Microbiota-Induced Type I Interferons Instruct a Poised Basal State of Dendritic Cells.

Environmental signals shape host physiology and fitness. Microbiota-derived cues are required to program conventional dendritic cells (cDCs) during the steady state so that they can promptly respond and initiate adaptive immune responses when encountering pathogens. However, the molecular underpinnings of microbiota-guided instructive programs are not well understood. Here, we report that the indigenous microbiota controls constitutive production of type I interferons (IFN-I) by plasmacytoid DCs. Using genome-wide analysis of transcriptional and epigenetic regulomes of cDCs from germ-free and IFN-I receptor (IFNAR)-deficient mice, we found that tonic IFNAR signaling instructs a specific epigenomic and metabolic basal state that poises cDCs for future pathogen combat. However, such beneficial biological function comes with a trade-off. Instructed cDCs can prime T cell responses against harmless peripheral antigens when removing roadblocks of peripheral tolerance. Our data provide fresh insights into the evolutionary trade-offs that come with successful adaptation of vertebrates to their microbial environment.

Lipid-Droplet Formation Drives Pathogenic Group 2 Innate Lymphoid Cells in Airway Inflammation.

Innate lymphoid cells (ILCs) play an important role in the control and maintenance of barrier immunity. However, chronic activation of ILCs results in immune-mediated pathology. Here, we show that tissue-resident type 2 ILCs (ILC2s) display a distinct metabolic signature upon chronic activation. In the context of allergen-driven airway inflammation, ILC2s increase their uptake of both external lipids and glucose. Externally acquired fatty acids are transiently stored in lipid droplets and converted into phospholipids to promote the proliferation of ILC2s. This metabolic program is imprinted by interleukin-33 (IL-33) and regulated by the genes Pparg and Dgat1, which are both controlled by glucose availability and mTOR signaling. Restricting dietary glucose by feeding mice a ketogenic diet largely ablated ILC2-mediated airway inflammation by impairing fatty acid metabolism and the formation of lipid droplets. Together, these results reveal that pathogenic ILC2 responses require lipid metabolism and identify ketogenic diet as a potent intervention strategy to treat airway inflammation.

Group 3 innate lymphoid cells continuously require the transcription factor GATA-3 after commitment.

The transcription factor GATA-3 is indispensable for the development of all innate lymphoid cells (ILCs) that express the interleukin 7 receptor α-chain (IL-7Rα). However, the function of low GATA-3 expression in committed group 3 ILCs (ILC3 cells) has not been identified. We found that GATA-3 regulated the homeostasis of ILC3 cells by controlling IL-7Rα expression. In addition, GATA-3 served a critical function in the development of the NKp46(+) ILC3 subset by regulating the balance between the transcription factors T-bet and RORγt. Among NKp46(+) ILC3 cells, although GATA-3 positively regulated genes specific to the NKp46(+) ILC3 subset, it negatively regulated genes specific to lymphoid tissue-inducer (LTi) or LTi-like ILC3 cells. Furthermore, GATA-3 was required for IL-22 production in both ILC3 subsets. Thus, despite its low expression, GATA-3 was critical for the homeostasis, development and function of ILC3 subsets.

Impaired ketogenesis ties metabolism to T cell dysfunction in COVID-19.

