Immune responses to gut microbiota-commensals and pathogens

Intestinal permeability disturbances: causes, diseases and therapy

Nowadays, a pathological increase in the permeability of the intestinal barrier (the so-called leaky gut) is increasingly being diagnosed. This condition can be caused by various factors, mainly from the external environment. Damage to the intestinal barrier entails a number of adverse phenomena: dysbiosis, translocation of microorganisms deep into the intestinal tissue, immune response, development of chronic inflammation. These phenomena can ultimately lead to a vicious cycle that promotes the development of inflammation and further damage to the barrier. Activated immune cells in mucosal tissues with broken barriers can migrate to other organs and negatively affect their functioning. Damaged intestinal barrier can facilitate the development of local diseases such as irritable bowel disease, inflammatory bowel disease or celiac disease, but also the development of systemic inflammatory diseases such as rheumatoid arthritis, ankylosing spondylitis, hepatitis, and lupus erythematosus, neurodegenerative or psychiatric conditions, or metabolic diseases such as diabetes or obesity. However, it must be emphasized that the causal links between a leaky gut barrier and the onset of certain diseases often remain unclear and require in-depth research. In light of recent research, it becomes crucial to prevent damage to the intestinal barrier, as well as to develop therapies for the barrier when it is damaged. This paper presents the current state of knowledge on the causes, health consequences and attempts to treat excessive permeability of the intestinal barrier.

Navigating commensal dysbiosis: Gastrointestinal host-pathogen interplay orchestrating opportunistic infections

The gut commensals, which are usually symbiotic or non-harmful bacteria that live in the gastrointestinal tract, have a positive impact on the health of the host. This review, however, specifically discuss distinct conditions where commensals aid in the development of pathogenic opportunistic infections. We discuss that the categorization of gut bacteria as either pathogens or non-pathogens depends on certain circumstances, which are significantly affected by the tissue microenvironment and the dynamic host-microbe interaction. Under favorable circumstances, commensals have the ability to transform into opportunistic pathobionts by undergoing overgrowth. These conditions include changes in the host's physiology, simultaneous infection with other pathogens, effective utilization of nutrients, interactions between different species of bacteria, the formation of protective biofilms, genetic mutations that enhance pathogenicity, acquisition of genes associated with virulence, and the ability to avoid the host's immune response. These processes allow commensals to both initiate infections themselves and aid other pathogens in populating the host. This review highlights the need of having a detailed and sophisticated knowledge of the two-sided nature of gut commensals. Although commensals mostly promote health, they may also become harmful in certain changes in the environment or the body's functioning. This highlights the need of acknowledging the intricate equilibrium in interactions between hosts and microbes, which is crucial for preserving intestinal homeostasis and averting diseases. Finally, we also emphasize the further need of research to better understand and anticipate the behavior of gut commensals in different situations, since they play a crucial and varied role in human health and disease.

Gut protozoa of wild rodents - a meta-analysis

Protozoa are well-known inhabitants of the mammalian gut and so of the gut microbiome. While there has been extensive study of a number of species of gut protozoa in laboratory animals, particularly rodents, the biology of the gut protozoa of wild rodents is much less well-known. Here we have systematically searched the published literature to describe the gut protozoa of wild rodents, in total finding records of 44 genera of protozoa infecting 228 rodent host species. We then undertook meta-analyses that estimated the overall prevalence of gut protozoa in wild rodents to be 24%, with significant variation in prevalence among some host species. We investigated how host traits may affect protozoa prevalence, finding that for some host lifestyles some protozoa differed in their prevalence. This synthesis of existing data on wild rodent gut protozoa provides a better understanding of the biology of these common gut inhabitants and suggests directions for their future study.

Antibiotic prescribing patterns and carriage of antibiotic-resistant Escherichia coli and Enterococcus species in healthy individuals from selected communities in Lusaka and Ndola districts, Zambia

Objectives

This study assessed antibiotic prescribing patterns in primary healthcare facilities and antimicrobial resistance (AMR) profiles of commensal Escherichia coli and enterococci isolated from pregnant women and children under 5 years of age.

Materials and methods

This cross-sectional study was conducted in Lusaka and Ndola districts of Zambia. Prescription pattern data were obtained from hospital pharmacies. Identification and antimicrobial susceptibility profiles of E. coli and enterococci were determined by conventional methods, while confirmation of both pathogens and AMR genes were determined by PCR. Data were analysed using WHONET and SPSS version 25.0.

Results

Most prescribed antibiotics at the primary healthcare facilities belonged to the Access group of the WHO Access, Watch and Reserve (AWaRe) classification. All the primary healthcare facilities adhered to the AWaRe framework of ≥60% prescribed antibiotics belonging to the Access group. However, resistance was highest in the Access group of antibiotics. E. coli resistance to ampicillin ranged from 71% to 77% and to co-trimoxazole from 74% to 80%, while enterococcal resistance to tetracycline was 59%-64%. MDR was highest in E. coli (75%) isolates, while XDR was highest in enterococcal isolates (97%). The identified AMR genes in E. coli included blaCTX-M, sul2 and qnrA, while those of enterococci included erm(B), erm(C) and erm(A).

Conclusions

Resistance was highest in the prescribed WHO Access group of antibiotics. These findings highlight the need to use local susceptibility data to formulate country-specific treatment guidelines in line with WHO AWaRe classification and enforce regulations that prohibit easy access to antibiotics.

A Comprehensive Exploration of Therapeutic Strategies in Inflammatory Bowel Diseases: Insights from Human and Animal Studies

Inflammatory bowel disease (IBD) is a collective term for a group of chronic inflammatory enteropathies which are characterized by intestinal inflammation and persistent or frequent gastrointestinal signs. This disease affects more than 3.5 million humans worldwide and presents some similarities between animal species, in particular, dogs and cats. Although the underlying mechanism that triggers the disease is not yet well understood, the evidence suggests a multifactorial etiology implicating genetic causes, environmental factors, microbiota imbalance, and mucosa immune defects, both in humans and in dogs and cats. Conventional immunomodulatory drug therapies, such as glucocorticoids or immunosuppressants, are related with numerous adverse effects that limit its long-term use, creating the need to develop new therapeutic strategies. Mesenchymal stromal cells (MSCs) emerge as a promising alternative that attenuates intestinal inflammation by modulating inflammatory cytokines in inflamed tissues, and also due to their pro-angiogenic, anti-apoptotic, anti-fibrotic, regenerative, anti-tumor, and anti-microbial potential. However, this therapeutic approach may have important limitations regarding the lack of studies, namely in veterinary medicine, lack of standardized protocols, and high economic cost. This review summarizes the main differences and similarities between human, canine, and feline IBD, as well as the potential treatment and future prospects of MSCs.

Latent gammaherpesvirus infection enhances type I IFN response and reduces virus spread in an influenza A virus co-infection model

Infections with persistent or latent viruses alter host immune homeostasis and have potential to affect the outcome of concomitant acute viral infections such as influenza A virus (IAV). Gammaherpesviruses establish life-long infections and require an on-going immune response to control reactivation. We have used a murine model of co-infection to investigate the response to IAV infection in mice latently infected with the gammaherpesvirus MHV-68. Over the course of infection, latently infected BALB/c mice showed less weight loss, clinical signs, pulmonary cellular infiltration and expression of inflammatory mediators than naïve mice infected with IAV and had significantly more activated CD8+ T cells in the lungs. Four days after IAV infection, virus spread in the lungs of latently infected animals was significantly lower than in naïve animals. By 7 days after IAV infection latently infected lungs express elevated levels of cytokines and chemokines indicating they are primed to respond to the secondary infection. Investigation at an early time point showed that 24 h after IAV infection co-infected animals had higher expression of IFNβ and Ddx58 (RIG-I) and a range of ISGs than mice infected with IAV alone suggesting that the type I IFN response plays a role in the protective effect. This effect was mouse strain dependent and did not occur in 129/Sv/Ev mice. These results offer insight into innate immune mechanisms that could be utilized to protect against IAV infection and highlight on-going and persistent viral infections as a significant factor impacting the severity of acute respiratory infections.

