Development of intestinal M cells and follicle-associated epithelium is regulated by TRAF6-mediated NF-κB signaling

Insights into oral lentinan immunomodulation: Dectin-1-mediated lymphatic transport from Peyer's patch M cells to mononuclear phagocytes

Lentinan (LNT), a natural polysaccharide, has been reported to exhibit immunomodulatory effects in the intestine after oral administration. Herein, we aimed to investigate the lymphatic transport of LNT in Peyer's patches (PPs) by traceable fluorescent labeling and to explore whether/how LNT contacts related immune cells. Near-infrared imaging confirmed the absorption of LNT in the small intestinal segment and its accumulation within PPs after oral administration. Subsequently, tissue imaging confirmed that M cells are the main cells responsible for transporting LNT to PPs, and an M cell model was established to explore the involvement of Dectin-1 in the absorption process. Systematic in vitro and in vivo studies revealed that the Dectin-1 further mediates the uptake of LNT by mononuclear phagocytes in PPs. Moreover, LNT can promote the proliferation and differentiation of mononuclear phagocytes, thereby activating immune responses. In summary, this study elucidates the pharmacokinetic mechanisms by which LNT exerts oral immunomodulatory effects, providing a theoretical basis for the development and application of other polysaccharides.

Effects of Intestinal M Cells on Intestinal Barrier and Neuropathological Properties in an AD Mouse Model

Intestinal microfold cells (M cells) play a critical role in the immune response of the intestinal mucosa by actively taking up antigens, facilitating antigen presentation to immune cells, and promoting the production of secretory immunoglobulin A by B cells. Despite their known important functions in the gut, the effect of M cells on the central nervous system remains unclear. We investigated the expression of M cell-related factor genes and protein levels in Peyer's patches (PPs) of 3-month-old and 9-month-old APP/PS1 mice, as well as the expression of intestinal barrier proteins in the ileum and colon of these mice. Furthermore, we employed intestinal M cell conditional ablation mice (i.e., RankΔIEC mice) to assess the influence of M cells on the intestinal barrier and Alzheimer's disease (AD)-like behavioral and pathological features. Our findings revealed that compared to wild-type mice, APP/PS1 mice showed altered M cell-related genes and disrupted intestinal barriers. In addition, there is a significant decrease in glycoprotein 2 (GP2) mRNA levels in the PPs of 3-month-old APP/PS1 mice, with the relative expression of GP2 mRNA tending to zero. Parameters related to the intestinal barrier (IgA, MUC2, Claudin-5, ZO-1) were significantly downregulated in both 3-month-old and 9-month-old APP/PS1 mice compared to wild-type controls, and the differences were more pronounced in the 9-month-old mice. Moreover, M cell ablation in APP/PS1 mice (i.e., APP/PS1ΔMC mice) resulted in more severe intestinal barrier destruction. Notably, we observed through water maze experiments that APP/PS1ΔMC mice at 6 months of age exhibited significantly poorer spatial learning memory compared to APP/PS1 mice. And the neuropathological alterations were also observed in APP/PS1ΔMC mice at 6 months of age that when intestinal M cells are damaged in APP/PS1 mice, brain microglia are activated, Tau phosphorylation is exacerbated, and the number of neurons is reduced. Our results suggest for the first time that the absence of intestinal M cells might further aggravate intestinal leakage, lead to neuropathological damage, and subsequently cause the impairment of learning memory ability in AD mice. Our research highlights the impact of intestinal M cells on the intestinal barrier and AD neuropathogenesis in AD mouse model.

Single cell transcriptional analysis of human adenoids identifies molecular features of airway microfold cells

The nasal, oropharyngeal, and bronchial mucosa are primary contact points for airborne pathogens like Mycobacterium tuberculosis (Mtb), SARS-CoV-2, and influenza virus. While mucosal surfaces can function as both entry points and barriers to infection, mucosa-associated lymphoid tissues (MALT) facilitate early immune responses to mucosal antigens. MALT contains a variety of specialized epithelial cells, including a rare cell type called a microfold cell (M cell) that functions to transport apical antigens to basolateral antigen-presenting cells, a crucial step in the initiation of mucosal immunity. M cells have been extensively characterized in the gastrointestinal (GI) tract in murine and human models. However, the precise development and functions of human airway M cells is unknown. Here, using single-nucleus RNA sequencing (snRNA-seq), we generated an atlas of cells from the human adenoid and identified 16 unique cell types representing basal, club, hillock, and hematopoietic lineages, defined their developmental trajectories, and determined cell-cell relationships. Using trajectory analysis, we found that human airway M cells develop from progenitor club cells and express a gene signature distinct from intestinal M cells. Surprisingly, we also identified a heretofore unknown epithelial cell type demonstrating a robust interferon-stimulated gene signature. Our analysis of human adenoid cells enhances our understanding of mucosal immune responses and the role of M cells in airway immunity. This work also provides a resource for understanding early interactions of pathogens with airway mucosa and a platform for development of mucosal vaccines.

Food antigens suppress small intestinal tumorigenesis

Food components suppressing small intestinal tumorigenesis are not well-defined partly because of the rarity of this tumor type compared to colorectal tumors. Using Apcmin/+ mice, a mouse model for intestinal tumorigenesis, and antigen-free diet, we report here that food antigens serve this function in the small intestine. By depleting Peyer's patches (PPs), immune inductive sites in the small intestine, we found that PPs have a role in the suppression of small intestinal tumors and are important for the induction of small intestinal T cells by food antigens. On the follicle-associated epithelium (FAE) of PPs, microfold (M) cells pass food antigens from lumen to the dendritic cells to induce T cells. Single-cell RNA-seq (scRNA-seq) analysis of immune cells in PPs revealed a significant impact of food antigens on the induction of the PP T cells and the antigen presentation capacity of dendritic cells. These data demonstrate the role of food antigens in the suppression of small intestinal tumorigenesis by PP-mediated immune cell induction.

The Imperative for Innovative Enteric Nervous System-Intestinal Organoid Co-Culture Models: Transforming GI Disease Modeling and Treatment

This review addresses the need for innovative co-culture systems integrating the enteric nervous system (ENS) with intestinal organoids. The breakthroughs achieved through these techniques will pave the way for a transformative era in gastrointestinal (GI) disease modeling and treatment strategies. This review serves as an introduction to the companion protocol paper featured in this journal. The protocol outlines the isolation and co-culture of myenteric and submucosal neurons with small intestinal organoids. This review provides an overview of the intestinal organoid culture field to establish a solid foundation for effective protocol application. Remarkably, the ENS surpasses the number of neurons in the spinal cord. Referred to as the "second brain", the ENS orchestrates pivotal roles in GI functions, including motility, blood flow, and secretion. The ENS is organized into myenteric and submucosal plexuses. These plexuses house diverse subtypes of neurons. Due to its proximity to the gut musculature and its cell type complexity, there are methodological intricacies in studying the ENS. Diverse approaches such as primary cell cultures, three-dimensional (3D) neurospheres, and induced ENS cells offer diverse insights into the multifaceted functionality of the ENS. The ENS exhibits dynamic interactions with the intestinal epithelium, the muscle layer, and the immune system, influencing epithelial physiology, motility, immune responses, and the microbiome. Neurotransmitters, including acetylcholine (ACh), serotonin (5-HT), and vasoactive intestinal peptide (VIP), play pivotal roles in these intricate interactions. Understanding these dynamics is imperative, as the ENS is implicated in various diseases, ranging from neuropathies to GI disorders and neurodegenerative diseases. The emergence of organoid technology presents an unprecedented opportunity to study ENS interactions within the complex milieu of the small and large intestines. This manuscript underscores the urgent need for standardized protocols and advanced techniques to unravel the complexities of the ENS and its dynamic relationship with the gut ecosystem. The insights gleaned from such endeavors hold the potential to revolutionize GI disease modeling and treatment paradigms.