Anorexia and fasting are host adaptations to acute infection, and induce a metabolic switch towards ketogenesis and the production of ketone bodies, including ß-hydroxybutyrate (BHB)1-6. However, whether ketogenesis metabolically influences the immune response in pulmonary infections remains unclear. Here we show that the production of BHB is impaired in individuals with SARS-CoV-2-induced acute respiratory distress syndrome (ARDS) but not in those with  influenza-induced ARDS. We found that BHB promotes both the survival of and the production of interferon-γ by CD4+ T cells. Applying a metabolic-tracing analysis, we established that BHB provides an alternative carbon source to fuel oxidative phosphorylation (OXPHOS) and the production of bioenergetic amino acids and glutathione, which is important for maintaining the redox balance. T cells from patients with SARS-CoV-2-induced ARDS were exhausted and skewed towards glycolysis, but could be metabolically reprogrammed by BHB to perform OXPHOS, thereby increasing their functionality. Finally, we show in mice that a ketogenic diet and the delivery of BHB as a ketone ester drink restores CD4+ T cell metabolism and function in severe respiratory infections, ultimately reducing the mortality of mice infected with SARS-CoV-2. Altogether, our data reveal that BHB is an alternative source of carbon that promotes T cell responses in pulmonary viral infections, and highlight impaired ketogenesis as a potential confounding factor in severe COVID-19.

More Is Less: IL-9 in the Resolution of Inflammation.

In a recent study in Nature Medicine, Rauber et al. (2017) identify interleukin-9 (IL-9) derived from group 2 innate lymphoid cells as crucial regulators inducing resolution of chronic inflammation in rheumatoid arthritis. Their findings provide insight into the varied functions of IL-9 and open the door to novel therapeutic interventions.

Reactive Neutrophil Responses Dependent on the Receptor Tyrosine Kinase c-MET Limit Cancer Immunotherapy.

Inhibitors of the receptor tyrosine kinase c-MET are currently used in the clinic to target oncogenic signaling in tumor cells. We found that concomitant c-MET inhibition promoted adoptive T cell transfer and checkpoint immunotherapies in murine cancer models by increasing effector T cell infiltration in tumors. This therapeutic effect was independent of tumor cell-intrinsic c-MET dependence. Mechanistically, c-MET inhibition impaired the reactive mobilization and recruitment of neutrophils into tumors and draining lymph nodes in response to cytotoxic immunotherapies. In the absence of c-MET inhibition, neutrophils recruited to T cell-inflamed microenvironments rapidly acquired immunosuppressive properties, restraining T cell expansion and effector functions. In cancer patients, high serum levels of the c-MET ligand HGF correlated with increasing neutrophil counts and poor responses to checkpoint blockade therapies. Our findings reveal a role for the HGF/c-MET pathway in neutrophil recruitment and function and suggest that c-MET inhibitor co-treatment may improve responses to cancer immunotherapy in settings beyond c-MET-dependent tumors.

Exogenous stimuli maintain intraepithelial lymphocytes via aryl hydrocarbon receptor activation.

The body's surfaces form the interface with the external environment, protecting the host. These epithelial barriers are also colonized by a controlled diversity of microorganisms, disturbances of which can give rise to disease. Specialized intraepithelial lymphocytes (IELs), which reside at these sites, are important as a first line of defense as well as in epithelial barrier organization and wound repair. We show here that the aryl hydrocarbon receptor (AhR) is a crucial regulator in maintaining IEL numbers in both the skin and the intestine. In the intestine, AhR deficiency or the lack of AhR ligands compromises the maintenance of IELs and the control of the microbial load and composition, resulting in heightened immune activation and increased vulnerability to epithelial damage. AhR activity can be regulated by dietary components, such as those present in cruciferous vegetables, providing a mechanistic link between dietary compounds, the intestinal immune system, and the microbiota.

Fluorogenic Chemical Probes for Wash-free Imaging of Cell Membrane Damage in Ferroptosis, Necrosis, and Axon Injury.

