N-acetylneuraminyllactose-binding fibrillar hemagglutinin of Campylobacter pylori: a putative colonization factor antigen

Virulence factors of Helicobacter pylori

To date a number of virulence factors have been identified and characterised from the gastric pathogen Helicobacter pylori. The vacuolating toxin (VacA) is a major determinant of H. pylori-associated gastric disease. In non-polarised cells, VacA alters the endocytic pathway, resulting in the release of acid hydrolases and the reduction of both extracellular ligand degradation and antigen processing. The toxin forms trans-membrane anion-specific channels and reduces the transepithelial electrical resistance of polarized monolayers. Localization of the VacA channels in acidic intracellular compartments causes osmotic swelling which, together with membrane fusion, leads to vacuole formation. The neutrophil-activating protein of H. pylori (HP-NAP) induces the production of oxygen radicals in human neutrophils via a cascade of intracellular activation events which may contribute to the damage of the stomach mucosa. This protein has recently been shown to be an important antigen in the human immune response to H. pylori infection. In addition, mice vaccinated with recombinant HP-NAP were protected against H. pylori challenge. H. pylori strains that are associated with severe tissue damage and inflammation possess the cag pathogenicity island that contains several genes encoding factors involved in the induction of proinflammatory cytokines/chemokines and of a type IV secretion system involved in the delivery of a highly immunogenic protein, CagA, into eukaryotic cells. Recent advances in our understanding of the involvement of VacA, HP-NAP and the CagA/Type IV secretion system in the H. pylori-associated disease process are discussed in this review.

Clinical relevance of the babA2 genotype of Helicobacter pylori in Japanese clinical isolates

Genotypic variation of Helicobacter pylori is speculated to associate with different clinical outcomes. In Western countries, the gene encoding blood group antigen-binding adhesin (BabA), babA2, is of high clinical relevance and is a useful marker to identify patients who are at higher risk for peptic ulceration and gastric adenocarcinoma, as are vacA and cagA. We investigated the presence of babA2 and cagA in 179 Japanese clinical isolates by PCR and Southern blot analysis and looked for correlations with various clinical outcomes (nonulcer dyspepsia, duodenal ulcers, gastric ulcers gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma). The prevalence of the babA2 genotype was 84.9% and that of the cagA genotype was 96.1%. There was no correlation between the babA2 and cagA genotypes, and there was no association between the babA2 or cagA status and clinical outcome. These results indicate that babA2 status is not of high clinical relevance in Japan and that Japanese strains are different from those infecting Western populations.

Serum immunoglobulin G immune response to Helicobacter pylori antigens in Mongolian gerbils

The Mongolian gerbil model for Helicobacter pylori infection is an animal model that mimics human disease. We examined the serum immune response to H. pylori infection in gerbils by enzyme-linked immunosorbent assay (ELISA) and Western blotting, both with whole-cell (H. pylori) extracts. A total of 66 7-week-old specific-pathogen-free male gerbils were inoculated orogastrically with H. pylori strain ATCC 43504. Sera were collected 1, 2, 4, 8, 12, 26, 38, and 52 weeks after H. pylori inoculation. Sixty-nine noninfected gerbils and their sera were used as controls. The specificity of the ELISA was 95.7%. The frequency of seropositivity increased over time: 2 of 10 (20%), 7 of 10 (70%), and 7 of 7 (100%) samples of sera from inoculated gerbils were positive for H. pylori at 2, 4, and 8 weeks postinoculation, respectively. Western blot assays showed that the primary immunoglobulin G (IgG) response against low-molecular-mass (25-, 30-, and 20-kDa) proteins appeared after a lag period of 2 to 8 weeks after inoculation. Antibodies against 160-, 150-, 110-, 120-, 80-, 66-, and 63-kDa proteins were observed 12 weeks after inoculation. The early reactive 30-kDa protein was identified as a urease alpha subunit by N-terminal amino acid sequencing. After 26 weeks, two groups of animals could be distinguished: one group developed ulcers (n = 5), and the other developed hyperplastic polyps without ulcers (n = 19). Gerbils in the gastric ulcer group showed significantly higher serum anti-H. pylori IgG levels than did gerbils in the hyperplastic group (P = 0.001) as measured by ELISA. Furthermore, a higher proportion of animals developed antibodies to H. pylori proteins of 26, 25, and 20 kDa in the ulcer group than those animals with hyperplastic polyps (75 to 100% versus 17 to 50%) in Western blot assays. These results highlight the importance of the immune response of the host in the development of H. pylori-related gastric lesions.

In vitro binding of Helicobacter pylori to monohexosylceramides

H. pylori is the major cause of human gastritis, duodenal ulcer and thus gastric adenocarcinoma. Many glycosphingolipid species have been postulated as receptors for H. pylori and it is likely that H. pylori attachment requires multiple, perhaps sequential receptor/ligand interactions. In this study, the binding of a number of H. pylori clinical isolates, as well as stock strains, to acid and neutral glycosphingolipids separated on thin-layer chromatograms was characterized under microaerobic conditions. All H. pylori clinical isolates, laboratory strains and type culture collection strains recognized galactosylceramide (Galbeta1Cer) with ceramide containing sphingosine and hydroxylated fatty acid (type I), or non-hydroxylated fatty acid (type II), on thin-layer chromatograms and when incorporated into liposomes. The clinical isolates bound stronger to Galbeta1Cer (type II) than Galbeta1Cer (type I) on TLC, whereas lab and culture collection strains showed the opposite binding preference. A clear preference in binding to Galbeta1Cer (type I) incorporated into liposome was shown by most tested strains. Clinical isolates bound well to glucosylceramide (Glcbeta1Cer) with hydroxylated fatty acid, whereas weak binding to this glycolipid was detected with the lab and type collection strains. None of the tested strains bound Glcbeta1Cer with non-hydroxylated fatty acid on the solid surface, but some strains of both clinical or type collection origins showed weak or very weak binding in the liposome assay. A clear distinction between the binding specificity of living organisms (under microaerobic conditions) as opposed to dying organisms (under normoxic conditions) illustrates the importance of cellular physiology in this process. These studies illustrate lipid modulation of the potential receptor function of monohexosylceramides and the distinction between the receptor repertoire of H. pylori clinical isolates and cultured strains commonly used to study host-cell adhesion.

Combined effect of rebamipide and ecabet sodium on Helicobacter pylori adhesion to gastric epithelial cells

Helicobacter pylori is a major etiological agent in gastroduodenal disorders. The adhesion of H. pylori to gastric epithelial cells is the initial step of H. pylori infection. Inhibition of H. pylori adhesion is thus a therapeutic target in the prevention of H. pylori infection. We have reported that rebamipide and ecabet sodium, mucoprotective antiulcer agents, independently inhibit H. pylori adhesion. However, the antiadhesion activity of each antiulcer agent was incomplete. Experiments were performed to evaluate the combined effect of rebamipide and ecabet sodium on H. pylori adhesion to gastric epithelial cells. MKN-28 and MKN-45 cells, derived from human gastric carcinomas, were used as target cells. Twelve clinical isolates of H. pylori were used in this study. We evaluated the effects of rebamipide and ecabet sodium, individually and in combination, on H. pylori adhesion to target cells quantitatively using our previously established enzyme-linked immunosorbent assay. Rebamipide and ecabet sodium each partially inhibited H. pylori adhesion. In contrast, adhesion was almost completely inhibited by pretreating target cells and H. pylori with the combination of rebamipide and ecabet sodium. Our studies suggest that the synergistic antiadhesion activity of rebamipide and ecabet sodium is greater than that of each antiulcer agent alone.