Sorbitol Destroyed Intestinal Microfold Cells (M Cells) Development through Inhibition of PDE4-Mediated RANKL Expression

Objective

Microfold cells (M cells) are specific intestinal epithelial cells for monitoring and transcytosis of antigens, microorganisms, and pathogens in the intestine. However, the mechanism for M-cell development remained elusive.

Materials and Methods

Real-time polymerase chain reaction, immunofluorescence, and western blotting were performed to analyze the effect of sorbitol-regulated M-cell differentiation in vivo and in vitro, and luciferase and chromatin Immunoprecipitation were used to reveal the mechanism through which sorbitol-modulated M-cell differentiation.

Results

Herein, in comparison to the mannitol group (control group), we found that intestinal M-cell development was inhibited in response to sorbitol treatment as evidenced by impaired enteroids accompanying with decreased early differentiation marker Annexin 5, Marcksl1, Spib, sox8, and mature M-cell marker glycoprotein 2 expression, which was attributed to downregulation of receptor activator of nuclear factor kappa-В ligand (RANKL) expression in vivo and in vitro. Mechanically, in the M-cell model, sorbitol stimulation caused a significant upregulation of phosphodiesterase 4 (PDE4) phosphorylation, leading to decreased protein kinase A (PKA)/cAMP-response element binding protein (CREB) activation, which further resulted in CREB retention in cytosolic and attenuated CREB binds to RANKL promoter to inhibit RANKL expression. Interestingly, endogenous PKA interacted with CREB, and this interaction was destroyed by sorbitol stimulation. Most importantly, inhibition of PDE4 by dipyridamole could rescue the inhibitory effect of sorbitol on intestinal enteroids and M-cell differentiation and mature in vivo and in vitro.

Conclusion

These findings suggested that sorbitol suppressed intestinal enteroids and M-cell differentiation and matured through PDE4-mediated RANKL expression; targeting to inhibit PDE4 was sufficient to induce M-cell development.

Discrimination of distinct chicken M cell subsets based on CSF1R expression

In mammals, a subset of follicle-associated epithelial (FAE) cells, known as M cells, conduct the transcytosis of antigens across the epithelium into the underlying lymphoid tissues. We previously revealed that M cells in the FAE of the chicken lung, bursa of Fabricius (bursa), and caecum based on the expression of CSF1R. Here, we applied RNA-seq analysis on highly enriched CSF1R-expressing bursal M cells to investigate their transcriptome and identify novel chicken M cell-associated genes. Our data show that, like mammalian M cells, those in the FAE of the chicken bursa also express SOX8, MARCKSL1, TNFAIP2 and PRNP. Immunohistochemical analysis also confirmed the expression of SOX8 in CSF1R-expressing cells in the lung, bursa, and caecum. However, we found that many other mammalian M cell-associated genes such as SPIB and GP2 were not expressed by chicken M cells or represented in the chicken genome. Instead, we show bursal M cells express high levels of related genes such as SPI1. Whereas our data show that bursal M cells expressed CSF1R-highly, the M cells in the small intestine lacked CSF1R and both expressed SOX8. This study offers insights into the transcriptome of chicken M cells, revealing the expression of CSF1R in M cells is tissue-specific.

The RANK-RANKL-OPG System: A Multifaceted Regulator of Homeostasis, Immunity, and Cancer

The RANK-RANKL-OPG system is a complex signaling pathway that plays a critical role in bone metabolism, mammary epithelial cell development, immune function, and cancer. RANKL is a ligand that binds to RANK, a receptor expressed on osteoclasts, dendritic cells, T cells, and other cells. RANKL signaling promotes osteoclast differentiation and activation, which leads to bone resorption. OPG is a decoy receptor that binds to RANKL and inhibits its signaling. In cancer cells, RANKL expression is often increased, which can lead to increased bone resorption and the development of bone metastases. RANKL-neutralizing antibodies, such as denosumab, have been shown to be effective in the treatment of skeletal-related events, including osteoporosis or bone metastases, and cancer. This review will provide a comprehensive overview of the functions of the RANK-RANKL-OPG system in bone metabolism, mammary epithelial cells, immune function, and cancer, together with the potential therapeutic implications of the RANK-RANKL pathway for cancer management.

TRAF6 signaling in dendritic cells plays protective role against infectious colitis by limiting C. rodentium infection through the induction of Th1 and Th17 responses

Tumor necrosis factor receptor-associated factor 6 (TRAF6) plays a pivotal role in the induction of inflammatory responses not only in innate immune cells but also in non-immune cells, leading to the activation of adaptive immunity. Signal transduction mediated by TRAF6, along with its upstream molecule MyD88 in intestinal epithelial cells (IECs) is crucial for the maintenance of mucosal homeostasis following inflammatory insult. The IEC-specific TRAF6-deficient (TRAF6ΔIEC) and MyD88-deficient (MyD88ΔIEC) mice exhibit increased susceptibility to DSS-induced colitis, emphasizing the critical role of this pathway. Moreover, MyD88 also plays a protective role in Citrobacter rodentium (C. rodentium) infection-induced colitis. However, its pathological role of TRAF6 in infectious colitis remains unclear. To investigate the site-specific roles of TRAF6 in response to enteric bacterial pathogens, we infected TRAF6ΔIEC and dendritic cell (DC)-specific TRAF6-deficient (TRAF6ΔDC) mice with C. rodentium and found that the pathology of infectious colitis was exacerbated with significantly decreased survival rates in TRAF6ΔDC mice, but not in TRAF6ΔIEC mice, compared to those in control mice. TRAF6ΔDC mice showed increased bacterial burdens, marked disruption of epithelial and mucosal structures with increased infiltration of neutrophils and macrophages, and elevated cytokine levels in the colon at the late stages of infection. The frequencies of IFN-γ producing Th1 cells and IL-17A producing Th17 cells in the colonic lamina propria were significantly reduced in TRAF6ΔDC mice. Finally, we demonstrated that TRAF6-deficient DCs failed to produce IL-12 and IL-23 in response to C. rodentium stimulation, and to induce both Th1 and Th17 cells in vitro. Thus, TRAF6 signaling in DCs, but not in IECs, protects against colitis induced by C. rodentium infection by producing IL-12 and IL-23 that induce Th1 and Th17 responses in the gut.

Associations of Gastrointestinal Tract Tumor Necrosis Factor Receptor-Associated Factor 6 Expression with Clinical Features and Prognosis of Eosinophilic Gastroenteritis

BACKGROUND

Few studies have been conducted to explore the expression of tumor necrosis factor receptor-associated factor 6 in eosinophilic gastroenteritis patients. Therefore, the expression profile of tumor necrosis factor receptor-associated factor 6 in the gastrointestinal tract of eosinophilic gastroenteritis patients and its associations with clinical features were explored in this study.

METHODS

Thirty-four eosinophilic gastroenteritis patients who presented in Ruijin Hospital from December 2012 to May 2019 and had accepted gastrointestinal endoscopic examinations were recruited. Medical records and endoscopic biopsies were collected, and the prognosis was followed up by telephone. Healthy persons were selected as the control group. Hematoxylin and eosin and immunohistochemical staining were performed in both eosinophilic gastroenteritis patients and healthy persons. The final results were analyzed by skilled pathologists, and mean optical density values of tumor necrosis factor receptor-associated factor 6 were calculated by Image J software. Final results were analyzed by Statistical Package for the Social Sciences software 22.0.

RESULTS

Thirty-four patients (mean age: 25.56 ± 21.14 years, 61.76% males) were recruited for this study. There was no significant difference in tumor necrosis factor receptor-associated factor 6 mean optical density values of gastric tissues in eosinophilic gastroenteritis patients and healthy people (0.22 ± 0.16 vs. 0.14 ± 0.05, P > .05). Eosinophilic gastroenteritis patients had a significantly lower level of intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values than that of healthy people (0.16 ± 0.05 vs. 0.23 ± 0.06, P < .05). Intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values negatively linearly correlated with serum interleukin-10 level (r = -0.618, P = .043 < .05). There were no differences between eosinophilic gastroenteritis patients with or without relapse regarding the expression level of intestinal tumor necrosis factor receptor-associated factor 6 (P = .227 > .05).

