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Inflammatory bowel diseases (IBDs) are chronic, relapsing, and inflammatory disorders of the gastrointestinal tract characterized by abnormal immune responses. Recently, STING has emerged as a promising therapeutic target for various autoinflammatory diseases. However, few STING-selective small molecules have been investigated as novel strategies for IBD. In this study, we sought to examine the effects of PROTAC-based STING degrader SP23 on acute colitis and explore its underlying mechanism. SP23 treatment notably alleviates dextran sulfate sodium (DSS)-induced colitis. Pharmacological degradation of STING significantly reduced the production of inflammatory cytokines, such as TNF-α, IL-1β, and IL-6, and inhibited macrophage polarization towards the M1 type. Furthermore, SP23 administration decreased the loss of tight junction proteins, including ZO-1, occludin, and claudin-1, and downregulated STING and NLRP3 signaling pathways in intestinal inflammation. In vitro, STING activated NLRP3 inflammasome-mediated pyroptosis in intestinal epithelial cells, which could be abrogated by SP23 and STING siRNA intervention. In conclusion, these findings provide new evidence for STING as a novel therapeutic target for IBD, and reveal that hyperactivation of STING could exaggerate colitis by inducing NLRP3/Caspase-1/GSDMD axis mediated intestinal epithelial cells pyroptosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Ectodermal mesenchymal stem cells-derived conditioned medium (EMSCs-CM) has been reported to protect against ulcerative colitis (UC) in mice, but its underlying mechanism in alleviating UC need to be further elucidated. Here, it is reported that EMSCs-CM could attenuate pro-inflammatory response of LPS-induced IEC-6 cells and regulate the polarization of macrophages towards anti-inflammatory type in vitro. Furthermore, PLGA microspheres prepared by the double emulsion method were constructed for oral delivery of EMSCs-CM (EMSCs-CM-PLGA), which are beneficial for colon-targeted adhesion of EMSCs-CM to the damaged colon mucosa. The results showed that orally-administered of EMSCs-CM-PLGA microspheres reduced inflammatory cells infiltration and maintained the intestinal mucosal barrier. Further investigation found that EMSCs-CM-PLGA microspheres treatment gradually inhibited the activation of NF-κB pathway to regulate M1/M2 polarization balance in colon tissue macrophages, thereby alleviating DSS-induced UC. These results of this study will provide a theoretical basis for clinical application of EMSCs-CM in UC repair., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Sepsis-induced intestinal injury is a common complication that increases the morbidity and mortality associated with sepsis. UCP2, a mitochondrial membrane protein, is involved in numerous cellular processes, including metabolism, inflammation, and pyroptosis. According to our previous studies, UCP2 expression increases in septic intestinal tissue. However, its function in intestinal damage is not known. This work investigated UCP2's role in intestinal injury caused by sepsis. A sepsis mouse model was established in wild-type and UCP2-knockout (UCP2-KO) animals using cecal ligation and puncture (CLP). MCC950, an NLRP3 inflammasome inhibitor, was injected intraperitoneally 3 h before CLP surgery. Overall, significantly higher levels of UCP2 were observed in the intestines of septic mice. UCP2-KO mice subjected to CLP exhibited exacerbated intestinal damage, characterized by enhanced mucosal erosion, inflammatory cell infiltration, and increased intestinal permeability. Furthermore, UCP2 knockout significantly increased oxidative stress, inflammation, and pyroptosis in the CLP mouse intestines. Interestingly, MCC950 not only inhibited pyroptosis but also reversed inflammation, oxidative stress as well as damage to intestinal tissues as a result of UCP2 knockout. Our results highlighted the protective functions of UCP2 in sepsis-associated intestinal injury through modulation of inflammation and oxidative stress via NLRP3 inflammasome-induced pyroptosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Zymogen granule 16 (ZG16) is a secretory glycoprotein found in zymogen granules, which also plays an important role in colorectal inflammation and cancer. Herein, a ZG16 gene knock-out (ZG16 -/- ) mouse line was established and we found that ZG16 deletion damaged the intestinal mucosal barrier and gut microbiota, which resulted in low-level inflammation and further promoted the development of ulcerative colitis and inflammation-related colorectal cancer. Meanwhile, a metabolomics analysis on mouse feces showed that the metabolites significantly differed between ZG16 -/- and WT mice, which were important mediators of host-microbiota communication and may impact the pulmonary inflammation of mice. Indeed, ZG16 -/- mice showed more severe inflammation in a bronchial asthma model. Taken together, the results demonstrate that ZG16 plays a pivotal role in inhibiting inflammation and regulating immune responses in colorectum and lung of experimental animals, which may provide a better understanding of the underlying mechanism of human inflammatory diseases associated with ZG16., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Crosstalk between the microbiome and gut mucosa-resident immune cells plays a pivotal role in modulating immune responses to pathogens, including responses to HIV infection. However, how these interactions may differ between young men who have sex with men (YMSM) disproportionately impacted by HIV, as compared with older adult MSM (AMSM), is not well understood. A broad analysis of associations between the microbiome and rectal transcriptome revealed 10 microbial families/genera correlated with immunologic gene pathways. Specifically, the rectal transcriptome of YMSM was characterized by upregulation of T cell activation/differentiation pathways and signaling from multiple cytokine families compared with AMSM. The microbiome of YMSM was enriched with pathogenic genera, including Peptostreptococcus, shown to be positively correlated with type I IFN pathways important for antiviral immunity. These findings demonstrate that YMSM have a unique immune phenotype and rectal microenvironment and support further evaluation of biological factors that influence rectal HIV transmission.

Clostridioides difficile infection (CDI) is a common cause of antibiotic-associated colitis. C. difficile proliferates and produces toxins that damage the colonic epithelium, leading to symptoms ranging from mild diarrhea to severe pseudomembranous colitis. The host's innate response to CDI occurs in two phases: an early phase in which neutrophils reduce the bacterial load and a late phase involving repair mechanisms to restore epithelial integrity. Group 3 innate lymphoid cells (ILC3s) are crucial in protecting the gut from CDI. Previous studies have shown that ILC3-derived IL-22 is essential in the late phase of CDI for epithelial repair and maintaining an intestinal microbiota that competes with C. difficile , preventing its expansion. Our study finds that ILC3s also protect during the early stages of CDI by sustaining neutrophils through GM-CSF. Less neutrophil production, accumulation, and activation was evident in ILC3-deficient mice than in wild-type (WT) mice, which led to exacerbated symptoms, impaired pathogen clearance, a compromised epithelial barrier, and increased mortality. The adoptive transfer of ILC3s into ILC3-deficient mice restored neutrophil responses and improved disease outcomes. Both in vitro and in vivo experiments revealed that GM-CSF production by ILC3s is crucial for neutrophil production and effective resistance during CDI. Using mice lacking NKp46 + ILC3s, we found that this subset significantly contributes to GM-CSF production in CDI. These findings highlight the critical role of the ILC3-neutrophil connection in early innate responses to CDI. Enhancing ILC3 production of GM-CSF could be a promising strategy for improving host defense against CDI and other enteric infections., Competing Interests: Competing interests statement:The authors declare no competing interest.

The maintenance of intestinal homeostasis is a fundamental process critical for organismal integrity. Sitting at the interface of the gut microbiome and mucosal immunity, adaptive and innate lymphoid populations regulate the balance between commensal micro-organisms and pathogens. Checkpoint inhibitors, particularly those targeting the CTLA-4 pathway, disrupt this fine balance and can lead to inflammatory bowel disease and immune checkpoint colitis. Here, we show that CTLA-4 is expressed by innate lymphoid cells and that its expression is regulated by ILC subset-specific cytokine cues in a microbiota-dependent manner. Genetic deletion or antibody blockade of CTLA-4 in multiple in vivo models of colitis demonstrates that this pathway plays a key role in intestinal homeostasis. Lastly, we have found that this observation is conserved in human IBD. We propose that this population of CTLA-4-positive ILC may serve as an important target for the treatment of idiopathic and iatrogenic intestinal inflammation., (© 2024. The Author(s).)

