Depletion Of Innate Lymphoid Cells Research Articles

Microbiota instruct IL-17A-producing innate lymphoid cells to promote skin inflammation in cutaneous leishmaniasis.

Innate lymphoid cells (ILCs) comprise a heterogeneous population of immune cells that maintain barrier function and can initiate a protective or pathological immune response upon infection. Here we show the involvement of IL-17A-producing ILCs in microbiota-driven immunopathology in cutaneous leishmaniasis. IL-17A-producing ILCs were RORγt+ and were enriched in Leishmania major infected skin, and topical colonization with Staphylococcus epidermidis before L. major infection exacerbated the skin inflammatory responses and IL-17A-producing RORγt+ ILC accumulation without impacting type 1 immune responses. IL-17A responses in ILCs were directed by Batf3 dependent CD103+ dendritic cells and IL-23. Moreover, experiments using Rag1-/- mice established that IL-17A+ ILCs were sufficient in driving the inflammatory responses as depletion of ILCs or neutralization of IL-17A diminished the microbiota mediated immunopathology. Taken together, this study indicates that the skin microbiota promotes RORγt+ IL-17A-producing ILCs, which augment the skin inflammation in cutaneous leishmaniasis.

Mist1+ gastric isthmus stem cells are regulated by Wnt5a and expand in response to injury and inflammation in mice

Background and aimsThe gastric epithelium undergoes continuous turnover. Corpus epithelial stem cells located in the gastric isthmus serve as a source of tissue self-renewal. We recently identified the transcription factor...

Graft Versus Host Disease Leads to Elimination of Tissue-Resident Innate Lymphoid Cells Following Experimental and Clinical Allogeneic Transplantation

A potential role for endogenous innate lymphoid cells (ILCs) in prevention of gastrointestinal (GI) GVHD has recently been described in murine and clinical models, and experimental approaches for adoptive cellular therapy with ILCs have recently been described as well. However, the specific in vivo roles of tissue-resident ILCs and their capacity for reconstitution post-transplant remain unclear. We thus sought to characterize the significance and tissue distribution of ILCs after allogeneic bone marrow transplant (allo-BMT) in mouse models and in patients. In order to specifically assess the functional role of ILCs after allo-BMT, we established a clinically relevant acute GVHD model based on sex mismatched H-Y antigens. Lethally irradiated Rag2-/-male mice (Thy1.2, B6) were transplanted with T cell-depleted (TCD) BM and purified T cells obtained from wild-type female mice (Thy1.1, B6). To specifically deplete host-derived ILCs (and not donor cells), recipient mice were treated with an anti-Thy1.2 antibody or an anti-isotype antibody prior to BMT. Pre-transplant depletion of ILCs induced significantly worse systemic signs of GVHD, as well as increased thymic injury and intestinal GVHD pathology, indicating an important role for endogenous ILCs in tissue protection after allo-BMT in this context. To better understand the roles of tissue-resident ILCs in reducing pathology post-BMT, we evaluated ILC subsets in different GVHD target organs after allo-BMT. Two weeks after MHC-mismatched (C57BL6 into BALB/c) TCD-BMT, both donor- and host-derived ILCs could be detected in the liver, lungs, and intestines. Liver was characterized by a high number of NK cells and ILC1s, while lungs contained a high proportion of ILC2s. The small intestine contained a relatively greater proportion of ILC3s. For all tissues analyzed, the majority of ILCs were host-derived. During T cell replete BMT resulting in GVHD, both donor and host-derived ILCs were significantly reduced in all three tissues compared to TCD-BMT mice, and this was true for all ILC lineages. To better understand the loss of donor-derived ILCs in GVHD, we investigated ILC precursors in recipient marrow post-BMT, hypothesizing that an impairment of ILC precursors could explain the loss of all ILC lineages in the various tissues analyzed. Indeed, we found a significant loss of CLPs, αLPs, CHILPs, and ILC2Ps in mice with GVHD, suggesting that bone marrow involvement with GVHD induced a loss of ILC precursors impairing their reconstitution. We next sought to evaluate if the loss of tissue-resident ILCs in GVHD target organs after experimental BMT was relevant for clinical transplantation. To evaluate ILC frequencies in patient tissues post-transplant, duodenal biopsies were collected from patients undergoing clinically indicated endoscopy to work up symptoms of acute upper GI (UGI) GVHD. In total, duodenal samples were collected from ten patients post-transplant and 6/10 had histologic evidence of GVHD on biopsy (Table 1). While frequencies were low, ILCs could be identified by FACS in digested lamina propria of duodenal biopsy specimens. Notably, ILC frequencies were significantly lower in patients with biopsy-proven UGI GVHD, and duodenal ILCs could be identified in only 1/6 patients with histologic evidence of GVHD (Fig 1). Among the ILCs that could be identified, ILC1s represented the greatest proportion of ILC populations within the duodenal lamina propria. Accordingly, the frequency of ILC1s was significantly reduced in transplant patients with biopsy-proven UGI GVHD. Additionally, we were able to evaluate paired peripheral blood and duodenal biopsy samples in a small subset of patients. Although the numbers were limiting, this cohort suggested that ILC2s may represent a greater proportion of ILCs in peripheral blood than in the duodenum post-transplant. Overall, clinical findings were consistent with experimental models demonstrating a reduction of ILCs in GVHD. In conclusion, tissue-resident ILCs contribute to tissue protection after allo-BMT, but GVHD leads to elimination of pre-existing ILCs and loss of ILC precursors in the marrow, impairing their reconstitution. Most duodenal ILCs in clinical biopsy samples post-transplant were ILC1s in this patient cohort, and patients with biopsy-proven UGI GVHD demonstrated significant loss of the few lamina propria ILCs that could be identified in clinical duodenal biopsies. Disclosures Hanash: Nexus Global Group LLC: Consultancy.

