Life at the margins: modulation of attachment proteins in Helicobacter pylori

Oral immunotherapy for Helicobacter pylori: Can it be trusted? A systematic review

BACKGROUND

Helicobacter pylori (H. pylori) is a rod-shaped, gram-negative, microaerophilic bacterium that can be identified by gram staining. Its relationship with cancer is significant since it is involved in approximately 80% of gastric cancers and 5.5% of all malignant cancers. Two lines of treatment have been defined for H. pylori, but almost 40% of patients do not respond to the first line. Recent trials have investigated oral Immunotherapy as a new treatment method. The aim of this systematic review was to investigate the potential effects of oral Immunotherapy on eradication rate of H. pylori in human studies.

METHODS

The systematic review was performed according to PRISMA guidelines. We searched online databases, including Scopus, PubMed, and Web of Science (ISI). Our search strategy was limited to English articles and studies on human populations that use oral immunotherapy for H. pylori.

RESULTS

The total number of primary research records in different databases was 2775. After removing duplicate articles (n = 870), we excluded 1829 for reasons including non-human studies, irrelevance to our study objective, non-English language, or lack of information. Of the remaining 76 articles, only seven had sufficient information, and the rest were excluded. The studies were divided into two groups: those that used bovine antibody and those that used immunoglobulin Y to eradicate H. pylori.

CONCLUSION

In the group of Immunoglobulin Y, three out of four studies suggest that using Immunoglobulin Y for the treatment of H. pylori infection is significant. However, the group using bovine antibody for the treatment of H. pylori infection has various results, as two out of three studies concluded that bovine antibody therapy is not significant.

Microbes in Tumoral In Situ Tissues and in Tumorigenesis

Cancerous tumors are severe diseases affecting human health that have a complicated etiology and pathogenesis. Microbes have been considered to be related to the development and progression of numerous tumors through various pathogenic mechanisms in recent studies. Bacteria, which have so far remained the most studied microbes worldwide, have four major possible special pathogenic mechanisms (modulation of inflammation, immunity, DNA damage, and metabolism) that are related to carcinogenesis. This review aims to macroscopically summarize and verify the relationships between microbes and tumoral in situ tissues from cancers of four major different systems (urinary, respiratory, digestive, and reproductive); the abovementioned four microbial pathogenic mechanisms, as well as some synergistic pathogenic mechanisms, are also discussed. Once the etiologic role of microbes and their precise pathogenic mechanisms in carcinogenesis are known, the early prevention, diagnosis, and treatment of cancers would progress significantly.

A genomic island in Brucella involved in the adhesion to host cells: Identification of a new adhesin and a translocation factor

Adhesion to host cells is the first step in the virulence cycle of any pathogen. In Gram-negative bacteria, adhesion is mediated, among other virulence factors such as the lipopolysaccharides, by specific outer-membrane proteins generally termed adhesins that belong to a wide variety of families and have different evolutionary origins. In Brucella, a widespread zoonotic pathogen of animal and human health concern, adhesion is central as it may determine the intracellular fate of the bacterium, an essential stage in its pathogenesis. In the present paper, we further characterised a genomic locus that we have previously reported encodes an adhesin (BigA) with a bacterial immunoglobulin-like domain (BIg-like). We found that this region encodes a second adhesin, which we have named BigB; and PalA, a periplasmic protein necessary for the proper display in the outer membrane of BigA and BigB. Deletion of bigB or palA diminishes the adhesion of the bacterium and overexpression of BigB dramatically increases it. Incubation of cells with the recombinant BIg-like domain of BigB induced important cytoskeletal rearrangements and affected the focal adhesion sites indicating that the adhesin targets cell-cell or cell-matrix proteins. We additionally show that PalA has a periplasmic localisation and is completely necessary for the proper display of BigA and BigB, probably avoiding their aggregation and facilitating their transport to the outer membrane. Our results indicate that this genomic island is entirely devoted to the adhesion of Brucella to host cells.

