Intestinal mucins: the binding sites for Salmonella typhimurium

Sortase-encoding genes, srtA and srtC, mediate Enterococcus faecalis OG1RF persistence in the Helicoverpa zea gastrointestinal tract

Enterococcus faecalis is a commensal and opportunistic pathogen in the gastrointestinal (GI) tract of mammals and insects. To investigate mechanisms of bacterial persistence in the gastrointestinal tract (GIT), we developed a non-destructive sampling model using Helicoverpa zea, a destructive agricultural pest, as host to study the role of bacterial sortase enzymes in mitigating persistence in the gastrointestinal tract. E. faecalis OG1RF ΔsrtA and E. faecalis OG1RF ΔsrtC, isogenic E. faecalis OG1RF sortase mutants grew similarly under planktonic growth conditions relative to a streptomycin-resistant E. faecalis OG1RFS WT in vitro but displayed impaired biofilm formation under, both, physiological and alkaline conditions. In the H. zea GI model, both mutants displayed impaired persistence relative to the WT. This represents one of the initial reports in which a non-destructive insect model has been used to characterize mechanisms of bacterial persistence in the Lepidopteran midgut and, furthermore, sheds light on new molecular mechanisms employed by diverse microorganisms to associate with invertebrate hosts.

Ovarian sex steroid and epithelial control of immune responses in the uterus and oviduct: human and animal models†

The female reproductive tract (FRT), including the uterus and oviduct (Fallopian tube), is responsible for maintaining an optimal microenvironment for reproductive processes, such as gamete activation and transportation, sperm capacitation, fertilization, and early embryonic and fetal development. The mucosal surface of the FRT may be exposed to pathogens and sexually transmitted microorganisms due to the opening of the cervix during mating. Pathogens and endotoxins may also reach the oviduct through the peritoneal fluid. To maintain an optimum reproductive environment while recognizing and killing pathogenic bacterial and viral agents, the oviduct and uterus should be equipped with an efficient and rigorously controlled immune system. Ovarian sex steroids can affect epithelial cells and underlying stromal cells, which have been shown to mediate innate and adaptive immune responses. This, in turn, protects against potential infections while maintaining an optimal milieu for reproductive events, highlighting the homeostatic involvement of ovarian sex steroids and reproductive epithelial cells. This article will discuss how ovarian sex steroids affect the immune reactions elicited by the epithelial cells of the non-pregnant uterus and oviduct in the bovine, murine, and human species. Finally, we propose that there are regional and species-specific differences in the immune responses in FRT.

Performance and characterization of snail adhesive mucus as a bioflocculant against toxic Microcystis

Toxic Microcystis blooms are widespread in aquatic bodies, posing major threats to aquatic and human life. Recently, bioflocculants have attracted considerable attention as a promising biomaterial for Microcystis management. In search of a novel organism that can produce an efficient bioflocculant for controlling harmful algae sustainably, the native gastropod Cipangopaludina chinensis was co-cultured continuously with toxic Microcystis under different initial algal cell densities. The bioflocculation effect of snail mucus on toxic Microcystis, microcystin removal, and toxin accumulation in snails was investigated. In addition, the properties of the adhesive mucus were characterized using microscopic, X-ray diffraction, infrared spectroscopy, and polysaccharide and proteome analyses. Microcystis cells were captured and flocculated by the snail mucus; removal efficiencies of up to 89.9% and 84.8% were achieved for microalgae and microcystin-leucine arginine (MC-LR), respectively, when co-cultured with C. chinensis for only one day. After nine-day exposure, less than 5.49 µg/kg DW microcystins accumulated in the snails, indicating safety for human consumption. The snail mucus contained 104.3 µg/mg protein and 72.7 µg/mg carbohydrate, which provide several functional groups beneficial for Microcystis bioflocculation. The main monosaccharide subunits of polysaccharides are galactose, galactosamine, glucosamine, fucose, glucose, and mannose. Most of them are key components of polysaccharides in many bioflocculants. Gene Ontology analysis indicated the protein enrichment in binding processes and catalytic activity, which may account for Microcystis bioflocculation via protein binding or enzymatic reactions. The findings indicate that native C. chinensis secretes adhesive mucus that can act as bioflocculant for toxic Microcystis from ambient water and can be an effective and eco-friendly tool for Microcystis suppression.

Salmonella-Based Biorodenticides: Past Applications and Current Contradictions

The idea of using pathogens to control pests has existed since the end of the 19th century. Enterobacteria from the genus Salmonella, discovered at that time, are the causative agents of many serious diseases in mammals often leading to death. Mostly, the strains of Salmonella are able to infect a wide spectrum of hosts belonging to vertebrates, but some of them show host restriction. Several strains of these bacteria have been used as biorodenticides due to the host restriction until they were banned in many countries in the second part of the 20th century. The main reason for the ban was their potential pathogenicity for some domestic animals and poultry and the outbreaks of gastroenteritis in humans. Since that time, a lot of data regarding the host specificity and host restriction of different strains of Salmonella have been accumulated, and the complexity of the molecular mechanisms affecting it has been uncovered. In this review, we summarize the data regarding the history of studying and application of Salmonella-based rodenticides, discuss molecular systems controlling the specificity of Salmonella interactions within its multicellular hosts at different stages of infection, and attempt to reconstruct the network of genes and their allelic variants which might affect the host-restriction mechanisms.

Cross-Talk Between the Intestinal Epithelium and Salmonella Typhimurium

Salmonella enterica serovars are invasive gram-negative bacteria, causing a wide range of diseases from gastroenteritis to typhoid fever, representing a public health threat around the world. Salmonella gains access to the intestinal lumen after oral ingestion of contaminated food or water. The crucial initial step to establish infection is the interaction with the intestinal epithelium. Human-adapted serovars such as S. Typhi or S. Paratyphi disseminate to systemic organs and induce life-threatening disease known as typhoid fever, whereas broad-host serovars such as S. Typhimurium usually are limited to the intestine and responsible for gastroenteritis in humans. To overcome intestinal epithelial barrier, Salmonella developed mechanisms to induce cellular invasion, intracellular replication and to face host defence mechanisms. Depending on the serovar and the respective host organism, disease symptoms differ and are linked to the ability of the bacteria to manipulate the epithelial barrier for its own profit and cross the intestinal epithelium.

