Interaction between gastric pathogen Helicobacter pylori and host cells

Abstract

H. pylori plays a causative role in the pathogenesis of gastritis, gastric atrophy, gastric and duodenal ulcer, and is believed to predispose to gastric adenocarcinoma as well as low-grade B-cell lymphoma.

Lewisb (Leb) blood group antigen is a receptor for Leb adhesin-positive H. pylori strains. Type I H. pylori strains frequently express the BabA adhesin preferentially recognizing the Leb blood group antigen.

Studies in children have demonstrated a marked clustering of infection within families. More than 80% of siblings to H. pylori-colonized children have serologic evidence of infection, in comparison to 13% of age-matched controls.

H. pylori has so far been considered to be an extracellular colonizer, but data are available supporting an intracellular location of bacteria in vivo. An ability to invade host cells could be a mean for H. pylori to achieve resistance to antibiotic therapy.

We found that all of H. pylori isolates from children and adults that were Leb binders were also cag-positive. Most cag-positive isolates from adults with gastritis and/or peptic ulcer disease also expressed a Leb adhesin. The finding of an upregulation of Leb with age might select for Leb binding H. pylori. H. pylori isolates from adults lacking symptoms were Leb binders at much lower frequency than adults with gastroduodenal disease, suggesting that bacterial expression of the Leb antigen is not necessary for colonization but might correlate to disease.

The expression of Leb adhesin on the bacteria as well as cellular expression of the Leb oligosaccharide on the host were required for adherence to fixed normal or pathological gastric tissue. In contrast, adherence of both type I and type II strains to cultured cells occurred also in the absence of the Leb epitope. For the weakly Leb-expressing gastric cell line AGS, adherence was significantly higher when viable type I strains were allowed to interact with viable AGS cells as compared to fixed cells, while adherence of type II strains to viable versus fixed AGS cells was not significantly different. The observation that chloramphenicol, an inhibitor of bacterial protein synthesis and cycloheximide, an inhibitor of eukaryotic protein synthesis, significantly reduced adherence of type 1, but not type II isolates, suggests that in type I isolates adherence depends on the up-regulation of one or more host cell receptors triggered by the bacterium.

Leb-containing proteins in gastric tissue and cell lines were found to be of similar size as membrane cofactor protein (MCP, CD46). Immunoprecipitations with polyclonal antisera and monoclonal antibody against MCP also brought down a Leb signal. The Leb signal from gastric tissue was reduced by antibody to MCP. In addition, both polyclonal and monoclonal MCP antibodies could inhibit H. pylori adherence to cultured cells. A monoclonal antibody directed against CCP-I on MCP was the most potent inhibitor of H. pylori attachment.

Finally, we found that H. pylori induced phosphorylation of 125-130 kD proteins, similar in size to the target proteins of Yersinia YopH. Adherence of H. pylori was inhibited by Yersinia expressing enzymatically active YopH, but not by inactive YopH. Adherence and entry of H. pylori was considerably higher with [beta]1-integrin transfected cells as compared to [beta]1-integrin-deficient cells. Antibodies directed against [alpha]5 as well as [beta]1-integrin chains reduced adherence to the [alpha]5[beta]1-integrin expressing gastric cell line AGS. Entry was inhibited by both cytochalasin D and genistein. In conclusion, invasion of gastric epithelium via an integrin-mediated pathway could contribute to the ability of H. pylori to establish persistent infection.