Helicobacter pylori γ-glutamyl transpeptidase and vacuolating cytotoxin promote gastric persistence and immune tolerance

Abstract

Infection with the gastric bacterial pathogen Helicobacter pylori is typically contracted in early childhood and often persists for decades. The immunomodulatory properties of H. pylori that allow it to colonize humans persistently are believed to also account for H. pylori's protective effects against allergic and chronic inflammatory diseases. H. pylori infection efficiently reprograms dendritic cells (DCs) toward a tolerogenic phenotype and induces regulatory T cells (Tregs) with highly suppressive activity in models of allergen-induced asthma. We show here that two H. pylori virulence determinants, the γ-glutamyl transpeptidase GGT and the vacuolating cytotoxin VacA, contribute critically and nonredundantly to H. pylori's tolerizing effects on murine DCs in vitro and in vivo. The tolerancepromoting effects of both factors are independent of their described suppressive activity on T cells. Isogenic H. pylori mutants lacking either GGT or VacA are incapable of preventing LPS-induced DC maturation and fail to drive DC tolerization as assessed by induction of Treg properties in cocultured naive T cells. The Δggt and ΔvacA mutants colonize mice at significantly reduced levels, induce stronger T-helper 1 (Th1) and T-helper 17 (Th17) responses, and/or trigger more severe gastric pathology. Both factors promote the efficient induction of Tregs in vivo, and VacA is required to prevent allergen-induced asthma. The defects of the Δggt mutant in vitro and in vivo are phenocopied by pharmacological inhibition of the transpeptidase activity of GGT in all readouts. In conclusion, our results reveal the molecular players and mechanistic basis for H. pyloriinduced immunomodulation, promoting persistent infection and conferring protection against allergic asthma.bacterial virulence factors | hygiene hypothesis | persistent bacterial infection | human microbiota | persistence strategies T he bacterial pathogen Helicobacter pylori persistently colonizes the gastric mucosa of humans. It is typically acquired in early childhood (1) and, in the absence of antibiotic therapy, may persist for the entire lifespan of the host (2, 3). The extraordinary ability of H. pylori to resist a vigorous adaptive immune response driven in large part by T-helper 1 (Th1) and/or T-helper 17 (Th17)-polarized effector T cells (4, 5) has been attributed to its perfect adaptation to-and manipulation of-the human innate and adaptive immune systems (6). H. pylori has colonized its human host for at least 60,000 y (7) and during this long period of coevolution has evolved elaborate ways to systemically manipulate adaptive immune responses and to promote its persistence through the preferential induction of regulatory T-cell (Treg) over T-effector cell responses. Treg-predominant responses are characteristic of heavily colonized but asymptomatic carriers (4) and of children with particularly mild forms of Helicobacter-associated gastritis (8). Several recent functional studies using experimentally infected animals have implicated Tregs and dendritic cells (...

Helicobacter pylori γ-Glutamyltranspeptidase Induces Tolerogenic Human Dendritic Cells by Activation of Glutamate Receptors

“…Notably, the enzymatic activity of gGT was shown to be required for its immunomodulatory effects (6). The results reported in this study support this function in human cells and, more importantly, provide a molecular mechanism linking bacterial gGT to glutamate-mediated tolerance.…”

“…Among those, H. pylori gGT has been linked to immune evasion by blocking T cell proliferation and function (1,17), whereas in murine models of infection, gGT was reported to induce tolerance by reprogramming DCs toward a tolerogenic phenotype (6). In the current study, we have analyzed whether H. pylori gGT shows the same immunomodulatory effects on human DCs.…”

“…In a murine model of infection, H. pylori gGT alters T cell polarization by inducing changes in DC maturation (6). Thus, we assessed the expression levels of the costimulatory molecule CD86 and the maturation marker CD83 on human DCs upon infection with H. pylori wild-type or deficient for gGT.…”

“…After 24 h, extracellular bacteria were killed using 100 mg/ml gentamicin (SigmaAldrich) for at least 3 h. Afterwards, freshly isolated naive CD4 + T cells were added to the infected DCs at a 2:1 ratio, as previously described (6). The final coculture medium was adjusted to 5 mM glutamine to avoid a dampened T cell proliferation due to gGT-dependent glutamine deprivation.…”

“…Hence, cytotoxinassociated gene A was shown to dampen DC maturation in mice (4), and we recently showed that cytotoxin-associated gene A induces tolerogenicity upon activation of the transcription factor STAT3 in human DCs (5). Other studies demonstrated an important role for vacuolating cytotoxin and g-glutamyltranspeptidase (gGT) in H. pylori-induced tolerance in mice (6). However, the molecular mechanisms behind this tolerance remained mostly unknown.…”