Metabolic Regulation of Innate Lymphoid Cell-Mediated Tissue Protection-Linking the Nutritional State to Barrier Immunity

Blocking CD226 regulates type 2 innate lymphoid cell effector function and alleviates airway hyperreactivity

BACKGROUND

Type 2 innate lymphoid cells (ILC2s) play a pivotal role in type 2 asthma. CD226 is a costimulatory molecule involved in various inflammatory diseases.

OBJECTIVE

We aimed to investigate CD226 expression and function within human and mouse ILC2s, and to assess the impact of targeting CD226 on ILC2-mediated airway hyperreactivity (AHR).

METHODS

We administered IL-33 intranasally to wild-type mice, followed by treatment with anti-CD226 antibody or isotype control. Pulmonary ILC2s were sorted for ex vivo analyses through RNA sequencing and flow cytometry. Next, we evaluated the effects of CD226 on AHR and lung inflammation in wild-type and Rag2-/- mice. Additionally, we compared peripheral ILC2s from healthy donors and asthmatic patients to ascertain the role of CD226 in human ILC2s.

RESULTS

Our findings demonstrated an inducible expression of CD226 in activated ILC2s, enhancing their cytokine secretion and effector functions. Mechanistically, CD226 alters intracellular metabolism and enhances PI3K/AKT and MAPK signal pathways. Blocking CD226 ameliorates ILC2-dependent AHR in IL-33 and Alternaria alternata-induced models. Interestingly, CD226 is expressed and inducible in human ILC2s, and its blocking reduces cytokine production. Finally, we showed that peripheral ILC2s in asthmatic patients exhibited elevated CD226 expression compared to healthy controls.

CONCLUSION

Our findings underscore the potential of CD226 as a novel therapeutic target in ILC2s, presenting a promising avenue for ameliorating AHR and allergic asthma.

Notch2 with retinoic acid license IL-23 expression by intestinal EpCAM+ DCIR2+ cDC2s in mice

Despite the importance of IL-23 in mucosal host defense and disease pathogenesis, the mechanisms regulating the development of IL-23-producing mononuclear phagocytes remain poorly understood. Here, we employed an Il23aVenus reporter strain to investigate the developmental identity and functional regulation of IL-23-producing cells. We showed that flagellin stimulation or Citrobacter rodentium infection led to robust induction of IL-23-producing EpCAM+ DCIR2+ CD103- cDC2s, termed cDCIL23, which was confined to gut-associated lymphoid tissues, including the mesenteric lymph nodes, cryptopatches, and isolated lymphoid follicles. Furthermore, we demonstrated that Notch2 signaling was crucial for the development of EpCAM+ DCIR2+ cDC2s, and the combination of Notch2 signaling with retinoic acid signaling controlled their terminal differentiation into cDCIL23, supporting a two-step model for the development of gut cDCIL23. Our findings provide fundamental insights into the developmental pathways and cellular dynamics of IL-23-producing cDC2s at steady state and during pathogen infection.

The modulation of pulmonary group 2 innate lymphoid cell function in asthma: from inflammatory mediators to environmental and metabolic factors

A dysregulated type 2 immune response is one of the fundamental causes of allergic asthma. Although Th2 cells are undoubtedly central to the pathogenesis of allergic asthma, the discovery of group 2 innate lymphoid cells (ILC2s) has added another layer of complexity to the etiology of this chronic disease. Through their inherent innate type 2 responses, ILC2s not only contribute to the initiation of airway inflammation but also orchestrate the recruitment and activation of other members of innate and adaptive immunity, further amplifying the inflammatory response. Moreover, ILC2s exhibit substantial cytokine plasticity, as evidenced by their ability to produce type 1- or type 17-associated cytokines under appropriate conditions, underscoring their potential contribution to nonallergic, neutrophilic asthma. Thus, understanding the mechanisms of ILC2 functions is pertinent. In this review, we present an overview of the current knowledge on ILC2s in asthma and the regulatory factors that modulate lung ILC2 functions in various experimental mouse models of asthma and in humans.

