH) cells, a member of group 2 innate lymphoid cells (ILC2), to secrete Th2 type-cytokines. Because IL-33 also can induce mast cells (MCs) to secrete Th2 type-cytokines, MCs are thought to cooperate with NH cells in enhancing protease or IL-33-mediated innate-type airway eosinophilia. However, we found that MC-deficient Kit(W-sh/W-sh) mice exhibited exacerbated protease-induced lung inflammation associated with reduced numbers of regulatory T (Treg) cells. Moreover, IL-2 produced by IL-33-stimulated MCs promoted expansion of numbers of Treg cells, thereby suppressing development of papain- or IL-33-induced airway eosinophilia. We have thus identified a unique anti-inflammatory pathway that can limit induction of innate-type allergic airway inflammation mediated by NH cells.

IL-25 contributes to development of chronic contact dermatitis in C57BL/6 mice, but not BALB/c mice.

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by type 2 immune responses. Interleukin-25 (IL-25) is produced predominantly by epithelial cells. It can activate Th2 cells to produce type 2 cytokines such as IL-4, IL-5 and IL-13, contributing to host defense against nematodes. However, excessive/inappropriate production of IL-25 is considered to be involved in development of type 2 cytokine-associated allergic disorders such as asthma. On the other hand, the contribution of IL-25 to the pathogenesis of AD remains poorly understood. In the present study, we found that expression of Il25 mRNA was significantly increased in the skin of mice during oxazolone-induced chronic contact hypersensitivity (CHS), which is a mouse model of human AD. In addition, development of oxazolone-induced chronic CHS was significantly reduced in IL-25-deficient (Il25-/-) mice compared with wild-type mice on the C57BL/6, but not BALB/c, background, although IL-25 was not essential for IL-4 production by hapten-specific T cells. Therefore, IL-25 is crucial for development of chronic CHS, although that is partly dependent on the genetic background of the mice.

Skin Treatment with Detergent Induces Dermatitis with H1-Antihistamine-Refractory Itch and Upregulates IL-4 and Th17/Th22 Cytokine Gene Expression in C57BL/6 Mice.

INTRODUCTION: Repeated skin contact to detergents causes chronic irritant contact dermatitis (ICD) associated with itch sensation and eczema. However, the mechanisms of detergent-induced ICD are poorly understood. Here, we established a new murine model of detergent-induced ICD with H1-antihistamine-refractory itch. METHODS: Ear skin of wild-type and mast cell-deficient mice on the C57BL/6 genetic background was treated with a detergent, sodium dodecyl/lauryl sulfate (SDS), daily for approximately 2 weeks with or without administration of an H1-antihistamine, fexofenadine. Skin inflammation, barrier dysfunction, and itching were analyzed. Quantitative PCR for earlobe gene expression and flow cytometry analysis for draining lymph node cells were conducted. RESULTS: SDS treatment induced skin inflammation with ear swelling, increased transepidermal water loss, and hind-paw scratching behaviors in the wild-type and mast cell-deficient mice. The peak value of scratching bouts was retained for at least 48 h after the last SDS treatment. H1-antihistamine administration showed no or little reduction in the responses. SDS treatment upregulated gene expression for a Th2 cytokine IL-4 and Th17/Th22 cytokines, IL-17A, IL-17F, and IL-22, and increased cell numbers in draining lymph nodes of CD4+ T, CD8+ T, and γδT cells with enhanced expression of GATA3, RORγt, T-bet, or FOXP3 compared with untreated mice. CONCLUSIONS: The present study showed that SDS treatment of ear skin in C57BL/6 mice induces mast cell-independent skin inflammation with H1-antihistamine-refractory itch and suggested a possible Th cytokine- and/or lymphocyte-mediated regulation of the model. The model would be useful for elucidation of mechanisms for inflammation with H1-antihistamine-refractory itch in detergent-induced ICD.

Critical role of IL-33, but not IL-25 or TSLP, in silica crystal-mediated exacerbation of allergic airway eosinophilia.