Gasdermin C is one of the least studied members of the gasdermin family of proteins, known for their critical involvement in pyroptosis and host defense. Furthermore, evidence for the role of Gasdermin C in the intestine is scarce and partly controversial. Here, we tested the functional role of Gasdermin C in intestinal homeostasis, inflammation and tumorigenesis. : We studied Gasdermin C in response to cytokines in intestinal organoids. We evaluated epithelial differentiation, cell death and immune infiltration under steady state conditions in a new mouse line deficient in Gasdermin C. The role of Gasdermin C was analyzed in acute colitis, infection and colitis-associated cancer. Gasdemin C is highly expressed in the intestinal epithelium and strongly induced by the type 2 cytokines IL-4 and IL-13 in a STAT6-dependent manner. Gasdermin C-deficient mice show no changes in tissue architecture and epithelial homeostasis. Epithelial organoids deficient in Gasdermin C develop normally and show no alterations in proliferation or cell death. No changes were found in models of acute colitis, type 2 intestinal infection and colitis-associated cancer. Gasdermin C genes are upregulated by type 2 immunity, yet appear dispensable for the development of intestinal inflammation, infection and colitis-associated cancer., (© 2024. The Author(s).)

To investigate intestinal health and its potential disruptors in vitro, representative models are required. Human induced pluripotent stem cell (hiPSC)-derived intestinal epithelial cells (IECs) more closely resemble the in vivo intestinal tissue than conventional in vitro models like human colonic adenocarcinoma Caco-2 cells. However, the potential of IECs to study immune-related responses upon external stimuli has not been investigated in detail yet. The aim of the current study was to evaluate immune-related effects of IECs by challenging them with a pro-inflammatory cytokine cocktail. Subsequently, the effects of Lactiplantibacillus plantarum WCFS1 were investigated in unchallenged and challenged IECs. All exposures were compared to Caco-2 cells and in vivo data where possible. Upon the inflammatory challenge, IECs and Caco-2 cells induced a pro-inflammatory response which was strongest in IECs. Heat-killed L. plantarum exerted the strongest effect on immune parameters in the IEC model, while L. plantarum in the stationary growth phase had most pronounced effects on immune-related gene expression in Caco-2 cells. Unfortunately, comparison to in vivo transcriptomics data showed limited similarities, which could be explained by essential differences in the study setups. Altogether, hiPSC-derived IECs show a high potential as a model to study immune-related responses in the intestinal epithelium in vitro., (© 2024. The Author(s).)

The IL-23 signaling pathway in both innate and adaptive immune cells is vital for orchestrating type 17 immunity, which is marked by the secretion of signature cytokines such as IL-17, IL-22, and GM-CSF. These proinflammatory mediators play indispensable roles in maintaining intestinal immune equilibrium and mucosal host defense; however, their involvement has also been implicated in the pathogenesis of chronic inflammatory disorders, such as inflammatory bowel diseases and autoimmunity. However, the implications of type 17 immunity across diverse inflammation models are complex. This review provides a comprehensive overview of the multifaceted roles of these cytokines in maintaining gut homeostasis and in perturbing gut barrier integrity, leading to acute and chronic inflammation in various models of gut infection and colitis. Additionally, this review focuses on type 17 immunity interconnecting multiple organs in autoimmune conditions, with a particular emphasis on the pathogenesis of autoimmune arthritis and neuroinflammation driven by T cells primed within the gut microenvironment., (© 2024. The Author(s).)

Akkermansia muciniphila (Akk), a second-generation probiotic known for its ability to regulate intestinal function in mammals, is not yet fully understood in the context of aquaculture. This study aims to investigate the effects of different forms of Akk on intestinal barrier function and immune response in zebrafish (Danio rerio) under high-fat diet conditions. The experimental groups included a control group, a high-fat diet group, an Akk group, and a group receiving various concentrations of pasteurized Akkermansia muciniphila (P-Akk) along with a high-fat diet. Evaluation methods included histological examination with hematoxylin and eosin staining, ultrastructural analysis using transmission electron microscopy, real-time fluorescence quantitative analysis, and transcriptome sequencing technology. The results showed that both the Akk and P-Akk groups exhibited a significant increase in villi number and length compared to the high-fat group. Furthermore the expression levels of claudin, claudin-2, occludin A, occludin B, and other genes were significantly upregulated, while the expression levels of intestinal proinflammatory factors genes and proteins were significantly downregulated. Compared to the high-fat group, the Akk group showed a more complete and well-preserved nucleus, mitochondria, and tight junction structures. Additionally, the morphology of intestinal epithelial microvilli in the medium and high concentration Akk group was complete and dense. The expressions of tlr2 and nf-κb were upregulated, while the expressions of myd88 and nod2 were downregulated in the medium- and high-concentration Akk groups. Akk may improve immune dysfunction in high-fat fed zebrafish through the TLR2/NF-κB signaling pathway, which requires further study. Transcriptome analysis revealed significant upregulation of the immune-related gene pigr, significant downregulation of stat3, and significant upregulation of the intercellular adhesion molecule f11r. In conclusion, dietary Akk supplementation alleviated intestinal barrier damage and immune dysfunction in high-fat zebrafish. This study provides important insights into the potential use of Akk in fish and lays the foundation for further studies on its role in fish immunity., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Porcine group A rotavirus (PoRVA) is one of the common enteric viruses causing severe diarrhea in piglets. Although PoRVA infection has been identified to promote IL-10 production, the role of IL-10 during viral infection remains unclear. In this study, we found that elevated IL-10 levels during PoRVA infection promote viral replication by inhibiting type I interferon production and response. IL-10 treatment upregulated the expression of SOCS3 in PoRVA-infected IPEC-J2 cells, which inhibited IFN-I production by preventing the degradation of IκB and nuclear translocation of NF-κB, thereby significantly promoting PoRVA replication. Furthermore, we determined that SOCS3 also inhibited type Ⅰ interferon signaling pathway, which led to a significantly reduced ISGs after IFN-α stimulation. In PoRVA-infected cells, overexpression of SOCS3 significantly inhibits phosphorylation and heterodimerization of STAT1, thereby promoting viral replication. Finally, we demonstrated the effect of IL-10 on PoRVA replication in vivo by murine models of PoRVA infection. PoRVA replication levels were lower in the ileum of IL-10 knockout (IL-10 -/- ) mice than that in PoRVA-infected wild-type mice, but PoRVA replication levels were higher in the ileum of IFNAR knockout (IFNAR -/- ) mice than that in PoRVA-infected wild-type mice. Taken together, our findings provide information to understand the strategies of PoRVA to evade host innate antiviral immunity., Competing Interests: Declaration of Competing Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Intraepithelial lymphocytes (IELs) expressing the TCRγδ survey the intestinal epithelium to limit the invasion of microbial pathogens. The production of type I IFN is a central component of an antiviral immune response, yet how these proinflammatory cytokines contribute to γδ IEL effector function remains unclear. Based on the unique activation status of IELs and their ability to bridge innate and adaptive immunity, we investigated the extent to which type I IFN signaling modulates γδ IEL function. Using an ex vivo culture model, we find that type I IFN alone is unable to drive IFN-γ production, yet low-level TCR activation synergizes with type I IFN to induce IFN-γ production in murine γδ IELs. Further investigation into the underlying molecular mechanisms of costimulation revealed that TCRγδ-mediated activation of NFAT and JNK is required for type I IFN to promote IFN-γ expression in a STAT4-dependent manner. Whereas type I IFN rapidly upregulates antiviral gene expression independent of a basal TCRγδ signal, neither tonic TCR triggering nor the presence of a TCR agonist was sufficient to elicit type I IFN-induced IFN-γ production in vivo. However, bypassing proximal TCR signaling events synergized with IFNAR/STAT4 activation to induce γδ IEL IFN-γ production. These findings indicate that γδ IELs contribute to host defense in response to type I IFN by mounting a rapid antimicrobial response independent of TCRγδ signaling, and may produce IFN-γ in a TCR-dependent manner under permissive conditions., (Copyright © 2024 by The American Association of Immunologists, Inc.)

