The Intestinal Epithelium: Central Coordinator of Mucosal Immunity

Health-Promoting Properties of Proanthocyanidins for Intestinal Dysfunction

The intestinal barrier is constantly exposed to potentially harmful environmental factors, including food components and bacterial endotoxins. When intestinal barrier function and immune homeostasis are compromised (intestinal dysfunction), inflammatory conditions may develop and impact overall health. Evidence from experimental animal and cell culture studies suggests that exposure of intestinal mucosa to proanthocyanidin (PAC)-rich plant products, such as grape seeds, may contribute to maintaining the barrier function and to ameliorating the pathological inflammation present in diet-induced obesity and inflammatory bowel disease. In this review, we aim to update the current knowledge on the bioactivity of PACs in experimental models of intestinal dysfunction and in humans, and to provide insights into the underlying biochemical and molecular mechanisms.

Blood Loss Leads to Increase in Relative Abundance of Opportunistic Pathogens in the Gut Microbiome of Rabbits

Massive blood loss, a common pathological complication in the clinic, is often accompanied by altered gut integrity and intestinal wall damage. Little is known to what extent the gut microbiome could be correlated with this process. The gut microbiome plays a crucial role in human health, especially in immune and inflammatory responses. This study aims to determine whether acute blood loss affects the gut microbiome and the dynamic variation of the gut microbiome following the loss of blood. We used New Zealand rabbits to mimic the blood loss complication and designed a five-time-point fecal sampling strategy including 24-h pre-blood loss procedure, 24 h, 36 h, 48 h, and 1-week post-blood loss procedure. Gut microbiome composition and diversity were analyzed using 16S rRNA gene sequencing and downstream α-diversity, β-diversity, and taxonomy analysis. The gut microbiome changed dramatically after blood loss procedure. There was a significant increase in diversity and richness of the gut microbiome at 24-h post-procedure (P = 0.038). Based on an analysis of similarities, the composition of gut microbiome in the samples collected at 24-h post-procedure was significantly different from that of pre-procedure samples (r = 0.79, P = 0.004 weighted unifrac distance; r = 0.99, P = 0.002, unweighted unifrac distance). The relative abundance of Lactobacillus was significantly decreased in the post-procedure samples (P = 0.0006), while the relative abundance of Clostridiales (P = 0.018) and Bacteroidales (P = 0.015) was significantly increased after procedure. We also found the relative abundance of Bacilli, Lactobacillus, Myroides, and Prevotella decreased gradually at different time points after blood loss. The relative abundance of the Clostridia, Alphaproteobacteria, and Sporosarcina increased at 24-h post-procedure and decreased thereafter. This preliminary study discovered potential connections between blood loss and dysbiosis of gut microbiome. The diversity and abundance of the gut microbiome was affected to various extents after acute blood loss and unable to be restored to the original microbiome profile even after one week. The increase in relative abundance of opportunistic pathogens after blood loss could be an important indication to reconsider immune and inflammatory responses after acute blood loss from the perspective of gut microbiome.

Single-Cell Transcriptional Profiling of the Intestinal Epithelium

Emerging single-cell technologies, like single-cell RNA sequencing (scRNA-seq), enable the study of heterogeneous biological systems at cellular resolution. By profiling the set of expressed transcripts in each cell, single-cell transcriptomics has allowed for the cataloging of the cellular constituents of multiple organs and tissues, both in health and disease. In addition, these technologies have provided mechanistic insights into cellular function, cell state transitions, developmental trajectories and lineage relationships, as well as helped to dissect complex, population-level responses to environmental perturbations. scRNA-seq is particularly useful for characterizing the intestinal epithelium because it is a dynamic, rapidly self-renewing tissue comprised of more than a dozen specialized cell types. Here we discuss the fundamentals of single-cell transcriptomics of the murine small intestinal epithelium. We review the principles of proper experimental design and provide methods for the dissociation of the small intestinal epithelium into single cells followed by fluorescence-activated cell sorting (FACS) and for scRNA-seq using the 10× Genomics Chromium platform.

Dysbiosis of gut microbiome affecting small intestine morphology and immune balance: a rhesus macaque model

There is a growing appreciation for the specific health benefits conferred by commensal microbiota on their hosts. Clinical microbiota analysis and animal studies in germ-free or antibiotic-treated mice have been crucial for improving our understanding of the role of the microbiome on the host mucosal surface; however, studies on the mechanisms involved in microbiome-host interactions remain limited to small animal models. Here, we demonstrated that rhesus monkeys under short-term broad-spectrum antibiotic treatment could be used as a model to study the gut mucosal host-microbiome niche and immune balance with steady health status. Results showed that the diversity and community structure of the gut commensal bacteria in rhesus monkeys were both disrupted after antibiotic treatment. Furthermore, the 16S rDNA amplicon sequencing results indicated that Escherichia-Shigella were predominant in stool samples 9 d of treatment, and the abundances of bacterial functional genes and predicted KEGG pathways were significantly changed. In addition to inducing aberrant morphology of small intestinal villi, the depletion of gut commensal bacteria led to increased proportions of CD3 ⁺ T, CD4 ⁺ T, and CD16 ⁺ NK cells in peripheral blood mononuclear cells (PBMCs), but decreased numbers of Treg and CD20 ⁺ B cells. The transcriptome of PBMCs from antibiotic-treated monkeys showed that the immune balance was affected by modulation of the expression of many functional genes, including IL-13, VCAM1, and LGR4.