Selectively labeling cells with damaged membranes is needed not only for identifying dead cells in culture, but also for imaging membrane barrier dysfunction in pathologies in vivo. Most membrane permeability stains are permanently colored or fluorescent dyes that need washing to remove their non-uptaken extracellular background and reach good image contrast. Others are DNA-binding environment-dependent fluorophores, which lack design modularity, have potential toxicity, and can only detect permeabilization of cell volumes containing a nucleus (i.e., cannot delineate damaged volumes in vivo nor image non-nucleated cell types or compartments). Here, we develop modular fluorogenic probes that reveal the whole cytosolic volume of damaged cells, with near-zero background fluorescence so that no washing is needed. We identify a specific disulfonated fluorogenic probe type that only enters cells with damaged membranes, then is enzymatically activated and marks them. The esterase probe MDG1 is a reliable tool to reveal live cells that have been permeabilized by biological, biochemical, or physical membrane damage, and it can be used in multicolor microscopy. We confirm the modularity of this approach by also adapting it for improved hydrolytic stability, as the redox probe MDG2. We conclude by showing the unique performance of MDG probes in revealing axonal membrane damage (which DNA fluorogens cannot achieve) and in discriminating damage on a cell-by-cell basis in embryos in vivo. The MDG design thus provides powerful modular tools for wash-free in vivo imaging of membrane damage, and indicates how designs may be adapted for selective delivery of drug cargoes to these damaged cells: offering an outlook from selective diagnosis toward therapy of membrane-compromised cells in disease.

The many lives of IL-9: a question of survival?

Although the cytokine interleukin 9 (IL-9) was discovered decades ago, it remains one of the most enigmatic cytokines identified so far, in particular because its functional activities remain far from clear. Breakthroughs made through the use of IL-9 reporter mice have allowed the identification of cell types that produce IL-9 in vivo and, contrary to expectations based on previous results obtained in vitro, it is not T cells but instead a previously unknown type of innate lymphoid cell, called the 'ILC2 cell', that is the main cell type that expresses IL-9 in vivo. In this perspective, we put forward a hypothesis about the potential biological functions of IL-9 in the immune system and beyond.

Enemy or ally? Fasting as an essential regulator of immune responses.

Nutrition is essential for supplying an organism with sufficient energy to maintain its bodily functions. Apart from serving as an energy supply, the immunomodulatory effects of diet are emerging as a central aspect of human health. The latest evidence suggests that dietary restriction may play an important regulatory role by influencing the activation and effector functions of immune cells. However, depending on the context, nutrient restriction may have both pathogenic and beneficial effects. Here, we discuss the diverse roles of fasting programs, including ketogenesis in infection and chronic inflammation, aiming to clarify their detrimental and/or beneficial effects. Understanding these differences may help identify conditions under which dietary interventions might serve as putative effective approaches to treat various diseases.

Bone-Marrow-Resident NK Cells Prime Monocytes for Regulatory Function during Infection.

Tissue-infiltrating Ly6C(hi) monocytes play diverse roles in immunity, ranging from pathogen killing to immune regulation. How and where this diversity of function is imposed remains poorly understood. Here we show that during acute gastrointestinal infection, priming of monocytes for regulatory function preceded systemic inflammation and was initiated prior to bone marrow egress. Notably, natural killer (NK) cell-derived IFN-γ promoted a regulatory program in monocyte progenitors during development. Early bone marrow NK cell activation was controlled by systemic interleukin-12 (IL-12) produced by Batf3-dependent dendritic cells (DCs) in the mucosal-associated lymphoid tissue (MALT). This work challenges the paradigm that monocyte function is dominantly imposed by local signals after tissue recruitment, and instead proposes a sequential model of differentiation in which monocytes are pre-emptively educated during development in the bone marrow to promote their tissue-specific function.

An IL-9 fate reporter demonstrates the induction of an innate IL-9 response in lung inflammation.

Interleukin 9 (IL-9) is a cytokine linked to lung inflammation, but its cellular origin and function remain unclear. Here we describe a reporter mouse strain designed to map the fate of cells that have activated IL-9. We found that during papain-induced lung inflammation, IL-9 production was largely restricted to innate lymphoid cells (ILCs). IL-9 production by ILCs depended on IL-2 from adaptive immune cells and was rapidly lost in favor of other cytokines, such as IL-13 and IL-5. Blockade of IL-9 production via neutralizing antibodies resulted in much lower expression of IL-13 and IL-5, which suggested that ILCs provide the missing link between the well-established functions of IL-9 in the regulation of type 2 helper T cell cytokines and responses.