Induction of autophagy in Cx3cr1+ mononuclear cells limits IL-23/IL-22 axis-mediated intestinal fibrosis

Intestinal fibrosis is an excessive proliferation of myofibroblasts and deposition of collagen, a condition frequently seen in Crohn’s disease (CD). The mechanism underlying myofibroblast hyper-proliferation in CD needs to be better understood. In this report, we found that mTOR inhibitor rapamycin or mTOR deletion in CX3Cr1+ mononuclear phagocytes inhibits expression of interleukin (IL)−23, accompanied by reduced intestinal production of IL-22 and ameliorated fibrosis in the TNBS-induced fibrosis mouse model. This inhibition of IL-23 expression is associated with elevated autophagy activity. Ablating the autophagy gene Atg7 increases the expression of IL-23, leading to increased expression of IL-22 and increased fibrosis. Both induction of IL-22 and intestinal fibrosis occurred in RAG−/− mice and depletion of innate lymphoid cells (ILCs) attenuates the fibrotic reaction, suggesting that the pro-fibrotic process is independent of T and B cells. Moreover, IL-22 facilitates the transformation of fibroblasts into myofibroblasts. Finally, the fibrotic reaction was attenuated upon neutralization of either IL-23 or IL-22. Altogether, this study elucidated a signaling cascade underlying intestinal fibrosis in which altered mTOR/autophagy in CX3Cr1+ mononuclear phagocytes up-regulates the IL-23/IL-22 axis, leading to an excessive fibrotic response. Thus, our findings suggest that this cascade could be a therapeutic target for alleviation of CD fibrosis.