Muc5ac null mice are predisposed to spontaneous gastric antro-pyloric hyperplasia and adenomas coupled with attenuated H. pylori-induced corpus mucous metaplasia

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide and is strongly associated with chronic Helicobacter pylori (Hp) infection. The ability of Hp to closely adhere to the gastric surface protective mucous layer containing mucins (MUC in humans and Muc in animals), primarily Muc5ac, is integral in the stepwise pathogenesis from gastritis to cancer. To probe the role of Muc5ac in Hp-induced gastric pathology, Muc5ac^-/- and Muc5ac^+/+ (WT) mice were experimentally infected with Hp Sydney strain (SS1). At 16 weeks and 32 weeks post infection (wpi), groups of mice were euthanized and evaluated for the following: gastric histopathological parameters, immunohistochemical expression of mucins (Muc5ac, Muc1, Muc2), Trefoil factor family proteins (Tff1 and Tff2), Griffonia (Bandeiraea) simplicifolia lectin II (GSL II) (mucous metaplasia marker) and Clusterin (Spasmolytic Polypeptide Expressing Metaplasia (SPEM) marker), Hp colonization density by qPCR and gastric cytokine mRNA levels. Our results demonstrate that Muc5ac^-/- mice developed spontaneous antro-pyloric proliferation, adenomas and in one case with neuroendocrine differentiation; these findings were independent of Hp infection along with strong expression levels of Tff1, Tff2 and Muc1. Hp-infected Muc5ac^-/- mice had significantly lowered gastric corpus mucous metaplasia at 16 wpi and 32 wpi (P = 0.0057 and P = 0.0016, respectively), with a slight reduction in overall gastric corpus pathology. GSII-positive mucous neck cells were decreased in Hp-infected Muc5ac^-/- mice compared to WT mice and clusterin positivity was noted within metaplastic glands in both genotypes following Hp infection. Additionally, Hp colonization densities were significantly higher in Muc5ac^-/- mice compared to WT at 16 wpi in both sexes (P = 0.05) along with a significant reduction in gastric Tnfα (16 wpi-males and females, P = 0.017 and P = 0.036, respectively and 32 wpi-males only, P = 0.025) and Il-17a (16 wpi-males) (P = 0.025). Taken together, our findings suggest a protective role for MUC5AC/Muc5ac in maintaining gastric antral equilibrium and inhibiting Hp colonization and associated inflammatory pathology.

Experimental models to study intestinal microbes–mucus interactions in health and disease

A close symbiotic relationship exists between the intestinal microbiota and its host. A critical component of gut homeostasis is the presence of a mucus layer covering the gastrointestinal tract. Mucus is a viscoelastic gel at the interface between the luminal content and the host tissue that provides a habitat to the gut microbiota and protects the intestinal epithelium. The review starts by setting up the biological context underpinning the need for experimental models to study gut bacteria-mucus interactions in the digestive environment. We provide an overview of the structure and function of intestinal mucus and mucins, their interactions with intestinal bacteria (including commensal, probiotics and pathogenic microorganisms) and their role in modulating health and disease states. We then describe the characteristics and potentials of experimental models currently available to study the mechanisms underpinning the interaction of mucus with gut microbes, including in vitro, ex vivo and in vivo models. We then discuss the limitations and challenges facing this field of research.

Biologic roles of the ABH and Lewis histo-blood group antigens Part I: infection and immunity

The ABH and Lewis antigens were among the first of the human red blood cell polymorphisms to be identified and, in the case of the former, play a dominant role in transfusion and transplantation. But these two therapies are largely twentieth century innovations, and the ABH and related carbohydrate antigens are not only expressed on a very wide range of human tissues, but were present in primates long before modern humans evolved. Although we have learned a great deal about the biochemistry and genetics of these structures, the biological roles that they play in human health and disease are incompletely understood. This review and its companion, to appear in a later issue of Vox Sanguinis, will focus on a few of the biologic and pathologic processes which appear to be affected by histo-blood group phenotype. The first of the two reviews will explore the interactions of two bacteria with the ABH and Lewis glycoconjugates of their human host cells, and describe the possible connections between the immune response of the human host to infection and the development of the AB-isoagglutinins. The second review will describe the relationship between ABO phenotype and thromboembolic disease, cardio-vascular disease states, and general metabolism.

