Tomohiro Tamachi

Involvement of TNF Receptor-Associated Factor 6 in IL-25 Receptor Signaling

IL-25 (IL-17E) induces IL-4, IL-5, and IL-13 production from an unidentified non-T/non-B cell population and subsequently induces Th2-type immune responses such as IgE production and eosinophilic airway inflammation. IL-25R is a single transmembrane protein with homology to IL-17R, but the IL-25R signaling pathways have not been fully understood. In this study, we investigated the signaling pathway under IL-25R, especially the possible involvement of TNFR-associated factor (TRAF)6 in this pathway. We found that IL-25R cross-linking induced NF-κB activation as well as ERK, JNK, and p38 activation. We also found that IL-25R-mediated NF-κB activation was inhibited by the expression of dominant negative TRAF6 but not of dominant negative TRAF2. Furthermore, IL-25R-mediated NF-κB activation, but not MAPK activation, was diminished in TRAF6-deficient murine embryonic fibroblast. In addition, coimmunoprecipitation assay revealed that TRAF6, but not TRAF2, associated with IL-25R even in the absence of ligand binding. Finally, we found that IL-25R-mediated gene expression of IL-6, TGF-β, G-CSF, and thymus and activation-regulated chemokine was diminished in TRAF6-deficient murine embryonic fibroblast. Taken together, these results indicate that TRAF6 plays a critical role in IL-25R-mediated NF-κB activation and gene expression.

Sox5 and c-Maf cooperatively induce Th17 cell differentiation via RORγt induction as downstream targets of Stat3

A novel isoform of Sox5, Sox5t, and c-Maf activate RORγt to induce Th17 cells. Sox5−/− mice exhibit impaired Th17 differentiation and are thus resistant to EAE and delayed-type hypersensitivity.

Indispensable Role of Stat5a in Stat6-Independent Th2 Cell Differentiation and Allergic Airway Inflammation

It is well-recognized that Stat6 plays a critical role in Th2 cell differentiation and the induction of allergic inflammation. We have previously shown that Stat5a is also required for Th2 cell differentiation and allergic airway inflammation. However, it is the relative importance and redundancy of Stat6 and Stat5a in Th2 cell differentiation and allergic airway inflammation are unknown. In this study we addressed these issues by comparing Stat5a-deficient (Stat5a−/−) mice, Stat6−/− mice, and Stat5a- and Stat6 double-deficient (Stat5a−/− Stat6−/−) mice on the same genetic background. Th2 cell differentiation was severely decreased in Stat6−/−CD4+ T cells, but Stat6-independent Th2 cell differentiation was still significantly observed in Stat6−/−CD4+ T cells. However, even in the Th2-polarizing condition (IL-4 plus anti-IFN-γ mAb), no Th2 cells developed in Stat5a−/−Stat6−/− CD4+ T cells. Moreover, Ag-induced eosinophil and lymphocyte recruitment in the airways was severely decreased in Stat5a−/−Stat6−/− mice compared with that in Stat6−/− mice. These results indicate that Stat5a plays an indispensable role in Stat6-independent Th2 cell differentiation and subsequent Th2 cell-mediated allergic airway inflammation.

Dectin-2 Promotes House Dust Mite–Induced T Helper Type 2 and Type 17 Cell Differentiation and Allergic Airway Inflammation in Mice