Graft-Versus-Host Disease Leads to Systemic Elimination of Innate Lymphoid Cells and Abolishes Their Development

Innate lymphoid cells (ILCs) are associated with protective mucosal response after experimental allogeneic BMT. However, the specific in vivo roles of ILCs and their capacity for reconstitution post-transplant remain unclear. We therefore sought to characterize the significance and tissue distribution of ILCs after allo-BMT. To study the role of ILCs after allo-BMT, we established a clinically relevant acute GVHD model based on H-Y antigen mismatch. Lethally irradiated Rag2−/− male mice (Thy1.2, B6) were transplanted with T cell depleted (TCD) bone marrow and purified T cells obtained from wild-type female mice (Thy1.1, B6). To deplete host-derived ILCs, recipient mice were treated with an anti-Thy1.2 antibody or an anti-isotype antibody prior to BMT. Pre-transplant depletion of ILCs induced significantly worse systemic signs of GVHD, as well as increased thymic injury and intestinal GVHD pathology, indicating an important role for ILCs after BMT (Fig. 1). To better understand the systemic roles of ILCs, we evaluated ILC subsets in the intestine, liver, and lungs after allo-BMT. Two weeks after MHC-mismatched (C57BL6 into BALB/c) TCD-BMT, both donor- and host-derived ILCs could be detected in all tissues. Liver was characterized by a high number of NK cells and ILC1s, while the lungs contained a high proportion of ILC2s, and small intestine contained relatively greater ILC3s. For all tissues analyzed, the majority of ILCs were host-derived. During T cell replete BMT resulting in GVHD, both donor and host-derived ILCs were significantly reduced in all tissues compared to TCD-BMT mice (Fig. 2). To better understand the loss of donor-derived ILCs caused by donor T cells, we investigated ILC precursors in recipient marrow post-BMT, and found a significant loss of CLPs, αLPs, CHILPs, and ILC2 precursors in mice with GVHD. These data suggested that bone marrow involvement with GVHD induced a loss of ILC precursors impairing their reconstitution post-BMT. Given the loss of ILCs occurring post-BMT and the increased GVHD severity in BMT recipients lacking ILCs, we hypothesized that expansion of the ILC compartment pre-transplant could help protect BMT recipients from GVHD. Aryl hydrocarbon receptor (AhR) signaling has been associated with ILC3 development and maintenance during intestinal homeostasis. We thus evaluated the effect of diet-derived AhR ligands (AhRL) on intestinal ILCs and BMT outcomes. Prior to transplantation, mice were given diets containing or lacking AhRL. Mice on an AhRL-poor diet showed reduced intestinal ILC3s, increased intestinal GVHD pathology, and increased mortality post-BMT. In conclusion, ILCs contribute to tissue protection following allo-BMT, but GVHD leads to elimination of pre-existing ILCs and abolishes their development. Dietary supplementation with AhRL-rich foods may represent an approach to enhance mucosal immunity and intestinal recovery post-BMT.

The JAK inhibitor ruxolitinib reduces inflammation in an ILC3-independent model of innate immune colitis.

Innate immunity contributes to the pathogenesis of inflammatory bowel disease (IBD). However, the mechanisms of IBD mediated by innate immunity are incompletely understood and there are limited models of spontaneous innate immune colitis to address this question. Here we describe a new robust model of colitis occurring in the absence of adaptive immunity. RAG1-deficient mice expressing TNFAIP3 in intestinal epithelial cells (TRAG mice) spontaneously developed 100% penetrant, early-onset colitis that was limited to the colon and dependent on intestinal microbes but was not transmissible to co-housed littermates. TRAG colitis was associated with increased mucosal numbers of innate lymphoid cells (ILC) and depletion of ILC prevented colitis in TRAG mice. ILC depletion also therapeutically reversed established colitis in TRAG mice. The colitis in TRAG mice was not prevented by interbreeding to mice lacking group 3 ILC, nor by depletion of TNF. Treatment with the JAK inhibitor ruxolitinib ameliorated colitis in TRAG mice. This new model of colitis, with its predictable onset and colon-specific inflammation will have direct utility in developing a more complete understanding of innate immune mechanisms that can contribute to colitis and in pre-clinical studies for effects of therapeutic agents on innate immune mediated IBD.