This review will focus on S. Typhimurium (STm). To better understand STm pathogenesis, it is crucial to characterize the crosstalk between STm and the intestinal epithelium and decipher the mechanisms and epithelial cell types involved. Thus, the purpose of this review is to summarize our current knowledge on the molecular dialogue between STm and the various cell types constituting the intestinal epithelium with a focus on the mechanisms developed by STm to cross the intestinal epithelium and access to subepithelial or systemic sites and survive host defense mechanisms.

Mucosal Defense Against Giardia at the Intestinal Epithelial Cell Interface

Human giardiasis, caused by the protozoan parasite Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis, Lamblia intestinalis), is one of the most commonly-identified parasitic diseases worldwide. Chronic G. duodenalis infections cause a malabsorption syndrome that may lead to failure to thrive and/or stunted growth, especially in children in developing countries. Understanding the parasite/epithelial cell crosstalk at the mucosal surfaces of the small intestine during human giardiasis may provide novel insights into the mechanisms underlying the parasite-induced immunopathology and epithelial tissue damage, leading to malnutrition. Efforts to identify new targets for intervening in the development of intestinal immunopathology and the progression to malnutrition are critical. Translating these findings into a clinical setting will require analysis of these pathways in cells and tissues from humans and clinical trials could be devised to determine whether interfering with unwanted mucosal immune responses developed during human giardiasis provide better therapeutic benefits and clinical outcomes for G. duodenalis infections in humans.

Biology, Significance and Immune Signaling of Mucin 1 in Hepatocellular Carcinoma

Mucin 1 (MUC 1) is a highly glycosylated tumor-associated antigen (TAA) overexpressed in hepatocellular carcinoma (HCC). This protein plays a critical role in various immune-mediated signaling pathways at its transcriptional and post-transcriptional levels, leading to immune evasion and metastasis in HCC. HCC cells maintain an immune-suppressive environment with the help of immunesuppressive tumor-associated antigens, resulting in a metastatic spread of the disease. The development of intense immunotherapeutic strategies to target tumor-associated antigen is critical to overcoming the progression of HCC. MUC 1 remains the most recognized tumor-associated antigen since its discovery over 30 years ago. A few promising immunotherapies targeting MUC 1 are currently under clinical trials, including CAR-T and CAR-pNK-mediated therapies. This review highlights the biosynthesis, significance, and clinical implication of MUC 1 as an immune target in HCC.

Tripartite relationship between gut microbiota, intestinal mucus and dietary fibers: towards preventive strategies against enteric infections

The human gut is inhabited by a large variety of microorganims involved in many physiological processes and collectively referred as to gut microbiota. Disrupted microbiome has been associated with negative health outcomes and especially could promote the onset of enteric infections. To sustain their growth and persistence within the human digestive tract, gut microbes and enteric pathogens rely on two main polysaccharide compartments, namely dietary fibers and mucus carbohydrates. Several evidences suggest that the three-way relationship between gut microbiota, dietary fibers and mucus layer could unravel the capacity of enteric pathogens to colonise the human digestive tract and ultimately lead to infection. The review starts by shedding light on similarities and differences between dietary fibers and mucus carbohydrates structures and functions. Next, we provide an overview of the interactions of these two components with the third partner, namely, the gut microbiota, under health and disease situations. The review will then provide insights into the relevance of using dietary fibers interventions to prevent enteric infections with a focus on gut microbial imbalance and impaired-mucus integrity. Facing the numerous challenges in studying microbiota-pathogen-dietary fiber-mucus interactions, we lastly describe the characteristics and potentialities of currently available in vitro models of the human gut.

Probiotics in poultry feed: A comprehensive review

The use of antibiotics to maintain animal well-being, promote growth and improve efficiency has been practised for more than 50 years. However, as early as the 1950s, researchers identified concern on the development of resistant bacteria for the antibiotics streptomycin and tetracycline used in turkeys and broilers respectively. These findings laid the groundwork for agricultural officials to impose stricter regulatory parameters on the use of antibiotics in poultry feeds. Probiotics are live micro-organisms included in the diet of animals as feed additives or supplements. Commonly known as a direct-fed microbial, probiotics provide beneficial properties to the host, primarily through action in the gastrointestinal tract (GIT) of the animal. Supplementation of probiotics in the diet can improve animal health and performance, through contributions to gut health and nutrient use. For instance, supplementation of probiotics has been demonstrated to benefit farm animals in immune modulation, structural modulation and increased cytokine production, which positively affect the intestinal mucosal lining against pathogens. Bacillus subtilis has been a popular bacterium used within the industry and was shown to improve intestinal villus height. Increasing the villus height and structure of the crypts in the GIT allows for the improvement of nutrient digestion and absorption. Tight junctions maintain important defences against pathogenic bacteria and cellular homeostasis. Heat stress can be a major environmental challenge in the poultry industry. Heat stress causes the bird to fluctuate its internal core temperature beyond their comfort zone. To overcome such challenges, poultry will attempt to balance its heat production and dissipation through behavioural and physiological adaptation mechanisms.

Mucus blocks probiotics but increases penetration of motile pathogens and induces TNF-α and IL-8 secretion

The mucosal barrier in combination with innate immune system are the first line of defense against luminal bacteria at the intestinal mucosa. Dysfunction of the mucus layer and bacterial infiltration are linked to tissue inflammation and disease. To study host-bacterial interactions at the mucosal interface, we created an experimental model that contains luminal space, a mucus layer, an epithelial layer, and suspended immune cells. Reconstituted porcine small intestinal mucus formed an 880 ± 230 µm thick gel layer and had a porous structure. In the presence of mucus, sevenfold less probiotic and nonmotile VSL#3 bacteria transmigrated across the epithelial barrier compared to no mucus. The higher bacterial transmigration caused immune cell differentiation and increased the concentration of interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α; p < .01). Surprisingly, the mucus layer increased transmigration of pathogenic Salmonella and increased secretion of TNF-α and IL-8 (p < .05). Nonmotile, flagella knockout Salmonella had lower transmigration and caused lower IL-8 and TNF-α secretion (p < .05). These results demonstrate that motility enables pathogenic bacteria to cross the mucus and epithelial layers, which could lead to infection. Using an in vitro coculture platform to understand the interactions of bacteria with the intestinal mucosa has the potential to improve the treatment of intestinal diseases.

