An essential function for the nuclear receptor RORgamma(t) in the generation of fetal lymphoid tissue inducer cells

(Inverse) Agonists of Retinoic Acid-Related Orphan Receptor γ: Regulation of Immune Responses, Inflammation, and Autoimmune Disease

Retinoic acid-related orphan receptor γt (RORγt) functions as a ligand-dependent transcription factor that regulates multiple proinflammatory genes and plays a critical role in several inflammatory and autoimmune diseases. Various endogenous and synthetic RORγ (inverse) agonists have been identified that regulate RORγ transcriptional activity, including many cholesterol intermediates and oxysterols. Changes in cholesterol biosynthesis and metabolism can therefore have a significant impact on the generation of oxysterol RORγ ligands and, consequently, can control RORγt activity and inflammation. These observations contribute to a growing literature that connects cholesterol metabolism to the regulation of immune responses and autoimmune disease. Loss of RORγ function in knockout mice and in mice treated with RORγ inverse agonists results in reduced production of proinflammatory cytokines, such as IL-17A/F, and increased resistance to autoimmune disease in several experimental rodent models. Thus, RORγt inverse agonists might provide an attractive therapeutic approach to treat a variety of autoimmune diseases.

Activation of DR3 signaling causes loss of ILC3s and exacerbates intestinal inflammation

TNF-like ligand 1 A (TL1A) and death receptor 3 (DR3) are a ligand-receptor pair involved in the pathogenesis of inflammatory bowel disease. Group 3 innate lymphoid cells (ILC3s) regulate intestinal immunity and highly express DR3. Here, we report that activation of DR3 signaling by an agonistic anti-DR3 antibody increases GM-CSF production from ILC3s through the p38 MAPK pathway. GM-CSF causes accumulation of eosinophils, neutrophils and CD11b⁺CD11c⁺ myeloid cells, resulting in loss of ILC3s from the intestine in an IL-23-dependent manner and exacerbating colitis. Blockade of GM-CSF or IL-23 reverses anti-DR3 antibody-driven ILC3 loss, whereas overexpression of IL-23 induces loss of ILC3s in the absence of GM-CSF. Neutralization of TL1A by soluble DR3 ameliorates both DSS and anti-CD40 antibody-induced colitis. Moreover, ILC3s are required for the deleterious effect of anti-DR3 antibodies on innate colitis. These findings clarify the process and consequences of DR3 signaling-induced intestinal inflammation through regulation of ILC3s.

Functional interactions between innate lymphoid cells and adaptive immunity

Innate lymphoid cells (ILCs) are enriched at barrier surfaces of the mammalian body where they rapidly respond to host, microbial or environmental stimuli to promote immunity or tissue homeostasis. Furthermore, ILCs are dysregulated in multiple human diseases. Over the past decade, substantial advances have been made in identifying the heterogeneity and functional diversity of ILCs, which have revealed striking similarities to T cell subsets. However, emerging evidence indicates that ILCs also have a complex role in directly influencing the adaptive immune response in the context of development, homeostasis, infection or inflammation. In turn, adaptive immunity reciprocally regulates ILCs, which indicates that these interactions are a crucial determinant of immune responses within tissues. Here, we summarize our current understanding of functional interactions between ILCs and the adaptive immune system, discuss limitations and future areas of investigation, and consider the potential for these interactions to be therapeutically harnessed to benefit human health.

Temporally Distinct Functions of the Cytokines IL-12 and IL-23 Drive Chronic Colon Inflammation in Response to Intestinal Barrier Impairment

Epithelial barrier defects are implicated in the pathogenesis of inflammatory bowel disease (IBD); however, the role of microbiome dysbiosis and the cytokine networks orchestrating chronic intestinal inflammation in response to barrier impairment remain poorly understood. Here, we showed that altered Schaedler flora (ASF), a benign minimal microbiota, was sufficient to trigger colitis in a mouse model of intestinal barrier impairment. Colitis development required myeloid-cell-specific adaptor protein MyD88 signaling and was orchestrated by the cytokines IL-12, IL-23, and IFN-γ. Colon inflammation was driven by IL-12 during the early stages of the disease, but as the mice aged, the pathology shifted toward an IL-23-dependent inflammatory response driving disease chronicity. These findings reveal that IL-12 and IL-23 act in a temporally distinct, biphasic manner to induce microbiota-driven chronic intestinal inflammation. Similar mechanisms might contribute to the pathogenesis of IBD particularly in patients with underlying intestinal barrier defects.

Innate lymphocytes-lineage, localization and timing of differentiation

Innate lymphocytes are a diverse population of cells that carry out specialized functions in steady-state homeostasis and during immune challenge. While circulating cytotoxic natural killer (NK) cells have been studied for decades, tissue-resident innate lymphoid cells (ILCs) have only been characterized and studied over the past few years. As ILCs have been largely viewed in the context of helper T-cell biology, models of ILC lineage and function have been founded within this perspective. Notably, tissue-resident innate lymphocytes with cytotoxic potential have been described in an array of tissues, yet whether they are derived from the NK or ILC lineage is only beginning to be elucidated. In this review, we aim to shed light on the identities of innate lymphocytes through the lenses of cell lineage, localization, and timing of differentiation.

New insights into the function, development, and plasticity of type 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s) are the most well defined group of ILCs. ILC2 development is controlled by the GATA-3 transcription factor and these cells produce archetypal type 2 cytokines, such as IL-5 and IL-13. These cytokines mediate parasite expulsion and tissue repair, but also contribute to type 2 inflammatory diseases, including allergy, asthma and chronic rhinosinusitis with nasal polyps. In response to tightly regulated local environmental cues ILCs can generate characteristics of other subtypes, a process known as plasticity. Recent advances in the ILC2 field has led to the discovery that ILC2s can promptly shift to functional IFN-γ-producing ILC1s or IL-17-producing ILC3s, depending on the cytokines and chemokines produced by antigen presenting cells or epithelial cells. Due to yet unknown triggers, this complex network of signals may become dysregulated. In this review, we will discuss general ILC characteristic, ILC2 development, plasticity, memory function, and implications in disease.

Innate lymphoid cells, mediators of tissue homeostasis, adaptation and disease tolerance

Innate lymphoid cells (ILC) are a recently identified group of tissue-resident innate lymphocytes. Available data support the view that ILC or their progenitors are deposited and retained in tissues early during ontogeny. Thereby, ILC become an integral cellular component of tissues and organs. Here, we will review the intriguing relationships between ILC and basic developmental and homeostatic processes within tissues. Studying ILC has already led to the appreciation of the integral roles of immune cells in tissue homeostasis, morphogenesis, metabolism, regeneration, and growth. This area of immunology has not yet been studied in-depth but is likely to reveal important networks contributing to disease tolerance and may be harnessed for future therapeutic approaches.

