Ro5-4864, a translocator protein ligand, regulates T cell-mediated inflammatory responses in skin.

Translocator protein (TSPO) is a mitochondrial outer membrane protein expressed on a variety of immune cells, including macrophages, dendritic cells, and T cells, in addition to neurons and steroid-producing cells. Previous studies of TSPO ligands have suggested that TSPO is involved in multiple cellular functions, including steroidogenesis, immunomodulation, and cell proliferation. Currently, there are limited reports on the effects of TSPO or TSPO ligands on T cell-mediated immune responses. We here investigated the involvement of TSPO/TSPO ligand in T cell responses using a 2,4-dinitro-1-fluorobenzene (DNFB)-induced contact hypersensitivity (CH) model. Treatment with Ro5-4864, a TSPO ligand, during DNFB sensitization reduced the number and activation status of CD4+ and CD8+ T cells in draining lymph nodes and alleviated skin inflammation after DNFB challenge. Adoptive transfer of Ro5-4864-treated mouse-derived DNFB-sensitized T cells to naïve mice inhibited CH responses after DNFB challenge. Ro5-4864-treated sensitized T cells showed lower proliferative responses when stimulated with DNFB-pulsed antigen-presenting cells compared to control-treated sensitized T cells. Ro5-4864 also suppressed cell proliferation, as well as adenosine triphosphate and lactate production, during T cell activation. Moreover, the inhibitory effects of Ro5-4864 on T cell responses were conserved in TSPO-deficient cells. Our results suggest that Ro5-4864 inhibits CH responses by suppressing energy metabolism, at least via glycolysis, to reduce the T cell primary response in a TSPO-independent manner.

The Prostaglandin D2 Receptor CRTH2 Contributes to Airway Hyperresponsiveness during Airway Inflammation Induced by Sensitization without an Adjuvant in Mice.

INTRODUCTION: Prostaglandin D2 (PGD2), which is produced mainly by Th2 cells and mast cells, promotes a type-2 immune response by activating Th2 cells, mast cells, eosinophils, and group 2 innate lymphoid cells (ILC2s) via its receptor, chemoattractant receptor-homologous molecules on Th2 cells (CRTH2). However, the role of CRTH2 in models of airway inflammation induced by sensitization without adjuvants, in which both IgE and mast cells may play major roles, remain unclear. METHODS: Wild-type (WT) and CRTH2-knockout (KO) mice were sensitized with ovalbumin (OVA) without an adjuvant and then challenged intranasally with OVA. Airway inflammation was assessed based on airway hyperresponsiveness (AHR), lung histology, number of leukocytes, and levels of type-2 cytokines in the bronchoalveolar lavage fluid (BALF). RESULTS: AHR was significantly reduced after OVA challenge in CRTH2 KO mice compared to WT mice. The number of eosinophils, levels of type-2 cytokines (IL-4, IL-5, and IL-13) in BALF, and IgE concentration in serum were decreased in CRTH2 KO mice compared to WT mice. However, lung histological changes were comparable between WT and CRTH2 KO mice. CONCLUSION: CRTH2 is responsible for the development of asthma responses in a mouse model of airway inflammation that features prominent involvement of both IgE and mast cells.

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.

Characterization of novel, severely immunodeficient PrkdcΔex57/Δex57 mice.

Severely immunodeficient mice are useful for understanding the pathogenesis of certain tumors and for developing therapeutic agents for such tumors. In addition, engraftment of these mice with human hematopoietic cells can yield information that helps us understand the in vivo molecular mechanisms underlying actual human viral infections. In our present research, we discovered a novel, severely immunodeficient strain of mice having a mutation in exon 57 of the Prkdc gene (PrkdcΔex57/Δex57) in an inbred colony of B10.S/SgSlc mice. Those PrkdcΔex57/Δex57 mice showed thymic hypoplasia and lack of mature T cells and B cells in peripheral lymphoid tissues, resulting in very low levels of production of serum immunoglobulins. In addition, those mice were highly susceptible to influenza viruses due to the lack of acquired immune cells. On the other hand, since they had sufficient numbers of NK cells, they rejected tumor transplants, similarly to Prkdc+/+ mice. Next, we generated Foxn1nu/nuPrkdcΔex57/Δex57Il2rg-/- (NPG) mice on the BALB/cSlc background, which lack all lymphocytes such as T cells, B cells and innate lymphoid cells, including NK cells. As expected, these mice were able to undergo engraftment of human tumor cell lines. These findings suggest that PrkdcΔex57/Δex57 mice will be useful as a novel model of immunodeficiency, while NPG mice will be useful for xenografting of various malignancies.