Comparative analysis of colonization of Helicobacter pylori and glycolipids receptor density in Mongolian gerbils and mice

The Mongolian gerbil has been used as an excellent experimental animal model for studying Helicobacter pylori infection because it can stably colonize and induce severe chronic gastritis, ulceration, and cancer-simulating human diseases in this animal. In contrast, H. pylori can only induce mild inflammation in many mouse models. The aim in this study is to clarify the difference of induction of pathological lesions in the two animal models. SPF ICR mice and Mongolian gerbils were inoculated with a clinically isolated strain of H. pylori. Six weeks after inoculation, bacteria colonizing the stomach were counted. Immunohistochemical staining and biochemical analyses of three putative receptor glycolipids were performed with monoclonal antibodies to the respective glycolipids. Significantly higher numbers of H. pylori were recovered from the stomachs of Mongolian gerbils than mice (5.77 +/- 0.46 log CFU vs 4.17 +/- 0.55 log CFU, P < 0.01). Immunohistochemical studies showed that sulfatide expression in the gastric mucosa of Mongolian gerbils was much stronger than that in mice, whereas the expression of Lewis(b) glycolipid and GM3 were almost equal. Quantitative analysis of each glycolipid by thin-layer chromatography confirmed the results of immunohistochemical study, showing 4.1 times higher sulfatide content in the Mongolian gerbil stomach. The content of both Lewis(b) and GM3 was almost equivalent in these two animals. In conclusions, higher levels of sulfatide expression, a putative adhesion receptor, in the gastric mucosa of Mongolian gerbils may allow abundant colonization by H. pylori, resulting in the development of gastric lesions in this animal model.

Pathogen-Host Protein-Carbohydrate Interactions as the Basis of Important Infections

Microbe-host protein-carbohydrate interactions are most likely the essential first step to produce an infection, although this has been strictly proven only in a few cases. Improved glycotechnology will help identification of new carbohydrate receptors and this knowledge may be used to identify microbial carbohydrate-binding proteins by affinity proteomics approaches. In some cases such conserved proteins may prove to be successful vaccine components, in other cases, like influenza, saccharide analogues may be the only rational alternative. The prognosis may be, based on these improvements, that infection medicine will make considerable progress in the near future.

Helicobacter pylori adhesins: review and perspectives

It is highly unlikely that chronic infection with H. pylori could occur in the absence of adhesin-host cell interactions. Also, there is no evidence that any of the serious outcomes of H. pylori infection such as gastric and duodenal ulcers, gastric cancer or mucosa-associated lymphoid tissue (MALT) lymphoma could occur without prior colonization of the gastric epithelium mediated by H. pylori adhesins. H. pylori is highly adaptable, as evidenced by the fact that it can occupy a single host for decades. An important facet of this adaptability is its ability to physically interact with various types of host cells and also with host mucins and extracellular matrix proteins using a number of different adhesins displaying a variety of unique receptor specificities. Thus it is highly unlikely that any one particular H. pylori adhesin will ever be proven responsible for a particular outcome such as duodenal ulcer, MALT lymphoma, or adenocarcinoma. Also, while the search for additional H. pylori adhesins should and certainly will continue, we suggest that the scope of this effort should be expanded to include investigations into the patterns of expression and interaction between individual outer membrane proteins. Which of the numerous H. pylori outer membrane proteins (OMPs) actually function as adhesins (i.e., have receptor-binding sites) and which OMPs are simply necessary for optimal display of the adhesive OMPs? There are many other important questions about H. pylori adhesins waiting to be answered. For example, which adhesins are responsible for loose adherence to host cells and which adhesins are responsible for intimate, or membrane-to-membrane, adherence, and do these adhesins normally work in concert or in a sequential fashion? Also, is a specific type of adhesin necessary for type IV protein translocation into host cells and, if so, is adhesin expression coregulated with the effector protein export?

Inhibition of nonopsonic Helicobacter pylori-induced activation of human neutrophils by sialylated oligosaccharides

Certain strains of Helicobacter pylori have nonopsonic neutrophil-activating capacity. Some H. pylori strains and the neutrophil-activating protein of H.pylori (HPNAP) bind selectively to gangliosides of human neutrophils. To determine if there is a relationship between the neutrophil-activating capacity and the ganglioside-binding ability, a number of H. pylori strains, and HPNAP, were incubated with oligosaccharides, and the effects on the oxidative burst of subsequently challenged neutrophils was measured by chemiluminescence and flow cytometry. Both by chemiluminescence and flow cytometry a reduced response was obtained by incubation of H.pylori with sialic acid-terminated oligosaccharides, whereas lactose had no effect. The reductions obtained with different sialylated oligosaccharides varied to some extent between the H. pylori strains, but in general 3'-sialyllactosamine was the most efficient inhibitor. Challenge of neutrophils with HPNAP gave no response in the chemiluminescence assay, and a delayed moderate response with flow cytometry. Preincubation of the protein with 3'-sialyllactosamine gave a slight reduction of the response, while 3'-sialyllactose had no effect. The current results suggest that the nonopsonic H. pylori-induced activation of neutrophils occurs by lectinophagocytosis, the recognition of sialylated glycoconjugates on the neutrophil cell surface by a bacterial adhesin leads to phagocytosis and an oxidative burst with the production of reactive oxygen metabolites.

Different patterns of Helicobacter pylori adherence to gastric mucosa cells in children and adults. An ultrastructural study

BACKGROUND

Infection with Helicobacter pylori in childhood may be the initiation of a lifelong coexistence between microorganisms and epithelial cells resulting in chronic inflammation. The adhesion pattern of H. pylori found in antral biopsies from a group of H. pylori-infected children with recurrent abdominal pain was compared with a group of H. pylori-infected adults suffering from dyspepsia, in an attempt to reveal differences in the type of adhesion.

METHODS

The histology of antrum biopsies and the ultrastructure of adherent H. pylori in biopsies from 26 children (median age, 10.1 years) were compared with organisms in biopsies from 19 adults (median age, 54.4 years).

RESULTS

More than 1000 adherent H. pylori were studied and divided into four types of adhesion: 1) contact to microvilli; 2) connection to the plasma membrane via filamentous material; 3) adhesive pedestal formation; and 4) abutting or making a depression in the plasma membrane. Contact to microvilli was significantly higher (69% versus 39%; P = 0.002) in children compared with adults and comprised two-thirds of all adherent organisms in children. The more intimate adhesion types as abutting or adhesive pedestals dominated in adults.

