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Timed feeding drives adipose browning, although the integrative mechanisms for the same remain unclear. Here, we show that twice-a-night (TAN) feeding generates biphasic oscillations of circulating insulin and leptin, representing their entrainment by timed feeding. Insulin and leptin surges lead to marked cellular, functional, and metabolic remodeling of subcutaneous white adipose tissue (sWAT), resulting in increased energy expenditure. Single-cell RNA-sequencing (scRNA-seq) analyses and flow cytometry demonstrate a role for insulin and leptin surges in innate lymphoid type 2 (ILC2) cell recruitment and sWAT browning, since sWAT depot denervation or loss of leptin or insulin receptor signaling or ILC2 recruitment each dampens TAN feeding-induced sWAT remodeling and energy expenditure. Consistently, recreating insulin and leptin oscillations via once-a-day timed co-injections is sufficient to favorably remodel innervated sWAT. Innervation is necessary for sWAT remodeling, since denervation of sWAT, but not brown adipose tissue (BAT), blocks TAN-induced sWAT remodeling and resolution of inflammation. In sum, reorganization of nutrient-sensitive pathways remodels sWAT and drives the metabolic benefits of timed feeding.

Adipose tissue homeostasis relies on the interplay between several regulatory lineages, such as type 2 innate lymphoid cells (ILC2s), T helper 2 (Th2) cells, regulatory T cells, eosinophils, and type 2 macrophages. Among them, ILC2s are numerically the dominant source of type 2 cytokines and are considered as major regulators of adiposity. Despite the overlap in immune effector molecules and sensitivity to alarmins (thymic stromal lymphopoietin and interleukin-33) between ILC2s and resident memory Th2 lymphocytes, the role of the adaptive axis of type 2 immunity remains unclear. We show that mice deficient in CD27, a member of the tumor necrosis factor receptor superfamily, are more resistant to obesity and associated disorders. A comparative analysis of the CD4 compartment of both strains revealed higher numbers of fat-resident memory Th2 cells in the adipose tissue of CD27 knockout mice, which correlated with decreased programmed cell death protein 1-induced apoptosis. Our data point to a non-redundant role for Th2 lymphocytes in obesogenic conditions., SCOPUS: ar.j, info:eu-repo/semantics/published

L’obésité représente un défi sanitaire global et substantiel. Engendrant de nombreuses comorbidités, son incidence augmente dans toutes les régions du monde et fait peser un poids important aussi bien sur les sociétés que les individus. Comprendre ses mécanismes et développer des stratégies thérapeutiques efficaces est donc un enjeu essentiel. A l’homéostasie, le tissu adipeux présente un environnement de type 2 anti-inflammatoire essentiel à sa fonction. La production de cytokines de type 2 (i.e. IL-5, IL-13) par les cellules lymphoïdes innées de type 2 (ILC2), et potentiellement les lymphocytes Th2, a notamment été associée au maintien de l’homéostasie par différents mécanismes impliquant l’accumulation d’éosinophiles et de macrophages anti-inflammatoires. Durant l’obésité, l’infiltrat immunitaire du tissu adipeux est profondément modifié. Les populations résidentes anti-inflammatoires deviennent alors dysfonctionnelles tandis que des cellules inflammatoires s’accumulent et mènent au développement d’une inflammation systémique chronique et de bas grade responsable des nombreuses comorbidités liées à l’obésité. De plus en plus d’études suggèrent que le maintien ou la restauration des populations anti-inflammatoires du tissu adipeux permet de limiter le développement de l’obésité et des troubles métaboliques associés. Identifier les mécanismes menant à la dysfonction des cellules anti-inflammatoires du tissu adipeux durant l’obésité présente donc un intérêt thérapeutique certain. Ce travail a ainsi permis d’identifier le rôle inattendu de deux voies de costimulation dans l’inhibition de la réponse de type 2 dans le tissu adipeux durant l’obésité. Premièrement, le récepteur costimulateur CD27, préalablement connu pour favoriser le développement de réponses lymphocytaires de type 1, a été identifié comme un régulateur négatif des Th2 du tissu adipeux, limitant à la fois leur survie et leur fonction. Ainsi, les souris CD27KO affichent un nombre de Th2 fonctionnels supé, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