Background & Aims: Intestinal epithelial cell (IEC) damage is a hallmark of celiac disease (CeD); however, its role in gluten-dependent T-cell activation is unknown. We investigated IEC-gluten-T-cell interactions in organoid monolayers expressing human major histocompatibility complex class II (HLA-DQ2.5), which facilitates gluten antigen recognition by CD4 + T cells in CeD., Methods: Epithelial major histocompatibility complex class II (MHCII) was determined in active and treated CeD, and in nonimmunized and gluten-immunized DR3-DQ2.5 transgenic mice, lacking mouse MHCII molecules. Organoid monolayers from DR3-DQ2.5 mice were treated with or without interferon (IFN)-γ, and MHCII expression was evaluated by flow cytometry. Organoid monolayers and CD4 + T-cell co-cultures were incubated with gluten, predigested, or not by elastase-producing Pseudomonas aeruginosa or its lasB mutant. T-cell function was assessed based on proliferation, expression of activation markers, and cytokine release in the co-culture supernatants., Results: Patients with active CeD and gluten-immunized DR3-DQ2.5 mice demonstrated epithelial MHCII expression. Organoid monolayers derived from gluten-immunized DR3-DQ2.5 mice expressed MHCII, which was upregulated by IFN-γ. In organoid monolayer T-cell co-cultures, gluten increased the proliferation of CD4 + T cells, expression of T-cell activation markers, and the release of interleukin-2, IFN-γ, and interleukin-15 in co-culture supernatants. Gluten metabolized by P aeruginosa, but not the lasB mutant, enhanced CD4 + T-cell proliferation and activation., Conclusions: Gluten antigens are efficiently presented by MHCII-expressing IECs, resulting in the activation of gluten-specific CD4 + T cells, which is enhanced by gluten predigestion with microbial elastase. Therapeutics directed at IECs may offer a novel approach for modulating both adaptive and innate immunity in patients with CeD., (Copyright © 2024 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Sialylation, a crucial post-translational modification of glycoconjugates, entails the attachment of sialic acid (SA) to the terminal glycans of glycoproteins and glycolipids through a tightly regulated enzymatic process involving various enzymes. This review offers a comprehensive exploration of sialylation within the gut, encompassing its involvement in mucosal protection and its impact on disease progression. The sialylation of mucins and epithelial glycoproteins contributes to the integrity of the intestinal mucosal barrier. Furthermore, sialylation regulates immune responses in the gut, shaping interactions among immune cells, as well as their activation and tolerance. Additionally, the gut microbiota and gut-brain axis communication are involved in the role of sialylation in intestinal health. Altered sialylation patterns have been implicated in various intestinal diseases, including inflammatory bowel disease (IBD), colorectal cancer (CRC), and other intestinal disorders. Emerging research underscores sialylation as a promising avenue for diagnostic, prognostic, and therapeutic interventions in intestinal diseases. Potential strategies such as sialic acid supplementation, inhibition of sialidases, immunotherapy targeting sialylated antigens, and modulation of sialyltransferases have been utilized in the treatment of intestinal diseases. Future research directions will focus on elucidating the molecular mechanisms underlying sialylation alterations, identifying sialylation-based biomarkers, and developing targeted interventions for precision medicine approaches., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Ulcerative colitis (UC) and Crohn's disease (CD) are two subtypes of inflammatory bowel disease (IBD) with rapidly increased incidence worldwide. Although multiple factors contribute to the occurrence and progression of IBD, the role of intestinal fungal species (gut mycobiota) in regulating the severity of these conditions has been increasingly recognized. C-type lectin receptors (CLRs) on hematopoietic cells, including Dectin-1, Dectin-2, Dectin-3, Mincle and DC-SIGN, are a group of pattern recognition receptors (PRRs) that primarily recognize fungi and mediate defense responses, such as oxidative stress. Recent studies have demonstrated the indispensable role of CLRs in protecting the colon from intestinal inflammation and mucosal damage., Methods and Results: This review provides a comprehensive overview of the role of CLRs in the pathogenesis of IBD. Given the significant impact of mycobiota and oxidative stress in IBD, this review also discusses recent advancements in understanding how these factors exacerbate or ameliorate IBD. Furthermore, the latest developments in CLR-guided IBD therapy are examined to highlight the modulation of CLRs in fungal recognition and oxidative burst during the IBD process., Conclusion: This review emphasizes the importance of CLRs in IBD, offering new perspectives on the etiology and therapeutic approaches for this disease.

The intestinal epithelium harbours a unique lymphocyte population, the intraepithelial lymphocytes (IELs). A large fraction of IELs is represented by γδ T cells. Their role in epithelial homeostasis and immune response is well documented, but a conclusive view of their developmental pathway is still missing. In this review, we discuss the existing literature as well as recent advances regarding the tissue adaptation of γδ IELs, both for the characteristic cytotoxic subset and the newly described noncytotoxic subset. We particularly highlight the environmental cues and the transcriptional regulation that equip γδ T cells with their IEL phenotype., (© 2024 The Author(s). European Journal of Immunology published by Wiley‐VCH GmbH.)

Allergic enteritis is an important phenotype of food allergies. However, there is not a suitable animal model for deeply exploring the natural progression and mechanism of allergic enteritis. In our study, we successfully developed an allergic enteritis animal model by feeding mice with an egg white diet. Following the dietary challenge, allergic mice displayed typical food allergy manifestations, including decreased core temperature, aversion to the allergenic diet, and elevated levels of serum sIgE and mMCP-1. Notably, these dietary challenged mice exhibited severe gut damage, characterized by disrupted intestinal microstructure, tissue inflammation, and edema that were evident morphologically. Moreover, upon exposure to food allergens, we observed a marked increase in caspase-3 and GSDMC levels in allergic mice. These two active proteins were found to be colocalized in damaged mucosal enterocytes and were associated with the secretion of epithelial sourced alarmins, such as IL25 and TSLP. Further data on the cellular and molecular levels suggest that such severe food-induced enteritis is mediated by the caspase-3-GSDMC pathway. We believe that this established animal model provides a valuable tool for advancing research on the mechanisms of food allergies.

To withstand complex microbial challenges, the mammalian gut largely depends on the secretion of diverse antimicrobial proteins. Type III interferons (IFNλs) are ordinarily considered inducible antiviral cytokines involved in intestinal immunity. Unlike other IFNλs, we found that newly identified IFNλ4 is an intestinal antibacterial protein. Large amounts of natural IFNλ4 are present in the secretory layer of the intestinal tracts of healthy piglets, which suggests that IFNλ4 is in direct physiological contact with microbial pathogens. We also identified two biochemical functions of mammalian IFNλ4, the induction of bacterial agglutination and direct microbial killing, which are not functions of the other IFNλs. Further mechanistic investigations revealed that after binding to the carbohydrate fraction of lipopolysaccharide, mammalian IFNλ4 self-assembles into bacteria-surrounding nanoparticles that agglutinate bacteria, and that its unique cationic amphiphilic molecular structure facilitates the destruction of bacterial membranes. Our data reveal features of IFNλ4 distinct from those of previously reported IFNλs and suggest that noncanonical IFNλ4 is deeply involved in intestinal immunity, beyond simply cytokine signaling., Competing Interests: Competing interests statement:The authors declare no competing interest.

Introduction: Yersinia enterocolitica (Ye) is a Gram-negative bacterium that causes gastrointestinal infections. The myeloid-derived suppressor cells (MDSCs) constitute a cellular population with the capacity of inducing the specific suppression of T cells. Although there is evidence supporting the role of MDSCs in controlling the immune responses in several bacterial infections, its role during Ye infection has not yet been reported. Therefore, the purpose of the present work was to analyze MDSCs after oral Ye infection., Methods: C57BL/6 wild-type mice were infected with Ye WAP-314 serotype O:8. The proliferation of splenocytes and mesenteric lymph nodes (MLN) cells was measured as well as the levels of cytokines and nitric oxide (NO) in culture supernatants. The frequency and subsets of MDSCs were analyzed in the intestinal mucosa and spleen by flow cytometry. Furthermore, monocytic-MDSCs (Mo-MDSCs) and polymorphonuclear-MDSCs (PMN-MDSCs) were purified from the spleen of infected mice and their suppressor activity was evaluated in co-cultures with purified T cells., Results: we observed a marked expansion of CD11b+Gr-1+ cells, a phenotype consistent with MDSCs, in the spleen and intestinal mucosa of Ye-infected mice. Interestingly, a robust proliferation of splenocytes and MLN cells was observed only when the MDSCs were depleted or the NO production was blocked. In addition, we determined that only Mo-MDSCs had the ability to suppress T-cell proliferation., Conclusion: Our results highlight a mechanism by which Ye may induce suppression of the immune responses. We suggest that NO-producing Mo-MDSCs expand and accumulate in MLN and spleen of Ye-infected mice. These cells can then suppress the T-cell function without interfering with the anti-bacterial effector response. Instead, these immature myeloid cells may perform an important function in regulating the inflammatory response and protecting affected tissues., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Leporati, Di Genaro and Eliçabe.)