Helicobacter pylori adhesin HopQ disrupts trans dimerization in human CEACAMs

The human gastric pathogen Helicobacter pylori is a major causative agent of gastritis, peptic ulcer disease, and gastric cancer. As part of its adhesive lifestyle, the bacterium targets members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family by the conserved outer membrane adhesin HopQ. The HopQ-CEACAM1 interaction is associated with inflammatory responses and enables the intracellular delivery and phosphorylation of the CagA oncoprotein via a yet unknown mechanism. Here, we generated crystal structures of HopQ isotypes I and II bound to the N-terminal domain of human CEACAM1 (C1ND) and elucidated the structural basis of H. pylori specificity toward human CEACAM receptors. Both HopQ alleles target the β-strands G, F, and C of C1ND, which form the trans dimerization interface in homo- and heterophilic CEACAM interactions. Using SAXS, we show that the HopQ ectodomain is sufficient to induce C1ND monomerization and thus providing H. pylori a route to influence CEACAM-mediated cell adherence and signaling events.

Helicobacter pylori BabA in adaptation for gastric colonization

Helicobacter pylori (H. pylori) as a causative agent of gastric complications, is well adapted for the colonization of gastric mucosa. Although the infectious process depends on several factors, the adhesion to the gastric mucosa is the first and important step. Among several outer membrane proteins, BabA is one of the significant protein involving in many inflammatory processes in addition to its role in the attachment for the persistent colonization. We performed a PubMed search using the key words: “babA”, “pylori”, “gastric complications”, “homologous recombination”, “slipped strand mispairing”; a total of 249 articles were displayed. Of these we mainly focused on articles with the full text in English and published between 2005 and 2016. H. pylori BabA is involved in binding with receptors; however, its synthesis is regulated by phase variation. In this review we confirm that H. pylori babA can be modulated at the molecular and functional levels to adapt to the stress within the gastro-intestinal tract.

Determinants of the regulation of Helicobacter pylori adhesins include repeat sequences in both promoter and coding regions as well as the two-component system ArsRS

PURPOSE

We investigated the transcription of adhesin-encoding genes sabA, hopZ and labA in Helicobacter pylori strain J99. Each possesses a repeating homopolymeric nucleotide tract within their promoter regions, and sabA and hopZ possess repeats within their 5' coding regions.

METHODOLOGY

We altered the repeat lengths associated with the adhesin genes and quantified mRNA levels by real-time quantitative PCR. Using adherence to AGS cells and IL-8 assays, we examined the effects of altered transcript levels. We assessed the role of ArsRS in transcription using an arsS null mutant and by examining ArsR binding to promoter regions via electrophoretic mobility shift assays.

RESULTS

Extensions or truncations of promoter region repeats in hopZ and labA increased transcript levels, mirroring results shown by our lab and others for mutations in the sabA promoter. Altered lengths of the poly-cytosine thymine tract within the 5' coding region of sabA demonstrated that switching from phase-off to phase-on significantly increased mRNA levels. However, mutations in the poly-thymine tract of sabA, which increased mRNA levels, do not behave synergistically with phase-on mutations. Phase-on mutations of sabA resulted in increased H. pylori adherence to AGS cells, but only a modest effect on IL-8. hopZ and labA, and sabA paralogue sabB, transcript levels were increased in an arsS mutant and ArsR bound the promoter regions for each of these genes in vitro.

CONCLUSION

This work highlights the complex nature of adhesin regulation, its impact on H. pylori attachment and the pervasive role of ArsRS in adhesin expression. Such regulation may help facilitate the decades-long persistence of infection.

Dynamic Expression of the BabA Adhesin and Its BabB Paralog during Helicobacter pylori Infection in Rhesus Macaques

Most Helicobacter pylori strains express the BabA adhesin, which binds to ABO/Leb blood group antigens on gastric mucin and epithelial cells and is found more commonly in strains that cause peptic ulcers or gastric cancer, rather than asymptomatic infection. We and others have previously reported that in mice, gerbils, and rhesus macaques, expression of babA is lost, either by phase variation or by gene conversion, in which the babB paralog recombines into the babA locus. The functional significance of loss of babA expression is unknown. Here we report that in rhesus monkeys, there is independent selective pressure for loss of babA and for overexpression of BabB, which confers a fitness advantage. Surprisingly, loss of babA by phase variation or gene conversion is not dependent on the capacity of BabA protein to bind Leb, which suggests that it may have other, unrecognized functions. These findings have implications for the role of outer membrane protein diversity in persistent H. pylori infection.