Deconstructing deployment of the innate immune lymphocyte army for barrier homeostasis and protection

The study of the immune system has shifted from a purely dichotomous separation between the innate and adaptive arms to one that is now highly complex and reshaping our ideas of how steady‐state health is assured. It is now clear that immune cells do not neatly fit into these two streams and immune homeostasis depends on continual dialogue between multiple lineages of the innate (including dendritic cells, innate lymphoid cells, and unconventional lymphocytes) and adaptive (T and B lymphocytes) arms together with a finely tuned synergy between the host and microbes which is essential to ensure immune homeostasis. Innate lymphoid cells are critical players in this new landscape. Here, we discuss recent studies that have elucidated in detail the development of ILCs from their earliest progenitors and examine factors that influence their identification and ability to drive immune homeostasis and long‐term immune protection.

Defining Genetic Variation in Widely Used Congenic and Backcrossed Mouse Models Reveals Varied Regulation of Genes Important for Immune Responses

Genetic variation influences how the genome is interpreted in individuals and in mouse strains used to model immune responses. We developed approaches to utilize next-generation sequencing datasets to identify sequence variation in genes and enhancer elements in congenic and backcross mouse models. We defined genetic variation in the widely used B6-CD45.2 and B6.SJL-CD45.1 congenic model, identifying substantial differences in SJL genetic content retained in B6.SJL-CD45.1 strains on the basis of the vendor source of the mice. Genes encoding PD-1, CD62L, Bcl-2, cathepsin E, and Cxcr4 were within SJL genetic content in at least one vendor source of B6.SJL-CD45.1 mice. SJL genetic content affected enhancer elements, gene regulation, protein expression, and amino acid content in CD4⁺ T helper 1 cells, and mice infected with influenza showed reduced expression of Cxcr4 on B6.SJL-CD45.1 T follicular helper cells. These findings provide information on experimental variables and aid in creating approaches that account for genetic variables.

Type 2 innate lymphoid cells in the induction and resolution of tissue inflammation

Type 2 immunity against pathogens is tightly regulated to ensure appropriate inflammatory responses that clear infection and prevent excessive tissue damage. Recent research has shown that type 2 innate lymphoid cells (ILC2s) contribute to steady-state tissue integrity and exert tissue-specific functions. However, upon exposure to inflammatory stimuli, they also initiate and amplify type 2 inflammation by inducing mucus production, eosinophilia, and Th2 differentiation. In this review, we discuss the regulation of ILC2 activation by transcription factors and metabolic pathways, as well as by extrinsic signals such as cytokines, lipid mediators, hormones, and neuropeptides. We also review recent discoveries about ILC2 plasticity and heterogeneity in different tissues, as revealed partly through single-cell RNA sequencing of transcriptional responses to various stimuli. Understanding the tissue-specific pathways that regulate ILC2 diversity and function is a critical step in the development of potential therapies for allergic diseases.

Tissue-Resident Group 2 Innate Lymphoid Cells Differentiate by Layered Ontogeny and In Situ Perinatal Priming

The perinatal period is a critical window for distribution of innate tissue-resident immune cells within developing organs. Despite epidemiologic evidence implicating the early-life environment in the risk for allergy, temporally controlled lineage tracing of group 2 innate lymphoid cells (ILC2s) during this period remains unstudied. Using complementary fate-mapping approaches and reporters for ILC2 activation, we show that ILC2s appeared in multiple organs during late gestation like tissue macrophages, but, unlike the latter, a majority of peripheral ILC2 pools were generated de novo during the postnatal window. This period was accompanied by systemic ILC2 priming and acquisition of tissue-specific transcriptomes. Although perinatal ILC2s were variably replaced across tissues with age, the dramatic increases in tissue ILC2s following helminth infection were mediated through local expansion independent of de novo generation by bone marrow hematopoiesis. We provide comprehensive temporally controlled fate mapping of an innate lymphocyte subset with notable nuances as compared to tissue macrophage ontogeny.

Suppression of Aiolos and Ikaros expression by lenalidomide reduces human ILC3-ILC1/NK cell transdifferentiation

The Ikaros family of transcription factors (TFs) are important regulators of lymphocyte function. However, their roles in human innate lymphoid cell (ILC) function remain unclear. Here, we found that Ikaros (IKZF1) is expressed by all ILC subsets, including NK cells, in blood, tonsil, and gut, while Helios (IKZF2) is preferentially expressed by ILC3 in tonsil and gut. Aiolos (IKZF3) followed the expression pattern of T-bet and Eomes, being predominantly expressed by ILC1 and NK cells. Differentiation of IFN-γ-producing ILC1 and NK cells from ILC3 by IL-1β plus IL-12-stimulation was associated with upregulation of T-bet and Aiolos. Selective degradation of Aiolos and Ikaros by lenalidomide suppressed ILC1 and NK cell differentiation and expression of ILC1 and NK cell-related transcripts (LEF1, PRF1, GRZB, CD244, NCR3, and IRF8). In line with reduced ILC1/NK cell differentiation, we observed an increase in the expression of the ILC3-related TF Helios, as well as ILC3 transcripts (TNFSF13B, IL22, NRP1, and RORC) and in the frequency of IL-22 producing ILC3 in cultures with IL-1β and IL-23. These data suggest that suppression of Aiolos and Ikaros expression inhibits ILC1 and NK cell differentiation while ILC3 function is maintained. Hence, our results open up for new possibilities in targeting Ikaros family TFs for modulation of type 1/3 immunity in inflammation and cancer.

IL-23-producing IL-10Rα-deficient gut macrophages elicit an IL-22-driven proinflammatory epithelial cell response

Cytokines maintain intestinal health, but precise intercellular communication networks remain poorly understood. Macrophages are immune sentinels of the intestinal tissue and are critical for gut homeostasis. Here, we show that in a murine inflammatory bowel disease (IBD) model based on macrophage-restricted interleukin-10 (IL-10) receptor deficiency (Cx3cr1Cre:Il10rafl/fl mice), proinflammatory mutant gut macrophages cause severe spontaneous colitis resembling the condition observed in children carrying IL-10R mutations. We establish macrophage-derived IL-23 as the driving factor of this pathology. Specifically, we report that Cx3cr1Cre:Il10rafl/fl:Il23afl/fl mice harboring macrophages deficient for both IL-10R and IL-23 are protected from colitis. By analyzing the epithelial response to proinflammatory macrophages, we provide evidence that T cells of colitic animals produce IL-22, which induces epithelial chemokine expression and detrimental neutrophil recruitment. Collectively, we define macrophage-specific contributions to the induction and pathogenesis of colitis, as manifested in mice harboring IL-10R deficiencies and human IBDs.