Silica crystals (silica), which are a major mineral component of volcanic ash and desert dust, contribute to the pathogenesis of pulmonary disorders such as asthma and fibrosis. Although administration of silica or sand dust to rodents exacerbates development of ovalbumin-induced or house dust mite-induced asthma-like airway inflammation, the detailed mechanisms remain unclear. Here, using murine models, we found that silica can induce IL-33 expression in pulmonary epithelial cells. IL-33, but not IL-25 or TSLP, and type 2 cytokines such as IL-5 and IL-13 were critically involved in silica's exacerbation of OVA-induced airway eosinophilia in mice. Innate lymphoid cells (ILCs), but not T, B or NKT cells, were also involved in the setting. Moreover, a scavenger receptor that recognized silica was important for silica's exacerbating effect. These observations suggest that IL-33 induced in epithelial cells by silica activates ILCs to produce IL-5 and/or IL-13, contributing to silica's exacerbation of OVA-induced airway eosinophilia in mice. Our findings provide new insight into the underlying mechanisms of exacerbation of pulmonary disorders such as asthma following inhalation of silica-containing materials such as volcanic ash and desert dust.

IL-25 enhances TH17 cell-mediated contact dermatitis by promoting IL-1ß production by dermal dendritic cells.

BACKGROUND: In addition to thymic stromal lymphopoietin and IL-33, IL-25 is known to induce TH2 cytokine production by various cell types, including TH2 cells, TH9 cells, invariant natural killer T cells, and group 2 innate lymphoid cells, involved in TH2-type immune responses. Because both TH2-type and TH17-type cells/cytokines are crucial for contact hypersensitivity (CHS), IL-25 can contribute to this by enhancing TH2-type immune responses. However, the precise role of IL-25 in the pathogenesis of fluorescein isothiocyanate-induced CHS is poorly understood. OBJECTIVE: We investigated the contribution of IL-25 to CHS using Il25-/- mice. METHODS: CHS was evaluated by means of measurement of ear skin thickness in mice after fluorescein isothiocyanate painting. Skin dendritic cell (DC) migration, hapten-specific TH cell differentiation, and detection of IL-1ß-producing cells were determined by using flow cytometry, ELISA, and immunohistochemistry, respectively. RESULTS: In contrast to thymic stromal lymphopoietin, we found that IL-25 was not essential for skin DC migration or hapten-specific TH cell differentiation in the sensitization phase of CHS. Unexpectedly, mast cell- and non-immune cell-derived IL-25 was important for hapten-specific TH17 cell-mediated rather than TH2 cell-mediated inflammation in the elicitation phase of CHS by enhancing TH17-related, but not TH2-related, cytokines in the skin. In particular, IL-1ß produced by dermal DCs in response to IL-25 was crucial for hapten-specific TH17 cell activation, contributing to induction of local inflammation in the elicitation phase of CHS. CONCLUSION: Our results identify a novel IL-25 inflammatory pathway involved in induction of TH17 cell-mediated, but not TH2 cell-mediated, CHS. IL-25 neutralization can be a potential approach for treatment of CHS.

Subcutaneous Allergic Sensitization to Protease Allergen Is Dependent on Mast Cells but Not IL-33: Distinct Mechanisms between Subcutaneous and Intranasal Routes.