BACKGROUND: Aspirin-exacerbated respiratory disease (AERD) is associated with high levels of cysteinyl leukotrienes, prostaglandin D2, and low levels of prostaglandin E2. Further, 15-hydroxyeicosatetraenoic acid (15-HETE) levels may have predictive value in therapeutic outcomes of aspirin desensitization. Accumulation of nasal group 2 innate lymphoid cells (ILC2s) has been demonstrated during COX-1 inhibition in AERD, although the relationships between tissue ILC2 accumulation, reaction symptom severity, and novel lipid biomarkers are unknown. OBJECTIVE: We sought to determine whether novel lipid mediators are predictive of nasal ILC2 accumulation and symptom scores during COX-1 inhibitor challenge in patients with AERD. METHODS: Blood and nasal scraping samples from patients with AERD were collected at baseline and COX-1 inhibitor reaction and then processed for flow cytometry for nasal ILC2s and serum for lipidomic analysis. RESULTS: Eight patients with AERD who were undergoing aspirin desensitization were recruited. Of the 161 eicosanoids tested, 42 serum mediators were detected. Baseline levels of 15-HETE were negatively correlated with the change in numbers of airway ILC2s (r = -0.6667; P = .0428). Docosahexaenoic acid epoxygenase metabolite 19,20-dihydroxy-4Z,7Z,10Z,13Z,16Z-docosapentaenoic acid (19,20-diHDPA) was positively correlated with both changes in airway ILC2s (r = 0.7143; P = .0305) and clinical symptom scores (r = 0.5000; P = .0081). CONCLUSION: Low levels of baseline 15-HETE predicted a greater accumulation of airway ILC2s in patients with AERD who were receiving COX-1 inhibition. Further, increases in the cytochrome P pathway metabolite 19,20-dihydroxy-4Z,7Z,10Z,13Z,16Z-docosapentaenoic acid (19,20-diHDPA) were associated with increased symptoms and nasal ILC2 accumulation. Future studies to assess how these mediators might control ILC2s may improve the understanding of AERD pathogenesis.

ILC2s are key players in the emergence of type 2 inflammation in many pulmonary diseases. While several phenotypic markers can be used to identify ILC2s, our method utilizes the surface markers CD127 and ST2 to classify a group of type 2 cytokine-producing ILC2s upon activation by the fungal allergen Alternaria alternata . Here, we provide our protocol for the detection and isolation of a highly pure population of pulmonary mouse ILCs via flow cytometry and cell sorting. We also describe the methods for in vitro stimulation to assess the functionality of ILC2s.

Demodex mites are commensal parasites of hair follicles (HFs). Normally asymptomatic, inflammatory outgrowth of mites can accompany malnutrition, immune dysfunction, and aging, but mechanisms restricting Demodex outgrowth are not defined. Here, we show that control of mite HF colonization in mice required group 2 innate lymphoid cells (ILC2s), interleukin-13 (IL-13), and its receptor, IL-4Ra-IL-13Ra1. HF-associated ILC2s elaborated IL-13 that attenuated HFs and epithelial proliferation at anagen onset; in their absence, Demodex colonization led to increased epithelial proliferation and replacement of gene programs for repair by aberrant inflammation, leading to the loss of barrier function and HF exhaustion. Humans with rhinophymatous acne rosacea, an inflammatory condition associated with Demodex, had increased HF inflammation with decreased type 2 cytokines, consistent with the inverse relationship seen in mice. Our studies uncover a key role for skin ILC2s and IL-13, which comprise an immune checkpoint that sustains cutaneous integrity and restricts pathologic infestation by colonizing HF mites.