Interactions of commensal and pathogenic microorganisms with the mucus layer in the colon

The intestinal mucosal barrier, which is composed of epithelial cells and mucus layers secreted by goblet cells and contains commensal bacteria, constitutes the first line of defense against pathogenic gut microbiota. However, homeostasis between the microbiota and mucus layer is easily disrupted by certain factors, resulting in alteration of the gut microbiota and entry of pathogens to the intestinal mucosal barrier. In this review, we describe the structures and functions of the mucus layer, expound several crucial influencing factors, including diet styles, medications and host genetics, and discuss how pathogenic microorganisms interact with the mucus layer and commensal microbiota, with the understanding that unraveling their complex interactions under homeostatic and dysbiosis conditions in the colon would help reveal some underlying pathogenic mechanisms and thus develop new strategies to prevent pathogenic microbiological colonization.

Host Mucin Is Exploited by Pseudomonas aeruginosa To Provide Monosaccharides Required for a Successful Infection

One of the primary functions of the mucosal barrier, found lining epithelial cells, is to serve as a first-line of defense against microbial pathogens. The major structural components of mucus are heavily glycosylated proteins called mucins. Mucins are key components of the innate immune system as they aid in the clearance of pathogens and can decrease pathogen virulence. It has also been recently reported that individual mucins and derived glycans can attenuate the virulence of the human pathogen Pseudomonas aeruginosa Here, we show data indicating that mucins not only play a role in host defense but that they can also be subverted by P. aeruginosa to cause disease. We found that the mucin MUL-1 and mucin-derived monosaccharides N-acetyl-galactosamine and N-acetylglucosamine are required for P. aeruginosa killing of Caenorhabditis elegans We also found that the defective adhesion of P. aeruginosa to human lung alveolar epithelial cells, deficient in the mucin MUC1, can be reversed by the addition of individual monosaccharides. The monosaccharides identified in this study are found in a wide range of organisms where they act as host factors required for bacterial pathogenesis. While mucins in C. elegans lack sialic acid caps, which makes their monosaccharides readily available, they are capped in other species. Pathogens such as P. aeruginosa that lack sialidases may rely on enzymes from other bacteria to utilize mucin-derived monosaccharides.IMPORTANCE One of the first lines of defense present at mucosal epithelial tissues is mucus, which is a highly viscous material formed by mucin glycoproteins. Mucins serve various functions, but importantly they aid in the clearance of pathogens and debris from epithelial barriers and serve as innate immune factors. In this study, we describe a requirement of host monosaccharides, likely derived from host mucins, for the ability of Pseudomonas aeruginosa to colonize the intestine and ultimately cause death in Caenorhabditis elegans We also demonstrate that monosaccharides alter the ability of bacteria to bind to both Caenorhabditis elegans intestinal cells and human lung alveolar epithelial cells, suggesting that there are conserved mechanisms underlying host-pathogen interactions in a range of organisms. By gaining a better understanding of pathogen-mucin interactions, we can develop better approaches to protect against pathogen infection.

Molecular Mechanisms of Salmonella Effector Proteins: A Comprehensive Review

Salmonella can be categorized into many serotypes, which are specific to known hosts or broadhosts. It makes no difference which one of the serotypes would penetrate the gastrointestinal tract because they all face similar obstacles such as mucus and microbiome. However, following their penetration, some species remain in the gastrointestinal tract; yet, others spread to another organ like gallbladder. Salmonella is required to alter the immune response to sustain its intracellular life. Changing the host response requires particular effector proteins and vehicles to translocate them. To this end, a categorized gene called Salmonella pathogenicity island (SPI) was developed; genes like Salmonella pathogenicity island encode aggressive or modulating proteins. Initially, Salmonella needs to be attached and stabilized via adhesin factor, without which no further steps can be taken. In this review, an attempt has been made to elaborate on each factor attached to the host cell or to modulating and aggressive proteins that evade immune systems. This review includes four sections: (A) attachment factors or T3SS- independent entrance, (B) effector proteins or T3SS-dependent entrance, (c) regulation of invasive genes, and (D) regulation of immune responses.

Fimbriae and related receptors for Salmonella Enteritidis

Infection with Salmonella Enteritidis (SE) is one of the main causes for food- and water-borne diseases, and is a major concern to public health for both humans and animals worldwide. Some fimbrial antigens expressed by SE strains have been described and characterized, containing SEF14, SEF17, SEF21, long polar fimbriae and plasmid-encoded fimbriae, they play a role in bacterial survival in the host or external environment. However, their functions remain to be well elucidated, with the initial attachment and binding for fimbriae-mediated SE infections only minimally understood. Meanwhile, host-pathogen interactions provide insights into receptor modulation of the host innate immune system. Therefore, to well understand the pathogenicity of SE bacteria and to comprehend the host response to infection, the host cell-SE interactions need to be characterized. This review describes SE fimbriae receptors with an emphasis on the interaction between the receptor and SE fimbriae.

Evolution of Salmonella-Host Cell Interactions through a Dynamic Bacterial Genome

Salmonella Typhimurium has a broad arsenal of genes that are tightly regulated and coordinated to facilitate adaptation to the various host environments it colonizes. The genome of Salmonella Typhimurium has undergone multiple gene acquisition events and has accrued changes in non-coding DNA that have undergone selection by regulatory evolution. Together, at least 17 horizontally acquired pathogenicity islands (SPIs), prophage-associated genes, and changes in core genome regulation contribute to the virulence program of Salmonella. Here, we review the latest understanding of these elements and their contributions to pathogenesis, emphasizing the regulatory circuitry that controls niche-specific gene expression. In addition to an overview of the importance of SPI-1 and SPI-2 to host invasion and colonization, we describe the recently characterized contributions of other SPIs, including the antibacterial activity of SPI-6 and adhesion and invasion mediated by SPI-4. We further discuss how these fitness traits have been integrated into the regulatory circuitry of the bacterial cell through cis-regulatory evolution and by a careful balance of silencing and counter-silencing by regulatory proteins. Detailed understanding of regulatory evolution within Salmonella is uncovering novel aspects of infection biology that relate to host-pathogen interactions and evasion of host immunity.