Gut-on-chip: Recreating human intestine in vitro

The human gut is important for food digestion and absorption, as well as a venue for a large number of microorganisms that coexist with the host. Although numerous in vitro models have been proposed to study intestinal pathology or interactions between intestinal microbes and host, they are far from recapitulating the real intestinal microenvironment in vivo. To assist researchers in further understanding gut physiology, the intestinal microbiome, and disease processes, a novel technology primarily based on microfluidics and cell biology, called "gut-on-chip," was developed to simulate the structure, function, and microenvironment of the human gut. In this review, we first introduce various types of gut-on-chip systems, then highlight their applications in drug pharmacokinetics, host-gut microbiota crosstalk, and nutrition metabolism. Finally, we discuss challenges in this field and prospects for better understanding interactions between intestinal flora and human hosts, and then provide guidance for clinical treatment of related diseases.

Smad7 in intestinal CD4+ T cells determines autoimmunity in a spontaneous model of multiple sclerosis

Environmental triggers acting at the intestinal barrier are thought to contribute to the initiation of autoimmune disorders. The transforming growth factor beta inhibitor Smad7 determines the phenotype of CD4+ T cells. We hypothesized that Smad7 in intestinal CD4+ T cells controls initiation of opticospinal encephalomyelitis (OSE), a murine model of multiple sclerosis (MS), depending on the presence of gut microbiota. Smad7 was overexpressed or deleted in OSE CD4+ T cells to determine the effect on clinical progression, T cell differentiation, and T cell migration from the intestine to the central nervous system (CNS). Smad7 overexpression worsened the clinical course of OSE and increased CNS inflammation and demyelination. It favored expansion of intestinal CD4+ T cells toward an inflammatory phenotype and migration of intestinal CD4+ T cells to the CNS. Intestinal biopsies from MS patients revealed decreased transforming growth factor beta signaling with a shift toward inflammatory T cell subtypes. Smad7 in intestinal T cells might represent a valuable therapeutic target for MS to achieve immunologic tolerance in the intestine and suppress CNS inflammation.

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Lactobacillus reuteri Stimulates Intestinal Epithelial Proliferation and Induces Differentiation into Goblet Cells in Young Chickens

Probiotics, such as Lactobacillus, have been proven to be effective in maintaining intestinal homeostasis. The modulatory effect of Lactobacillus on intestinal epithelial development in early life is still unclear. In this study, Lactobacillus isolates with good probiotic abilities were screened and orally administered to detect their regulatory effect on intestinal development in chickens. L. reuteri 22 was isolated from chickens and chosen for subsequent chicken experiments due to its strong acid and bile salt resistance and ability to adhere to epithelial cells. The 3-day-old chickens were orally administrated with 10⁸ CFU L. reuteri 22 for consecutive 7 days. L. reuteri 22 increased Lgr5 mRNA expression (3.23 ± 0.40, P = 0.001) and activated the Wnt/β-catenin signaling pathway, with increasing expression of proliferating cell nuclear antigen (PCNA) (49.27 ± 9.81, P = 0.021) to support the proliferation of chicken intestinal epithelial cells. Moreover, L. reuteri 22 also inhibited the Notch signaling pathway to induce intestinal stem cell differentiation into goblet cells with increased mucin 2 (Muc-2) expression (1.72 ± 0.34, P = 0.047). L. reuteri 22 significantly enhanced lysozyme mRNA expression (2.32 ± 0.55, P = 0.019) to improve intestinal innate mucosal immunity. This study demonstrated that L. reuteri administration could regulate chicken intestinal epithelium development to ensure the function of the intestinal mucosal barrier, which is beneficial for newborn animals.

Keep calm: the intestinal barrier at the interface of peace and war

Epithelial barriers have to constantly cope with both harmless and harmful stimuli. The epithelial barrier therefore serves as a dynamic and not static wall to safeguard its proper physiological function while ensuring protection. This is achieved through multiple defence mechanisms involving various cell types - epithelial and non-epithelial - that work in an integrated manner to build protective barriers at mucosal sites. Damage may nevertheless occur, due to pathogens, physical insults or dysregulated immune responses, which trigger a physiologic acute or a pathologic chronic inflammatory cascade. Inflammation is often viewed as a pathological condition, particularly due to the increasing prevalence of chronic inflammatory (intestinal) diseases. However, inflammation is also necessary for wound healing. The aetiology of chronic inflammatory diseases is incompletely understood and identification of the underlying mechanisms would reveal additional therapeutic approaches. Resolution is an active host response to end ongoing inflammation but its relevance is under-appreciated. Currently, most therapies aim at dampening inflammation at damaged mucosal sites, yet these approaches do not efficiently shut down the inflammation process nor repair the epithelial barrier. Therefore, future treatment strategies should also promote the resolution phase. Yet, the task of repairing the barrier can be an arduous endeavour considering its multiple integrated layers of defence - which is advantageous for damage prevention but becomes challenging to repair at multiple levels. In this review, using the intestines as a model epithelial organ and barrier paradigm, we describe the consequences of chronic inflammation and highlight the importance of the mucosae to engage resolving processes to restore epithelial barrier integrity and function. We further discuss the contribution of pre-mRNA alternative splicing to barrier integrity and intestinal homeostasis. Following discussions on current open questions and challenges, we propose a model in which resolution of inflammation represents a key mechanism for the restoration of epithelial integrity and function.

