Transcriptional Atlas of Intestinal Immune Cells Reveals that Neuropeptide α-CGRP Modulates Group 2 Innate Lymphoid Cell Responses

NRP1 downregulation correlates with enhanced ILC2 responses during IL-33 challenge

Group 2 innate lymphoid cells (ILC2s) play critical roles in driving the pathogenesis of allergic airway inflammation. The mechanisms underlying the regulation of ILC2s remain to be fully understood. Here, we identified neuropilin-1 (NRP1) as a surface marker of ILC2s in response to IL-33 stimulation. NRP1 was abundantly expressed in ILC2s from lung under steady state, which was significantly reduced upon IL-33 stimulation. ILC2s with high expression of NRP1 (NRP1high) displayed lower response to IL-33, as compared with NRP1low ILC2s. Transcriptional profiling and flow cytometric analysis showed that downregulation of AKT-mTOR signalling participated in the diminished functionality of NRP1high ILC2s. These observations revealed a potential role of NRP1 in ILC2s responses under allergic inflammatory condition.

Dietary fiber is a critical determinant of pathologic ILC2 responses and intestinal inflammation

Innate lymphoid cells (ILCs) can promote host defense, chronic inflammation, or tissue protection and are regulated by cytokines and neuropeptides. However, their regulation by diet and microbiota-derived signals remains unclear. We show that an inulin fiber diet promotes Tph1-expressing inflammatory ILC2s (ILC2INFLAM) in the colon, which produce IL-5 but not tissue-protective amphiregulin (AREG), resulting in the accumulation of eosinophils. This exacerbates inflammation in a murine model of intestinal damage and inflammation in an ILC2- and eosinophil-dependent manner. Mechanistically, the inulin fiber diet elevated microbiota-derived bile acids, including cholic acid (CA) that induced expression of ILC2-activating IL-33. In IBD patients, bile acids, their receptor farnesoid X receptor (FXR), IL-33, and eosinophils were all upregulated compared with controls, implicating this diet-microbiota-ILC2 axis in human IBD pathogenesis. Together, these data reveal that dietary fiber-induced changes in microbial metabolites operate as a rheostat that governs protective versus pathologic ILC2 responses with relevance to precision nutrition for inflammatory diseases.

Epithelial-neuronal-immune cell interactions: Implications for immunity, inflammation, and tissue homeostasis at mucosal sites

The epithelial lining of the respiratory tract and intestine provides a critical physical barrier to protect host tissues against environmental insults, including dietary antigens, allergens, chemicals, and microorganisms. In addition, specialized epithelial cells communicate directly with hematopoietic and neuronal cells. These epithelial-immune and epithelial-neuronal interactions control host immune responses and have important implications for inflammatory conditions associated with defects in the epithelial barrier, including asthma, allergy, and inflammatory bowel diseases. In this review, we discuss emerging research that identifies the mechanisms and impact of epithelial-immune and epithelial-neuronal cross talk in regulating immunity, inflammation, and tissue homeostasis at mucosal barrier surfaces. Understanding the regulation and impact of these pathways could provide new therapeutic targets for inflammatory diseases at mucosal sites.

Modulation of host immunity by sensory neurons

Recent studies have uncovered a new role for sensory neurons in influencing mammalian host immunity, challenging conventional notions of the nervous and immune systems as separate entities. In this review we delve into this groundbreaking paradigm of neuroimmunology and discuss recent scientific evidence for the impact of sensory neurons on host responses against a wide range of pathogens and diseases, encompassing microbial infections and cancers. These valuable insights enhance our understanding of the interactions between the nervous and immune systems, and also pave the way for developing candidate innovative therapeutic interventions in immune-mediated diseases highlighting the importance of this interdisciplinary research field.

RAG suppresses group 2 innate lymphoid cells

Antigen specificity is the central trait distinguishing adaptive from innate immune function. Assembly of antigen-specific T cell and B cell receptors occurs through V(D)J recombination mediated by the Recombinase Activating Gene endonucleases RAG1 and RAG2 (collectively called RAG). In the absence of RAG, mature T and B cells do not develop and thus RAG is critically associated with adaptive immune function. In addition to adaptive T helper 2 (Th2) cells, group 2 innate lymphoid cells (ILC2s) contribute to type 2 immune responses by producing cytokines like Interleukin-5 (IL-5) and IL-13. Although it has been reported that RAG expression modulates the function of innate natural killer (NK) cells, whether other innate immune cells such as ILC2s are affected by RAG remains unclear. We find that in RAG-deficient mice, ILC2 populations expand and produce increased IL-5 and IL-13 at steady state and contribute to increased inflammation in atopic dermatitis (AD)-like disease. Further, we show that RAG modulates ILC2 function in a cell-intrinsic manner independent of the absence or presence of adaptive T and B lymphocytes. Lastly, employing multiomic single cell analyses of RAG1 lineage-traced cells, we identify key transcriptional and epigenomic ILC2 functional programs that are suppressed by a history of RAG expression. Collectively, our data reveal a novel role for RAG in modulating innate type 2 immunity through suppression of ILC2s.

An esophagus cell atlas reveals dynamic rewiring during active eosinophilic esophagitis and remission

Coordinated cell interactions within the esophagus maintain homeostasis, and disruption can lead to eosinophilic esophagitis (EoE), a chronic inflammatory disease with poorly understood pathogenesis. We profile 421,312 individual cells from the esophageal mucosa of 7 healthy and 15 EoE participants, revealing 60 cell subsets and functional alterations in cell states, compositions, and interactions that highlight previously unclear features of EoE. Active disease displays enrichment of ALOX15+ macrophages, PRDM16+ dendritic cells expressing the EoE risk gene ATP10A, and cycling mast cells, with concomitant reduction of TH17 cells. Ligand-receptor expression uncovers eosinophil recruitment programs, increased fibroblast interactions in disease, and IL-9+IL-4+IL-13+ TH2 and endothelial cells as potential mast cell interactors. Resolution of inflammation-associated signatures includes mast and CD4+ TRM cell contraction and cell type-specific downregulation of eosinophil chemoattractant, growth, and survival factors. These cellular alterations in EoE and remission advance our understanding of eosinophilic inflammation and opportunities for therapeutic intervention.

Sensory neurons: An integrated component of innate immunity

The sensory nervous system possesses the ability to integrate exogenous threats and endogenous signals to mediate downstream effector functions. Sensory neurons have been shown to activate or suppress host defense and immunity against pathogens, depending on the tissue and disease state. Through this lens, pro- and anti-inflammatory neuroimmune effector functions can be interpreted as evolutionary adaptations by host or pathogen. Here, we discuss recent and impactful examples of neuroimmune circuitry that regulate tissue homeostasis, autoinflammation, and host defense. Apparently paradoxical or conflicting reports in the literature also highlight the complexity of neuroimmune interactions that may depend on tissue- and microbe-specific cues. These findings expand our understanding of the nuanced mechanisms and the greater context of sensory neurons in innate immunity.