Intestinal parasites are part of the intestinal ecosystem and have been shown to establish close interactions with the intestinal microbiota. However, little is known about the influence of intestinal protozoa on the regulation of the immune response. In this study, we analyzed the regulation of the immune response of germ-free mice transplanted with fecal microbiota (FMT) from individuals with multiple parasitic protozoans (P) and non-parasitized individuals (NP). We determined the production of intestinal cytokines, the lymphocyte populations in both the colon and the spleen, and the genetic expression of markers of intestinal epithelial integrity. We observed a general downregulation of the intestinal immune response in mice receiving FMT-P. We found significantly lower intestinal production of the cytokines IL-6, TNF, IFN-γ, MCP-1, IL-10, and IL-12 in the FMT-P. Furthermore, a significant decrease in the proportion of CD3+, CD4+, and Foxp3+ T regulatory cells (Treg) was observed in both, the colon and spleen with FMT-P in contrast to FMT-NP. We also found that in FMT-P mice there was a significant decrease in tjp1 expression in all three regions of the small intestine; ocln in the ileum; reg3γ in the duodenum and relmβ in both the duodenum and ileum. We also found an increase in colonic mucus layer thickness in mice colonized with FMT-P in contrast with FMT-NP. Finally, our results suggest that gut protozoa, such as Blastocystis hominis, Entamoeba coli, Endolimax nana, Entamoeba histolytica/E. dispar, Iodamoeba bütschlii, and Chilomastix mesnili consortia affect the immunoinflammatory state and induce functional changes in the intestine via the gut microbiota. Likewise, it allows us to establish an FMT model in germ-free mice as a viable alternative to explore the effects that exposure to intestinal parasites could have on the immune response in humans., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Partida-Rodríguez et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Protein tyrosine kinase 6 (PTK6) is an intracellular tyrosine kinase that is distantly related to the SRC family of tyrosine kinases. It is expressed in epithelial linings and regulates regeneration and repair of the intestinal epithelium. Analysis of publicly available datasets showed Ptk6 is upregulated in tuft cells upon activation of type 2 immunity. We found that disruption of Ptk6 influences gene expression involved in intestinal immune responses. Administration of succinate, which mimics infection and activates tuft cells, revealed PTK6-dependent activation of innate immune responses in male but not female mice. In contrast to all wild type and Ptk6-/- female mice, Ptk6-/- male mice do not activate innate immunity or upregulate differentiation of the tuft and goblet secretory cell lineages following succinate treatment. Mechanistically, we found that PTK6 regulates Il25 and Irag2, genes that are required for tuft cell effector functions and activation of type 2 innate immunity, in organoids derived from intestines of male but not female mice. In patients with Crohn's disease, PTK6 is upregulated in tuft cells in noninflamed regions of intestine. These data highlight roles for PTK6 in contributing to sex differences in intestinal innate immunity and provide new insights into the regulation of IL-25., (© 2024. The Author(s).)

Background: It has been previously demonstrated that intestinal barrier damage is one of the underlying mechanisms leading to frailty in non-HIV-infected aging populations. However, there is a paucity of direct evidence which demonstrates the association between intestinal barrier damage and frailty in people living with HIV (PLWH)., Methods: The present study is a retrospective case control study. Participants older than 50 years old were stratified into a frail/pre-frail group (case group) and non-frail group (control group) according to the Fried frailty phenotype. We collected and curated data concerning socio-demographic variables, psychological states and social functioning, and clinical information associated with the identification of biomarkers of intestinal barrier damage, microbial translocation, and levels of inflammatory cytokines of participants., Results: The case group had significantly higher levels of Reg-3α ( p =0.042) and I-FABP ( p =0.045) compared to the control group. We further observed, after adjusting for confounding factors by logistic regression analysis, that I-FABP levels remained significantly higher in the case group compared to the control group ( p =0.033). Also, Fried Phenotype scores positively correlated with I-FABP levels (r s =0.21, p =0.01), LPS levels (r s =0.20, p =0.02), and sCD14 levels (r s =0.18, p =0.04). Moreover, the study confirmed both the positive correlation between inflammatory cytokines (IL-6 and IP-10) with frailty in aging PLWH, and between inflammatory cytokines (IL-6, IL-8 and IP-10) with biomarkers of intestinal barrier dysfunction in older PLWH., Conclusion: The present study indicates that the inflammation induced by intestinal barrier damage/dysfunction is likely to contribute to frailty in aging PLWH., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Xu, Ouyang, Yan, Lu, Harypursat, Wu and Chen.)

Background: Inflammatory bowel disease (IBD) is a refractory inflammatory disorder of the intestine, which is probably triggered by dysfunction of the intestinal epithelial barrier. Secretory leukocyte protease inhibitor (SLPI) secreted by colon epithelial cells protects against intestinal inflammation by exerting anti-protease and anti-microbial activities. Daikenchuto (DKT) is one of the most commonly prescribed Japanese traditional herbal medicines for various digestive diseases. Although several animal studies have revealed that DKT exerts anti-inflammatory effects, its detailed molecular mechanism is unclear. This study aimed to clarify the anti-inflammatory mechanism of DKT using a murine colitis model, and to evaluate its potential as a therapeutic agent for IBD., Methods: Experimental colitis was induced in wild-type (WT) mice and SLPI-deficient (KO) mice by dextran sulfate sodium (DSS) after oral administration of DKT. The resultant clinical symptoms, histological changes, and pro-inflammatory cytokine levels in the colon were assessed. Expression of SLPI in the colon was detected by Western blotting and immunohistochemistry. Composition of the gut microbiota was analyzed by 16S rRNA metagenome sequencing and intestinal metabolites were measured by gas chromatography-mass spectrometry analysis. Intestinal epithelial barrier function was assessed by oral administration of FITC-dextran and immunostaining of tight junction proteins (TJPs)., Results: Oral administration of DKT increased the number of butyrate-producing bacteria, such as Parabacteroides , Allobaculum , and Akkermansia , enhanced the levels of short-chain fatty acids, including butyrate, in the colon, induced SLPI expression, and ameliorated DSS-induced colitis in WT mice. We found that mouse colon carcinoma cell line treatment with either DKT or butyrate significantly enhanced the expression of SLPI. Moreover, supplementation of DKT protected the intestinal epithelial barrier with augmented expression of TJPs in WT mice, but not in KO mice. Finally, the composition of the gut microbiota was changed by DKT in WT mice, but not in KO mice, suggesting that DKT alters the colonic bacterial community in an SLPI-dependent manner., Conclusion: These results indicate that DKT exerts anti-inflammatory effects on the intestinal epithelial barrier by SLPI induction, due, at least in part, to increased butyrate-producing bacteria and enhanced butyrate levels in the colon. These results provide insight into the mechanism of the therapeutic effects of DKT on IBD., Competing Interests: Authors SI and MN were employed by the company Tsumura & Co. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare that this study received funding from Tsumura & Co. The funder had the following involvement in the study: analysis of the gut microbiota., (Copyright © 2024 Ozaka, Sonoda, Kudo, Ito, Kamiyama, Sachi, Chalalai, Kagoshima, Soga, Ekronarongchai, Ariki, Mizukami, Ishizawa, Nishiyama, Murakami, Takeda and Kobayashi.)

Serotonergic neurons in the central nervous system control behavior and mood, but knowledge of the roles of serotonergic circuits in the regulation of immune homeostasis is limited. Here, we employ mouse genetics to investigate the functions of enteric serotonergic neurons in the control of immune responses and find that these circuits regulate IgA induction and boost host defense against oral, but not systemic Salmonella Typhimurium infection. Enteric serotonergic neurons promote gut-homing, retention and activation of intestinal plasmacytoid dendritic cells (pDC). Mechanistically, this neuro-immune crosstalk is achieved through a serotonin-5-HT receptor 7 (HTR7) signaling axis that ultimately facilitates the pDC-mediated differentiation of IgA + B cells from IgD + precursors in the gut. Single-cell RNA-seq data further reveal novel patterns of bidirectional communication between specific subsets of enteric neurons and lamina propria DC. Our findings thus reveal a close interplay between enteric serotonergic neurons and gut immune homeostasis that enhances mucosal defense., (© 2024. The Author(s).)

Gastrointestinal (GI) B cells and plasma cells (PCs) are critical to mucosal homeostasis and the host response to HIV-1 infection. Here, high-resolution mapping of human B cells and PCs sampled from the colon and ileum during both viremic and suppressed HIV-1 infection identified a reduction in germinal center (GC) B cells and follicular dendritic cells (FDCs) during HIV-1 viremia. Immunoglobulin A-positive (IgA + ) PCs are the major cellular output of intestinal GCs and were significantly reduced during viremic HIV-1 infection. PC-associated transcriptional perturbations, including type I interferon signaling, persisted in antiretroviral therapy (ART)-treated individuals, suggesting ongoing disruption of the intestinal immune milieu during ART. GI humoral immune perturbations were associated with changes in the intestinal microbiome composition and systemic inflammation. These findings highlight a key immune defect in the GI mucosa due to HIV-1 viremia.