Interactions of Intestinal Bacteria with Components of the Intestinal Mucus

The human gut is colonized by a variety of large amounts of microbes that are collectively called intestinal microbiota. Most of these microbial residents will grow within the mucus layer that overlies the gut epithelium and will act as the first line of defense against both commensal and invading microbes. This mucus is essentially formed by mucins, a family of highly glycosylated protein that are secreted by specialize cells in the gut. In this Review, we examine how commensal members of the microbiota and pathogenic bacteria use mucus to their advantage to promote their growth, develop biofilms and colonize the intestine. We also discuss how mucus-derived components act as nutrient and chemical cues for adaptation and pathogenesis of bacteria and how bacteria can influence the composition of the mucus layer.

The impact of hypoxia on intestinal epithelial cell functions: consequences for invasion by bacterial pathogens

The maintenance of oxygen homeostasis in human tissues is mediated by several cellular adaptations in response to low-oxygen stress, called hypoxia. A decrease in tissue oxygen levels is initially counteracted by increasing local blood flow to overcome diminished oxygenation and avoid hypoxic stress. However, studies have shown that the physiological oxygen concentrations in several tissues are much lower than atmospheric (normoxic) conditions, and the oxygen supply is finely regulated in individual cell types. The gastrointestinal tract has been described to subsist in a state of physiologically low oxygen level and is thus depicted as a tissue in the state of constant low-grade inflammation. The intestinal epithelial cell layer plays a vital role in the immune response to inflammation and infections that occur within the intestinal tissue and is involved in many of the adaptation responses to hypoxic stress. This is especially relevant in the context of inflammatory disorders, such as inflammatory bowel disease (IBD). Therefore, this review aims to describe the intestinal epithelial cellular response to hypoxia and the consequences for host interactions with invading gastrointestinal bacterial pathogens.

Mimicking microbial strategies for the design of mucus-permeating nanoparticles for oral immunization

Dealing with mucosal delivery systems means dealing with mucus. The name mucosa comes from mucus, a dense fluid enriched in glycoproteins, such as mucin, which main function is to protect the delicate mucosal epithelium. Mucus provides a barrier against physiological chemical and physical aggressors (i.e., host secreted digestive products such as bile acids and enzymes, food particles) but also against the potentially noxious microbiota and their products. Intestinal mucosa covers 400m(2) in the human host, and, as a consequence, is the major portal of entry of the majority of known pathogens. But, in turn, some microorganisms have evolved many different approaches to circumvent this barrier, a direct consequence of natural co-evolution. The understanding of these mechanisms (known as virulence factors) used to interact and/or disrupt mucosal barriers should instruct us to a rational design of nanoparticulate delivery systems intended for oral vaccination and immunotherapy. This review deals with this mimetic approach to obtain nanocarriers capable to reach the epithelial cells after oral delivery and, in parallel, induce strong and long-lasting immune and protective responses.

Expression of the Blood-Group-Related Gene B4galnt2 Alters Susceptibility to Salmonella Infection

Glycans play important roles in host-microbe interactions. Tissue-specific expression patterns of the blood group glycosyltransferase β-1,4-N-acetylgalactosaminyltransferase 2 (B4galnt2) are variable in wild mouse populations, and loss of B4galnt2 expression is associated with altered intestinal microbiota. We hypothesized that variation in B4galnt2 expression alters susceptibility to intestinal pathogens. To test this, we challenged mice genetically engineered to express different B4galnt2 tissue-specific patterns with a Salmonella Typhimurium infection model. We found B4galnt2 intestinal expression was strongly associated with bacterial community composition and increased Salmonella susceptibility as evidenced by increased intestinal inflammatory cytokines and infiltrating immune cells. Fecal transfer experiments demonstrated a crucial role of the B4galnt2-dependent microbiota in conferring susceptibility to intestinal inflammation, while epithelial B4galnt2 expression facilitated epithelial invasion of S. Typhimurium. These data support a critical role for B4galnt2 in gastrointestinal infections. We speculate that B4galnt2-specific differences in host susceptibility to intestinal pathogens underlie the strong signatures of balancing selection observed at the B4galnt2 locus in wild mouse populations.

Human Clostridium difficile infection: altered mucus production and composition

The majority of antibiotic-induced diarrhea is caused by Clostridium difficile (C. difficile). Hospitalizations for C. difficile infection (CDI) have tripled in the last decade, emphasizing the need to better understand how the organism colonizes the intestine and maintain infection. The mucus provides an interface for bacterial-host interactions and changes in intestinal mucus have been linked host health. To assess mucus production and composition in healthy and CDI patients, the main mucins MUC1 and MUC2 and mucus oligosaccharides were examined. Compared with healthy subjects, CDI patients demonstrated decreased MUC2 with no changes in surface MUC1. Although MUC1 did not change at the level of the epithelia, MUC1 was the primary constituent of secreted mucus in CDI patients. CDI mucus also exhibited decreased N-acetylgalactosamine (GalNAc), increased N-acetylglucosamine (GlcNAc), and increased terminal galactose residues. Increased galactose in CDI specimens is of particular interest since terminal galactose sugars are known as C. difficile toxin A receptor in animals. In vitro, C. difficile is capable of metabolizing fucose, mannose, galactose, GlcNAc, and GalNAc for growth under healthy stool conditions (low Na(+) concentration, pH 6.0). Injection of C. difficile into human intestinal organoids (HIOs) demonstrated that C. difficile alone is sufficient to reduce MUC2 production but is not capable of altering host mucus oligosaccharide composition. We also demonstrate that C. difficile binds preferentially to mucus extracted from CDI patients compared with healthy subjects. Our results provide insight into a mechanism of C. difficile colonization and may provide novel target(s) for the development of alternative therapeutic agents.

Mucosal Inflammatory Response to Salmonella typhimurium Infection

The human intestinal epithelium consists of a single layer of epithelial cells that forms a barrier against food antigens and the resident microbiota within the lumen. This delicately balanced organ functions in a highly sophisticated manner to uphold the fidelity of the intestinal epithelium and to eliminate pathogenic microorganisms. On the luminal side, this barrier is fortified by a thick mucus layer, and on the serosal side exists the lamina propria containing a resident population of immune cells. Pathogens that are able to breach this barrier disrupt the healthy epithelial lining by interfering with the regulatory mechanisms that govern the normal balance of intestinal architecture and function. This disruption results in a coordinated innate immune response deployed to eliminate the intruder that includes the release of antimicrobial peptides, activation of pattern-recognition receptors, and recruitment of a variety of immune cells. In the case of Salmonella enterica serovar typhimurium (S. typhimurium) infection, induction of an inflammatory response has been linked to its virulence mechanism, the type III secretion system (T3SS). The T3SS secretes protein effectors that exploit the host’s cell biology to facilitate bacterial entry and intracellular survival, and to modulate the host immune response. As the role of the intestinal epithelium in initiating an immune response has been increasingly realized, this review will highlight recent research that details progress made in understanding mechanisms underlying the mucosal inflammatory response to Salmonella infection, and how such inflammatory responses impact pathogenic fitness of this organism.