Progress and Current Status in Hajdu-Cheney Syndrome with Focus on Novel Genetic Research.

Hajdu-Cheney syndrome (HCS) is a rare autosomal dominant manifestation of a congenital genetic disorder caused by a mutation in the NOTCH2 gene. NOTCH signaling has variations from NOTCH 1 to 4 and maintains homeostasis by determining and regulating the proliferation and differentiation of various cells. In HCS, the over-accumulated NOTCH2 causes abnormal bone resorption due to its continuous excessive signaling. HCS is characterized by progressive bone destruction, has complex wide-range clinical manifestations, and significantly impacts the patient's quality of life. However, no effective treatment has been established for HCS to date. There are genetic variants of NOTCH2 that have been reported in the ClinVar database of the U.S. National Institutes of Health. In total, 26 mutant variants were detected based on the American College of Medical Genetics and Genomics (ACMC). To date, there has been no comprehensive compilation of HCS mutations. In this review, we provide the most comprehensive list possible of HCS variants, nucleotide changes, amino acid definitions, and molecular consequences reported to date, following the ACMC guidelines.

TSLP is a negative regulator of RANKL-induced osteoclastogenesis.

Thymic stromal lymphopoietin (TSLP) is a member of the IL-2 cytokine family, which is known to activate type 2 innate lymphoid cells, mast cells, and Th2 cells; this activation results in allergic inflammation and host defense against parasites. TSLP has also been shown to promote Th17-mediated immune responses, such as those observed in the development of rheumatoid arthritis; however, its role in osteoclastogenesis remains poorly understood. Here, we investigated the functional involvement of TSLP in RANKL-induced osteoclast differentiation from murine bone marrow-derived macrophages (BMMs). Both RANK- and RANK+ macrophages expressed TSLP receptor (TSLPR), while RANK+ osteoclast precursors maintained TSLPR expression after RANKL stimulation. TSLP stimulation led to inhibition of RANK-induced osteoclast differentiation in wild-type BMMs, but not Tslpr-/- BMMs; TSLP stimulation also led to suppression of osteoclastogenic gene expression (Nfatc1, Acp5, Mmp9, and Ctsk). These inhibitory effects of TSLP were significantly reduced following STAT1 inhibition. Finally, we found that LPS stimulation induced TSLP production in murine calvarial osteoblasts, but not BMMs. Together, these observations suggest that TSLP acts directly on osteoclast precursors to suppress osteoclastogenesis. Osteoblasts, along with other TSLP-producing cells, may therefore contribute to the inhibition of osteoclastogenesis under inflammatory conditions.

Endogenous IL-33 exerts CD8+ T cell antitumor responses overcoming pro-tumor effects by regulatory T cells in a colon carcinoma model.

Interleukin-33 (IL-33) is a nuclear-associated cytokine of the IL-1 family. IL-33 and its receptor ST2 axis exert conflicting anti-tumor and pro-tumor effects in various tumors. In this study, we examined the role of endogenously produced IL-33 in the colon-26 tumor model, in which involvement of the IL-33:ST2 pathway was negligible on the tumor side. We found that the generation of regulatory T cells (Tregs) and CD8+ T cells, and IFN-γ expression by both CD4+ and CD8+ T cells (T cell activation) were impaired in IL-33-deficient mice. Overall antitumor responses, assessed by tumor growth and IFN-γ expression by tumor-infiltrating CD8+ T cells, were also impaired, even after Treg adjustment prior to tumor inoculation. These results indicate that endogenous IL-33 augmented CD8+ T cell-mediated antitumor responses in this colon carcinoma model, with higher CD8+ T cell-infiltration and overcoming pro-tumor effects by increased Tregs. Exogenous application of IL-33 into the tumors did not enhance CD8+ T cell-mediated antitumor responses despite marked elevation of innate responses showing upregulation of proinflammatory cytokine/chemokine expression, neutrophil recruitment, and dendritic cell activation. Our results suggest a dual role for endogenous IL-33 in antitumor responses and suggest that the balance of CD8+ T cells:Tregs in the tumor microenvironment is one of key factors for estimating the contribution of IL-33-mediated antitumor responses. Therefore, the development of IL-33-based cancer immunotherapy may require a target cell-specific approach.