Cooperation of ILC2s and TH2 cells in the expulsion of intestinal helminth parasites

Type 2 immune responses form a critical defence against enteric worm infections. In recent years, mouse models have revealed shared and unique functions for group 2 innate lymphoid cells and T helper 2 cells in type 2 immune response to intestinal helminths. Both cell types use similar innate effector functions at the site of infection, whereas each population has distinct roles during different stages of infection. In this Perspective, we review the underlying mechanisms used by group 2 innate lymphoid cells and T helper 2 cells to cooperate with each other and suggest an overarching model of the interplay between these cell types over the course of a helminth infection.

Navigating the blurred path of mixed neuroimmune signaling

Evolution has created complex mechanisms to sense environmental danger and protect tissues, with the nervous and immune systems playing pivotal roles. These systems work together, coordinating local and systemic reflexes to restore homeostasis in response to tissue injury and infection. By sharing receptors and ligands, they influence the pathogenesis of various diseases. Recently, a less-explored aspect of neuroimmune communication has emerged: the release of neuropeptides from immune cells and cytokines/chemokines from sensory neurons. This article reviews evidence of this unique neuroimmune interplay and its impact on the development of allergy, inflammation, itch, and pain. We highlight the effects of this neuroimmune signaling on vital processes such as host defense, tissue repair, and inflammation resolution, providing avenues for exploration of the underlying mechanisms and therapeutic potential of this signaling.

Functional Diversity of Memory CD8 T Cells is Spatiotemporally Imprinted

Tissue-resident memory CD8 T cells (TRM) kill infected cells and recruit additional immune cells to limit pathogen invasion at barrier sites. Small intestinal (SI) TRM cells consist of distinct subpopulations with higher expression of effector molecules or greater memory potential. We hypothesized that occupancy of diverse anatomical niches imprints these distinct TRM transcriptional programs. We leveraged human samples and a murine model of acute systemic viral infection to profile the location and transcriptome of pathogen-specific TRM cell differentiation at single-transcript resolution. We developed computational approaches to capture cellular locations along three anatomical axes of the small intestine and to visualize the spatiotemporal distribution of cell types and gene expression. TRM populations were spatially segregated: with more effector- and memory-like TRM preferentially localized at the villus tip or crypt, respectively. Modeling ligand-receptor activity revealed patterns of key cellular interactions and cytokine signaling pathways that initiate and maintain TRM differentiation and functional diversity, including different TGFβ sources. Alterations in the cellular networks induced by loss of TGFβRII expression revealed a model consistent with TGFβ promoting progressive TRM maturation towards the villus tip. Ultimately, we have developed a framework for the study of immune cell interactions with the spectrum of tissue cell types, revealing that T cell location and functional state are fundamentally intertwined.

From orphan to oncogene: The role of GPR35 in cancer and immune modulation

G protein-coupled receptors (GPCRs) are well-studied and the most traceable cell surface receptors for drug discovery. One of the intriguing members of this family is G protein-coupled receptors 35 (GPR35), which belongs to the class A rhodopsin-like family of GPCRs identified over two decades ago. GPR35 presents interesting features such as ubiquitous expression and distinct isoforms. Moreover, functional and genome-wide association studies on its widespread expression have linked GPR35 with pathophysiological disease progression. Various pieces of evidence have been accumulated regarding the independent or endogenous ligand-dependent role of GPR35 in cancer progression and metastasis. In the current scenario, the relationship of this versatile receptor and its putative endogenous ligands for the activation of oncogenic signal transduction pathways at the cellular level is an active area of research. These intriguing features offered by GPR35 make it an oncological target, justifying its uniqueness at the physiological and pathophysiological levels concerning other GPCRs. For pharmacologically targeting receptor-induced signaling, few potential competitive antagonists have been discovered that offer high selectivity at a human level. In addition to its fascinating features, targeting GPR35 at rodent and human orthologue levels is distinct, thus contributing to the sub-species selectivity. Strategies to modulate these issues will help us understand and truly target GPR35 at the therapeutic level. In this article, we have provided prospects on each topic mentioned above and suggestions to overcome the challenges. This review discusses the molecular mechanism and signal transduction pathways activated by endogenous ligands or spontaneous auto-activation of GPR35 that contributes towards disease progression. Furthermore, we have highlighted the GPR35 structure, ubiquitous expression, its role in immunomodulation, and at the pathophysiological level, especially in cancer, indicating its status as a versatile receptor. Subsequently, we discussed the various proposed ligands and their mechanism of interaction with GPR35. Additionally, we have summarized the GPR35 antagonist that provides insights into the opportunities for therapeutically targeting this receptor.

Vagal sensory pathway for the gut-brain communication

The communication between the gut and brain is crucial for regulating various essential physiological functions, such as energy balance, fluid homeostasis, immune response, and emotion. The vagal sensory pathway plays an indispensable role in connecting the gut to the brain. Recently, our knowledge of the vagal gut-brain axis has significantly advanced through molecular genetic studies, revealing a diverse range of vagal sensory cell types with distinct peripheral innervations, response profiles, and physiological functions. Here, we review the current understanding of how vagal sensory neurons contribute to gut-brain communication. First, we highlight recent transcriptomic and genetic approaches that have characterized different vagal sensory cell types. Then, we focus on discussing how different subtypes encode numerous gut-derived signals and how their activities are translated into physiological and behavioral regulations. The emerging insights into the diverse cell types and functional properties of vagal sensory neurons have paved the way for exciting future directions, which may provide valuable insights into potential therapeutic targets for disorders involving gut-brain communication.

Neuropeptide Calcitonin Gene-Related Peptide Promotes Immune Homeostasis of Bacterial Meningitis by Inducing Major Histocompatibility Complex Class II Ubiquitination

BACKGROUND

Calcitonin gene-related peptide (CGRP), an immunomodulatory neuropeptide, is important for regulating pain transmission, vasodilation, and the inflammatory response. However, the molecular mechanisms of the CGRP-mediated immune response remain unknown.

METHODS

The effects of CGRP on bacterial meningitis (BM) and its underlying mechanisms were investigated in BM mice in vivo and macrophages in vitro.

RESULTS

Peripheral injection of CGRP attenuated cytokine storms and protected mice from fatal pneumococcal meningitis, marked by increased bacterial clearance, improved neuroethology, and reduced mortality. When the underlying mechanisms were investigated, we found that CGRP induces proteasome-dependent degradation of major histocompatibility complex class II (MHC-II) in macrophages and then inhibits CD4+ T-cell activation. MARCH1 was identified as an E3 ligase that can be induced by CGRP engagement and promote K48-linked ubiquitination and degradation of MHC-II in macrophages. These results provide new insights into neuropeptide CGRP-mediated immune regulation mechanisms.

CONCLUSIONS

We conclude that targeting the nervous system and manipulating neuroimmune communication is a promising strategy for treating intracranial infections like BM.