CONCLUSION

Patients with eosinophilic gastroenteritis might have a deficiency of intestinal tumor necrosis factor receptor-associated factor 6 compared to healthy controls.

Challenges and Opportunities in the Oral Delivery of Recombinant Biologics

Recombinant biological molecules are at the cutting-edge of biomedical research thanks to the significant progress made in biotechnology and a better understanding of subcellular processes implicated in several diseases. Given their ability to induce a potent response, these molecules are becoming the drugs of choice for multiple pathologies. However, unlike conventional drugs which are mostly ingested, the majority of biologics are currently administered parenterally. Therefore, to improve their limited bioavailability when delivered orally, the scientific community has devoted tremendous efforts to develop accurate cell- and tissue-based models that allow for the determination of their capacity to cross the intestinal mucosa. Furthermore, several promising approaches have been imagined to enhance the intestinal permeability and stability of recombinant biological molecules. This review summarizes the main physiological barriers to the oral delivery of biologics. Several preclinical in vitro and ex vivo models currently used to assess permeability are also presented. Finally, the multiple strategies explored to address the challenges of administering biotherapeutics orally are described.

RANKL and RANK in Cancer Therapy

Receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) are key regulators of mammalian physiology such as bone metabolism, immune tolerance and antitumor immunity, and mammary gland biology. Here, we explore the multiple functions of RANKL/RANK in physiology and pathophysiology and discuss underlying principles and strategies to modulate the RANKL/RANK pathway as a therapeutic target in immune-mediated cancer treatment.

Fatty acid overproduction by gut commensal microbiota exacerbates obesity

Although recent studies have highlighted the impact of gut microbes on the progression of obesity and its comorbidities, it is not fully understood how these microbes promote these disorders, especially in terms of the role of microbial metabolites. Here, we report that Fusimonas intestini, a commensal species of the family Lachnospiraceae, is highly colonized in both humans and mice with obesity and hyperglycemia, produces long-chain fatty acids such as elaidate, and consequently facilitates diet-induced obesity. High fat intake altered the expression of microbial genes involved in lipid production, such as the fatty acid metabolism regulator fadR. Monocolonization with a FadR-overexpressing Escherichia coli exacerbated the metabolic phenotypes, suggesting that the change in bacterial lipid metabolism is causally involved in disease progression. Mechanistically, the microbe-derived fatty acids impaired intestinal epithelial integrity to promote metabolic endotoxemia. Our study thus provides a mechanistic linkage between gut commensals and obesity through the overproduction of microbe-derived lipids.

A primary cell-based in vitro model of the human small intestine reveals host olfactomedin 4 induction in response to Salmonella Typhimurium infection

Infection research largely relies on classical cell culture or mouse models. Despite having delivered invaluable insights into host-pathogen interactions, both have limitations in translating mechanistic principles to human pathologies. Alternatives can be derived from modern Tissue Engineering approaches, allowing the reconstruction of functional tissue models in vitro. Here, we combined a biological extracellular matrix with primary tissue-derived enteroids to establish an in vitro model of the human small intestinal epithelium exhibiting in vivo-like characteristics. Using the foodborne pathogen Salmonella enterica serovar Typhimurium, we demonstrated the applicability of our model to enteric infection research in the human context. Infection assays coupled to spatio-temporal readouts recapitulated the established key steps of epithelial infection by this pathogen in our model. Besides, we detected the upregulation of olfactomedin 4 in infected cells, a hitherto unrecognized aspect of the host response to Salmonella infection. Together, this primary human small intestinal tissue model fills the gap between simplistic cell culture and animal models of infection, and shall prove valuable in uncovering human-specific features of host-pathogen interplay.

Type II taste cells participate in mucosal immune surveillance

The oral microbiome is second only to its intestinal counterpart in diversity and abundance, but its effects on taste cells remains largely unexplored. Using single-cell RNASeq, we found that mouse taste cells, in particular, sweet and umami receptor cells that express taste 1 receptor member 3 (Tas1r3), have a gene expression signature reminiscent of Microfold (M) cells, a central player in immune surveillance in the mucosa-associated lymphoid tissue (MALT) such as those in the Peyer's patch and tonsils. Administration of tumor necrosis factor ligand superfamily member 11 (TNFSF11; also known as RANKL), a growth factor required for differentiation of M cells, dramatically increased M cell proliferation and marker gene expression in the taste papillae and in cultured taste organoids from wild-type (WT) mice. Taste papillae and organoids from knockout mice lacking Spib (SpibKO), a RANKL-regulated transcription factor required for M cell development and regeneration on the other hand, failed to respond to RANKL. Taste papillae from SpibKO mice also showed reduced expression of NF-κB signaling pathway components and proinflammatory cytokines and attracted fewer immune cells. However, lipopolysaccharide-induced expression of cytokines was strongly up-regulated in SpibKO mice compared to their WT counterparts. Like M cells, taste cells from WT but not SpibKO mice readily took up fluorescently labeled microbeads, a proxy for microbial transcytosis. The proportion of taste cell subtypes are unaltered in SpibKO mice; however, they displayed increased attraction to sweet and umami taste stimuli. We propose that taste cells are involved in immune surveillance and may tune their taste responses to microbial signaling and infection.

GP2-expressing cells: a new guardian with divergent functions in the intestine, eyes, and nose

GP (glycoprotein)-2, originally identified as a predominant membranous component of pancreatic acinar cells, has attracted the interest of researchers in mucosal immunology for its role as a functional molecule specific for antigen-sampling cells in the intestinal Peyer's patches. GP2 is involved in the detection of pathological bacteria and is also histologically useful for the identification of the M cell lineage and their differentiation in lymphoid tissues. Subsequent immunohistochemistry for GP2 has revealed a broad distribution of M cells and related cells in the nasopharyngeal lymphoid tissues, conjunctiva, tear duct, and airway. Especially, GP2 cells in the paranasal sinuses and tear duct have been identified as novel types of epithelial cells. The systematic administration of RANKL can induce extra-M cells in conventional epithelia of body. The production and release of GP2 by conjunctival goblet cells and several mucous glands suggests leading roles for mucous cells in protection, including the entrapment of microorganisms for infections. The ocular surface and conjunctiva are connected to the lacrimal sac, nasolacrimal duct, and further nasal cavity, comprising another canal that passes through the body. The broad distribution of GP2-expressingcells may indicate its function as a new guardian in the intestine, eyes, and nose, all of which are exposed to external milieu.

Advancing intestinal organoid technology to decipher nano-intestine interactions and treat intestinal disease

With research burgeoning in nanoscience and nanotechnology, there is an urgent need to develop new biological models that can simulate native structure, function, and genetic properties of tissues to evaluate the adverse or beneficial effects of nanomaterials on a host. Among the current biological models, three-dimensional (3D) organoids have developed as powerful tools in the study of nanomaterial-biology (nano-bio) interactions, since these models can overcome many of the limitations of cell and animal models. A deep understanding of organoid techniques will facilitate the development of more efficient nanomedicines and further the fields of tissue engineering and personalized medicine. Herein, we summarize the recent progress in intestinal organoids culture systems with a focus on our understanding of the nature and influencing factors of intestinal organoid growth. We also discuss biomimetic extracellular matrices (ECMs) coupled with nanotechnology. In particular, we analyze the application prospects for intestinal organoids in investigating nano-intestine interactions. By integrating nanotechnology and organoid technology, this recently developed model will fill the gaps left due to the deficiencies of traditional cell and animal models, thus accelerating both our understanding of intestine-related nanotoxicity and the development of nanomedicines.

