Small intestinal resident eosinophils maintain gut homeostasis following microbial colonization

TGF-β signaling promotes eosinophil activation in inflammatory responses

Eosinophils, traditionally associated with allergic phenomena, play a pivotal role in inflammatory responses. Despite accumulating evidence suggesting their pro-inflammatory function upon activation, the underlying mechanisms governing eosinophil activation remain incompletely characterized. In this study, we investigate the local activation of pulmonary and colon eosinophils within the inflammatory microenvironment. Leveraging transcriptional sequencing, we identify TGF-β as a putative regulator of eosinophil activation, leading to the secretion of granule proteins, including peroxidase. Genetic deletion of TGF-β receptors on eosinophils resulted in the inhibition of peroxidase synthesis, affirming the significance of TGF-β signaling in eosinophil activation. Using models of HDM-induced asthma and DSS-induced colitis, we demonstrate the indispensability of TGF-β-driven eosinophil activation in both disease contexts. Notably, while TGF-β signaling did not significantly influence asthmatic inflammation, its knockout conferred protection against experimental colitis. This study delineates a distinct pattern of eosinophil activation within inflammatory responses, highlighting the pivotal role of TGF-β signaling in regulating eosinophil behavior. These findings deepen our comprehension of eosinophil-related pathophysiology and may pave the way for targeted therapeutic approaches in allergic and inflammatory diseases.

Stromal cell and B cell dialogue potentiates IL-33-enriched lymphoid niches to support eosinophil recruitment and function during type 2 immunity

Eosinophils are involved in host protection against multicellular organisms. However, their recruitment to the mesenteric lymph node (mLN) during type 2 immunity is understudied. Our results demonstrate that eosinophil association with lymphoid stromal niches constructed by fibroblastic reticular cells (FRCs) and lymphatic endothelial cells is diminished in mice selectively lacking interleukin (IL)-4Rα or lymphotoxin-β (LTβ) expression on B cells. Furthermore, eosinophil survival, activation, and enhanced Il1rl1 receptor expression are driven by stromal cell and B cell dialogue. The ligation of lymphotoxin-β receptor (LTβR) on FRCs improves eosinophil survival and significantly augments IL-33 expression and eosinophil homing to the mLN, thus confirming the significance of lymphotoxin signaling for granulocyte recruitment. Eosinophil-deficient ΔdblGATA-1 mice show diminished mLN expansion, reduced interfollicular region (IFR) alarmin expression, and delayed helminth clearance, elucidating their importance in type 2 immunity. These findings provide insight into dialogue between stromal cells and B cells, which govern mLN eosinophilia, and the relevance of these mechanisms during type 2 immunity.

Helminth infection driven gastrointestinal hypermotility is independent of eosinophils and mediated by alterations in smooth muscle instead of enteric neurons

Intestinal helminth infection triggers a type 2 immune response that promotes a 'weep-and sweep' response characterised by increased mucus secretion and intestinal hypermotility, which function to dislodge the worm from its intestinal habitat. Recent studies have discovered that several other pathogens cause intestinal dysmotility through major alterations to the immune and enteric nervous systems (ENS), and their interactions, within the gastrointestinal tract. However, the involvement of these systems has not been investigated for helminth infections. Eosinophils represent a key cell type recruited by the type 2 immune response and alter intestinal motility under steady-state conditions. Our study aimed to investigate whether altered intestinal motility driven by the murine hookworm, Nippostrongylus brasiliensis, infection involves eosinophils and how the ENS and smooth muscles of the gut are impacted. Eosinophil deficiency did not influence helminth-induced intestinal hypermotility and hypermotility did not involve gross structural or functional changes to the ENS. Hypermotility was instead associated with a dramatic increase in smooth muscle thickness and contractility, an observation that extended to another rodent nematode, Heligmosomoides polygyrus. In summary our data indicate that, in contrast to other pathogens, helminth-induced intestinal hypermotility is driven by largely by myogenic, rather than neurogenic, alterations with such changes occurring independently of eosinophils. (<300 words).

The AHR repressor limits expression of antimicrobial genes but not AHR-dependent genes in intestinal eosinophils

Intestinal eosinophils express the aryl hydrocarbon receptor (AHR), an environmental sensor and ligand-activated transcription factor that responds to dietary or environmental ligands. AHR regulates tissue adaptation, survival, adhesion, and immune functions in intestinal eosinophils. The AHR repressor (AHRR) is itself induced by AHR and believed to limit AHR activity in a negative feedback loop. We analyzed gene expression in intestinal eosinophils from wild-type and AHRR knockout mice and found that AHRR did not suppress most AHR-dependent genes. Instead, AHRR limited the expression of a distinct small set of genes involved in the innate immune response. These included S100 proteins, antimicrobial proteins, and alpha-defensins. Using bone marrow-derived eosinophils, we found that AHRR knockout eosinophils released more reactive oxygen species upon stimulation. This work shows that the paradigm of AHRR as a repressor of AHR transcriptional activity does not apply to intestinal eosinophils. Rather, AHRR limits the expression of innate immune response and antimicrobial genes, possibly to maintain an anti-inflammatory phenotype in eosinophils when exposed to microbial signals in the intestinal environment.

