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Helicobacter pylori (H. pylori) induces chronic gastritis in humans, and infection can persist for decades. One H. pylori strain-specific constituent that augments disease risk is the cag pathogenicity island. The cag island encodes a type IV secretion system (T4SS) that translocates DNA into host cells. Toll-like receptor 9 (TLR9) is an innate immune receptor that detects hypo-methylated CpG DNA motifs. In this study, we sought to define the role of the H. pylori cag T4SS on TLR9-mediated responses in vivo. H. pylori strain PMSS1 or its cagE mutant, which fails to assemble a T4SS, were used to infect wild-type or Tlr9-/- C57BL/6 mice. PMSS1-infected Tlr9-/- mice developed significantly higher levels of inflammation, despite similar levels of colonization density, compared with PMSS1-infected wild-type mice. These changes were cag dependent, as both mouse genotypes infected with the cagE mutant only developed minimal inflammation. Tlr9-/- genotypes did not alter the microbial phenotypes of in vivo-adapted H. pylori strains; therefore, we examined host immunological responses. There were no differences in levels of TH1 or TH2 cytokines in infected mice when stratified by host genotype. However, gastric mucosal levels of IL-17 were significantly increased in infected Tlr9-/- mice compared with infected wild-type mice, and H. pylori infection of IL-17A-/- mice concordantly led to significantly decreased levels of gastritis. Thus loss of Tlr9 selectively augments the intensity of IL-17-driven immune responses to H. pylori in a cag T4SS-dependent manner. These results suggest that H. pylori utilizes the cag T4SS to manipulate the intensity of the host immune response. [ABSTRACT FROM AUTHOR]

Purpose: To feasibly analyze associations of Helicobacter pylori (H. pylori) with disease in large cohort studies, assays are needed to assess H. pylori prevalence in existing biospecimens. However, serology has traditionally been unable to distinguish active from past infection. We sought to determine the sensitivity of seropositivity to H. pylori proteins to detect active infection. Methods: We measured antibody responses to 13 H. pylori proteins using multiplex serology in serum samples of a training (n = 78) and validation set (n = 49) collected concurrently from patients undergoing urea breath test (UBT). To determine sensitivity of seropositivity to H. pylori proteins for active infection, a cutoff was applied to achieve 90% specificity. Antibody levels were retested in a subset of participants (n = 16) 6 months after baseline. Results: With a specificity of 91%, seropositivity to H. pylori proteins VacA, GroEl, HcpC, and HP1564 ascertained active infection from 100% to 75% sensitivity. Positivity to a combination of these proteins (≥2 out of the 4) resulted in specificity of 90% and sensitivity of 100%. The validation set replicated results from the training set. Among those participants with successful H. pylori eradication after baseline, antibody levels decreased significantly for VacA, HcpC, and HP1564 when assessed 6 months later. Conclusion: Utilizing the cutoffs for seropositivity established through comparison with UBT, seropositivity to ≥2 of the H. pylori proteins VacA, GroEl, HcpC, and HP1564 determines active H. pylori infection at high specificity and sensitivity and may approximate the prevalence of active H. pylori infection in large cohorts. [ABSTRACT FROM AUTHOR]