Protease activity of papain, a plant-derived occupational allergen homologous to mite major allergens, is essential to IgE/IgG1 production and lung eosinophilia induced by intranasal papain administration in mice, and IL-33 contributes to these responses. In this work, we investigate skin and Ab responses induced by s.c. papain administration into ear lobes and responses induced by subsequent airway challenge with papain. Subcutaneous papain injection induced swelling associated with increased epidermal thickness, dermal inflammation, serum IgE/IgG1 responses, and Th2 cytokine production in draining lymph node cells restimulated in vitro. These responses were markedly less upon s.c. administration of protease inhibitor-treated papain. Results obtained by using mast cell-deficient mice and reconstitution of tissue mast cells suggested the contribution of mast cells to papain-specific IgE/IgG1 responses and eosinophil infiltration. The responses were equivalent between wild-type and IL-33(-/-) mice. After the subsequent airway challenge, the s.c. presensitized wild-type mice showed more severe lung eosinophilia than those without the presensitization. The presensitized IL-33(-/-) mice showed modest lung eosinophilia, which was absent without the presensitization, but its severity and IgE boost by the airway challenge were markedly less than the presensitized wild-type mice, in which protease activity of inhaled papain contributed to the responses. The results suggest that mechanisms for the protease-dependent sensitization differ between skin and airway and that cooperation of mast cell-dependent, IL-33-independent initial sensitization via skin and protease-induced, IL-33-mediated mechanism in re-exposure via airway to protease allergens maximizes the magnitude of the transition from skin inflammation to asthma in natural history of progression of allergic diseases.

IL-33-mediated innate response and adaptive immune cells contribute to maximum responses of protease allergen-induced allergic airway inflammation.

How the innate and adaptive immune systems cooperate in the natural history of allergic diseases has been largely unknown. Plant-derived allergen, papain, and mite allergens, Der f 1 and Der p 1, belong to the same family of cysteine proteases. We examined the role of protease allergens in the induction of Ab production and airway inflammation after repeated intranasal administration without adjuvants and that in basophil/mast cell stimulation in vitro. Papain induced papain-specific IgE/IgG1 and lung eosinophilia. Der f 1 induced Der f 1-specific IgG1 and eosinophilia. Although papain-, Der f 1-, and Der p 1-stimulated basophils expressed allergy-inducing cytokines, including IL-4 in vitro, basophil-depleting Ab and mast cell deficiency did not suppress the papain-induced in vivo responses. Protease inhibitor-treated allergens and a catalytic site mutant did not induce the responses. These results indicate that protease activity is essential to Ab production and eosinophilia in vivo and basophil activation in vitro. IL-33-deficient mice lacked eosinophilia and had reduced papain-specific IgE/IgG1. Coadministration of OVA with papain induced OVA-specific IgE/IgG1, which was reduced in IL-33-deficient mice. We demonstrated IL-33 release, subsequent IL-33-dependent IL-5/IL-13 release, and activation of T1/ST2-expressing lineage(-)CD25(+)CD44(+) innate lymphoid cells in the lung after papain inhalation, suggesting the contribution of the IL-33-type 2 innate lymphoid cell-IL-5/IL-13 axis to the papain-induced airway eosinophilia. Rag2-deficient mice, which lack adaptive immune cells, showed significant, but less severe, eosinophilia. Collectively, these results suggest cooperation of adaptive immune cells and IL-33-responsive innate cells in protease-dependent allergic airway inflammation.

Periostin contributes to epidermal hyperplasia in psoriasis common to atopic dermatitis.

BACKGROUND: Epidermal hyperplasia is a histological hallmark observed in both atopic dermatitis (AD) and psoriasis, although the clinical features and the underlying immunological disorders of these diseases are different. We previously showed that periostin, a matricellular protein, plays a critical role in epidermal hyperplasia in AD, using a mouse model and a 3-dimensional organotypic coculture system. In this study, we explore the hypothesis that periostin is involved in epidermal hyperplasia in psoriasis. METHODS: To examine expression of periostin in psoriasis patients, we performed immunohistochemical analysis on skin biopsies from six such patients. To investigate periostin's role in the pathogenesis of psoriasis, we evaluated periostin-deficient mice in a psoriasis mouse model induced by topical treatment with imiquimod (IMQ). RESULTS: Periostin was substantially expressed in the dermis of all investigated psoriasis patients. Epidermal hyperplasia induced by IMQ treatment was impaired in periostin-deficient mice, along with decreased skin swelling. However, upon treatment with IMQ, periostin deficiency did not alter infiltration of inflammatory cells such as neutrophils; production of IL-17, -22, or -23; or induction/expansion of IL-17- and IL-22-producing group 3 innate lymphoid cells. CONCLUSIONS: Periostin plays an important role during epidermal hyperplasia in IMQ-induced skin inflammation, independently of the IL-23-IL-17/IL-22 axis. Periostin appears to be a mediator for epidermal hyperplasia that is common to AD and psoriasis.