The immune checkpoint molecule VISTA regulates allergen-specific Th2-mediated immune responses.

V-domain immunoglobulin suppressor of T-cell activation (VISTA) is a novel immune checkpoint receptor and ligand that regulates T-cell activation. We investigated the functional involvement of VISTA in Th2 cell-mediated immune responses using an ovalbumin (OVA)-induced allergic asthma model. Treatment with an anti-VISTA monoclonal antibody (mAb) during allergen sensitization increased the production of antibodies, including total IgE, OVA-specific IgG1 and IgG2a and allergen-specific IL-5 and IL-13; it also increased the expression of IL-13 by splenic CD4+ T cells. However, treatment with the anti-VISTA mAb during sensitization did not accelerate asthmatic responses, including airway hyper-responsiveness (AHR) or the number of eosinophils in bronchoalveolar lavage (BAL) fluid. In contrast, treatment with the anti-VISTA mAb during allergen challenge significantly augmented AHR and BAL fluid eosinophilia. This treatment also increased the production of IL-5 and IL-13 in BAL fluid and the expression of IL-13 by CD4+ T cells in draining lymph nodes. These results suggest that VISTA is involved in the regulation of Th2 cell generation and Th2 cell-mediated antibody production and regulates asthmatic responses, especially in the effector phase.

Site-specific regulation of oral mucosa-recruiting CD8+ T cells in a mouse contact allergy model.

Contact allergy is a T cell-mediated, delayed-type hypersensitivity generated by contact exposure of an allergen to the skin and mucosal surface. The clinical manifestations of allergic responses between the skin and oral mucosa vary and the differences in immunopathology have not been clarified. We generated hapten-induced contact hypersensitivity (CH) of the buccal mucosa (BM) in parallel studies with ear skin (ES) CH, and observed several characteristic findings of BM CH. The BM challenge induced more rapid and more severe inflammation than the ES challenge, with abundant granulocyte and CD8+ T cell infiltration. However, these inflammatory responses diminished quickly. Recruiting CD8+ T cells in the BM had higher ratios of CD62L-CD44low-hi memory-type cells, and showed impaired IFN-γ, greater PD-1, and comparable Ki-67 expression, suggesting that the recruiting-proliferating CD8+ T cells were unable to differentiate into effector T cells and converted into exhausted T cells at the local site. This finding may explain the rapid recovery of the BM from severe inflammation. Preferentially greater expression of PD-1 ligand (B7-H1), was observed in the BM epithelium under the peak inflammation, and the absence of B7-H1 further accelerated CH responses, suggesting the occurrence of PD-1:B7-H1-mediated immune regulation at the local site. Our results may facilitate the understanding of the unique features of contact allergies in the oral mucosa, and guide the development of new strategies for control of contact allergy.

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.

HPV16 E2 protein promotes innate immunity by modulating immunosuppressive status.

The balance between active immune responses against human papillomavirus (HPV) and HPV-induced immune escape regulates viral clearance and carcinogenesis. To understand the role of the early viral protein HPV16 E2 in host innate immune responses, the HPV16 E2-transfected murine squamous cell carcinoma cell line SCCVII (SCC/E2) was generated and anti-tumor responses in T-cell-depleted mice were evaluated. Tumor growth of SCC/E2 was markedly reduced. Cytotoxicity against the NK-sensitive targets YAC-1 and SCCVII was clearly enhanced in SCC/E2-inoculated mice. Despite the comparable ratio of NK cells, the proportion of CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) was significantly decreased in SCC/E2-inoculated mice. The transcription of MDSC-related mediators such as inducible nitric oxide synthase, indoleamine 2,3-dioxygenase, and heme oxygenase-1 was significantly impaired in the SCC/E2-inoculated tumor tissues on day 3. Our results suggest that HPV16 E2 promotes anti-tumor innate effector function by modulating immunoregulatory events mediated by MDSCs and their mediators. This report describes a new role for HPV16 E2 as a local immunomodulator at infected sites.

Small interfering RNA against CD86 during allergen challenge blocks experimental allergic asthma.