Host Determinants of Expression of the Helicobacter pylori BabA Adhesin

Expression of the Helicobacter pylori blood group antigen binding adhesin A (BabA) is more common in strains isolated from patients with peptic ulcer disease or gastric cancer, rather than asymptomatic colonization. Here we used mouse models to examine host determinants that affect H. pylori BabA expression. BabA expression was lost by phase variation as frequently in WT mice as in RAG2−/− mice that do not have functional B or T cells, and in MyD88−/−, TLR2−/− and TLR4−/− mice that are defective in toll like receptor signaling. The presence of other bacteria had no effect on BabA expression as shown by infection of germ free mice. Moreover, loss of BabA expression was not dependent on Le^b expression or the capacity of BabA to bind Le^b. Surprisingly, gender was the host determinant most associated with loss of BabA expression, which was maintained to a greater extent in male mice and was associated with greater bacterial load. These results suggest the possibility that loss of BabA expression is not driven by adaptive immunity or toll-like receptor signaling, and that BabA may have other, unrecognized functions in addition to serving as an adhesin that binds Le^b.

Effect of Helicobacter pylori Eradication and ABO Genotype on Gastric Cancer Development

BACKGROUND

Evidence is lacking regarding how Helicobacter pylori infection status, eradication history, and ABO blood type affect the development of gastric cancer (GC) given the multifactorial and distinctive etiology according to cancer location (noncardia vs cardia) and histologic type (intestinal vs diffuse-type). We evaluated the effect of H. pylori infection status incorporated with H. pylori eradication history and ABO genotype on GC development according to cancer location and histologic type.

METHODS

A case-control study of 997 patients with noncardia GC (NCGC) and 1147 control subjects was performed using risk analyses with 14 factors including H. pylori infection with eradication history and ABO genotype. As final analyses, multivariable logistic regression models were fitted. Additionally, H. pylori infection status with eradication history was tested for its association with age, atrophic gastritis (AG), and intestinal metaplasia (IM).

RESULTS

The ABO genotype with the B allele was associated with a significantly lower risk of NCGC of both histologic types. The reduction in risk for NCGC by adding the B allele was more prominent in diffuse-type than that in the intestinal-type. H. pylori infection with eradication history was associated with a significantly lower risk of NCGC of both histologic types, compared with those without eradication history (odds ratio (OR), 0.22; 95% confidence interval (CI), 0.14-0.34) approaching that of uninfected subjects. Past infection status without an eradication history was associated with older age, AG, and IM.

CONCLUSIONS

H. pylori eradication and the B allele decreased the risks of the intestinal and diffuse-types of NCGC. H. pylori eradication revealed a strong association against developing NCGC. Therefore, it should be considered as a primary measure in NCGC prevention.

Helicobacter pylori Strains from Duodenal Ulcer Patients Exhibit Mixed babA/B Genotypes with Low Levels of BabA Adhesin and Lewis b Binding

BACKGROUND

BabA is a Helicobacter pylori cell surface adhesin, which binds to the ABO/Le(b) histo-blood group antigens (Le(b)) and serves as a virulence factor.

METHODS

H. pylori single colonies were isolated from 156 [non-ulcer dyspepsia (NUD) = 97, duodenal ulcer (DU) = 34, gastric cancer (GC) = 25)] patients. babA and babB genes were evaluated by gene/locus-specific PCR. BabA protein expression and Le(b) binding activity were determined by immunoblotting and ELISA, respectively.