The Role of the Microbiome in the Pathogenesis and Treatment of Ulcerative Colitis-A Literature Review

Ulcerative colitis (UC) is a chronic inflammatory bowel disease affecting the colon and rectum. UC's pathogenesis involves colonic epithelial cell abnormalities and mucosal barrier dysfunction, leading to recurrent mucosal inflammation. The purpose of the article is to show the complex interplay between ulcerative colitis and the microbiome. The literature search was conducted using the PubMed database. After a screening process of studies published before October 2023, a total of 136 articles were selected. It has been discovered that there is a fundamental correlation of a robust intestinal microbiota and the preservation of gastrointestinal health. Dysbiosis poses a grave risk to the host organism. It renders the host susceptible to infections and has been linked to the pathogenesis of chronic diseases, with particular relevance to conditions such as ulcerative colitis. Current therapeutic strategies for UC involve medications such as aminosalicylic acids, glucocorticoids, and immunosuppressive agents, although recent breakthroughs in monoclonal antibody therapies have significantly improved UC treatment. Furthermore, modulating the gut microbiome with specific compounds and probiotics holds potential for inflammation reduction, while fecal microbiota transplantation shows promise for alleviating UC symptoms. This review provides an overview of the gut microbiome's role in UC pathogenesis and treatment, emphasizing areas for further research.

The opportunistic nature of gut commensal microbiota

The abundance of gut commensals has historically been associated with health-promoting effects despite the fact that the definition of good or bad microbiota remains condition-specific. The beneficial or pathogenic nature of microbiota is generally dictated by the dimensions of host-microbiota and microbe-microbe interactions. With the increasing popularity of gut microbiota in human health and disease, emerging evidence suggests opportunistic infections promoted by those gut bacteria that are generally considered beneficial. Therefore, the current review deals with the opportunistic nature of the gut commensals and aims to summarise the concepts behind the occasional commensal-to-pathogenic transformation of the gut microbes. Specifically, relevant clinical and experimental studies have been discussed on the overgrowth and bacteraemia caused by commensals. Three key processes and their underlying mechanisms have been summarised to be responsible for the opportunistic nature of commensals, viz. improved colonisation fitness that is dictated by commensal-pathogen interactions and availability of preferred nutrients; pathoadaptive mutations that can trigger the commensal-to-pathogen transformation; and evasion of host immune response as a survival and proliferation strategy of the microbes. Collectively, this review provides an updated concept summary on the underlying mechanisms of disease causative events driven by gut commensal bacteria.

Diet-induced gut dysbiosis and inflammation: Key drivers of obesity-driven NASH

Sucrose, the primary circulating sugar in plants, contains equal amounts of fructose and glucose. The latter is the predominant circulating sugar in animals and thus the primary fuel source for various tissue and cell types in the body. Chronic excessive energy intake has, however, emerged as a major driver of obesity and associated pathologies including nonalcoholic fatty liver diseases (NAFLD) and the more severe nonalcoholic steatohepatitis (NASH). Consumption of a high-caloric, western-style diet induces gut dysbiosis and inflammation resulting in leaky gut. Translocation of gut-derived bacterial content promotes hepatic inflammation and ER stress, and when either or both of these are combined with steatosis, it can cause NASH. Here, we review the metabolic links between diet-induced changes in the gut and NASH. Furthermore, therapeutic interventions for the treatment of obesity and liver metabolic diseases are also discussed with a focus on restoring the gut-liver axis.

Genomics and pathotypes of the many faces of Escherichia coli

Escherichia coli is the most researched microbial organism in the world. Its varied impact on human health, consisting of commensalism, gastrointestinal disease, or extraintestinal pathologies, has generated a separation of the species into at least eleven pathotypes (also known as pathovars). These are broadly split into two groups, intestinal pathogenic E. coli (InPEC) and extraintestinal pathogenic E. coli (ExPEC). However, components of E. coli's infinite open accessory genome are horizontally transferred with substantial frequency, creating pathogenic hybrid strains that defy a clear pathotype designation. Here, we take a birds-eye view of the E. coli species, characterizing it from historical, clinical, and genetic perspectives. We examine the wide spectrum of human disease caused by E. coli, the genome content of the bacterium, and its propensity to acquire, exchange, and maintain antibiotic resistance genes and virulence traits. Our portrayal of the species also discusses elements that have shaped its overall population structure and summarizes the current state of vaccine development targeted at the most frequent E. coli pathovars. In our conclusions, we advocate streamlining efforts for clinical reporting of ExPEC, and emphasize the pathogenic potential that exists throughout the entire species.

The next frontier in vaccine design: blending immune correlates of protection into rational vaccine design

Despite the extraordinary speed and success in SARS-Cov-2 vaccine development, the emergence of variants of concern perplexed the vaccine development community. Neutralizing antibodies waned antibodies waned and were evaded by viral variants, despite the preservation of protection against severe disease and death across vaccinated populations. Similar to other vaccine design efforts, the lack of mechanistic correlates of immunity against Coronavirus Disease 2019, raised questions related to the need for vaccine redesign and boosting. Hence, our limited understanding of mechanistic correlates of immunity - across pathogens - remains a major obstacle in vaccine development. The identification and incorporation of mechanistic correlates of immunity are key to the accelerated design of highly impactful globally relevant vaccines. Systems-biology tools can be applied strategically to define a complete understanding of mechanistic correlates of immunity. Embedding immunological dissection and target immune profile identification, beyond canonical antibody binding and neutralization, may accelerate the design and success of durable protective vaccines.

The female reproductive tract microbiotas, inflammation, and gynecological conditions

The intricate interactions between the host cells, bacteria, and immune components that reside in the female reproductive tract (FRT) are essential in maintaining reproductive tract homeostasis. Much of our current knowledge surrounding the FRT microbiota relates to the vaginal microbiota, where ‘health’ has long been associated with low bacterial diversity and Lactobacillus dominance. This concept has recently been challenged as women can have a diverse vaginal microbial composition in the absence of symptomatic disease. The structures of the upper FRT (the endocervix, uterus, Fallopian tubes, and ovaries) have distinct, lower biomass microbiotas than the vagina; however, the existence of permanent microbiotas at these sites is disputed. During homeostasis, a balance exists between the FRT bacteria and the immune system that maintains immune quiescence. Alterations in the bacteria, immune system, or local environment may result in perturbances to the FRT microbiota, defined as dysbiosis. The inflammatory signature of a perturbed or “dysbiotic” FRT microbiota is characterized by elevated concentrations of pro-inflammatory cytokines in cervical and vaginal fluid. It appears that vaginal homeostasis can be disrupted by two different mechanisms: first, a shift toward increased bacterial diversity can trigger vaginal inflammation, and second, local immunity is altered in some manner, which disrupts the microbiota in response to an environmental change. FRT dysbiosis can have negative effects on reproductive health. This review will examine the increasing evidence for the involvement of the FRT microbiotas and inflammation in gynecologic conditions such as endometriosis, infertility, and endometrial and ovarian cancer; however, the precise mechanisms by which bacteria are involved in these conditions remains speculative at present. While only in their infancy, the use of antibiotics and probiotics to therapeutically alter the FRT microbiota is being studied and is discussed herein. Our current understanding of the intimate relationship between immunity and the FRT microbiota is in its early days, and more research is needed to deepen our mechanistic understanding of this relationship and to assess how our present knowledge can be harnessed to assist in diagnosis and treatment of gynecologic conditions.