Eosinophil expression of triggering receptor expressed on myeloid cells 1 (TREM-1) restricts type 2 lung inflammation

Asthma affects 25 million Americans, and recent advances in treatment are effective for only a portion of severe asthma patients. TREM-1, an innate receptor that canonically amplifies inflammatory signaling in neutrophils and monocytes, plays a central role in regulating lung inflammation. It is unknown how TREM-1 contributes to allergic asthma pathology. Utilizing a murine model of asthma, flow cytometry revealed TREM-1+ eosinophils in the lung tissue and airway during allergic airway inflammation. TREM-1 expression was restricted to recruited, inflammatory eosinophils. Expression was induced on bone marrow-derived eosinophils by incubation with interleukin 33, lipopolysaccharide, or granulocyte-macrophage colony-stimulating factor. Compared to TREM-1- airway eosinophils, TREM-1+ eosinophils were enriched for proinflammatory gene sets, including migration, respiratory burst, and cytokine production. Unexpectedly, eosinophil-specific ablation of TREM-1 exacerbated airway interleukin (IL) 5 production, airway MUC5AC production, and lung tissue eosinophil accumulation. Further investigation of transcriptional data revealed apoptosis and superoxide generation-related gene sets were enriched in TREM-1+ eosinophils. Consistent with these findings, annexin V and caspase-3/7 staining demonstrated higher rates of apoptosis among TREM-1+ eosinophils compared to TREM-1- eosinophils in the inflammatory airway. In vitro, Trem1/3-/- bone marrow-derived eosinophils consumed less oxygen than wild-type in response to phorbol myristate acetate, suggesting that TREM-1 promotes superoxide generation in eosinophils. These data reveal protein-level expression of TREM-1 by eosinophils, define a population of TREM-1+ inflammatory eosinophils, and demonstrate that eosinophil TREM-1 restricts key features of type 2 lung inflammation.

Eosinophils, Eosinophilic Gastrointestinal Diseases, and Inflammatory Bowel Disease: A Critical Review

BACKGROUND/OBJECTIVES

Inflammatory bowel disease (IBD) and eosinophilic gastrointestinal diseases (EGIDs) are complex, multifactorial chronic inflammatory disorders affecting the gastrointestinal tract. Their epidemiology, particularly for eosinophilic esophagitis (EoE), is increasing worldwide, with a rise in the co-diagnosis of IBD and EGIDs. Both disorders share common risk factors, such as early exposure to antibiotics or specific dietary habits. Moreover, from a molecular perspective, eosinophilic infiltration is crucial in the diagnosis of eosinophilic disorders, and it also plays a pivotal role in IBD histological diagnosis. Indeed, recent evidence highlights the significant role of eosinophils in the health of the intestinal mucosal barrier and as mediators between innate and acquired immunity, even indicating a potential role in IBD pathogenesis. This narrative review aims to summarize the current evidence regarding the common clinical and molecular aspects of EGIDs and IBD and the current state of knowledge regarding overlap conditions and their pathogenesis.

METHODS

Pubmed was searched until May 2023 to assess relevant studies describing the epidemiology, pathophysiology, and therapy of EGIDs in IBD.

RESULTS

The immune pathways and mechanisms underlying both EGIDs and IBD remain partially known. An improved understanding of the role of eosinophils in overlapping conditions could lead to enhanced diagnostic precision, the development of more effective future therapeutic strategies, and a more accurate prediction of patient response. Consequently, the identification of red flags indicative of an eosinophilic disorder in IBD patients is of paramount importance and must be evaluated on a case-by-case basis.

Single-cell proteomics and transcriptomics capture eosinophil development and identify the role of IL-5 in their lineage transit amplification

The activities, ontogeny, and mechanisms of lineage expansion of eosinophils are less well resolved than those of other immune cells, despite the use of biological therapies targeting the eosinophilia-promoting cytokine interleukin (IL)-5 or its receptor, IL-5Rα. We combined single-cell proteomics and transcriptomics and generated transgenic IL-5Rα reporter mice to revisit eosinophilopoiesis. We reconciled human and murine eosinophilopoiesis and provided extensive cell-surface immunophenotyping and transcriptomes at different stages along the continuum of eosinophil maturation. We used these resources to show that IL-5 promoted eosinophil-lineage expansion via transit amplification, while its deletion or neutralization did not compromise eosinophil maturation. Informed from our resources, we also showed that interferon response factor-8, considered an essential promoter of myelopoiesis, was not intrinsically required for eosinophilopoiesis. This work hence provides resources, methods, and insights for understanding eosinophil ontogeny, the effects of current precision therapeutics, and the regulation of eosinophil development and numbers in health and disease.

Spatial adaptation of eosinophils and their emerging roles in homeostasis, infection and disease

Eosinophils are bone marrow-derived granulocytes that are traditionally associated with type 2 immune responses, such as those that occur during parasite infections and allergy. Emerging evidence demonstrates the remarkable functional plasticity of this elusive cell type and its pleiotropic functions in diverse settings. Eosinophils broadly contribute to tissue homeostasis, host defence and immune regulation, predominantly at mucosal sites. The scope of their activities primarily reflects the breadth of their portfolio of secreted mediators, which range from cytotoxic cationic proteins and reactive oxygen species to multiple cytokines, chemokines and lipid mediators. Here, we comprehensively review basic eosinophil biology that is directly related to their activities in homeostasis, protective immunity, regeneration and cancer. We examine how dysregulation of these functions contributes to the physiopathology of a broad range of inflammatory diseases. Furthermore, we discuss recent findings regarding the tissue compartmentalization and adaptation of eosinophils, shedding light on the factors that likely drive their functional diversification within tissues.

