Bacteria and mucosal inflammation of the gut: lessons from Helicobacter pylori

The Role of Adhesion in Helicobacter pylori Persistent Colonization

Helicobacter pylori (H. pylori) has coevolved with its human host for more than 100 000 years. It can safely colonize around the epithelium of gastric glands via their specific microstructures and proteins. Unless patients receive eradication treatment, H. pylori infection is always lifelong. However, few studies have discussed the reasons. This review will focus on the adhesion of H. pylori from the oral cavity to gastric mucosa and summarize the possible binding and translocation characteristics. Adhesion is the first step for persistent colonization after the directional motility, and factors related to adhesion are necessary. Outer membrane proteins, such as the blood group antigen binding adhesin (BabA) and the sialic acid binding adhesin (SabA), play pivotal roles in binding to human mucins and cellular surfaces. And this may offer different perspectives on eradication.

Discussion on the common controversies of Helicobacter pylori infection

BACKGROUND

Helicobacter pylori ( H. pylori ) can persistently colonize on the gastric mucosa after infection and cause gastritis, atrophy, metaplasia, and even gastric cancer (GC).

METHODS

Therefore, the detection and eradication of H. pylori are the prerequisite.

RESULTS

Clinically, there are some controversial issues, such as why H. pylori infection is persistent, why it translocases along with the lesser curvature of the stomach, why there is oxyntic antralization, what the immunological characteristic of gastric chronic inflammation caused by H. pylori is, whether H. pylori infection is associated with extra-gastric diseases, whether chronic atrophic gastritis (CAG) is reversible, and what the potential problems are after H. pylori eradication. What are the possible answers?

CONCLUSION

In the review, we will discuss these issues from the attachment to eradication in detail.

New insights into regulatory B cells biology in viral, bacterial, and parasitic infections

B lymphocytes are primarily well known for their contribution to immunity by antibody production, antigen presentation and, the production of cytokines. In recent years several studies demonstrated the existence of B cells with regulatory functions, which have been termed regulatory B cells (B_regs), similar to regulatory T cells (T_regs). B_regs are a subpopulation of B cells that have immunosuppressive effects via the production of regulatory cytokines including interleukin-10 (IL-10), transforming growth factor-β (TGF-β), and IL-35. B_regs limit host defense against various pathogens. In addition, B_regs contribute to increased levels of regulatory cytokines and leads to an induction of suppressive T_regs, which exert broader suppressive functions against various pathogens. The high percentage of B_regs is positively associated with viral and bacterial load and can contribute to poor vaccine responses. B_regs can also facilitate pathogen survival at an early stage of infection, and subsequently cause increased severity of disease by inhibiting pro-inflammatory cytokine production, macrophage activation, and inflammatory T cells activation such as Th1, Th17, and Th22. Also, B_regs afford protection against the hyper-inflammatory response in parasitic infections. Here we review the central role of B_regs in many major bacterial and viral human infections, and provide an overview of the immunoregulatory mechanisms used by B_regs.

H.pylori Infection Alleviates Acute and Chronic Colitis with the Expansion of Regulatory B Cells in Mice

Epidemiological studies showed that there was an inverse relationship between Helicobacter pylori (H. pylori) infection and the incidence of inflammatory bowel diseases (IBD). Our previous research indicated that the regulatory immune responses induced by H. pylori infection were not limited to gastric mucosa, and the balance of intestinal mucosal immunity was influenced. In this study, mice were infected with H. pylori SS1, and then colitis was induced by 3% dextran sulphate sodium (DSS), to investigate the role of the regulatory B cells in the effects of H. pylori infection on acute and chronic colitis. In acute and chronic colitis groups, DAI and colonic histological scores reduced significantly and colon length shorted less, the proinflammatory cytokines mRNA expression downregulated in colonic mucosa, and the percentages of CD19⁺IL-10⁺Breg cells were higher in the H. pylori/DSS co-treated groups compared with the DSS-treated groups. Our study suggests that H. pylori infection can alleviate the acute and chronic colitis induced by DSS, and CD19⁺IL-10⁺Breg cells may play a critical role in the alleviation of acute and chronic colitis following H. pylori infection.

Human Gastric Epithelium Produces IL-4 and IL-4δ2 Isoform Only upon Helicobacter Pylori Infection