The role of γδ T cells in the interaction between commensal and pathogenic bacteria in the intestinal mucosa

The intestinal mucosa is an important structure involved in resistance to pathogen infection. It is mainly composed of four barriers, which have different but interrelated functions. Pathogenic bacteria can damage these intestinal mucosal barriers. Here, we mainly review the mechanisms of pathogen damage to biological barriers. Most γδ T cells are located on the surface of the intestinal mucosa, with the ability to migrate and engage in crosstalk with microorganisms. Commensal bacteria are involved in the activation and migration of γδ T cells to monitor the invasion of pathogens. Pathogen invasion alters the migration pattern of γδ T cells. γδ T cells accelerate pathogen clearance and limit opportunistic invasion of commensal bacteria. By discussing these interactions among γδ T cells, commensal bacteria and pathogenic bacteria, we suggest that γδ T cells may link the interactions between commensal bacteria and pathogenic bacteria.

COVID-19 and gut dysbiosis, understanding the role of probiotic supplements in reversing gut dysbiosis and immunity

In December 2019, an outbreak of novel beta-coronavirus started in Wuhan, China, spread globally as coronavirus disease 2019 (COVID-19) pandemic and is still underway. The causative agent for COVID-19 identified as a novel strain of beta coronavirus named nSARS-CoV-2. The nSARS-CoV-2 primarily targets the respiratory tract and results in severe acute respiratory distress (ARDS), leading to the collapse of the respiratory tract. The virus internalizes primarily via ACEII receptor, and many tissues reported a significant level of expression of ACEII receptor including lungs, hearts, kidneys, and gastrointestinal tract. The clinical manifestations of COVID-19 are diverse, but growing evidence suggests that gut dysbiosis is one of them and poses a threat to native immunity. The human microbial ecology plays a vital role in human physiology, including building immunity. The gastrointestinal tract (GIT) habitats trillions of beneficial microbes’ precisely bacterial species synchronize with human physiology and remain symbiotic. On the contrary, harmful microbiota seeks an opportunity to break the equilibrium failure of balance between beneficial and detrimental human gut microbiota results in impaired physiology and immunity. The grown research evidence demonstrated that infection caused by the nSARS-CoV-2 result in moderate to severe diarrheal outcomes. The diarrheal conditions in COVID-19 patients are due to alteration of gut microbial ecology. The management of COVID-19 requires specialized therapeutics along with a series of nutraceuticals. Probiotics remain vital nutrient supplements in COVID-19 management, offer relief in diarrhea and improve/restore immunity. This study uses available data/findings to emphasize an association between COVID-19 and gut dysbiosis. The study also provides a scientific basis of impaired immunity during gut dysbiosis in COVID-19 and how probiotics help restore and improve impaired immunity and diarrhea.

Alterations in the Gut Microbial Composition and Diversity of Tibetan Sheep Infected With Echinococcus granulosus

Hydatidosis/cystic echinococcosis (CE) caused by Echinococcus granulosus is a parasitic zoonotic disease worldwide, threatening animal health and production and public health safety. However, it is still unclear that whether E. granulosus infection can result in the alteration of gut microbiota in Tibetan sheep. Therefore, a study was designed to investigate the influences of E. granulosus infection on gut microbiota of Tibetan sheep. A total of 10 ovine small intestinal contents (five from healthy and five from infected) were obtained and subjected to high-throughput sequencing by MiSeq platform. A total of 2,395,641 sequences and 585 operational taxonomic units (OTUs) were identified. Firmicutes and Proteobacteria were the most dominant phyla in all samples. Moreover, the proportions of Armatimonadetes and Firmicutes in the infected Tibetan sheep were significantly decreased, whereas Actinobacteria, Chloroflexi, and Acidobacteria had significantly increased. At the genus level, the Christensenellaceae_R-7_group and Ruminococcaceae_NK4A214_group were the predominant bacterial genera in all the samples. Furthermore, the healthy Tibetan sheep exhibited higher abundances of Intestinimonas, Butyrivibrio, Pseudobutyrivibrio, Ruminococcaceae, Eubacterium_coprostanoligenes_group, Oxobacter, Prevotella_1, Ruminiclostridium_6, Coprococcus_1, Ruminococcus, Lachnospiraceae_UCG-002, Olsenella, and Acetitomaculum, whereas Kocuria, Clostridium_sensu_stricto_1, Slackia, Achromobacter, and Stenotrophomonas levels were lower. In conclusion, our results conveyed an information that E. granulosus infection may cause an increase in pathogenic bacteria and a decrease in beneficial bacteria. Additionally, a significant dynamical change in gut microbiota could be associated with E. granulosus infection.

Does the epithelial barrier hypothesis explain the increase in allergy, autoimmunity and other chronic conditions?

There has been a steep increase in allergic and autoimmune diseases, reaching epidemic proportions and now affecting more than one billion people worldwide. These diseases are more common in industrialized countries, and their prevalence continues to rise in developing countries in parallel to urbanization and industrialization. Intact skin and mucosal barriers are crucial for the maintenance of tissue homeostasis as they protect host tissues from infections, environmental toxins, pollutants and allergens. A defective epithelial barrier has been demonstrated in allergic and autoimmune conditions such as asthma, atopic dermatitis, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, coeliac disease and inflammatory bowel disease. In addition, leakiness of the gut epithelium is also implicated in systemic autoimmune and metabolic conditions such as diabetes, obesity, multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis and autoimmune hepatitis. Finally, distant inflammatory responses due to a 'leaky gut' and microbiome changes are suspected in Alzheimer disease, Parkinson disease, chronic depression and autism spectrum disorders. This article introduces an extended 'epithelial barrier hypothesis', which proposes that the increase in epithelial barrier-damaging agents linked to industrialization, urbanization and modern life underlies the rise in allergic, autoimmune and other chronic conditions. Furthermore, it discusses how the immune responses to dysbiotic microbiota that cross the damaged barrier may be involved in the development of these diseases.

Mutual interaction of microbiota and host immunity during health and diseases

Microbiota-host interaction has attracted more and more attentions in recent years. The association between microbiota and host health is largely attributed to its influence on host immune system. Microbial-derived antigens and metabolites play a critical role in shaping the host immune system, including regulating its development, activation, and function. However, during various diseases the microbiota-host communication is frequently found to be disordered. In particular, gut microbiota dysbiosis associated with or led to the occurrence and progression of infectious diseases, autoimmune diseases, metabolic diseases, and neurological diseases. Pathogenic microbes and their metabolites disturb the protective function of immune system, and lead to disordered immune responses that usually correlate with disease exacerbation. In the other hand, the immune system also regulates microbiota composition to keep host homeostasis. Here, we will discuss the current advances of our knowledge about the interactions between microbiota and host immune system during health and diseases.

Human immunology and immunotherapy: main achievements and challenges

The immune system is a fascinating world of cells, soluble factors, interacting cells, and tissues, all of which are interconnected. The highly complex nature of the immune system makes it difficult to view it as a whole, but researchers are now trying to put all the pieces of the puzzle together to obtain a more complete picture. The development of new specialized equipment and immunological techniques, genetic approaches, animal models, and a long list of monoclonal antibodies, among many other factors, are improving our knowledge of this sophisticated system. The different types of cell subsets, soluble factors, membrane molecules, and cell functionalities are some aspects that we are starting to understand, together with their roles in health, aging, and illness. This knowledge is filling many of the gaps, and in some cases, it has led to changes in our previous assumptions; e.g., adaptive immune cells were previously thought to be unique memory cells until trained innate immunity was observed, and several innate immune cells with features similar to those of cytokine-secreting T cells have been discovered. Moreover, we have improved our knowledge not only regarding immune-mediated illnesses and how the immune system works and interacts with other systems and components (such as the microbiome) but also in terms of ways to manipulate this system through immunotherapy. The development of different types of immunotherapies, including vaccines (prophylactic and therapeutic), and the use of pathogens, monoclonal antibodies, recombinant proteins, cytokines, and cellular immunotherapies, are changing the way in which we approach many diseases, especially cancer.