Cross-talk between insulin resistance and nitrogen species in hypoxia leads to deterioration of tissue and homeostasis

Hypoxia has been linked with insulin resistance as it produces changes in the metabolism of the cell; in which the adipocytes impede the insulin receptor tyrosine, phosphorylation, directing at decreased levels of transport of glucose. At this juncture, we are focusing on cross-talk between insulin resistance and nitrogen species in hypoxia, leading to the deterioration of tissue and homeostasis. Physiological levels of nitric oxide play a very crucial role in acting as a priority effector and signaling molecule, arbitrating the body's responses to hypoxia. Both ROS and RNS are associated with a reduction in IRS1 phosphorylation in tyrosine, which leads to reduced levels of IRS1 content and insulin response, which further leads to insulin resistance. Cellular hypoxia is a trigger to inflammatory mediators which signal tissue impairment and initiate survival requirements. But, hypoxia-mediated inflammation act as a protective role by an immune response and promotes wound healing during infection. In this review, we abridge the crosstalk between the inflammation and highlight the dysregulation in physiological consequences due to diabetes mellitus. Finally, we review various treatments available for its related physiological complications.

Memory-like innate lymphoid cells in the pathogenesis of asthma

Innate lymphoid cells (ILCs) are recently discovered innate immune cells that reside and self-renew in mucosal tissues and serve as the first line of defense against various external insults. They include natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer cells. The development and functions of ILC1-3 reflect those of their adaptive immunity TH1, TH2, and TH17 T-cell counterparts. Asthma is a heterogeneous disease caused by repeated exposure to specific allergens or host/environmental factors (e.g., obesity) that stimulate pathogenic pulmonary immune cells, including ILCs. Memory used to be a hallmark of adaptive immune cells until recent studies of monocytes, macrophages, and NK cells showed that innate immune cells can also exhibit greater responses to re-stimulation and that these more responsive cells can be long-lived. Besides, a series of studies suggest that the tissue-resident innate lymphoid cells have memory-like phenotypes, such as increased cytokine productions or epigenetic modifications following repetitive exposure to allergens. Notably, both clinical and mouse studies of asthma show that various allergens can generate memory-like features in ILC2s. Here, we discuss the biology of ILCs, their roles in asthma pathogenesis, and the evidence supporting ILC memory. We also show evidence suggesting memory ILCs could help drive the phenotypic heterogeneity in asthma. Thus, further research on memory ILCs may be fruitful in terms of developing new therapies for asthma.

Immunometabolism - The Role of Branched-Chain Amino Acids

Immunometabolism has been the focus of extensive research over the last years, especially in terms of augmenting anti-tumor immune responses. Regulatory T cells (Tregs) are a subset of CD4+ T cells, which have been known for their immunosuppressive roles in various conditions including anti-tumor immune responses. Even though several studies aimed to target Tregs in the tumor microenvironment (TME), such approaches generally result in the inhibition of the Tregs non-specifically, which may cause immunopathologies such as autoimmunity. Therefore, specifically targeting the Tregs in the TME would be vital in terms of achieving a successful and specific treatment. Recently, an association between Tregs and isoleucine, which represents one type of branched-chain amino acids (BCAAs), has been demonstrated. The presence of isoleucine seems to affect majorly Tregs, rather than conventional T cells. Considering the fact that Tregs bear several distinct metabolic features in the TME, targeting their immunometabolic pathways may be a rational approach. In this Review, we provide a general overview on the potential distinct metabolic features of T cells, especially focusing on BCAAs in Tregs as well as in their subtypes.

β-carotene improves fecal dysbiosis and intestinal dysfunctions in a mouse model of vitamin A deficiency

Vitamin A deficiency (VAD) results in intestinal inflammation, increased redox stress and reactive oxygen species (ROS) levels, imbalanced inflammatory and immunomodulatory cytokines, compromised barrier function, and perturbations of the gut microbiome. To combat VAD dietary interventions with β-carotene, the most abundant precursor of vitamin A, are recommended. However, the impact of β-carotene on intestinal health during VAD has not been fully clarified, especially regarding the VAD-associated intestinal dysbiosis. Here we addressed this question by using Lrat^-/-Rbp^-/- (vitamin A deficient) mice deprived of dietary preformed vitamin A and supplemented with β-carotene as the sole source of the vitamin, alongside with WT (vitamin A sufficient) mice. We found that dietary β-carotene impacted intestinal vitamin A status, barrier integrity and inflammation in both WT and Lrat^-/-Rbp^-/- (vitamin A deficient) mice on the vitamin A-free diet. However, it did so to a greater extent under overt VAD. Dietary β-carotene also modified the taxonomic profile of the fecal microbiome, but only under VAD. Given the similarity of the VAD-associated intestinal phenotypes with those of several other disorders of the gut, collectively known as Inflammatory Bowel Disease (IBD) Syndrome, these findings are broadly relevant to the effort of developing diet-based intervention strategies to ameliorate intestinal pathological conditions.