Lack of Type 2 Innate Lymphoid Cells Promotes a Type I-Driven Enhanced Immune Response in Contact Hypersensitivity

Allergic contact dermatitis and its animal model, contact hypersensitivity, are T-cell-mediated inflammatory skin diseases that require activation of the innate immune system. Here we investigate the role of innate lymphoid cells (ILCs) during the elicitation phase of 2,4,6-trinitrochlorobenzene-induced contact hypersensitivity using EomesGfp/+ x Rorc(γt)-CreTg x Rosa26RYfp/+ reporter mice. Ear swelling responses, cutaneous ILC numbers, and cytokine production were determined at different time points. Functional analyses were performed in a CD90.1/.2 congenic adoptive transfer model that allowed selective antibody-mediated depletion of ILCs before hapten challenge, and in Rorasg/floxIl7rCre/+ mice, which lack ILC2. Hapten challenge induced early increases of natural killer cells in skin and ear draining lymph nodes corresponding to the peak ear swelling response. In contrast, ILC1, 2, and 3 showed a delayed increase in numbers corresponding to the contact hypersensitivity resolution phase. Hapten challenge induced increased marker cytokines in all ILC subtypes and an activated phenotype in ILC2. Depletion of all ILC resulted in a significantly enhanced ear swelling response. Similarly, ILC2-deficient mice (Rorasg/floxIl7rCre/+) displayed increased ear swelling responses on hapten challenge, suggesting that ILC2 act as negative regulators in the type 1-dominated immune response of contact hypersensitivity.

Hvem expression in innate lymphoid cells mediates host defense against intestinal infection

Abstract The herpes virus entry mediator (HVEM), a member of the tumor necrosis factor receptor super family (TNFRSF14), has diverse functions in augmenting or inhibiting the immune response. We previously reported that epithelial HVEM signaling at mucosal barriers provides host defense against pathogenic bacteria, but the role of HVEM expression in innate lymphoid cells (ILC) in the mucosal immune system was unknown. To address this issue, we exposed RORgt-Cre × Hvemfl/fl mice with Yersinia enterocolitica (Y. enterocolitica), a small intestine infection model. We found increased bacterial translocation and decreased survival at an early time point. In these mice, Hvem is deleted in NK cells, ILC3 and in all T lymphocytes. Ifng−/− mice also showed reduced survival and increased bacterial translocation early after infection with Y. enterocolitica, demonstrating the importance of this cytokine for host defense. Interestingly, ILC from infected RORgt-Cre × Hvemfl/fl mice produced less IFNg after infection, but IFNg production by CD4+ T cells was not affected. Furthermore, in CD4-Cre × Hvemfl/fl mice, which deleted HVEM only in CD4+ T cells but not in ILCs, were not more susceptible to Y. enterocolitica. Additionally, we found that depletion of ILC from Rag1-deficient mice resulted in increased bacterial translocation and decreased body weight at an early time point. Taken together, our data indicate first, that IFNg production by ILCs, such as NK cells and ILC3, is important for host defense during Y. enterocolitica infection. Second, although the activation of ILCs is regulated by cytokines, our data show that HVEM, a member of the TNF super family, also is required for their ability to respond by producing IFNg early after infection.

Innate lymphoid cells contribute to allergic airway disease exacerbation by obesity