Organoids in gastrointestinal diseases: from experimental models to clinical translation

We are entering an era of medicine where increasingly sophisticated data will be obtained from patients to determine proper diagnosis, predict outcomes and direct therapies. We predict that the most valuable data will be produced by systems that are highly dynamic in both time and space. Three-dimensional (3D) organoids are poised to be such a highly valuable system for a variety of gastrointestinal (GI) diseases. In the lab, organoids have emerged as powerful systems to model molecular and cellular processes orchestrating natural and pathophysiological human tissue formation in remarkable detail. Preclinical studies have impressively demonstrated that these organs-in-a-dish can be used to model immunological, neoplastic, metabolic or infectious GI disorders by taking advantage of patient-derived material. Technological breakthroughs now allow to study cellular communication and molecular mechanisms of interorgan cross-talk in health and disease including communication along for example, the gut-brain axis or gut-liver axis. Despite considerable success in culturing classical 3D organoids from various parts of the GI tract, some challenges remain to develop these systems to best help patients. Novel platforms such as organ-on-a-chip, engineered biomimetic systems including engineered organoids, micromanufacturing, bioprinting and enhanced rigour and reproducibility will open improved avenues for tissue engineering, as well as regenerative and personalised medicine. This review will highlight some of the established methods and also some exciting novel perspectives on organoids in the fields of gastroenterology. At present, this field is poised to move forward and impact many currently intractable GI diseases in the form of novel diagnostics and therapeutics.

T Cell Responses to the Microbiota

The immune system employs recognition tools to communicate with its microbial evolutionary partner. Among all the methods of microbial perception, T cells enable the widest spectrum of microbial recognition resolution, ranging from the crudest detection of whole groups of microbes to the finest detection of specific antigens. The application of this recognition capability to the crucial task of combatting infections has been the focus of classical immunology. We now appreciate that the coevolution of the immune system and the microbiota has led to development of a lush immunological decision tree downstream of microbial recognition, of which an inflammatory response is but one branch. In this review we discuss known T cell-microbe interactions in the gut and place them in the context of an algorithmic framework of recognition, context-dependent interpretation, and response circuits across multiple levels of microbial recognition resolution. The malleability of T cells in response to the microbiota presents an opportunity to edit immune response cellularity, identity, and functionality by utilizing microbiota-controlled pathways to promote human health.

T Cell Responses to the Microbiota

The immune system employs recognition tools to communicate with its microbial evolutionary partner. Among all the methods of microbial perception, T cells enable the widest spectrum of microbial recognition resolution, ranging from the crudest detection of whole groups of microbes to the finest detection of specific antigens. The application of this recognition capability to the crucial task of combatting infections has been the focus of classical immunology. We now appreciate that the coevolution of the immune system and the microbiota has led to development of a lush immunological decision tree downstream of microbial recognition, of which an inflammatory response is but one branch. In this review we discuss known T cell-microbe interactions in the gut and place them in the context of an algorithmic framework of recognition, context-dependent interpretation, and response circuits across multiple levels of microbial recognition resolution. The malleability of T cells in response to the microbiota presents an opportunity to edit immune response cellularity, identity, and functionality by utilizing microbiota-controlled pathways to promote human health.

Advancing animal health and disease research in the lab with three-dimensional cell culture systems

The development of three-dimensional cell culture systems representative of tissues from animals of veterinary interest is accelerating research that seeks to address specific questions tied to animal health. In terms of their relevance and complexity, these in vitro models can be seen as a midpoint between the more reductionist single-cell culture systems and complex live animals. Organoids in particular represent a significant development due to their organised multicellular structure that more closely represents in vivo tissues than any other cell culture technology previously developed. In this review, we provide an overview of the different three-dimensional cell culture systems available to veterinary researchers and give examples of their application in contexts relating to animal health.

A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity

[Figure: see text].

MyD88 Mediates Colitis- and RANKL-Induced Microfold Cell Differentiation

Intestinal microfold (M) cells are critical for sampling antigens in the gut and initiating the intestinal mucosal immune response. In this study, we found that the oral administration of dextran sulfate sodium (DSS) and Salmonella infection induced colitis. In the process, the expression levels of M cell differentiation-related genes were synchronized with the kinetics of pro-inflammatory cytokines. Compared to wild-type (WT) mice, MyD88^-/- mice exhibited significantly lower expression levels of M cell differentiation-related genes. However, DSS induced colitis in MyD88^-/- mice but failed to promote the transcription of M cell differentiation related genes. Furthermore, the receptor activator of the Nuclear Factor-κB ligand (RANKL) upregulated the transcription of M cell differentiation related genes in murine intestinal organoids prepared from both WT and MyD88^-/- mice. Meanwhile, fewer changes in M cell differentiation related genes were found in MyD88^-/- mice as compared to WT mice. Hence, we concluded that myeloid differentiation factor 88 (MyD88) is an essential molecule for colitis- and RANKL-related differentiation of M cells.

Aging-Related Impairments to M Cells in Peyer's Patches Coincide With Disturbances to Paneth Cells

The decline in mucosal immunity during aging increases susceptibility, morbidity and mortality to infections acquired via the gastrointestinal and respiratory tracts in the elderly. We previously showed that this immunosenescence includes a reduction in the functional maturation of M cells in the follicle-associated epithelia (FAE) covering the Peyer’s patches, diminishing the ability to sample of antigens and pathogens from the gut lumen. Here, co-expression analysis of mRNA-seq data sets revealed a general down-regulation of most FAE- and M cell-related genes in Peyer’s patches from aged mice, including key transcription factors known to be essential for M cell differentiation. Conversely, expression of ACE2, the cellular receptor for SARS-Cov-2 virus, was increased in the aged FAE. This raises the possibility that the susceptibility of aged Peyer’s patches to infection with the SARS-Cov-2 virus is increased. Expression of key Paneth cell-related genes was also reduced in the ileum of aged mice, consistent with the adverse effects of aging on their function. However, the increased expression of these genes in the villous epithelium of aged mice suggested a disturbed distribution of Paneth cells in the aged intestine. Aging effects on Paneth cells negatively impact on the regenerative ability of the gut epithelium and could indirectly impede M cell differentiation. Thus, restoring Paneth cell function may represent a novel means to improve M cell differentiation in the aging intestine and increase mucosal vaccination efficacy in the elderly.

Depression of lncRNA MINCR antagonizes LPS-evoked acute injury and inflammatory response via miR-146b-5p and the TRAF6-NFkB signaling

BACKGROUND

Inflammation plays an important role in the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). The long non-coding RNA (lncRNA) MINCR is closely related to inflammation injury. This study was performed to explore the protective effects and mechanisms of MINCR in lipopolysaccharide (LPS)-induced lung injury and inflammation.

METHODS

The expression levels of MINCR and miR-146b-5p in lung tissue status were detected by using quantitative real-time polymerase chain reaction (qRT-PCR), hematoxylin and eosin staining, immunohistochemical staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Enzyme-linked immunosorbent assay and Western blotting analysis were used to detect the expression of inflammatory factors such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10 in lung tissue. The relationship between MINCR, miR-146b-5p, and TRAF6 was explored using bioinformatics analysis and luciferase assay.

RESULTS

The expression levels of MINCR were increased in a mouse model of LPS-induced ALI and small airway epithelial cells (SAECs). shMINCR resulted in increased cell viability and decreased apoptosis, which protected against LPS-induced cell damage. shMINCR can inhibit the formation of neutrophil extracellular traps, neutrophil numbers, myeloperoxidase activity, and the production of inflammatory cytokines IL-6, IL-1β, and TNF-α induced by LPS. The silencing of miR-146b-5p reversed the effects of MINCR on LPS-induced lung damage. Sh-MINCR decreased the expression levels of TRAF6 and p-P65 in LPS-induced SAECs and lung tissues. Co-transfection of sh-MINCR with miR-146b-5p inhibitor reversed the effect of sh-MINCR on the expression of TRAF6 and p-P65.

CONCLUSIONS

MINCR may induce alveolar epithelial cell injury and inflammation and aggravate the progression of ALI/ARDS through miR-146b-5p and TRAF6/NF-κB pathways, which would provide a promising target for the treatment of ALI/ARDS.