The neuropeptide VIP potentiates intestinal innate type 2 and type 3 immunity in response to feeding

The nervous system and the immune system both rely on an extensive set of modalities to perceive and act on perturbations in the internal and external environments. During feeding, the intestine is exposed to nutrients that may contain noxious substances and pathogens. Here we show that Vasoactive Intestinal Peptide (VIP), produced by the nervous system in response to feeding, potentiates the production of effector cytokines by intestinal type 2 and type 3 innate lymphoid cells (ILC2s and ILC3s). Exposure to VIP alone leads to modest activation of ILCs, but strongly potentiates ILCs to concomitant or subsequent activation by the inducer cytokines IL-33 or IL-23, via mobilization of cAMP and energy by glycolysis. Consequently, VIP increases resistance to intestinal infection by the helminth Trichuris muris and the enterobacteria Citrobacter rodentium. These findings uncover a functional neuro-immune crosstalk unfolding during feeding that increases the reactivity of innate immunity necessary to face potential threats associated with food intake.

Food for thought - ILC metabolism in the context of helminth infections

Helminths are multicellular ancient organisms residing as parasites at mucosal surfaces of their host. Through adaptation and co-evolution with their hosts, helminths have been able to develop tolerance mechanisms to limit inflammation and avoid expulsion. The study of helminth infections as an integral part of tissue immunology allowed us to understand fundamental aspects of mucosal and barrier immunology, which led to the discovery of a new group of tissue-resident immune cells, innate lymphoid cells (ILC), over a decade ago. Here, we review the intricate interplay between helminth infections and type 2 ILC (ILC2) biology, discuss the host metabolic adaptation to helminth infections and the metabolic pathways fueling ILC2 responses. We hypothesize that nutrient competition between host and helminths may have prevented chronic inflammation in the past and argue that a detailed understanding of the metabolic restraints imposed by helminth infections may offer new therapeutic avenues in the future.

Tissue-Specific Molecular Markers and Heterogeneity in Type 2 Innate Lymphoid Cells

Innate lymphoid cells (ILCs) are the most recently described group of lymphoid subpopulations. These tissue-resident cells display a heterogeneity resembling that observed on different groups of T cells, hence their categorization as cytotoxic NK cells and helper ILCs type 1, 2 and 3. Each one of these groups is highly diverse and expresses different markers in a context-dependent manner. Type 2 innate lymphoid cells (ILC2s) are activated in response to helminth parasites and regulate the immune response. They are involved in the etiology of diseases associated with allergic responses as well as in the maintenance of tissue homeostasis. Markers associated with their identification differ depending on the tissue and model used, making the study and understanding of these cells a cumbersome task. This review compiles evidence for the heterogeneity of ILC2s as well as discussion and analyses of molecular markers associated with their identity, function, tissue-dependent expression, and how these markers contribute to the interaction of ILC2s with specific microenvironments to maintain homeostasis or respond to pathogenic challenges.

Group 2 innate lymphoid cells in bone marrow regulate osteoclastogenesis in a reciprocal manner via RANKL, GM-CSF and IL-13

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells that play different roles in different organs by sensing surrounding environmental factors. Initially, it was thought that ILC2s in bone marrow (BM) are progenitors for systemic ILC2s, which migrate to other organs and acquire effector functions. However, accumulating evidence that ILC2s differentiate in peripheral tissues suggests that BM ILC2s may play a specific role in the BM as a unique effector per se. Here, we demonstrate that BM ILC2s highly express the receptor activator of nuclear factor κB ligand (RANKL), a robust cytokine for osteoclast differentiation and activation, and RANKL expression on ILC2s is up-regulated by interleukin (IL)-2, IL-7 and all-trans retinoic acid (ATRA). BM ILC2s co-cultured with BM-derived monocyte/macrophage lineage cells (BMMs) in the presence of IL-7 induce the differentiation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in a RANKL-dependent manner. In contrast, BM ILC2s stimulated with IL-33 down-regulate RANKL expression and convert BMMs differentiation into M2 macrophage-like cells rather than osteoclasts by granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-13 production. Intravital imaging using two-photon microscopy revealed that a depletion of ILC2s prominently impaired in vivo osteoclast activity in an IL-7 plus ATRA-induced bone loss mouse model. These results suggest that ILC2s regulate osteoclast activation and contribute to bone homeostasis in both steady state and IL-33-induced inflammation.