Gut Mycobiota in Immunity and Inflammatory Disease

The mammalian intestine is colonized by a wealth of microorganisms-including bacteria, viruses, protozoa, and fungi-that are all integrated into a functional trans-kingdom community. Characterization of the composition of the fungal community-the mycobiota-has advanced further than the much-needed mechanistic studies. Recent findings have revealed roles for the gut mycobiota in the regulation of host immunity and in the development and progression of human diseases of inflammatory origin. We review these findings here while placing them in the context of the current understanding of the pathways and cellular networks that induce local and systemic immune responses to fungi in the gastrointestinal tract. We discuss gaps in knowledge and argue for the importance of considering bacteria-fungal interactions as we aim to define the roles of mycobiota in immune homeostasis and immune-associated pathologies.

Intestinal epithelial PKM2 serves as a safeguard against experimental colitis via activating β-catenin signaling

The pyruvate kinase M2 (PKM2)-mediated aerobic glycolysis has been shown to play a critical role in promoting cell survival and proliferation. However, little is known about the function of intestinal epithelial PKM2 in intestine homeostasis. Here we investigate whether and how intestinal epithelial PKM2 modulates the morphology and function of the adult intestine in experimental colitis. Analyzing colonoscopic biopsies from Crohn's disease and ulcerative colitis patients, we found significantly decreased level of intestinal epithelial PKM2 in patients compared to that in non-inflamed tissues. Similar reduction of intestinal epithelial PKM2 was observed in mice with dextran sulfate sodium-induced colitis. Moreover, intestinal epithelial-specific PKM2-knockout (Pkm2-/-) mice displayed more severe intestinal inflammation, as evidenced by a shortened colon, disruption of epithelial tight junctions, an increase in inflammatory cytokine levels, and immune cell infiltration, when compared to wild-type mice. Gene profiling, western blot, and function analyses indicated that cell survival signals, particularly the Wnt/β-catenin pathways, were associated with PKM2 activity. Increasing mouse intestinal epithelial PKM2 expression via delivery of a PKM2-expressing plasmid attenuated experimental colitis. In conclusion, our studies demonstrate that intestinal epithelial PKM2 increases cell survival and wound healing under the colitic condition via activating the Wnt/β-catenin signaling.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.

Histopathological changes induced by the digenean intestinal parasite Masenia nkomatiensis Dumbo, Dos Santos, & Avenant-Oldewage, 2019 of the catfish Clarias gariepinus (Burchell) from Incomati Basin, Mozambique

The intestines of 154 Clarias gariepinus were examined of which 29 were naturally infected with Masenia nkomatiensis, and of these, seven (intensity ranging from 8 to 231) were examined for pathology. Destruction of the epithelium covering the villi, detachment of epithelial cells and parts of villi were observed. Excessive mucus secretion occurred in the vicinity of the worm and catarrh was observed, indicative of an inflammatory response. The number of mucous and mast cells was higher at the attachment site than at an area 5,000 µm away and in uninfected individuals, suggesting that the parasite triggered a localized innate immune response. The number of neutrophils, basophils and lymphocytes in infected tissue was not significantly different from uninfected tissue confirming that no acquired immune response was produced against the maseniid. The caecae in the anterior part of the parasites' intestine consisted of convoluted epithelium forming invaginations or "crypts." Contraction of the thick layer of circular muscle fibres of the caeca facilitates the movement of digested material. Observation of digested host cells and cell debris within the caecae provides further evidence that M. nkomatiensis is consuming host cells.

Cyclophosphamide Treatment Mimics Sub-Lethal Infections With Encephalitozoon intestinalis in Immunocompromised Individuals

Microsporidia, including Encephalitozoon intestinalis, are emerging pathogens which cause opportunistic infections in immunocompromised patients, such as those with AIDS, cancer, the elderly and people on immunosuppressive drugs. Intestinal mucosa (IM) is crucial for developing an efficient adaptive immune response against pathogenic micro-organisms, thereby preventing their colonization and subsequent infection. As immunosuppressive drugs affect the intestinal immune response is little known. In the present study, we investigated the immune response to E. intestinalis infection in the IM and gut-associated lymphoid tissue (GALT) in cyclophosphamide (Cy) immunosuppressed mice, to mimic an immunocompromised condition. Histopathology revealed lymphoplasmacytic enteritis at 7 and 14 days-post-infection (dpi) in all infected groups, however, inflammation diminished at 21 and 28 dpi. Cy treatment also led to a higher number of E. intestinalis spores and lesions, which reduced at 28 dpi. In addition, flow cytometry analysis demonstrated CD4⁺ and CD8⁺ T cells to be predominant immune cells, with up-regulation in both Th1 and Th2 cytokines at 7 and 14 dpi, as demonstrated by histopathology. In conclusion, Cy treatment reduced GALT (Peyer’s plaques and mesenteric lymph nodes) and peritoneum populations but increased the T-cell population in the intestinal mucosa and the production of pro-and anti-inflammatory cytokines, which were able to eliminate this opportunistic fungus and reduced the E. intestinalis infection.