The neuroimmune CGRP-RAMP1 axis tunes cutaneous adaptive immunity to the microbiota

The somatosensory nervous system surveils external stimuli at barrier tissues, regulating innate immune cells under infection and inflammation. The roles of sensory neurons in controlling the adaptive immune system, and more specifically immunity to the microbiota, however, remain elusive. Here, we identified a mechanism for direct neuroimmune communication between commensal-specific T lymphocytes and somatosensory neurons mediated by the neuropeptide calcitonin gene-related peptide (CGRP) in the skin. Intravital imaging revealed that commensal-specific T cells are in close proximity to cutaneous nerve fibers in vivo. Correspondingly, we observed upregulation of the receptor for the neuropeptide CGRP, RAMP1, in CD8+ T lymphocytes induced by skin commensal colonization. The neuroimmune CGRP-RAMP1 signaling axis functions in commensal-specific T cells to constrain Type 17 responses and moderate the activation status of microbiota-reactive lymphocytes at homeostasis. As such, modulation of neuroimmune CGRP-RAMP1 signaling in commensal-specific T cells shapes the overall activation status of the skin epithelium, thereby impacting the outcome of responses to insults such as wounding. The ability of somatosensory neurons to control adaptive immunity to the microbiota via the CGRP-RAMP1 axis underscores the various layers of regulation and multisystem coordination required for optimal microbiota-reactive T cell functions under steady state and pathology.

Mast cells help organize the Peyer's patch niche for induction of IgA responses

Peyer's patches (PPs) are lymphoid structures situated adjacent to the intestinal epithelium that support B cell responses that give rise to many intestinal IgA-secreting cells. Induction of isotype switching to IgA in PPs requires interactions between B cells and TGFβ-activating conventional dendritic cells type 2 (cDC2s) in the subepithelial dome (SED). However, the mechanisms promoting cDC2 positioning in the SED are unclear. Here, we found that PP cDC2s express GPR35, a receptor that promotes cell migration in response to various metabolites, including 5-hydroxyindoleacetic acid (5-HIAA). In mice lacking GPR35, fewer cDC2s were found in the SED, and frequencies of IgA+ germinal center (GC) B cells were reduced. IgA plasma cells were reduced in both the PPs and lamina propria. These phenotypes were also observed in chimeric mice that lacked GPR35 selectively in cDCs. GPR35 deficiency led to reduced coating of commensal bacteria with IgA and reduced IgA responses to cholera toxin. Mast cells were present in the SED, and mast cell-deficient mice had reduced PP cDC2s and IgA+ cells. Ablation of tryptophan hydroxylase 1 (Tph1) in mast cells to prevent their production of 5-HIAA similarly led to reduced PP cDC2s and IgA responses. Thus, mast cell-guided positioning of GPR35+ cDC2s in the PP SED supports induction of intestinal IgA responses.

Analysis of brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving peripheral leukocytes and brain resident cells that contribute to both tissue injury and repair. However, their dynamics and diversity remain poorly understood. To address these limitations, we performed a single-cell transcriptomic study of brain and blood cells 2 or 14 days after ischemic stroke in mice. We observed a strong divergence of post-ischemic microglia, monocyte-derived macrophages and neutrophils over time, while endothelial cells and brain-associated macrophages showed altered transcriptomic signatures at 2 days poststroke. Trajectory inference predicted the in situ trans-differentiation of macrophages from blood monocytes into day 2 and day 14 phenotypes, while neutrophils were projected to be continuously de novo recruited from the blood. Brain single-cell transcriptomes from both female and male aged mice were similar to that of young male mice, but aged and young brains differed in their immune cell composition. Although blood leukocyte analysis also revealed altered transcriptomes after stroke, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification occurs within the brain in the early and recovery phases of ischemic stroke. A portal ( https://anratherlab.shinyapps.io/strokevis/ ) is provided to allow user-friendly access to our data.

The crosstalk between enteric nervous system and immune system in intestinal development, homeostasis and diseases

The gut is the largest digestive and absorptive organ, which is essential for induction of mucosal and systemic immune responses, and maintenance of metabolic-immune homeostasis. The intestinal components contain the epithelium, stromal cells, immune cells, and enteric nervous system (ENS), as well as the outers, such as gut microbiota, metabolites, and nutrients. The dyshomeostasis of intestinal microenvironment induces abnormal intestinal development and functions, even colon diseases including dysplasia, inflammation and tumor. Several recent studies have identified that ENS plays a crucial role in maintaining the immune homeostasis of gastrointestinal (GI) microenvironment. The crosstalk between ENS and immune cells, mainly macrophages, T cells, and innate lymphoid cells (ILCs), has been found to exert important regulatory roles in intestinal tissue programming, homeostasis, function, and inflammation. In this review, we mainly summarize the critical roles of the interactions between ENS and immune cells in intestinal homeostasis during intestinal development and diseases progression, to provide theoretical bases and ideas for the exploration of immunotherapy for gastrointestinal diseases with the ENS as potential novel targets.

The neuroimmune CGRP-RAMP1 axis tunes cutaneous adaptive immunity to the microbiota

The somatosensory nervous system surveils external stimuli at barrier tissues, regulating innate immune cells under infection and inflammation. The roles of sensory neurons in controlling the adaptive immune system, and more specifically immunity to the microbiota, however, remain elusive. Here, we identified a novel mechanism for direct neuroimmune communication between commensal-specific T lymphocytes and somatosensory neurons mediated by the neuropeptide Calcitonin Gene-Related Peptide (CGRP) in the skin. Intravital imaging revealed that commensal-specific T cells are in close proximity to cutaneous nerve fibers in vivo . Correspondingly, we observed upregulation of the receptor for the neuropeptide CGRP, RAMP1, in CD8 + T lymphocytes induced by skin commensal colonization. Neuroimmune CGRP-RAMP1 signaling axis functions in commensal-specific T cells to constrain Type 17 responses and moderate the activation status of microbiota-reactive lymphocytes at homeostasis. As such, modulation of neuroimmune CGRP-RAMP1 signaling in commensal-specific T cells shapes the overall activation status of the skin epithelium, thereby impacting the outcome of responses to insults such as wounding. The ability of somatosensory neurons to control adaptive immunity to the microbiota via the CGRP-RAMP1 axis underscores the various layers of regulation and multisystem coordination required for optimal microbiota-reactive T cell functions under steady state and pathology.

Significance statement

Multisystem coordination at barrier surfaces is critical for optimal tissue functions and integrity, in response to microbial and environmental cues. In this study, we identified a novel neuroimmune crosstalk mechanism between the sensory nervous system and the adaptive immune response to the microbiota, mediated by the neuropeptide CGRP and its receptor RAMP1 on skin microbiota-induced T lymphocytes. The neuroimmune CGPR-RAMP1 axis constrains adaptive immunity to the microbiota and overall limits the activation status of the skin epithelium, impacting tissue responses to wounding. Our study opens the door to a new avenue to modulate adaptive immunity to the microbiota utilizing neuromodulators, allowing for a more integrative and tailored approach to harnessing microbiota-induced T cells to promote barrier tissue protection and repair.