Background: Exosomes derived from endometrial regenerative cells (ERC-Exos) can inherit the immunomodulatory function from ERCs, however, whether ERC-Exos exhibit such effect on inflammatory bowel diseases with mucosal immune dysregulation has not been explored. Insulin-like growth factor-Ⅱ (IGF2) is considered to possess the potential to induce an anti-inflammatory phenotype in immune cells. In this study, the contribution of IGF2 in mediating the protective efficacy of ERC-Exos on colitis was investigated., Methods: Lentiviral transfection was employed to obtain IGF2-specific knockout ERC-Exos (IGF2 -/- -ERC-Exos). Experimental colitis mice induced by dextran sulfate sodium (DSS) were divided into the phosphate-buffered saline (untreated), ERC-Exos-treated and IGF2 -/- -ERC-Exos-treated groups. Colonic histopathological analysis and intestinal barrier function were explored. The infiltration of CD4 + T cells and dendritic cells (DCs) were analyzed by immunofluorescence staining and flow cytometry. The maturation and function of bone marrow-derived dendritic cells (BMDCs) in different exosome administrations were evaluated by flow cytometry, ELISA and the coculture system, respectively., Results: Compared with the untreated group, ERC-Exos treatment significantly attenuated DSS-induced weight loss, bloody stools, shortened colon length, pathological damage, as well as repaired the weakened intestinal mucosal barrier, including promoting the goblet cells retention, restoring the intestinal barrier integrity and enhancing the expression of tight junction proteins, while the protective effect of exosomes was impaired with the knockout of IGF2 in ERC-Exos. Additionally, IGF2-expressing ERC-Exos decreased the proportions of Th1 and Th17, increased the proportions of Treg, as well as attenuated DC infiltration and maturation in mesenteric lymph nodes and lamina propria of the colitis mice. ERC-Exos were also observed to be phagocytosed by BMDCs and IGF2 is responsible for the modulating effect of ERC-Exos on BMDCs in vitro., Conclusions: Exosomes derived from ERCs can exert a therapeutic effect on experimental colitis with remarkable alleviation of the intestinal barrier damage and the abnormal mucosal immune responses. We emphasized that IGF2 plays a critical role for ERC-Exos mediated immunomodulatory function and protection against colitis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Dihydromyricetin (DMY), a natural flavonoid compound, are believed to prevent inflammatory response, dealing with pathogens and repairing the intestinal barrier. The objective of this study was to investigate whether DMY supplementation could attenuate intestinal damage in the context of enterotoxigenic Escherichia coli K88 (ETEC F4 + ) infection. After weaning, different litters of pigs were randomly assigned to one of the following treatments: (1) non-challenged control (CON, fed with basal diet); (2) ETEC-challenged control (ECON, fed with basal diet); and (3) ETEC challenge + DMY treatment (EDMY, fed with basal diet plus 300 mg kg -1 DMY). We observed a significant reduction in fecal Escherichia coli shedding and diarrhea incidence, but an increase in ADG in pigs of EDMY group compared to the pigs of ECON group. Relative to the pigs of ECON group, dietary DMY treatment decreased (P < 0.05) concentrations of the serum D-xylose, D-lactate and diamine oxidase (DAO), but increased the abundance of zonula occludens-1 (ZO-1) in the jejunum of pigs. In addition, DMY also decreased (P < 0.05) the number of S-phase cells and the percentage of total apoptotic epithelial cells of jejunal epithelium in pigs of the EDMY group compared to the pigs of the ECON group. Furthermore, DMY decreased the mRNA expression levels of critical immune-associated genes TLR4, NFκB, Caspase3, Caspase9, IL-1β, IL-6, TNF-α and the protein p-NFκB and p-IκBα expressions of intestinal epithelium in pigs of the EDMY group compared to the pigs of the ECON group. Compared to the ECON group, DMY elevated (P < 0.05) the expression levels of β-defensins PBD1, PBD2, PBD3, PBD129, as well as the abundance of secreted IgA in intestinal mucosae of the EDMY group. Thus, our results indicate that DMY may relieve intestinal integrity damage due to Escherichia coli F4., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Dendritic cells (DCs) are crucial for initiating protective immune responses and have also been implicated in the generation and regulation of Foxp3 + regulatory T cells (Treg cells). Here, we show that in the lamina propria of the small intestine, the alternative NF-κB family member RelB is necessary for the differentiation of cryptopatch and isolated lymphoid follicle-associated DCs (CIA-DCs). Moreover, single-cell RNA sequencing reveals a RelB-dependent signature in migratory DCs in mesenteric lymph nodes favoring DC-Treg cell interaction including elevated expression and release of the chemokine CCL22 from RelB-deficient conventional DCs (cDCs). In line with the key role of CCL22 to facilitate DC-Treg cell interaction, RelB-deficient DCs have a selective advantage to interact with Treg cells in an antigen-specific manner. In addition, DC-specific RelB knockout animals show increased total Foxp3 + Treg cell numbers irrespective of inflammatory status. Consequently, DC-specific RelB knockout animals fail to mount protective Th2-dominated immune responses in the intestine after infection with Heligmosomoides polygyrus bakeri. Thus, RelB expression in cDCs acts as a rheostat to establish a tolerogenic set point that is maintained even during strong type 2 immune conditions and thereby is a key regulator of intestinal homeostasis., (© 2024. The Author(s).)

SARS-CoV-2 infects via the respiratory tract, but COVID-19 includes an array of non-respiratory symptoms, among them gastrointestinal (GI) manifestations such as vomiting and diarrhea. Here we investigated the GI pathology of SARS-CoV-2 infections in rhesus macaques and humans. Macaques experienced mild infection with USA-WA1/2020 and shed viral RNA in the respiratory tract and stool, including subgenomic RNA indicative of replication in the GI tract. Intestinal immune cell populations were disturbed, with significantly fewer proliferating (Ki67+) jejunal B cells in SARS-CoV-2-infected macaques than uninfected ones. Modest translocation of bacteria/bacterial antigen was observed across the colonic epithelium, with a corresponding significant increase in plasma soluble CD14 (sCD14) that may be induced by LPS. Human plasma demonstrated significant decreases in interleukin (IL)-6 and sCD14 upon recovery from COVID-19, suggesting resolution of inflammation and response to translocated bacteria. sCD14 significantly positively correlated with zonulin, an indicator of gut barrier integrity, and IL-6. These results demonstrate that GI perturbations such as microbial translocation can occur in even mild SARS-CoV-2 infections and may contribute to the COVID-19 inflammatory state.IMPORTANCEThis study investigates gastrointestinal (GI) barrier disruption in SARS-CoV-2 infections and how it may contribute to disease. We observed bacteria or bacterial products crossing from the colon interior (the lumen) to the lamina propria during SARS-CoV-2 infection in macaques. Bacteria/bacterial products are tolerated in the lumen but may induce immune responses if they translocate to the lamina propria. We also observed a significant increase in soluble CD14, which is associated with an immune response to bacterial products. In addition, we observed that humans recovering from COVID-19 experienced a significant decrease in soluble CD14, as well as the inflammatory marker interleukin (IL)-6. IL-6 and sCD14 correlated significantly across macaque and human samples. These findings suggest that SARS-CoV-2 infection results in GI barrier disruption that permits microbial translocation and a corresponding immune response. These findings could aid in developing interventions to improve COVID-19 patient outcomes., Competing Interests: The authors declare no conflict of interest.

In patients with rheumatoid arthritis (RA), intestinal flora imbalance and butyrate metabolism disorders precede clinical arthritis and are associated with the pathogenesis of RA. This imbalance can alter the immunology and intestinal permeability of the intestinal mucosa, leading to damage to the intestinal barrier. In this context, bacteria and their metabolites can enter the bloodstream and reach the distant target tissues of the host, resulting in local inflammation and aggravating arthritis. Additionally, arthritis is also exacerbated by bone destruction and immune tolerance due to disturbed differentiation of osteoclasts and adaptive immune cells. Of note, butyrate is a metabolite of intestinal flora, which not only locally inhibits intestinal immunity and targets zonulin and tight junction proteins to alleviate intestinal barrier-mediated arthritis but also inhibits osteoclasts and autoantibodies and balances the immune responses of T and B lymphocytes throughout the body to repress bone erosion and inflammation. Therefore, butyrate is a key intermediate linking intestinal flora to the host. As a result, restoring the butyrate-producing capacity of intestinal flora and using exogenous butyrate are potential therapeutic strategies for RA in the future., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Cao, Chen, Xiao, Hong, Xu and Zhu.)