Intestinal epithelial barrier functions in ageing

The intestinal epithelial barrier protects the mucosa of the gastrointestinal (GI)-tract and plays a key role in maintaining the host homeostasis. It encompasses several elements that include the intestinal epithelium and biochemical and immunological products, such as the mucus layer, antimicrobial peptides (AMPs) and secretory immunologlobulin A (sIgA). These components are interlinked with the large microbial community inhabiting the gut to form a highly sophisticated biological system that plays an important role on many aspects of human health both locally and systemically. Like any other organ and tissue, the intestinal epithelial barrier is affected by the ageing process. New insights have surfaced showing that critical functions, including intestinal stem cell regeneration and regulation of the intestinal crypt homeostasis, barrier integrity, production of regulatory cytokines, and epithelial innate immunity to pathogenic antigens change across life. Here we review the age-associated changes of the various components of the intestinal epithelial barrier and we highlight the necessity to elucidate further the mechanisms underlying these changes. Expanding our knowledge in this area is a goal of high medical relevance and it will help to define intervention strategies to ameliorate the quality of life of the ever-expanding elderly population.

Could probiotics be the panacea alternative to the use of antimicrobials in livestock diets?

Probiotics are most frequently derived from the natural microbiota of healthy animals. These bacteria and their metabolic products are viewed as nutritional tools for promoting animal health and productivity, disease prevention and therapy, and food safety in an era defined by increasingly widespread antimicrobial resistance in bacterial pathogens. In contemporary livestock production, antimicrobial usage is indispensable for animal welfare, and employed to enhance growth and feed efficiency. Given the importance of antimicrobials in both human and veterinary medicine, their effective replacement with direct-fed microbials or probiotics could help reduce antimicrobial use, perhaps restoring or extending the usefulness of these precious drugs against serious infections. Thus, probiotic research in livestock is rapidly evolving, aspiring to produce local and systemic health benefits on par with antimicrobials. Although many studies have clearly demonstrated the potential of probiotics to positively affect animal health and inhibit pathogens, experimental evidence suggests that probiotics' successes are modest, conditional, strain-dependent, and transient. Here, we explore current understanding, trends, and emerging applications of probiotic research and usage in major livestock species, and highlight successes in animal health and performance.

The Hippo and Wnt signalling pathways: crosstalk during neoplastic progression in gastrointestinal tissue

The Hippo and Wnt signalling pathways play crucial roles in maintaining tissue homeostasis and organ size by orchestrating cell proliferation, differentiation and apoptosis. These pathways have been frequently found to be dysregulated in human cancers. While the canonical signal transduction of Hippo and Wnt has been well studied, emerging evidence shows that these two signalling pathways contribute to and exhibit overlapping functions in gastrointestinal (GI) tumorigenesis. In fact, the core effectors YAP/TAZ in Hippo signalling pathway cooperate with β-catenin in Wnt signalling pathway to promote GI neoplasia. Here, we provide a brief review to summarize the molecular mechanisms underlying the crosstalk between these two pathways and elucidate their involvement in GI tumorigenesis, particularly focusing on the intestine, stomach and liver.

Effects of dietary tuna dark muscle enzymatic hydrolysis and cooking drip supplementations on growth performance, antioxidant activity and gut microbiota modulation of Bama mini-piglets

Experiments were conducted to evaluate the enzymatic hydrolysis of tuna dark muscle (EH-TDM) and cooking drip (EH-TCD) as nutrition supplements in Bama mini-piglets. Our results showed that EH-TDM treatment produce considerable benefits for the Bama mini-piglets in terms of the feed efficiency, the prevention of oxidative damage and the control of blood lipid levels. The EH-TCD treatment also improved the growth performance, whereas all other aspects deteriorated. The analyses of the gut microbiota revealed an increased proportion of bacteria involved in energy metabolism and protein utilization in these two groups. Furthermore, short chain fatty acid producing bacteria were increased, as well as the genera Lactobacillus and Bifidobacterium, which are involved in intestinal dysfunction regulation. This study will provide valuable information for the development of marine protein hydrolysates as feed ingredients for the swine industry.

A High Efficient Method to Isolate Exosomes from Small Intestinal Epithelium

The intestinal epithelium is an important receptor that is not only exposed to nutrients but also to pathogens, such as ingested toxins, bacterial flora, and their metabolites. The sensory information is communicated to extensive endocrine, neural, immune systems, and the exosomes acts as carriers of communication from cell-to-cell. Isolation of exosomes from small intestinal epithelium remains more complex to obtain as a source of exosomes, as it contains varying proportions of exosomes derived from many different cells. Current studies on exosomes have been largely performed using supernatants of cultured cells. This is because, in a cell culture, the origin of exosomes can be determined and isolation of exosomes devoid of 'contaminating' proteins, lipids, and sugars involves relatively simple composition of most culture media facilitates. However, this is hard to achieve in intestinal epithelial cells (IECs) due to several technical issues, including recapitulation of in vivo physiology, operational simplicity, culture stability over time, and assay throughput. Meanwhile, separation of exosomes from a specific cell type remains to be a considerable problem, as the isolated supernatant exosomal fraction may represent only a small fraction of the total instead of reflecting the overall situation. Herein, we proposed an efficient protocol for enrichment of exosomes from the interstitial space of small intestinal epithelium. This method maintains the integrity of the vesicles as well as their contents. Also, it may help to better understand the properties of exosomes and explore their role in cell-to-cell communication of small intestinal epithelium.