Helminth infection induces a distinct subset of CD101hi lung tissue-infiltrating eosinophils that are differentially regulated by type 2 cytokines

Eosinophils play divergent roles in health and disease, contributing to both immunoregulatory and proinflammatory responses. Helminth infection is strongly associated with eosinophilia and the induction of the type 2 cytokines interleukin (IL)-5, IL-4 and IL-13. This study aimed to elucidate the heterogeneity of pulmonary eosinophils in response to helminth infection and the roles of IL-5, IL-4 and IL-13 in driving pulmonary eosinophil responses. Using the murine helminth model Nippostrongylus brasiliensis (Nb), we characterize a subtype of eosinophils, defined by high expression of CD101, that is induced in the lungs of Nb-infected mice and are phenotypically distinct from lung eosinophils that express low levels of CD101. Strikingly, we show that the two eosinophil subtypes have distinct anatomical localization within the lung: CD101low eosinophils are predominantly localized in the lung vasculature, whereas Nb-induced CD101hi eosinophils are predominantly localized in the extravascular lung niche. We show that CD101hi eosinophils are also induced across other models of pulmonary infection and inflammation, including a nonlung-migrating helminth infection, house dust mite-induced allergic inflammation and influenza infection. Furthermore, we demonstrate that the induction of CD101hi tissue eosinophils is independent of IL-5 and IL-4 signaling, but is dependent on intact IL-13 signaling. These results suggest that IL-13 produced during helminth infection and other disease states promotes a pulmonary tissue-infiltrating program in eosinophils defined by high expression of CD101.

Activated eosinophils in early life impair lung development and promote long-term lung damage

Exaggeration of type 2 immune responses promotes lung inflammation and altered lung development; however, eosinophils, despite expansion in the postnatal lung, have not been specifically assessed in the context of neonatal lung disease. Furthermore, early life factors including prematurity and respiratory infection predispose infants to chronic obstructive pulmonary disease later in life. To assess eosinophils in the developing lung and how they may contribute to chronic lung disease, we generated mice harboring eosinophil-specific deletion of the negative regulatory enzyme SH2 domain-containing inositol 5' phosphatase-1. This increased the activity and number of pulmonary eosinophils in the developing lung, which was associated with impaired lung development, expansion of activated alveolar macrophages (AMφ), multinucleated giant cell formation, enlargement of airspaces, and fibrosis. Despite regression of eosinophils following completion of lung development, AMφ-dominated inflammation persisted, alongside lung damage. Bone marrow chimera studies showed that SH2 domain-containing inositol 5' phosphatase-1-deficient eosinophils were not sufficient to drive inflammatory lung disease in adult steady-state mice but once inflammation and damage were present, it could not be resolved. Depletion of eosinophils during alveolarization alleviated pulmonary inflammation and lung pathology, demonstrating an eosinophil-intrinsic effect. These results show that the presence of activated eosinophils during alveolarization aggravates AMφs and promotes sustained inflammation and long-lasting lung pathology.

Birthmode and environment-dependent microbiota transmission dynamics are complemented by breastfeeding during the first year

The composition and maturation of the early-life microbiota are modulated by a number of perinatal factors, whose interplay in relation to microbial vertical transmission remains inadequately elucidated. Using recent strain-tracking methodologies, we analyzed mother-to-infant microbiota transmission in two different birth environments: hospital-born (vaginal/cesarean) and home-born (vaginal) infants and their mothers. While delivery mode primarily explains initial compositional differences, place of birth impacts transmission timing-being early in homebirths and delayed in cesarean deliveries. Transmission patterns vary greatly across species and birth groups, yet certain species, like Bifidobacterium longum, are consistently vertically transmitted regardless of delivery setting. Strain-level analysis of B. longum highlights relevant and consistent subspecies replacement patterns mainly explained by breastfeeding practices, which drive changes in human milk oligosaccharide (HMO) degrading capabilities. Our findings highlight how delivery setting, breastfeeding duration, and other lifestyle preferences collectively shape vertical transmission, impacting infant gut colonization during early life.

Neuroimmunophysiology of the gastrointestinal tract

Gut physiology is the epicenter of a web of internal communication systems (i.e., neural, immune, hormonal) mediated by cell-cell contacts, soluble factors, and external influences, such as the microbiome, diet, and the physical environment. Together these provide the signals that shape enteric homeostasis and, when they go awry, lead to disease. Faced with the seemingly paradoxical tasks of nutrient uptake (digestion) and retarding pathogen invasion (host defense), the gut integrates interactions between a variety of cells and signaling molecules to keep the host nourished and protected from pathogens. When the system fails, the outcome can be acute or chronic disease, often labeled as "idiopathic" in nature (e.g., irritable bowel syndrome, inflammatory bowel disease). Here we underscore the importance of a holistic approach to gut physiology, placing an emphasis on intercellular connectedness, using enteric neuroimmunophysiology as the paradigm. The goal of this opinion piece is to acknowledge the pace of change brought to our field via single-cell and -omic methodologies and other techniques such as cell lineage tracing, transgenic animal models, methods for culturing patient tissue, and advanced imaging. We identify gaps in the field and hope to inspire and challenge colleagues to take up the mantle and advance awareness of the subtleties, intricacies, and nuances of intestinal physiology in health and disease by defining communication pathways between gut resident cells, those recruited from the circulation, and "external" influences such as the central nervous system and the gut microbiota.