GPR35 acts a dual role and therapeutic target in inflammation

GPR35 is a G protein-coupled receptor with notable involvement in modulating inflammatory responses. Although the precise role of GPR35 in inflammation is not yet fully understood, studies have suggested that it may have both pro- and anti-inflammatory effects depending on the specific cellular environment. Some studies have shown that GPR35 activation can stimulate the production of pro-inflammatory cytokines and facilitate the movement of immune cells towards inflammatory tissues or infected areas. Conversely, other investigations have suggested that GPR35 may possess anti-inflammatory properties in the gastrointestinal tract, liver and certain other tissues by curbing the generation of inflammatory mediators and endorsing the differentiation of regulatory T cells. The intricate role of GPR35 in inflammation underscores the requirement for more in-depth research to thoroughly comprehend its functional mechanisms and its potential significance as a therapeutic target for inflammatory diseases. The purpose of this review is to concurrently investigate the pro-inflammatory and anti-inflammatory roles of GPR35, thus illuminating both facets of this complex issue.

Retinoid X receptor gamma dictates the activation threshold of group 2 innate lymphoid cells and limits type 2 inflammation in the small intestine

Group 2 innate lymphoid cells (ILC2s) are crucial in promoting type 2 inflammation that contributes to both anti-parasite immunity and allergic diseases. However, the molecular checkpoints in ILC2s that determine whether to immediately launch a proinflammatory response are unknown. Here, we found that retinoid X receptor gamma (Rxrg) was highly expressed in small intestinal ILC2s and rapidly suppressed by alarmin cytokines. Genetic deletion of Rxrg did not impact ILC2 development but facilitated ILC2 responses and the tissue inflammation induced by alarmins. Mechanistically, RXRγ maintained the expression of its target genes that support intracellular cholesterol efflux, which in turn reduce ILC2 proliferation. Furthermore, RXRγ expression prevented ILC2 response to mild stimulations, including low doses of alarmin cytokine and mechanical skin injury. Together, we propose that RXRγ expression and its mediated lipid metabolic states function as a cell-intrinsic checkpoint that confers the threshold of ILC2 activation in the small intestine.

Enteric neuro-immune interactions in intestinal health and disease

The enteric nervous system is an autonomous neuronal circuit that regulates many processes far beyond the peristalsis in the gastro-intestinal tract. This circuit, consisting of enteric neurons and enteric glial cells, can engage in many intercellular interactions shaping the homeostatic microenvironment in the gut. Perhaps the most well documented interactions taking place, are the intestinal neuro-immune interactions which are essential for the fine-tuning of oral tolerance. In the context of intestinal disease, compelling evidence demonstrates both protective and detrimental roles for this bidirectional neuro-immune signaling. This review discusses the different immune cell types that are recognized to engage in neuronal crosstalk during intestinal health and disease. Highlighting the molecular pathways involved in the neuro-immune interactions might inspire novel strategies to target intestinal disease.

Both Horatio and Polonius: Innate Lymphoid Cells in Tissue Homeostasis and Repair

Innate lymphoid cells (ILCs) have emerged as critical tissue-resident lymphocytes that coordinate responses to environmental stress and injury. Traditionally, their function was thought to mirror adaptive lymphocytes that respond to specific pathogens. However, recent work has uncovered a more central role for ILCs in maintaining homeostasis even in the absence of infection. ILCs are now better conceptualized as an environmental rheostat that helps maintain the local tissue setpoint during environmental challenge by integrating sensory stimuli to direct homeostatic barrier and repair programs. In this article, we trace the developmental origins of ILCs, relate how ILCs sense danger signals, and describe their subsequent engagement of appropriate repair responses using a general paradigm of ILCs functioning as central controllers in tissue circuits. We propose that these interactions form the basis for how ILC subsets maintain organ function and organismal homeostasis, with important implications for human health.

Understanding food allergy through neuroimmune interactions in the gastrointestinal tract

Food allergies are adverse immune reactions to food proteins in the absence of oral tolerance, and the incidence of allergies to food, including peanut, cow's milk, and shellfish, has been increasing globally. Although advancements have been made toward understanding the contributions of the type 2 immune response to allergic sensitization, crosstalk between these immune cells and neurons of the enteric nervous system is an area of emerging interest in the pathophysiology of food allergy, given the close proximity of neuronal cells of the enteric nervous system and type 2 effector cells, including eosinophils and mast cells. At mucosal sites, such as the gastrointestinal tract, neuroimmune interactions contribute to the sensing and response to danger signals from the epithelial barrier. This communication is bidirectional, as immune cells express receptors for neuropeptides and transmitters, and neurons express cytokine receptors, allowing for the detection of and response to inflammatory insults. In addition, it seems that neuromodulation of immune cells including mast cells, eosinophils, and innate lymphoid cells is critical for amplification of the type 2 allergic immune response. As such, neuroimmune interactions may be critical targets for future food allergy therapies. This review evaluates the contributions of local enteric neuroimmune interactions to the underlying immune response in food allergy and discusses considerations for future investigations into targeting neuroimmune pathways for treatment of food allergies.

The role of cellular and molecular neuroimmune crosstalk in gut immunity

The gastrointestinal tract is densely innervated by the peripheral nervous system and populated by the immune system. These two systems critically coordinate the sensations of and adaptations to dietary, microbial, and damaging stimuli from the external and internal microenvironment during tissue homeostasis and inflammation. The brain receives and integrates ascending sensory signals from the gut and transduces descending signals back to the gut via autonomic neurons. Neurons regulate intestinal immune responses through the action of local axon reflexes or through neuronal circuits via the gut-brain axis. This neuroimmune crosstalk is critical for gut homeostatic maintenance and disease resolution. In this review, we discuss the roles of distinct types of gut-innervating neurons in the modulation of intestinal mucosal immunity. We will focus on the molecular mechanisms governing how different immune cells respond to neural signals in host defense and inflammation. We also discuss the therapeutic potential of strategies targeting neuroimmune crosstalk for intestinal diseases.

Regulatory T cells in the face of the intestinal microbiota

Regulatory T cells (Treg cells) are key players in ensuring a peaceful coexistence with microorganisms and food antigens at intestinal borders. Startling new information has appeared in recent years on their diversity, the importance of the transcription factor FOXP3, how T cell receptors influence their fate and the unexpected and varied cellular partners that influence Treg cell homeostatic setpoints. We also revisit some tenets, maintained by the echo chambers of Reviews, that rest on uncertain foundations or are a subject of debate.