The balance of power: innate lymphoid cells in tissue inflammation and repair

Over the last ten years, immunologists have recognized the central importance of an emerging group of innate lymphoid cells (ILCs) in health and disease. Characterization of these cells has provided a molecular definition of ILCs and their tissue-specific functions. Although the lineage-defining transcription factors, cytokine production, and nomenclature parallel those of T helper cells, ILCs do not require adaptive immune programming. Both environmental and host-derived signals shape the function of these evolutionarily ancient cells, which provide pathogen protection and promote tissue restoration. As such, ILCs function as a double-edged sword, balancing the inflammatory and reparative responses that arise during injury and disease. This Review highlights our recent understanding of tissue-resident ILCs and the signals that regulate their contribution to inflammation and tissue repair in health and disease.

Non-canonical B cell functions in transplantation

B cells are differentiated to recognize antigen and respond by producing antibodies. These activities, governed by recognition of ancillary signals, defend the individual against microorganisms and the products of microorganisms and constitute the canonical function of B cells. Despite the unique differentiation (e.g. recombination and mutation of immunoglobulin gene segments) toward this canonical function, B cells can provide other, "non-canonical" functions, such as facilitating of lymphoid organogenesis and remodeling and fashioning T cell repertoires and modifying T cell responses. Some non-canonical functions are exerted by antibodies, but most are mediated by other products and/or direct actions of B cells. The diverse set of non-canonical functions makes the B cell as much as any cell a central organizer of innate and adaptive immunity. However, the diverse products and actions also confound efforts to weigh the importance of individual non-canonical B cell functions. Here we shall describe the non-canonical functions of B cells and offer our perspective on how those functions converge in the development and governance of immunity, particularly immunity to transplants, and hurdles to advancing understanding of B cell functions in transplantation.

TCF-1 limits the formation of Tc17 cells via repression of the MAF-RORγt axis

Mielke et al. show that TCF-1 limits IL-17–producing CD8⁺ T (Tc17) cell development from double-positive thymocytes through the sequential suppression of MAF and RORγt, while cementing conventional CD8⁺ T cell fate.

Interleukin (IL)-17–producing CD8⁺ T (Tc17) cells have emerged as key players in host-microbiota interactions, infection, and cancer. The factors that drive their development, in contrast to interferon (IFN)-γ–producing effector CD8⁺ T cells, are not clear. Here we demonstrate that the transcription factor TCF-1 (Tcf7) regulates CD8⁺ T cell fate decisions in double-positive (DP) thymocytes through the sequential suppression of MAF and RORγt, in parallel with TCF-1–driven modulation of chromatin state. Ablation of TCF-1 resulted in enhanced Tc17 cell development and exposed a gene set signature to drive tissue repair and lipid metabolism, which was distinct from other CD8⁺ T cell subsets. IL-17–producing CD8⁺ T cells isolated from healthy humans were also distinct from CD8⁺IL-17⁻ T cells and enriched in pathways driven by MAF and RORγt. Overall, our study reveals how TCF-1 exerts central control of T cell differentiation in the thymus by normally repressing Tc17 differentiation and promoting an effector fate outcome.

Polychromic Reporter Mice Reveal Unappreciated Innate Lymphoid Cell Progenitor Heterogeneity and Elusive ILC3 Progenitors in Bone Marrow

Innate lymphoid cells (ILCs) play strategic roles in tissue homeostasis and immunity. ILCs arise from lymphoid progenitors undergoing lineage restriction and the development of specialized ILC subsets. We generated “5x polychromILC” transcription factor reporter mice to delineate ILC precursor states by revealing the multifaceted expression of key ILC-associated transcription factors (Id2, Bcl11b, Gata3, RORγt, and RORα) during ILC development in the bone marrow. This approach allowed previously unattained enrichment of rare progenitor subsets and revealed hitherto unappreciated ILC precursor heterogeneity. In vivo and in vitro assays identified precursors with potential to generate all ILC subsets and natural killer (NK) cells, and also permitted discrimination of elusive ILC3 bone marrow antecedents. Single-cell gene expression analysis identified a discrete ILC2-committed population and delineated transition states between early progenitors and a highly heterogeneous ILC1, ILC3, and NK precursor cell cluster. This diversity might facilitate greater lineage potential upon progenitor recruitment to peripheral tissues.

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Five-color “polychromILC” transcription factor reporter mice define ILC precursors

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ILC precursors give rise to ILC1, ILC2, and ILC3 and retain NK potential

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A Rorc^Kat allele allows resolution of extremely rare ILC3 progenitors

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Detection of divergent trajectories for ILC2 and common ILC1, ILC3, and NK development

Necroptosis of Intestinal Epithelial Cells Induces Type 3 Innate Lymphoid Cell-Dependent Lethal Ileitis

A short form of cellular FLICE-inhibitory protein encoded by CFLARs promotes necroptosis. Although necroptosis is involved in various pathological conditions, the detailed mechanisms are not fully understood. Here we generated transgenic mice wherein CFLARs was integrated onto the X chromosome. All male CFLARs Tg mice died perinatally due to severe ileitis. Although necroptosis was observed in various tissues of CFLARs Tg mice, large numbers of intestinal epithelial cells (IECs) died by apoptosis. Deletion of Ripk3 or Mlkl, essential genes of necroptosis, prevented both necroptosis and apoptosis, and rescued lethality of CFLARs Tg mice. Type 3 innate lymphoid cells (ILC3s) were activated and recruited to the small intestine along with upregulation of interleukin-22 (Il22) in CFLARs Tg mice. Deletion of ILC3s or Il22 rescued lethality of CFLARs Tg mice by preventing apoptosis, but not necroptosis of IECs. Together, necroptosis-dependent activation of ILC3s induces lethal ileitis in an IL-22-dependent manner.

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CFLARs Tg mice develop severe ileitis in utero

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Intestinal epithelial cells die by apoptosis and necroptosis in CFLARs Tg mice

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Blockade of necroptosis rescues lethality of CFLARs Tg mice

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Necroptosis activates type 3 innate lymphoid cells, resulting in severe ileitis

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.