Epidemiologic and clinical observations identify obesity as an important risk factor for asthma exacerbation, but the underlying mechanisms remain poorly understood. Type 2 innate lymphoid cells (ILC2s) and type 3 innate lymphoid cells (ILC3s) have been implicated, respectively, in asthma and adipose tissue homeostasis and in obesity-associated airway hyperresponsiveness (AHR). We sought to determine the potential involvement of innate lymphoid cells (ILCs) in allergic airway disease exacerbation caused by high-fat diet (HFD)-induced obesity. Obesity was induced by means of HFD feeding, and allergic airway inflammation was subsequently induced by means of intranasal administration of house dust mite (HDM) extract. AHR, lung and visceral adipose tissue inflammation, humoral response, cytokines, and innate and adaptive lymphoid populations were analyzed in the presence or absence of ILCs. HFD feeding exacerbated allergic airway disease features, including humoral response, airway and tissue eosinophilia, AHR, and TH2 and TH17 pulmonary profiles. Notably, nonsensitized obese mice already exhibited increased lung ILC counts and tissue eosinophil infiltration compared with values in lean mice in the absence of AHR. The numbers of total and cytokine-expressing lung ILC2s and ILC3s further increased in HDM-challenged obese mice compared with those in HDM-challenged lean mice, and this was accompanied by high IL-33 and IL-1β levels and decreased ILC markers in visceral adipose tissue. Furthermore, depletion of ILCs with an anti-CD90 antibody, followed by T-cell reconstitution, led to a profound decrease in allergic airway inflammatory features in obese mice, including TH2 and TH17 infiltration. These results indicate that HFD-induced obesity might exacerbate allergic airway inflammation through mechanisms involving ILC2s and ILC3s.

Expansion of CD25+ Innate Lymphoid Cells Reduces Atherosclerosis.

Innate lymphoid cells (ILCs) are a newly discovered subset of immune cells that promote tissue homeostasis and protect against pathogens. ILCs produce cytokines also produced by T lymphocytes that have been shown to affect atherosclerosis, but the influence of ILCs on atherosclerosis has not been explored. We demonstrate that CD25(+) ILCs that produce type 2 cytokines (ILC2s) are present in the aorta of atherosclerotic immunodeficient ldlr(-/-)rag1(-/-) mice. To investigate the role of ILCs in atherosclerosis, ldlr(-/-)rag1(-/-) mice were concurrently fed an atherogenic diet and treated with either ILC-depleting anti-CD90.2 antibodies or IL-2/anti-IL-2 complexes that expand CD25(+) ILCs. Lesion development was not affected by anti-CD90.2 treatment, but was reduced in IL-2/anti-IL-2-treated mice. These IL-2-treated mice had reduced very low-density lipoprotein cholesterol and increased triglycerides compared with controls and reduced apolipoprotein B100 gene expression in the liver. IL-2/anti-IL-2 treatment caused expansion of ILC2s in aorta and other tissues, elevated levels of IL-5, systemic eosinophila, and hepatic eosinophilic inflammation. Blockade of IL-5 reversed the IL-2 complex-induced eosinophilia but did not change lesion size. This study demonstrates that expansion of CD25-expressing ILCs by IL-2/anti-IL-2 complexes leads to a reduction in very low-density lipoprotein cholesterol and atherosclerosis. Global depletion of ILCs by anti-CD90.2 did not significantly affect lesion size indicating that different ILC subsets may have divergent effects on atherosclerosis.

TNF-α Producing Innate Lymphoid Cells (ILCs) Are Increased in Active Celiac Disease and Contribute to Promote Intestinal Atrophy in Mice.