Fate mapping of IL-17-producing T cells in inflammatory responses.

Here we describe a reporter mouse strain designed to map the fate of cells that have activated interleukin 17A (IL-17A). We found that IL-17-producing helper T cells (T(H)17 cells) had distinct plasticity in different inflammatory settings. Chronic inflammatory conditions in experimental autoimmune encephalomyelitis (EAE) caused a switch to alternative cytokines in T(H)17 cells, whereas acute cutaneous infection with Candida albicans did not result in the deviation of T(H)17 cells to the production of alternative cytokines, although IL-17A production was shut off in the course of the infection. During the development of EAE, interferon-γ (IFN-γ) and other proinflammatory cytokines in the spinal cord were produced almost exclusively by cells that had produced IL-17 before their conversion by IL-23 ('ex-T(H)17 cells'). Thus, this model allows the actual functional fate of effector T cells to be related to T(H)17 developmental origin regardless of IL-17 expression.

Impact of digital health interventions for adolescents with type 1 diabetes mellitus on health literacy: a systematic review.

BACKGROUND: Evidence shows that living with diabetes mellitus type 1 (T1DM) in adolescent age is particularly challenging and difficult to manage. A high level of health literacy is important to prevent and avoid debilitating complications. Despite the increasing prevalence and incidence of T1DM by adolescent and the large use of digital health interventions, little is known about the association between this use and health literacy. This systematic review provides an overview on the impact of digital health interventions for adolescents with type 1 diabetes on health literacy and derive recommendations for further research. METHODS: Electronic searches were performed in five databases in Medline (Medline, PubMed + via PubMed), The Cochrane Library, EMBASE (via Ovid), Web of Science and PsycINFO from 2011 to 2021. In addition, grey literature searches were conducted in Google Scholar, OAlster and Trip. Relevant studies that have been missed by electronic and hand-searching strategies were searched in the reference lists of all included studies. The review followed PRISMA guidelines. Two researchers independently screened abstracts for initial eligibility and applied the inclusion and exclusion criteria to the relevant full-text articles. Quality was assessed using the tools RoB2 Cochrane, ROBINS I, NOS (Newcastle-Ottawa Scale), CASP (Critical Appraisal Skills Programme) for primary studies and Amstar-2 for secondary studies. RESULTS: Out of 981 studies, 22 were included in the final review. Most primary studies included in this review were judged as moderate overall risk of bias or with some concerns and most of the secondary studies as critically low quality reviews. Our findings suggest that the interplay of health care providers (HCP) and patients through social media helps the management of the disease. This corroborates Bröder et al.' (2017) dimension of 'communication and interactions' in their concept of health literacy. CONCLUSIONS: For adolescents with T1DM, social media may be a specific and beneficial intervention for an improved communication and interaction with their HCP. Further research should investigate what specific form of social media suits best for which adolescents. TRIAL REGISTRATION: The study protocol was registered on the 15th of November 2021 on Prospero (reg. NR: CRD42021282199).

Mitochondrial Dysfunction Contributes to Impaired Cytokine Production of CD56bright Natural Killer Cells From Human Immunodeficiency Virus-Infected Individuals Under Effective Antiretroviral Therapy.

Human immunodeficiency virus (HIV) infection is associated with impaired natural killer (NK) cell activity, which is only incompletely restored under antiretroviral therapy. Analyzing the bioenergetics profiles of oxygen consumption, we observed that several parameters were significantly reduced in HIV+ NK cells, indicating a mitochondrial defect. Accordingly, we found HIV+ CD56bright NK cells to display a decreased mitochondrial membrane potential and mitochondrial mass. Both parameters were positively correlated with interferon gamma (IFN-γ) production of NK cells. Finally, we demonstrated that stimulation of HIV+ NK cells with MitoTEMPO, a mitochondria-targeting antioxidant, significantly improved IFN-γ production. We identified mitochondrial dysfunction as a mechanism that contributes to impaired NK cell function.