Modeling Infectious Diseases in Mice with a "Humanized" Immune System

Human immune system (HIS) mice are created by transplanting human immune cells or their progenitor cells into highly immunodeficient recipient mouse hosts, thereby "humanizing" their immune systems. Over past decades, the field of HIS mice has evolved rapidly, as modifications of existing immunodeficient mouse strains have been developed, resulting in increasing levels of human tissue engraftment as humanization is optimized. Current HIS mouse models not only permit elevated levels of human cell engraftment but also demonstrate graft stability. As such, HIS mice are being extensively used to study the human innate and adaptive immune response against microbial infections in vivo. Compared to nonhumanized animal models, which are frequently infected with surrogate or adapted microbes, the HIS mouse models allow the analysis of interactions between human immune cells and bona fide pathogenic microbes, making them a more clinically relevant model. This article reviews the development of HIS mice and covers the different strategies used to humanize mice, as well as discussing the use of HIS mice for studying bacterial infections that cause human disease.

Innate Lymphoid Cells in Mucosal Immunity

Innate lymphoid cells (ILCs) are innate counterparts of T cells that contribute to immune responses by secreting effector cytokines and regulating the functions of other innate and adaptive immune cells. ILCs carry out some unique functions but share some tasks with T cells. ILCs are present in lymphoid and non-lymphoid organs and are particularly abundant at the mucosal barriers, where they are exposed to allergens, commensal microbes, and pathogens. The impact of ILCs in mucosal immune responses has been extensively investigated in the gastrointestinal and respiratory tracts, as well as in the oral cavity. Here we review the state-of-the-art knowledge of ILC functions in infections, allergy and autoimmune disorders of the mucosal barriers.

Aire-expressing ILC3-like cells in the lymph node display potent APC features

The autoimmune regulator (Aire) serves an essential function for T cell tolerance by promoting the "promiscuous" expression of tissue antigens in thymic epithelial cells. Aire is also detected in rare cells in peripheral lymphoid organs, but the identity of these cells is poorly understood. Here, we report that Aire protein-expressing cells in lymph nodes exhibit typical group 3 innate lymphoid cell (ILC3) characteristics such as lymphoid morphology, absence of "classical" hematopoietic lineage markers, and dependence on RORγt. Aire+ cells are more frequent among lineage-negative RORγt+ cells of peripheral lymph nodes as compared with mucosa-draining lymph nodes, display a unique Aire-dependent transcriptional signature, express high surface levels of MHCII and costimulatory molecules, and efficiently present an endogenously expressed model antigen to CD4+ T cells. These findings define a novel type of ILC3-like cells with potent APC features, suggesting that these cells serve a function in the control of T cell responses.

BCL6 corepressor contributes to Th17 cell formation by inhibiting Th17 fate suppressors

Th17 cells provide a protective immunity against extracellular bacterial and fungal pathogens. Kotov et al. identify and characterize a mechanism by which BCOR promotes Th17 formation after Streptococcus pyogenes infection by repressing genes that inhibit the Th17 lineage.

CD4⁺ T helper 17 (Th17) cells protect vertebrate hosts from extracellular pathogens at mucosal surfaces. Th17 cells form from naive precursors when signals from the T cell antigen receptor (TCR) and certain cytokine receptors induce the expression of the RORγt transcription factor, which activates a set of Th17-specific genes. Using T cell–specific loss-of-function experiments, we find that two components of the Polycomb repressive complex 1.1 (PRC1.1), BCL6 corepressor (BCOR) and KDM2B, which helps target the complex to unmethylated CpG DNA islands, are required for optimal Th17 cell formation in mice after Streptococcus pyogenes infection. Genome-wide expression and BCOR chromatin immunoprecipitation studies revealed that BCOR directly represses Lef1, Runx2, and Dusp4, whose products inhibit Th17 differentiation. Together, the results suggest that the PRC1.1 components BCOR and KDM2B work together to enhance Th17 cell formation by repressing Th17 fate suppressors.

IgG and Fcγ Receptors in Intestinal Immunity and Inflammation

Fcγ receptors (FcγR) are cell surface glycoproteins that mediate cellular effector functions of immunoglobulin G (IgG) antibodies. Genetic variation in FcγR genes can influence susceptibility to a variety of antibody-mediated autoimmune and inflammatory disorders, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). More recently, however, genetic studies have implicated altered FcγR signaling in the pathogenesis of inflammatory bowel disease (IBD), a condition classically associated with dysregulated innate and T cell immunity. Specifically, a variant of the activating receptor, FcγRIIA, with low affinity for IgG, confers protection against the development of ulcerative colitis, a subset of IBD, leading to a re-evaluation of the role of IgG and FcγRs in gastrointestinal tract immunity, an organ system traditionally associated with IgA. In this review, we summarize our current understanding of IgG and FcγR function at this unique host-environment interface, from the pathogenesis of colitis and defense against enteropathogens, its contribution to maternal-fetal cross-talk and susceptibility to cancer. Finally, we discuss the therapeutic implications of this information, both in terms of how FcγR signaling pathways may be targeted for the treatment of IBD and how FcγR engagement may influence the efficacy of therapeutic monoclonal antibodies in IBD.

Group 3 ILCs: Peacekeepers or Troublemakers? What's Your Gut Telling You?!

A complex network of interactions exists between the microbiome, the epithelium, and immune cells that reside along the walls of the gastrointestinal tract. The intestinal immune system has been assigned with the difficult task of discriminating between commensal, harmless bacteria, and invading pathogens that translocate across the epithelial monolayer. Importantly, it is trained to maintain tolerance against commensals, and initiate protective immune responses against pathogens to secure intestinal homeostasis. Breakdown of this fine balance between the host and its intestinal microbiota can lead to intestinal inflammation and subsequently to development of inflammatory bowel disease (IBD). A decade since their discovery, innate lymphoid cells (ILCs) are now recognized as important regulators of intestinal homeostasis. ILC3s have emerged as a critical subset in the gut. They are the most phenotypically diverse ILC population and interact directly with numerous different cell types (haematopoietic and non-haematopoeitic), as well as interface with the bacterial flora. In addition to their contribution to intestinal pathogen immunity, they also mitigate against tissue damage occurring following acute injury, by facilitating tissue repair and regeneration, a key function in the maintenance of intestinal homeostasis. However, in chronic inflammation the tables are turned and ILC3s may acquire a pro-inflammatory phenotype in the gut. Chronic ILC activation can lead to persistent inflammation contributing to IBD and/or colorectal cancer. In this review, we discuss current knowledge of group 3 ILCs and their contributions to intestinal homeostasis and disease leading to novel therapeutic targets and clinical approaches that may inform novel treatment strategies for immune-mediated disorders, including IBD.