Critical role of the gut microbiota in immune responses and cancer immunotherapy

The gut microbiota plays a critical role in the progression of human diseases, especially cancer. In recent decades, there has been accumulating evidence of the connections between the gut microbiota and cancer immunotherapy. Therefore, understanding the functional role of the gut microbiota in regulating immune responses to cancer immunotherapy is crucial for developing precision medicine. In this review, we extract insights from state-of-the-art research to decipher the complicated crosstalk among the gut microbiota, the systemic immune system, and immunotherapy in the context of cancer. Additionally, as the gut microbiota can account for immune-related adverse events, we discuss potential interventions to minimize these adverse effects and discuss the clinical application of five microbiota-targeted strategies that precisely increase the efficacy of cancer immunotherapy. Finally, as the gut microbiota holds promising potential as a target for precision cancer immunotherapeutics, we summarize current challenges and provide a general outlook on future directions in this field.

Eosinophil Specialization Is Regulated by Exposure to the Esophageal Epithelial Microenvironment

Distinct subsets of eosinophils are reported in inflammatory and healthy tissues, yet the functions of uniquely specialized eosinophils and the signals that elicit them, particularly in eosinophilic esophagitis (EoE), are not well understood. Herein, we report an ex-vivo system wherein freshly isolated human eosinophils were cocultured with esophageal epithelial cells and disease-relevant pro-inflammatory (IL-13) or pro-fibrotic (TGF-β) cytokines. Compared with untreated cocultures, IL-13 increased expression of CD69 on eosinophils, whereas TGF-β increased expression of CD81, CD62L, and CD25. Eosinophils from IL-13-treated cocultures demonstrated increased secretion of GRO-α, IL-8, and M-CSF and also generated increased extracellular peroxidase activity following activation. Eosinophils from TGF-β-treated cocultures secreted increased IL-6 and exhibited increased chemotactic response to CCL11 compared with eosinophils from untreated or IL-13-treated coculture conditions. When eosinophils from TGF-β-treated cocultures were cultured with fibroblasts, they upregulated SERPINE1 expression and fibronectin secretion by fibroblasts compared with eosinophils that were cultured with GM-CSF, alone. Translational studies revealed that CD62L was heterogeneously expressed by eosinophils in patient biopsies. Our results demonstrate that disease-relevant pro-inflammatory and pro-fibrotic signals present in the esophagus of EoE patients cause distinct profiles of eosinophil activation and gene expression.

Nonlinear DNA methylation trajectories in aging male mice

Although DNA methylation data yields highly accurate age predictors, little is known about the dynamics of this quintessential epigenomic biomarker during lifespan. To narrow the gap, we investigate the methylation trajectories of male mouse colon at five different time points of aging. Our study indicates the existence of sudden hypermethylation events at specific stages of life. Precisely, we identify two epigenomic switches during early-to-midlife (3-9 months) and mid-to-late-life (15-24 months) transitions, separating the rodents' life into three stages. These nonlinear methylation dynamics predominantly affect genes associated with the nervous system and enrich in bivalently marked chromatin regions. Based on groups of nonlinearly modified loci, we construct a clock-like classifier STageR (STage of aging estimatoR) that accurately predicts murine epigenetic stage. We demonstrate the universality of our clock in an independent mouse cohort and with publicly available datasets.

Epithelial regulation of microbiota-immune cell dynamics

The mammalian gastrointestinal tract hosts a diverse community of trillions of microorganisms, collectively termed the microbiota, which play a fundamental role in regulating tissue physiology and immunity. Recent studies have sought to dissect the cellular and molecular mechanisms mediating communication between the microbiota and host immune system. Epithelial cells line the intestine and form an initial barrier separating the microbiota from underlying immune cells, and disruption of epithelial function has been associated with various conditions ranging from infection to inflammatory bowel diseases and cancer. From several studies, it is now clear that epithelial cells integrate signals from commensal microbes. Importantly, these non-hematopoietic cells also direct regulatory mechanisms that instruct the recruitment and function of microbiota-sensitive immune cells. In this review, we discuss the central role that has emerged for epithelial cells in orchestrating intestinal immunity and highlight epithelial pathways through which the microbiota can calibrate tissue-intrinsic immune responses.

Role reversals: non-canonical roles for immune and non-immune cells in the gut

The intestine is home to an intertwined network of epithelial, immune, and neuronal cells as well as the microbiome, with implications for immunity, systemic metabolism, and behavior. While the complexity of this microenvironment has long since been acknowledged, recent technological advances have propelled our understanding to an unprecedented level. Notably, the microbiota and non-immune or structural cells have emerged as important conductors of intestinal immunity, and by contrast, cells of both the innate and adaptive immune systems have demonstrated non-canonical roles in tissue repair and metabolism. This review highlights recent works in the following two streams: non-immune cells of the intestine performing immunological functions; and traditional immune cells exhibiting non-immune functions in the gut.

Nutrient-derived signals regulate eosinophil adaptation to the small intestine

Eosinophils are well recognized as effector cells of type 2 immunity, yet they also accumulate in many tissues under homeostatic conditions. However, the processes that govern homeostatic eosinophil accumulation and tissue-specific adaptation, and their functional significance, remain poorly defined. Here, we investigated how eosinophils adapt to the small intestine (SI) microenvironment and the local signals that regulate this process. We observed that eosinophils gradually migrate along the crypt-villus axis, giving rise to a villus-resident subpopulation with a distinct transcriptional signature. Retinoic acid signaling was specifically required for maintenance of this subpopulation, while IL-5 was largely dispensable outside of its canonical role in eosinophil production. Surprisingly, we found that a high-protein diet suppressed the accumulation of villus-resident eosinophils. Purified amino acids were sufficient for this effect, which was a consequence of accelerated eosinophil turnover within the tissue microenvironment and was not due to altered development in the bone marrow. Our study provides insight into the process of eosinophil adaptation to the SI, highlighting its reliance on nutrient-derived signals.