GoM DE: interpreting structure in sequence count data with differential expression analysis allowing for grades of membership

Parts-based representations, such as non-negative matrix factorization and topic modeling, have been used to identify structure from single-cell sequencing data sets, in particular structure that is not as well captured by clustering or other dimensionality reduction methods. However, interpreting the individual parts remains a challenge. To address this challenge, we extend methods for differential expression analysis by allowing cells to have partial membership to multiple groups. We call this grade of membership differential expression (GoM DE). We illustrate the benefits of GoM DE for annotating topics identified in several single-cell RNA-seq and ATAC-seq data sets.

Neuroanatomy of lymphoid organs: Lessons learned from whole-tissue imaging studies

Decades of extensive research have documented the presence of neural innervations of sensory, sympathetic, or parasympathetic origin in primary and secondary lymphoid organs. Such neural inputs can release neurotransmitters and neuropeptides to directly modulate the functions of various immune cells, which represents one of the essential aspects of the body's neuroimmune network. Notably, recent studies empowered by state-of-the-art imaging techniques have comprehensively assessed neural distribution patterns in BM, thymus, spleen, and LNs of rodents and humans, helping clarify several controversies lingering in the field. In addition, it has become evident that neural innervations in lymphoid organs are not static but undergo alterations in pathophysiological contexts. This review aims to update the current information on the neuroanatomy of lymphoid organs obtained through whole-tissue 3D imaging and genetic approaches, focusing on anatomical features that may designate the functional modulation of immune responses. Moreover, we discuss several critical questions that call for future research, which will advance our in-depth understanding of the importance and complexity of neural control of lymphoid organs.

An underlying mechanism behind interventional pulmonology techniques for refractory asthma treatment: Neuro-immunity crosstalk

Asthma is a common disease that seriously threatens public health. With significant developments in bronchoscopy, different interventional pulmonology techniques for refractory asthma treatment have been developed. These technologies achieve therapeutic purposes by targeting diverse aspects of asthma pathophysiology. However, even though these newer techniques have shown appreciable clinical effects, their differences in mechanisms and mutual commonalities still deserve to be carefully explored. Therefore, in this review, we summarized the potential mechanisms of bronchial thermoplasty, targeted lung denervation, and cryoablation, and analyzed the relationship between these different methods. Based on available evidence, we speculated that the main pathway of chronic airway inflammation and other pathophysiologic processes in asthma is sensory nerve-related neurotransmitter release that forms a "neuro-immunity crosstalk" and amplifies airway neurogenic inflammation. The mechanism of completely blocking neuro-immunity crosstalk through dual-ablation of both efferent and afferent fibers may have a leading role in the clinical efficacy of interventional pulmonology in the treatment of asthma and deserves further investigation.

Gut microbiota regulate migration of lymphocytes from gut to lung

The community of microorganisms known as gut microbiota that lives in the intestine confers significant health benefits on its host, primarily in the form of immunological homeostasis regulation. Gut microbiota not only can shape immune responses in the gut but also in other organs. This review focus on the gut-lung axis. Aberrant gut microbiota development is associated with greater lung disease susceptibility and respiratory disease induced by a variety of pathogenic bacteria. They are known to cause changes in gut microbiota. Recent research has found that immune cells in the intestine migrate to distant lung to exert anti-infective effects. Moreover, evidence indicates that the gut microbiota and their metabolites influence intestinal immune cells. Therefore, we suspect that intestine-derived immune cells may play a significant role against pulmonary pathogenic infections by receiving instructions from gut microbiota.

Central regulation of stress-evoked peripheral immune responses

Stress-linked psychiatric disorders, including anxiety and major depressive disorder, are associated with systemic inflammation. Recent studies have reported stress-induced alterations in haematopoiesis that result in monocytosis, neutrophilia, lymphocytopenia and, consequently, in the upregulation of pro-inflammatory processes in immunologically relevant peripheral tissues. There is now evidence that this peripheral inflammation contributes to the development of psychiatric symptoms as well as to common co-morbidities of psychiatric disorders such as metabolic syndrome and immunosuppression. Here, we review the specific brain and spinal regions, and the neuronal populations within them, that respond to stress and transmit signals to peripheral tissues via the autonomic nervous system or neuroendocrine pathways to influence immunological function. We comprehensively summarize studies that have employed retrograde tracing to define neurocircuits linking the brain to the bone marrow, spleen, gut, adipose tissue and liver. Moreover, we highlight studies that have used chemogenetic or optogenetic manipulation or intracerebroventricular administration of peptide hormones to control somatic immune responses. Collectively, this growing body of literature illustrates potential mechanisms through which stress signals are conveyed from the CNS to immune cells to regulate stress-relevant behaviours and comorbid pathophysiology.

Dynamic single-cell regulomes characterize human peripheral blood innate lymphoid cell subpopulations

Innate lymphoid cells (ILCs) are plastic immune cells divided into 3 main subsets, characterized by distinct phenotypic and functional profiles. Using single cell approaches, heightened heterogeneity of mouse ILCs has been appreciated, imprinted by tissue signals that shape their transcriptome and epigenome. Intra-subset diversity has also been observed in human ILCs. However, combined transcriptomic and epigenetic analyses of single ILCs in humans are lacking. Here, we show high transcriptional and epigenetic heterogeneity among human circulating ILCs in healthy individuals. We describe phenotypically distinct subclusters and diverse chromatin accessibility within main ILC populations, compatible with differentially poised states. We validate the use of this healthy donor-based analysis as resource dataset to help inferring ILC changes occurring in disease conditions. Overall, our work provides insights in the complex human ILC biology. We anticipate it to facilitate hypothesis-driven studies in patients, without the need to perform single cell OMICs using precious patients' material.

GoM DE: interpreting structure in sequence count data with differential expression analysis allowing for grades of membership

Parts-based representations, such as non-negative matrix factorization and topic modeling, have been used to identify structure from single-cell sequencing data sets, in particular structure that is not as well captured by clustering or other dimensionality reduction methods. However, interpreting the individual parts remains a challenge. To address this challenge, we extend methods for differential expression analysis by allowing cells to have partial membership to multiple groups. We call this grade of membership differential expression (GoM DE). We illustrate the benefits of GoM DE for annotating topics identified in several single-cell RNA-seq and ATAC-seq data sets.

Solar ultraviolet B radiation promotes α-MSH secretion to attenuate the function of ILC2s via the pituitary-lung axis

The immunomodulatory effects of ultraviolet B (UVB) radiation in human diseases have been described. Whether type 2 lung inflammation is directly affected by solar ultraviolet (UV) radiation is not fully understood. Here, we show a possible negative correlation between solar UVB radiation and asthmatic inflammation in humans and mice. UVB exposure to the eyes induces hypothalamus-pituitary activation and α-melanocyte-stimulating hormone (α-MSH) accumulation in the serum to suppress allergic airway inflammation by targeting group 2 innate lymphoid cells (ILC2) through the MC5R receptor in mice. The α-MSH/MC5R interaction limits ILC2 function through attenuation of JAK/STAT and NF-κB signaling. Consistently, we observe that the plasma α-MSH concentration is negatively correlated with the number and function of ILC2s in the peripheral blood mononuclear cells (PBMC) of patients with asthma. We provide insights into how solar UVB radiation-driven neuroendocrine α-MSH restricts ILC2-mediated lung inflammation and offer a possible strategy for controlling allergic diseases.