Epidemiological and experimental studies have shown that di-(2-ethylhexyl) phthalate (DEHP), a plasticizer, can aggravate allergic diseases. DEHP promotes adaptive immune responses, although its effect on the innate immune system remains largely unknown. The present study investigated the effects of DEHP on group 2 innate lymphoid cells (ILC2) that produce Th2 cytokines in response to epithelial cell-derived cytokines, such as interleukin (IL)-33. ILC2 (lineage-negative, CD45.2⁺, Sca1⁺, KLRG1⁺) were isolated from the lungs of C57BL/6 J mice. Co-exposure to DEHP and IL-33 significantly increased IL-5 release from ILC2, whose level was higher than that of the vehicle and IL-33 alone. The effects of DEHP in the presence of IL-33 showed an inverted-U dose-response. The present is the first report showing that DEHP exacerbates allergy through the innate immune system.

Despite the well-accepted view that chronic inflammation contributes to the pathogenesis of Duchenne muscular dystrophy (DMD), the function and regulation of eosinophils remain an unclear facet of type II innate immunity in dystrophic muscle. We report the observation that group 2 innate lymphoid cells (ILC2s) are present in skeletal muscle and are the principal regulators of muscle eosinophils during muscular dystrophy. Eosinophils were elevated in DMD patients and dystrophic mice along with interleukin (IL)-5, a major eosinophil survival factor that was predominantly expressed by muscle ILC2s. We also find that IL-33 was upregulated in dystrophic muscle and was predominantly produced by fibrogenic/adipogenic progenitors (FAPs). Exogenous IL-33 and IL-2 complex (IL-2c) expanded muscle ILC2s and eosinophils, decreased the cross-sectional area (CSA) of regenerating myofibers, and increased the expression of genes associated with muscle fibrosis. The deletion of ILC2s in dystrophic mice mitigated muscle eosinophilia and impaired the induction of IL-5 and fibrosis-associated genes. Our findings highlight a FAP/ILC2/eosinophil axis that promotes type II innate immunity, which influences the balance between regenerative and fibrotic responses during muscular dystrophy.

Innate lymphoid cells (ILCs) are a specialized arm of the innate immune system responsible for protecting the mucosal barrier and defending against infection. ILC activation and cytokine production occurs in response to stimuli in the local environment making them an important initiators of the early immune response. However, they also contribute to inflammatory diseases and thus must be tightly regulated. The development and function of ILCs is dependent on the tight regulation of transcription factors. Two transcription factors GFI1 and GFI1B are involved in this differentiation but have been poorly studied and thus how they shape differentiation is not clear. GFI1 and GFI1B was differentially expressed throughout ILC development. GFI1B expression was limited to the early progenitors whereas GFI1 was expressed in both early progenitors and in all mature ILC subsets in the peripheral organs. GFI1B expression identified the early progenitors in the bone marrow with the capacity to give rise to all ILC subsets. GFI1B expression is also required for the development of progenitors in the bone marrow and lung ILC2. This impacted the lung inflammatory response induced in mice treated with papain as the eosinophil recruitment by ILC2s was impaired. In contrast, GFI1 was highly expressed in mature NK cells and was vital for development and maintenance of these cells. GFI1 regulated multiple NK cell pathways, including proliferation, homing to peripheral organs and effector functions. Defects in these functions impaired the protection mediated by NK cells against metastatic melanoma cells. Together, GFI1 and GFI1B are both key regulators of ILC development, although they regulate different stages of ILC development and function. ILCs are enriched at the mucosal barrier, particularly at the gastrointestinal tract. They play an important role in protecting against infections but also have the capacity to promote inflammation when dysregulated. Their role in the development of

Aging impairs the integrated immunometabolic responses, which have evolved to maintain core body temperature in homeotherms to survive cold stress, infections, and dietary restriction. Adipose tissue inflammation regulates the thermogenic stress response, but how adipose tissue-resident cells instigate thermogenic failure in the aged are unknown. Here, we define alterations in the adipose-resident immune system and identify that type 2 innate lymphoid cells (ILC2s) are lost in aging. Restoration of ILC2 numbers in aged mice to levels seen in adults through IL-33 supplementation failed to rescue old mice from metabolic impairment and increased cold-induced lethality. Transcriptomic analyses revealed intrinsic defects in aged ILC2, and adoptive transfer of adult ILC2s are sufficient to protect old mice against cold. Thus, the functional defects in adipose ILC2s during aging drive thermogenic failure.