Effects of a high-fat diet and global aryl hydrocarbon receptor deficiency on energy balance and liver retinoid status in male Sprague-Dawley rats

The physiological functions of the aryl hydrocarbon receptor (AHR) are only beginning to unfold. Studies in wildtype and AHR knockout (AHRKO) mice have recently disclosed that AHR activity is required for obesity and steatohepatitis to develop when mice are fed with a high-fat diet (HFD). In addition, a line of AHRKO mouse has been reported to accumulate retinoids in the liver. Whether these are universal manifestations across species related to AHR activity level is not known yet. Therefore, we here subjected wildtype and AHRKO male rats (on Sprague-Dawley background) to HFD feeding coupled with free access to 10% sucrose solution and water; controls received a standard diet and water. Although the HFD-fed rats consumed more energy throughout the 24-week feeding regimen, they did not get overweight. However, relative weights of the brown and epididymal adipose tissues were elevated in HFD-fed rats, while that of the liver was lower in AHRKO than wildtype rats. Moreover, the four groups exhibited diet- or genotype-dependent differences in biochemical variables, some of which suggested marked dissimilarities from AHRKO mice. Expression of pro- and anti-inflammatory genes was induced in livers of HFD-fed AHRKO rats, but histologically they did not differ from others. HFD reduced the hepatic concentrations of retinyl palmitate, 9-cis-4-oxo-13,14-dihydroretinoic acid and (suggestively) retinol, whereas AHR status had no effect. Hence, the background strain/line of AHRKO rat is resistant to diet-induced obesity, and AHR does not modulate this or liver retinoid concentrations. Yet, subtle AHR-dependent differences in energy balance-related factors exist despite similar weight development.

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.

Impact of vitamin A transport and storage on intestinal retinoid homeostasis and functions

Lecithin:retinol acyltransferase and retinol-binding protein enable vitamin A (VA) storage and transport, respectively, maintaining tissue homeostasis of retinoids (VA derivatives). The precarious VA status of the lecithin:retinol acyltransferase-deficient (Lrat-/-) retinol-binding protein-deficient (Rbp-/-) mice rapidly deteriorates upon dietary VA restriction, leading to signs of severe vitamin A deficiency (VAD). As retinoids impact gut morphology and functions, VAD is often linked to intestinal pathological conditions and microbial dysbiosis. Thus, we investigated the contribution of VA storage and transport to intestinal retinoid homeostasis and functionalities. We showed the occurrence of intestinal VAD in Lrat-/-Rbp-/- mice, demonstrating the critical role of both pathways in preserving gut retinoid homeostasis. Moreover, in the mutant colon, VAD resulted in a compromised intestinal barrier as manifested by reduced mucins and antimicrobial defense, leaky gut, increased inflammation and oxidative stress, and altered mucosal immunocytokine profiles. These perturbations were accompanied by fecal dysbiosis, revealing that the VA status (sufficient vs. deficient), rather than the amount of dietary VA per se, is likely a major initial discriminant of the intestinal microbiome. Our data also pointed to a specific fecal taxonomic profile and distinct microbial functionalities associated with VAD. Overall, our findings revealed the suitability of the Lrat-/-Rbp-/- mice as a model to study intestinal dysfunctions and dysbiosis promoted by changes in tissue retinoid homeostasis induced by the host VA status and/or intake.

Innate lymphoid cells in kidney diseases

It is well known that innate immune cells, including dendritic cells, macrophages, and natural killer cells, contribute to pathogenesis and protection in various kidney diseases. The understanding of innate immunity has been advanced recently by the discovery of a new group of innate lymphoid cells (ILCs), including ILC1, ILC2, and ILC3. ILCs lack adaptive antigen receptors, yet can be triggered by various pathogens and rapidly provide an abundant source of immunomodulatory cytokines to exert immediate immune reactions and direct subsequent innate and adaptive immune responses. ILCs play critical roles in immunity, tissue homeostasis, and pathological inflammation. In this review, we highlight the biological function of ILC subpopulations in the normal kidney, and their important roles in acute and chronic kidney diseases, thus demonstrating the emerging importance of ILC-regulated immunity in this special organ and providing insights for future research directions and therapeutic interventions.