Evaluation of the Immunomodulatory Activities of the Probiotic Strain Lactobacillus fermentum UCO-979C

Lactobacillus fermentum UCO-979C, a strain isolated from a human stomach, was previously characterized by its potential probiotic properties. The UCO-979C strain displayed the ability to beneficially regulate the innate immune response triggered by Helicobacter pylori infection in human gastric epithelial cells. In this work, we conducted further in vitro studies in intestinal epithelial cells (IECs) and in vivo experiments in mice in order to characterize the potential immunomodulatory effects of L. fermentum UCO-979C on the intestinal mucosa. Results demonstrated that the UCO-979C strain is capable to differentially modulate the immune response of IECs triggered by Toll-like receptor 4 (TLR4) activation through the modulation of TLR negative regulators' expression. In addition, we demonstrated for the first time that L. fermentum UCO-979C is able to exert its immunomodulatory effect in the intestinal mucosa in vivo. The feeding of mice with L. fermentum UCO-979C significantly increased the production of intestinal IFN-γ, stimulated intestinal and peritoneal macrophages and increased the number of Peyer's patches CD4⁺ T cells. In addition, L. fermentum UCO-979C augmented intestinal IL-6, reduced the number of immature B220⁺CD24^high B cells from Peyer's patches, enhanced the number of mature B B220⁺CD24^low cells, and significantly increased intestinal IgA content. The results of this work revealed that L. fermentum UCO-979C has several characteristics making it an excellent candidate for the development of immunobiotic functional foods aimed to differentially regulate immune responses against gastric and intestinal pathogens.

"Candida Albicans Interactions With The Host: Crossing The Intestinal Epithelial Barrier"

Formerly a commensal organism of the mucosal surfaces of most healthy individuals, Candida albicans is an opportunistic pathogen that causes infections ranging from superficial to the more life-threatening disseminated infections, especially in the ever-growing population of vulnerable patients in the hospital setting. In these situations, the fungus takes advantage of its host following a disturbance in the host defense system and/or the mucosal microbiota. Overwhelming evidence suggests that the gastrointestinal tract is the main source of disseminated C. albicans infections. Major risk factors for disseminated candidiasis include damage to the mucosal intestinal barrier, immune dysfunction, and dysbiosis of the resident microbiota. A better understanding of C. albicans' interaction with the intestinal epithelial barrier will be useful for designing future therapies to avoid systemic candidiasis. In this review, we provide an overview of the current knowledge regarding the mechanisms of pathogenicity that allow the fungus to reach and translocate the gut barrier.

EspF is crucial for Citrobacter rodentium-induced tight junction disruption and lethality in immunocompromised animals

Attaching/Effacing (A/E) bacteria include human pathogens enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and their murine equivalent Citrobacter rodentium (CR), of which EPEC and EHEC are important causative agents of foodborne diseases worldwide. While A/E pathogen infections cause mild symptoms in the immunocompetent hosts, an increasing number of studies show that they produce more severe morbidity and mortality in immunocompromised and/or immunodeficient hosts. However, the pathogenic mechanisms and crucial host-pathogen interactions during A/E pathogen infections under immunocompromised conditions remain elusive. We performed a functional screening by infecting interleukin-22 (IL-22) knockout (Il22-/-) mice with a library of randomly mutated CR strains. Our screen reveals that interruption of the espF gene, which encodes the Type III Secretion System effector EspF (E. coli secreted protein F) conserved among A/E pathogens, completely abolishes the high mortality rates in CR-infected Il22-/- mice. Chromosomal deletion of espF in CR recapitulates the avirulent phenotype without impacting colonization and proliferation of CR, and EspF complement in ΔespF strain fully restores the virulence in mice. Moreover, the expression levels of the espF gene are elevated during CR infection and CR induces disruption of the tight junction (TJ) strands in colonic epithelium in an EspF-dependent manner. Distinct from EspF, chromosomal deletion of other known TJ-damaging effector genes espG and map failed to impede CR virulence in Il22-/- mice. Hence our findings unveil a critical pathophysiological function for EspF during CR infection in the immunocompromised host and provide new insights into the complex pathogenic mechanisms of A/E pathogens.

The peculiar aging of human liver: A geroscience perspective within transplant context

An appraisal of recent data highlighting aspects inspired by the new Geroscience perspective are here discussed. The main findings are summarized as follows: i) liver has to be considered an immunological organ, and new studies suggest a role for the recently described cells named telocytes; ii) the liver-gut axis represents a crucial connection with environment and life style habits and may influence liver diseases onset; iii) the physiological aging of liver shows relatively modest alterations. Nevertheless, several molecular changes appear to be relevant: a) an increase of microRNA-31-5p; -141-3p; -200c-3p expressions after 60 years of age; b) a remodeling of genome-wide DNA methylation profile evident until 60 years of age and then plateauing; c) changes in transcriptome including the metabolic zones of hepatocyte lobules; d) liver undergoes an accelerated aging in presence of chronic inflammation/liver diseases in a sort of continuum, largely as a consequence of unhealthy life styles and exposure to environmental noxious agents. We argue that chronic liver inflammation has all the major characteristics of "inflammaging" and likely sustains the onset and progression of liver diseases. Finally, we propose to use a combination of parameters, mostly obtained by omics such as transcriptomics and epigenomics, to evaluate in deep both the biological age of liver (in comparison with the chronological age) and the effects of donor-recipient age-mismatches in the context of liver transplant.