Chronic intestinal inflammation, the predominant characteristic of Inflammatory Bowel Diseases (IBD), can have serious long-term complications. Most notable is the promotion of tumorigenesis and colorectal cancer (CRC), or colitis associated cancer (CAC). Similarly, the development of small bowel cancer has also been attributed to chronic inflammation. In addition to environmental factors and genetic susceptibility, the inflammation associated with IBD can result from an intolerance to commensal organisms, which are recognized by pattern recognition receptors (PRRs). One of these PRRs, Absent In Melanoma 2 (AIM2), binds microbial- and host-derived dsDNA released into the cytosol, promoting formation of the multi-protein complex known as the inflammasome, in both epithelial and immune cells. AIM2-mediated cytokine release and signaling facilitates host defenses as well as intestinal epithelial cell (IEC) homeostasis. Additionally, AIM2 protects against aberrant activation of the PI3K and c-Myc pathways during CRC but has yet to be studied in small intestine inflammation induced cancer. This anti-tumorigenic response in the colon has been attributed to AIM2 expression in intestinal stem cells (ISCs), while other IEC populations have not been explored. Homeostasis in IEC populations require tightly coordinated equilibrium mediated by the constant shedding and self-renewing property of ISCs. Type 2 cytokine-secreting Tuft cells are IECs characterized by their expression of Doublecortin-Like Kinase 1 (DCLK1). Tuft cells can promote tissue repair, resolution of inflammation, and host defense against helminth infections. Although not fully understood, DCLK1 has also been proposed to mark a distinct cancer-associated stem cell population in the colon. However, the contribution of DCLK1 and Tuft cells during small bowel tumorigenesis is unknown. When examining markers of intestinal epithelium differentiation IEC cultures with Aim2 deletion repeatedly demonstrated diminished

Background: Systemic mastocytosis is a hematological disease in which aberrant mast cells accumulate because of gain-of-function mutations in the KIT receptor. Group 2 innate lymphoid cells (ILC2s) are effector cells of type 2 immune responses that also express KIT and colocalize with mast cells at barrier tissue sites. In mouse models, mast cell-ILC2 crosstalk can drive local inflammation. However, a possible role for ILC2s in the pathophysiology of mastocytosis remains unexplored. Objective: We sought to characterize circulating ILC2s in a clinically diverse cohort of patients with mastocytosis. Methods: We included 21 adults with systemic mastocytosis and 18 healthy controls. Peripheral blood ILC2 abundance and phenotype were analyzed by flow cytometry and correlated to clinical characteristics, including the presence of the D816V KIT mutation. Results: ILC2 levels were significantly higher in D816V+ patients with mastocytosis compared with D816V− patients or healthy controls. We observed increased proportions of KIT+ ILC2s among patients with mastocytosis, regardless of D816V status. Patients with skin involvement and itch showed the highest levels of ILC2s, which was independent from atopy or serum tryptase levels. Allele-specific quantitative PCR showed that the vast majority of ILC2s did not carry the D816V mutation. Conclusions: Our findings suggest a role for ILC2s and pathogenic ILC2-mast cell crosstalk in mastocytosis. We hypothesize that a high cutaneous D816V+ m

Innate lymphoid cells (ILCs) are generated early during ontogeny and persist predominantly as tissue-resident cells. Here, we examined how ILCs are maintained and renewed within tissues. We generated a single cell atlas of lung ILC2s and found that Il18r1+ ILCs comprise circulating and tissue-resident ILC progenitors (ILCP) and effector-cells with heterogeneous expression of the transcription factors Tcf7 and Zbtb16, and CD103. Our analyses revealed a continuous differentiation trajectory from Il18r1+ ST2- ILCPs to Il18r- ST2+ ILC2s, which was experimentally validated. Upon helminth infection, recruited and BM-derived cells generated the entire spectrum of ILC2s in parabiotic and shield chimeric mice, consistent with their potential role in the renewal of tissue ILC2s. Our findings identify local ILCPs and reveal ILCP in situ differentiation and tissue adaptation as a mechanism of ILC maintenance and phenotypic diversification. Local niches, rather than progenitor origin, or the developmental window during ontogeny, may dominantly imprint ILC phenotypes in adult tissues.