The fact that sensitization against fungi is closely related to the severity of asthma suggests that immune systems recognizing fungi are involved in the pathogenesis of severe asthma. Recently, Dectin-2 (gene symbol, Clec4n), a C-type lectin receptor, has been shown to function as not only a major pattern-recognition receptor for fungi, but also a receptor for some components of house dust mite (HDM) extract, a major allergen for asthma. However, the roles of Dectin-2 in the induction of HDM-induced allergic airway inflammation remain largely unknown. Our objective was to determine the roles of Dectin-2 in HDM-induced allergic airway inflammation. We examined the roles of Dectin-2 in the induction of HDM-induced T helper (Th) 2 and Th17 cell differentiation and subsequent allergic airway inflammation by using Clec4n-deficient (Clec4n(-/-)) mice. We also investigated Dectin-2-expressing cells in the lung and their roles in HDM-induced allergic airway inflammation. Clec4n(-/-) mice showed significantly attenuated HDM-induced allergic airway inflammation and decreased Th2 and Th17 cell differentiation. Dectin-2 mRNA, together with Dectin-3 and Fc receptor-γ mRNAs, was expressed in CD11b(+) dendritic cells (DCs), but not in CD4(+) T cells or epithelial cells in the lung. CD11b(+) DCs isolated from Clec4n(-/-) mice expressed lower amounts of proinflammatory cytokines and costimulatory molecules, which could lead to Th2 and Th17 cell differentiation than those from wild-type mice. HDM-pulsed Clec4n(-/-) DCs were less efficient for the induction of allergic airway inflammation than HDM-pulsed wild-type DCs. In conclusion, Dectin-2 expressed on CD11b(+) DCs promotes HDM-induced Th2 and Th17 cell differentiation and allergic airway inflammation.

Interleukin 25 in Allergic Airway Inflammation

T helper 2 (Th2) cells induce allergic inflammation through the production of cytokines such as interleukin (IL)-4, IL-5 and IL-13. Recently, it has been demonstrated that a novel IL-17 family cytokine IL-25 (IL-17E) is a product of activated Th2 cells and mast cells. Interestingly, when systemically administered to mice, IL-25 induces IL-4, IL-5 and IL-13 production from undefined non-T/non-B cells and then induces Th2-type immune responses such as blood eosinophilia and increased serum immunoglobulin E levels. In addition, we have recently shown that IL-25 mRNA is expressed in the lung after an inhaled antigen challenge in sensitized mice and that neutralization of the produced IL-25 by soluble IL-25 receptor decreases antigen-induced eosinophil and CD4+ T cell recruitment into the airways. Moreover, we have shown that the enforced expression of IL-25 in the lung significantly enhances antigen-induced Th2 cytokine production and eosinophil recruitment into the airways, and that the IL-25-mediated enhancement of antigen-induced eosinophil recruitment is inhibited by the depletion of CD4+ T cells. Thus, it is suggested that IL-25 plays an important role in enhancing allergic airway inflammation by a CD4+ T-cell-dependent mechanism.

Overlapping and Distinct Roles of STAT4 and T-bet in the Regulation of T Cell Differentiation and Allergic Airway Inflammation

T-bet and STAT4 play critical roles in helper T cell differentiation, especially for Th1 cells. However, it is still unknown about the relative importance and redundancy of T-bet and STAT4 for Th1 differentiation. It is also unknown about their independent role of T-bet and STAT4 in the regulation of allergic airway inflammation. In this study, we addressed these issues by comparing T-bet-deficient (T-bet−/−) mice, STAT4−/− mice, and T-bet- and STAT4-double-deficient (T-bet−/−STAT4−/−) mice on the same genetic background. Th1 differentiation was severely decreased in T-bet−/− mice and STAT4−/− mice as compared with that in wild-type mice, but Th1 differentiation was still observed in T-bet−/− mice and STAT4−/− mice. However, Th1 cells were hardly detected in T-bet−/−STAT4−/− mice. In contrast, the maintenance of Th17 cells was enhanced in T-bet−/− mice but was reduced in STAT4−/− mice and T-bet−/−STAT4−/− mice. In vivo, Ag-induced eosinophil and neutrophil recruitment into the airways was enhanced in T-bet−/− mice but was attenuated in STAT4−/− mice and T-bet−/−STAT4−/− mice. Ag-induced IL-17 production in the airways was also diminished in STAT4−/− mice and T-bet−/−STAT4−/− mice. These results indicate that STAT4 not only plays an indispensable role in T-bet-independent Th1 differentiation but also is involved in the maintenance of Th17 cells and the enhancement of allergic airway inflammation.

Helios Enhances Treg Cell Function in Cooperation With FoxP3.

Helios+FoxP3+CD4+ (Helios+) Treg cells are believed to be involved in the regulation of various autoimmune diseases; however, the regulatory mechanisms underlying the development of Helios+ Treg cells remain uncertain. This study was undertaken to elucidate the regulatory mechanisms of Helios expression in CD4+ T cells and its roles in transforming growth factor β (TGFβ)–induced Treg cell function.

