Kazuyo Moro

Innate production of TH2 cytokines by adipose tissue-associated c-Kit+Sca-1+ lymphoid cells

Innate immune responses are important in combating various microbes during the early phases of infection. Natural killer (NK) cells are innate lymphocytes that, unlike T and B lymphocytes, do not express antigen receptors but rapidly exhibit cytotoxic activities against virus-infected cells and produce various cytokines. Here we report a new type of innate lymphocyte present in a novel lymphoid structure associated with adipose tissues in the peritoneal cavity. These cells do not express lineage (Lin) markers but do express c-Kit, Sca-1 (also known as Ly6a), IL7R and IL33R. Similar lymphoid clusters were found in both human and mouse mesentery and we term this tissue ‘FALC’ (fat-associated lymphoid cluster). FALC Lin-c-Kit+Sca-1+ cells are distinct from lymphoid progenitors and lymphoid tissue inducer cells. These cells proliferate in response to IL2 and produce large amounts of TH2 cytokines such as IL5, IL6 and IL13. IL5 and IL6 regulate B-cell antibody production and self-renewal of B1 cells. Indeed, FALC Lin-c-Kit+Sca-1+ cells support the self-renewal of B1 cells and enhance IgA production. IL5 and IL13 mediate allergic inflammation and protection against helminth infection. After helminth infection and in response to IL33, FALC Lin-c-Kit+Sca-1+ cells produce large amounts of IL13, which leads to goblet cell hyperplasia—a critical step for helminth expulsion. In mice devoid of FALC Lin-c-Kit+Sca-1+ cells, such goblet cell hyperplasia was not induced. Thus, FALC Lin-c-Kit+Sca-1+ cells are TH2-type innate lymphocytes, and we propose that these cells be called ‘natural helper cells’.

The transcriptional regulators IRF4, BATF and IL-33 orchestrate development and maintenance of adipose tissue-resident regulatory T cells

Foxp3+ regulatory T (Treg) cells in visceral adipose tissue (VAT-Treg cells) are functionally specialized tissue-resident cells that prevent obesity-associated inflammation and preserve insulin sensitivity and glucose tolerance. Their development depends on the transcription factor PPAR-γ; however, the environmental cues required for their differentiation are unknown. Here we show that interleukin 33 (IL-33) signaling through the IL-33 receptor ST2 and myeloid differentiation factor MyD88 is essential for development and maintenance of VAT-Treg cells and sustains their transcriptional signature. Furthermore, the transcriptional regulators BATF and IRF4 were necessary for VAT-Treg differentiation through direct regulation of ST2 and PPAR-γ expression. IL-33 administration induced vigorous population expansion of VAT-Treg cells, which tightly correlated with improvements in metabolic parameters in obese mice. Human omental adipose tissue Treg cells also showed high ST2 expression, suggesting an evolutionarily conserved requirement for IL-33 in VAT-Treg cell homeostasis.

Stress-induced production of chemokines by hair follicles regulates the trafficking of dendritic cells in skin

Langerhans cells (LCs) are epidermal dendritic cells with incompletely understood origins that associate with hair follicles for unknown reasons. Here we show that in response to external stress, mouse hair follicles recruited Gr-1hi monocyte-derived precursors of LCs whose epidermal entry was dependent on the chemokine receptors CCR2 and CCR6, whereas the chemokine receptor CCR8 inhibited the recruitment of LCs. Distinct hair-follicle regions had differences in their expression of ligands for CCR2 and CCR6. The isthmus expressed the chemokine CCL2; the infundibulum expressed the chemokine CCL20; and keratinocytes in the bulge produced the chemokine CCL8, which is the ligand for CCR8. Thus, distinct hair-follicle keratinocyte subpopulations promoted or inhibited repopulation with LCs via differences in chemokine production, a feature also noted in humans. Pre-LCs failed to enter hairless skin in mice or humans, which establishes hair follicles as portals for LCs.