RESULTS

The combined categorization of H. pylori strains based on high, low or no levels of BabA expression and Le(b) binding, produced 4 groups: (I) BabA-high/Le(b)-high (36 %), (II) BabA-low/Le(b)-low (26 %), (III) BabA-neg/Le(b)-low (30 %) and (IV) BabA-neg/Le(b)-neg (8 %) strains. The majority (63 %) of the BabA-low/Le(b)-low strains exhibited mixed babA/B genotypes as compared to merely 18 % of the BabA-high/Le(b)-high, 15 % of the BabA-neg/Le(b)-neg and 11 % of the BabA-neg/Le(b)-low (P = 0.0001) strains. In contrast to NUD strains, the great majority (70 %) of DU strains were BabA-low/Le(b)-low (11 %, P = 0.0001), which compared to NUD strains, enhanced the risk of DU by 18.8-fold. In parallel, infection with babA/B mixed genotype strains amplified the risk of DU by 3.6-fold (vs. babA-positive: P = 0.01) to 6.9-fold (vs. babA-negative: P = 0.007).

CONCLUSIONS

Here, we show higher prevalence of mixed babA/B genotypes among BabA-low/Le(b)-low clinical strains. Recombination of babA and babB genes across their loci may yield lower BabA expression and lower Le(b) binding activity. We conclude that H. pylori strains with lower Le(b) binding activity are better adapted for colonization of the gastric metaplastic patches in the duodenum and enhance the risk of duodenal ulcers.

Mucin-Type O-Glycosylation in Gastric Carcinogenesis

Mucin-type O-glycosylation plays a crucial role in several physiological and pathological processes of the gastric tissue. Modifications in enzymes responsible for key glycosylation steps and the consequent abnormal biosynthesis and expression of their glycan products constitute well-established molecular hallmarks of disease state. This review addresses the major role played by mucins and associated O-glycan structures in Helicobacter pylori adhesion to the gastric mucosa and the subsequent establishment of a chronic infection, with concomitant drastic alterations of the gastric epithelium glycophenotype. Furthermore, alterations of mucin expression pattern and glycan signatures occurring in preneoplastic lesions and in gastric carcinoma are also described, as well as their impact throughout the gastric carcinogenesis cascade and in cancer progression. Altogether, mucin-type O-glycosylation alterations may represent promising biomarkers with potential screening and prognostic applications, as well as predictors of cancer patients' response to therapy.

Muc5ac gastric mucin glycosylation is shaped by FUT2 activity and functionally impacts Helicobacter pylori binding

The gastrointestinal tract is lined by a thick and complex layer of mucus that protects the mucosal epithelium from biochemical and mechanical aggressions. This mucus barrier confers protection against pathogens but also serves as a binding site that supports a sheltered niche of microbial adherence. The carcinogenic bacteria Helicobacter pylori colonize the stomach through binding to host glycans present in the glycocalyx of epithelial cells and extracellular mucus. The secreted MUC5AC mucin is the main component of the gastric mucus layer, and BabA-mediated binding of H. pylori to MUC5AC confers increased risk for overt disease. In this study we unraveled the O-glycosylation profile of Muc5ac from glycoengineered mice models lacking the FUT2 enzyme and therefore mimicking a non-secretor human phenotype. Our results demonstrated that the FUT2 determines the O-glycosylation pattern of Muc5ac, with Fut2 knock-out leading to a marked decrease in α1,2-fucosylated structures and increased expression of the terminal type 1 glycan structure Lewis-a. Importantly, for the first time, we structurally validated the expression of Lewis-a in murine gastric mucosa. Finally, we demonstrated that loss of mucin FUT2-mediated fucosylation impairs gastric mucosal binding of H. pylori BabA adhesin, which is a recognized feature of pathogenicity.

Blood Groups in Infection and Host Susceptibility

Blood group antigens represent polymorphic traits inherited among individuals and populations. At present, there are 34 recognized human blood groups and hundreds of individual blood group antigens and alleles. Differences in blood group antigen expression can increase or decrease host susceptibility to many infections. Blood groups can play a direct role in infection by serving as receptors and/or coreceptors for microorganisms, parasites, and viruses. In addition, many blood group antigens facilitate intracellular uptake, signal transduction, or adhesion through the organization of membrane microdomains. Several blood groups can modify the innate immune response to infection. Several distinct phenotypes associated with increased host resistance to malaria are overrepresented in populations living in areas where malaria is endemic, as a result of evolutionary pressures. Microorganisms can also stimulate antibodies against blood group antigens, including ABO, T, and Kell. Finally, there is a symbiotic relationship between blood group expression and maturation of the gastrointestinal microbiome.

