Usage of Murine T-cell Hybridoma Cells as Responder Cells Reveals Interference of Helicobacter Pylori with Human Dendritic Cell-mediated Antigen Presentation.

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Abstract

Direct effects of Helicobacter pylori (H. pylori) on human CD4(+) T-cells hamper disentangling a possible bacterial-mediated interference with major histocompatibility complex class II (MHC-II)-dependent antigen presentation to these cells. To overcome this limitation, we employed a previously described assay, which enables assessing human antigen-processing cell function by using murine T-cell hybridoma cells restricted by human leukocyte antigen (HLA) alleles. HLA-DR1(+) monocyte-derived dendritic cells were exposed to H. pylori and pulsed with the antigen 85B from Mycobacterium tuberculosis (M. tuberculosis). Interleukin-2 (IL-2) secretion by AG85Baa97-112-specific hybridoma cells was then evaluated as an integral reporter of cognate antigen presentation. This methodology enabled revealing of interference of H. pylori with the antigen-presenting capacity of human dendritic cells.

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Helicobacter pylori vacuolating cytotoxin inhibits T lymphocyte activation.

B Gebert, Rainer Haas, Wolfgang Fischer … (2003)

Helicobacter pylori (Hp) vacuolating cytotoxin VacA induces cellular vacuolation in epithelial cells. We found that VacA could efficiently block proliferation of T cells by inducing a G1/S cell cycle arrest. It interfered with the T cell receptor/interleukin-2 (IL-2) signaling pathway at the level of the Ca2+-calmodulin-dependent phosphatase calcineurin. Nuclear translocation of nuclear factor of activated T cells (NFAT), a transcription factor acting as a global regulator of immune response genes, was abrogated, resulting in down-regulation of IL-2 transcription. VacA partially mimicked the activity of the immunosuppressive drug FK506 by possibly inducing a local immune suppression, explaining the extraordinary chronicity of Hp infections.

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Immunization of Mice with Urease Vaccine Affords Protection against Helicobacter pylori Infection in the Absence of Antibodies and Is Mediated by MHC Class II–restricted Responses

Thomas H Ermak, Paul J. Giannasca, Richard Nichols … (1998)

We examined the roles of cell- and antibody-mediated immunity in urease vaccine–induced protection against Helicobacter pylori infection. Normal and knockout mice deficient in major histocompatibility complex (MHC) class I, MHC class II, or B cell responses were mucosally immunized with urease plus Escherichia coli heat-labile enterotoxin (LT), or parenterally immunized with urease plus aluminum hydroxide or a glycolipid adjuvant, challenged with H. pylori strain X47-2AL, and H. pylori organisms and leukocyte infiltration in the gastric mucosa quantified. In an adjuvant/route study in normal mice, there was a direct correlation between the level of protection and the density of T cells recruited to the gastric mucosa. In knockout studies, oral immunization with urease plus LT protected MHC class I knockout mice [β2-microglobulin (−/−)] but not MHC class II knockout mice [I-Ab (−/−)]. In B cell knockout mice [μMT (−/−)], vaccine-induced protection was equivalent to that observed in immunized wild-type (+/+) mice; no IgA+ cells were detected in the stomach, but levels of CD4+ cells equivalent to those in the wild-type strain (+/+) were seen. These studies indicate that protection of mice against H. pylori infection by immunization with the urease antigen is dependent on MHC class II–restricted, cell-mediated mechanisms, and antibody responses to urease are not required for protection.

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Inhibition of T-cell proliferation by Helicobacter pylori gamma-glutamyl transpeptidase.

Christian Prinz, Christian Schmees, Tilman Treptau … (2007)

Helicobacter pylori colonizes the human gastric mucosa of >50% of the world's population. Most of the patients have no overt clinical symptoms. However, the infection is invariably associated with the development of active chronic gastritis, leading in some cases to the development of peptic ulcer disease, distal gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. In contrast to most other pathogens, infection with H pylori persists lifelong, but reasons for the persistence remain obscure. CD4-positive T cells are crucial for bacterial elimination but are inhibited by H pylori. We aimed to identify the factor responsible for suppression of T-cell response and characterize this inhibitory effect on a cellular and molecular level. Using size-exclusion chromatography, sodium dodecyl sulfate/polyacrylamide gel electrophoresis, and a spectrophotometric enzyme assay, we identified the secreted gamma-glutamyl transpeptidase of H pylori (HPGGT) as the factor responsible for inhibition of T-cell proliferation. Mutagenesis of HPGGT in different H pylori strains completely abrogated this inhibitory effect. Recombinantly expressed HPGGT protein showed full antiproliferative activity. Site-directed mutagenesis and application of the GGT inhibitor acivicin revealed that inhibition of T cells depends on catalytic activity of HPGGT. Cell cycle analysis of human T cells indicated that HPGGT was necessary and sufficient to induce G(1) arrest. Reduced levels of c-Myc and phosphorylated c-Raf protein suggest the disruption of Ras-dependent signaling by HPGGT. GGT is a novel immunosuppressive factor of H pylori inhibiting T-cell proliferation by induction of a cell cycle arrest in the G(1) phase.