Potential role of myeloid cell/eosinophil-derived IL-17 in LPS-induced endotoxin shock.

IL-17RA is a shared receptor subunit for several cytokines of the IL-17 family, including IL-17A, IL-17C, IL-17E (also called IL-25) and IL-17F. It has been shown that mice deficient in IL-17RA are more susceptible to sepsis than wild-type mice, suggesting that IL-17RA is important for host defense against sepsis. However, it is unclear which ligands for IL-17RA, such as IL-17A, IL-17C, IL-17E/IL-25 and/or IL-17F, are involved in the pathogenesis of sepsis. Therefore, we examined IL-17A, IL-17E/IL-25 and IL-17F for possible involvement in LPS-induced endotoxin shock. IL-17A-deficient mice, but not IL-25- or IL-17F-deficient mice, were resistant to LPS-induced endotoxin shock, as compared with wild-type mice. Nevertheless, studies using IL-6-deficient, IL-21Rα-deficient and Rag-2-deficient mice, revealed that neither IL-6 and IL-21, both of which are important for Th17 cell differentiation, nor Th17 cells were essential for the development of LPS-induced endotoxin shock, suggesting that IL-17A-producing cells other than Th17 cells were important in the setting. In this connection, IL-17A was produced by macrophages, DCs and eosinophils after LPS injection. Taken together, these findings indicate that IL-17A, but not IL-17F or IL-25, is crucial for LPS-induced endotoxin shock. In addition, macrophages, DCs and eosinophils, but not Th17 cells or γδ T cells, may be sources of IL-17A during LPS-induced endotoxin shock.

Epithelial cell-derived IL-25, but not Th17 cell-derived IL-17 or IL-17F, is crucial for murine asthma.

IL-17A, IL-17F, and IL-25 are ligands for IL-17RA. In the current study, we demonstrated that IL-25-deficient mice-but not IL-17A-, IL-17F-, IL-17A/F-, IL-23p19-, or retinoic acid-related orphan receptor (ROR)-γt-deficient mice-showed significant suppression of 1) the number of eosinophils and the levels of proinflammatory mediators in bronchoalveolar lavage fluids, 2) airway hyperresponsiveness to methacholine, and 3) OVA-specific IgG1 and IgE levels in the serum during OVA-induced Th2-type/eosinophilic airway inflammation. The IL-25 deficiency did not affect lung dendritic cell migration or Ag-specific memory-Th2 cell expansion during Ag sensitization. Adoptive transfer of T cells, mast cells, or bone marrow cells from IL-25-deficient mice revealed that induction of Th2-type/eosinophilic airway inflammation was dependent on activation of lung epithelial cells and eosinophils by IL-25 produced by airway structural cells such as epithelial cells but not by such hematopoietic stem-cell-origin immune cells as T cells and mast cells. Therefore, airway structural cell-derived IL-25-rather than Th17 cell-derived IL-17A and IL-17F-is responsible for induction of local inflammation by promoting activation of lung epithelial cells and eosinophils in the elicitation phase of Th2-type/eosinophilic airway inflammation. It is not required for Ag-specific Th2 cell differentiation in the sensitization phase.

Measurement of human skin moisture via high-frequency spectroscopy.

High-frequency spectroscopy (HFS) is an analytical method that is sensitive to slight changes in the dielectric properties of materials. Since water has high permittivity, HFS can be used to detect changes in water content in materials. In this study, we employed HFS to measure human skin moisture during a water sorption-desorption test. Skin without any treatment showed a resonance peak at approximately 1150 MHz. Furthermore, the peak shifted to lower frequency immediately after the application of water to the skin and gradually returned to its original frequency as time progressed. The resonance frequency obtained via least-squares fitting showed that the applied water remained in the skin after 240 s from the beginning of the measurement. These results illustrated that HFS measurements can monitor the progression of decreasing moisture content in human skin during a water sorption-desorption test.