Cebp1 and Cebpβ transcriptional axis controls eosinophilopoiesis in zebrafish

Eosinophils are a group of granulocytes well known for their capacity to protect the host from parasites and regulate immune function. Diverse biological roles for eosinophils have been increasingly identified, but the developmental pattern and regulation of the eosinophil lineage remain largely unknown. Herein, we utilize the zebrafish model to analyze eosinophilic cell differentiation, distribution, and regulation. By identifying eslec as an eosinophil lineage-specific marker, we establish a Tg(eslec:eGFP) reporter line, which specifically labeled cells of the eosinophil lineage from early life through adulthood. Spatial-temporal analysis of eslec+ cells demonstrates their organ distribution from larval stage to adulthood. By single-cell RNA-Seq analysis, we decipher the eosinophil lineage cells from lineage-committed progenitors to mature eosinophils. Through further genetic analysis, we demonstrate the role of Cebp1 in balancing neutrophil and eosinophil lineages, and a Cebp1-Cebpβ transcriptional axis that regulates the commitment and differentiation of the eosinophil lineage. Cross-species functional comparisons reveals that zebrafish Cebp1 is the functional orthologue of human C/EBPεP27 in suppressing eosinophilopoiesis. Our study characterizes eosinophil development in multiple dimensions including spatial-temporal patterns, expression profiles, and genetic regulators, providing for a better understanding of eosinophilopoiesis.

Effects of Dietary Lycopene on the Growth Performance, Antioxidant Capacity, Meat Quality, Intestine Histomorphology, and Cecal Microbiota in Broiler Chickens

The experiment aimed to investigate the effects of dietary lycopene on the growth performance, antioxidant capacity, meat quality, intestine histomorphology, and cecal microbiota in broiler chickens. We randomly divided five hundred and seventy-six one-day-old male broilers into four groups each with six replicates and 24 chickens in each replicate. The control group (CG) was fed the basal diet, and the other groups were given powder lycopene of 10, 20, and 30 mg/kg lycopene (LP10, LP20, and LP30, respectively). Compared with the control group, (1) the dietary lycopene increased (p = 0.001) the average daily gain and decreased (p = 0.033) the feed conversion ratio in the experimental groups; (2) the glutathione peroxidase enzyme contents in LP20 were higher (p =< 0.001) in myocardium; (3) the crude protein contents were higher (p = 0.007) in the group treated with 30 mg/kg dietary lycopene; (4) the jejunum villous height was higher (p = 0.040) in LP20; (5) the Unclassified-f-Ruminococcaceae relative abundance was significantly higher (p = 0.043) in LP20. In this study, adding 20 mg/kg dietary lycopene to the broiler chickens' diets improved the growth performance, antioxidant capacity, meat quality, intestine histomorphology, and cecal microbiota in broiler chickens.

Mechanisms and functions of intestinal vascular specialization

The intestinal vasculature has been studied for the last 100 years, and its essential role in absorbing and distributing ingested nutrients is well known. Recently, fascinating new insights into the organization, molecular mechanisms, and functions of intestinal vessels have emerged. These include maintenance of intestinal epithelial cell function, coping with microbiota-induced inflammatory pressure, recruiting gut-specific immune cells, and crosstalk with other organs. Intestinal function is also regulated at the systemic and cellular levels, such that the postprandial hyperemic response can direct up to 30% of systemic blood to gut vessels, while micron-sized endothelial cell fenestrations are necessary for nutrient uptake. In this review, we will highlight past discoveries made about intestinal vasculature in the context of new findings of molecular mechanisms underpinning gut function. Such comprehensive understanding of the system will pave the way to breakthroughs in nutrient uptake optimization, drug delivery efficiency, and treatment of human diseases.

Eosinophils at diagnosis are elevated in amyotrophic lateral sclerosis

Introduction

Amyotrophic lateral sclerosis (ALS) is a rare, devastating neurodegenerative disease that affects upper and lower motor neurons. To date, no effective treatment or reliable biomarker for ALS has been developed. In recent years, many factors have been proposed as possible biomarkers of ALS; however, no consensus has been reached. Therefore, a reliable biomarker is urgently needed. Eosinophils may play a crucial role in healthy humans and diseases, and serve as a biomarker for many chronic diseases.

Methods

Routine blood test results were collected from 66 healthy controls and 59 patients with ALS. The percentages and total numbers of each cell population were analyzed, and the correlation between these indicators and patient ALS functional rating scale-revised (ALSFRS-R) score or disease progression rate (ΔFS score) was analyzed.