PRC2 Regulated Atoh8 Is a Regulator of Intestinal Microfold Cell (M Cell) Differentiation

Intestinal microfold cells (M cells) are a dynamic lineage of epithelial cells that initiate mucosal immunity in the intestine. They are responsible for the uptake and transcytosis of microorganisms, pathogens, and other antigens in the gastrointestinal tract. A mature M cell expresses a receptor Gp2 which binds to pathogens and aids in the uptake. Due to the rarity of these cells in the intestine, their development and differentiation remain yet to be fully understood. We recently demonstrated that polycomb repressive complex 2 (PRC2) is an epigenetic regulator of M cell development, and 12 novel transcription factors including Atoh8 were revealed to be regulated by the PRC2. Here, we show that Atoh8 acts as a regulator of M cell differentiation; the absence of Atoh8 led to a significant increase in the number of Gp2+ mature M cells and other M cell-associated markers such as Spi-B and Sox8. In vitro organoid analysis of RankL treated organoid showed an increase of mature marker GP2 expression and other M cell-associated markers. Atoh8 null mice showed an increase in transcytosis capacity of luminal antigens. An increase in M cell population has been previously reported to be detrimental to mucosal immunity because some pathogens like orally acquired prions have been able to exploit the transcytosis capacity of M cells to infect the host; mice with an increased population of M cells are also susceptible to Salmonella infections. Our study here demonstrates that PRC2 regulated Atoh8 is one of the factors that regulate the population density of intestinal M cell in the Peyer's patch.

The immunological significance of tumor necrosis factor receptor-associated factors (TRAFs)

The tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family of molecules are intracellular signaling adaptors and control diverse signaling pathways mediated not only by the TNFR superfamily and the Toll-like receptor/interleukin-1 receptor superfamily but also by unconventional cytokine receptors such as IL-6 and IL-17 receptors. There are seven family members, TRAF1 to TRAF7, in mammals. Exaggerated immune responses induced through TRAF signaling downstream of these receptors often lead to inflammatory and autoimmune diseases including rheumatoid arthritis, inflammatory bowel disease, psoriasis and autoinflammatory syndromes, and thus those signals are major targets for therapeutic intervention. For this reason, it has been very important to understand signaling mechanisms regulated by TRAFs that greatly impact on life/death decisions and the activation, differentiation and survival of cells of the innate and adaptive immune systems. Accumulating evidence suggests that dysregulated cellular expression and/or signaling of TRAFs causes overproduction of proinflammatory cytokines, which facilitates aberrant activation of immune cells. In this review, I will explain the structural and functional aspects that are responsible for the cellular activity and disease outcomes of TRAFs, and summarize the findings of recent studies on TRAFs in terms of how individual TRAF family molecules regulates biological and disease processes in the body in both positive and negative ways. This review also discusses how TRAF mutations contribute to human disease.

Intestinal immunity: to be, or not to be, induced? That is the question

The intestinal immune system maintains intestinal homeostasis in collaboration with diverse immune cell subsets residing at the epithelial layer, lamina propria and gut-associated lymphoid tissue (GALT). Bacterial components and their metabolites are essential for the establishment of the gut immune system. In addition, nutritional signals contribute to maintaining the mucosal immune response. Specialized epithelial microfold (M) cells in GALT facilitate immune surveillance on the mucosal surface by actively taking up external antigens to transport them into the lymphoid follicles. Because hyperplasia of M cells causes an excessive immune response in GALT, there is a self-regulatory mechanism to control the development of M cells appropriately. In this review, we will discuss the molecular mechanisms of mucosal immune regulation and their biological importance.

Acetate differentially regulates IgA reactivity to commensal bacteria

The balance between bacterial colonization and its containment in the intestine is indispensable for the symbiotic relationship between humans and their bacteria. One component to maintain homeostasis at the mucosal surfaces is immunoglobulin A (IgA), the most abundant immunoglobulin in mammals^1,2. Several studies have revealed important characteristics of poly-reactive IgA^3,4, which is produced naturally without commensal bacteria. Considering the dynamic changes within the gut environment, however, it remains uncertain how the commensal-reactive IgA pool is shaped and how such IgA affects the microbial community. Here we show that acetate-one of the major gut microbial metabolites-not only increases the production of IgA in the colon, but also alters the capacity of the IgA pool to bind to specific microorganisms including Enterobacterales. Induction of commensal-reactive IgA and changes in the IgA repertoire by acetate were observed in mice monocolonized with Escherichia coli, which belongs to Enterobacterales, but not with the major commensal Bacteroides thetaiotaomicron, which suggests that acetate directs selective IgA binding to certain microorganisms. Mechanistically, acetate orchestrated the interactions between epithelial and immune cells, induced microbially stimulated CD4 T cells to support T-cell-dependent IgA production and, as a consequence, altered the localization of these bacteria within the colon. Collectively, we identified a role for gut microbial metabolites in the regulation of differential IgA production to maintain mucosal homeostasis.

Impact of Interleukin 10 Deficiency on Intestinal Epithelium Responses to Inflammatory Signals

Interleukin 10 (IL-10) is a pleiotropic, anti-inflammatory cytokine that has a major protective role in the intestine. Although its production by cells of the innate and adaptive immune system has been extensively studied, its intrinsic role in intestinal epithelial cells is poorly understood. In this study, we utilised both ATAC sequencing and RNA sequencing to define the transcriptional response of murine enteroids to tumour necrosis factor (TNF). We identified that the key early phase drivers of the transcriptional response to TNF within intestinal epithelium were NFκB transcription factor dependent. Using wild-type and Il10-/- enteroid cultures, we showed an intrinsic, intestinal epithelium specific effect of IL-10 deficiency on TNF-induced gene transcription, with significant downregulation of identified NFκB target genes Tnf, Ccl20, and Cxcl10, and delayed overexpression of NFκB inhibitor encoding genes, Nfkbia and Tnfaip3. IL-10 deficiency, or immunoblockade of IL-10 receptor, impacted on TNF-induced endogenous NFκB activity and downstream NFκB target gene transcription. Intestinal epithelium-derived IL-10 appears to play a crucial role as a positive regulator of the canonical NFκB pathway, contributing to maintenance of intestinal homeostasis. This is particularly important in the context of an inflammatory environment and highlights the potential for future tissue-targeted IL-10 therapeutic intervention.

Polycomb Repressive Complex 2 Regulates Genes Necessary for Intestinal Microfold Cell (M Cell) Development

BACKGROUND & AIMS

Microfold cells (M cells) are immunosurveillance epithelial cells located in the Peyer's patches (PPs) in the intestine and are responsible for monitoring and transcytosis of antigens, microorganisms, and pathogens. Mature M cells use the receptor glycoprotein 2 (GP2) to aid in transcytosis. Recent studies have shown transcription factors, Spi-B and SRY-Box Transcription Factor 8 (Sox8). are necessary for M-cell differentiation, but not sufficient. An exhaustive set of factors sufficient for differentiation and development of a mature GP2+ M cell remains elusive. Our aim was to understand the role of polycomb repressive complex 2 (PRC2) as an epigenetic regulator of M-cell development. Estrogen-related-receptor γ (Esrrg), identified as a PRC2-regulated gene, was studied in depth, in addition to its relationship with Spi-B and Sox8.

METHODS

Comparative chromatin immunoprecipitation and global run-on sequencing analysis of mouse intestinal organoids were performed in stem condition, enterocyte conditions, and receptor activator of nuclear factor κ B ligand-induced M-cell condition. Esrrg, which was identified as one of the PRC2-regulated transcription factors, was studied in wild-type mice and knocked out in intestinal organoids using guide RNA's. Sox8 null mice were used to study Esrrg and its relation to Sox8.