Calcitonin Gene-Related peptide receptor antagonist suppresses allergic asthma responses via downregulation of group 2 innate lymphoid cells in mice

Allergic asthma is caused by chronic inflammation and hyper-responsiveness of the airway and is thought to be mediated by adaptive T helper type 2 (Th2)-driven immunity. However, recent studies have demonstrated that neuropeptide calcitonin gene-related peptide (CGRP)-mediated activation of group 2 innate lymphoid cells (ILC2s) may contribute to the development of asthma pathogenesis. Here, we investigated the therapeutic effects of the systemic administration of rimegepant, a CGRP receptor antagonist, on allergic asthma. Hyperplasia of CGRP-immunoreactive pulmonary neuroendocrine cells (PNECs) was observed in ovalbumin (OVA)-induced asthmatic mice. Concomitant with this, we observed an increase in the content of total lung CGRP. Upon antigen challenge, the concentration of plasma CGRP was transiently upregulated, whereas CGRP immunoreactivity within PNECs was intensively downregulated, suggesting that PNECs were the most likely source of CGRP. When rimegepant was administered according to CGRP kinetics, it suppressed asthma phenotypes, including airway hyper-responsiveness, infiltration of inflammatory cells in bronchoalveolar lavage fluid (BALF), hyperplasia of mucus-producing cells, and production of the Th2 cytokine IL-5. Moreover, we observed a decrease in the number of ILC2s and their capacity for IL-5 release in the presence of IL-33 in rimegepant-treated mice. In the allergic asthma model, rimegepant suppressed the activation of ILC2s mediated by PNEC-derived CGRP and subsequently impaired adaptive Th2-driven immunity, which ameliorated asthmatic phenotypes. Thus, an anti-CGRP signal strategy to target ILC2 will be a novel and attractive approach for treating allergic asthma that is refractory to other treatments.

Microbiota-mediated shaping of mouse spleen structure and immune function characterized by scRNA-seq and Stereo-seq

Gut microbes exhibit complex interactions with their hosts and shape an organism's immune system throughout its lifespan. As the largest secondary lymphoid organ, the spleen has a wide range of immunological functions. To explore the role of microbiota in regulating and shaping the spleen, we employ scRNA-seq and Stereo-seq technologies based on germ-free (GF) mice to detect differences in tissue size, anatomical structure, cell types, functions, and spatial molecular characteristics. We identify 18 cell types, 9 subtypes of T cells, and 7 subtypes of B cells. Gene differential expression analysis reveals that the absence of microorganisms results in alterations in erythropoiesis within the red pulp region and congenital immune deficiency in the white pulp region. Stereo-seq results demonstrate a clear hierarchy of immune cells in the spleen, including marginal zone (MZ) macrophages, MZ B cells, follicular B cells and T cells, distributed in a well-defined pattern from outside to inside. However, this hierarchical structure is disturbed in GF mice. Ccr7 and Cxcl13 chemokines are specifically expressed in the spatial locations of T cells and B cells, respectively. We speculate that the microbiota may mediate the structural composition or partitioning of spleen immune cells by modulating the expression levels of chemokines.

Guardians of the gut: influence of the enteric nervous system on the intestinal epithelial barrier

The intestinal mucosal surface forms one of the largest areas of the body, which is in direct contact with the environment. Co-ordinated sensory functions of immune, epithelial, and neuronal cells ensure the timely detection of noxious queues and potential pathogens and elicit proportional responses to mitigate the threats and maintain homeostasis. Such tuning and maintenance of the epithelial barrier is constantly ongoing during homeostasis and its derangement can become a gateway for systemic consequences. Although efforts in understanding the gatekeeping functions of immune cells have led the way, increasing number of studies point to a crucial role of the enteric nervous system in fine-tuning and maintaining this delicate homeostasis. The identification of immune regulatory functions of enteric neuropeptides and glial-derived factors is still in its infancy, but has already yielded several intriguing insights into their important contribution to the tight control of the mucosal barrier. In this review, we will first introduce the reader to the current understanding of the architecture of the enteric nervous system and the epithelial barrier. Next, we discuss the key discoveries and cellular pathways and mediators that have emerged as links between the enteric nervous, immune, and epithelial systems and how their coordinated actions defend against intestinal infectious and inflammatory diseases. Through this review, the readers will gain a sound understanding of the current neuro-immune-epithelial mechanisms ensuring intestinal barrier integrity and maintenance of intestinal homeostasis.

Expanded ILC2s in human infant intestines promote tissue growth

Early life is characterized by extraordinary challenges, including rapid tissue growth and immune adaptation to foreign antigens after birth. During this developmental stage, infants have an increased risk of immune-mediated diseases. Here, we demonstrate that tissue-resident, interleukin (IL)-13- and IL-4-producing group 2 innate lymphoid cells (ILC2s) are enriched in human infant intestines compared to adult intestines. Organoid systems were employed to assess the role of infant intestinal ILC2s in intestinal development and showed that IL-13 and IL-4 increased epithelial cell proliferation and skewed cell differentiation toward secretory cells. IL-13 furthermore upregulated the production of mediators of type-2 immunity by infant intestinal epithelial cells, including vascular endothelial growth factor-A and IL-26, a chemoattractant for eosinophils. In line with these in vitro findings increased numbers of eosinophils were detected in vivo in infant intestines. Taken together, ILC2s are enriched in infant intestines and can support intestinal development while inducing an epithelial secretory response associated with type 2 immune-mediated diseases.

Immune sensing of food allergens promotes avoidance behaviour

In addition to its canonical function of protection from pathogens, the immune system can also alter behaviour1,2. The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Here, using mouse models of food allergy, we show that allergic sensitization drives antigen-specific avoidance behaviour. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus and central amygdala. Allergen avoidance requires immunoglobulin E (IgE) antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote avoidance requires cysteinyl leukotrienes and growth and differentiation factor 15. Finally, a comparison of C57BL/6 and BALB/c mouse strains revealed a strong effect of the genetic background on the avoidance behaviour. These findings thus point to antigen-specific behavioural modifications that probably evolved to promote niche selection to avoid unfavourable environments.

Exposure of iPSC-derived human microglia to brain substrates enables the generation and manipulation of diverse transcriptional states in vitro

Microglia, the macrophages of the brain parenchyma, are key players in neurodegenerative diseases such as Alzheimer's disease. These cells adopt distinct transcriptional subtypes known as states. Understanding state function, especially in human microglia, has been elusive owing to a lack of tools to model and manipulate these cells. Here, we developed a platform for modeling human microglia transcriptional states in vitro. We found that exposure of human stem-cell-differentiated microglia to synaptosomes, myelin debris, apoptotic neurons or synthetic amyloid-beta fibrils generated transcriptional diversity that mapped to gene signatures identified in human brain microglia, including disease-associated microglia, a state enriched in neurodegenerative diseases. Using a new lentiviral approach, we demonstrated that the transcription factor MITF drives a disease-associated transcriptional signature and a highly phagocytic state. Together, these tools enable the manipulation and functional interrogation of human microglial states in both homeostatic and disease-relevant contexts.