Basophil-Derived Interleukin-4 Controls the Function of Natural Helper Cells, a Member of ILC2s, in Lung Inflammation

Allergic asthma is an inflammatory disease characterized by lung eosinophilia controlled by type 2 cytokines. Cysteine proteases are potent triggers of allergic inflammation by causing barrier disruption in lung epithelial cells inducing the elevation of interleukin-5 (IL-5) and IL-13 from natural helper (NH) cells, a member of ILC2s, which leads to lung eosinophilia. In this study, we found that basophils play a crucial role in NH cell-mediated eosinophilic inflammation induced by protease allergens. Conditional deletion of basophils caused a resolution of the papain-induced eosinophilia and mucus production. Resolution of eosinophilia was also observed in mice lacking IL-4 specifically in basophils, indicating that basophil-derived IL-4 enhanced expression of the chemokine CCL11, as well as IL-5, IL-9, and IL-13 in NH cells, thus attracting eosinophils. These results demonstrate that IL-4 from basophils has an important role in the NH-derived cytokine and chemokine expression, subsequently leading to protease allergen-induced airway inflammation.

Interferon and IL-27 antagonize the function of group 2 innate lymphoid cells and type 2 innate immune responses

Group 2 innate lymphoid cells (ILC2 cells) are type 2 cytokine–producing cells of the innate immune system with important roles in helminth infection and allergic inflammation. Here we found that tissue-resident ILC2 cells proliferated in situ without migrating during inflammatory responses. Both type I and type II interferons and interleukin 27 (IL-27) suppressed ILC2 function in a manner dependent on the transcription factor STAT1. ILC2-mediated lung inflammation was enhanced in the absence of the interferon-γ (IFN-γ) receptor on ILC2 cells in vivo. IFN-γ effectively suppressed the function of tissue-resident ILC2 cells but not that of inflammatory ILC2 cells, and IL-27 suppressed tissue-resident ILC2 cells but not tissue-resident TH2 cells during lung inflammation induced by Alternaria alternata. Our results demonstrate that suppression mediated by interferon and IL-27 is a negative feedback mechanism for ILC2 function in vivo.

Thymic stromal lymphopoietin induces corticosteroid resistance in natural helper cells during airway inflammation

Type-2 innate immune responses that occur in airways and are accompanied by goblet-cell hyperplasia and mucus production are largely driven by interleukin-33 (IL-33) and natural helper (NH) cells, a member of group 2 innate lymphoid cells (ILC2s) and the major target of IL-33. Here we report that the corticosteroid resistance observed as a result of airway inflammation triggered by sensitization and exposure to allergen is induced via the IL-33/NH-cell axis. Thymic stromal lymphopoietin (TSLP) synthesized during airway inflammation plays a pivotal role in the induction of NH-cell corticosteroid resistance in vitro and in vivo, by controlling phosphorylation of STAT5 and expression of Bcl-xL in NH cells. Blockade of TSLP with a neutralizing antibody or blocking the TSLP/STAT5 signalling pathway with low molecular-weight STAT5 inhibitors such as pimozide restores corticosteroid sensitivity. Thus, the TSLP-STAT5 pathway could be a new therapeutic target in severe, corticosteroid-resistant asthma.

Role of Peyer's patches in the induction of Helicobacter pylori-induced gastritis

Helicobacter pylori is a Gram-negative spiral bacterium that causes gastritis and peptic ulcer and has been implicated in the pathogenesis of gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. Although Th1 immunity is involved in gastritis and the accumulation of H. pylori-specific CD4+ T cells in the H. pylori-infected gastric mucosa in human patients, how T cells are primed with H. pylori antigens is unknown because no apparent lymphoid tissues are present in the stomach. We demonstrate here that Peyers patches (PPs) in the small intestine play critical roles in H. pylori-induced gastritis; no gastritis is induced in H. pylori-infected mice lacking PPs. We also observed that the coccoid form of H. pylori is phagocytosed by dendritic cells in PPs. We propose that H. pylori converts to the coccoid form in the anaerobic small intestine and stimulates the host immune system through PPs.