Tumour markers and kidney function: a systematic review

Tumour markers represent useful tools in diagnosis and clinical management of patients with cancer, because they are easy to use, minimally invasive, and easily measured in either blood or urine. Unfortunately, such an ideal marker, as yet, does not exist. Different pathological states may increase the level of a tumour marker in the absence of any neoplasia. Alternatively, low levels of tumour markers could be also found in the presence of neoplasias. We aimed at reviewing studies currently available in the literature examining the association between tumour markers and different renal impairment conditions. Each tumour marker was found to be differently influenced by these criteria; additionally we revealed in many cases a lack of available published data.

Human milk mucin 1 and mucin 4 inhibit Salmonella enterica serovar Typhimurium invasion of human intestinal epithelial cells in vitro

Many human milk glycans inhibit pathogen binding to host receptors and their consumption by infants is associated with reduced risk of disease. Salmonella infection is more frequent among infants than among the general population, but the incidence is lower in breast-fed babies, suggesting that human milk could contain components that inhibit Salmonella. This study aimed to test whether human milk per se inhibits Salmonella invasion of human intestinal epithelial cells in vitro and, if so, to identify the milk components responsible for inhibition. Salmonella enterica serovar Typhimurium SL1344 (SL1344) invasion of FHs 74 Int and Caco-2 cells were the models of human intestinal epithelium infection. Internalization of fluorescein-5-isothiocyanate-labeled SL1344 into intestinal cells was measured by flow cytometry to quantify infection. Human milk and its fractions inhibited infection; the inhibitory activity localized to the high molecular weight glycans. Mucin 1 and mucin 4 were isolated to homogeneity. At 150 μg/L, a typical concentration in milk, human milk mucin 1 and mucin 4 inhibited SL1344 invasion of both target cell types. These mucins inhibited SL1344 invasion of epithelial cells in a dose-dependent manner. Thus, mucins may prove useful as a basis for developing novel oral prophylactic and therapeutic agents that inhibit infant diseases caused by Salmonella and related pathogens.

Microencapsulated sorbic acid and nature-identical compounds reduced Salmonella Hadar and Salmonella Enteritidis colonization in experimentally infected chickens

The reduction of Salmonella prevalence in broilers is a priority in European Union agricultural policies because treatment with antibiotics is forbidden by Regulation (EC) 2160/2003. Two trials were conducted to evaluate the efficacy of a microencapsulated blend of sorbic acid and nature-identical compounds (i.e., chemically synthesized botanicals; SAB) on the reduction of the cecal prevalence and contents of Salmonella enterica serovars Hadar and Enteritidis in experimentally infected chickens. In the first trial, 125 one-day-old Lohmann specific-pathogen-free chickens were assigned to one of the following treatments: negative control (not challenged and not treated), positive control (challenged and not treated), SAB0.3, SAB1, or SAB5 (challenged and treated with the microencapsulated blend included in the feed at 0.03, 0.1, or 0.5%, respectively). At 30 d of age, birds were infected with 10(6) cfu of Salmonella Hadar, and after 5, 10, or 20 d postinfection, 5, 10, and 10 birds per treatment, respectively, were killed and the cecal contents and liver and spleen samples were analyzed for Salmonella Hadar. In the second trial, 100 one-day-old Ross 708 chickens were assigned to 1 of 5 treatments: control (not treated), SAB0.3, SAB1, SAB2, or SAB5 (treated with the blend included in the feed at 0.03, 0.1, 0.2, or 0.5%, respectively). At 7 d of age, the birds were challenged with 10(5) cfu of Salmonella Enteritidis, and after 7, 14, or 24 d after challenge, 5, 5, and 10 birds per treatment, respectively, were killed and cecal contents were analyzed for Salmonella Enteritidis. Results showed that in the early stage of infection Salmonella prevalence was high in both studies, whereas at the end of the observation periods, the blends at 0.03, 0.1, and 0.5 in the challenge with Salmonella Hadar and at 0.2 and 0.5% in the challenge with Salmonella Enteritidis significantly reduced (by 2 log(10) cfu) the cecal content of Salmonella. This study showed that intestinal delivery of microencapsulated sorbic acid and nature-identical compounds can result in a 100-fold reduction of Salmonella at the intestinal level in broilers at slaughter age.

Salmonella Interaction with and Passage through the Intestinal Mucosa: Through the Lens of the Organism

Salmonella enterica serotypes are invasive enteric pathogens spread through fecal contamination of food and water sources, and represent a constant public health threat around the world. The symptoms associated with salmonellosis and typhoid disease are largely due to the host response to invading Salmonella, and to the mechanisms these bacteria employ to survive in the presence of, and invade through the intestinal mucosal epithelia. Surmounting this barrier is required for survival within the host, as well as for further dissemination throughout the body, and subsequent systemic disease. In this review, we highlight some of the major hurdles Salmonella must overcome upon encountering the intestinal mucosal epithelial barrier, and examine how these bacteria surmount and exploit host defense mechanisms.

Rise and fall of an anti-MUC1 specific antibody

BACKGROUND

So far, human antibodies with good affinity and specificity for MUC1, a transmembrane protein overexpressed on breast cancers and ovarian carcinomas, and thus a promising target for therapy, were very difficult to generate.

RESULTS

A human scFv antibody was isolated from an immune library derived from breast cancer patients immunised with MUC1. The anti-MUC1 scFv reacted with tumour cells in more than 80% of 228 tissue sections of mamma carcinoma samples, while showing very low reactivity with a large panel of non-tumour tissues. By mutagenesis and phage display, affinity of scFvs was increased up to 500fold to 5,7×10(-10) M. Half-life in serum was improved from below 1 day to more than 4 weeks and was correlated with the dimerisation tendency of the individual scFvs. The scFv bound to T47D and MCF-7 mammalian cancer cell lines were recloned into the scFv-Fc and IgG format resulting in decrease of affinity of one binder. The IgG variants with the highest affinity were tested in mouse xenograft models using MCF-7 and OVCAR tumour cells. However, the experiments showed no significant decrease in tumour growth or increase in the survival rates. To study the reasons for the failure of the xenograft experiments, ADCC was analysed in vitro using MCF-7 and OVCAR3 target cells, revealing a low ADCC, possibly due to internalisation, as detected for MCF-7 cells.