Alcohol-mediated susceptibility to lung fibrosis is associated with group 2 innate lymphoid cells in mice

Chronic alcohol ingestion promotes acute lung injury and impairs immune function. However, the mechanisms involved are incompletely understood. Here, we show that alcohol feeding enhances bleomycin-induced lung fibrosis and inflammation via the regulation of type 2 innate immune responses, especially by group 2 innate lymphoid cells (ILC2s). Neuroimmune interactions have emerged as critical modulators of lung inflammation. We found alcohol consumption induced the accumulation of ILC2 and reduced the production of the neuropeptide calcitonin gene-related peptide (CGRP), primarily released from sensory nerves and pulmonary neuroendocrine cells (PNECs). CGRP potently suppressed alcohol-driven type 2 cytokine signals in vivo. Vagal ganglia TRPV1+ afferents mediated immunosuppression occurs through the release of CGRP. Inactivation of the TRPV1 receptor enhanced bleomycin-induced fibrosis. In addition, mice lacking the CGRP receptor had the increased lung inflammation and fibrosis and type 2 cytokine production as well as exaggerated responses to alcohol feeding. Together, these data indicate that alcohol consumption regulates the interaction of CGRP and ILC2, which is a critical contributor of lung inflammation and fibrosis.

Brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving both peripheral leukocytes and brain resident cells. Recent evidence indicates that their differentiation into a variety of functional phenotypes contributes to both tissue injury and repair. However, the temporal dynamics and diversity of post-stroke immune cell subsets remain poorly understood. To address these limitations, we performed a longitudinal single-cell transcriptomic study of both brain and mouse blood to obtain a composite picture of brain-infiltrating leukocytes, circulating leukocytes, microglia and endothelium diversity over the ischemic/reperfusion time. Brain cells and blood leukocytes isolated from mice 2 or 14 days after transient middle cerebral artery occlusion or sham surgery were purified by FACS sorting and processed for droplet-based single-cell transcriptomics. The analysis revealed a strong divergence of post-ischemic microglia, macrophages, and neutrophils over time, while such diversity was less evident in dendritic cells, B, T and NK cells. Conversely, brain endothelial cells and brain associated-macrophages showed altered transcriptomic signatures at 2 days post-stroke, but low divergence from sham at day 14. Pseudotime trajectory inference predicted the in-situ longitudinal progression of monocyte-derived macrophages from their blood precursors into day 2 and day 14 phenotypes, while microglia phenotypes at these two time points were not connected. In contrast to monocyte-derived macrophages, neutrophils were predicted to be continuously de-novo recruited from the blood. Brain single-cell transcriptomics from both female and male aged mice did not show major changes in respect to young mice, but aged and young brains differed in their immune cell composition. Furthermore, blood leukocyte analysis also revealed altered transcriptomes after stroke. However, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification into cellular subsets occurs within the brain in the early and the recovery phase of ischemic stroke. In addition, this resource report contains a searchable database https://anratherlab.shinyapps.io/strokevis/ to allow user-friendly access to our data. The StrokeVis tool constitutes a comprehensive gene expression atlas that can be interrogated at the gene and cell type level to explore the transcriptional changes of endothelial and immune cell subsets from mouse brain and blood after stroke.

HTR2A agonists play a therapeutic role by restricting ILC2 activation in papain-induced lung inflammation

Group 2 innate lymphoid cells (ILC2s) are a category of heterogeneous cells that produce the cytokines IL-5 and IL-13, which mediate the type 2 immune response. However, specific drug targets on lung ILC2s have rarely been reported. Previous studies have shown that type 2 cytokines, such as IL-5 and IL-13, are related to depression. Here, we demonstrated the negative correlation between the depression-associated monoamine neurotransmitter serotonin and secretion of the cytokines IL-5 and IL-13 by ILC2s in individuals with depression. Interestingly, serotonin ameliorates papain-induced lung inflammation by suppressing ILC2 activation. Our data showed that the serotonin receptor HTR2A was highly expressed on ILC2s from mouse lungs and human PBMCs. Furthermore, an HTR2A selective agonist (DOI) impaired ILC2 activation and alleviated the type 2 immune response in vivo and in vitro. Mice with ILC2-specific depletion of HTR2A (Il5cre/+·Htr2aflox/flox mice) abolished the DOI-mediated inhibition of ILC2s in a papain-induced mouse model of inflammation. In conclusion, serotonin and DOI could restrict the type 2 lung immune response, indicating a potential treatment strategy for type 2 lung inflammation by targeting HTR2A on ST2+ ILC2s.

Group 2 innate lymphoid cells and their surrounding environment

Since the discovery of group 2 innate lymphoid cells (ILC2s) in 2010, subsequent studies have revealed their developmental pathways, mechanisms of activation and regulation, and immunological roles in tissue homeostasis and tissue-specific diseases in various organs. Although ILC2s are known to express tissue-specific features depending on where they reside, how the surrounding environment affects the functions of ILC2s remains to be fully elucidated. Recent histologic analyses revealed that ILC2s resides in specific perivascular regions in peripheral tissues with their function being controlled by the surrounding cells via cytokines, lipid mediators, neurotransmitters, and cell-cell interactions through surface molecules. This review summarizes the interactions between ILC2s and surrounding cells, including epithelial cells, neurons, immune cells, and mesenchymal cells, with the objective of promoting the development of novel diagnostic and therapeutic methods for ILC2-related diseases.

Network Approaches to Uncover Pathogenesis and Therapeutic Targets of Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) are currently recognized to involve chronic intestinal inflammation in genetically susceptible individuals. Patients with IBD mainly develop gastrointestinal inflammation, but it is sometimes accompanied by extraintestinal manifestations such as arthritis, erythema nodosum, episcleritis, pyoderma gangrenosum, uveitis, and primary sclerosing cholangitis. These clinical aspects imply the importance of interorgan networks in IBD. In the gastrointestinal tract, immune cells are influenced by multiple local environmental factors including microbiota, dietary environment, and intercellular networks, which further alter molecular networks in immune cells. Therefore, deciphering networks at interorgan, intercellular, and intracellular levels should help to obtain a comprehensive understanding of IBD. This review focuses on the intestinal immune system, which governs the physiological and pathological functions of the digestive system in harmony with the other organs.