Type 2 innate immune responses and the natural helper cell

The T helper type 2 (Th2) immune response, characterized by the production of interleukin‐4 (IL‐4), IL‐5 and IL‐13, is a critical immune response against helminths invading cutaneous or mucosal sites. It also plays a critical role in the pathophysiology of allergic diseases such as asthma and allergic diarrhoea. The Th2 cytokines are induced soon after helminth infection, even before a pathogen‐specific adaptive immune response is established. Recent studies have shed light on such innate Th2 cytokine production by formerly uncharacterized innate immune cells such as natural helper cells capable of producing Th2 cytokines in response to IL‐25 and IL‐33 independently of adaptive immune responses. These cells produce large amounts of Th2 cytokines, most notably IL‐5 and IL‐13, leading to eosinophilia and goblet cell hyperplasia. We discuss here the mechanisms of innate production of Th2 cytokines in host immune responses against helminth infection as well as allergic immune responses and the similarities and differences between recently identified Th2‐cytokine producing cells.

Critical Role of p38 and GATA3 in Natural Helper Cell Function

Natural helper (NH) cells, a member of Lin−IL-2R+IL-7R+IL-25R+IL-33R+GATA3+ group 2 innate lymphoid cell subset, are characterized by the expression of transcription factors GATA3 and RORα and production of large amounts of Th2 cytokines such as IL-5, IL-6, and IL-13 upon IL-33 stimulation or a combination of IL-2 and IL-25. We have studied the signal transduction pathways critical for the cytokine expression and development of NH cell. Either stimulation with IL-33 or a combination of IL-2 and IL-25 induced p38 activation and phosphorylation of GATA3 in NH cells, and the phosphorylated form of GATA3 bound to the IL-5 and IL-13 promoters. All these events were blocked by SB203580, a p38 inhibitor. Inhibition of p38 also blocked IL-6 production. The mature NH cells lacking Gata3 were impaired in the proliferation and production of IL-5 and IL-13, but not IL-6, indicating that both p38 and GATA3 are critical for the proliferation and production of IL-5 and IL-13 and that the mechanisms downstream of p38 differ between IL-6 and IL-5/IL-13. In contrast, the NH cells lacking RORα showed no impairment in the proliferation and cytokine production, indicating that GATA3 but not RORα plays a pivotal role in the effector functions of mature NH cell. However, deletion of either GATA3 or RORα in hematopoietic stem cells severely blocked the development into NH cells. Our results demonstrate the important roles of p38 and GATA3 in NH cell functions.

Intestinal γδ T Cells Develop in Mice Lacking Thymus, All Lymph Nodes, Peyer’s Patches, and Isolated Lymphoid Follicles

Through analysis of athymic (nu/nu) mice carrying a transgenic gene encoding GFP instead of RAG-2 product, it has recently been reported that, in the absence of thymopoiesis, mesenteric lymph nodes and Peyer’s patches (PP) but not gut cryptopatches are pivotal birthplace of mature T cells such as the thymus-independent intestinal intraepithelial T cells (IEL). To explore and evaluate this important issue, we generated nu/nu mice lacking all lymph nodes (LN) and PP by administration of lymphotoxin-β receptor-Ig and TNF receptor 55-Ig fusion proteins into the timed pregnant nu/+ mice that had been mated with male nu/nu mice (nu/nu LNP− mice). We also generated nu/nu aly/aly (aly, alymphoplasia) double-mutant mice that inherently lacked all LN, PP, and isolated lymphoid follicles. Although γδ-IEL were slightly smaller in number than those in nu/nu mice, substantial colonization of γδ-IEL was found to take place in the intestinal epithelia of nu/nu LNP− and nu/nu aly/aly mice. Notably, the population size of a major CD8αα+ γδ-IEL subset was maintained, the use of TCR-γ-chain variable gene segments by these γδ-IEL was unaltered, and the development of cryptopatches remained intact in these nu/nu LNP− and nu/nu aly/aly mice. These findings indicate that all LN, including mesenteric LN, PP, and isolated lymphoid follicles, are not an absolute requirement for the development of γδ-IEL in athymic nu/nu mice.