The Transcription Factor T-Bet Is Required for Optimal Type I Follicular Helper T Cell Maintenance During Acute Viral Infection

Follicular helper T cells (TFH cells), known as the primary “helpers” of the germinal center (GC) reaction, promote the humoral immune response to defend against various pathogens. Under conditions of infection by different types of pathogens, many shared transcription factors (TFs), such as Bcl-6, TCF-1, and Maf, are selectively enriched in pathogen-specific TFH cells, orchestrating TFH cell differentiation and function. In addition, TFH cells also coexpress environmentally associated TFs as their conventional T cell counterparts (such as T-bet, GATA-3, or ROR-γt, which are expressed in Th1, Th2, or Th17 cells, respectively). These features likely indicate both the lineage-specificity and environmental adaption of the TFH cell responses. However, the extent to which the TFH cell response relies on these environmentally specific TFs is not completely understood. Here, we found that T-bet was specifically expressed in Type I TFH cells but not Type II TFH cells. While dispensable for the early fate commitment of TFH cells, T-bet was essential for the maintenance of differentiated TFH cells, promoting their proliferation, and inhibiting their apoptosis during acute viral infection. Microarray analysis showed both similarities and differences in transcriptome dependency on T-bet in TFH and TH1 cells, suggesting the distinctive role of T-bet in TFH cells. Collectively, our findings reveal an important and specific supporting role for T-bet in type I TFH cell response, which can help us gain a deeper understanding of TFH cell subsets.

Immune Cell-Epithelial/Mesenchymal Interaction Contributing to Allergic Airway Inflammation Associated Pathology

The primary function of the lung is efficient gas exchange between alveolar air and alveolar capillary blood. At the same time, the lung protects the host from continuous invasion of harmful viruses and bacteria by developing unique epithelial barrier systems. Thus, the lung has a complex architecture comprising a mixture of various types of cells including epithelial cells, mesenchymal cells, and immune cells. Recent studies have revealed that Interleukin (IL-)33, a member of the IL-1 family of cytokines, is a key environmental cytokine that is derived from epithelial cells and induces type 2 inflammation in the barrier organs, including the lung. IL-33 induces allergic diseases, such as asthma, through the activation of various immune cells that express an IL-33 receptor, ST2, including ST2⁺ memory (CD62L^lowCD44^hi) CD4⁺ T cells. ST2⁺ memory CD4⁺ T cells have the capacity to produce high levels of IL-5 and Amphiregulin and are involved in the pathology of asthma. ST2⁺ memory CD4⁺ T cells are maintained by IL-7- and IL-33-produced lymphatic endothelial cells within inducible bronchus-associated lymphoid tissue (iBALT) around the bronchioles during chronic lung inflammation. In this review, we will discuss the impact of these immune cells-epithelial/mesenchymal interaction on shaping the pathology of chronic allergic inflammation. A better understanding of pathogenic roles of the cellular and molecular interaction between immune cells and non-immune cells is crucial for the development of new therapeutic strategies for intractable allergic diseases.

Differential Effects of the Absence of Nkx2-3 and MAdCAM-1 on the Distribution of Intestinal Type 3 Innate Lymphoid Cells and Postnatal SILT Formation in Mice

Seeding of leukocytes to developing lymphoid tissues in embryonic and early postnatal age and to the mucosa throughout adulthood depends on the interaction between endothelial MAdCAM-1 addressin and its cognate ligand α4β7 integrin. Nkx2-3 as a transcriptional regulator of MAdCAM-1 controls vascular patterning in visceral lymphoid tissues in mice, and has been identified as a susceptibility factor for inflammatory bowel diseases in humans, associated with lymphoid neogenesis in the inflamed intestines. The role of Nkx2-3 in the organogenesis of the solitary intestinal lymphoid tissues (SILTs) involving type 3 innate lymphoid cells (ILC3) is still unknown. Here we investigated the effect of Nkx2-3 on the postnatal distribution of intestinal ILC3s and the development of SILTs, comparing these to mice lacking MAdCAM-1, but preserving Nkx2-3. At 1 week of age small intestines (SI) contained significantly higher number of ILC3s relative to the colon, with a substantial reduction in MAdCAM-1^−/− mice compared to C57BL/6 controls. One week later SI ILC3 number decreased in all genotypes, the number of colonic ILC3 of both Nkx2-3-deficient and Nkx2-3-heterozygous mice significantly increased. On the fourth postnatal week a further reduction of SI ILC3s was observed in both Nkx2-3-deficient and Nkx2-3-heterozygous mice, while in the colon the number of ILC3s showed a significant reduction in all genotypes. At 1 week of age only sporadic SILT components were present in all genotypes. By the second week mice deficient for either Nkx2-3 or MAdCAM-1 showed absence of SILT maturation compared to their relevant controls, lacking mature isolated lymphoid follicles (ILF). By the fourth week both Nkx2-3-deficient and Nkx2-3-heterozygous mice showed a similar distribution of ILFs relative to cryptopatches (CP), whereas in MAdCAM-1^−/− mice CPs and immature ILFs were present, mature ILFs were scarce. Our data demonstrate that the complete absence of MAdCAM-1 partially impairs intestinal seeding of ILC3s and causes partial blockade of SILT maturation, without affecting peripheral lymph node development. In contrast, the inactivation of Nkx2-3 permits postnatal seeding, and its blocking effect on SILT maturation prevails at later stage, thus other adhesion molecules may compensate for the intestinal homing of ILC3s in the absence of MAdCAM-1.

Innate lymphoid cells: A potential link between microbiota and immune responses against cancer

The adaptive immune system plays a crucial role in anti-tumor surveillance. Enhancement of T cell responses through checkpoint blockade has become a major therapeutic avenue of intervention for several tumors. Because it shapes immune responses and regulates their amplitude and duration, the microbiota has a substantial impact on anti-tumor immunity. Innate lymphoid cells (ILCs) comprise a heterogeneous population of lymphocytes devoid of antigen-specific receptors that mirror T helper cells in their ability to secrete cytokines that activate immune responses. Ongoing studies suggest that ILCs contribute to anti-tumor responses. Moreover, since ILCs are present at barrier surfaces, they are stimulated by the microbiota and, reciprocally, influence the composition of the microbiota by regulating the surface barrier microenvironment. Thus, ILC-microbiota cross-talk may in part underpin the effects of the microbiota on anti-tumor responses. In this article, we review current evidence linking ILCs to cancer and discuss the potential impact of ILC-microbiota cross-talk in anti-tumor immune responses.