Changes in the small intestine mucosal immune barrier in Muscovy ducklings infected with Muscovy duck reovirus

Muscovy duck reovirus (MDRV) causes serious immunodeficiency in the intestinal mucosa, although the underlying histopathological mechanisms remain unclear. Thus, we investigated the impact of MDRV infection on intestinal morphology using hematoxylin and eosin staining. Immune-related cells were also quantified by staining with hematoxylin and eosin, toluidine blue, and periodic acid-Schiff stain, or by immunohistochemistry and cytochemistry for lectin. Similarly, CD4⁺ and CD8⁺ cells were quantified by flow cytometry, and the expression of several immune-related molecules was quantified by radioimmunoassay. We found that MDRV clearly damaged the intestinal mucosa, based on tissue morphology, villus length, villus width, intestinal thickness, villus height/crypt depth ratio, and villus surface area. MDRV also altered the density or distribution of lymphocytes, mastocytes, and goblet cells in the small intestinal mucosa, as well as microfold cells in Peyer's patches. In addition, MDRV markedly depleted CD4⁺ cells from the intestinal mucosa and lowered the CD4⁺:CD8⁺ ratio in peripheral blood. Moreover, MDRV diminished the levels of secretory IgA and mucosal addressin cell adhesion molecule-1 (p < 0.01), but elevated those of histamine and nitric oxide (p < 0.01 or p < 0.05). Finally, MDRV significantly suppressed IL-1β, IL-4, IL-5, and IL-8 levels (p < 0.01 or p < 0.05) mid-infection. Collectively, our data suggest that MDRV severely damages the structure and function of the intestinal mucosa by modulating immune cells and immune-related factors, thus leading to local immunodeficiency. Our findings lay the foundation for further research on the pathogenesis of MDRV.

Gut integrity in critical illness

Background

The gut is hypothesized to be the “motor” of critical illness. Under basal conditions, the gut plays a crucial role in the maintenance of health. However, in critical illness, all elements of the gut are injured, potentially worsening multiple organ dysfunction syndrome.

Main body

Under basal conditions, the intestinal epithelium absorbs nutrients and plays a critical role as the first-line protection against pathogenic microbes and as the central coordinator of mucosal immunity. In contrast, each element of the gut is impacted in critical illness. In the epithelium, apoptosis increases, proliferation decreases, and migration slows. In addition, gut barrier function is worsened via alterations to the tight junction, resulting in intestinal hyperpermeability. This is associated with damage to the mucus that separates the contents of the intestinal lumen from the epithelium. Finally, the microbiome of the intestine is converted into a pathobiome, with an increase in disease-promoting bacteria and induction of virulence factors in commensal bacteria. Toxic factors can then leave the intestine via both portal blood flow and mesenteric lymph to cause distant organ damage.

Conclusion

The gut plays a complex role in both health and critical illness. Here, we review gut integrity in both health and illness and highlight potential strategies for targeting the intestine for therapeutic gain in the intensive care unit.

Interactions Between Autophagy and the Unfolded Protein Response: Implications for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis, is characterized by chronic inflammation of the gastrointestinal tract. The etiology involves a combination of genetic and environmental factors resulting in abnormal immune responses to intestinal microbiota. Genetic studies have strongly linked genes involved in autophagy to CD, and genes involved in the unfolded protein response (UPR) to IBD. The UPR is triggered in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER), and autophagy plays a key role in relieving ER stress and restoring homeostasis. This review summarizes the known interactions between autophagy and the UPR and discusses the impact of these converging pathways on IBD pathogenesis. With a paucity of effective long-term treatments for IBD, targeting of synergistic pathways may provide novel and more effective therapeutic options.

From Entry to Early Dissemination-Toxoplasma gondii's Initial Encounter With Its Host

Toxoplasma gondii is a zoonotic intracellular parasite, able to infect any warm-blooded animal via ingestion of infective stages, either contained in tissue cysts or oocysts released into the environment. While immune responses during infection are well-studied, there is still limited knowledge about the very early infection events in the gut tissue after infection via the oral route. Here we briefly discuss differences in host-specific responses following infection with oocyst-derived sporozoites vs. tissue cyst-derived bradyzoites. A focus is given to innate intestinal defense mechanisms and early immune cell events that precede T. gondii's dissemination in the host. We propose stem cell-derived intestinal organoids as a model to study early events of natural host-pathogen interaction. These offer several advantages such as live cell imaging and transcriptomic profiling of the earliest invasion processes. We additionally highlight the necessity of an appropriate large animal model reflecting human infection more closely than conventional infection models, to study the roles of dendritic cells and macrophages during early infection.

Molecular basis and cellular mechanisms of eosinophilic esophagitis for the clinical practice

Eosinophilic esophagitis (EoE) is a chronic, allergen-driven inflammatory esophageal disease characterized by predominantly eosinophilic inflammation leading to esophageal dysfunction. Recent efforts to understand EoE have increased our knowledge of the disease. Areas covered: Multiple cells, molecules, and genes interplay with early life environmental factors in the pathophysiology of EoE to converge in the esophageal epithelium at the center of disease pathogenesis. Epithelial cells constitute a mayor cytokine source for TSLP and Calpain-14; an impaired epithelial barrier function allowing penetration of food and microbiota-derived antigens is involved in triggering and maintaining inflammation. Eosinophil and mast cell-derived products, including TGFβ, together with IL-1β and TNFα, promote epithelial mesenchymal transition in EoE, contributing to tissue remodeling by synthetizing and depositing extracellular matrix in subepithelial layers. This article aims to provide a state-of-the-art update on the pathophysiology of EoE applied to clinical practice, and latest research and developments with potential interest to improve the diagnosis and treatment of patients with EoE are revised. Expert commentary: Preliminary approaches have provided promising results toward incorporating minimally invasive methods for patient diagnosis and monitoring in clinical practice. Early diagnosis and optimized therapies will allow for personalized medicine in EoE.