Introduction: The maintenance of intestinal homeostasis depends on a complex interaction between the immune system, intestinal epithelial barrier, and microbiota. Alteration in one of these components could lead to the development of inflammatory bowel diseases (IBD). Variants within the autophagy gene ATG16L1 have been implicated in susceptibility and severity of Crohn's disease (CD). Individuals carrying the risk ATG16L1 T300A variant have higher caspase 3-dependent degradation of ATG16L1 resulting in impaired autophagy and increased cellular stress. ATG16L1-deficiency induces enhanced IL-1β secretion in dendritic cells in response to bacterial infection. Infection of ATG16L1-deficient mice with a persistent strain of murine norovirus renders these mice highly susceptible to dextran sulfate sodium colitis. Moreover, persistent norovirus infection leads to intestinal virus specific CD8 + T cells responses. Both Toll-like receptor 7 (TLR7), which recognizes single-stranded RNA viruses, and ATG16L1, which facilitates the delivery of viral nucleic acids to the autolysosome endosome, are required for anti-viral immune responses., Results and Discussion: However, the role of the enteric virome in IBD is still poorly understood. Here, we investigate the role of TLR7 and ATG16L1 in intestinal homeostasis and inflammation. At steady state, Tlr7 -/- mice have a significant increase in large intestinal lamina propria (LP) granzyme B + tissue-resident memory CD8 + T (T RM ) cells compared to WT mice, reminiscent of persistent norovirus infection. Deletion of Atg16l1 in myeloid ( Atg16l1 ΔLyz2 ) or dendritic cells ( Atg16l1 ΔCd11c ) leads to a similar increase of LP T RM . Furthermore, Tlr7 -/- and Atg16l1 ΔCd11c mice were more susceptible to dextran sulfate sodium colitis with an increase in disease activity index, histoscore, and increased secretion of IFN-γ and TNF-α. Treatment of Atg16l1 ΔCd11c mice with the TLR7 agonist Imiquimod attenuated colonic inflammation in these mice. Our data demonstrate that ATG16L1-deficiency in myeloid and dendritic cells leads to an increase in LP T RM and consequently to increased susceptibility to colitis by impairing the recognition of enteric viruses by TLR7., Conclusion: In conclusion, the convergence of ATG16L1 and TLR7 signaling pathways plays an important role in the immune response to intestinal viruses. Our data suggest that activation of the TLR7 signaling pathway could be an attractive therapeutic target for CD patients with ATG16L1 risk variants., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hamade, Tsuda, Oshima, Stamps, Wong, Stamps, Thomas, Salumbides, Jin, Nunnelee, Dhall, Targan and Michelsen.)

Background/objectives: Cow's milk allergy is one of the most common food allergies in children, and its pathomechanism is still under investigation. Recently, an increasing number of studies have linked food allergy to intestinal barrier dysfunction. The present study aimed to investigate changes in the intestinal microenvironment during the development of β -lactoglobulin ( β -lg) allergy under conditions of early intestinal dysfunction., Methods: BALB/c mice received intraperitoneal β -lg with Freund's adjuvant, followed by oral β -lg while receiving dextran sulphate sodium salt (DSS) in their drinking water (0.2% w / v ). The immunized group without DSS and the groups receiving saline, oral β -lg, or DSS served as controls., Results: The study showed that the immunization effect was greater in mice with mild intestinal barrier dysfunction. Although DSS did not affect the mice's humoral response to β -lg, in combination with β -lg, it significantly altered their cellular response, affecting the induction and distribution of T cells in the inductive and peripheral tissues and the activation of immune mediators. Administration of β -lg to sensitized mice receiving DSS increased disease activity index (DAI) scores and pro-inflammatory cytokine activity, altered the distribution of claudins and zonulin 1 (ZO-1) in the colonic tissue, and negatively affected the balance and activity of the gut microbiota., Conclusions: The research model used appears attractive for studying food allergen sensitization, particularly in relation to the initial events leading to mucosal inflammation and the development of food hypersensitivity.

In the mucosa, T cells and B cells of the immune system are essential for maintaining immune homeostasis by suppressing reactions to harmless antigens and upholding the integrity of intestinal mucosal barrier functions. Host immunity and homeostasis are regulated by metabolites produced by the gut microbiota, which has developed through the long-term coevolution of the host and the gut biome. This is achieved by the immunological system's tolerance for symbiote microbiota, and its ability to generate a proinflammatory response against invasive organisms. The imbalance of the intestinal immune system with commensal organisms is causing a disturbance in the homeostasis of the gut microbiome. The lack of balance results in microbiota dysbiosis, the weakened integrity of the gut barrier, and the development of inflammatory immune reactions toward symbiotic organisms. Researchers may uncover potential therapeutic targets for preventing or regulating inflammatory diseases by understanding the interactions between adaptive immunity and the microbiota. This discussion will explore the connection between adaptive immunity and microbiota., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest, (Copyright © 2024 Heidari, Maleki Vareki, Yaghobi and Karimi.)

Paneth cells located within intestinal crypts support epithelial stem cells and immunity through growth factors and antimicrobial peptides. In this issue of Cell Host & Microbe, Wallaeys et al. report that TNF sensing by Paneth cells disrupts the unfolded protein response and decreases antimicrobial peptides, causing bacterial translocation and sepsis., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Microbiota and feeding modes influence the susceptibility of premature newborns to necrotizing enterocolitis (NEC) through mechanisms that remain unknown. Here, we show that microbiota colonization facilitated by breastmilk feeding promotes NOD-like receptor family CARD domain containing 5 (Nlrc5) gene expression in mouse intestinal epithelial cells (IECs). Notably, inducible knockout of the Nlrc5 gene in IECs predisposes neonatal mice to NEC-like injury in the small intestine upon viral inflammation in an NK1.1 + cell-dependent manner. By contrast, formula feeding enhances neonatal gut colonization with environment-derived tilivalline-producing Klebsiella spp. Remarkably, tilivalline disrupts microbiota-activated STAT1 signaling that controls Nlrc5 gene expression in IECs through a PPAR-γ-mediated mechanism. Consequently, this dysregulation hinders the resistance of neonatal intestinal epithelium to self-NK1.1 + cell cytotoxicity upon virus infection/colonization, promoting NEC development. Together, we discover the underappreciated role of intestinal microbiota colonization in shaping a disease tolerance program to viral inflammation and elucidate the mechanisms impacting NEC development in neonates., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The immune system recognizes a multitude of innocuous antigens from food and intestinal commensal microbes toward which it orchestrates appropriate, non-inflammatory responses. This process requires antigen-presenting cells (APCs) that induce T cells with either regulatory or effector functions. Compromised APC function disrupts the T cell balance, leading to inflammation and dysbiosis. Although their precise identities continue to be debated, it has become clear that multiple APC lineages direct the differentiation of distinct microbiota-specific CD4 + T cell programs. Here, we review how unique APC subsets instruct T cell differentiation and function in response to microbiota and dietary antigens. These discoveries provide new opportunities to investigate T cell-APC regulatory networks controlling immune homeostasis and perturbations associated with inflammatory and allergic diseases., Competing Interests: Declaration of interests D.R.L. consults for and has equity interest in Vedanta Bioscience, Sonoma Immunotherapeutics, Immunai, and IMIDomics, and is a Director of Pfizer, Inc., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Toll/interleukin-1/resistance (TIR)-domain proteins with enzymatic activity are essential for immunity in plants, animals, and bacteria. However, it is not known how these proteins function in pathogen sensing in animals. We discovered that the lone enzymatic TIR-domain protein in the nematode C. elegans (TIR-1, homolog of mammalian sterile alpha and TIR motif-containing 1 [SARM1]) was strategically expressed on the membranes of a specific intracellular compartment called lysosome-related organelles. The positioning of TIR-1 on lysosome-related organelles enables intestinal epithelial cells in the nematode C. elegans to survey for pathogen effector-triggered host damage. A virulence effector secreted by the bacterial pathogen Pseudomonas aeruginosa alkalinized and condensed lysosome-related organelles. This pathogen-induced morphological change in lysosome-related organelles triggered TIR-1 multimerization, which engaged its intrinsic NAD + hydrolase (NADase) activity to activate the p38 innate immune pathway and protect the host against microbial intoxication. Thus, TIR-1 is a guard protein in an effector-triggered immune response, which enables intestinal epithelial cells to survey for pathogen-induced host damage., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Intraepithelial lymphocytes (IELs) reside in the epithelial layer and protect against foreign pathogens, maintaining the epithelial barrier function in the intestine. Interactions between IEL and epithelial cells are required for IELs to function effectively; however, the underlying molecular machinery remains to be elucidated. In this study, we found that intestinal epithelium-specific deficiency of the clathrin adaptor protein (AP)-1B, which regulates basolateral protein sorting, led to a massive reduction in IELs. Quantitative proteomics demonstrated that dozens of proteins, including known IEL-interacting proteins (E-cadherin, butyrophilin-like 2, and plexin B2), were decreased in the basolateral membrane of AP-1B-deficient epithelial cells. Among these proteins, CD166 interacted with CD6 on the surface of induced IEL. CD166 knockdown, using shRNA in intestinal organoid cultures, significantly inhibited IEL recruitment to the epithelial layer. These findings highlight the essential role of AP-1B-mediated basolateral sorting in IEL maintenance and survival within the epithelial layer. This study reveals a novel function of AP-1B in the intestinal immune system., (© 2024. The Author(s).)