CONCLUSIONS

These results indicate a change in contact types between H. pylori and gastric epithelial cells in adults compared with children and this may be a natural development in the lifelong infection of humans.

The human gastric colonizer Helicobacter pylori: a challenge for host-parasite glycobiology

The Gram-negative bacterium Helicobacter pylori was first described in 1983 and currently represents one of the most active single research topics in biomedicine. It is specific for the human stomach and chronically colonizes a majority of the global population, which results in a symptom-free local inflammation. In 10-20% of carriers, gastroduodenal disease develops, including gastric or duodenal ulcer, and atrophic gastritis, which is a precondition to gastric cancer. A probable long coevolution of microbe and homo sapiens in a restricted niche has apparently generated a complex and sophisticated interplay. Access to complete bacterial genome sequences assists in a comparative functional characterization. A dynamic glycosylation of both microbe and host cells is of growing interest to analyze. Several glycoforms of bacterial surface lipopolysaccharides show advanced molecular mimicry of host epitopes and a distinct phase variation. An unusually large family of 32 outer membrane proteins probably reflects the complex interrelationship with the host. The unique diversity found for carbohydrate-binding specificities may be mediated by these surface proteins, of which the Lewis b-binding adhesin is the only known example so far, and these binding activities are subject to phase variation. The host mucosa glycosylation may also vary with different conditions, allowing a modulated crosstalk between microbe and host. The bacterium actively stimulates the host inflammatory response, apparently for nutritional purposes, and there is no evidence for a spontaneous elimination of the microbe. Colonization appears to be preventive for upper stomach and esophageal diseases. Current antibiotic treatment eradicates the microbe and cures ulcer disease. Alternative approaches must, however, be developed for a potential global prevention of disease.

Immune response against a cross-reactive epitope on the heat shock protein 60 homologue of Helicobacter pylori

We previously established a monoclonal antibody (MAb), designated H9, which reacts with the heat shock protein 60 (HSP60) homologue of Helicobacter pylori as well as with other bacterial and human HSP60s. To determine the importance of a cross-reactive epitope on H. pylori HSP60 in H. pylori immunopathogenesis, we performed (i) mapping of an epitope on H. pylori HSP60 recognized by the H9 MAb, (ii) analysis of immunoglobulin G responses of patients with or without H. pylori infection to its epitope region, and (iii) studies of the protective effect of immunization with its epitope region on H. pylori infection in mice. The epitope recognized by the H9 MAb was mapped to the sequence of amino acids 189 to 203 (VEGMQFDRGYLSPYF) on the H. pylori HSP60 molecule. It was confirmed that the synthesized peptide designated pH9 was recognized by the H9 MAb. Enzyme-linked immunosorbent assay analysis showed that patients with H. pylori infection (n = 349) had significantly lower titers of pH9 antibody than did uninfected patients (n = 200) (P < 0.001), but this was not the case with purified H. pylori HSP60 recombinant Escherichia coli GroEL, or recombinant human HSP60. In C57BL/6 mice immunized with the pH9 peptide with Freund's complete adjuvant (FCA), the number of H. pylori organisms colonizing the stomach was significantly lower than that in mice immunized with pCont plus FCA (P < 0.0001) or FCA only (P < 0.005). The results suggest that the immune response to the cross-reactive epitope (pH9 region) on H. pylori HSP60 is unique and might be associated with protection against H. pylori infection.

Lewis X structures in the O antigen side-chain promote adhesion of Helicobacter pylori to the gastric epithelium

Helicobacter pylori NCTC11637 expresses a lipopolysaccharide (LPS) that comprises an O antigen side-chain with structural homology to the human blood group antigen Lewis X (Le(x)). The role of this molecule in adhesion of H. pylori to gastric epithelial cells was investigated. Mutants expressing truncated LPS structures were generated through insertional mutagenesis of rfbM and galE; genes encode GDP mannose pyrophosphorylase and galactose epimerase respectively. Compositional and structural analysis revealed that the galE mutant expressed a rough LPS that lacked an O antigen side-chain. In contrast, an O antigen side-chain was still synthesized by the rfbM mutant, but it lacked fucose and no longer reacted with anti-Le(x) monoclonal antibodies (Mabs). The ability of these mutants to bind to paraffin-embedded sections from the antrum region of a human stomach was assessed. Adhesion of the wild type was characterized by tropic binding to the apical surface of mucosal epithelial cells and cells lining gastric pits. In contrast, both the rfbM and galE mutants failed to demonstrate tropic binding and adhered to the tissue surface in a haphazard manner. These results indicate that LPS and, more specifically, Le(x) structures in the O antigen side-chain play an important role in targeting H. pylori to specific cell lineages within the gastric mucosa. The role of Le(x) in this interaction was confirmed by the tropic binding of synthetic Le(x), conjugated to latex beads, to gastric tissue. The observed pattern of adhesion was indistinguishable from that of wild-type H. pylori.

Treatment of Helicobacter pylori infection in rhesus monkeys using a novel antiadhesion compound

BACKGROUND & AIMS

Helicobacter pylori can be eradicated by administration of antimicrobials, but resistant strains have emerged, and there is a need for novel therapeutic approaches against this infection. This study aimed to determine the safety and efficacy of 3'-sialyllactose sodium salt (3'SL), an oligosaccharide that occurs naturally in human and bovine milk and that can inhibit the adhesion of H. pylori to human epithelial cells in vitro.

METHODS

Twelve H. pylori-positive rhesus monkeys were given 3'SL, either alone (regimens 1 and 2; n = 6) or in combination with omeprazole (regimen 3; n = 4), or bismuth subsalicylate (regimen 4; n = 6). Videogastroscopies were performed before, during, and after treatment, and gastric biopsy specimens were obtained for quantitative cultures and histology. The H. pylori strains colonizing the animals were genotyped.

RESULTS

After regimen 1 or 2, 2 of 6 animals were cured permanently, and a third animal was transiently cleared. The 3 other animals remained persistently colonized and did not respond to regimen 3. Regimen 4 resulted in transient decreases in colony counts in 3 of 6 other animals. Gastritis was suppressed only in the 2 animals who became persistently H. pylori negative. There was no apparent relation between 3'SL efficacy and any of the H. pylori tested genotypes. No side effects were observed in any of the animals receiving 3'SL.

CONCLUSIONS

Antiadhesive therapy is safe; it can cure or decrease H. pylori colonization in some rhesus monkeys, but the addition of a proton pump inhibitor or bismuth subsalicylate does not increase cure rate.