Microbiota-host interactions shape ageing dynamics

Occupying the interface between host and environment, host-associated microbes play fundamental roles in nutrient absorption, essential metabolite synthesis, development of the immune system, defence against pathogens and pathogenesis. Microbiota composition and function is rather stable during adulthood, while it dramatically changes during early development, frailty and disease. Ageing is associated with progressive decrease of homeostasis, often resulting in disruption of the physiological balance between host and commensal microbes, ultimately leading to dysbiosis and host demise. Generally, high microbial diversity is associated with health and a youthful state, while low individual microbial diversity and larger inter-individual microbial diversity is associated with ageing and disease states. Different species are equipped with species-specific commensal, symbiotic and pathogenic microbial communities. How and whether the specific host-microbiota consortia co-evolved with host physiology to ensure homeostasis and promote individual fitness remains an open question. In this essay, we propose that the evolution of vertebrate-specific immune adaptations may have enabled the establishment of highly diverse, species-specific commensal microbial communities. We discuss how the maintenance of intact immune surveillance mechanisms, which allow discrimination between commensal and pathogenic bacteria, fail during ageing and lead to the onset of known ageing-related diseases. We discuss how host-microbiota interactions are key to maintaining homeostasis despite external perturbations, but also how they affect a range of host-specific ageing-related phenotypes. This article is part of the theme issue 'The role of the microbiome in host evolution'.

Advances in Ca2+ modulation of gastrointestinal anion secretion and its dysregulation in digestive disorders (Review)

Intracellular calcium (Ca²⁺) is a critical cell signaling component in gastrointestinal (GI) physiology. Cytosolic calcium ([Ca²⁺]_cyt), as a secondary messenger, controls GI epithelial fluid and ion transport, mucus and neuropeptide secretion, as well as synaptic transmission and motility. The key roles of Ca²⁺ signaling in other types of secretory cell (including those in the airways and salivary glands) are well known. However, its action in GI epithelial secretion and the underlying molecular mechanisms have remained to be fully elucidated. The present review focused on the role of [Ca²⁺]_cyt in GI epithelial anion secretion. Ca²⁺ signaling regulates the activities of ion channels and transporters involved in GI epithelial ion and fluid transport, including Cl^- channels, Ca²⁺-activated K⁺ channels, cystic fibrosis (CF) transmembrane conductance regulator and anion/HCO₃^- exchangers. Previous studies by the current researchers have focused on this field over several years, providing solid evidence that Ca²⁺ signaling has an important role in the regulation of GI epithelial anion secretion and uncovering underlying molecular mechanisms. The present review is largely based on previous studies by the current researchers and provides an overview of the currently known molecular mechanisms of GI epithelial anion secretion with an emphasis on Ca²⁺-mediated ion secretion and its dysregulation in GI disorders. In addition, previous studies by the current researchers demonstrated that different regulatory mechanisms are in place for GI epithelial HCO₃^- and Cl^- secretion. An increased understanding of the roles of Ca²⁺ signaling and its targets in GI anion secretion may lead to the development of novel strategies to inhibit GI diseases, including the enhancement of fluid secretion in CF and protection of the GI mucosa in ulcer diseases.

Interactions between Gut Microbiota and Immunomodulatory Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases caused by abnormal immune activation and immune tolerance. Immunomodulatory cells (ICs) play a critical role in the maintenance and homeostasis of normal immune function and in the pathogenesis of RA. The human gastrointestinal tract is inhabited by trillions of commensal microbiota on the mucosal surface that play a fundamental role in the induction, maintenance, and function of the host immune system. Gut microbiota dysbiosis can impact both the local and systemic immune systems and further contribute to various diseases, such as RA. The neighbouring intestinal ICs located in distinct intestinal mucosa may be the most likely intermediary by which the gut microbiota can affect the occurrence and development of RA. However, the reciprocal interaction between the components of the gut microbiota and their microbial metabolites with distinct ICs and how this interaction may impact the development of RA are not well studied. Therefore, a better understanding of the gut microbiota, ICs, and their interactions might improve our knowledge of the mechanisms by which the gut microbiota contribute to RA and facilitate the further development of novel therapeutic approaches. In this review, we have summarized the roles of the gut microbiota in the immunopathogenesis of RA, especially the interactions between the gut microbiota and ICs, and further discussed the strategies for treating RA by targeting/regulating the gut microbiota.

The lung microbiota: role in maintaining pulmonary immune homeostasis and its implications in cancer development and therapy

Like other body districts, lungs present a complex bacteria community. An emerging function of lung microbiota is to promote and maintain a state of immune tolerance, to prevent uncontrolled and not desirable inflammatory response caused by inhalation of harmless environmental stimuli. This effect is mediated by a continuous dialog between commensal bacteria and immune cells resident in lungs, which express a repertoire of sensors able to detect microorganisms. The same receptors are also involved in the recognition of pathogens and in mounting a proper immune response. Due to its important role in preserving lung homeostasis, the lung microbiota can be also considered a mirror of lung health status. Indeed, several studies indicate that lung bacterial composition drastically changes during the occurrence of pulmonary pathologies, such as lung cancer, and the available data suggest that the modifications of lung microbiota can be part of the etiology of tumors in lungs and can influence their progression and response to therapy. These results provide the scientific rationale to analyze lung microbiota composition as biomarker for lung cancer and to consider lung microbiota a new potential target for therapeutic intervention to reprogram the antitumor immune microenvironment. In the present review, we discussed about the role of lung microbiota in lung physiology and summarized the most relevant data about the relationship between lung microbiota and cancer.

Optimization and standardization of the culturomics technique for human microbiome exploration

Culturomics is a high-throughput culture approach that has dramatically contributed to the recent renewal of culture. While metagenomics enabled substantial advances in exploring the microbiota, culturomics significantly expanded our knowledge regarding the bacterial gut repertoire through the discovery and the description of hundreds of new taxa. While this approach relies on the variation of culture conditions and media, we have tested so far more than 300 conditions since the beginning of culturomics studies. In this context, we aimed herein to identify the most profitable conditions for optimizing culturomics approach. For this purpose, we have analysed a set of 58 culturomics conditions that were previously applied to 8 faecal specimens, enabling the isolation of 497 bacterial species. As a result, we were able to reduce the number of conditions used to isolate these 497 of more than a half (i.e. to 25 culture conditions). We have also established a list of the 16 conditions that allowed to capture 98% of the total number of species previously isolated. These data constitute a methodological starting point for culture-based microbiota studies by improving the culturomics workflow without any loss of captured bacterial diversity.

Selected Indonesian Medicinal Plants for the Management of Metabolic Syndrome: Molecular Basis and Recent Studies

Increased prevalence of metabolic syndrome (MetS) in the world influences quality of health in all respective countries, including Indonesia. Data from Indonesian Family Life Survey reported in 2019 showed that the prevalence of MetS in Indonesia currently is 21.66%, estimated with the provincial incidence ranging up to 50%; additionally, the most common components of MetS discovered in Indonesia were poor high-density lipoprotein (HDL) cholesterol and hypertension. Management treatment of MetS involves a combination of lifestyle changes and pharmacological interventions to decrease cerebrovascular disease. Various natural substances have been shown to govern any cardiovascular or metabolic disorders through different mechanisms, such as triggering anti-inflammation, lipid profile correction, sensitization of insulin reception, or blood glucose control. In Indonesia, the utilization of natural compounds is part of the nation's culture. The community widely uses them; even though in general, their effectiveness and safety have not been thoroughly assessed by rigorous clinical trials. Scientific evidence suggested that cinnamon, mangosteen, and curcumin, as well as their derived components possess a broad spectrum of pharmacological activity. In this review, an enormous potential of cinnamon, mangosteen, and curcumin, which originated and are commonly used in Indonesia, could be treated against MetS, such as diabetes, hyperlipidemia, hypertension, and obesity. The findings suggested that cinnamon, mangosteen, curcumin and their derivatives may reflect areas of promise in the management of MetS.