Innate lymphoid cells (ILCs) are an emerging family of innate hematopoietic cells producing inflammatory cytokines and involved in the pathogenesis of several immune-mediated diseases. The aim of this study was to characterize the tissue distribution of ILCs in celiac disease (CD), a gluten-driven enteropathy, and analyze their role in gut tissue damage. ILC subpopulations were analyzed in lamina propria mononuclear cells (LPMCs) isolated from duodenal biopsies of CD patients and healthy controls (CTR) and jejunal specimens of patients undergoing gastro-intestinal bypass by flow cytometry. Cytokines and Toll-like receptors (TLR) were assessed in ILCs either freshly isolated or following incubation of control LPMC with peptidoglycan, poly I:C, or CpG, the agonists of TLR2, TLR3, or TLR9 respectively, by flow cytometry. The role of ILCs in gut tissue damage was evaluated in a mouse model of poly I:C-driven small intestine atrophy. Although the percentage of total ILCs did not differ between CD patients and CTR, ILCs producing TNF-α and IFN-γ were more abundant in CD mucosa compared to controls. ILCs expressed TLR2, TLR3 and TLR9 but neither TLR7 nor TLR4. Stimulation of LPMC with poly I:C but not PGN or CpG increased TNF-α and IFN-γ in ILCs. RAG1-deficient mice given poly I:C exhibited increased frequency of TNF-α but not IFN-γ/IL17A-producing ILCs in the gut and depletion of ILCs prevented the poly I:C-driven intestinal damage. Our data indicate that CD-related inflammation is marked by accumulation of ILCs producing TNF-α and IFN-γ in the mucosa. Moreover, ILCs express TLR3 and are functionally able to respond to poly I:C with increased synthesis of TNF-α thus contributing to small intestinal atrophy.

Peyer's patch innate lymphoid cells regulate commensal bacteria expansion

Anatomical containment of commensal bacteria in the intestinal mucosa is promoted by innate lymphoid cells (ILCs). However, the mechanism by which ILCs regulate bacterial localization to specific regions remains unknown. Here we show that Peyer's patch (PP) ILCs robustly produce IL-22 and IFN-γ in the absence of exogenous stimuli. Antibiotic treatment of mice decreased both IL-22+ and IFN-γ+ cells in PPs. Blockade of both IL-2 and IL-23 signaling in vitro lowered IL-22 and IFN-γ production. PP ILCs induced mRNA expression of the antibacterial proteins RegIIIβ and RegIIIγ in intestinal epithelial cells. Furthermore, in vivo depletion of ILCs rather than T cells altered bacterial composition and allowed bacterial proliferation in PPs. Collectively, our results show that ILCs regulate the expansion of commensal bacteria in PPs.

The microbiota regulates neutrophil homeostasis and host resistance to Escherichia coli K1 sepsis in neonatal mice.

Acquisition of microbes by the neonate, which begins immediately during birth, is influenced by gestational age and mother’s microbiota and modified by exposure to antibiotics1. In neonates, prolonged duration of antibiotic therapy is associated with increased risk of sepsis after 4 days of life, known as late-onset sepsis (LOS)2, a disorder critically controlled by neutrophils3, but a role for the microbiota in regulating neutrophil behavior in the neonate has not been described. We exposed pregnant mouse dams to antibiotics in drinking water to limit transfer of maternal microbes to the neonates. Antibiotic exposure of dams decreased the total number of microbes in the intestine, altered the structure of intestinal microbiota and changed the pattern of microbial colonization. These changes were associated with decreased numbers of circulating and bone marrow neutrophils and granulocyte/macrophage restricted progenitor cells in the bone marrow. Antibiotic-exposure of dams attenuated the postnatal granulocytosis by reducing the number of interleukin (IL) 17-producing cells in intestine and consequent production of granulocyte colony stimulating factor (G-CSF). Relative granulocytopenia contributed to increased susceptibility of antibiotic-exposed neonatal mice to Escherichia coli K1 and Klebsiella pneumoniae sepsis, which could be partially reversed by administration of G-CSF. Restoration of normal microbiota, through TLR4- and MYD88-dependent mechanism, induced accumulation of IL17-producing type 3 innate lymphoid cells (ILC) in the intestine, promoted granulocytosis, and restored the IL17-dependent resistance to sepsis. Specific depletion of ILCs prevented the IL17- and G-CSF-dependent granulocytosis and resistance to sepsis. These data support a role for the intestinal microbiota in regulation of granulocytosis and host resistance to sepsis in the neonates.