Neu5Acalpha3Gal is part of the Helicobacter pylori binding epitope in polyglycosylceramides of human erythrocytes

The sialic acid dependent binding by the human pathogen Helicobacter pylori to polyglycosylceramides of human erythrocytes was investigated. Polyglycosylceramides, complex glycosphingolipids with a branched N-acetyllactosamine core, were isolated from human erythrocytes, blood group O, and subfractionated after peracetylation by anion-exchange chromatography. Three subfractions were deacetylated, analysed by matrix-assisted laser desorption ionization-time of flight MS and 2D 1H NMR spectroscopy. The observed mass ranges were m/z = 3093-7622, 3968-7255 and 3459-7987 in the mass spectra of the first, second and third fractions, respectively. The observed ions agreed with the general formula Hex(x+2)HexNAcxFucyNeu5AczCer. Two-dimensional 1H total correlation spectra of the mixtures showed that the first fraction contained 3-linked sialic acid and the second and third fractions contained both 3-linked and 6-linked sialic acid. Thin-layer chromatogram binding assays using the lectins from Maackia amurensis, specific for Neu5Acalpha3Galbeta4GlcNAc, and Sambucus nigra, specific for Neu5Acalpha6Gal/GalNAc, were used to confirm this distribution. H. pylori recognized all three fractions in the binding assay, indicating that the 3-linked, rather than 6-linked, sialic acid is essential for binding.

Helicobacter pylori and neutrophils: sialic acid-dependent binding to various isolated glycoconjugates

Helicobacter pylori has been shown to agglutinate erythrocytes in a sialic acid-dependent manner. However, very few studies have examined relevant target cells in the human stomach. Neutrophils are required for the onset of gastritis, and the inflammatory reaction may be induced on contact between bacteria and neutrophils. In the present work, glycolipids and glycoproteins were isolated from neutrophils and were studied for binding by overlay with radiolabeled bacteria on thin-layer chromatograms and on membrane blots. There was a complex pattern of binding bands. The only practical binding activity found was sialic acid dependent, since treatment of glycoconjugates with neuraminidase or mild periodate eliminated binding. As shown before for binding to erythrocytes and other glycoconjugates, bacterial cells grown on agar bound to many glycoconjugates, while growth in broth resulted in bacteria that would bind only to polyglycosylceramides, which are highly heterogeneous and branched poly-N-acetyllactosamine-containing glycolipids. Approximately seven positive bands were found for glycoproteins, and the traditional ganglioside fraction showed a complex, slow-moving interval with very strong sialic-acid-dependent binding, probably explained by Fuc substitutions on GlcNAc.

Analysis of Helicobacter pylori binding site on HEp-2 cells and three cell lines from human gastric carcinoma

Helicobacter pylori (H. pylori) is a pathogen responsible for chronic gastritis and peptic ulcer diseases. It colonises the gastric mucus layer and adheres to the gastric epithelial cell surface. As this adherence is the first step of infection, it is important to study the adherence mechanism. The aim of this study was to analyse the specific binding assay of H. pylori to HEp-2 cells and three gastric phenotype cell lines, AGS, MKN-45 and AZ-521. H. pylori NCTC 11637 grown on agar plates was harvested and used in experiments. H. pylori was inoculated to pre-cultured cell monolayers. Adhered bacteria were labelled with an anti-H. pylori antibody and an FITC-conjugated secondary antibody and quantified by using a fluorescent plate reader. Microbial adherence to HEp-2 cells increased with incubation time and incubated concentration of H. pylori. No further increase was obtained with four or more hours of incubation or with a concentration of 4 x 10(7) bacteria/well or more. Scatchard analysis revealed a linear plot and the Bmax value was 88.3. Similar adherence patterns were obtained when AGS, AZ-521 and MKN-45 cells were used for adherence assays, but they had a lower binding affinity than HEp-2 cells and AZ-521. MKN-45 cells had less receptors than HEp-2 and AGS cells. In conclusion, H. pylori adhered to the cell surface could be quantified by this assay method. H. pylori adhesion to cell surfaces has a single population of binding site and one type of binding site on HEp-2, AGS, AZ-521 and MKN-45 cells.

Glycolipid receptors for verotoxin and Helicobacter pylori: role in pathology

Eukaryotic cell surface glycolipids can act as both the primary interface between bacteria and their host and secondly as a targeting mechanism for bacterial virulence factors. The former is characterized by redundancy in adhesin-receptor interactions and the latter by a higher affinity, more restrictive glycolipid binding specificity for targeting. Interactions of verotoxin with its glycolipid receptor globotriaosylceramide and Helicobacter pylori binding to a variety of different glycolipids, which can be environmentally regulated, provide examples of these differing modes of glycolipid receptor function. Verotoxins are involved in endothelial targeting in the microangiopathies of hemorrhagic colitis and hemolytic uremic syndrome (HUS). The highly restricted binding specificity and crystal structure of the verotoxin B subunit have allowed theoretical modeling of the Gb3 binding site of the verotoxin B subunit pentamer which provides an approach to intervention. Studies of the role of glycolipid function in verotoxin-induced disease have concentrated on the distribution of Gb3 and its ability to mediate the internalization of the toxin within the target cell. The distribution of Gb3 within the renal glomerulus plays a central role in defining the age-related etiology of HUS following gastrointestinal infection with VT producing Escherichia coli. H. pylori, on the other hand, instigates a less distinct but more complex disseminated gastric inflammation. Studies on the role of glycolipid receptors in H. pylori infection have been bogged down in establishing the importance of each binding specificity defined. In addition, the physiological condition of the organism within the various binding assays has not been extensively considered, such that spurious non-physiological interactions may have been elucidated. The identification and cloning of a Le(b) binding adhesin and the identification of cell surface hsp70 as a mediator of sulfoglycolipid binding under stress conditions may now allow a more molecular approach to define the role of glycolipid recognition in this infection.

Rat gastric mucous gel layer contains sialomucin not produced by the stomach

The sialylated mucus components of the normal gastric mucosa and mucous gel layer of rats were studied by using various histochemical staining methods including Maackia amurensis II (MAL-II) and Sambucus nigra (SNA) lectins, alcian blue (AB) pH 2.5 -- periodic acid Schiff (PAS) and high iron diamine (HID) -- AB pH 2.5. The acidic and neutral mucins characterized by the AB-PAS staining were abundantly present in the mucous gel layer as well as in the gastric mucosa. The sialomucin characterized by HID-AB was barely found in either the mucous gel layer or the mucosa. The sialomucin positive to MAL-II and SNA, which react with the N-acetyl neuraminic acid residue linked to galactose via an alpha-linkage, was moderately detected only in the mucous gel layer, but not in the entire mucosal layer. Furthermore, in animals given surgery to form an esophageal fistula through which saliva was excluded or in animals subjected to salivectomy, the mucous gel layer stained with MAL-II and SNA lectins was markedly decreased. These results indicate that a part of the sialomucin containing-mucous gel layer covering normal rat gastric mucosa originates from the saliva and that MAL-II and SNA lectins are useful for detecting this specific sialomucin.