Results

Compared to healthy controls, the number of blood leukocytes, neutrophils, monocytes, and basophils was significantly decreased in patients with ALS (p = 0.002, p = 0.001, p = 0.049, and p < 0.0001, respectively). There was an increase in the number of eosinophils (p < 0.0001), but no difference in the number of lymphocytes between patients with ALS and healthy controls was found (p = 0.563). Compared to healthy controls, the percentage of neutrophils was decreased and the percentage of lymphocytes and eosinophils was increased in patients with ALS (p = 0.01, p = 0.012, and p = 0.001, respectively). There was no difference between patients with ALS and healthy controls in the percentage of monocytes and basophils (p = 0.622 and p = 0.09, respectively). However, only the percentage and number of eosinophils had a correlation with the ΔFS score. Further multivariate analysis revealed a significant correlation between the disease duration, eosinophil count and percentage, and the disease progression rate (p < 0.0001, p = 0.048, and p = 0.023, respectively). The neutrophil-to-eosinophil ratio (NER), lymphocyte-to-eosinophil ratio (LER), and monocyte-to-eosinophil ratio (MER) were significantly lower in patients with ALS than in healthy controls. However, only the LER was significantly correlated with the ΔFS score.

Conclusion

These observations implicate neutrophils, lymphocytes, and eosinophils as important factors, and increasing eosinophil counts were negatively correlated with the ΔFS score in patients with ALS.

Assessment of intestinal status in MPLW515L mutant myeloproliferative neoplasms mice model

The MPLW515L mutation is a prevalent genetic mutation in patients with myeloproliferative neoplasms (MPN), and utilizing this mutation in mice model can provide important insights into the disease. However, the relationship between intestinal homeostasis and MPN mice model remains elusive. In this study, we utilized a retroviral vector to transfect hematopoietic stem cells with the MPLW515L mutation, creating mutated MPN mice model to investigate their intestinal status. Our results revealed that the MPLW515L in MPN mice model aggravated inflammation in the intestines, decreased the levels of tight junction proteins and receptors for bacteria metabolites. Additionally, there was increased activation of the caspase1/IL-1β signaling pathway and a significant reduction in phos-p38 levels in the intestinal tissue in MPN mice. The MPLW515L mutation also led to up-expression of anti-microbial genes in the intestinal tract. Though the mutation had no impact on the alpha diversity and dominant bacterial taxa, it did influence the rare bacterial taxa/sub-communities and consequently impacted intestinal homeostasis. Our findings demonstrate the significance of MPLW515L mice model for studying MPN disease and highlight the mutation's influence on intestinal homeostasis, including inflammation, activation of the IL-1β signaling pathway, and the composition of gut microbial communities.

Targeting helminths: The expanding world of type 2 immune effector mechanisms

In this new review, Rick Maizels and Bill Gause summarize how type 2 immune responses combat helminth parasites through novel mechanisms, coordinating multiple innate and adaptive cell and molecular players that can eliminate infection and repair-resultant tissue damage.

Oat β-glucan supplementation pre- and during pregnancy alleviates fetal intestinal immunity development damaged by gestational diabetes in rats

Oat β-glucan (OG) has been shown to improve intestinal microecology in gestational diabetes mellitus (GDM), but the effect on fetal intestine health is unknown. Herein, we aimed to investigate the effects of OG supplementation during gestation in GDM dams on fetal intestinal immune development. OG was supplemented one week before mating until the end of the experiment. GDM rats were made with a high-fat diet (HFD) with a minimal streptozotocin (STZ) dose. The fetal intestines were sampled at gestation day (GD) 19.5, and the intestinal morphology, chemical barrier molecules, intraepithelial immune cell makers, and levels of inflammatory cytokines were investigated. The results showed that OG supplementation alleviated the decrease of the depth of fetal intestinal villi and crypts, the number of goblet cells (GCs), protein expression of mucin-1 (Muc1) and Muc2, the mRNA levels of Gpr41, Gpr43, and T cell markers, and increased the number of paneth cells (PCs), the mRNA levels of defensin-6 (defa6), and macrophage (Mø) marker and the expression of cytokines induced by GDM. In addition, OG supplementation alleviated the function of immune cell self-proliferation, chemotaxis and assembly capabilities, protein, fat, folic acid, and zinc absorption damaged by GDM. As indicated by these findings, OG supplementation before and during pregnancy improved the fetal intestinal chemical barriers, immune cells, cytokines, and the metabolism of nutrients to protect the fetal intestinal immunity.

Neuromedin U programs eosinophils to promote mucosal immunity of the small intestine

Eosinophils are granulocytes that play an essential role in type 2 immunity and regulate multiple homeostatic processes in the small intestine (SI). However, the signals that regulate eosinophil activity in the SI at steady state remain poorly understood. Through transcriptome profiling of eosinophils from various mouse tissues, we found that a subset of SI eosinophils expressed neuromedin U (NMU) receptor 1 (NMUR1). Fate-mapping analyses showed that NMUR1 expression in SI eosinophils was programmed by the local microenvironment and further enhanced by inflammation. Genetic perturbation and eosinophil-organoid coculture experiments revealed that NMU-mediated eosinophil activation promotes goblet cell differentiation. Thus, NMU regulates epithelial cell differentiation and barrier immunity by stimulating NMUR1-expressing eosinophils in the SI, which highlights the importance of neuroimmune-epithelial cross-talk in maintaining tissue homeostasis.