BACKGROUND: CD86-CD28 interaction has been suggested as the principal costimulatory pathway for the activation and differentiation of naïve T cells in allergic inflammation. However, it remains uncertain whether this pathway also has an essential role in the effector phase. We sought to determine the contribution of CD86 on dendritic cells in the reactivation of allergen-specific Th2 cells. METHODS: We investigated the effects of the downregulation of CD86 by short interfering RNAs (siRNAs) on Th2 cytokine production in the effector phase in vitro and on asthma phenotypes in ovalbumin (OVA)-sensitized and -challenged mice. RESULTS: Treatment of bone marrow-derived dendritic cells (BMDCs) with CD86 siRNA attenuated LPS-induced upregulation of CD86. CD86 siRNA treatment impaired BMDCs' ability to activate OVA-specific Th2 cells. Intratracheal administration of CD86 siRNA during OVA challenge downregulated CD86 expression in the airway mucosa. CD86 siRNA treatment ameliorated OVA-induced airway eosinophilia, airway hyperresponsiveness, and the elevations of OVA-specific IgE in the sera and IL-5, IL-13, and CCL17 in the bronchoalveolar lavage fluid, but not the goblet cell hyperplasia. CONCLUSION: These results suggest that local administration of CD86 siRNA during the effector phase ameliorates lines of asthma phenotypes. Targeting airway dendritic cells with siRNA suppresses airway inflammation and hyperresponsiveness in an experimental model of allergic asthma.

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.

Novel artificial nerve transplantation of human iPSC-derived neurite bundles enhanced nerve regeneration after peripheral nerve injury.

BACKGROUND: Severe peripheral nerve damage always requires surgical treatment. Autologous nerve transplantation is a standard treatment, but it is not sufficient due to length limitations and extended surgical time. Even with the available artificial nerves, there is still large room for improvement in their therapeutic effects. Novel treatments for peripheral nerve injury are greatly expected. METHODS: Using a specialized microfluidic device, we generated artificial neurite bundles from human iPSC-derived motor and sensory nerve organoids. We developed a new technology to isolate cell-free neurite bundles from spheroids. Transplantation therapy was carried out for large nerve defects in rat sciatic nerve with novel artificial nerve conduit filled with lineally assembled sets of human neurite bundles. Quantitative comparisons were performed over time to search for the artificial nerve with the therapeutic effect, evaluating the recovery of motor and sensory functions and histological regeneration. In addition, a multidimensional unbiased gene expression profiling was carried out by using next-generation sequencing. RESULT: After transplantation, the neurite bundle-derived artificial nerves exerted significant therapeutic effects, both functionally and histologically. Remarkably, therapeutic efficacy was achieved without immunosuppression, even in xenotransplantation. Transplanted neurite bundles fully dissolved after several weeks, with no tumor formation or cell proliferation, confirming their biosafety. Posttransplant gene expression analysis highlighted the immune system's role in recovery. CONCLUSION: The combination of newly developed microfluidic devices and iPSC technology enables the preparation of artificial nerves from organoid-derived neurite bundles in advance for future treatment of peripheral nerve injury patients. A promising, safe, and effective peripheral nerve treatment is now ready for clinical application.

IL-33 is a crucial amplifier of innate rather than acquired immunity.

IL-33, a member of the IL-1-related cytokines, is considered to be a proallergic cytokine that is especially involved in Th2-type immune responses. Moreover, like IL-1α, IL-33 has been suggested to act as an "alarmin" that amplifies immune responses during tissue injury. In contrast to IL-1, however, the precise roles of IL-33 in those settings are poorly understood. Using IL-1- and IL-33-deficient mice, we found that IL-1, but not IL-33, played a substantial role in induction of T cell-mediated type IV hypersensitivity such as contact and delayed-type hypersensitivity and autoimmune diseases such as experimental autoimmune encephalomyelitis. Most notably, however, IL-33 was important for innate-type mucosal immunity in the lungs and gut. That is, IL-33 was essential for manifestation of T cell-independent protease allergen-induced airway inflammation as well as OVA-induced allergic topical airway inflammation, without affecting acquisition of antigen-specific memory T cells. IL-33 was significantly involved in the development of dextran-induced colitis accompanied by T cell-independent epithelial cell damage, but not in streptozocin-induced diabetes or Con A-induced hepatitis characterized by T cell-mediated apoptotic tissue destruction. In addition, IL-33-deficient mice showed a substantially diminished LPS-induced systemic inflammatory response. These observations indicate that IL-33 is a crucial amplifier of mucosal and systemic innate, rather than acquired, immune responses.