Effects of in ovo Inoculation of Multi-Strain Lactobacilli on Cytokine Gene Expression and Antibody-Mediated Immune Responses in Chickens

This study was conducted to investigate the effects of various doses of a multi-strain lactobacilli mixture (Lactobacillus salivarius, Lactobacillus reuteri, Lactobacillus crispatus, and Lactobacillus johnsonii) on the innate and adaptive immune responses in broiler chickens. At embryonic day eighteen, 200 eggs were injected with PBS, or three different doses of a multi-strain lactobacilli mixture (1 × 105, 1 × 106, and 1 × 107 CFU/egg, P1, P2, and P3 respectively) along with a group of negative control. On days 5 and 10 post-hatch, cecal tonsil, bursa of fabricius, and spleen were collected for gene expression and cellular analysis. On days 14 and 21 post-hatch, birds were immunized intramuscularly with both sheep red blood cells (SRBC) and keyhole limpet hemocyanin (KLH). Serum samples were collected on days 0, 7, 14, and 21 after primary immunization. The results demonstrated that lactobacilli inoculation increased the splenic expression of cytokines, including interferon (IFN) - α, IFN-β, IFN-γ, interleukin (IL)-8, and IL-12 on day 5 post-hatch compared to the control group (PBS). However, in cecal tonsils, lactobacilli treatment downregulated the expression of IL-6 on day 5 post-hatch and IL-2 and IL-8 on day 10 post-hatch. No significant differences were observed in the expression of cytokine genes in the bursa except for IL-13 which was upregulated in lactobacilli-treated groups P2 and P3 on days 5 and 10 post-hatch. Flow cytometry analysis showed that the percentage of KUL01, CD4+ and CD8+ splenocytes was not affected by treatments. In addition, no significant differences were observed for antibody titers against SRBC. However, lactobacilli treatment (P1, P2, and P3) was found to increase IgM titers on day 21 post-primary immunization compared to controls. Furthermore, in ovo injection of the highest dose of probiotics (1 × 107, P3) increased serum IgG titers against KLH on day 7 post-primary immunization. In conclusion, this study demonstrated that that in ovo administration of lactobacilli can improve antibody-mediated immune responses and differentially modulate cytokine expression in mucosal and systemic lymphoid tissues of chickens.

Immunopathogenesis of Immune Checkpoint Inhibitor-Related Adverse Events: Roles of the Intestinal Microbiome and Th17 Cells

The advent of novel, innovative, and effective anti-cancer immunotherapies has engendered an era of renewed optimism among cancer specialists and their patients. Foremost among these successful immunotherapies are monoclonal antibodies (MAbs) which target immune checkpoint inhibitor (ICI) molecules, most prominently cytotoxic T-lymphocyte-associated protein (CTLA-4) and programmed cell death protein-1 (PD-1) and its major ligand, PD-L1. These immunotherapeutic agents are, however, often associated with the occurrence of immune-mediated toxicities known as immune-related adverse events (IRAEs). The incidence of severe toxicities increases substantially when these agents are used together, particularly with CTLA-4 in combination with PD-1 or PD-L1 antagonists. Accordingly, dissociating the beneficial anti-tumor therapeutic activity of these agents from the emergence of IRAEs represents a significant challenge to attaining the optimum efficacy of ICI-targeted immunotherapy of cancer. This situation is compounded by an increasing awareness, possibly unsurprising, that both the beneficial and harmful effects of ICI-targeted therapies appear to result from an over-reactive immune system. Nevertheless, this challenge may not be insurmountable. This contention is based on acquisition of recent insights into the role of the gut microbiome and its products as determinants of the efficacy of ICI-targeted immunotherapy, as well as an increasing realization of the enigmatic involvement of Th17 cells in both anti-tumor activity and the pathogenesis of some types of IRAEs. Evidence linking the beneficial and harmful activities of ICI-targeted immunotherapy, recent mechanistic insights focusing on the gut microbiome and Th17 cells, as well as strategies to attenuate IRAEs in the setting of retention of therapeutic activity, therefore represent the major thrusts of this review.

Gastrointestinal Barrier Breakdown and Adipose Tissue Inflammation

PURPOSE OF REVIEW

Obesity is a state of chronic inflammation. This review aims to summarize recent data supporting the role of the intestinal mucosal barrier and the microbiome in causing adipose tissue inflammation as well as metabolic factors that can affect the intestinal barrier.

RECENT FINDINGS

Obesity and its metabolic consequences, such as diabetes mellitus, are associated with disruption of the intestinal barrier function. Intestinal microbiota and diet play a key role in the maintenance of a healthy intestinal epithelium. Intestinal barrier dysfunction can lead to heightened inflammation, which in turn can further damage the intestinal barrier through the disruption of tight junction proteins. Intestinal barrier breakdown is associated with adipose tissue inflammation in different disease states, such as obesity, diabetes mellitus, HIV, and inflammatory bowel disease. Future therapeutic strategies to ameliorate intestinal barrier function may help reduce inflammation in obesity and other chronic conditions of increased intestinal permeability.

The Immunomodulatory Properties of Extracellular Vesicles Derived from Probiotics: A Novel Approach for the Management of Gastrointestinal Diseases

Probiotics, included in functional foods, nutritional supplements, or nutraceuticals, exhibit different beneficial effects on gut function. They are extensively used to improve the digestive processes as well as reduce the symptoms and progression of different diseases. Probiotics have shown to improve dysbiosis and modulate the immune response of the host by interacting with different cell types. Probiotics and the host can interact in a direct way, but it is becoming apparent that communication occurs also through extracellular vesicles (EVs) derived from probiotics. EVs are key for bacteria-bacteria and bacteria-host interactions, since they carry a wide variety of components that can modulate different signaling pathways, including those involved in the immune response. Interestingly, EVs are recently starting to be considered as an alternative to probiotics in those cases for which the use of live bacteria could be dangerous, such as immunocompromised individuals or situations where the intestinal barrier is impaired. EVs can spread through the mucus layer and interact with the host, avoiding the risk of sepsis. This review summarizes the existing knowledge about EVs from different probiotic strains, their properties, and their potential use for the prevention or treatment of different gastrointestinal diseases.

Cellular and Mucosal Immune Responses Following Vaccination with Inactivated Mutant of Escherichia coli O157:H7

Shiga toxin-producing Escherichia coli O157:H7 (O157) can cause mild to severe gastrointestinal disease in humans. Cattle are the primary reservoir for O157, which colonizes the intestinal tract without inducing any overt clinical symptoms. Parenteral vaccination can reduce O157 shedding in cattle after challenge and limit zoonotic transmission to humans, although the impact of vaccination and vaccine formulation on cellular and mucosal immune responses are undetermined. To better characterize the cattle immune response to O157 vaccination, cattle were vaccinated with either water-in-oil-adjuvanted, formalin-inactivated hha deletion mutant of Shiga toxin 2 negative (stx2^-) O157 (Adj-Vac); non-adjuvanted (NoAdj-Vac); or non-vaccinated (NoAdj-NoVac) and peripheral T cell and mucosal antibody responses assessed. Cattle in Adj-Vac group had a higher percentage of O157-specific IFNγ producing CD4⁺ and γδ⁺ T cells in recall assays compared to the NoAdj-Vac group. Furthermore, O157-specific IgA levels detected in feces of the Adj-Vac group were significantly lower in NoAdj-Vac group. Extracts prepared only from Adj-Vac group feces blocked O157 adherence to epithelial cells. Taken together, these data suggest parenteral administration of adjuvanted, inactivated whole-cell vaccines for O157 can induce O157-specific cellular and mucosal immune responses that may be an important consideration for a successful vaccination scheme.