ILC3-derived OX40L is essential for homeostasis of intestinal Tregs in immunodeficient mice

OX40L is one of the co-stimulatory molecules that can be expressed by splenic lymphoid tissue inducer (Lti) cells, a subset of group 3 innate lymphoid cells (ILC3s). OX40L expression in subsets of intestinal ILC3s and the molecular regulation of OX40L expression in ILC3s are unknown. Here, we showed intestinal ILC3s marked as an OX40L^high population among all the intestinal leukocytes and were the dominant source of OX40L in Rag1^-/- mice. All ILC3 subsets expressed OX40L, and NCR^-ILC3s were the most abundant source of OX40L. The expression of OX40L in ILC3s could be upregulated during inflammation. In addition to tumor necrosis factor (TNF)-like cytokine 1A (TL1A), which has been known as a trigger for OX40L, we found that Poly (I:C) representing viral stimulus promoted OX40L expression in ILC3s via a cell-autonomous manner. Furthermore, we demonstrated that IL-7-STAT5 signaling sustained OX40L expression by ILC3s. Intestinal regulatory T cells (Tregs), most of which expressed OX40, had defective expansion in chimeric mice, in which ILC3s were specifically deficient for OX40L expression. Consistently, co-localization of Tregs and ILC3s was found in the cryptopatches of the intestine, which suggests the close interaction between ILC3s and Tregs. Our study has unveiled the crosstalk between Tregs and ILC3s in mucosal tissues through OX40-OX40L signaling, which is crucial for the homeostasis of intestinal Tregs.

Intestinal non-canonical NFκB signaling shapes the local and systemic immune response

Microfold cells (M-cells) are specialized cells of the intestine that sample luminal microbiota and dietary antigens to educate the immune cells of the intestinal lymphoid follicles. The function of M-cells in systemic inflammatory responses are still unclear. Here we show that epithelial non-canonical NFkB signaling mediated by NFkB-inducing kinase (NIK) is highly active in intestinal lymphoid follicles, and is required for M-cell maintenance. Intestinal NIK signaling modulates M-cell differentiation and elicits both local and systemic IL-17A and IgA production. Importantly, intestinal NIK signaling is active in mouse models of colitis and patients with inflammatory bowel diseases; meanwhile, constitutive NIK signaling increases the susceptibility to inflammatory injury by inducing ectopic M-cell differentiation and a chronic increase of IL-17A. Our work thus defines an important function of non-canonical NFkB and M-cells in immune homeostasis, inflammation and polymicrobial sepsis.

Innate Lymphoid Cell Development: A T Cell Perspective

Innate lymphoid cells (ILCs) and natural killer (NK) cells have garnered considerable interest due to their unique functional properties in immune defense and tissue homeostasis. Our current understanding of how these cells develop has been greatly facilitated by knowledge of T cell biology. Models of T cell differentiation provided the basis for a conceptual classification of these innate effectors and inspired a scheme of their activation and regulation. In this review, we discuss NK cell and ILC development from a "T cell standpoint" in an attempt to extend the analogy between adaptive T cells and their innate ILC and NK cell counterparts.

Expression of B and T lymphocyte attenuator, retinoid-related orphan receptor gamma-isoform-t and interleukin 7 in psoriasis vulgaris

BACKGROUND/OBJECTIVES

Psoriasis is one of the immune-mediated inflammatory diseases where CD4+ T lymphocytes, mainly Th1 cells, and B lymphocytes contribute in their pathogenesis through a pro-inflammatory effect, production of antibodies, activation of T cells and cytokine synthesis. B and T lymphocyte attenuator (BTLA) is a co-inhibitory molecule expressed on T and B lymphocytes as well as other immune cells, and it is necessary to inhibit homoeostatic expansion and activation of lymph node and skin-resident γδ T cells. BTLA expression is regulated by RORγt and IL-7. The study aimed at adding more insight on the role played by co-inhibitory molecule BTLA in psoriasis vulgaris and its inter-relation with RORγt and IL-7 to establish a basis for novel treatment strategies.

METHODS

This case-control study included 25 patients and 25 controls examined for gene expression of BTLA, RORγt and IL-7.

RESULTS

B and T lymphocyte attenuator was significantly lower in psoriasis patients, whereas both RORγt and IL-7 were higher in comparison with controls. A significant positive correlation between disease severity (PASI) and both RORγt and IL-7 as well as between RORγt and IL-7 was found. A significant negative correlation between BTLA and both RORγt and IL-7 was found. Neither the age nor the duration of disease had any correlation with BTLA, RORγt or IL-7. BTLA had no correlation with PASI. Regarding the control group, a significant negative correlation between RORγt and IL-7 was found.

CONCLUSION

B and T lymphocyte attenuator, RORγt and IL-7 play an important role in psoriasis.

Innate Lymphoid Cells in Colorectal Cancers: A Double-Edged Sword

The immune system plays a fundamental role at mucosal barriers in maintaining tissue homeostasis. This is particularly true for the gut where cells are flooded with microbial-derived signals and antigens, which constantly challenge the integrity of the intestinal barrier. Multiple immune cell populations equipped with both pro- and anti-inflammatory functions reside in the gut tissue and these cells tightly regulate intestinal health and functions. Dysregulation of this finely tuned system can progressively lead to autoimmune disease and inflammation-driven carcinogenesis. Over the last decade, the contribution of the adaptive immune system in controlling colorectal cancer has been studied in detail, but the role of the innate system, particularly innate lymphoid cells (ILCs), have been largely overlooked. By sensing their microenvironment, ILCs are essential in supporting gut epithelium repair and controling bacterial- and helminth-mediated intestinal infections, highlighting their important role in maintaining tissue integrity. Accumulating evidence also suggests that they may play an important role in carcinogenesis including intestinal cancers. In this review, we will explore the current knowledge about the pro- and anti-tumor functions of ILCs in colorectal cancer.