OC.12.4 INNATE LYMPHOID CELLS ARE INCREASED IN CELIAC DISEASE INTESTINAL MUCOSA AND HAVE A PATHOGENIC ROLE IN A MOUSE MODEL OF SMALL INTESTINE ATROPHY

Background and aim: Innate lymphoid cells (ILCs) are an emerging family of innate hematopoietic cells producing inflammatory cytokines and involved in the pathogenesis of several immune-mediated diseases. The aim of our study was to characterize the tissue distribution of ILCs in celiac disease (CD) and analyze their role in gut tissue damage. Materials and methods: ILC subpopulations were analyzed in lamina propria mononuclear cells (LPMCs), isolated from duodenal biopsies of patients with active CD, patients with inactive CD on a gluten-free diet and healthy controls (HC) and jejunal specimens of patients undergoing gastro-intestinal bypass by flow cytometry. Cytokines, transcription factors and receptors for interleukin (IL)-15, interferon (IFN)-alpha and Toll-like receptors (TLR) were assessed in ILCs either freshly isolated or following incubation of control LPMC with IL-15, IFNalpha and poly I:C, a TLR agonist, by flow cytometry. The role of ILCs in gut tissue damage was evaluated in a mouse model of poly I:C-driven small intestine atrophy. Results: The percentage of total ILCs did not differ between CD (both active and inactive) patients and HC. However, the fractions of ILCs type 1 expressing T-bet and ILCs type 3 expressing ROR-(g)t were significantly increased in active CD compared to controls, while there was no difference in term of ILCs type 2 among groups. ILCs expressed TLR3, IL-15R, little TLR2 but not IFN-alphaR and TLR4. IL-15 and poly I:C, but not IFN-alpha increased IFNgamma expression in ILCs. In vivo in mice, depletion of ILCs significantly reduced TLR3driven small intestinal damage. Conclusions: Active CD is characterized by preferential accumulation of type 1 and type 3 ILC subpopulations and these cells respond to IL-15, a cytokine over-produced in CD, by enhancing IFN-gamma production. The demonstration that ILCs express TLR3, are functionally able to respond to poly I:C with increased synthesis of inflammatory cytokines, and contribute to TLR3-driven small intestinal atrophy delineates a novel mechanism underlying the CD-associated tissue damage.

Candida albicans Airway Exposure Primes the Lung Innate Immune Response against Pseudomonas aeruginosa Infection through Innate Lymphoid Cell Recruitment and Interleukin-22-Associated Mucosal Response

Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the intensive care unit microbial community. We have demonstrated that C. albicans airway exposure protected against P. aeruginosa-induced lung injury. The goal of the present study was to characterize the cellular and molecular mechanisms associated with C. albicans-induced protection. Airway exposure by C. albicans led to the recruitment and activation of natural killer cells, innate lymphoid cells (ILCs), macrophages, and dendritic cells. This recruitment was associated with the secretion of interleukin-22 (IL-22), whose neutralization abolished C. albicans-induced protection. We identified, by flow cytometry, ILCs as the only cellular source of IL-22. Depletion of ILCs by anti-CD90.2 antibodies was associated with a decreased IL-22 secretion and impaired survival after P. aeruginosa challenge. Our results demonstrate that the production of IL-22, mainly by ILCs, is a major and inducible step in protection against P. aeruginosa-induced lung injury. This cytokine may represent a clinical target in Pseudomonas aeruginosa-induced lung injury.

Loss and aberrant function of NKp44+ ILCs in the SIV-infected gut are associated with RORγt suppression (P6175)