Malnutrition is linked to 45% of global childhood mortality, however, the impact of maternal malnutrition on the child's health remains elusive. Previous studies suggested that maternal malnutrition does not affect breast milk composition. Yet, malnourished children often develop a so-called environmental enteropathy, assumed to be triggered by frequent pathogen uptake and unfavorable gut colonization. Here, we show in a murine model that maternal malnutrition induces a persistent inflammatory gut dysfunction in the offspring that establishes during nursing and does not recover after weaning onto standard diet. Early intestinal influx of neutrophils, impaired postnatal development of gut-regulatory functions, and expansion of Enterobacteriaceae were hallmarks of this enteropathy. This gut phenotype resembled those developing under deficient S100a8/a9-supply via breast milk, which is a known key factor for the postnatal development of gut homeostasis. We could confirm that S100a8/a9 is lacking in the breast milk of malnourished mothers and the offspring's intestine. Nutritional supply of S100a8 to neonates of malnourished mothers abrogated the aberrant development of gut mucosal immunity and microbiota colonization and protected them lifelong against severe enteric infections and non-infectious bowel diseases. S100a8 supplementation after birth might be a promising measure to counteract deleterious imprinting of gut immunity by maternal malnutrition., (© 2024. The Author(s).)

The gut microbiota, a pivotal component of the intestinal mucosal barrier, is critical for host resistance to enteric pathogen infection. Here, we report a novel function of the potentially probiotic Lactococcus garvieae strain LG1 ( L. garvieae strain LG1) in maintaining intestinal mucosal barrier integrity and protecting against foodborne Clostridium perfringens ( C. perfringens ) infection. L. garvieae was isolated from the intestinal contents of Chinese Mongolian sheep (MS) and exhibited potential probiotic properties. In a C. perfringens enterocolitis model, L. garvieae- pretreated mice were less susceptible to C. perfringens infection compared with Phosphate buffered solution (PBS) - pretreated mice, which manifested as higher survival rates, lower pathogen loads, less weight loss, mild clinical symptoms and intestinal damage, and minor inflammation. Further mechanistic analysis showed that L. garvieae could ameliorate the disruption of intestinal permeability and maintain the integrity of the intestinal mucosal barrier by promoting the expression of tight junction proteins and mucoproteins. Moreover, L. garvieae was also able to facilitate antimicrobial peptide expression and ameliorate dysbiosis of the gut microbiota caused by C. perfringens . Together, these findings highlight the prospect of immunomodulatory potentially probiotic L. garvieae and might offer valuable strategies for prophylaxis and/or treatment of pathogenic C. perfringens mucosal infection., Importance: C. perfringens necrotic enteritis leads to losses of about US $2 billion to the poultry industry worldwide every year. Worse, US Centers for Disease Control and Prevention (CDC) has estimated that C. perfringens causes nearly 1 million foodborne illnesses in the United States annually. Nowadays, the treatment recommendation is a combination of a broad-spectrum synergistic penicillin with clindamycin or a carbapenem, despite growing scientific concern over antibiotic resistance. The global understanding of the gut microbiome for C. perfringens infection may provide important insights into the intervention. L. garvieae originated from Mongolian sheep intestine, exhibited potentially probiotic properties, and was able to limit C. perfringens enterocolitis and pathogenic colonization. Importantly, we found that L. garvieae limits C. perfringens invasion via improving intestinal mucosal barrier function. Also, L. garvieae alleviates C. perfringens -induced gut microbiota dysbiosis. It allowed us to convince that utilization of probiotics to promote protective immunity against pathogens infection is of pivotal importance., Competing Interests: The authors declare no conflict of interest.

Astragali Radix (AS) is a widely used herb in traditional Chinese medicine, with calycosin as its main isoflavonoid. Our previous study discovered that calycosin triggers host defense peptide (HDP) production in IPEC-J2 cells. The aim of this study is to investigate the alleviation effects of AS total flavone and AS calycosin on growth performance, intestinal immunity, and microflora in weaned piglets. Sixty-four piglets were assigned randomly to 4 treatment groups, (1) CON: the basal diet, (2) P-CON: the basal diet plus antibiotics (1 g/kg), (3) AS-TF: the basal diet plus AS total flavone at 60 mg/day per piglet, (4) AS-CA: the basal diet plus AS calycosin at 30 mg/day per piglet. Each treatment consists of 4 replicates with 4 piglets per replicate. Results showed that treatment with AS-TF and AS-CA enhanced average daily growth and average daily feed intake compared to the CON group ( P < 0.01), while AS-CA significantly reduced the diarrhea rate ( P < 0.05). Both AS-TF and AS-CA significantly increased serum immunoglobulin (Ig) A and IgG levels, with AS-CA further boosting intestinal mucosal secretory IgA levels ( P < 0.05). Histological analysis revealed improvements in the morphology of the jejunum and ileum and goblet cell count by AS-TF and AS-CA ( P < 0.05). Supplementation of AS-TF and AS-CA promoted the expression of several intestinal HDPs ( P < 0.05), and the effect of AS-CA was better than that of AS-TF. In addition, the AS-TF and AS-CA regulated jejunal microbial diversity and composition, with certain differential bacteria genera were showing high correlation with serum cytokines and immunoglobulin levels, suggesting that the intestinal flora affected by AS-TF and AS-CA may contribute to host immunity. Overall, AS CA and AS TF all improved growth performance and health, likely by enhancing nutrition digestibility, serum and intestinal immunity, and intestinal microbial composition. They showed the similar beneficial effect, indicating AS CA appears to be a major compound contributing to the effects of AS TF. This study demonstrated the positive effect of AS flavonoids on weaned piglets and provided a scientific reference for the efficient use of AS products., Competing Interests: Author LD was employed by the company Feed Branch of Beijing Sanyuan Breeding Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Che, Li, Kong, Geng, Wang, Li, Deng, Chen and Wang.)

The gut microbiota exerts a significant influence on human health and disease. While compositional changes in the gut microbiota in specific diseases can easily be determined, we lack a detailed mechanistic understanding of how these changes exert effects at the cellular level. However, the putative local and systemic effects on human physiology that are attributed to the gut microbiota are clearly being mediated through molecular communication. Here, we determined the effects of gut microbiome-derived metabolites l-tryptophan, butyrate, trimethylamine (TMA), 3-methyl-4-(trimethylammonio)butanoate (3,4-TMAB), 4-(trimethylammonio)pentanoate (4-TMAP), ursodeoxycholic acid (UDCA), glycocholic acid (GCA) and benzoate on the first line of defence in the gut. Using in vitro models of intestinal barrier integrity and studying the interaction of macrophages with pathogenic and non-pathogenic bacteria, we could ascertain the influence of these metabolites at the cellular level at physiologically relevant concentrations. Nearly all metabolites exerted positive effects on barrier function, but butyrate prevented a reduction in transepithelial resistance in the presence of the pathogen Escherichia coli , despite inducing increased apoptosis and exerting increased cytotoxicity. Induction of IL-8 was unaffected by all metabolites, but GCA stimulated increased intra-macrophage growth of E. coli and tumour necrosis-alpha (TNF-α) release. Butyrate, 3,4-TMAB and benzoate all increased TNF-α release independent of bacterial replication. These findings reiterate the complexity of understanding microbiome effects on host physiology and underline that microbiome metabolites are crucial mediators of barrier function and the innate response to infection. Understanding these metabolites at the cellular level will allow us to move towards a better mechanistic understanding of microbiome influence over host physiology, a crucial step in advancing microbiome research.