MHCII+CD80+ thymic eosinophils increase in abundance during neonatal development in mice and their accumulation is microbiota dependent

Eosinophils are present in the thymus of mammals, yet their function at this site during homeostatic development is unknown. We used flow cytometry to determine the abundance and phenotype of eosinophils (here defined as SSchigh SiglecF+ CD11b+ CD45+ cells) in the thymus of mice during the neonatal period, the later postnatal period, and into adulthood. We show that both the total number of thymic eosinophils and their frequency among leukocytes increase over the first 2 wk of life and that their accumulation in the thymus is dependent on the presence of an intact bacterial microbiota. We report that thymic eosinophils express the interleukin-5 receptor (CD125), CD80, and IDO, and that subsets of thymic eosinophils express CD11c and major histocompatibility complex II (MHCII). We found that the frequency of MHCII-expressing thymic eosinophils increases over the first 2 wk of life, and that during this early-life period the highest frequency of MHCII-expressing thymic eosinophils is located in the inner medullary region. These data suggest a temporal and microbiota-dependent regulation of eosinophil abundance and functional capabilities in the thymus.

Microbial-host-isozyme analyses reveal microbial DPP4 as a potential antidiabetic target

A mechanistic understanding of how microbial proteins affect the host could yield deeper insights into gut microbiota-host cross-talk. We developed an enzyme activity-screening platform to investigate how gut microbiota-derived enzymes might influence host physiology. We discovered that dipeptidyl peptidase 4 (DPP4) is expressed by specific bacterial taxa of the microbiota. Microbial DPP4 was able to decrease the active glucagon like peptide-1 (GLP-1) and disrupt glucose metabolism in mice with a leaky gut. Furthermore, the current drugs targeting human DPP4, including sitagliptin, had little effect on microbial DPP4. Using high-throughput screening, we identified daurisoline-d4 (Dau-d4) as a selective microbial DPP4 inhibitor that improves glucose tolerance in diabetic mice.

Emerging functions of tissue-resident eosinophils

Eosinophils are typically considered tissue-damaging effector cells in type 2 immune-related diseases. However, they are also increasingly recognized as important modulators of various homeostatic processes, suggesting they retain the ability to adapt their function to different tissue contexts. In this review, we discuss recent progress in our understanding of eosinophil activities within tissues, with particular emphasis on the gastrointestinal tract, where a large population of these cells resides under non-inflammatory conditions. We further examine evidence of their transcriptional and functional heterogeneity and highlight environmental signals emerging as key regulators of their activities, beyond classical type 2 cytokines.

How to train your myeloid cells: a way forward for helminth vaccines?

Soil-transmitted helminths affect approximately 1.5 billion people worldwide. However, as no vaccine is currently available for humans, the current strategy for elimination as a public health problem relies on preventive chemotherapy. Despite more than 20 years of intense research effort, the development of human helminth vaccines (HHVs) has not yet come to fruition. Current vaccine development focuses on peptide antigens that trigger strong humoral immunity, with the goal of generating neutralizing antibodies against key parasite molecules. Notably, this approach aims to reduce the pathology of infection, not worm burden, with only partial protection observed in laboratory models. In addition to the typical translational hurdles that vaccines struggle to overcome, HHVs face several challenges (1): helminth infections have been associated with poor vaccine responses in endemic countries, probably due to the strong immunomodulation caused by these parasites, and (2) the target population displays pre-existing type 2 immune responses to helminth products, increasing the likelihood of adverse events such as allergy or anaphylaxis. We argue that such traditional vaccines are unlikely to be successful on their own and that, based on laboratory models, mucosal and cellular-based vaccines could be a way to move forward in the fight against helminth infection. Here, we review the evidence for the role of innate immune cells, specifically the myeloid compartment, in controlling helminth infections. We explore how the parasite may reprogram myeloid cells to avoid killing, notably using excretory/secretory (ES) proteins and extracellular vesicles (EVs). Finally, learning from the field of tuberculosis, we will discuss how anti-helminth innate memory could be harnessed in a mucosal-trained immunity-based vaccine.

IL-4 and IL-13: Regulators and Effectors of Wound Repair

Type 2 immunity mediates protective responses to helminths and pathological responses to allergens, but it also has broad roles in the maintenance of tissue integrity, including wound repair. Type 2 cytokines are known to promote fibrosis, an overzealous repair response, but their contribution to healthy wound repair is less well understood. This review discusses the evidence that the canonical type 2 cytokines, IL-4 and IL-13, are integral to the tissue repair process through two main pathways. First, essential for the progression of effective tissue repair, IL-4 and IL-13 suppress the initial inflammatory response to injury. Second, these cytokines regulate how the extracellular matrix is modified, broken down, and rebuilt for effective repair. IL-4 and/or IL-13 amplifies multiple aspects of the tissue repair response, but many of these pathways are highly redundant and can be induced by other signals. Therefore, the exact contribution of IL-4Rα signaling remains difficult to unravel.

Metabolism in type 2 immune responses

The immune response is tailored to the environment in which it takes place. Immune cells sense and adapt to changes in their surroundings, and it is now appreciated that in addition to cytokines made by stromal and epithelial cells, metabolic cues provide key adaptation signals. Changes in immune cell activation states are linked to changes in cellular metabolism that support function. Furthermore, metabolites themselves can signal between as well as within cells. Here, we discuss recent progress in our understanding of how metabolic regulation relates to type 2 immunity firstly by considering specifics of metabolism within type 2 immune cells and secondly by stressing how type 2 immune cells are integrated more broadly into the metabolism of the organism as a whole.

Role of CD34 in inflammatory bowel disease

Inflammatory bowel disease (IBD) is caused by a variety of pathogenic factors, including chronic recurrent inflammation of the ileum, rectum, and colon. Immune cells and adhesion molecules play an important role in the course of the disease, which is actually an autoimmune disease. During IBD, CD34 is involved in mediating the migration of a variety of immune cells (neutrophils, eosinophils, and mast cells) to the inflammatory site, and its interaction with various adhesion molecules is involved in the occurrence and development of IBD. Although the function of CD34 as a partial cell marker is well known, little is known on its role in IBD. Therefore, this article describes the structure and biological function of CD34, as well as on its potential mechanism in the development of IBD.