A comprehensive understanding of the gut mucosal immune system in allergic inflammation

Despite its direct exposure to huge amounts of microorganisms and foreign and dietary antigens, the gut mucosa maintains intestinal homeostasis by utilizing the mucosal immune system. The gut mucosal immune system protects the host from the invasion of infectious pathogens and eliminates harmful non-self antigens, but it allows the cohabitation of commensal bacteria in the gut and the entry of dietary non-self antigens into the body via the mucosal surface. These physiological and immunological activities are regulated by the ingenious gut mucosal immune network, comprising such features as gut-associated lymphoid tissue, mucosal immune cells, cytokines, chemokines, antimicrobial peptides, secretory IgA, and commensal bacteria. The gut mucosal immune network keeps a fine tuned balance between active immunity (against pathogens and harmful non-self antigens) and immune tolerance (to commensal microbiota and dietary antigens), thus maintaining intestinal healthy homeostasis. Disruption of gut homeostasis results in persistent or severe gastrointestinal infection, inflammatory bowel disease, or allergic inflammation. In this review, we comprehensively introduce current knowledge of the gut mucosal immune system, focusing on its interaction with allergic inflammation.

The TNF Family of Ligands and Receptors: Communication Modules in the Immune System and Beyond

The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies (TNFSF/TNFRSF) include 19 ligands and 29 receptors that play important roles in the modulation of cellular functions. The communication pathways mediated by TNFSF/TNFRSF are essential for numerous developmental, homeostatic, and stimulus-responsive processes in vivo. TNFSF/TNFRSF members regulate cellular differentiation, survival, and programmed death, but their most critical functions pertain to the immune system. Both innate and adaptive immune cells are controlled by TNFSF/TNFRSF members in a manner that is crucial for the coordination of various mechanisms driving either co-stimulation or co-inhibition of the immune response. Dysregulation of these same signaling pathways has been implicated in inflammatory and autoimmune diseases, highlighting the importance of their tight regulation. Investigation of the control of TNFSF/TNFRSF activities has led to the development of therapeutics with the potential to reduce chronic inflammation or promote anti-tumor immunity. The study of TNFSF/TNFRSF proteins has exploded over the last 30 yr, but there remains a need to better understand the fundamental mechanisms underlying the molecular pathways they mediate to design more effective anti-inflammatory and anti-cancer therapies.

Innate lymphoid cells in the upper airways: importance of CD117 and IL-1RI expression

Although type 1, 2 and 3 innate lymphoid cells (ILC1s, ILC2s and ILC3s, respectively) are emerging as important cell populations regulating tissue homeostasis, remodelling and inflammation, a vast majority of our knowledge stems from in vitro and murine experiments, and requires thorough confirmation in human diseases.Relative levels of ILCs were evaluated by means of flow cytometry in freshly resected human upper airways mucosa of patients with chronic rhinosinusitis without nasal polyps (CRSsNP) and with nasal polyps (CRSwNP), taking into account the patient's clinical parameters and disease comorbidities.We report that the CD117 and interleukin-receptor type I (IL-1RI) expression status of human ILC2s depends on the local tissue environment. Only CD117⁺ IL-1RI⁺ ILC2s, exclusively present in CRSwNP, possess an interrelationship with type 2 T-helper cell cytokine and eosinophil levels in human upper airway mucosa. In CRSsNP, mainly CD117^-IL-1RI^- ILC2s are increased, yielding lower eosinophilia in this disease despite the high levels of ILC2s.These data unveil that the CD117^- and CD117⁺ fractions within the native human ILC2 population are not a random phenomenon, in contrast to what could be concluded from in vitro data, and that the IL-1RI expression is not ubiquitous in ILC2s in vivo in humans, which cannot be assessed via in vitro and murine experiments.

Innate Lymphoid Cells (ILCs): Cytokine Hubs Regulating Immunity and Tissue Homeostasis

Innate lymphoid cells (ILCs) have emerged as an expanding family of effector cells particularly enriched in the mucosal barriers. ILCs are promptly activated by stress signals and multiple epithelial- and myeloid-cell-derived cytokines. In response, ILCs rapidly secrete effector cytokines, which allow them to survey and maintain the mucosal integrity. Uncontrolled action of ILCs might contribute to tissue damage, chronic inflammation, metabolic diseases, autoimmunity, and cancer. Here we discuss the recent advances in our understanding of the cytokine network that modulate ILC immune responses: stimulating cytokines, signature cytokines secreted by ILC subsets, autocrine cytokines, and cytokines that induce cell plasticity.

Innate Lymphoid Cells in the Maternal and Fetal Compartments

Pregnancy success is orchestrated by the complex balance between the maternal and fetal immune systems. Herein, we summarize the potential role of innate lymphoid cells (ILCs) in the maternal and fetal compartments. We reviewed published literature describing different ILC subsets [ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTi) cells] in the uterus, decidua, fetal tissues [liver, secondary lymphoid organs (SLO), intestine, and lung] and amniotic cavity. ILC1s, ILC2s, and ILC3s are present in the murine uterus prior to and during pregnancy but have only been detected in the non-pregnant endometrium in humans. Specifically, ILC2s reside in the murine uterus from mid-pregnancy to term, ILC1s increase throughout gestation, and ILC3s remain constant. Yet, LTi cells have only been detected in the non-pregnant murine uterus. In the human decidua, ILC1s, ILC3s, and LTi-like cells are more abundant during early gestation, whereas ILC2s increase at the end of pregnancy. Decidual ILC1s were also detected during mid-gestation in mice. Interestingly, functional decidual ILC2s and ILC3s increased in women who underwent spontaneous preterm labor, indicating the involvement of such cells in this pregnancy complication. Fetal ILCs exist in the liver, SLO, intestine, lung, and amniotic cavity. The fetal liver is thought to be the source of ILC progenitors since the differentiation of these cells from hematopoietic stem cells occurs at this site, and mature ILC subsets can be found in this compartment as well. The interaction between LTi cells and specialized stromal cells is important during the formation of SLO. Mature ILCs are found at the mucosal surfaces of the lung and intestine, from where they can extravasate into the amniotic cavity. Amniotic fluid ILCs express high levels of RORγt, CD161, and CD103, hallmarks of ILC3s. Such cells are more abundant in the second trimester than later in gestation. Although amniotic fluid ILC3s produce IL-17A and TNFα, indicating their functionality, their numbers in patients with intra-amniotic infection/inflammation remain unchanged compared to those without this pregnancy complication. Collectively, these findings suggest that maternal (uterine and decidual) ILCs play central roles in both the initiation and maintenance of pregnancy, and fetal ILCs participate in the development of immunity.