Host determinants of Helicobacter pylori infection and its clinical outcome

Greater than one-half of the world's population harbors Helicobacter pylori. The majority of infected individuals, however, remain asymptomatic, with only 10% to 20% developing diseases, including peptic ulcer disease, gastric cancer, and gastric mucosa-associated lymphoid tissue lymphoma. This article reviews host factors that may predispose an individual to both the acquisition of H. pylori infection and subsequent clinical outcome. Individuals with specific blood group antigens and human leukocyte antigen genotypes may be more susceptible to H. pylori infection. Additional factors, such as the age of acquisition, the host immune response, the site of infection, acid secretion, and interactions with nonhost factors (including bacterial virulence factors and environmental influences) may play a role in determining clinical outcome. Further investigation is required to clarify the mechanisms by which these interactions occur and, more critically, to determine their relative importance. This knowledge will enable the identification of individuals at risk of developing clinical disease with H. pylori infection.

Metabolism and genetics of Helicobacter pylori: the genome era

The publication of the complete sequence of Helicobacter pylori 26695 in 1997 and more recently that of strain J99 has provided new insight into the biology of this organism. In this review, we attempt to analyze and interpret the information provided by sequence annotations and to compare these data with those provided by experimental analyses. After a brief description of the general features of the genomes of the two sequenced strains, the principal metabolic pathways are analyzed. In particular, the enzymes encoded by H. pylori involved in fermentative and oxidative metabolism, lipopolysaccharide biosynthesis, nucleotide biosynthesis, aerobic and anaerobic respiration, and iron and nitrogen assimilation are described, and the areas of controversy between the experimental data and those provided by the sequence annotation are discussed. The role of urease, particularly in pH homeostasis, and other specialized mechanisms developed by the bacterium to maintain its internal pH are also considered. The replicational, transcriptional, and translational apparatuses are reviewed, as is the regulatory network. The numerous findings on the metabolism of the bacteria and the paucity of gene expression regulation systems are indicative of the high level of adaptation to the human gastric environment. Arguments in favor of the diversity of H. pylori and molecular data reflecting possible mechanisms involved in this diversity are presented. Finally, we compare the numerous experimental data on the colonization factors and those provided from the genome sequence annotation, in particular for genes involved in motility and adherence of the bacterium to the gastric tissue.

Oligosaccharides in human milk during different phases of lactation

Twenty-one oligosaccharides of human milk were quantified by high-performance anion-exchange chromatography. Milk samples were collected from 18 mothers during the first 3 mo of lactation. The data show that the highest amount of all oligosaccharides is present at day 4 postpartum (20 g l(-1)) and then decreases by about 20% at day 30 of lactation. The protective role played by these substances against different infectious agents, in different organs and systems of the breastfed baby, is emphasized.

Mechanisms of Helicobacter pylori infection: bacterial factors

Since the discovery of H. pylori in 1982 (MARSHALL 1983; WARREN 1983), research on the mechanisms of virulence of H. pylori has advanced substantially. It is now well established that urease and flagella are virulence factors of H. pylori. Although known for some time to be toxic to epithelial cells in vitro, VacA has only recently been established as a virulence factor. The cag pathogenicity island has also emerged as another virulence contender, although the specific genes involved in virulence are still being determined. Other possible virulence factors, not yet confirmed by gene disruptions, are hapA, katA, sodA, cagA, and iron-regulated genes. As of yet, no adhesins have been confirmed as being important for in vivo survival of H. pylori. With the sequence of the H. pylori genome in hand, it should be possible to more easily determine the role of specific genes in virulence. Genes of immediate interest are the OMPs, which may under go phase and antigenic variation and may represent adhesins. Additionally, virulence-related orthologs and vacA-related genes may provide some interesting findings. Once we define the genes that contribute to H. pylori virulence, we may be able to more easily develop novel therapeutic drugs or vaccines to treat and prevent H. pylori infection.

Gastric epithelial cells stimulate Helicobacter pylori growth

Helicobacter pylori infects only human gastric epithelium, causes gastritis, and is strongly associated with gastroduodenal ulceration and gastric cancer. Colonization of the stomach with H. pylori is accompanied in the acute stage by an increased number of neutrophils in the lamina propria, indicative of gastric inflammation. It is interesting that H. pylori colonizes specifically human gastric-type epithelial cells. We studied whether the presence of gastric epithelial cells influenced H. pylori growth. H. pylori (NCTC 11637) was cultured on Skirrow agar with 7% horse blood. Kato-III cells, a human gastric cancer cell line, were cultured with RPMI 1640 plus 10% fetal bovine serum (FBS). Kato-III cells (10(5)/ml) were cultured with/ without H. pylori (10(8) cfu/ml) with RPMI 1640 + 1% FBS for 3 days. The number of Kato-III cells was counted with a hemacytometer. H. pylori with/without Kato-III cells was cultured with RPMI 1640 + 10% FBS for 2 hours, and plated on Skirrow agar. After 3 days we counted the number of H. pylori colonies. To detect the H. pylori colonies, we used a colony hybridization method. DNA of colonies was transferred to positively charged nylon membrane and hybridized by PCR with Hpl (5'-CTG-GAG-AGA-CTA-AGC-CCT-CC-3') and Hp2 (5'-ATT-ACT-GAC-GCT-GAT-TGT-GC-3')-amplified primers. We previously reported that the number of Kato-III cells was significantly decreased by co-incubation with H. pylori. The number of H. pylori colonies was significantly increased by coincubation with Kato-III cells. We conclude that the presence of human gastric epithelial cells is important for the growth of H. pylori.

Novel therapies for Helicobacter pylori infection

BACKGROUND

Increasing antibiotic resistance has begun to impair our ability to cure Helicobacter pylori infection.

AIM

To evaluate orally administered novel therapies for the treatment of H. pylori infection.

METHODS

Healthy H. pylori infected volunteers received: (a) hyperimmune bovine colostral immune globulins, (b) an oligosaccharide containing an H. pylori adhesion target, Neu5Aca2-3Galb1-4Glc-(3'-sialyllactose), or (c) recombinant human lactoferrin. Outcome was assessed by urea breath test or histological assessment of the number of H. pylori present.

RESULTS

None of the novel therapies appeared effective and no adverse events occurred.

CONCLUSION

Although in vitro data appeared promising, in vivo results were disappointing. Higher doses, longer duration of therapy, adjunctive acid suppression, or a combination could possibly yield better results.