CONCLUSIONS

Antibody phage display starting with immune libraries and followed by affinity maturation is a powerful strategy to generate high affinity human antibodies to difficult targets, in this case shown by the creation of a highly specific antibody with subnanomolar affinity to a very small epitope consisting of four amino acids. Despite these "best in class" binding parameters, the therapeutic success of this antibody was prevented by the target biology.

Effect of dietary glutamine supplementation on Salmonella colonization in the ceca of young broiler chicks

Live poultry is an important vehicle for transmitting Salmonella Typhimurium to humans that have salmonellosis. It is therefore imperative to reduce Salmonella Typhimurium levels in the gastrointestinal tract of live chickens. Glutamine is an established immunonutrient that is capable of alleviating disease conditions in humans and rats. Thus, 2 experiments that used Ross broiler chicks were conducted to evaluate the effect of glutamine supplementation at 1% level of the diet on cecal Salmonella Typhimurium levels in young broiler chicks. Experiment 1 consisted of i) treatment 1 (control, CN), in which chicks were given an unmedicated corn-soybean meal basal starter diet without glutamine supplementation or Salmonella Typhimurium challenge; ii) treatment 2 (CST), in which chicks were given the same diet as CN but challenged with 3.6 x 10(6) cfu Salmonella Typhimurium/mL at 3 d of age; and iii) treatment 3 (GST), in which chicks were given the unmedicated corn-soybean meal basal starter diet supplemented with glutamine at 1% level, and challenged with 3.6 x 10(6) cfu at 3 d of age. Experiment 2 used similar treatments (CN, CST, and GST), except that chicks in CST and GST were challenged with 7.4 x 10(7) cfu Salmonella Typhimurium/mL, and a fourth treatment was added. The fourth treatment consisted of chicks that were not challenged with Salmonella Typhimurium but given the same diet as in GST. Duration of each experiment was 14 d. Growth performance of chicks was monitored weekly, and cecal Salmonella Typhimurium concentration was microbiologically enumerated on d 4, 10, or 11 postchallenge. Results showed that glutamine supplementation improved BW and BW gain in experiment 2 (P < 0.05) but did not reduce cecal Salmonella Typhimurium levels in either experiment (P > 0.05). The optimum supplemental level of glutamine that will enhance intestinal resistance to Salmonella Typhimurium colonization should be determined.

Muc2 protects against lethal infectious colitis by disassociating pathogenic and commensal bacteria from the colonic mucosa

Despite recent advances in our understanding of the pathogenesis of attaching and effacing (A/E) Escherichia coli infections, the mechanisms by which the host defends against these microbes are unclear. The goal of this study was to determine the role of goblet cell-derived Muc2, the major intestinal secretory mucin and primary component of the mucus layer, in host protection against A/E pathogens. To assess the role of Muc2 during A/E bacterial infections, we inoculated Muc2 deficient (Muc2^−/−) mice with Citrobacter rodentium, a murine A/E pathogen related to diarrheagenic A/E E. coli. Unlike wildtype (WT) mice, infected Muc2^−/− mice exhibited rapid weight loss and suffered up to 90% mortality. Stool plating demonstrated 10–100 fold greater C. rodentium burdens in Muc2^−/− vs. WT mice, most of which were found to be loosely adherent to the colonic mucosa. Histology of Muc2^−/− mice revealed ulceration in the colon amid focal bacterial microcolonies. Metabolic labeling of secreted mucins in the large intestine demonstrated that mucin secretion was markedly increased in WT mice during infection compared to uninfected controls, suggesting that the host uses increased mucin release to flush pathogens from the mucosal surface. Muc2 also impacted host-commensal interactions during infection, as FISH analysis revealed C. rodentium microcolonies contained numerous commensal microbes, which was not observed in WT mice. Orally administered FITC-Dextran and FISH staining showed significantly worsened intestinal barrier disruption in Muc2^−/− vs. WT mice, with overt pathogen and commensal translocation into the Muc2^−/− colonic mucosa. Interestingly, commensal depletion enhanced C. rodentium colonization of Muc2^−/− mice, although colonic pathology was not significantly altered. In conclusion, Muc2 production is critical for host protection during A/E bacterial infections, by limiting overall pathogen and commensal numbers associated with the colonic mucosal surface. Such actions limit tissue damage and translocation of pathogenic and commensal bacteria across the epithelium.

Enteropathogenic E. coli (EPEC) and Enterohemorrhagic E. coli (EHEC) are important causes of diarrheal disease and other serious complications worldwide. Despite many studies addressing the pathogenic strategies used by these microbes, how the host protects itself from these pathogens is poorly understood. A critical question we address here is whether the thick mucus layer that overlies the intestinal surface plays a role in host protection. Since EPEC and EHEC do not infect mice efficiently, we used a related mouse pathogen called Citrobacter rodentium to infect and compare responses between wildtype mice and Muc2-deficient mice, which are defective in mucus production. We show that Muc2-deficient mice are extremely susceptible to C. rodentium infection-induced mortality and disease. Muc2-deficient mice were also colonized faster and had higher pathogen burdens throughout the experiment. Resident (non-pathogenic) bacteria were found to interact with C. rodentium and host tissues in Muc2-deficient mice, indicating Muc2 regulates all forms of intestinal microbiota at the gut surface. Deficiency in mucus production also contributed to increased leakiness of the gut, which allowed microbes to enter mucosal tissues. Our study shows that Muc2-dependent mucus production is critical for effective management of both pathogenic and non-pathogenic bacteria during infection by an EPEC/EHEC-like pathogen.