Role of interleukin-33 in innate-type immune cells in allergy.

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is preferentially and constitutively expressed in epithelial cells, and it is especially localized in the cells' nucleus. The nuclear IL-33 is released by necrotic cells after tissue injury and/or trauma, and subsequently provokes local inflammation as an alarmin, like high-mobility group box protein-1 (HMGB-1) and IL-1α. IL-33 mainly activates Th2 cells and such innate-type immune cells as mast cells, basophils, eosinophils and natural helper cells that express IL-33R (a heterodimer of IL-1 receptor-like 1 [IL-1RL1; also called ST2, T1, Der4, fit-1] and IL-1 receptor accessory protein [IL-1RAcP]). That activation causes the cells to produce Th2 cytokines, which contribute to host defense against nematodes. On the other hand, excessive and/or inappropriate production of IL-33 is also considered to be involved in the development of such disorders as allergy. In this review, we summarize current knowledge regarding the pathogenic roles of IL-33 in the development of allergic inflammation by focusing on its effects on innate-type immune cells.

IL-33 deficiency suppresses alveolar bone loss in a ligature-induced periodontitis model.

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family that has been studied primarily in the context of type 2 immune responses. Recent reports suggest that IL-33 also enhances the func- tions of various immune cells and contributes to the development of different inflammatory diseas- es. Interestingly, IL-33 and its receptor ST2 axis exerted either inhibitory or promotional effects on alveolar bone loss in various periodontitis models. Using a mouse model of ligature-induced periodontitis, we found that the levels of mRNAs encoding IL-33 and other inflammatory cyto- kines (IL-1α, IL-1ß, IL-6, and TNFα) were augmented in gingival tissues of wild-type (WT) mice, and that the alveolar bone loss amount was lower in IL-33-deficient than WT mice. The numbers and proportions of IFN-γ-producing CD8+ T and regulatory T cells were decreased while those of Th17 cells were increased in the draining lymph nodes of IL-33-deficient mice compared to WT mice. Additionally, the level of RNA encoding an osteoclastogenic molecule, i.e., receptor activa- tor of nuclear factor kappa-B ligand (RANKL), in ligated gingival tissue was higher in IL-33-defi- cient than WT mice. These results suggest that IL-33 is involved in alveolar bone loss in the ligature-induced periodontitis model, although IL-33 may inhibit osteoclast differentiation.

Subgingival titanium wire implantation induces weak inflammatory responses but does not promote substantial T cell activation.

Titanium is a biocompatible material commonly used for dental treatments. However, the detailed mechanism underlying the weak biological activity of titanium has not been elucidated. We investigated both the inflammatory responses and T cell activation induced by solid titanium in the gingiva in mice. Both titanium and nickel wire implantation promoted neutrophil infiltration into the gingiva on day 2. Nickel, but not titanium, wire implantation enhanced proinflammatory cytokine expression and dendritic cell activity in gingival tissue by day 2. Nickel wire implantation enhanced the activity of T cells in draining lymph nodes on day 5. Moreover, T cell and neutrophil infiltration and elevated proinflammatory cytokine expression in the gingival tissue were still observed on day 5. However, no such augmented biological responses were observed after titanium wire implantation. These findings suggest that, unlike nickel, solid titanium does not induce sufficient inflammatory responses leading to T cell activation in gingival tissue.

Interleukin-33 in allergy.

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, which includes IL-1 and IL-18, and is considered to be important for host defense against nematodes by inducing Th2 cytokine production via the IL-33 receptor. IL-33 receptor is a heterodimer of IL-1 receptor-like 1 (IL-1RL1; also called ST2, T1, Der4, and fit-1) and IL-1 receptor accessory protein (IL-1RAcP). On the other hand, excessive and/or inappropriate production of IL-33 is considered to be involved in the development of various disorders, such as allergic and autoimmune diseases. Unlike IL-1ß and IL-18, IL-33 does not seem to be secreted through the activation of inflammasomes in events such as apoptosis. However, IL-33 is localized in the nucleus of cells and is released during tissue injury associated with necrosis. This suggests that it acts as an alarmin, like IL-1α and high-mobility group box chromosomal protein-1 (HMGB-1). This review summarizes current knowledge regarding the roles of IL-33 in the functions of various cell types and the pathogenesis of allergy.

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.