Analysis of 3- and 6-linked sialic acids in mixtures of gangliosides using blotting to polyvinylidene difluoride membranes, binding assays, and various mass spectrometry techniques with application to recognition by Helicobacter pylori

A convenient approach to analyze 3- and 6-linked sialic acids in mixtures of biologically active gangliosides was developed. The procedure was adapted to work on small amounts of material and included parallel tests, which allowed direct analysis of structure and activity. The initial step in the procedure was separation of a mixture of gangliosides by thin-layer chromatography (TLC) and blotting to a polyvinylidene difluoride membrane. The gangliosides were then analyzed (a) by direct desorption from the membrane and fast atom bombardment mass spectrometry (FAB MS), (b) by membrane-binding assay using the NeuAcalpha3- and NeuAcalpha6-specific lectins from Maackia amurensis and Sambucus nigra, respectively, and (c) by TLC binding assay with radiolabeled bacteria. All experiments were performed on a mixture of gangliosides from human leucocytes, which contained species with affinity for the human gastric pathogen Helicobacter pylori. The procedure was used with good results for gangliosides with up to seven sugars per ceramide. A three-sugar ganglioside was identified as GM3 with ceramides composed of sphingosine (d18:1) and 20:0, h20:0, and 24:0 fatty acids. The sequences of four bands in the five-sugar region were consistent with sialylparagloboside (NeuAcalpha3/6Galbeta4GlcNAcbeta3Galbeta4GlcbetaCer). The ceramides were composed of d18:1 and 24:1 fatty acid in the first and third bands, and d18:1 and 16:0 fatty acid in the second and fourth bands from the top. The sialic acid was shown to be 3-linked in the upper two bands and 6-linked in the lower two bands. The same distribution of sialic acid and ceramides but the sequence elongated with one N-acetyllactosamine unit was observed in the less resolved interval containing seven-sugar glycosphingolipids. The direct comparison of binding of lectins and radiolabeled bacteria showed that H. pylori recognized 3-linked sialic acid only. These results were supported by a novel technique of analysis of the sialic acid linkage position by trifluoroacetolysis and gas chromatography/MS. Direct membrane/FAB MS was ineffective for species migrating below the seven-sugar region on the TLC. In this case, the membranes were instead cut in bands and the gangliosides extracted by methanol before analysis by FAB MS.

Oligosaccharide receptors for bacteria: a view to a kill

Oligosaccharide recognition is a major means of bacterial-host cell attachment. Bacterial-host receptor binding can subvert host signaling pathways to cause pathology. In addition, pathogenic bacteria can utilize more than one recognition system to bind host cells. Recent studies of Helicobacter pylori illustrate both these points. Together with this redundancy in recognition, the importance of multivalent sugar binding has become apparent. Multivalent sugar receptor analogs have been used to both prevent and detach adherent bacteria. Several new chemical technologies for the generation of bioactive glycopolymers have been developed and may be successfully adapted to address both these issues.

Characterization of an acidic-pH-inducible stress protein (hsp70), a putative sulfatide binding adhesin, from Helicobacter pylori

The in vitro glycolipid binding specificity of the gastric pathogen Helicobacter pylori is altered to include sulfated glycolipids (sulfatides) following brief exposure of the organism to acid pH typical of the stomach. This change is prevented by anti-hsp70 antibodies, suggesting that hsp70 may be a stress-induced surface adhesin, mediating sulfatide recognition. To facilitate investigation of the role of hsp70 in attachment, we have cloned and sequenced the H. pylori hsp70 gene (dnaK). The hsp70 gene was identified by probing a cosmid DNA library made from H. pylori 439 with a PCR amplicon generated with oligonucleotides synthesized to highly conserved regions of dnaK. The 1.9-kb H. pylori hsp70 gene encodes a product of 616 amino acids. Primer extension analysis revealed a single transcription start site, while Northern blot analysis established that hsp70 was preferentially induced by low pH rather than by heat shock. The ability of H. pylori to alter its glycolipid binding specificity following exposure to low pH by upregulating hsp70 and by expressing hsp70 on the bacterial surface may provide a survival advantage during periods of high acid stress.

Detection and characterization of Helicobacter pylori from patients with gastroduodenal diseases

Polymerase chain reaction and cytotoxin assays were performed to identify as Helicobacter pylori type I (cagA+/tox+) or type II (cagA-/tox-) 56 (59.6%) strains from 94 patients. Of these patients 64 were affected by nonulcer dyspepsia (NUD), 10 by gastric ulcer (GU), 19 by duodenal ulcer (DU), and 1 by both GU and DU. H. pylori strains were tested for cagA using two sets of primers; target sequences were detected in 40-42/56 (71.4-75%) depending on the set of primers used, while cytotoxin-producing strains (tox +) were 26/56 (46.4%). Tox+ strains were isolated in 13/32 (40.6%), 2/7 (28.6%), and 11/17 (64.7%) in NUD, GU, and DU patients, respectively. However, the different percentage between cagA+ strains from NUD patients (13/32; 40.6%) and patients with ulcerative diseases (13/23; 54.2%) is not statistically significant (p = 0.462). Because the two sets of primers employed for amplification of cagA target sequences give different results, we concluded that cagA alone could not be taken as predictive factor for severity of gastroduodenal disease. It has been found that H. pylori type I is associated with duodenal ulcer disease.

Effect of rebamipide, a novel antiulcer agent, on Helicobacter pylori adhesion to gastric epithelial cells

Helicobacter pylori is a major etiological agent in gastroduodenal disorders. The adhesion of H. pylori to human gastric epithelial cells is the initial step of H. pylori infection. Inhibition of H. pylori adhesion is thus a therapeutic target in the prevention of H. pylori infection. Experiments were performed to evaluate the effect of rebamipide, a novel antiulcer agent, on H. pylori adhesion to gastric epithelial cells. MKN-28 and MKN-45 cells, derived from human gastric carcinomas, were used as target cells. Ten H. pylori strains isolated from patients with chronic gastritis and gastric ulcer were used in the study. We evaluated the effect of rebamipide on H. pylori adhesion to MKN-28 and MKN-45 cells quantitatively using our previously established enzyme-linked immunosorbent assay. The adhesion of H. pylori to MKN-28 and MKN-45 cells was significantly inhibited by pretreatment of these cells with 100 microg of rebamipide per ml. However, the adhesion was not affected by the pretreatment of H. pylori with rebamipide. On the other hand, the viabilities of H. pylori, MKN-28 cells, and MKN-45 cells were not affected by rebamipide. Our studies suggest that rebamipide inhibits the adhesion of H. pylori to gastric epithelial cells.

Selective binding by Helicobacter pylori of leucocyte gangliosides with 3-linked sialic acid, as identified by a new approach of linkage analysis

The human gastric pathogen Helicobacter pylori has been shown to bind to glycoconjugates of human leucocytes in a sialic acid-dependent way. In order to improve the identification of the binding epitope, a new technique was developed to analyze the ketosidic linkage position between a terminal sialic acid and the consecutive monosaccharide. Permethylation and reduction with LiAlH4 followed by trifluoroacetolysis in 1000:1 trifluoroacetic anhydride:trifluoroacetic acid (24 h, 100 degrees C) results in the cleavage of glycosidic but not ketosidic bonds. The disaccharide products were analyzed by gas chromatography-mass spectrometry and sialyl-3 or -6 position and NeuAc or NeuGc are identified by their separate retention times and mass spectra. The method was worked out on model saccharides and applied on five-sugar gangliosides (sialylparaglobosides) of human leucocytes. Radiolabeled Helicobacter pylori was shown to bind to the upper part, but not to the lower part, of the five-sugar interval of a mixture of gangliosides separated on a thin-layer chromatogram. Using a membrane blotting procedure the active and inactive bands were isolated and shown to be NeuAcalpha2-3- and NeuAcalpha2-6-paraglobosides, respectively.