RESULTS

chromatin immunoprecipitation and global run-on sequencing analysis showed 12 novel PRC2 regulated transcription factors, PRC2-regulated Esrrg is a novel M-cell-specific transcription factor acting on a receptor activator of nuclear factor κB ligand-receptor activator of nuclear factor κB-induced nuclear factor-κB pathway, upstream of Sox8, and necessary but not sufficient for a mature M-cell marker of Gp2 expression.

CONCLUSIONS

PRC2 regulates a significant set of genes in M cells including Esrrg, which is critical for M-cell development and differentiation. Loss of Esrrg led to an immature M-cell phenotype lacking in Sox8 and Gp2 expression. Transcript profiling: the data have been deposited in the NCBI Gene Expression Omnibus database (GSE157629).

Receptor activator of NF-κB mediates podocyte injury in diabetic nephropathy

Receptor activator of NF-κB (RANK) expression is increased in podocytes of patients with diabetic nephropathy. However, the relevance of RANK to diabetic nephropathy pathobiology remains unclear. Here, to evaluate the role of podocyte RANK in the development of diabetic nephropathy, we generated a mouse model of podocyte-specific RANK depletion (RANK^-/-Cre T), and a model of podocyte-specific RANK overexpression (RANK TG), and induced diabetes in these mice with streptozotocin. We found that podocyte RANK depletion alleviated albuminuria, mesangial matrix expansion, and basement membrane thickening, while RANK overexpression aggravated these indices in streptozotocin-treated mice. Moreover, streptozotocin-triggered oxidative stress was increased in RANK overexpression but decreased in the RANK depleted mice. Particularly, the expression of NADPH oxidase 4, and its obligate partner, P22phox, were enhanced in RANK overexpression, but reduced in RANK depleted mice. In parallel, the transcription factor p65 was increased in the podocyte nuclei of RANK overexpressing mice but decreased in the RANK depleted mice. The relevant findings were largely replicated with high glucose-treated podocytes in vitro. Mechanistically, p65 could bind to the promoter regions of NADPH oxidase 4 and P22phox, and increased their respective gene promoter activity in podocytes, dependent on the levels of RANK. Taken together, these findings suggested that high glucose induced RANK in podocytes and caused the increase of NADPH oxidase 4 and P22phox via p65, possibly together with the cytokines TNF- α, MAC-2 and IL-1 β, resulting in podocyte injury. Thus, we found that podocyte RANK was induced in the diabetic milieu and RANK mediated the development of diabetic nephropathy, likely by promoting glomerular oxidative stress and proinflammatory cytokine production.

Gastrointestinal epithelial innate immunity-regionalization and organoids as new model

The human gastrointestinal tract is in constant contact with microbial stimuli. Its barriers have to ensure co-existence with the commensal bacteria, while enabling surveillance of intruding pathogens. At the centre of the interaction lies the epithelial layer, which marks the boundaries of the body. It is equipped with a multitude of different innate immune sensors, such as Toll-like receptors, to mount inflammatory responses to microbes. Dysfunction of this intricate system results in inflammation-associated pathologies, such as inflammatory bowel disease. However, the complexity of the cellular interactions, their molecular basis and their development remains poorly understood. In recent years, stem cell-derived organoids have gained increasing attention as promising models for both development and a broad range of pathologies, including infectious diseases. In addition, organoids enable the study of epithelial innate immunity in vitro. In this review, we focus on the gastrointestinal epithelial barrier and its regional organization to discuss innate immune sensing and development.

New insight into function and dysfunction of gut microfold cells

Microfold cells (M cells), derived from intestinal crypt Lgr5⁺ stem cells, are distributed in gut-associated lymphoid tissue (GALT), nasopharyngeal-associated lymphoid tissue (NALT), and bronchial-associated lymphoid tissue (BALT). The basement membrane of mature M cells protrudes upward, showing a "pocket-like" shape. M cell differentiation is mainly regulated by two pathways, one is the non-canonical NF-κB pathway, and the other is the canonical NF-κB pathway. The differentiation and maturation of M cells are closely related to RANKL and S100A4. M cells can not only transport antigens and trigger an immune response, but also are the gateway for various pathogens to invade the body. The occurrence and development of tuberculosis, prion disease, and Crohn's disease are closely related to M cells.

Inflammatory Bowel Disease-associated GP2 Autoantibodies Inhibit Mucosal Immune Response to Adherent-invasive Bacteria

Adherent-invasive Escherichia coli have been suggested to play a pivotal role within the pathophysiology of inflammatory bowel disease (IBD). Autoantibodies against distinct splicing variants of glycoprotein 2 (GP2), an intestinal receptor of the bacterial adhesin FimH, frequently occur in IBD patients. Hence, we aimed to functionally characterize GP2-directed autoantibodies as a putative part of IBD's pathophysiology. Ex vivo, GP2-splicing variant 4 (GP2#4) but not variant 2 was expressed on intestinal M or L cells with elevated expression patterns in IBD patients. The GP2#4 expression was induced in vitro by tumor necrosis factor (TNF)-α. The IBD-associated GP2 autoantibodies inhibited FimH binding to GP2#4 and were decreased in anti-TNFα-treated Crohn's disease patients with ileocolonic disease manifestation. In vivo, mice immunized against GP2 before infection with adherent-invasive bacteria displayed exacerbated intestinal inflammation. In summary, autoimmunity against intestinal expressed GP2#4 results in enhanced attachment of flagellated bacteria to the intestinal epithelium and thereby may drive IBD's pathophysiology.

S100A4 Protein Is Essential for the Development of Mature Microfold Cells in Peyer's Patches

Intestinal microfold cells (M cells) in Peyer's patches are a special subset of epithelial cells that initiate mucosal immune responses through uptake of luminal antigens. Although the cytokine receptor activator of nuclear factor-κB ligand (RANKL) expressed on mesenchymal cells triggers differentiation into M cells, other environmental cues remain unknown. Here, we show that the metastasis-promoting protein S100A4 is required for development of mature M cells. S100A4-producing cells are a heterogenous cell population including lysozyme-expressing dendritic cells and group 3 innate lymphoid cells. We found that in the absence of DOCK8, a Cdc42 activator critical for interstitial leukocyte migration, S100A4-producing cells are reduced in the subepithelial dome, resulting in a maturation defect of M cells. While S100A4 promotes differentiation into mature M cells in organoid culture, genetic inactivation of S100a4 prevents the development of mature M cells in mice. Thus, S100A4 is a key environmental cue that regulates M cell differentiation in collaboration with RANKL.

Effects of Qingshen Granules on Immune Function in Patients with Comorbid Chronic Renal Failure and Damp-Heat Syndrome: A Multicenter, Randomized, Controlled Trial

OBJECTIVE

The current study sought to compare the effects of the addition of Qingshen granules to conventional Western medicine on immune function in patients with comorbid chronic renal failure and damp-heat syndrome and to explore the possible mechanisms responsible for any differences observed.

METHODS

Through a multicenter, randomized, controlled study, a total of 282 eligible patients were divided into experimental (n = 136) and control groups (n = 146). All of the patients were treated with conventional Western medical therapy. The experimental group also received Qingshen granules three times daily for 12 weeks. Clinical efficacy was observed in the two groups. Peripheral blood levels of CD4+ T cells, CD8+ T cells, Th17 cells, nuclear factor-κB p65 (NF-κB p65) activity, serum interleukin-17 (IL-17), serum interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), tumor necrosis factor receptor-associated factor 6 (TRAF6), fibronectin (FN), and type IV collagen (Col-IV) were detected in both groups.

RESULTS

The total clinical curative effective rate was significantly higher (p < 0.05) in the experimental group (79.41%) than in the control group (67.12%). Before treatment, there were no significant differences in CD4+/CD8+ T cell ratio, Th17 cell level, NF-κB p65 activity, serum IL-17, IL-6, TNF-α, TRAF6, FN, and Col-IV between the experimental and control groups (p > 0.05); however, all of the measures were significantly higher than those observed in a healthy comparison group (p < 0.05 or p < 0.01). After treatment, the above indexes in the experimental group were significantly lower than those before treatment (p < 0.05 or p < 0.01). Similarly, NF-κB p65 activity, serum IL-17, TNF-α, TRAF6, FN, and Col-IV in the control group were significantly lower than the levels observed prior to treatment (p < 0.05 or p < 0.01); however, while all of the other indexes were lower than those observed before treatment, the differences were not statistically significant (p > 0.05).