The clearance effect of bovine anti-Helicobacter pylori antibody-containing milk in O blood group Helicobacter pylori-infected patients: a randomized double-blind clinical trial

BACKGROUND

The failure in standard triple therapy has recently increased to high levels in China, primarily because of insufficient patient compliance, antimicrobial resistance, and high costs. Effective prevention and eradication of Helicobacter pylori (H. pylori) by artificial passive immunization with orally administered bovine antibodies in the milk has been demonstrated in many animal studies, but the clinical studies that are available have shown no H. pylori eradication. This study was to evaluate the efficacy and safety of orally administered bovine anti-H. pylori antibodies for the clearance of H. pylori infecting O blood group subpopulations.

METHODS

Two local epidemic H. pylori strains that were prevalent locally were screened and then used to immunize dairy cows. After confirmation of the presence of anti-H. pylori polyclonal antibodies in the milk by enzyme-linked immunosorbent assay, the milk was subsequently defatted and processed into sterile milk by pasteurization. This study was designed as a double-blind placebo-controlled randomized clinical trial. Our 61 H. pylori-infected O blood group subjects were assigned to two groups; 31 subjects were treated with bovine milk containing antibodies and 30 subjects with the placebo. The medication-based study was continued for 28 days. Subjects were followed up for 56 days. The effect was assessed by the C-14 urea breath test (UBT). SPSS 17.0 software for Windows was used to analyze the data.

RESULTS

Of the 61 subjects enrolled, 58 completed the protocol. One volunteer in the antibodies group and two volunteers in the control group dropped out. Of the 30 antibody-treated subjects, 13 became UBT negative, whereas none of the 30 of the placebo-treated subjects became UBT negative after the medication. Of 13 UBT negative patients, 3 became positive again at the end of the follow-up. Both intention to treat and per-protocol analysis indicated a significant difference in the clearance rate of infected patients between the groups treated with bovine antibody-containing milk and the placebo (P = 0.001, P < 0.05) and no significant difference in adverse effects (P > 0.05 all).

CONCLUSIONS

Bovine antibody-based oral immunotherapy appears to be safe and has a significant clearance effect on intragastric H. pylori that infects O blood group adults.

TRIAL REGISTRATION

ChiCTR-TRC-14005212.

Persistent and transient Helicobacter pylori infections in early childhood

BACKGROUND

Helicobacter pylori, the main cause of peptic ulcer disease and gastric cancer in adult populations, is generally acquired during the first years of life. Infection can be persistent or transient and bacterial and host factors determining persistence are largely unknown and may prove relevant for future disease.

METHODS

Two cohorts of healthy Chilean infants (313 total) were evaluated every 3 months for 18-57 months to determine pathogen- and host-factors associated with persistent and transient infection.

RESULTS

One-third had at least one positive stool ELISA by age 3, with 20% overall persistence. Persistent infections were acquired at an earlier age, associated with more household members, decreased duration of breastfeeding, and nonsecretor status compared to transient infections. The cagA positive strains were more common in persistent stools, and nearly 60% of fully characterized persistent stool samples amplified cagA/vacAs1m1. Persistent children were more likely to elicit a serologic immune response, and both infection groups had differential gene expression profiles, including genes associated with cancer suppression when compared to healthy controls.

CONCLUSIONS

These results indicate that persistent H. pylori infections acquired early in life are associated with specific host and/or strain profiles possibly associated with future disease occurrence.

Dynamics of Lewis b binding and sequence variation of the babA adhesin gene during chronic Helicobacter pylori infection in humans