Active eosinophils regulate host defence and immune responses in colitis

In the past decade, single-cell transcriptomics has helped to uncover new cell types and states and led to the construction of a cellular compendium of health and disease. Despite this progress, some difficult-to-sequence cells remain absent from tissue atlases. Eosinophils-elusive granulocytes that are implicated in a plethora of human pathologies1-5-are among these uncharted cell types. The heterogeneity of eosinophils and the gene programs that underpin their pleiotropic functions remain poorly understood. Here we provide a comprehensive single-cell transcriptomic profiling of mouse eosinophils. We identify an active and a basal population of intestinal eosinophils, which differ in their transcriptome, surface proteome and spatial localization. By means of a genome-wide CRISPR inhibition screen and functional assays, we reveal a mechanism by which interleukin-33 (IL-33) and interferon-γ (IFNγ) induce the accumulation of active eosinophils in the inflamed colon. Active eosinophils are endowed with bactericidal and T cell regulatory activity, and express the co-stimulatory molecules CD80 and PD-L1. Notably, active eosinophils are enriched in the lamina propria of a small cohort of patients with inflammatory bowel disease, and are closely associated with CD4+ T cells. Our findings provide insights into the biology of eosinophils and highlight the crucial contribution of this cell type to intestinal homeostasis, immune regulation and host defence. Furthermore, we lay a framework for the characterization of eosinophils in human gastrointestinal diseases.

Regulation of innate immune system function by the microbiome: Consequences for tumor immunity and cancer immunotherapy

Innate effector cells are immune cells endowed with host protective features and cytotoxic functions. By sensing the tissue environment, innate cells have an important role in regulating the transition from homeostasis to inflammation and the establishment of pathological states, including the onset and development of cancer. The tumor microenvironment induces molecular and functional modifications in innate cells, dampening their capability to initiate and sustain anti-tumor immune responses. Emerging studies clearly showed a contribution of the microbiota in modulating the functions of innate cells in cancer. Commensal microorganisms can not only directly interact with innate cells in the tumor microenvironment but can also exert immunomodulatory features from non-tumor sites through the release of microbial products. The microbiota can mediate the priming of innate cells at mucosal tissues and determine the strength of immune responses mediated by such cells when they migrate to non-mucosal tissues, having an impact on cancer. Finally, several evidences reported a strong contribution of the microbiota in promoting innate immune responses during anti-cancer therapies leading to enhanced therapeutic efficacy. In this review, we considered the current knowledge on the role of the microbiota in shaping host innate immune responses in cancer.

Innate lymphoid cells: More than just immune cells

Since their discovery, innate lymphoid cells (ILCs) have been described as the innate counterpart of the T cells. Indeed, ILCs and T cells share many features including their common progenitors, transcriptional regulation, and effector cytokine secretion. Several studies have shown complementary and redundant roles for ILCs and T cells, leaving open questions regarding why these cells would have been evolutionarily conserved. It has become apparent in the last decade that ILCs, and rare immune cells more generally, that reside in non-lymphoid tissue have non-canonical functions for immune cells that contribute to tissue homeostasis and function. Viewed through this lens, ILCs would not be just the innate counterpart of T cells, but instead act as a link between sensory cells that monitor any changes in the environment that are not necessarily pathogenic and instruct effector cells that act to maintain body homeostasis. As these non-canonical functions of immune cells are operating in absence of pathogenic signals, it opens great avenues of research for immunologists that they now need to identify the physiological cues that regulate these cells and how the process confers a finer level of control and a greater flexibility that enables the organism to adapt to changing environmental conditions. In the review, we highlight how ILCs participate in the physiologic function of the tissue in which they reside and how physiological cues, in particular neural inputs control their homeostatic activity.

Faecalibaculum rodentium remodels retinoic acid signaling to govern eosinophil-dependent intestinal epithelial homeostasis

The intestinal epithelium plays critical roles in sensing and integrating dietary and microbial signals. How microbiota and intestinal epithelial cell (IEC) interactions regulate host physiology in the proximal small intestine, particularly the duodenum, is unclear. Using single-cell RNA sequencing of duodenal IECs under germ-free (GF) and different conventional microbiota compositions, we show that specific microbiota members alter epithelial homeostasis by increasing epithelial turnover rate, crypt proliferation, and major histocompatibility complex class II (MHCII) expression. Microbiome profiling identified Faecalibaculum rodentium as a key species involved in this regulation. F. rodentium decreases enterocyte expression of retinoic-acid-producing enzymes Adh1, Aldh1a1, and Rdh7, reducing retinoic acid signaling required to maintain certain intestinal eosinophil populations. Eosinophils suppress intraepithelial-lymphocyte-mediated production of interferon-γ that regulates epithelial cell function. Thus, we identify a retinoic acid-eosinophil-interferon-γ-dependent circuit by which the microbiota modulates duodenal epithelial homeostasis.

Eo, what are we doing here?

A plethora of studies have established the importance of eosinophils in protective immunity against infections and in allergy. In this issue of Immunity, Ignacio et al. (2022) define a vital for eosinophils in coordinating a microbiota-epithelial-immune axis that maintains intestinal homeostasis.