title: Negative selection of T cells by Helicobacter pylori as a model for bacterial strain selection by immune evasion.
abstract: The majority of humans infected with Helicobacter pylori maintain a lifelong infection with strains bearing the cag pathogenicity island (PAI). H. pylori inhibits T cell responses and evades immunity so the mechanism by which infection impairs responsiveness was investigated. H. pylori caused apoptotic T cell death, whereas Campylobacter jejuni did not. The induction of apoptosis by H. pylori was blocked by an anti-Fas Ab (ZB4) or a caspase 8 inhibitor. In addition, a T cell line with the Fas rendered nonfunctional by a frame shift mutation was resistant to H. pylori-induced death. H. pylori strains bearing the cag PAI preferentially induced the expression of Fas ligand (FasL) on T cells and T cell death, whereas isogenic mutants lacking these genes did not. Inhibiting protein synthesis blocked FasL expression and apoptosis of T cells. Preventing the cleavage of FasL with a metalloproteinase inhibitor increased H. pylori-mediated killing. Thus, H. pylori induced apoptosis in Fas-bearing T cells through the induction of FasL expression. Moreover, this effect was linked to bacterial products encoded by the cag PAI, suggesting that persistent infection with this strain may be favored through the negative selection of T cells encountering specific H. pylori Ags.
authors: Department of Pediatrics, University of Texas Medical Branch, Galveston, TX 77555, USA.
authors: J
authors: J
authors: Wang
authors: E G
authors: EG
authors: Brooks
authors: K B
authors: KB
authors: Bamford
authors: T L
authors: TL
authors: Denning
authors: J
authors: J
authors: Pappo
authors: P B
authors: PB
authors: Ernst
mesh_terms: D000942:Antigens, Bacterial; D017209:Apoptosis / Q000276:immunology; D001426:Bacterial Proteins / Q000276:immunology; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D016480:Helicobacter pylori / Q000276:immunology* / Q000472:pathogenicity; D006801:Humans; D019169:Jurkat Cells; D008024:Ligands; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D018448:Models, Immunological; D014176:Protein Biosynthesis; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000276:immunology; D019014:fas Receptor / Q000378:metabolism / Q000502:physiology
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008024:Ligands; D008562:Membrane Glycoproteins; C080866:cagA protein, Helicobacter pylori; D019014:fas Receptor