Innate Lymphoid Cell Activation and Sustained Depletion in Blood and Tissue of Children Infected with HIV from Birth Despite Antiretroviral Therapy

Innate lymphoid cells (ILCs) are important for response to infection and for immune development in early life. HIV infection in adults depletes circulating ILCs, but the impact on children infected from birth remains unknown. We study vertically HIV-infected children from birth to adulthood and find severe and persistent depletion of all circulating ILCs that, unlike CD4+ T cells, are not restored by long-term antiretroviral therapy unless initiated at birth. Remaining ILCs upregulate genes associated with cellular activation and metabolic perturbation. Unlike HIV-infected adults, ILCs are also profoundly depleted in tonsils of vertically infected children. Transcriptional profiling of remaining ILCs reveals ongoing cell-type-specific activity despite antiretroviral therapy. Collectively, these data suggest an important and ongoing role for ILCs in lymphoid tissue of HIV-infected children from birth, where persistent depletion and sustained transcriptional activity are likely to have long-term immune consequences that merit further investigation.

Metabolism of Natural Killer Cells and Other Innate Lymphoid Cells

Natural killer (NK) cells are the host's first line of defense against tumors and viral infections without prior sensitization. It is increasingly accepted that NK cells belong to the innate lymphoid cell (ILC) family. Other ILCs, comprising ILC1s, ILC2s, ILC3s and lymphoid tissue inducer (LTi) cells, are largely non-cytotoxic, tissue-resident cells, which function to protect local microenvironments against tissue insults and maintain homeostasis. Recently, evidence has accumulated that metabolism supports many aspects of the biology of NK cells and other ILCs, and that metabolic reprogramming regulates their development and function. Here, we outline the current understanding of ILC metabolism, and describe how metabolic processes are affected, and how metabolic defects are coupled to dysfunction of ILCs, in disease settings. Furthermore, we summarize the current and potential directions for immunotherapy involving targeting of ILC metabolism. Finally, we discuss the open questions in the rapidly expanding field of ILC metabolism.

Immune modulating effects of additional supplementation of estradiol combined with testosterone in murine testosterone-deficient NAFLD model

Nonalcoholic fatty liver disease (NAFLD) is associated with testosterone deficiency. However, NAFLD patients generally do not respond to treatment with testosterone alone. We investigated the innate immune mechanisms underlying the effects of treatment with testosterone alone, estrogen alone, or combined testosterone and estrogen on high-fat diet (HFD)-induced NAFLD due to testosterone deficiency. Orchiectomized (OCX) male Rag2^-/- mice were used as a model of testosterone deficiency. To assess NAFLD severity, NAFLD activity score (NAS) is adopted. Moreover, immunological change was analyzed by multicolor flow cytometry. Treatment with both testosterone and estrogen significantly decreased body weight to that of the sham mice/normal diet (ND). NAS and liver fibrosis in OCX-HFD mice were significantly deteriorated, and treatment with testosterone and estrogen improved same as sham-ND mice. HFD increased the ratio of both type 2 and 3 innate lymphoid cells (ILC2s and ILC3s) to CD45-positive cells in the liver. Treatment with testosterone alone decreased the ratio of ILC2 to CD45 but not the ILC3-to-CD45 ratio. Addition of estrogen to the treatment reduced the ratios of ILC2-to-CD45 and ILC3-to-CD45 to the same level observed in sham-HFD mice. Moreover, OCX-HFD mice had a decreased proportion of M2 macrophages compared with sham-ND mice. Treatment with testosterone alone did not restore the proportion of M2 macrophages; however, combination treatment with both estrogen and testosterone increased that to the same level as that in sham-HFD mice. Treatment with both testosterone and estrogen improves liver fibrosis and decreases ILC3 and increases M2 macrophage abundance in the liver.NEW & NOTEWORTHY The progression of nonalcoholic fatty liver disease (NAFLD) is associated with testosterone deficiency. NAFLD patients generally do not respond to treatment with testosterone alone. In animal studies, treatment with testosterone and estrogen reduced the ratios of ILC2:CD45 and ILC3:CD45 and increased M2 macrophages in liver. Our study suggests, based on our immunological data, that a combination of estrogen and testosterone may be clinically relevant for the treatment of NAFLD in patients with male menopause.