CONCLUSION

Qingshen granules adjust immune dysfunction, improve immunity mediated inflammatory response, and attenuate renal fibrosis in patients with comorbid chronic renal failure and damp-heat syndrome.

MicroRNA-3614 regulates inflammatory response via targeting TRAF6-mediated MAPKs and NF-κB signaling in the epicardial adipose tissue with coronary artery disease

OBJECTIVE

The inflammatory status of epicardial adipose tissue (EAT) is one of the factors leading to the development of related diseases such as coronary artery disease (CAD). The thickness of CAD EAT increases and is accompanied with increased macrophage infiltration and heightened inflammatory responses. However, microRNAs (miRNAs) regulating the inflammatory responses of macrophages in CAD EAT remain unclear.

METHOD

miRNA expression profiles of CAD EATs and non-CAD EATs were determined by miRNA microarrays. Quantitative real-time reverse transcription-polymerase chain reaction, Western blotting, immunohistochemical assay, and fluorescence in-situ hybridization were adopted to detect miR-3614 expression and function in EATs and macrophages. The interaction between miR-3614 and tumor necrosis factor receptor-associated factor 6 (TRAF6) was identified using an online website combined with a dual-luciferase reporter assay. Enzyme-linked immunosorbent assay was performed to detect the expression of inflammatory cytokines.

RESULTS

The decreased expression of miR-3614 was identified in CAD EAT. The level of miR-3614 was down-regulated by lipopolysaccharide (LPS) in macrophages, whereas LPS-induced inflammatory injury can be reduced by miR-3614 overexpression. TRAF6 was predicted and verified to be a target of miR-3614. The phosphorylated levels of kinases in the mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB pathways were inhibited by miR-3614 overexpression. Importantly, the knockdown of TRAF6 inhibited the LPS-induced inflammatory cytokine expressions in cells.

CONCLUSION

A novel negative feedback loop by miR-3614 possibly contribute to the regulation of inflammatory processes via targeting the TRAF6/MAPK/NF-κB pathway in EATs and prevents an overwhelming inflammatory response.

Transport of artificial virus-like nanocarriers through intestinal monolayers via microfold cells

Compared with subcutaneous or intramuscular routes for vaccination, vaccine delivery via the gastrointestinal mucosa has tremendous potential as it is easy to administer and pain-free. Robust immune responses can be triggered successfully once the vaccine carrying an antigen reaches the mucosal associated lymphoid sites (e.g., Peyer's patches). However, the absence of an efficient delivery method has always been an issue for successful oral vaccine development. In our study, inspired by mammalian orthoreovirus (MRV) transport into the gut mucosal lymphoid tissue via Microfold cells (M cells), artificial virus-like nanocarriers (AVNs), consisting of gold nanocages functionalized with the σ1 protein from mammalian reovirus (MRV), were tested as an effective oral vaccine delivery vehicle targeting M cells. AVNs were shown to have a significantly higher transport compared to other experimental groups across mouse organoid monolayers containing M cells. These findings suggest that AVNs have the potential to be an M cell-specific oral vaccine/drug delivery vehicle.

10-Hydroxydecanoic Acid Potentially Elicits Antigen-Specific IgA Responses

The effective antigen (Ag) uptake by microfold cells (M-cells) is important for the induction of an efficient mucosal immune responses. Here, we show that 10-hydroxydecanoic acid (10-HDAA) from royal jelly (RJ) potentially supports M-cell differentiation and induces effective antigen-specific mucosal immune responses in cynomolgus macaques. 10-HDAA increases the expression level of receptor activator of nuclear factor-kappaB (NF-κB) (RANK) in Caco-2 cells, which suggests that 10-HDAA potentially prompts the differentiation of Caco-2 cells into M-cells and increased transcytosis efficiency. This idea is supported by the following observations. Intranasal administration of 10-HDAA increased the number of M-cells in the epithelium overlying nasopharynx-associated lymphoid tissue (NALT) in macaques. Oral administration of 10-HDAA increased the number of M-cells in the follicle-associated epithelium (FAE) covering Peyer's patches (PPs) and significantly increased the antigen-specific immunoglobulin A (IgA) level in macaques. These findings suggest that the exogenous honeybee-derived medium-chain fatty acid 10-HDAA may effectively enhance antigen-specific immune responses.

Retinoic Acid and Lymphotoxin Signaling Promote Differentiation of Human Intestinal M Cells

BACKGROUND & AIMS

Intestinal microfold (M) cells are a unique subset of intestinal epithelial cells in the Peyer's patches that regulate mucosal immunity, serving as portals for sampling and uptake of luminal antigens. The inability to efficiently develop human M cells in cell culture has impeded studies of the intestinal immune system. We aimed to identify signaling pathways required for differentiation of human M cells and establish a robust culture system using human ileum enteroids.

METHODS

We analyzed transcriptome data from mouse Peyer's patches to identify cell populations in close proximity to M cells. We used the human enteroid system to determine which cytokines were required to induce M-cell differentiation. We performed transcriptome, immunofluorescence, scanning electron microscope, and transcytosis experiments to validate the development of phenotypic and functional human M cells.

RESULTS

A combination of retinoic acid and lymphotoxin induced differentiation of glycoprotein 2-positive human M cells, which lack apical microvilli structure. Upregulated expression of innate immune-related genes within M cells correlated with a lack of viral antigens after rotavirus infection. Human M cells, developed in the enteroid system, internalized and transported enteric viruses, such as rotavirus and reovirus, across the intestinal epithelium barrier in the enteroids.

CONCLUSIONS

We identified signaling pathways required for differentiation of intestinal M cells, and used this information to create a robust culture method to develop human M cells with capacity for internalization and transport of viruses. Studies of this model might increase our understanding of antigen presentation and the systemic entry of enteric pathogens in the human intestine.

SNHG16/miR-605-3p/TRAF6/NF-κB feedback loop regulates hepatocellular carcinoma metastasis

The mechanism by which miR‐605‐3p regulates hepatocellular carcinoma (HCC) metastasis has not been clarified. In this study, we found that miR‐605‐3p was down‐regulated in HCC and that low miR‐605‐3p expression was associated with tumour thrombus and tumour satellites. HCC patients with low miR‐605‐3p expression showed shorter overall survival and disease‐free survival after surgery. Overexpression of miR‐605‐3p inhibited epithelial‐mesenchymal transition and metastasis of HCC through NF‐κB signalling by directly inhibiting expression of TRAF6, while silencing of miR‐605‐3p had the opposite effect. We also found that SNHG16 directly bound to miR‐605‐3p as a competing endogenous RNA. Mechanistically, high expression of SNHG16 promoted binding to miR‐605‐3p and inhibited its activity, which led to up‐regulation of TRAF6 and sustained activation of the NF‐κB pathway, which in turn promoted epithelial‐mesenchymal transition and metastasis of HCC. TRAF6 increased SNHG16 promoter activity by activating NF‐κB, thereby promoting the transcriptional expression of SNHG16 and forming a positive feedback loop that aggravated HCC malignancy. Our findings reveal a mechanism for the sustained activation of the SNHG16/miR‐605‐3p/TRAF6/NF‐κB feedback loop in HCC and provide a potential target for a new HCC treatment strategy.