Old Friends, immunoregulation, and stress resilience

There is a considerable body of evidence indicating that chronic adverse experience, especially chronic psychosocial stress/trauma, represents a major risk factor for the development of many somatic and affective disorders, including inflammatory bowel disease (IBD) and posttraumatic stress disorder (PTSD). However, the mechanisms underlying the development of chronic stress-associated disorders are still in large part unknown, and current treatment and prevention strategies lack efficacy and reliability. A greater understanding of mechanisms involved in the development and persistence of chronic stress-induced disorders may lead to novel approaches to prevention and treatment of these disorders. In this review, we provide evidence indicating that increases in immune (re-)activity and inflammation, potentially promoted by a reduced exposure to immunoregulatory microorganisms ("Old Friends") in today's modern society, may be causal factors in mediating the vulnerability to development and persistence of stress-related pathologies. Moreover, we discuss strategies to increase immunoregulatory processes and attenuate inflammation, as for instance contact with immunoregulatory Old Friends, which appears to be a promising strategy to promote stress resilience and to prevent/treat chronic stress-related disorders.

The effect of saturated and unsaturated fatty acids on the production of outer membrane vesicles from Bacteroides fragilis and Bacteroides thetaiotaomicron

AIM

The aim of present study is to investigate the effect of fatty acids on the outer membrane vesicles (OMVs) produced by Bacteroides spp.

BACKGROUND

Bacteroides spp. is the important member of Gut microbiota that employ OMVs production for interact with host. Besides, dietary fatty acids could influence on determination of gut microbiota composition and immune response. In this regard, we evaluated the effect of fatty acids on the growth and OMVs production of Bacteroides fragilis and Bacteroides thetaiotaomicron.

METHODS

B. fragilis and B. thetaiotaomicron were grown on BHI broth with and without palmitic and palmitoleic acids as saturated and unsaturated fatty acids, respectively. OMVs were extracted using multiple centrifugation and tris-ethylene diamine tetra acetic acid (EDTA)-Sodium deoxy cholate buffers. Physicochemical properties of OMVs were detected by electron microscopy (SEM), Bradford Coomassie brilliant blue assay and SDS-PAGE. Data were analyzed with One-way ANOVA using SPSS.

RESULTS

The growths of both Bacteroides were significantly increased by palmitic acid. Nevertheless, palmitoleic acid had no significant effect on them. Palmitic acid significantly decreased and increased the production of B. fragilis OMVs at low and high concentration, respectively. However, the production of B. thetaiotaomicron OMVs was not significantly affected by palmitic acid. Although palmitoleic acid had a significant decreasing effect on the production of B. fragilis OMVs, it significantly increased the production of B. thetaiotaomicron OMVs at low concentration.

CONCLUSION

In conclusion we reported that palmitic acid had a stimulatory effect on the growth of B. fragilis and B. thetaiotaomicron and had a dose dependent effect on the production of B. fragilis OMVs. Also producing of B. thetaiotaomicron OMVs was affected by palmitoleic acid in a dose dependent manner.

Gut Microbiota as a Prospective Therapeutic Target for Curcumin: A Review of Mutual Influence

Background

Turmeric is a spice that has recently received much interest and has been widely used in Ayurvedic medicine. Turmeric products are diarylheptanoids and have been characterized as safe. They are termed as curcuminoids that consists essentially of three major compounds: curcumin, demethoxycurcumin, and bisdemethoxycurcumin. Curcumin is a lipophilic polyphenol that has poor systemic bioavailability and suffers from biotransformation by human intestinal microflora to yield different metabolites that are easily conjugated to glucuronides and sulfate O-conjugated derivatives. Recently, an increasing number of studies have indicated that dysbiosis is linked with many metabolic diseases, though gut microbiota could be a novel potential therapeutic target.

Scope and Approach

Thus, it is suspected that curcumin and its derivatives exert direct regulative effects on the gut microbiota which could explain the paradox between curcumin's poor systemic bioavailability and its widely reported pharmacological activities.

Key Findings and Conclusions

This article summarizes a range of studies that highlight the interaction between curcumin and gut microbiota and considers opportunities for microbiome-targeting therapies using turmeric extract.

Oral fluoroquinolones and risk of fibromyalgia

The Food and Drug Administration (FDA) has recently included a black box warning on fibromyalgia-like symptoms with fluoroquinolones (FQs) but no large epidemiologic study is to date available. We undertook a case-control study using a random sample of 9 053 240 subjects obtained from the PharMetrics Plus health claims database in the United States. Cases received at least two fibromyalgia diagnoses coded by a rheumatologist matched to ten randomly selected controls. After identifying 5148 cases of fibromyalgia and 51 480 controls, the adjusted rate ratio (RR) of fibromyalgia for use of any fluoroquinolones, amoxicillin and azithromycin were 1.63 (95% CI: 1.41-1.87), 1.64 (95% CI: 1.46-1.85) and 1.68 (95% CI, 1.49-1.89), respectively. The adjusted RR for any use of FQ compared to any use of amoxicillin or azithromycin was 0.99 (95% CI: 0.83-1.18) and azithromycin is 0.97 (95%CI: 0.82-1.16), respectively. The risk of fibromyalgia with FQs is similar to that with amoxicillin and azithromycin.

Advancing risk assessment: mechanistic dose-response modelling of Listeria monocytogenes infection in human populations

The utility of characterizing the effects of strain variation and individual/subgroup susceptibility on dose-response outcomes has motivated the search for new approaches beyond the popular use of the exponential dose-response model for listeriosis. While descriptive models can account for such variation, they have limited power to extrapolate beyond the details of particular outbreaks. By contrast, this study exhibits dose-response relationships from a mechanistic basis, quantifying key biological factors involved in pathogen-host dynamics. An efficient computational algorithm and geometric interpretation of the infection pathway are developed to connect dose-response relationships with the underlying bistable dynamics of the model. Relying on in vitro experiments as well as outbreak data, we estimate plausible parameters for the human context. Despite the presence of uncertainty in such parameters, sensitivity analysis reveals that the host response is most influenced by the pathogen-immune system interaction. In particular, we show how variation in this interaction across a subgroup of the population dictates the shape of dose-response curves. Finally, in terms of future experimentation, our model results provide guidelines and highlight vital aspects of the interplay between immune cells and particular strains of Listeria monocytogenes that should be examined.

The making of a miscreant: tobacco smoke and the creation of pathogen-rich biofilms

We have previously reported that oral biofilms in clinically healthy smokers are pathogen-rich, and that this enrichment occurs within 24 h of biofilm formation. The present investigation aimed to identify a mechanism by which smoking creates this altered community structure. By combining in vitro microbial–mucosal interface models of commensal (consisting of Streptococcus oralis, Streptococcus sanguis, Streptococcus mitis, Actinomyces naeslundii, Neisseria mucosa and Veillonella parvula) and pathogen-rich (comprising S.oralis, S.sanguis, S.mitis, A.naeslundii, N.mucosa and V.parvula, Fusobacterium nucleatum, Porphyromonas gingivalis, Filifactor alocis, Dialister pneumosintes, Selenonomas sputigena, Selenominas noxia, Catonella morbi, Parvimonas micra and Tannerella forsythia) communities with metatranscriptomics, targeted proteomics and fluorescent microscopy, we demonstrate that smoke exposure significantly downregulates essential metabolic functions within commensal biofilms, while significantly increasing expression of virulence genes, notably lipopolysaccharide (LPS), flagella and capsule synthesis. By contrast, in pathogen-rich biofilms several metabolic pathways were over-expressed in response to smoke exposure. Under smoke-rich conditions, epithelial cells mounted an early and amplified pro-inflammatory and oxidative stress response to these virulence-enhanced commensal biofilms, and a muted early response to pathogen-rich biofilms. Commensal biofilms also demonstrated early and widespread cell death. Similar results were observed when smoke-free epithelial cells were challenged with smoke-conditioned biofilms, but not vice versa. In conclusion, our data suggest that smoke-induced transcriptional shifts in commensal biofilms triggers a florid pro-inflammatory response, leading to early commensal death, which may preclude niche saturation by these beneficial organisms. The cytokine-rich, pro-oxidant, anaerobic environment sustains inflammophilic bacteria, and, in the absence of commensal antagonism, may promote the creation of pathogen-rich biofilms in smokers.