Meaning and therapeutic potential of microbial recognition of host glycoconjugates

The microbe-host interface is currently in focus because of attempts to develop infection therapy in humans based on either natural receptor saccharide (respiratory and gastrointestinal disease) or sophisticated sialic acid analogues designed from crystal structures (influenza). Most of the known host receptors for microbes are glycoconjugates, and the diversity and selectivity of host tissue glycosylation allow for the tropism of infections. However, among the many binding specificities detected so far, the biological role has been proven only in a few infectious model systems. The existence of multiple specificities of a single microbe is both a complicating factor and a challenge, requiring expanded research with a special demand on glycoscience.

Growth inhibition of Helicobacter pylori by monoclonal antibody to heat-shock protein 60

The H20mAb recognizing the 60-kilodalton protein, which existed in the outer membrane and was induced by heat shock at 42 C, was established. The molecule recognized with the mAb was a heat-shock protein 60 (HSP60) of Helicobacter pylori. To understand the role of HSP60 on the cell surface of H. pylori, whether or not H20mAb affects the growth of H. pylori was investigated. When bacteria were cultured with H20mAb, growth was markedly inhibited after 24 hr, although an initial 5 hr-incubation with the mAb induced no significant inhibition of H. pylori growth. The 24- and 48 hr growth of the bacteria after washing to remove the mAb at 5 hr was also inhibited though the inhibitory effect was not strong. In electron microscopical analysis, the spots with high electron density in the cytoplasm of the bacteria treated with H20mAb were increased, depending on the length of incubation time from 5 to 24 hr. After 24 hr treatment with H20mAb, bacterial destruction was also observed, indicating bactericidal activity by H20mAb. These results suggest that the HSP60 on the cell surface of H. pylori might have an essential role in the growth of the bacteria.

Neutrophil-activating protein mediates adhesion of Helicobacter pylori to sulfated carbohydrates on high-molecular-weight salivary mucin

The in vitro binding of surface-exposed material and outer membrane proteins of Helicobacter pylori to high-molecular-weight salivary mucin was studied. We identified a 16-kDa surface protein which adhered to high-molecular-weight salivary mucin. This protein binds specifically to sulfated oligosaccharide structures such as sulfo-Lewis a, sulfogalactose and sulfo-N-acetyl-glucosamine on mucin. Sequence analysis of the protein proved that it was identical to the N-terminal amino acid sequence of neutrophil-activating protein. Moreover, this adhesin was able to bind to Lewis x blood group antigen.

Quantification of conserved antigens in Helicobacter pylori during different culture conditions

In this study, we raised monoclonal antibodies (MAbs) against three conserved Helicobacter pylori antigens, i.e., the N-acetylneuraminyllactose-binding fibrillar hemagglutinin, HpaA; the flagellin subunits, FlaA and FlaB; and a species-specific 26-kDa protein. The MAbs were used for the development of sensitive inhibition enzyme-linked immunosorbent assays for quantification of these antigens in H. pylori during various culture conditions. The quantities of these antigens varied considerably (up to 8-fold) during different culture procedures and between strains (up to 10-fold).

A flagellar sheath protein of Helicobacter pylori is identical to HpaA, a putative N-acetylneuraminyllactose-binding hemagglutinin, but is not an adhesin for AGS cells

The gene encoding a 29-kDa flagellar sheath protein was cloned and found to be similar to hpaA, reported to encode an N-acetylneuraminyllactose-binding fibrillar hemagglutinin (D. G. Evans, T. K. Karjalainen, D. J. Evans, Jr., D. Y. Graham, and C. H. Lee, J. Bacteriol. 175:674-683, 1993). The transcriptional start was mapped by primer extension from Helicobacter pylori mRNA, indicating an active consensus promoter at a location different from that suggested by Evans et al. Immunogold labelling of the flagellar sheath with a monoclonal antibody to HpaA was demonstrated in four strains, contrary to previous reports of a surface (D. G. Evans, T. K. Karjalainen, D. J. Evans, Jr., D. Y. Graham, and C. H. Lee, J. Bacteriol. 175:674-683, 1993) or a cytoplasmic (P. W. O'Toole, L. Janzon, P. Doig, J. Huang, M. Kostrzynska, and T. J. Trust, J. Bacteriol. 177:6049-6057, 1995) locale. Agglutination of erythrocytes and adherence to AGS cells by a delta hpaA mutant were no different from those of the parent strain, confirming a recent finding of O'Toole et al.

Recognition of glycoconjugates by Helicobacter pylori. Comparison of two sialic acid-dependent specificities based on haemagglutination and binding to human erythrocyte glycoconjugates

Helicobacter pylori expresses separate binding characteristics depending on growth conditions, as documented by binding to human erythrocyte glycoconjugates. Cells grown in Ham's F12 liquid medium exhibited a selective sialic acid-dependent binding to polyglycosylceramides, PGCs (Miller-Podraza et al.(1996) Glycoconjugate J13:453-60). There was no binding to traditional sialylated glycoconjugates like shorter-chain gangliosides, glycophorin or fetuin. However, cells grown on Brucella agar bound both to PGCs and other sialylated glycoconjugates. Fetuin was an effective inhibitor of haemagglutination caused by agar-grown cells, but had no or a very weak inhibitory effect on haemagglutination by F12-grown bacteria. PGCs were strong inhibitors in both cases, while asialofetuin was completely ineffective. The results indicate that H. pylori is able to express two separate sialic acid-dependent specificities, one represented by binding to fetuin, as described before, and another represented by a selective binding to PGCs.

Binding of Helicobacter pylori to sialic acid-containing glycolipids of various origins separated on thin-layer chromatograms

Two standard strains of Helicobacter pylori, grown on solid or in liquid medium, were studied for their binding to sialic acid-containing glycosphingolipids on thin-layer plates. NCTC 11637, but not strain 11638, bound to mixtures of gangliosides of various human and animal origins with similar binding patterns and also to polyglycosylceramides of human erythrocytes, leukocytes, and placenta. There was an apparent specificity for NeuAc alpha3Gal of the neolacto series of gangliosides, since NeuAc alpha6Gal or ganglio-series gangliosides did not bind.