Helicobacter pylori undergoes rapid microevolution during chronic infection, but very little is known about how this affects host interaction factors. The best-studied adhesin of H. pylori is BabA, which mediates binding to the blood group antigen Lewis b [Le(b)]. To study the dynamics of Le(b) adherence during human infection, we analyzed paired H. pylori isolates obtained sequentially from chronically infected individuals. A complete loss or significant reduction of Le(b) binding was observed in strains from 5 out of 23 individuals, indicating that the Le(b) binding phenotype is quite stable during chronic human infection. Sequence comparisons of babA identified differences due to mutation and/or recombination in 12 out of 16 strain pairs analyzed. Most amino acid changes were found in the putative N-terminal extracellular adhesion domain. One strain pair that had changed from a Le(b) binding to a nonbinding phenotype was used to study the role of distinct sequence changes in Le(b) binding. By transformations of the nonbinding strain with a babA gene amplified from the binding strain, H. pylori strains with mosaic babA genes were generated. Recombinants were enriched for a gain of Le(b) binding by biopanning or for BabA expression on the bacterial surface by pulldown assay. With this approach, we identified several amino acid residues affecting the strength of Le(b) binding. Additionally, the data showed that the C terminus of BabA, which is predicted to encode an outer membrane β-barrel domain, plays an essential role in the biogenesis of this protein.

Helicobacter pylori causes a chronic infection of the human stomach that can lead to ulcers and cancer. The bacterium can bind to gastric epithelial cells with specialized outer membrane proteins. The best-studied protein is the BabA adhesin which binds to the Lewis b blood group antigen. Since H. pylori is a bacterium with very high genetic variability, we asked whether babA evolves during chronic infection and how mutations or recombination in babA affect binding. We found that BabA-mediated adherence was stable in most individuals but observed a complete loss of binding or reduced binding in 22% of individuals. One strain pair in which binding was lost was used to generate babA sequences that were mosaics of a functional allele and a nonfunctional allele, and the mosaic sequences were used to identify amino acids critically involved in binding of BabA to Lewis b.

Expression, purification and X-ray crystallographic analysis of the Helicobacter pylori blood group antigen-binding adhesin BabA

Helicobacter pylori is a human pathogen that colonizes about 50% of the world's population, causing chronic gastritis, duodenal ulcers and even gastric cancer. A steady emergence of multiple antibiotic resistant strains poses an important public health threat and there is an urgent requirement for alternative therapeutics. The blood group antigen-binding adhesin BabA mediates the intimate attachment to the host mucosa and forms a major candidate for novel vaccine and drug development. Here, the recombinant expression and crystallization of a soluble BabA truncation (BabA(25-460)) corresponding to the predicted extracellular adhesin domain of the protein are reported. X-ray diffraction data for nanobody-stabilized BabA(25-460) were collected to 2.25 Å resolution from a crystal that belonged to space group P21, with unit-cell parameters a = 50.96, b = 131.41, c = 123.40 Å, α = 90.0, β = 94.8, γ = 90.0°, and which was predicted to contain two BabA(25-460)-nanobody complexes per asymmetric unit.

Studies of mucus in mouse stomach, small intestine, and colon. III. Gastrointestinal Muc5ac and Muc2 mucin O-glycan patterns reveal a regiospecific distribution

The mouse intestinal mucus is mainly made up by the gel-forming Muc2 mucin and the stomach surface mucus Muc5ac, both extensively O-glycosylated. The oligosaccharide diversity provides a vast library of potential recognition sites for both commensal and pathogenic organisms. The mucin glycans are thus likely very important for the selection and maintenance of a stable intestinal flora. Here we have explored the O-glycan patterns of the mouse gastrointestinal tract mucins. The mucins from the mucus of the distal and proximal colon, ileum, jejunum, duodenum, and stomach of conventionally raised wild-type (C57BL/6) mice were separated by composite gel electrophoresis. The O-linked glycans were released by reductive elimination and structurally characterized by liquid chromatography-mass spectrometry. The mucins glycans were mostly core 2 type [Galβ1-3(GlcNAcβ1-6)GalNAcol], but also core 1 (Galβ1-3GalNAcol). In the stomach about half of the Muc5ac mucin O-glycans were neutral and many monosulfated, but with a low grade of sialylation and fucosylation. Mouse ileum, jejunum, and duodenum had similar glycan patterns dominated by sialylated and sulfated core 2 glycans, but few fucosylated. Colon was on the other hand dominated by highly charged fucosylated glycans. The distal colon is different from the proximal colon because different biosynthetic pathways are utilized, although sialylated and sulfated glycans were highly abundant in both parts. The sulfation was higher in the distal colon, whereas sialic acid was more common in the proximal colon. Many fucosylated glycans were found in both the proximal and distal colon. Thus the mucin O-glycans vary along the mouse gastrointestinal tract.