Multiple roles of lymphatic vessels in peripheral lymph node development

This work shows how blood and lymphatic vessels contribute to lymph node organogenesis. Both vessel types transport lymphoid tissue inducer cells, while lymphatics also generate interstitial flow, important for mechanical stromal activation and further lymph node expansion.

The mammalian lymphatic system consists of strategically located lymph nodes (LNs) embedded into a lymphatic vascular network. Mechanisms underlying development of this highly organized system are not fully understood. Using high-resolution imaging, we show that lymphoid tissue inducer (LTi) cells initially transmigrate from veins at LN development sites using gaps in venous mural coverage. This process is independent of lymphatic vasculature, but lymphatic vessels are indispensable for the transport of LTi cells that egress from blood capillaries elsewhere and serve as an essential LN expansion reservoir. At later stages, lymphatic collecting vessels ensure efficient LTi cell transport and formation of the LN capsule and subcapsular sinus. Perinodal lymphatics also promote local interstitial flow, which cooperates with lymphotoxin-β signaling to amplify stromal CXCL13 production and thereby promote LTi cell retention. Our data unify previous models of LN development by showing that lymphatics intervene at multiple points to assist LN expansion and identify a new role for mechanical forces in LN development.

An RORγt Oral Inhibitor Modulates IL-17 Responses in Peripheral Blood and Intestinal Mucosa of Crohn's Disease Patients

Background and Aims: Despite the negative results of blocking IL-17 in Crohn's disease (CD) patients, selective modulation of Th17-dependent responses warrants further study. Inhibition of retinoic acid-related orphan receptor gamma (RORγt), the master regulator of the Th17 signature, is currently being explored in inflammatory diseases. Our aim was to determine the effect of a novel oral RORγt antagonist (BI119) in human CD and on an experimental model of intestinal inflammation.

Methods: 51 CD patients and 11 healthy subjects were included. The effects of BI119 were tested on microbial-stimulated peripheral blood mononuclear cells (PBMCs), intestinal crypts and biopsies from CD patients. The ability of BI119 to prevent colitis in vivo was assessed in the CD4⁺CD45RB^high T cell transfer model.

Results: In bacterial antigen-stimulated PBMCs from CD patients, BI119 inhibits Th17-related genes and proteins, while upregulating Treg and preserving Th1 and Th2 signatures. Intestinal crypts cultured with supernatants from BI119-treated commensal-specific CD4⁺ T cells showed decreased expression of CXCL1, CXCL8 and CCL20. BI119 significantly reduced IL17 and IL26 transcription in colonic and ileal CD biopsies and did not affect IL22. BI119 has a more profound effect in ileal CD with additional significant downregulation of IL23R, CSF2, CXCL1, CXCL8, and S100A8, and upregulation of DEFA5. BI119 significantly prevented development of clinical, macroscopic and molecular markers of colitis in the T-cell transfer model.

Conclusions: BI119 modulated CD-relevant Th17 signatures, including downregulation of IL23R while preserving mucosa-associated IL-22 responses, and abrogated experimental colitis. Our results provide support to the use of RORγt antagonists as a novel therapy to CD treatment.

Interplay of innate lymphoid cells and the microbiota

Innate lymphoid cells (ILC) are a recently identified group of innate lymphocytes that are preferentially located at barrier surfaces. Barrier surfaces are in direct contact with complex microbial ecosystems, collectively referred to as the microbiota. It is now believed that the interplay of the microbiota with host components (i.e. epithelial cells and immune cells) promotes host fitness by regulating organ homeostasis, metabolism, and host defense against pathogens. In this review, we will give an overview of this multifaceted interplay between ILC and components of the microbiota.

Neutrophils instruct homeostatic and pathological states in naive tissues

Immune protection relies on the capacity of neutrophils to infiltrate challenged tissues. Naive tissues, in contrast, are believed to remain free of these cells and protected from their toxic cargo. Here, we show that neutrophils are endowed with the capacity to infiltrate multiple tissues in the steady-state, a process that follows tissue-specific dynamics. By focusing in two particular tissues, the intestine and the lungs, we find that neutrophils infiltrating the intestine are engulfed by resident macrophages, resulting in repression of Il23 transcription, reduced G-CSF in plasma, and reinforced activity of distant bone marrow niches. In contrast, diurnal accumulation of neutrophils within the pulmonary vasculature influenced circadian transcription in the lungs. Neutrophil-influenced transcripts in this organ were associated with carcinogenesis and migration. Consistently, we found that neutrophils dictated the diurnal patterns of lung invasion by melanoma cells. Homeostatic infiltration of tissues unveils a facet of neutrophil biology that supports organ function, but can also instigate pathological states.

NKR-P1B expression in gut-associated innate lymphoid cells is required for the control of gastrointestinal tract infections

Helper-type innate lymphoid cells (ILC) play an important role in intestinal homeostasis. Members of the NKR-P1 gene family are expressed in various innate immune cells, including natural killer (NK) cells, and their cognate Clr ligand family members are expressed in various specialized tissues, including the intestinal epithelium, where they may play an important role in mucosal-associated innate immune responses. In this study, we show that the inhibitory NKR-P1B receptor, but not the Ly49 receptor, is expressed in gut-resident NK cells, ILC, and a subset of γδT cells in a tissue-specific manner. ILC3 cells constitute the predominant cell subset expressing NKR-P1B in the gut lamina propria. The known NKR-P1B ligand Clr-b is broadly expressed in gut-associated cells of hematopoietic origin. The genetic deletion of NKR-P1B results in a higher frequency and number of ILC3 and γδT cells in the gut lamina propria. However, the function of gut-resident ILC3, NK, and γδT cells in NKR-P1B-deficient mice is impaired during gastrointestinal tract infection by Citrobacter rodentium or Salmonella typhimurium, resulting in increased systemic bacterial dissemination in NKR-P1B-deficient mice. Our findings highlight the role of the NKR-P1B:Clr-b recognition system in the modulation of intestinal innate immune cell functions.

Role of Vitamin A in the Immune System

Vitamin A (VitA) is a micronutrient that is crucial for maintaining vision, promoting growth and development, and protecting epithelium and mucus integrity in the body. VitA is known as an anti-inflammation vitamin because of its critical role in enhancing immune function. VitA is involved in the development of the immune system and plays regulatory roles in cellular immune responses and humoral immune processes. VitA has demonstrated a therapeutic effect in the treatment of various infectious diseases. To better understand the relationship between nutrition and the immune system, the authors review recent literature about VitA in immunity research and briefly introduce the clinical application of VitA in the treatment of several infectious diseases.