Abstract Recent studies have identified a novel NK cell-like population found in mucosal tissues and mucosae-draining lymph nodes distinguishable by high surface expression of NKp44 and referred to as innate lymphoid cells (ILCs). ILCs secrete IL-17/IL-22 which are critical for epithelial homeostasis and thus could play a role in gut integrity, a major factor in HIV/SIV pathogenesis. During chronic SIV infection, numbers of ILCs declined ~8-fold in gastrointestinal tissues, but remained comparable to naïve animals in distal sites such as mesenteric lymph nodes and lungs. Loss of ILCs was associated with up to 100-fold increases in apoptosis. Interestingly, gut ILCs expressed NFIL3, a classic NK cell-related transcription factor, as well as the IL-17 transcriptional regulator, RORγt, but during SIV infection RORγt was significantly downregulated associated with decreased IL-17 secretion. In these same animals increased IFN-γ secretion and acquired cytotoxicity were associated with an increase in ILC NFIL3. Loss and functional skewing of ILCs in vivo correlated with upregulated IDO-1 and IFN-α in the gut, and in vitro treatment of ILCs with IDO-1 catabolites and IFN-α also suppressed RORγt expression, ablated IL-17 production and induced apoptosis. SIV infection results in massive numerical and functional depletion of ILCs in the inflamed gut, but not distal sites. This phenomenon was due, at least in part, to IDO-1- and IFN-α-induced apoptosis and suppression of RORγt.

Cutting Edge: IL-17–Secreting Innate Lymphoid Cells Are Essential for Host Defense against Fungal Infection

IL-17-mediated immunity has emerged as a crucial host defense mechanism against fungal infections. Although Th cells are generally thought to act as the major source of IL-17 in response to Candida albicans, we show that fungal control is mediated by IL-17-secreting innate lymphoid cells (ILCs) and not by Th17 cells. By using a mouse model of oropharyngeal candidiasis we found that IL-17A and IL-17F, which are both crucial for pathogen clearance, are produced promptly upon infection in an IL-23-dependent manner, and that ILCs in the oral mucosa are the main source for these cytokines. Ab-mediated depletion of ILCs in RAG1-deficient mice or ILC deficiency in retinoic acid-related orphan receptor c(-/-) mice resulted in a complete failure to control the infection. Taken together, our data uncover the cellular basis for the IL-23/IL-17 axis, which acts right at the onset of infection when it is most needed for fungal control and host protection.

Innate lymphoid cells promote lung-tissue homeostasis after infection with influenza virus.

Innate lymphoid cells (ILCs), a recently identified heterogeneous cell population, are critical in orchestrating immunity and inflammation in the intestine but whether ILCs can influence immune responses or tissue homeostasis at other mucosal sites remains poorly characterized. Here we identify a population of lung-resident ILCs in mice and humans that expressed CD90, CD25, CD127 and T1-ST2. Strikingly, mouse ILCs accumulated in the lung following influenza virus infection and depletion of ILCs resulted in loss of airway epithelial integrity, decreased lung function and impaired airway remodeling. These defects could be restored by administration of the lung ILC product amphiregulin. Collectively, these results demonstrate a critical role for lung ILCs in restoring airway epithelial integrity and tissue homeostasis following influenza virus infection.

Innate lymphoid cells promote lung-tissue homeostasis after infection with influenza virus

Cytokine-producing innate lymphoid cells are found at mucosal surfaces. Artis and Wherry and their colleagues show that innate 'nuocyte-like' cells accumulate in virus-infected lungs and contribute to the repair of tissues. Innate lymphoid cells (ILCs), a heterogeneous cell population, are critical in orchestrating immunity and inflammation in the intestine, but whether ILCs influence immune responses or tissue homeostasis at other mucosal sites remains poorly characterized. Here we identify a population of lung-resident ILCs in mice and humans that expressed the alloantigen Thy-1 (CD90), interleukin 2 (IL-2) receptor α-chain (CD25), IL-7 receptor α-chain (CD127) and the IL-33 receptor subunit T1-ST2. Notably, mouse ILCs accumulated in the lung after infection with influenza virus, and depletion of ILCs resulted in loss of airway epithelial integrity, diminished lung function and impaired airway remodeling. These defects were restored by administration of the lung ILC product amphiregulin. Collectively, our results demonstrate a critical role for lung ILCs in restoring airway epithelial integrity and tissue homeostasis after infection with influenza virus.