HIF-1β Positively Regulates NF-κB Activity via Direct Control of TRAF6

NF-κB signalling is crucial for cellular responses to inflammation but is also associated with the hypoxia response. NF-κB and hypoxia inducible factor (HIF) transcription factors possess an intense molecular crosstalk. Although it is known that HIF-1α modulates NF-κB transcriptional response, very little is understood regarding how HIF-1β contributes to NF-κB signalling. Here, we demonstrate that HIF-1β is required for full NF-κB activation in cells following canonical and non-canonical stimuli. We found that HIF-1β specifically controls TRAF6 expression in human cells but also in Drosophila melanogaster. HIF-1β binds to the TRAF6 gene and controls its expression independently of HIF-1α. Furthermore, exogenous TRAF6 expression is able to rescue all of the cellular phenotypes observed in the absence of HIF-1β. These results indicate that HIF-1β is an important regulator of NF-κB with consequences for homeostasis and human disease.

Osteoprotegerin-dependent M cell self-regulation balances gut infection and immunity

Microfold cells (M cells) are responsible for antigen uptake to initiate immune responses in the gut-associated lymphoid tissue (GALT). Receptor activator of nuclear factor-κB ligand (RANKL) is essential for M cell differentiation. Follicle-associated epithelium (FAE) covers the GALT and is continuously exposed to RANKL from stromal cells underneath the FAE, yet only a subset of FAE cells undergoes differentiation into M cells. Here, we show that M cells express osteoprotegerin (OPG), a soluble inhibitor of RANKL, which suppresses the differentiation of adjacent FAE cells into M cells. Notably, OPG deficiency increases M cell number in the GALT and enhances commensal bacterium-specific immunoglobulin production, resulting in the amelioration of disease symptoms in mice with experimental colitis. By contrast, OPG-deficient mice are highly susceptible to Salmonella infection. Thus, OPG-dependent self-regulation of M cell differentiation is essential for the balance between the infectious risk and the ability to perform immunosurveillance at the mucosal surface.

Microfold cells (M cells) sit at the gut epithelial surface to sample antigens and maintain local immune homeostasis. Here the authors show that M cells are feedback-regulated by M cell-originated osteoprotegerin (OPG) to suppress RNAKL-induced M cell differentiation, and that OPG deficiency alters both gut colitis and infection phenotypes.

Asymmetric distribution of TLR3 leads to a polarized immune response in human intestinal epithelial cells

Intestinal epithelial cells (IECs) act as a physical barrier separating the commensal-containing intestinal tract from the sterile interior. These cells have found a complex balance allowing them to be prepared for pathogen attacks while still tolerating the presence of bacterial or viral stimuli present in the lumen of the gut. Using primary human IECs, we probed the mechanisms that allow for such a tolerance. We discovered that viral infections emanating from the basolateral side of IECs elicit a stronger intrinsic immune response in comparison to lumenal apical infections. We determined that this asymmetric immune response is driven by the clathrin-sorting adaptor AP-1B, which mediates the polarized sorting of Toll-like receptor 3 (TLR3) towards the basolateral side of IECs. Mice and human IECs lacking AP-1B showed an exacerbated immune response following apical stimulation. Together, these results suggest a model where the cellular polarity program plays an integral role in the ability of IECs to partially tolerate apical commensals while remaining fully responsive to invasive basolateral pathogens.

Organoids in immunological research

Much of our knowledge regarding the interactions between epithelial tissues and the immune system has been gathered from animal models and co-cultures with cell lines. However, unique features of human cells cannot be modelled in mice, and cell lines are often transformed or genetically immortalized. Organoid technology has emerged as a powerful tool to maintain epithelial cells in a near-native state. In this Review, we discuss how organoids are being used in immunological research to understand the role of epithelial cell-immune cell interactions in tissue development and homeostasis, as well as in diseases such as cancer.

BAFF is involved in the pathogenesis of IgA nephropathy by activating the TRAF6/NF‑κB signaling pathway in glomerular mesangial cells

The aim of the present study was to investigate the involvement of B cell-activating factor (BAFF) in the pathogenesis of IgA nephropathy by activating the tumor necrosis factor receptor-associated factor 6 (TRAF6)/NF-κB signaling pathway in glomerular mesangial cells. For the clinical analysis, blood, urine and kidney tissue samples were collected from 58 patients diagnosed with primary IgA nephropathy by renal biopsy. For the in vitro study, glomerular mesangial cells were divided into five groups: Control (con)-short hairpin RNA (shRNA) (control group); con-shRNA + BAFF (20 ng/ml); con-shRNA + BAFF + BAFF-RFc chimera protein (500 µg/ml); TRAF6-shRNA; and TRAF6-shRNA + BAFF (20 ng/ml). For the in vivo experiments, 60 Sprague-Dawley rats were randomly divided into four groups: Con-small interfering RNA (siRNA) (control group); con-siRNA + IgA (IgA nephropathy group), BAFF-RFc chimera protein (2 µg/ml) + IgA, and TRAF6-siRNA (0.2 µM) + IgA. Reverse transcription-quantitative PCR was performed to evaluate the mRNA expression levels of TRAF6, connective tissue growth factor (CTGF), fibronectin (FN) and NF-κBP65. Western blot analysis was used to detect the protein expression levels of TRAF6, FN, CTGF and phosphorylated-NF-κBP65 in glomerular mesangial cells and kidney tissues. The results revealed that plasma BAFF levels were positively correlated with the severity of pathological damage in patients with IgA nephropathy. In vitro, BAFF induced the mRNA and protein expression of TRAF6, CTGF, FN and NF-κBP65 in glomerular mesangial cells. After the BAFF-RFc chimera protein was added to inhibit the binding of BAFF and BAFF-receptor (-R), this effect was reduced. In vivo, inhibition of the effects of BAFF via injection with the BAFF-R Fc chimera protein reduced kidney damage in rats suffering from IgA nephropathy. The effect on the expression of signaling pathway-associated proteins was also alleviated. In conclusion, BAFF enhanced the expression of fibroblast factors in the kidneys by activating the TRAF6/NF-κB signaling pathway.

Perinatal hormones favor CC17 group B Streptococcus intestinal translocation through M cells and hypervirulence in neonates

Group B Streptococcus (GBS) is the leading cause of invasive bacterial neonatal infections. Late-onset diseases (LOD) occur between 7 and 89 days of life and are largely due to the CC17 GBS hypervirulent clone. We studied the impact of estradiol (E2) and progesterone (P4), which impregnate the fetus during pregnancy, on GBS neonatal infection in cellular and mouse models of hormonal exposure corresponding to concentrations found at birth (E2-P4 C₀) and over 7 days old (E2-P4 C₇). Using representative GBS isolates, we show that E2-P4 C₇ concentrations specifically favor CC17 GBS meningitis following mice oral infection. CC17 GBS crosses the intestinal barrier through M cells. This process mediated by the CC17-specific surface protein Srr2 is enhanced by E2-P4 C₇ concentrations which promote M cell differentiation and CC17 GBS invasiveness. Our findings provide an explanation for CC17 GBS responsibility in LOD in link with neonatal gastrointestinal tract maturation and hormonal imprint.

The Roles of Peyer's Patches and Microfold Cells in the Gut Immune System: Relevance to Autoimmune Diseases

Microfold (M) cells are located in the epithelium covering mucosa-associated lymphoid tissues, such as the Peyer's patches (PPs) of the small intestine. M cells actively transport luminal antigens to the underlying lymphoid follicles to initiate an immune response. The molecular machinery of M-cell differentiation and function has been vigorously investigated over the last decade. Studies have shed light on the role of M cells in the mucosal immune system and have revealed that antigen uptake by M cells contributes to not only mucosal but also systemic immune responses. However, M-cell studies usually focus on infectious diseases; the contribution of M cells to autoimmune diseases has remained largely unexplored. Accumulating evidence suggests that dysbiosis of the intestinal microbiota is implicated in multiple systemic diseases, including autoimmune diseases. This implies that the uptake of microorganisms by M cells in PPs may play a role in the pathogenesis of autoimmune diseases. We provide an outline of the current understanding of M-cell biology and subsequently discuss the potential contribution of M cells and PPs to the induction of systemic autoimmunity, beyond the mucosal immune response.