Acute kidney injury (AKI) can be fatal and is a well-defined risk factor for the development of chronic kidney disease. Group 2 innate lymphoid cells (ILC2s) are innate producers of type-2 cytokines and are critical regulators of homeostasis in peripheral organs. However, our knowledge of their function in the kidney is relatively limited. Recent evidence suggests that increasing ILC2 numbers by systemic administration of recombinant interleukin (IL)-25 or IL-33 protects against renal injury. Whilst ILC2s can be induced to protect against ischemic- or chemical-induced AKI, the impact of ILC2 deficiency or depletion on the severity of renal injury is unknown. Firstly, the phenotype and location of ILC2s in the kidney was assessed under homeostatic conditions. Kidney ILC2s constitutively expressed high levels of IL-5 and were located in close proximity to the renal vasculature. To test the functional role of ILC2s in the kidney, an experimental model of renal ischemia-reperfusion injury (IRI) was used and the severity of injury was assessed in wild-type, ILC2-reduced, ILC2-deficient, and ILC2-depleted mice. Surprisingly, there were no differences in histopathology, collagen deposition or mRNA expression of injury-associated (Lcn2), inflammatory (Cxcl1, Cxcl2, and Tnf) or extracellular matrix (Col1a1, Fn1) factors following IRI in the absence of ILC2s. These data suggest the absence of ILC2s does not alter the severity of renal injury, suggesting possible redundancy. Therefore, other mechanisms of type 2-mediated immune cell activation likely compensate in the absence of ILC2s. Hence, a loss of ILC2s is unlikely to increase susceptibility to, or severity of AKI.

The recent discovery of innate lymphoid cells has revolutionized our understanding of the pathogenesis of immune diseases including allergy and asthma. Innate lymphoid cells (ILCs) are a heterogeneous collection of lymphocytes that lack antigen-specificity (non-T, non-B cells) and potently produce characteristic cytokines of T cell subsets (Th1, Th2, Th17). ILCs are divided into group 1 (ILC1s), group 2 (ILC2s), or group 3 (ILC3s). Similar to Th2 cells, ILC2s produce IL-4, IL-5, and IL-13, among others, and are present in increased numbers in samples from patients with many allergic disorders including asthma and chronic rhinosinusitis (CRS). Animal models have identified that ILC2s contribute to eosinophilic tissue infiltration, airway hyperresponsiveness, mucus production, as well as coordinate adaptive immune responses. Finally, recent studies support regulation of ILC2s by neuro-immune mechanisms as well as demonstrate a significant degree of plasticity between ILC subsets that may impact the immune responses in asthma and allergic airway diseases. Here, we review the current literature on ILC2s in human asthma and allergic airway diseases, as well as highlight some recent mechanistic insights into ILC2 function from in vitro studies and in vivo animal models.

Background: Group 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E-2 is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation. Objective: We set out to investigate how PGE(2) regulates human ILC2 function. Methods: The effects of PGE(2) on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE(2) receptor expression. Results: PGE(2) inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE(2) downregulated the expression of IL-2 receptor alpha (CD25). In line with this observation, PGE(2) decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s. Conclusion: Our findings reveal that PGE(2) limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