ST2 requires Th2-, but not Th17-, type airway inflammation in epicutaneously antigen- sensitized mice.

BACKGROUND: IL-33 is known to induce Th2-type cytokine production by various types of cells through its receptors, ST2 and IL-1RAcP. Polymorphism in the ST2 and/or IL-33 genes was found in patients with atopic dermatitis and asthma, implying that the IL-33/ST2 pathway is closely associated with susceptibility to these diseases. Exposure to allergens through damaged skin is suspected to be a trigger for allergen sensitization, resulting in development of such allergic disorders as asthma and atopic dermatitis. METHODS: To elucidate the role(s) of the IL-33/ST2 pathway in asthma in individuals who had been epicutaneously sensitized to an antigen, wild-type and ST2-/- mice were epicutaneously sensitized with ovalbumin (OVA) and then were intranasally challenged with OVA. The degree of airway inflammation, the number of leukocytes and the activities of myeloperoxidase (MPO) and eosinophil peroxidase (EPO) in bronchoalveolar lavage fluids (BALFs), The levels of cytokines and chemokines in lungs and OVA-specific IgE levels in sera were determined by histological analysis, a hemocytometer, colorimetric assay, quantitative PCR or ELISA, respectively. RESULTS: The number of eosinophils in BALFs, the levels of Th2 cytokines and chemoattractants in the lungs and OVA-specific IgE in sera from ST2-/- mice were significantly reduced compared with wild-type mice. Although the number of neutrophils in BALFs and the pulmonary levels of IL-17 were comparable in both mice, the levels of MPO activity in BALFs and neutrophil chemoattractants in the lung were reduced in ST2-/- mice. CONCLUSIONS: The IL-33/ST2 pathway is crucial for Th2-cytokine-mediated eosinophilic, rather than Th17-cytokine-mediated neutrophilic, airway inflammation in mice that had been epicutaneously sensitized with antigens and then challenged with antigen.

Interleukin-33 and thymic stromal lymphopoietin, but not interleukin-25, are crucial for development of airway eosinophilia induced by chitin.

Exposure to various antigens derived from house dust mites (HDM) is considered to be a risk factor for development of certain allergic diseases such as atopic asthma, atopic dermatitis, rhinitis and conjunctivitis. Chitin is an insoluble polysaccharide (ß-(1-4)-poly-N-acetyl-D-glucosamine) and a major component in the outer shell of HDMs. Mice exposed to chitin develop asthma-like airway eosinophilia. On the other hand, several lines of evidence show that the effects of chitin on immune responses are highly dependent on the size of chitin particles. In the present study, we show that chitin induced production of IL-33 and TSLP by alveolar and bronchial epithelial cells, respectively, in mice. IL-25, IL-33 and TSLP were reported to be important for group 2 innate lymphoid cell (ILC2)-, but not Th2 cell-, dependent airway eosinophilia in a certain model using chitin beads. Here, we show that-in our murine models-epithelial cell-derived IL-33 and TSLP, but not IL-25, were crucial for activation of resident lung Th2 cells as well as group 2 innate lymphoid cells (ILC2s) to produce IL-5, resulting in development of chitin-induced airway eosinophilia. Our findings provide further insight into the underlying mechanisms of development of HDM-mediated allergic disorders.

IL-25 exacerbates autoimmune aortitis in IL-1 receptor antagonist-deficient mice.