IL-22 Preserves Gut Epithelial Integrity and Promotes Disease Remission during Chronic Salmonella Infection

The cytokine IL-22 is rapidly induced at barrier surfaces where it regulates host-protective antimicrobial immunity and tissue repair but can also enhance disease severity in some chronic inflammatory settings. Using the chronic Salmonella gastroenteritis model, Ab-mediated neutralization of IL-22 impaired intestinal epithelial barrier integrity and, consequently, exaggerated expression of proinflammatory cytokines. As disease normally resolved, neutralization of IL-22 caused luminal narrowing of the cecum-a feature reminiscent of fibrotic strictures seen in Crohn disease patients. Corresponding to the exaggerated immunopathology caused by IL-22 suppression, Salmonella burdens in the gut were reduced. This enhanced inflammation and pathogen clearance was associated with alterations in gut microbiome composition, including the overgrowth of Bacteroides acidifaciens Our findings thus indicate that IL-22 plays a protective role by limiting infection-induced gut immunopathology but can also lead to persistent pathogen colonization.

Tales from the crypt: new insights into intestinal stem cells

The intestinal epithelium withstands continuous mechanical, chemical and biological insults despite its single-layered, simple epithelial structure. The crypt-villus tissue architecture in combination with rapid cell turnover enables the intestine to act both as a barrier and as the primary site of nutrient uptake. Constant tissue replenishment is fuelled by continuously dividing stem cells that reside at the bottom of crypts. These cells are nurtured and protected by specialized epithelial and mesenchymal cells, and together constitute the intestinal stem cell niche. Intestinal stem cells and early progenitor cells compete for limited niche space and, therefore, the ability to retain or regain stemness. Those cells unable to do so differentiate to one of six different mature cell types and move upwards towards the villus, where they are shed into the intestinal lumen after 3-5 days. In this Review, we discuss the signals, cell types and mechanisms that control homeostasis and regeneration in the intestinal epithelium. We investigate how the niche protects and instructs intestinal stem cells, which processes drive differentiation of mature cells and how imbalance in key signalling pathways can cause human disease.

TTC7A: Steward of Intestinal Health

The increasing incidence of pediatric inflammatory bowel disease, coupled with the efficiency of whole-exome sequencing, has led to the identification of tetratricopeptide repeat domain 7A (TTC7A) as a steward of intestinal health. TTC7A deficiency is an autosomal-recessively inherited disease. In the 5 years since the original description, more than 50 patients with more than 20 distinct disease-causing TTC7A mutations have been identified. Patients show heterogenous intestinal and immunologic disease manifestations, including but not limited to multiple intestinal atresias, very early onset inflammatory bowel disease, loss of intestinal architecture, apoptotic enterocolitis, combined immunodeficiency, and various extraintestinal features related to the skin and/or hair. The focus of this review is to highlight trends in patient phenotypes and to consolidate functional data related to the role of TTC7A in maintaining intestinal homeostasis. TTC7A deficiency is fatal in approximately two thirds of patients, and, as more patients continue to be discovered, elucidating the comprehensive role of TTC7A could show druggable targets that may benefit the growing cohort of individuals suffering from inflammatory bowel disease.

Microbiota and gut neuropeptides: a dual action of antimicrobial activity and neuroimmune response

The gut microbiota is comprised of a vast variety of microbes that colonize the gastrointestinal tract and exert crucial roles for the host health. These microorganisms, partially via their breakdown of dietary components, are able to modulate immune response, mood, and behavior, establishing a chemical dialogue in the microbiota-gut-brain interphase. Changes in the gut microbiota composition and functionality are associated with multiple diseases, in which altered levels of gut-associated neuropeptides are also detected. Gut neuropeptides are strong neuroimmune modulators; they mediate the communication between the gut microbiota and the host (including gut-brain axis) and have also recently been found to exert antimicrobial properties. This highlights the importance of understanding the interplay between gut neuropeptides and microbiota and their implications on host health. Here, we will discuss how gut neuropeptides help to maintain a balanced microbiota and we will point at the missing gaps that need to be further investigated in order to elucidate whether these molecules are related to neuropsychiatric disorders, which are often associated with gut dysbiosis and altered gut neuropeptide levels.

Systemic instruction of cell-mediated immunity by the intestinal microbiome

Recent research has shed light on the plethora of mechanisms by which the gastrointestinal commensal microbiome can influence the local immune response in the gut (in particular, the impact of the immune system on epithelial barrier homeostasis and ensuring microbial diversity). However, an area that is much less well explored but of tremendous therapeutic interest is the impact the gut microbiome has on systemic cell-mediated immune responses. In this commentary, we highlight some key studies that are beginning to broadly examine the different mechanisms by which the gastrointestinal microbiome can impact the systemic immune compartment. Specifically, we discuss the effects of the gut microbiome on lymphocyte polarisation and trafficking, tailoring of resident immune cells in the liver, and output of circulating immune cells from the bone marrow. Finally, we explore contexts in which this new understanding of long-range effects of the gut microbiome can have implications, including cancer therapies and vaccination.