In the small intestine, type 2 responses are regulated by a signaling circuit that involves tuft cells and group 2 innate lymphoid cells (ILC2s). Here, we identified the microbial metabolite succinate as an activating ligand for small intestinal (SI) tuft cells. Sequencing analyses of tuft cells isolated from the small intestine, gall bladder, colon, thymus, and trachea revealed that expression of tuft cell chemosensory receptors is tissue specific. SI tuft cells expressed the succinate receptor (SUCNR1), and providing succinate in drinking water was sufficient to induce a multifaceted type 2 immune response via the tuft-ILC2 circuit. The helminth Nippostrongylus brasiliensis and a tritrichomonad protist both secreted succinate as a metabolite. In vivo sensing of the tritrichomonad required SUCNR1, whereas N. brasiliensis was SUCNR1 independent. These findings define a paradigm wherein tuft cells monitor microbial metabolites to initiate type 2 immunity and suggest the existence of other sensing pathways triggering the response to helminths.

Although mutations of the dystrophin gene are the causative defect in Duchenne muscular dystrophy (DMD) patients, secondary disease processes such as inflammation contribute greatly to the pathogenesis of DMD. Genetic and histological studies have shown that distinct facets of the immune system promote muscle degeneration or regeneration during muscular dystrophy through mechanisms that are only beginning to be defined. Although histological methods have allowed the enumeration and localization of immune cells within dystrophic muscle, they are limited in their ability to assess the full spectrum of phenotypic states of an immune cell population and its functional characteristics. This chapter highlights flow cytometry methods for the isolation and functional study of immune cell populations from muscle of the mdx mouse model of DMD. We include a detailed description of preparing single-cell suspensions of dystrophic muscle that maintain the integrity of cell-surface markers used to identify macrophages, eosinophils, group 2 innate lymphoid cells, and regulatory T cells. This method complements the battery of histological assays that are currently used to study the role of inflammation in muscular dystrophy, and provides a platform capable of being integrated with multiple downstream methodologies for the mechanistic study of immunity in muscle degenerative diseases.

Recent observations clearly highlight the critical role of type 2 innate lymphoid cells in maintaining the homeostasis of adipose tissues in humans and mice. This cell population promotes beiging and limits adiposity directly and indirectly by sustaining a Th2-prone environment enriched in eosinophils and alternatively activated macrophages. Accordingly, the number and function of type 2 innate lymphoid cells (ILC2s) are strongly impaired in obese individuals. In this work, we identify the PD-1-PD-L1 pathway as a factor leading to ILC2 destabilization upon high-fat feeding resulting in impaired tissue metabolism. Tumor necrosis factor (TNF) appears to play a central role, triggering interleukin-33 (IL-33)-dependent PD-1 expression on ILC2s and recruiting and activating PD-L1hi M1 macrophages. PD-1 blockade partially restores the type 2 innate axis, raising the possibility of restoring tissue homeostasis. The function of ILC2s is compromised during obesity. Here, Oldenhove et al. show that ILC2 inhibition is mediated by the PD-1-PD-L1 pathway. PD-1 blockade in obese mice improved ILC2 function, reinforced type 2 innate responses, and promoted tissue homeostasis. PD-1 may therefore represent a target for immune intervention in obesity-associated disorders., SCOPUS: ar.j, info:eu-repo/semantics/published

To investigate the role of immune cells in lung regeneration, we used a unilateral pneumonectomy model that promotes the formation of new alveoli in the remaining lobes. Immunofluorescence and single-cell RNA sequencing found CD115+ and CCR2+ monocytes and M2-like macrophages accumulating in the lung during the peak of type 2 alveolar epithelial stem cell (AEC2) proliferation. Genetic loss of function in mice and adoptive transfer studies revealed that bone marrow-derived macrophages (BMDMs) traffic to the lung through a CCL2-CCR2 chemokine axis and are required for optimal lung regeneration, along with Il4ra-expressing leukocytes. Our data suggest that these cells modulate AEC2 proliferation and differentiation. Finally, we provide evidence that group 2 innate lymphoid cells are a source of IL-13, which promotes lung regeneration. Together, our data highlight the potential for immunomodulatory therapies to stimulate alveologenesis in adults.