Tobacco smoke inhibits the metabolism of beneficial bacteria in biofilms, while activating specific genes in pathogenic bacteria. This suggests a mechanism to explain how smoking quickly leads to the formation of damaging biofilms in the mouth and respiratory tract. Purnima Kumar and colleagues at Ohio State University, USA studied the effect of tobacco smoke on cultured biofilms used to model those that form on mucous membranes. They detected specific and varied changes in the activity of genes, proteins and metabolism that allowed pathogenic bacteria to displace beneficial “commensal” bacteria. The research suggests the transition toward pathogen-rich biofilms may contribute to the health effects of smoking by causing increased inflammation of mucous membranes and the production of damaging oxidant chemicals. Further research should investigate the chemical constituents of smoke responsible for these effects.

Effect of antibiotic, probiotic, and human rotavirus infection on colonisation dynamics of defined commensal microbiota in a gnotobiotic pig model

We developed a gnotobiotic (Gn) pig model colonised with defined commensal microbiota (DMF) to provide a simplified and controlled system to study the interactions between intestinal commensals, antibiotics (ciprofloxacin, CIP), probiotics (Escherichia coli Nissle 1917, EcN) and virulent human rotavirus (VirHRV). The DMF included seven gut commensal species of porcine origin that mimic the predominant species in the infant gut. Gn piglets were divided into four groups: DMF control (non-treated), DMF+CIP (CIP treated), DMF+CIP+EcN (CIP/EcN treated), DMF+EcN (EcN treated) and inoculated orally with 10⁵ cfu of each DMF strain. The pig gut was successfully colonised by all DMF species and established a simplified bacterial community by post-bacteria colonisation day (PBCD) 14/post-VirHRV challenge day (PCD) 0. Overall, Bifidobacterium adolescentis was commonly observed in faeces in all groups and time points. At PCD0, after six days of CIP treatment (DMF+CIP), we observed significantly decreased aerobic and anaerobic bacteria counts especially in jejunum (P<0.001), where no DMF species were detected in jejunum by T-RFLP. Following HRV challenge, 100% of pigs in DMF+CIP group developed diarrhoea with higher diarrhoea scores and duration as compared to all other groups. However, only 33% of pigs treated with EcN plus CIP developed diarrhoea. EcN treatment also enhanced the bacterial diversity and all seven DMF species were detected with a higher proportion of Bifidobacterium longum in jejunum in the DMF+CIP+EcN group on PBCD14/PCD0. Our results suggest that EcN increased the proportion of B. longum especially in jejunum and mitigated adverse impacts of antibiotic use during acute-infectious diarrhoea. The DMF model with a simplified gut commensal community can further our knowledge of how commensals and probiotics promote intestinal homeostasis and contribute to host health.

Modulation of the gut microbiota by prebiotic fibres and bacteriocins

The gut microbiota is considered an organ that co-develops with the host throughout its life. The composition and metabolic activities of the gut microbiota are subject to a complex interplay between the host genetics and environmental factors, such as lifestyle, diet, stress and antimicrobials. It is evident that certain prebiotics, and antimicrobials produced by lactic acid bacteria (LAB), can shape the composition of the gut microbiota and its metabolic activities to promote host health and/or prevent diseases. In this review, we aim to give an overview of the impact of prebiotic fibres, and bacteriocins from LAB, on the gut microbiota and its activities, which affect the physiology and health of the host. These represent two different mechanisms in modulating the gut microbiota, the first involving exploitative competition by which the growth of beneficial bacteria is promoted and the latter involving interference competition by which the growth of pathogens and other unwanted bacteria is prevented. For interference competition in the gut, bacteriocins offer special advantages over traditional antibiotics, in that they can be designed to act towards specific unwanted bacteria and other pathogens, without any remarkable collateral effects on beneficial microbes sharing the same niche.

Unraveling the dose-response puzzle of L. monocytogenes: A mechanistic approach

Food-borne disease outbreaks caused by Listeria monocytogenes continue to impose heavy burdens on public health in North America and globally. To explore the threat L. monocytogenes presents to the elderly, pregnant woman and immuno-compromised individuals, many studies have focused on in-host infection mechanisms and risk evaluation in terms of dose-response outcomes. However, the connection of these two foci has received little attention, leaving risk prediction with an insufficient mechanistic basis. Consequently, there is a critical need to quantifiably link in-host infection pathways with the dose-response paradigm. To better understand these relationships, we propose a new mathematical model to describe the gastro-intestinal pathway of L. monocytogenes within the host. The model dynamics are shown to be sensitive to inoculation doses and exhibit bi-stability phenomena. Applying the model to guinea pigs, we show how it provides useful tools to identify key parameters and to inform critical values of these parameters that are pivotal in risk evaluation. Our preliminary analysis shows that the effect of gastro-environmental stress, the role of commensal microbiota and immune cells are critical for successful infection of L. monocytogenes and for dictating the shape of the dose-response curves.

Dental Pulp Defence and Repair Mechanisms in Dental Caries

Dental caries is a chronic infectious disease resulting from the penetration of oral bacteria into the enamel and dentin. Microorganisms subsequently trigger inflammatory responses in the dental pulp. These events can lead to pulp healing if the infection is not too severe following the removal of diseased enamel and dentin tissues and clinical restoration of the tooth. However, chronic inflammation often persists in the pulp despite treatment, inducing permanent loss of normal tissue and reducing innate repair capacities. For complete tooth healing the formation of a reactionary/reparative dentin barrier to distance and protect the pulp from infectious agents and restorative materials is required. Clinical and in vitro experimental data clearly indicate that dentin barrier formation only occurs when pulp inflammation and infection are minimised, thus enabling reestablishment of tissue homeostasis and health. Therefore, promoting the resolution of pulp inflammation may provide a valuable therapeutic opportunity to ensure the sustainability of dental treatments. This paper focusses on key cellular and molecular mechanisms involved in pulp responses to bacteria and in the pulpal transition between caries-induced inflammation and dentinogenic-based repair. We report, using selected examples, different strategies potentially used by odontoblasts and specialized immune cells to combat dentin-invading bacteria in vivo.

Dysbiosis of the gut microbiota in disease

There is growing evidence that dysbiosis of the gut microbiota is associated with the pathogenesis of both intestinal and extra-intestinal disorders. Intestinal disorders include inflammatory bowel disease, irritable bowel syndrome (IBS), and coeliac disease, while extra-intestinal disorders include allergy, asthma, metabolic syndrome, cardiovascular disease, and obesity.