Toxin-mediated effects on the innate mucosal defenses: implications for enteric vaccines

Recent studies have confirmed older observations that the enterotoxins enhance enteric bacterial colonization and pathogenicity. How and why this happens remains unknown at this time. It appears that toxins such as the heat-labile enterotoxin (LT) from Escherichia coli can help overcome the innate mucosal barrier as a key step in enteric pathogen survival. We review key observations relevant to the roles of LT and cholera toxin in protective immunity and the effects of these toxins on innate mucosal defenses. We suggest either that toxin-mediated fluid secretion mechanically disrupts the mucus layer or that toxins interfere with innate mucosal defenses by other means. Such a breach gives pathogens access to the enterocyte, leading to binding and pathogenicity by enterotoxigenic E. coli (ETEC) and other organisms. Given the common exposure to LT(+) ETEC by humans visiting or residing in regions of endemicity, barrier disruption should frequently render the gut vulnerable to ETEC and other enteric infections. Conversely, toxin immunity would be expected to block this process by protecting the innate mucosal barrier. Years ago, Peltola et al. (Lancet 338:1285-1289, 1991) observed unexpectedly broad protective effects against LT(+) ETEC and mixed infections when using a toxin-based enteric vaccine. If toxins truly exert barrier-disruptive effects as a key step in pathogenesis, then a return to classic toxin-based vaccine strategies for enteric disease is warranted and can be expected to have unexpectedly broad protective effects.

Interaction between host cells and septicemic Salmonella enterica serovar typhimurium isolates from pigs

Salmonella enterica serovar Typhimurium is an important pathogen in swine and is also a frequently reported zoonotic agent. The objective of this study was to characterize isolates of S. enterica serovar Typhimurium associated with septicemia in swine and to compare them to isolates recovered from clinically healthy pigs. We were particularly interested in comparing the two groups of isolates for their ability to adhere to and invade host cells, to be phagocytized and survive in monocyte cells, to induce apoptosis, and to adhere to intestinal mucus. Their surface properties were also evaluated by interactions with solvents. The isolates recovered from diseased animals were shown to invade intestinal epithelial cell lines at a higher rate (P = 0.003) than isolates from healthy pigs. Septicemic isolates were phagocytized by human monocytes at a higher rate than isolates from healthy pigs (P = 0.009). The mean percentages of phagocytosis were significantly lower for human monocytes than for porcine monocytes (P = 0.02 and P = 0.008, respectively) for isolates from both diseased and healthy animals. Healthy animal isolates were phagocytized more by porcine monocytes at 15 min (P = 0.02) than septicemic isolates. No difference between isolates from septicemic pigs and isolates from healthy pigs was detected for other tested parameters. These results suggest that septicemic isolates have a particular pattern of invasion.

Lactobacillus fermentum BCS87 expresses mucus- and mucin-binding proteins on the cell surface

AIMS

To identify and characterize adhesion-associated proteins in the potential probiotic Lactobacillus fermentum BCS87.

METHODS AND RESULTS

Protein suspensions obtained from the treatment of Lact. fermentum BCS87 with 1 mol 1(-1) LiCl were analysed by Western blotting using HRP-labelled porcine mucus and mucin. Two adhesion-associated proteins with relative molecular weight of 29 and 32 kDa were identified. The N-terminal and internal peptides of the 32 kDa protein (32-Mmubp) were sequenced, and the corresponding gene (32-mmub) was found by inverse polymerase chain reaction. The complete nucleotide sequence of 32-mmub revealed an open reading frame of 903 bp encoding a primary protein of 300 amino acids and a mature protein of 272 residues. A basic local alignment search showed 47-99% identity to solute-binding components of ATP binding cassette transporter proteins in Lactobacillus, Streptococcus and Clostridium. An OpuAC-conserved domain was identified and phylogenetic relationship analysis confirmed that 32-Mmubp belongs to the OpuAC family.

CONCLUSIONS

Adhesion of Lact. fermentum BCS87 appeared to be mediated by two surface-associated proteins. 32-Mmubp is a component of ABC transporter system that also functions as an adhesin.

SIGNIFICANCE AND IMPACT OF THE STUDY

Characterization of 32-Mmubp and 32-mmub will contribute to understanding the host-bacteria interactions of Lact. fermentum with the intestinal tract of pigs.

Adherence, anti-adherence, and oligosaccharides preventing pathogens from sticking to the host

For many pathogenic bacteria, infections are initiated only after the organism has first adhered to the host cell surface. If adherence can be inhibited, then the subsequent infection can also be inhibited. This approach forms the basis of anti-adherence strategies, which have been devised to prevent a variety of bacterial infections. In this chapter, the molecular basis by which respiratory, urinary, and gastrointestinal tract pathogens adhere to host cells will be described. The five general types of anti-adherence agents will also be reviewed. The most well-studied are the receptor analogs, which include oligosaccharides produced synthetically or derived from natural sources, including milk, berries, and other plants. Their ability to inhibit pathogen adherence may lead to development of novel, food-grade anti-infective agents that are inexpensive and safe.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

Bacterial modulation of small intestinal goblet cells and mucin composition during early posthatch development of poultry

Mucins possess potential binding sites for both commensal and pathogenic organisms and may perform a defensive role during establishment of the intestinal barrier. To observe the effects of bacteria on intestinal goblet cell mucin production during posthatch development, differences in the small intestine of conventionally reared (CR) and low bacterial load (LBL) broiler chicks were examined. Jejunal and ileal goblet cells were stained with either periodic acid-Schiff stain or high iron diaminealcian blue pH 2.5 to discriminate among neutral, sulfated, and sialylated acidic mucins. Total goblet cell numbers and morphology of goblet cells containing neutral and acidic mucins did not differ significantly between CR and LBL birds. However, significant differences in acidic mucin composition from primarily sulfated to an increase in sialylated sugars at d 4 posthatch were observed in CR chicks, with greater numbers of jejunal and ileal goblet cells displaying this mucin type (CR, 0.5 +/- 0.1 x 10(3) cells/mm(2); LBL, 0.04 +/- 0.02 x10(3) cells/mm(2)). This change in mucin profile in response to bacterial colonization suggests a potential role as a protective mechanism against pathogenic invasion of the intestinal mucosa during early development.