Recent evidence suggests that interleukin-4 (IL-4) is related to mucosal tolerance by which an injurious immune response is prevented, suppressed or shifted to a non-injurious response. We investigated the expression of IL-4 and its splice variant isoform IL-4δ2 in gastric epithelial cells of healthy subjects and gastritis patients infected with Helicobacter pylori (H. pylori) with or without the cag pathogenicity island ( cag-PAI). IL-4 and IL-4δ2 mRNAs were evaluated in microdissected gastric epithelium and in AGS cell lines co-cultured with H. pylori B128 or SSI strains. IL-4 mRNA was consistently detected in microdissected gastric epithelial cells from healthy subjects. The IL-4 mRNA expression was low in H. pylori-infected patients, and markedly reduced in cag-PAI-positive ones. IL-4δ2 mRNA was expressed on gastric epithelium of H. pylori-infected patients, but not in healthy subjects. The IL-452 expression was lower in cag-PAI-positive than in cag-PAI-negative H. pylori infected patients. AGS cells also produced IL-4 mRNA upon SSI strain stimulation, whereas IL-4δ2 mRNA expression was detected in AGS co-cultured with either SSI or B128 strains. An inverse correlation was documented between IL-4 and IL-482 mRNA expression by microdissected gastric epithelial cells and the score of gastritis. IL-4, but not IL-452, is expressed by gastric epithelium of healthy subjects, whereas IL-452 and lesser IL-4 mRNA are detectable in the gastric epithelium of H. pylori-infected patients. Data suggest that gastric epithelial cells might regulate the balance between tolerance and immune response by the fine tuning of IL-4 and IL-4δ2 expression.

The three-dimensional structure of the extracellular adhesion domain of the sialic acid-binding adhesin SabA from Helicobacter pylori

The gastric pathogen Helicobacter pylori is a major cause of acute chronic gastritis and the development of stomach and duodenal ulcers. Chronic infection furthermore predisposes to the development of gastric cancer. Crucial to H. pylori survival within the hostile environment of the digestive system are the adhesins SabA and BabA; these molecules belong to the same protein family and permit the bacteria to bind tightly to sugar moieties Lewis(B) and sialyl-Lewis(X), respectively, on the surface of epithelial cells lining the stomach and duodenum. To date, no representative SabA/BabA structure has been determined, hampering the development of strategies to eliminate persistent H. pylori infections that fail to respond to conventional therapy. Here, using x-ray crystallography, we show that the soluble extracellular adhesin domain of SabA shares distant similarity to the tetratricopeptide repeat fold family. The molecule broadly resembles a golf putter in shape, with the head region featuring a large cavity surrounded by loops that vary in sequence between different H. pylori strains. The N-terminal and C-terminal helices protrude at right angles from the head domain and together form a shaft that connects to a predicted outer membrane protein-like β-barrel trans-membrane domain. Using surface plasmon resonance, we were able to detect binding of the SabA adhesin domain to sialyl-Lewis(X) and Lewis(X) but not to Lewis(A), Lewis(B), or Lewis(Y). Substitution of the highly conserved glutamine residue 159 in the predicted ligand-binding pocket abrogates the binding of the SabA adhesin domain to sialyl-Lewis(X) and Lewis(X). Taken together, these data suggest that the adhesin domain of SabA is sufficient in isolation for specific ligand binding.

Follow-up study on a high risk population of gastric cancer in north China by serum pepsinogen assay

OBJECTIVE

To explore the features and clinical significance of serum pepsinogen (PG) assay in a follow-up study on a high-risk gastric cancer (GC) population.

METHODS

A total of 444 participants from a high-risk area of GC in north China were enrolled in this follow-up study from April 1997 to December 1999. Serum PG was measured by enzyme-linked immunosorbent assay (ELISA), and the percentage changes in PG were calculated with 'PG( follow-up)/PG (first test)' thrice from the beginning to the end of these 30 months. Stomach diseases were diagnosed by a gastroscopy with biopsy examination. Helicobacter pylori (H. pylori) status was assessed by histopathological examination and serum H. pylori-immunoglobulin (Ig)G antibody assay with ELISA.

RESULTS

In all groups except for the 51-60-year olds no significant differences of percentage changes in PGII and the PGI/II ratio were observed during 30-month follow-up period. In the superficial gastritis (SG) group the percentage change in PGI of group A (after 6 months' follow up) was significantly lower than that of group B (after 12 months' follow up) (0.69 vs 0.97, P = 0.002) in SG-->SG; while in SG-->normal (NOR), it was significantly higher than that in SG-->atrophic gastritis (AG) (0.94 vs 0.79, P = 0.022). In the AG group the percentage change in the PGI/II ratio of group A was significantly higher than that of group C (after 30 months' follow up) (1.13 vs 0.75, P = 0.042) in AG-->AG; and the percentage changes in PGI and PGII in AG-->NOR were significantly lower than those in AG-->SG (0.43 vs 0.87, P = 0.000; 0.60 vs 1.11, P = 0.010, respectively). In the H. pylori(-) (Hp(-)) group, the percentage change in PG of Hp(-)-->Hp(+) was significantly higher than that of Hp(-)-->Hp(-) (0.94 vs 0.81, P = 0.026). Percentage changes in PGI and PGII of Hp(+)-->Hp(-) were significantly lower than those of Hp(+)-->Hp(+) (0.74 vs 0.93, P = 0.000; 0.86 vs 1.15, P = 0.000, respectively), while the percentage change in the PGI/II ratio was higher than that the group of Hp(+)-->Hp(-) (0.90 vs 0.70, P = 0.022).

CONCLUSION

The serum PG levels were influenced by the physiopathologic status of gastric mucosa and H. pylori infection, but they altered during the period of follow up. Serum PG assay might be a feasible and appropriate procedure to use in following up on a high-risk GC population.