Allergic airway inflammation: key players beyond the Th2 cell pathway

Allergic asthma is characterized by eosinophilic airway inflammation, mucus hyperproduction, and airway hyperreactivity, causing reversible airway obstruction. Accumulating evidence indicates that antigen‐specific Th2 cells and their cytokines such as IL‐4, IL‐5, and IL‐13 orchestrate these pathognomonic features of asthma. However, over the past decade, the understanding of asthma pathogenesis has made a significant shift from a Th2 cell‐dependent, IgE‐mediated disease to a more complicated heterogeneous disease. Recent studies clearly show that not only Th2 cytokines but also other T cell‐related cytokines such as IL‐17A and IL‐22 as well as epithelial cell cytokines such as IL‐25, IL‐33, and thymic stromal lymphopoietin (TSLP) are involved in the pathogenesis of asthma. In this review, we focus on the roles of these players beyond Th2 pathways in the pathogenesis of asthma.

β-Glucan Curdlan Induces IL-10–Producing CD4+ T Cells and Inhibits Allergic Airway Inflammation

A number of studies have suggested a correlation between a decreased incidence in infectious diseases and an increased incidence of allergic diseases, including asthma. Although several pathogen-derived products have been shown to possess therapeutic potential for allergic diseases, it remains largely unknown whether β-glucan, a cell wall component of a variety of fungi, yeasts, and bacteria, has a regulatory potential for allergic diseases. In this study, we examined the effect of curdlan, a linear β-(1-3)-glucan, on the development of allergic airway inflammation. We found that i.p. injection of curdlan significantly inhibited Ag-induced eosinophil recruitment and Th2 cytokine production in the airways. The activation of CD4+ T cells in the presence of curdlan induced IL-10–producing CD4+ T cells with high levels of c-Maf expression. Curdlan-induced development of IL-10–producing CD4+ T cells required the presence of APCs and ICOS/ICOS ligand interaction. Curdlan-induced development of IL-10–producing CD4+ T cells also required intrinsic expression of STAT6. Furthermore, the transfer of Ag-specific CD4+ T cells that were stimulated in the presence of curdlan inhibited Ag-induced eosinophil recruitment into the airways. Taken together, these results suggest that curdlan is capable of inducing IL-10–producing CD4+ T cells and inhibiting the development of eosinohilic airway inflammation, underscoring the therapeutic potential of curdlan for allergic diseases.

Dectin-1 Plays an Important Role in House Dust Mite–Induced Allergic Airway Inflammation through the Activation of CD11b+ Dendritic Cells

It is well known that sensitization against fungi is closely associated with severity of asthma. Dectin-1 (gene symbol Clec7a), a C-type lectin receptor, recognizes the fungal cell wall component β-glucan, as well as some component(s) in house dust mite (HDM) extract. However, the roles of Dectin-1 in HDM-induced allergic airway inflammation remain unclear. In this study, we used Dectin-1–deficient (Clec7a−/−) mice to examine whether Dectin-1 is involved in HDM-induced allergic airway inflammation. We found that HDM-induced eosinophil and neutrophil recruitment into the airways was significantly attenuated in Clec7a−/− mice compared with that in wild-type mice. In addition, HDM-induced IL-5, IL-13, and IL-17 production from mediastinum lymph node cells was reduced in HDM-sensitized Clec7a−/− mice. Dectin-1 was expressed on CD11b+ dendritic cells (DCs), an essential DC subset for the development of allergic inflammation, but not on CD103+ DCs, plasmacytoid DCs, or lung epithelial cells. Transcriptome analysis revealed that the expression of chemokine/chemokine receptors, including CCR7, which is indispensable for DC migration to draining lymph nodes, was decreased in Clec7a−/− DCs. In accordance with these results, the number of HDM-labeled CD11b+ DCs in mediastinum lymph nodes was significantly reduced in Clec7a−/− mice compared with wild-type mice. Taken together, these results suggest that Dectin-1 expressed on CD11b+ DCs senses some molecule(s) in HDM extract and plays a critical role in the induction of HDM-induced allergic airway inflammation by inducing the expression of chemokine/chemokine receptors in DCs.