The Role of Helicobacter pylori Outer Membrane Proteins in Adherence and Pathogenesis

Helicobacter pylori is one of the most successful human pathogens, which colonizes the mucus layer of the gastric epithelium of more than 50% of the world’s population. This curved, microaerophilic, Gram-negative bacterium induces a chronic active gastritis, often asymptomatic, in all infected individuals. In some cases, this gastritis evolves to more severe diseases such as peptic ulcer disease, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. H. pylori has developed a unique set of factors, actively supporting its successful survival and persistence in its natural hostile ecological niche, the human stomach, throughout the individual’s life, unless treated. In the human stomach, the vast majority of H. pylori cells are motile in the mucus layer lining, but a small percentage adheres to the epithelial cell surfaces. Adherence to the gastric epithelium is important for the ability of H. pylori to cause disease because this intimate attachment facilitates: (1) colonization and persistence, by preventing the bacteria from being eliminated from the stomach, by mucus turnover and gastric peristalsis; (2) evasion from the human immune system and (3) efficient delivery of proteins into the gastric cell, such as the CagA oncoprotein. Therefore, bacteria with better adherence properties colonize the host at higher densities. H. pylori is one of the most genetically diverse bacterial species known and is equipped with an extraordinarily large set of outer membrane proteins, whose role in the infection and persistence process will be discussed in this review, as well as the different receptor structures that have been so far described for mucosal adherence.

The gastrointestinal mucus system in health and disease

Mucins--large, highly glycosylated proteins--are important for the luminal protection of the gastrointestinal tract. Enterocytes have their apical surface covered by transmembrane mucins and goblet cells produce the secreted gel-forming mucins that form mucus. The small intestine has a single unattached mucus layer, which in cystic fibrosis becomes attached, accounting for the intestinal manifestations of this disease. The stomach and colon have two layers of mucus; the inner layer is attached and the outer layer is less dense and unattached. In the colon, the outer mucus layer is the habitat for commensal bacteria. The inner mucus layer is impervious to bacteria and is renewed every hour by surface goblet cells. The crypt goblet cells have the ability to restitute the mucus layer by secretion, for example after an ischaemic challenge. Proteases of certain parasites and some bacteria can cleave mucins and dissolve the mucus as part of their pathogenicity. The inner mucus layer can, however, also become penetrable to bacteria by several other mechanisms, including aberrations in the immune system. When bacteria reach the epithelial surface, the immune system is activated and inflammation is triggered. This mechanism might occur in some types of ulcerative colitis.

Goblet cells and mucins: role in innate defense in enteric infections

Goblet cells reside throughout the gastrointestinal (GI) tract and are responsible for the production and preservation of a protective mucus blanket by synthesizing and secreting high molecular weight glycoproteins known as mucins. The concept of the mucus layer functioning as a dynamic protective barrier is suggested by studies showing changes in mucins in inflammatory conditions of the GI tract, by the altered goblet cell response in germ-free animals, and by the enhanced mucus secretion seen in response to infections. The mucin-containing mucus layer coating the GI epithelium is the front line of innate host defense. Mucins are likely to be the first molecules that invading pathogens interact with at the cell surface and thus, can limit binding to other glycoproteins and neutralize the pathogen. This review will focus on what is known about goblet cell response in various GI infections and the regulatory networks that mediate goblet cell function and mucin production in response to intestinal insults. In addition, we describe the current knowledge on the role of mucins in intestinal innate defense. It is the aim of this review to provide the readers with an update on goblet cell biology and current understanding on the role of mucins in host defense in enteric infections.

Role of mucus layers in gut infection and inflammation

The intestinal mucus is an efficient system for protecting the epithelium from bacteria by promoting their clearance and separating them from the epithelial cells, thereby inhibiting inflammation and infection. The function of the colon inner mucus layer is especially important as this explains how we can harbor the large number of bacteria in our gut. The major component of this mucus system is the MUC2 mucin which organizes the mucus by its enormously large net-like polymers. Pathogenic microorganisms, in turn, have developed mechanisms for circumventing this well-organized mucus protective system.