IL-25, a member of the IL-17 family of cytokines, is known to enhance type 2 immune responses, but suppress type 3 (IL-17A)-mediated immune responses. Mice deficient in IL-1 receptor antagonist (Il1rn-/- mice) have excessive IL-1 signaling, resulting in spontaneous development of IL-1-, TNF- and IL-17A-dependent aortitis. We found that expression of II25 mRNA was increased in the aortae of Il1rn-/- mice, suggesting that IL-25 may suppress development of IL-1-, TNF- and IL-17A-dependent aortitis in Il1rn-/- mice by inhibiting type 3-mediated immune responses. However, we unexpectedly found that Il25-/-Il1rn-/- mice showed attenuated development of aortitis, accompanied by reduced accumulation of inflammatory cells such as dendritic cells, macrophages and neutrophils and reduced mRNA expression of Il17a and Tnfa-but not Il4 or Il13-in local lesions compared with Il1rn-/- mice. Tissue-, but not immune cell-, derived IL-25 was crucial for development of aortitis. IL-25 enhanced IL-1ß and TNF production by IL-25 receptor-expressing dendritic cells and macrophages, respectively, at inflammatory sites of aortae of Il1rn-/- mice, contributing to exacerbation of development of IL-1-, TNF- and IL-17A-dependent aortitis in those mice. Our findings suggest that neutralization of IL-25 may be a potential therapeutic target for aortitis.

Phenotypic differences between Th1 and Th17 cells and negative regulation of Th1 cell differentiation by IL-17.

Recent evidence from several groups indicates that IL-17-producing Th17 cells, rather than, as once was thought, IFN-gamma-producing Th1 cells, can represent the key effector cells in the induction/development of several autoimmune and allergic disorders. Although Th17 cells exhibit certain phenotypic and developmental differences from Th1 cells, the extent of the differences between these two T cell subsets is still not fully understood. We found that the expression profile of cell surface molecules on Th17 cells has more similarities to that of Th1 cells than Th2 cells. However, although certain Th1-lineage markers [i.e., IL-18 receptor alpha, CXCR3, and T cell Ig domain, mucin-like domain-3 (TIM-3)], but not Th2-lineage markers (i.e., T1/ST2, TIM-1, and TIM-2), were expressed on Th17 cells, the intensity of expression was different between Th17 and Th1 cells. Moreover, the expression of CTLA-1, ICOS, programmed death ligand 1, CD153, Fas, and TNF-related activation-induced cytokine was greater on Th17 cells than on Th1 cells. We found that IL-23 or IL-17 can suppress Th1 cell differentiation in the presence of exogenous IL-12 in vitro. We also confirmed that IL-12 or IFN-gamma can negatively regulate Th17 cell differentiation. However, these cytokines could not modulate such effects on T cell differentiation in the absence of APC.

IL-33 induces IL-13 production by mouse mast cells independently of IgE-FcepsilonRI signals.

The IL-1-related molecules, IL-1 and IL-18, can promote Th2 cytokine production by IgE/antigen-FcepsilonRI-stimulated mouse mast cells. Another IL-1-related molecule, IL-33, was identified recently as a ligand for T1/ST2. Although mouse mast cells constitutively express ST2, the effects of IL-33 on mast cell function are poorly understood. We found that IL-33, but not IL-1beta or IL-18, induced IL-13 and IL-6 production by mouse bone marrow-derived, cultured mast cells (BMCMCs) independently of IgE. In BMCMCs incubated with the potently cytokinergic SPE-7 IgE without specific antigen, IL-33, IL-1beta, and IL-18 each promoted IL-13 and IL-6 production, but the effects of IL-33 were more potent than those of IL-1beta or IL-18. IL-33 promoted cytokine production via a MyD88-dependent but Toll/IL-1R domain-containing adaptor-inducing IFN-beta-independent pathway. By contrast, IL-33 neither induced nor enhanced mast cell degranulation. At 200 ng/ml, IL-33 prolonged mast cell survival in the absence of IgE and impaired survival in the presence of SPE-7 IgE, whereas at 100 ng/ml, IL-33 had no effect on mast cell survival in the absence of IgE and reduced mast cell survival in the presence of IgE. These observations suggest potential roles for IL-33 in mast cell- and Th2 cytokine-associated immune responses and disorders.