Tetracycline ameliorates silica-induced pulmonary inflammation and fibrosis via inhibition of caspase-1.

BACKGROUND: Inhalation of dust containing silica particles is associated with severe pulmonary inflammation and lung injury leading to chronic silicosis including fibrotic remodeling of the lung. Silicosis represents a major global health problem causing more than 45.000 deaths per year. The inflammasome-caspase-1 pathway contributes to the development of silica-induced inflammation and fibrosis via IL-1ß and IL-18 production. Recent studies indicate that tetracycline can be used to treat inflammatory diseases mediated by IL-1ß and IL-18. Therefore, we hypothesized that tetracycline reduces silica-induced lung injury and lung fibrosis resulting from chronic silicosis via limiting IL-1ß and IL-18 driven inflammation. METHODS: To investigate whether tetracycline is a therapeutic option to block inflammasome-caspase-1 driven inflammation in silicosis, we incubated macrophages with silica alone or combined with tetracycline. The in vivo effect of tetracycline was determined after intratracheal administration of silica into the mouse lung. RESULTS: Tetracycline selectively blocks IL-1ß production and pyroptotic cell death via inhibition of caspase-1 in macrophages exposed to silica particles. Consistent, treatment of silica-instilled mice with tetracycline significantly reduced pulmonary caspase-1 activation as well as IL-1ß and IL-18 production, thereby ameliorating pulmonary inflammation and lung injury. Furthermore, prolonged tetracycline administration in a model of chronic silicosis reduced lung damage and fibrotic remodeling. CONCLUSIONS: These findings suggest that tetracycline inhibits caspase-1-dependent production of IL-1ß in response to silica in vitro and in vivo. The results were consistent with tetracycline reducing silica-induced pulmonary inflammation and chronic silicosis in terms of lung injury and fibrosis. Thus, tetracycline could be effective in the treatment of patients with silicosis as well as other diseases involving silicotic inflammation.

Inhibition of Caspase-1 with Tetracycline Ameliorates Acute Lung Injury.

Rationale: Acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome with a mortality of up to 40%. Precision medicine approaches targeting patients on the basis of their molecular phenotypes of ARDS might help to identify effective pharmacotherapies. The inflammasome-caspase-1 pathway contributes to the development of ARDS via IL-1ß and IL-18 production. Recent studies indicate that tetracycline can be used to treat inflammatory diseases mediated by IL-1ß and IL-18, although the molecular mechanism by which tetracycline inhibits inflammasome-caspase-1 signaling remains unknown. Objectives: To identify patients with ARDS characterized by IL-1ß and IL-18 expression and investigate the ability of tetracycline to inhibit inflammasome-caspase-1 signaling in ARDS. Methods: IL-1ß and IL-18 concentrations were quantified in BAL fluid from patients with ARDS. Tetracycline's effects on lung injury and inflammation were assessed in two mouse models of direct (pulmonary) acute lung injury, and its effects on IL-1ß and IL-18 production were assessed by alveolar leukocytes from patients with direct ARDS ex vivo. Murine macrophages were used to further characterize the effect of tetracycline on the inflammasome-caspase-1 pathway. Measurements and Main Results: BAL fluid concentrations of IL-1ß and IL-18 are significantly higher in patients with direct ARDS than those with indirect (nonpulmonary) ARDS. In experimental acute lung injury, tetracycline significantly diminished lung injury and pulmonary inflammation by selectively inhibiting caspase-1-dependent IL-1ß and IL-18 production, leading to improved survival. Tetracycline also reduced the production of IL-1ß and IL-18 by alveolar leukocytes from patients with direct ARDS. Conclusions: Tetracycline may be effective in the treatment of direct ARDS in patients with elevated caspase-1 activity. Clinical Trial registered with www.clinicaltrials.gov (NCT04079426).