Modulation of intestinal goblet cell function during infection by an attaching and effacing bacterial pathogen

The attaching and effacing (A/E) bacterial pathogens enteropathogenic Escherichia coli and enterohemorrhagic E. coli and the related mouse pathogen Citrobacter rodentium colonize their hosts' intestines by infecting the apical surfaces of enterocytes, subverting their function, and they ultimately cause diarrhea. Surprisingly, little is known about the interactions of these organisms with goblet cells, which are specialized epithelial cells that secrete the protective molecules Muc2 and trefoil factor 3 (Tff3) into the intestinal lumen. C. rodentium infection leads to dramatic goblet cell depletion within the infected colon, yet it is not clear whether C. rodentium infects goblet cells or if this pathology is pathogen or host mediated. As determined by immunostaining and PCR, both the number of goblet cells and the expression of genes encoding Muc2 and Tff3 were significantly reduced by day 10 postinfection. While electron microscopy and immunostaining revealed that C. rodentium directly infected a fraction of colonic goblet cells, C. rodentium localization did not correlate with goblet cell depletion. To assess the role of the host immune system in these changes, Rag1 knockout (KO) (T- and B-cell-deficient) mice were infected with C. rodentium. Rag1 KO mice did not exhibit the reduction in the number of goblet cells or in mediator (Muc2 and Tff3) expression observed in infected immunocompetent mice. However, reconstitution of Rag1 KO mice with T and B lymphocytes from C57BL/6 mice restored the goblet cell depletion phenotype during C. rodentium infection. In conclusion, these studies demonstrated that while colonic goblet cells can be subject to direct infection and potential subversion by A/E pathogens in vivo, it is the host immune system that primarily modulates the function of these cells during infection.

Gastrointestinal Maturation is Accelerated in Turkey Poults Supplemented with a Mannan-Oligosaccharide Yeast Extract (Alphamune)

Alphamune, a yeast extract antibiotic alternative, has been shown to stimulate the immune system, increase BW in pigs, and reduce Salmonella colonization in chickens. The influence of Alphamune on gastrointestinal tract development has not been reported. Two trials were conducted to evaluate the effects of Alphamune on gut maturation of 7- and 21-d-old turkey poults. Poults were fed a standard control unmedicated turkey starter diet or the same diet supplemented with either 1 or 2 lb/ton of Alphamune (n = 18/group). Poults were weighed on d 7 and 21, euthanized, and a 2-cm section was collected from the midpoint of the duodenum, jejunum, and ileum of each bird (9 poults/d per treatment) and fixed in a 10% formalin solution for 72 h and then stained. Twenty measurements of villus height, villus surface area, lamina propria thickness, crypt depth, and density of neutral, sialomucin, and sulfomucin goblet cells were taken per section per poult. On d 7, BW were higher for the poults given the Alphamune treatments compared with control poults; however, no differences were observed on d 21. Alphamune supplementation influenced intestinal morphology differently based on gut location. Ileum villus height, surface area, lamina propria thickness, crypt depth, and neutral, sialomucin, and sulfomucin goblet cell density were enhanced with Alphamune treatments on d 7 and 21 (P < 0.05) and in a dose-dependent manner for many of the parameters evaluated. Jejunum results were mixed. Surface area, crypt depth, and sialomucin and sulfomucin goblet cells were consistently higher for the 2 lb/ton of Alphamune groups compared with the control group on d 7 and 21. Duodenum villus height, surface area, and goblet cell density were higher for the 2 lb/ton of Alphamune groups on d 7; however, intestinal morphology of the duodenum was not different between the control and treated birds on d 21. These results suggest that feed supplemented with Alphamune can accelerate gastrointestinal maturation in turkey poults and is more pronounced in the ileum than in other portions of the small intestine.

Factors involved in binding of Lactobacillus plantarum Lp6 to rat small intestinal mucus

AIM

To investigate the adhesion determinants of Lactobacillus plantarum Lp6, a dairy isolate.

METHODS AND RESULTS

Small intestinal mucus extracted from rats was used as a substrate for adhesion. Adhesion determinants were studied by physical, chemical and enzymatic pretreatments of the bacteria, and adhesion inhibition assay. The mannose-specific adhesins were explored by studying the effect of d-mannose on adhesion and the yeast-agglutinating ability of the bacteria. It was found that adhesion decreased after bacteria were treated with sodium metaperiodate, protease K, trypsin, lithium chloride and trichloroacetic acid. However, adhesion did not decrease after trypsin-treated bacteria were incubated with cell surface protein extract. Cell surface bound exopolysaccharides were found to inhibit the adhesion. D-mannose inhibited the adhesion in a dose-dependent manner. The bacteria could significantly agglutinate yeast and lost this ability after protease K treatment.

CONCLUSIONS

Adhesion was mainly mediated by the mannose specific adhesins, which might be proteins that reversibly bind to the cell surface components. Cell surface-bound exopolysaccharides were also involved in adhesion.

SIGNIFICANCE AND IMPACT OF THE STUDY

The mannose-specific adhesion of Lact. plantarum Lp6 to rat mucus might be important for competing with pathogens-binding sites in gut, which may be used to resist the colonization of the pathogens.

The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota

The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

Mucins and TFF peptides of the tear film and lacrimal apparatus

The three-dimensional organization of the tear film, which is produced and drained by the different structures of the ocular adnexa, is essential for maintainance and protection of the ocular surface. This is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins, the mucins, which are usually expressed in association with a class of peptides having a well-defined, structurally conserved trefoil domain, the mammalian trefoil factor family (TFF) peptides. In this review, the latest information regarding mucin and TFF peptide function and regulation in the human lacrimal system, the tear film and the ocular surface is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes and certain disease states such as dry eye, dacryostenosis and dacryolith formation.

The increase in mucin exocytosis and the upregulation of MUC genes encoding for membrane-bound mucins induced by the thiol-activated exotoxin listeriolysin O is a host cell defence response that inhibits the cell-entry of Listeria monocytogenes

In vivo Listeria monocytogenes infection results in the massive release of mucus by goblet cells into the lumen of the intestine. We have previously reported that apical infection by L. monocytogenes is followed by listeriolysin O (LLO)-dependent stimulation of mucus exocytosis, and the upregulation of the MUC genes. Here, we report that L. monocytogenes EGD wild-type bacteria enter cultured human polarized, mucin-secreting, HT29-MTX cells apically by an InlA-dependent mechanism. The LLO-induced increase in mucin secretion together with an increase in transcription of the MCU4 and MUC12 genes encoding for membrane-bound mucins, results in the inhibition of the cell-entry of L. monocytogenes into mucin-secreting, HT29-MTX cells. Moreover, we report that sialic acid residues in mucins are crucial for the inhibition of L. monocytogenes internalization. Based on these findings, we suggest that the LLO-induced mucin exocytosis and upregulation of the MUC genes encoding for membrane-bound mucins constitute a host cell defence response that inhibits the cell-entry of L. monocytogenes.