Helicobacter hepaticus HHGI1 is a pathogenicity island associated with typhlocolitis in B6.129-IL10tm1Cgn mice

Helicobacter hepaticus strain 3B1 (H. hepaticus) contains a genomic island of ∼71 kb, HHGI1, with some of the common features shared among known bacterial pathogenicity islands. In this study, we characterized the pathogenic potential of HHGI1 by infecting B6.129-IL10tm1Cgn (IL10−/−) mice with an isogenic mutant (namely HhPAId1) lacking 19 predicted genes within HHGI1. In contrast to H. hepaticus (P < 0.001), HhPAId1 did not cause typhlocolitis and hyperplasia in IL10−/− mice. Colonization levels of HhPAId1 were significantly higher in the cecum (P < 0.007) and similar in the colon (P = 0.27) when compared to H. hepaticus by 13 or 16 weeks post inoculation (WPI). The magnitude of the Th1-associated IgG2c response against HhPAId1 was less than that against H. hepaticus (P < 0.004). There was no significant difference in Th2-associated IgG1 responses against these two strains. Cecal and colonic mRNA levels of proinflammatory cytokines IFN-γ, TNF-α and IL-17a in the HhPAId1-infected mice were significantly lower than those in the H. hepaticus-infected mice (P < 0.05) at 13 WPI. These results demonstrate that genes in the HHGI1 contribute to the pathogenicity of H. hepaticus, at least in part via up-regulation of proinflammatory mediators IFN-γ, TNF-α and IL-17a.