In many of these conditions, the mechanisms leading to disease development involves the pivotal mutualistic relationship between the colonic microbiota, their metabolic products, and the host immune system. The establishment of a ‘healthy’ relationship early in life appears to be critical to maintaining intestinal homeostasis. Whilst we do not yet have a clear understanding of what constitutes a ‘healthy’ colonic microbiota, a picture is emerging from many recent studies identifying particular bacterial species associated with a healthy microbiota. In particular, the bacterial species residing within the mucus layer of the colon, either through direct contact with host cells, or through indirect communication via bacterial metabolites, may influence whether host cellular homeostasis is maintained or whether inflammatory mechanisms are triggered. In addition to inflammation, there is some evidence that perturbations in the gut microbiota is involved with the development of colorectal cancer. In this case, dysbiosis may not be the most important factor, rather the products of interaction between diet and the microbiome. High-protein diets are thought to result in the production of carcinogenic metabolites from the colonic microbiota that may result in the induction of neoplasia in the colonic epithelium.

Ever more sensitive metabolomics methodologies reveal a suite of small molecules produced in the microbiome which mimic or act as neurosignallers or neurotransmitters. Coupled with evidence that probiotic interventions may alter psychological endpoints in both humans and in rodent models, these data suggest that CNS-related co-morbidities frequently associated with GI disease may originate in the intestine as a result of microbial dysbiosis.

This review outlines the current evidence showing the extent to which the gut microbiota contributes to the development of disease. Based on evidence to date, we can assess the potential to positively modulate the composition of the colonic microbiota and ameliorate disease activity through bacterial intervention.

Functional genomic and metagenomic approaches to understanding gut microbiota-animal mutualism

Accumulating data sets of gut microbiome by next-generation sequencing allow us to gain a comprehensive view of the functional diversity of the gut-associated metagenome. However, many microbiome functions are unknown and/or have only been predicted, and may not necessarily reflect the in vivo function within a gut niche. Functional genomic and metagenomic approaches have been successfully applied to broaden the understanding of invertebrate and vertebrate gut microbiome involved in diverse functions, including colonization ability, nutritional processing, antibiotic resistance, microbial physiology and metabolism, and the modulation of the host physiology. In this review, we discuss the recent knowledge obtained from the study of functional genomics and metagenomics of the animal intestine and its potential values for understanding gut microbiota-animal mutualism.

Dysbiosis of the gut microbiota in disease

There is growing evidence that dysbiosis of the gut microbiota is associated with the pathogenesis of both intestinal and extra-intestinal disorders. Intestinal disorders include inflammatory bowel disease, irritable bowel syndrome (IBS), and coeliac disease, while extra-intestinal disorders include allergy, asthma, metabolic syndrome, cardiovascular disease, and obesity.

Protective role of gut commensal microbes against intestinal infections

The human gastrointestinal tract is colonized by multitudes of microorganisms that exert beneficial effects on human health. Mounting evidence suggests that intestinal microbiota contributes to host resistance against enteropathogenic bacterial infection. However, molecular details that account for such an important role has just begun to be understood. The commensal microbes in the intestine regulate gut homeostasis through activating the development of host innate immunity and producing molecules with antimicrobial activities that directly inhibit propagation of pathogenic bacteria. Understanding the protective roles of gut microbiota will provide a better insight into the molecular basis that underlies complicated interaction among host-pathogen-symbiont. In this review, we highlighted recent findings that help us broaden our knowledge of the intestinal ecosystem and thereby come up with a better strategy for combating enteropathogenic infection.

Batf3 deficiency is not critical for the generation of CD8α⁺ dendritic cells

Recently, we have reported that CD8α(+) DCs, rather than CD8(+) T cells, are involved in the establishment and maintenance of HSV-1 latency in the trigeminal ganglia (TG) of ocularly infected mice. In the current study, we investigated whether similar results can be obtained using Batf3(-/-) mice that previously were reported to lack CD8α(+) DCs. However, our results demonstrate that Batf3(-/-) mice, without any known infection, express CD8α(+) DCs. Consequently, due to the presence of CD8α(+) DCs, no differences were detected in the level of HSV-1 latency between Batf3(-/-) mice compared with wild type control mice.

Immunomodulation by gut microbiota: role of Toll-like receptor expressed by T cells

A close relationship exists between gut microbiota and immune responses. An imbalance of this relationship can determine local and systemic immune diseases. In fact the immune system plays an essential role in maintaining the homeostasis with the microbiota that normally resides in the gut, while, at the same time, the gut microbiota influences the immune system, modulating number and function of effector and regulatory T cells. To achieve this aim, mutual regulation between immune system and microbiota is achieved through several mechanisms, including the engagement of toll-like receptors (TLRs), pathogen-specific receptors expressed on numerous cell types. TLRs are able to recognize ligands from commensal or pathogen microbiota to maintain the tolerance or trigger the immune response. In this review, we summarize the latest evidences about the role of TLRs expressed in adaptive T cells, to understand how the immune system promotes intestinal homeostasis, fights invasion by pathogens, and is modulated by the intestinal microbiota.

An intestinal commensal symbiosis factor controls neuroinflammation via TLR2-mediated CD39 signalling

The mammalian immune system constitutively senses vast quantities of commensal bacteria and their products through pattern recognition receptors, yet excessive immune reactivity is prevented under homeostasis. The intestinal microbiome can influence host susceptibility to extra-intestinal autoimmune disorders. Here we report that polysaccharide A (PSA), a symbiosis factor for the human intestinal commensal Bacteroides fragilis, protects against central nervous system demyelination and inflammation during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, through Toll-like receptor 2 (TLR2). TLR2 mediates tissue-specific expansion of a critical regulatory CD39(+) CD4 T-cell subset by PSA. Ablation of CD39 signalling abrogates PSA control of EAE manifestations and inflammatory cytokine responses. Further, CD39 confers immune-regulatory phenotypes to total CD4 T cells and Foxp3(+) CD4 Tregs. Importantly, CD39-deficient CD4 T cells show an enhanced capability to drive EAE progression. Our results demonstrate the therapeutic potential and underlying mechanism by which an intestinal symbiont product modulates CNS-targeted demyelination.

Phasic study of intestinal homeostasis disruption in experimental intestinal obstruction

AIM: To investigate the phasic alteration of intestinal homeostasis in an experimental model of intestinal obstruction.

METHODS: A rabbit model of intestinal obstruction was established by transforming parts of an infusion set into an in vivo pulled-type locking clamp and creating a uniform controllable loop obstruction in the mesenteric non-avascular zone 8 cm from the distal end of the ileum. The phasic alteration of intestinal homeostasis was studied after intestinal obstruction. The changes in goblet cells, intraepithelial lymphocytes, lamina propria lymphocytes, and intestinal epithelium were quantified from periodic acid-Schiff-stained sections. Ornithine decarboxylase (ODC) activity and serum citrulline levels were measured by high-performance liquid chromatography. Claudin 1 mRNA expression was examined by real-time polymerase chain reaction analysis. Intestinal microorganisms, wet/dry weight ratios, pH values, and endotoxin levels were determined at multiple points after intestinal obstruction. Furthermore, the number and ratio of CD3⁺, CD4⁺ and CD8⁺ T cells were determined by flow cytometry, and secretory IgA levels were measured with an enzyme-linked immunosorbent assay.

RESULTS: A suitable controllable rabbit model of intestinal obstruction was established. Intestinal obstruction induced goblet cell damage and reduced cell number. Further indicators of epithelial cell damage were observed as reduced serum citrulline levels and claudin 1 gene expression, and a transient increase in ODC activity. In addition, the wet/dry weight ratio and pH of the intestinal lumen were also dramatically altered. The ratio of Bacillus bifidus and enterobacteria was reversed following intestinal obstruction. The number and area of Peyer’s patches first increased then sharply decreased after the intestinal obstruction, along with an alteration in the ratio of CD4/CD8⁺ T cells, driven by an increase in CD3⁺ and CD8⁺ T cells and a decrease in CD4⁺ T cells. The number of lamina propria lymphocytes also gradually decreased with prolonged obstruction.

CONCLUSION: Intestinal obstruction can induce disruption of intestinal homeostasis.