The role of the gut microbiome in shaping the immune system of chickens

Most animals are colonised by at least as many microbial cells as somatic cells, potentially comprising at least 100 times more genes within just the gut microbiota than the host itself. It is, therefore, evident that such a conglomeration can have a profound effect on various bodily systems, particularly the (gut) immune system. Chickens are major providers of efficiently produced protein for humans but also harbour common foodborne pathogens and are susceptible to significant and costly diseases, making a thorough understanding of the influence of the gut microbiome on the immune system very pertinent. Major colonisation of the chicken intestine occurs after hatch and this, along with subsequent microbiota composition and activity, are influenced by numerous host and environmental factors, such that each individual has a unique microbiome signature. However, both extreme (e.g. germ free) and more subtle (e.g. diet changes) microbiome modifications can profoundly impact the development of the gut immune system, particularly adaptive immune apparatus and function. This review will consider the influence of the chicken gut microbiome on immune system development, the implications of this relationship in terms of disease susceptibility, vaccine response, optimal health and productivity, and thus exogenous approaches to positively shape microbiome-immune system interactions.

Diabetic gut microbiota dysbiosis as an inflammaging and immunosenescence condition that fosters progression of retinopathy and nephropathy

The increased prevalence of type 2 diabetes mellitus (T2DM) and life expectancy of diabetic patients fosters the worldwide prevalence of retinopathy and nephropathy, two major microvascular complications that have been difficult to treat with contemporary glucose-lowering medications. The gut microbiota (GM) has become a lively field research in the last years; there is a growing recognition that altered intestinal microbiota composition and function can directly impact the phenomenon of ageing and age-related disorders. In fact, human GM, envisaged as a potential source of novel therapeutics, strongly modulates host immunity and metabolism. It is now clear that gut dysbiosis and their products (e.g. p-cresyl sulfate, trimethylamine‑N‑oxide) dictate a secretory associated senescence phenotype and chronic low-grade inflammation, features shared in the physiological process of ageing ("inflammaging") as well as in T2DM ("metaflammation") and in its microvascular complications. This review provides an in-depth look on the crosstalk between GM, host immunity and metabolism. Further, it characterizes human GM signatures of elderly and T2DM patients. Finally, a comprehensive scrutiny of recent molecular findings (e.g. epigenetic changes) underlying causal relationships between GM dysbiosis and diabetic retinopathy/nephropathy complications is pinpointed, with the ultimate goal to unravel potential pathophysiological mechanisms that may be explored, in a near future, as personalized disease-modifying therapeutic approaches.

Receptors and Signaling Pathways for Recognition of Bacteria in Livestock and Crops: Prospects for Beneficial Microbes in Healthy Growth Strategies

Modern animal and crop production practices are associated with the regular use of antimicrobials, potentially increasing selection pressure on bacteria to become resistant. Alternative approaches are needed in order to satisfy the demands of the growing human population without the indiscriminate use of antimicrobials. Researchers have brought a different perspective to solve this problem and have emphasized the exploitation of animal- and plant-associated microorganisms that are beneficial to their hosts through the modulation of the innate immune system. There is increasing evidence that plants and animals employ microbial perception and defense pathways that closely resemble each other. Formation of pattern recognition receptor (PRR) complexes involving leucine-rich repeat (LRR)-containing proteins, mitogen-activated protein kinase (MAPK)-mediated activation of immune response genes, and subsequent production of antimicrobial products and reactive oxygen species (ROS) and nitric oxide (NO) to improve defenses against pathogens, add to the list of similarities between both systems. Recent pioneering work has identified that animal and plant cells use similar receptors for sensing beneficial commensal microbes that are important for the maintenance of the host's health. Here, we reviewed the current knowledge about the molecular mechanisms involved in the recognition of pathogenic and commensal microbes by the innate immune systems of animal and plants highlighting their differences and similarities. In addition, we discuss the idea of using beneficial microbes to modulate animal and plant immune systems in order to improve the resistance to infections and reduce the use of antimicrobial compounds.

Construction of a Bioluminescent Labelling Plasmid Vector for Bifidobacteria

Bifidobacterium is recognized as one of the most beneficial microorganisms in our gut. Many researches on bifidobacteria have been done to understand their roles in the gut. The objective of the present study was to develop a bioluminescent labelling plasmid vector for bifidobacteria to facilitate their visualization in vitro, in situ, and in vivo. A plasmid replicon (2.0 kb) of plasmid pFI2576 previously identified from B. longum FI10564 was amplified by PCR and cloned into pUC19 plasmid vector (2.68 kb). The cloned replicon was subcloned into pTG262 (luc⁺) recombinant plasmid vector (7.4 kb) where a luciferase gene (luc⁺) from pLuc2 (8.5 kb), an Escherichia coli and lactobacilli shuttle vector, was inserted into pTG262 plasmid vector. The final recombinant DNA, pTG262::pFI2576 rep (luc⁺), was transferred into a B. catenulatum strain. This recombinant strain showed 3,024 relative luminescence units at OD₆₀₀ value of 0.352. Thus, this recombinant plasmid construct can be broadly used for labelling bifidobacteria.