Chitin promotes antigen-specific Th2 cell-mediated murine asthma through induction of IL-33-mediated IL-1ß production by DCs.

Chitin, which is a major component of house dust mites (HDM), fungi, crustaceans, etc., can activate immune cells, suggesting that it contributes to development of allergic disorders such as asthma. Although the pathophysiological sensitization route of asthmatic patients to allergens is considered via the respiratory tract, the roles of intranasally-administered chitin in development of asthma remain unclear. After ovalbumin (OVA) challenge, development of airway inflammation was profoundly exacerbated in mice sensitized with OVA in the presence of chitin. The exacerbation was dependent on IL-33, but not IL-25, thymic stromal lymphopoietin or IL-17A. Chitin enhanced IL-33-dependent IL-1ß production by dendritic cells (DCs). Furthermore, chitin- and IL-33-stimulated DC-derived IL-1ß promoted OVA-specific Th2 cell activation, resulting in aggravation of OVA-induced airway inflammation. These findings indicate the adjuvant activity of chitin via a new mechanism and provide important clues for development of therapeutics for allergic disorders caused by HDM, fungi and crustaceans.

IL-33, IL-25 and TSLP contribute to development of fungal-associated protease-induced innate-type airway inflammation.

Certain proteases derived from house dust mites and plants are considered to trigger initiation of allergic airway inflammation by disrupting tight junctions between epithelial cells. It is known that inhalation of proteases such as house dust mite-derived Der p1 and/or papaya-derived papain caused airway eosinophilia in naïve mice and even in Rag-deficient mice that lack acquired immune cells such as T, B and NKT cells. In contrast, little is known regarding the possible involvement of proteases derived from Aspergillus species (fungal-associated proteases; FAP), which are ubiquitous saprophytic fungi in the environment, in the development of allergic airway eosinophilia. Here, we found that inhalation of FAP by naïve mice led to airway eosinophilia that was dependent on protease-activated receptor-2 (PAR2), but not TLR2 and TLR4. Those findings suggest that the protease activity of FAP, but not endotoxins in FAP, are important in the setting. In addition, development of that eosinophilia was mediated by innate immune cells (ILCs) such as innate lymphoid cells, but not by acquired immune cells such as T, B and NKT cells. Whereas IL-33, IL-25 and thymic stromal lymphopoietin (TSLP) are involved in induction of FAP-induced ILC-mediated airway eosinophilia, IL-33-rather than IL-25 and/or TSLP-was critical for the eosinophilia in our model. Our findings improve our understanding of the molecular mechanisms involved in induction of airway inflammation by FAP.

Role of interleukin-25 in development of spontaneous arthritis in interleukin-1 receptor antagonist-deficient mice.

Interleukin (IL)-25, which is a member of the IL-17 family of cytokines, induces production of such Th2 cytokines as IL-4, IL-5, IL-9 and/or IL-13 by various types of cells, including Th2 cells, Th9 cells and group 2 innate lymphoid cells (ILC2). On the other hand, IL-25 can suppress Th1- and Th17-associated immune responses by enhancing Th2-type immune responses. Supporting this, IL-25 is known to suppress development of experimental autoimmune encephalitis, which is an IL-17-mediated autoimmune disease in mice. However, the role of IL-25 in development of IL-17-mediated arthritis is not fully understood. Therefore, we investigated this using IL-1 receptor antagonist-deficient (IL-1Ra-/-) mice, which spontaneously develop IL-17-dependent arthritis. However, development of spontaneous arthritis (incidence rate, disease severity, proliferation of synovial cells, infiltration of PMNs, and bone erosion in joints) and differentiation of Th17 cells in draining lymph nodes in IL-25-/- IL-1Ra-/- mice were similar to in control IL-25+/+ IL-1Ra-/- mice. These observations indicate that IL-25 does not exert any inhibitory and/or pathogenic effect on development of IL-17-mediated spontaneous arthritis in IL-1Ra-/- mice.