Innate immune cells have been acknowledged as trainable in recent years. While intestinal tuft cells are recognized for their crucial roles in the host defense against intestinal pathogens, there remains uncertainty regarding their trainability. Enterovirus 71 (EV71), a prevalent enterovirus that primarily infects children but rarely infects adults. At present, there is a significant expansion of intestinal tuft cells in the EV71-infected mouse model, which is associated with EV71-induced interleukin-25 (IL-25) production. Further, we found that IL-25 pre-treatment at 2 weeks old mouse enabled tuft cells to acquire immune memory. This was evidenced by the rapid expansion and stronger response of IL-25-trained tuft cells in response to EV71 infection at 6 weeks old, surpassing the reactivity of naïve tuft cells in mice without IL-25-trained progress. Interestingly, IL-25-trained intestinal tuft cells exhibit anti-enteroviral effect via producing a higher level of IL-25. Mechanically, IL-25 treatment upregulates spermidine/spermine acetyl-transferase enzyme (SAT1) expression, mediates intracellular polyamine deficiency, further inhibits enterovirus replication. In summary, tuft cells can be trained by IL-25, which supports faster and higher level IL-25 production in response to EV71 infection and further exhibits anti-enteroviral effect via SAT1-mediated intracellular polyamine deficiency. Given that IL-25 can be induced by multiple gut microbes during human growth and development, including shifts in gut flora abundance, which may partially explain the different susceptibility to enteroviral infections between adults and children., (© 2024. The Author(s).)

Dietary proteins are taken up by intestinal dendritic cells (DCs), cleaved into peptides, loaded to major histocompatibility complexes, and presented to T cells to generate an immune response. Amino acid (AA)-diets do not have the same effects because AAs cannot bind to major histocompatibility complex to activate T cells. Here, we show that impairment in regulatory T cell generation and loss of tolerance in mice fed a diet lacking whole protein is associated with major transcriptional changes in intestinal DCs including downregulation of genes related to DC maturation, activation and decreased gene expression of immune checkpoint molecules. Moreover, the AA-diet had a profound effect on microbiome composition, including an increase in Akkermansia muciniphilia and Oscillibacter and a decrease in Lactococcus lactis and Bifidobacterium. Although microbiome transfer experiments showed that AA-driven microbiome modulates intestinal DC gene expression, most of the unique transcriptional change in DC was linked to the absence of whole protein in the diet. Our findings highlight the importance of dietary proteins for intestinal DC function and mucosal tolerance., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Being the first line of defense, intestinal mucosal immunity serves as in maintaining immune homeostasis among organisms. This study investigated the impact of the areca inflorescence polysaccharide (AFP) on intestinal mucosal immunity and elucidated the mechanisms responsible for the immunomodulatory effects of AFP. The immunosuppression mouse model was established using the cyclophosphamide. The intestinal mucosal status was evaluated based on the intestinal integrity, chemical and mucosal immune barriers, and intestinal flora. According to the findings, AFP enhances intestinal integrity by up-regulating the expression of tight junction proteins and reinforcing the chemical barrier through increased mucin-2, β-defensins, and SIgA expression and secretion. Furthermore, AFP restores the mucosal immune barrier by regulating immune cells within Peyer's patches and lamina propria. AFP also reverses the intestinal flora balance and regulates its metabolism. Additionally, AFP effectively modulates the immune response in the spleen and peripheral blood. Together, these results indicated that AFP repairs mucosal damage and restores mucosal immunity, thereby preserving the immune homeostasis of organisms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study aimed to investigate whether bergapten (BG), a furanocoumarin phytohormone, holds promise for Crohn's disease (CD)-like colitis treatment and to preliminarily explore its potential mechanisms. 2,4,6-Trinitrobenzenesufonic acid (TNBS)-treated mice were applied to establish an in vivo research model, and BG was administered with different concentrations. The status of mice in each group was evaluated by disease activity index (DAI), and the severity was evaluated by pathological sections. The intestinal barrier was assessed by measuring in vivo intestinal permeability, peripheral blood intestinal fatty acid-binding protein (I-FABP) levels, epithelial resistance values, and tight junction protein levels. Markers were then used to assess Th17/Treg levels, mitophagy, and the peroxisome proliferator-activated receptor (PPAR)γ/ nuclear factor kappa B (NF-κB) signaling pathway. BG significantly reduced colon tissue damage in a concentration-dependent manner. DAI scores showed that the loose feces, occult blood, and weight loss of mice in the BG treatment were significantly reduced, and pathological section results revealed reduced inflammatory infiltration and fibrosis. Reduced serum FITC-dextran and I-FABP and increased levels of epithelial resistance and tight junction proteins support that the intestinal barrier was protected upon BG. The proportion of Th17 in mesenteric lymph nodes increased while Treg decreased in the model group. BG treatment effectively reduced the conversion of Treg to Th17. Additionally, BG was found to enhance mitophagy and activate the PPARγ/NF-κB signaling. BG demonstrates promising effects in ameliorating intestinal barrier damage and Th17/Treg imbalance in a murine model of CD-like colitis, while also promoting intracellular mitophagy. The PPARγ/NF-κB signaling pathway may serve as a key mediator of BG's regulatory mechanisms., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease in preterm infants and the most common cause of neonatal death, whereas the molecular mechanism of intestinal injury remains unclear accompanied by deficiency of effective therapeutic approaches. GIT2 (G-protein-coupled receptor kinase interacting proteins 2) can affect innate and adaptive immunity and has been involved in multiple inflammatory disorders. In this study, we investigated whether GIT2 participates in the pathogenesis of NEC. Here we found that intestinal Git2 gene expression was significantly increased in NEC patients and NEC mice, which positively correlated with the tissue damage severity, and Git2 deficiency could potently protect against NEC development in mice. Mechanistically, Git2 gene knockout dramatically increased the recruitment of MDSCs in the intestine, and in vivo depletion of MDSCs almost completely abrogated the protective effect of Git2 deficiency on NEC. Moreover, Git2 deficiency induced MDSCs intestinal accumulation mainly relied on CXCL1/CXCL12 signaling, as evidenced by the significant increment of CXCL1 and CXCL12 levels in intestinal epithelium of Git2 -/- mice and dramatically decrease of MDSCs accumulation in intestine as well as increase of NEC severity upon treatment of CXCL1/CXCL12 pathway inhibitors. In addition, Git2 deficiency induced up-regulation of CXCL1 and CXCL12 is at least partially mediated through activating NF-κB signaling. Thus, our findings suggest that GIT2 is involved in the pathogenesis of NEC, and targeting GIT2 may be a potential preventive and therapeutic approach for NEC., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The prevalence of obesity in the United States has continued to increase over the past several decades. Understanding how diet-induced obesity modulates mucosal immunity is of clinical relevance. We previously showed that consumption of a high fat, high sugar "Western" diet (WD) reduces the density and function of small intestinal Paneth cells, a small intestinal epithelial cell type with innate immune function. We hypothesized that obesity could also result in repressed gut adaptive immunity. Using small intestinal intraepithelial lymphocytes (IEL) as a readout, we found that in non-inflammatory bowel disease (IBD) subjects, high body mass index correlated with reduced IEL density. We recapitulated this in wild type (WT) mice fed with WD. A 4-week WD consumption was able to reduce IEL but not splenic, blood, or bone marrow lymphocytes, and the effect was reversible after another 2 weeks of standard diet (SD) washout. Importantly, WD-associated IEL reduction was not dependent on the presence of gut microbiota, as WD-fed germ-free mice also showed IEL reduction. We further found that WD-mediated Farnesoid X Receptor (FXR) activation in the gut triggered IEL reduction, and this was partially mediated by intestinal phagocytes. Activated FXR signaling stimulated phagocytes to secrete type I IFN, and inhibition of either FXR or type I IFN signaling within the phagocytes prevented WD-mediated IEL loss. Therefore, WD consumption represses both innate and adaptive immunity in the gut. These findings have significant clinical implications in the understanding of how diet modulates mucosal immunity., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: T. Stappenbeck advises Janssen, Boehringer Ingelheim, Kallyope, Takada, and Roche. T.C. Liu has research contracts with Denali Therapeutics and Interline Therapeutics. All other authors declare no relevant competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The proximal part of the small intestine, including duodenum and jejunum, is not only dedicated to nutrient digestion and absorption but is also a highly regulated immune site exposed to environmental factors. Host-protective responses against pathogens and tolerance to food antigens are essential functions in the small intestine. The cellular ecology and molecular pathways to maintain those functions are complex. Maladaptation is highlighted by common immune-mediated diseases such as coeliac disease, environmental enteric dysfunction or duodenal Crohn's disease. An expanding spectrum of more than 100 rare monogenic disorders inform on causative molecular mechanisms of nutrient absorption, epithelial homeostasis and barrier function, as well as inflammatory immune responses and immune regulation. Here, after summarizing the architectural and cellular traits that underlie the functions of the proximal intestine, we discuss how the integration of tissue immunopathology and molecular mechanisms can contribute towards our understanding of disease and guide diagnosis. We propose an integrated mechanism-based taxonomy and discuss the latest experimental approaches to gain new mechanistic insight into these disorders with large disease burden worldwide as well as implications for therapeutic interventions., (© 2024. Springer Nature Limited.)