Interleukin-33 Induces the Enzyme Tryptophan Hydroxylase 1 to Promote Inflammatory Group 2 Innate Lymphoid Cell-Mediated Immunity

Group 2 innate lymphoid cells (ILC2s) regulate immunity, inflammation, and tissue homeostasis. Two distinct subsets of ILC2s have been described: steady-state natural ILC2s and inflammatory ILC2s, which are elicited following helminth infection. However, how tissue-specific cues regulate these two subsets of ILC2s and their effector functions remains elusive. Here, we report that interleukin-33 (IL-33) promotes the generation of inflammatory ILC2s (ILC2^INFLAM) via induction of the enzyme tryptophan hydroxylase 1 (Tph1). Tph1 expression was upregulated in ILC2s upon activation with IL-33 or following helminth infection in an IL-33-dependent manner. Conditional deletion of Tph1 in lymphocytes resulted in selective impairment of ILC2^INFLAM responses and increased susceptibility to helminth infection. Further, RNA sequencing analysis revealed altered gene expression in Tph1 deficient ILC2s including inducible T cell co-stimulator (Icos). Collectively, these data reveal a previously unrecognized function for IL-33, Tph1, and ICOS in promoting inflammatory ILC2 responses and type 2 immunity at mucosal barriers.

Dietary Fiber-Induced Microbial Short Chain Fatty Acids Suppress ILC2-Dependent Airway Inflammation

Group 2 Innate lymphoid cells (ILC2) contribute significantly to allergic inflammation. However, the role of microbiota on ILC2s remains to be unraveled. Here we show that short chain fatty acids (SCFAs), such as butyrate, derived from fermentation of dietary fibers by the gut microbiota inhibit pulmonary ILC2 functions and subsequent development of airway hyperreactivity (AHR). We further show that SCFAs modulate GATA3, oxidative phosphorylation, and glycolytic metabolic pathways in pulmonary ILC2s. The observed phenotype is associated with increased IL-17a secretion by lung ILC2s and linked to enhanced neutrophil recruitment to the airways. Finally, we show that butyrate-producing gut bacteria in germ-free mice effectively suppress ILC2-driven AHR. Collectively, our results demonstrate a previously unrecognized role for microbial-derived SCFAs on pulmonary ILC2s in the context of AHR. The data suggest strategies aimed at modulating metabolomics and microbiota in the gut, not only to treat, but to prevent lung inflammation and asthma.

Immunity, Hypoxia, and Metabolism-the Ménage à Trois of Cancer: Implications for Immunotherapy

It is generally accepted that metabolism is able to shape the immune response. Only recently we are gaining awareness that the metabolic crosstalk between different tumor compartments strongly contributes to the harsh tumor microenvironment (TME) and ultimately impairs immune cell fitness and effector functions. The major aims of this review are to provide an overview on the immune system in cancer; to position oxygen shortage and metabolic competition as the ground of a restrictive TME and as important players in the anti-tumor immune response; to define how immunotherapies affect hypoxia/oxygen delivery and the metabolic landscape of the tumor; and vice versa, how oxygen and metabolites within the TME impinge on the success of immunotherapies. By analyzing preclinical and clinical endeavors, we will discuss how a metabolic characterization of the TME can identify novel targets and signatures that could be exploited in combination with standard immunotherapies and can help to predict the benefit of new and traditional immunotherapeutic drugs.

Current Understanding of Innate Immune Cell Dysfunction in Childhood Undernutrition

Undernutrition affects millions of children in low- and middle-income countries (LMIC) and underlies almost half of all deaths among children under 5 years old. The growth deficits that characterize childhood undernutrition (stunting and wasting) result from simultaneous underlying defects in multiple physiological processes, and current treatment regimens do not completely normalize these pathways. Most deaths among undernourished children are due to infections, indicating that their anti-pathogen immune responses are impaired. Defects in the body's first-line-of-defense against pathogens, the innate immune system, is a plausible yet understudied pathway that could contribute to this increased infection risk. In this review, we discuss the evidence for innate immune cell dysfunction from cohort studies of childhood undernutrition in LMIC, highlighting knowledge gaps in almost all innate immune cell types. We supplement these gaps with insights from relevant experimental models and make recommendations for how human and animal studies could be improved. A better understanding of innate immune function could inform future tractable immune-targeted interventions for childhood undernutrition to reduce mortality and improve long-term health, growth and development.