Type 2 immune responses are generated to provide protection against parasitic helminth infections, however these responses also cause the pathologies associated with allergic inflammation. Studies of the cell types and signalling pathways that mediate Type 2 immune responses have been previously undertaken with the goals of efficient development of vaccines against helminths, and identification of pathways that can be inhibited to decrease the damage caused by allergic inflammation. The cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13) mediate many of the downstream effector functions of the Type 2 immune response. To study the mechanisms that control expression of these two cytokines I have used a novel dual cytokine IL-4 and IL-13 transgenic reporter mouse. Utilising this tool along with other IL-4 reporter mice I have discovered that the amount of T cell receptor (TCR) signalling modulates the allelic expression of IL-4 by CD4⁺ T cells. The transgenic IL-4 reporter mouse has for the first time allowed independent measurement of the effects of IL-4 deficiency on the expression of IL-4 in vivo. Using this system I have found that IL- 4 is not required for the in vivo generation or expansion of IL-4 producing CD4⁺ T cells. Th2 differentiated CD4⁺ T cells also expresses IL-13, however the dual reporter mice have demonstrated that IL-13 is expressed consistently later than IL-4 in vitro, and IL-13 requires constant, or multiple exposures to TCR stimulus for expression to be induced. IL-13 expression is absent from lymph node CD4⁺ T cells during exposure to allergens or helminth infection. Sequestration of CD4⁺ T cells in the lymph node does not impact the number of IL-13 expressing CD4⁺ T cells in the lung during a helminth infection, indicating that adaptive immune cell derived IL-13 may be entirely produced by lung resident cells not requiring transit through the lymph node. I have characterised a population of innate lymphoid cells (ILCs) within the skin an

In humans, allergic disease bears striking resemblance to the host response to helminth infection. Thus, we studied N. brasiliensis infection in mice to identify factors that initiate host immunity and identified three that bind the environmental polysaccharide chitin. We further demonstrated that purified chitin acutely induces lung inflammation in mice, similar to that observed in human allergic disease, dependent on resident group 2 innate lymphoid cells (ILC2s). Given their number, distribution and function, lung ILC2s likely coordinate responses with resident epithelial cells that monitor barrier interactions with the environment. In this thesis, we demonstrate that alveolar type II (ATII) cells are the main source of interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP) generated in response to chitin or N. brasiliensis challenge. IL-33 and TSLP synergistically activate ILC2s to produce IL-5, IL-13 and IL-9, and autocrine IL-9 promotes an ILC2 transcriptional program associated with rapid and robust cytokine production necessary to optimize epithelial gene responses in the conducting airways. Thus, ILC2s link a specialized, distal, epithelial population involved in alveolar function with more proximal epithelia that regulate airway flow, revealing a key role for ILC2s in tissue homeostasis that might underlie similar organizational hierarchies for innate lymphoid cells in other organs.

Type II innate lymphoid cells (ILC2) are a novel population of lineage-negative cells that produce high levels of Th2 cytokines IL-5 and IL-13. ILC2 are found in human respiratory and gastrointestinal tissue as well as in skin. Studies from mouse models of asthma and atopic dermatitis suggest a role for ILC2 in promoting allergic inflammation. The epithelial cytokines IL-25, IL-33, and TSLP, as well as the lipid mediator leukotriene D4, have been shown to potently activate ILC2 under specific conditions and supporting the notion that many separate pathways in allergic disease may result in stimulation of ILC2. Ongoing investigations are required to better characterize the relative contribution of ILC2 in allergic inflammation as well as mechanisms by which other cell types including conventional T cells regulate ILC2 survival, proliferation, and cytokine production. Importantly, therapeutic strategies to target ILC2 may reduce allergic inflammation in afflicted individuals. This review summarizes the development, surface marker profile, cytokine production, and upstream regulation of ILC2, and focuses on the role of ILC2 in common allergic diseases.

by Verena Rinnofner, Masterarbeit University of Innsbruck 2020

by Verena Rinnofner, Masterarbeit University of Innsbruck 2020