Identification of the N-acetylneuraminyllactose-specific laminin-binding protein of Helicobacter pylori

The interaction of the gastroduodenal pathogen Helicobacter pylori with the glycoprotein laminin was investigated. Binding of 125I-radiolabelled laminin in a liquid-phase assay by both hemagglutinating and poorly hemagglutinating strains was rapid, saturable, specific, partially reversible, of high affinity, and insensitive to pH. Inhibition of laminin binding by fetuin, but not asialofetuin, and reduced bacterial binding to periodate- or sialidase-treated laminin indicated that glycosylation, particularly sialylation, was important for laminin binding by H. pylori. Inhibition experiments with monosaccharides, disaccharides, and trisaccharides showed that the strains bound to a region spanning a trisaccharide. In particular, inhibition and displacement studies showed that binding to the trisaccharide N-acetylneuraminyl-alpha(2-3)-lactose [NeuAc(2-3)Lac] was preferential to that to the NeuAc(2-6)Lac isomer. Complete inhibition of laminin binding by both hemagglutinating and poorly hemagglutinating strains was achieved only when isolated lipopolysaccharide (LPS) was used as an inhibitor in combination with heat or protease treatment of H. pylori cells, thereby confirming the involvement of both LPS and a protein adhesin in laminin binding. Further inhibition experiments indicated that the protein receptor, rather than LPS, on H. pylori bound NeuAc(2-3)Lac. By using a Western blotting procedure, a 25-kDa outer membrane protein was identified as mediating laminin binding by both hemagglutinating and poorly hemagglutinating H. pylori strains. The specificity of binding was confirmed by complete inhibition of laminin binding by the 25-kDa protein with NeuAc(2-3)Lac. The data collectively suggest that a 25-kDa outer membrane protein acts in a lectin-like manner with LPS to mediate attachment of H. pylori to laminin.

Inhibition of Helicobacter pylori binding to gastrointestinal epithelial cells by sialic acid-containing oligosaccharides

Helicobacterpylori, the ulcer pathogen residing in the human stomach, binds to epithelial cells of the gastric antrum. We have examined binding of 13 bacterial isolates to epithelial cell lines by use of a sensitive microtiter plate method in which measurement of bacterial urease activity provides the means for quantitation of bound organisms. Several established human gastrointestinal carcinoma cell lines grown as monolayers were compared for suitability in these assays, and the duodenum-derived cell line HuTu-80 was selected for testing bacterial binding inhibitors. When bacteria are pretreated with oligosaccharides, glycoproteins, and glycolipids, a complex picture of bacterial-epithelial adherence specificities emerges. Among the monovalent inhibitors tested, 3'-sialyllactose (NeuAc alpha2-3Gal beta1-4Glc; 3'SL) was the most active oligosaccharide, inhibiting adherence for recent clinical isolates of H. pylori with a millimolar 50% inhibitory concentration (IC50). Its alpha2-6 isomer (6'SL) was less active. Most of the recent clinical isolates examined were inhibited by sialyllactose, whereas long-passaged isolates were insensitive. Among the long-passaged bacterial strains whose binding was not inhibited by 3'SL was the strain ATCC 43504, also known as NCTC 11637 and CCUG 17874, in which the proposed sialyllactose adhesin was recently reported to lack surface expression (P. G. O'Toole, L. Janzon, P. Doig, J. Huang, M. Kostrzynska, and T. H. Trust, J. Bacteriol. 177:6049-6057, 1995). Pretreatment of the epithelial monolayer with neuraminidase reduced the extent of binding by those bacteria that are sensitive to inhibition by 3'SL. Other potent inhibitors of bacterial binding are the glycoproteins alpha1-acid glycoprotein, fetuin, porcine gastric and bovine submaxillary mucins, and the glycolipid sulfatide, all of which present multivalent sialylated and/or sulfated galactosyl residues under the conditions of the binding assay. Consistent with this pattern, a multivalent neoglycoconjugate containing 20 mol of 3'SL per mol of human serum albumin inhibited bacterial binding with micromolar IC50. The H. pylori isolate most sensitive to inhibition by 3'SL was least sensitive to inhibition by sulfatide, gastric mucin, and other sulfated oligosaccharides. Bacteria that have been allowed to bind epithelial cells are also effectively detached by 3'SL. These results describe a heterogeneous adherence repertoire for these bacteria, but they also confirm the critical role of the 3'SL structure on human gastric epithelial cells as an adherence ligand for recent isolates of H. pylori.

Pathophysiology of Helicobacter pylori-induced gastritis and peptic ulcer disease

Helicobacter pylori causes persistent infection and inflammation in the human stomach, yet only a small fraction of persons harboring this organism develop peptic ulcer disease. An important question is why this variation in infection outcome exists. Recent studies have demonstrated that H pylori isolates possess substantial phenotypic and genotypic diversity that may engender differential host inflammatory responses that influence clinical outcome. Further investigation in this field may help to define which H pylori-infected persons bear the highest risk for subsequent development of peptic ulcer disease, and thus enable physicians to focus eradication therapy.

Sialic acids in molecular and cellular interactions

Sialic acids (Sias) are terminal components of many glycoproteins and glycolipids especially of higher animals. In this exposed position they contribute significantly to the structural properties of these molecules, both in solution and on cell surfaces. Therefore, it is not surprising that Sias are important regulators of cellular and molecular interactions, in which they play a dual role. They can either mask recognition sites or serve as recognition determinants. Whereas the role of Sias in masking and in binding of pathogens to host cells has been documented over many years, their role in nonpathological cellular interaction has only been shown recently. The aim of this chapter is to summarize our knowledge about Sias in masking, for example, galactose residues, and to review the progress made during the past few years with respect to Sias as recognition determinants in the adhesion of pathogenic viruses, bacteria, and protozoa, and particularly as binding sites for endogenous cellular interaction molecules. Finally, perspectives for future research on these topics are discussed.

Cell surface glycosaminoglycans are not involved in the adherence of Helicobacter pylori to cultured Hs 198.St human gastric cells, Hs 746T human gastric adenocarcinoma cells, or HeLa cells

Hs 198.St cells (a line derived from normal human gastric tissue), Hs 746T cells (a line derived from human gastric adenocarcinoma), and HeLa cells were used together with 3H-labelled Helicobacter pylori, strain NCTC 11637 to determine if cell surface glycosaminoglycans could act as initial receptors for adherence of the bacteria. Although as much as 40% of the 3H-labelled bacteria adhered to monolayers of the cultured cells, removal of glycosaminoglycans by prior treatment of the cells with heparitinase, heparinase, or chondroitin ABC lyase had no effect in modifying the adherence. Prior addition of heparan sulfate, heparin, or chondroitin/dermatan sulfate to bacteria had no effect on adherence, nor were bacteria released when these same glycosaminoglycans or these same enzymes were added to cultures already containing adherent bacteria. These results indicated that neither heparan sulfate nor chondroitin/dermatan sulfate are involved as receptors in the initial adherence step of H. pylori to these cultured cells.

Diagnosis of Helicobacter pylori infection

A number of diagnostic tests have been developed for the detection of H. pylori. Diagnostic techniques can be divided into invasive and noninvasive methods. The invasive methods require upper gastrointestinal endoscopy and involve culture of gastric biopsy specimens, examination of stained biopsies and detection of urease activity in the biopsies themselves. In addition, we have developed endoscopic diagnosis of H. pylori infection in gastric mucosa using phenol red dye-spraying. The noninvasive methods include urea breath test and serological techniques. Although there has been considerable improvement in the techniques, a combination of at least two different techniques should be used in order to optimize the diagnostic yield. We recommend the use of one rapid test in the combination. The rapid urease test, cytology and the phenol red dye-spraying endoscopy give results available before the patient leaves the endoscopy suite.