Nuclear Receptors Regulate Intestinal Inflammation in the Context of IBD

Gastrointestinal (GI) homeostasis is strongly dependent on nuclear receptor (NR) functions. They play a variety of roles ranging from nutrient uptake, sensing of microbial metabolites, regulation of epithelial intestinal cell integrity to shaping of the intestinal immune cell repertoire. Several NRs are associated with GI pathologies; therefore, systematic analysis of NR biology, the underlying molecular mechanisms, and regulation of target genes can be expected to help greatly in uncovering the course of GI diseases. Recently, an increasing number of NRs has been validated as potential drug targets for therapeutic intervention in patients with inflammatory bowel disease (IBD). Besides the classical glucocorticoids, especially PPARγ, VDR, or PXR-selective ligands are currently being tested with promising results in clinical IBD trials. Also, several pre-clinical animal studies are being performed with NRs. This review focuses on the complex biology of NRs and their context-dependent anti- or pro-inflammatory activities in the regulation of gastrointestinal barrier with special attention to NRs already pharmacologically targeted in clinic and pre-clinical IBD treatment regimens.

Immunometabolism features of metabolic deregulation and cancer

Immunometabolism is a branch dealing at the interface of immune functionalities and metabolic regulations. Considered as a bidirectional trafficking, metabolic contents and their precursors bring a considerable change in immune cells signal transductions which as a result affect the metabolic organs and states as an implication. Lipid metabolic ingredients form a major chunk of daily diet and have a proven contribution in immune cells induction, which then undergo metabolic pathway shuffling inside their ownself. Lipid metabolic states activate relevant metabolic pathways inside immune cells that in turn prime appropriate responses to outside environment in various states including lipid metabolic disorders itself and cancers as an extension. Although data on Immunometabolism are still growing, but scientific community need to adjust and readjust according to recent data on given subject. This review attempts to provide current important data on Immunometabolism and consequently its metabolic ramifications. Incumbent data on various lipid metabolic deregulations like obesity, metabolic syndrome, obese asthma and atherosclerosis are analysed. Further, metabolic repercussions on cancers and its immune modalities are also analysed.

Metabolic regulation of innate and adaptive lymphocyte effector responses

Innate and adaptive lymphocytes employ diverse effector programs that provide optimal immunity to pathogens and orchestrate tissue homeostasis, or conversely can become dysregulated to drive progression of chronic inflammatory diseases. Emerging evidence suggests that CD4+ T helper cell subsets and their innate counterparts, the innate lymphoid cell family, accomplish these complex biological roles by selectively programming their cellular metabolism in order to instruct distinct modules of lymphocyte differentiation, proliferation, and cytokine production. Further, these metabolic pathways are significantly influenced by tissue microenvironments and disease states. Here, we summarize our current knowledge on how cell-intrinsic metabolic factors modulate the context-dependent bioenergetic pathways that govern innate and adaptive lymphocytes. Further, we propose that a greater understanding of these pathways may lead to the identification of unique features in each population and provoke the development of novel therapeutic strategies to modulate lymphocytes in health and disease.

Hypoxia, Metabolism and Immune Cell Function

Hypoxia is a hallmark of inflamed, infected or damaged tissue, and the adaptation to inadequate tissue oxygenation is regulated by hypoxia-inducible factors (HIFs). HIFs are key mediators of the cellular response to hypoxia, but they are also associated with pathological stress such as inflammation, bacteriological infection or cancer. In addition, HIFs are central regulators of many innate and adaptive immunological functions, including migration, antigen presentation, production of cytokines and antimicrobial peptides, phagocytosis as well as cellular metabolic reprogramming. A characteristic feature of immune cells is their ability to infiltrate and operate in tissues with low level of nutrients and oxygen. The objective of this article is to discuss the role of HIFs in the function of innate and adaptive immune cells in hypoxia, with a focus on how hypoxia modulates immunometabolism.