The neuropeptide CGRP enters the macrophage cytosol to suppress the NLRP3 inflammasome during pulmonary infection

The NLRP3 inflammasome plays an essential role in resistance to bacterial infection. The nervous system secretes multiple neuropeptides affecting the nervous system as well as immune cells. The precise impact of the neuropeptide CGRP on NLRP3 inflammasome activation is still unclear. Here, we show that CGRP negatively regulates the antibacterial process of host cells. CGRP prevents NLRP3 inflammasome activation and reduces mature IL-1β secretion. Following NLRP3 inflammasome stimulation that triggers endosome leakage, CGRP internalized to endosomal compartments is released into the cell cytosol. Cytosolic CGRP binds directly to NLRP3 and dismantles the NLRP3-NEK7 complex, which is crucial for NLRP3 inflammasome activation. CGRP administration exacerbates bacterial infection, while the treatment with a CGRP antagonist has the opposite effect. Our study uncovers a unique role of CGRP in inhibiting inflammasome activation during infections, which might shed new light on antibacterial therapies in the future.

Neuromedin U Induces Pulmonary ILC2 Activation via the NMUR1 Pathway during Acute Respiratory Syncytial Virus Infection

Activated group 2 innate lymphoid cells (ILC2s) play a crucial role in respiratory syncytial virus (RSV)-induced airway inflammation and allergy-like symptoms because of their ability to secrete large quantities of type 2 cytokines. Cytokines such as IL-33, IL-25, and thymic stromal lymphopoietin are activators of ILC2s. Besides, a regulatory effect of neurotransmitters on ILC2 activation has been reported recently. However, whether and how RSV infection induces neurotransmitter production in the lungs and regulates pulmonary ILC2 activation remains unclear. In this study, using a murine model established by intranasal infection with RSV, we found that acute RSV infection induced the production of a neurotransmitter, neuromedin U (NMU), in the lungs of RSV-infected mice and upregulated the expression of NMUR1 (neuromedin U receptor 1) on ILC2s. Moreover, in vivo administration of NMU exacerbated RSV-induced airway inflammation by promoting the proliferation and activation of pulmonary ILC2s via the NMUR1 pathway, which involved PI3K, mitogen-activated protein kinase kinase, and NFAT signaling proteins. Furthermore, pulmonary neurons responded to the stimulation of RSV infection and secreted NMU in a Toll-like receptor 4- and Toll-like receptor 7-dependent manner. Collectively, our data suggest that NMU is a powerful neuropeptide to activate ILC2s, highlighting the critical regulatory effects of neurotransmitters on antiviral, inflammatory, and tissue homeostasis at the mucosal barrier during a viral respiratory infection.

Metabolic regulation by prostaglandin E2 impairs lung group 2 innate lymphoid cell responses

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) play a critical role in asthma pathogenesis. Non-steroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (NERD) is associated with reduced signaling via EP2, a receptor for prostaglandin E2 (PGE2 ). However, the respective roles for the PGE2 receptors EP2 and EP4 (both share same downstream signaling) in the regulation of lung ILC2 responses has yet been deciphered.

METHODS

The roles of PGE2 receptors EP2 and EP4 on ILC2-mediated lung inflammation were investigated using genetically modified mouse lines and pharmacological approaches in IL-33-induced lung allergy model. The effects of PGE2 receptors and downstream signals on ILC2 metabolic activation and effector function were examined using in vitro cell cultures.

RESULTS

Deficiency of EP2 rather than EP4 augments IL-33-induced mouse lung ILC2 responses and eosinophilic inflammation in vivo. In contrast, exogenous agonism of EP4 and EP2 or inhibition of phosphodiesterase markedly restricts IL-33-induced lung ILC2 responses. Mechanistically, PGE2 directly suppresses IL-33-dependent ILC2 activation through the EP2/EP4-cAMP pathway, which downregulates STAT5 and MYC pathway gene expression and ILC2 energy metabolism. Blocking glycolysis diminishes IL-33-dependent ILC2 responses in mice where endogenous PG synthesis or EP2 signaling is blocked but not in mice with intact PGE2 -EP2 signaling.

CONCLUSION

We have defined a mechanism for optimal suppression of mouse lung ILC2 responses by endogenous PGE2 -EP2 signaling which underpins the clinical findings of defective EP2 signaling in patients with NERD. Our findings also indicate that exogenously targeting the PGE2 -EP4-cAMP and energy metabolic pathways may provide novel opportunities for treating the ILC2-initiated lung inflammation in asthma and NERD.

Metagenomic and single-cell RNA-Seq survey of the Helicobacter pylori-infected stomach in asymptomatic individuals

Helicobacter pylori colonization of the gastric niche can persist for years in asymptomatic individuals. To deeply characterize the host-microbiota environment in H. pylori-infected (HPI) stomachs, we collected human gastric tissues and performed metagenomic sequencing, single-cell RNA-Seq (scRNA-Seq), flow cytometry, and fluorescent microscopy. HPI asymptomatic individuals had dramatic changes in the composition of gastric microbiome and immune cells compared with noninfected individuals. Metagenomic analysis uncovered pathway alterations related to metabolism and immune response. scRNA-Seq and flow cytometry data revealed that, in contrast to murine stomachs, ILC2s are virtually absent in the human gastric mucosa, whereas ILC3s are the dominant population. Specifically, proportion of NKp44+ ILC3s out of total ILCs were highly increased in the gastric mucosa of asymptomatic HPI individuals, and correlated with the abundance of selected microbial taxa. In addition, CD11c+ myeloid cells and activated CD4+ T cells and B cells were expanded in HPI individuals. B cells of HPI individuals acquired an activated phenotype and progressed into a highly proliferating germinal-center stage and plasmablast maturation, which correlated with the presence of tertiary lymphoid structures within the gastric lamina propria. Our study provides a comprehensive atlas of the gastric mucosa-associated microbiome and immune cell landscape when comparing asymptomatic HPI and uninfected individuals.

Dopamine inhibits group 2 innate lymphoid cell-driven allergic lung inflammation by dampening mitochondrial activity

Neuronal signals have emerged as pivotal regulators of group 2 innate lymphoid cells (ILC2s) that regulate tissue homeostasis and allergic inflammation. The molecular pathways underlying the neuronal regulation of ILC2 responses in lungs remain to be fully elucidated. Here, we found that the abundance of neurotransmitter dopamine was negatively correlated with circulating ILC2 numbers and positively associated with pulmonary function in humans. Dopamine potently suppressed lung ILC2 responses in a DRD1-receptor-dependent manner. Genetic deletion of Drd1 or local ablation of dopaminergic neurons augmented ILC2 responses and allergic lung inflammation. Transcriptome and metabolic analyses revealed that dopamine impaired the mitochondrial oxidative phosphorylation (OXPHOS) pathway in ILC2s. Augmentation of OXPHOS activity with oltipraz antagonized the inhibitory effect of dopamine. Local administration of dopamine alleviated allergen-induced ILC2 responses and airway inflammation. These findings demonstrate that dopamine represents an inhibitory regulator of ILC2 responses in allergic airway inflammation.