IL-17 signaling protects against <i>Helicobacter pylori-</i> induced gastric cancer

<i>Helicobacter pylori</i> infection is the predominant risk factor for the development of gastric cancer. Risk is enhanced by specific <i>H. pylori</i> virulence factors, diet, and the inflammatory response. Chronic activation of T helper (Th) 1 and Th17 pathways contributes to prolonged inflammation; yet, higher expression of IL-17 receptor (IL-17RA) is a favorable prognostic marker for survival after gastric cancer diagnosis. The protective impact of IL-17RA signaling is not understood. To investigate if IL-17RA signaling protects during <i>H. pylori-</i>induced carcinogenesis, the transgenic <i>InsGAS</i>^<i>tg/tg</i> mouse, which is prone to <i>H. pylori</i>-induced gastric cancer, was utilized. <i>InsGAS</i>^<i>tg/tg</i> mice and <i>InsGAS</i>^<i>tg/tg</i><i>Il17ra</i>^<i>-/-</i> mice were infected with a cag type 4 secretion system (T4SS) positive <i>H. pylori</i> strain for up to 6 months. Six weeks post-infection, IL-17RA deficiency led to increased bacterial burden, increased gastritis, and development of lymphoid follicles. Increased inflammation was associated with heightened cellular proliferation and earlier loss of parietal and chief cells in <i>InsGAS</i>^<i>tg/tg</i><i>Il17ra</i>^<i>-/-</i> mice. Gastric cancers developed more frequently by 3- and 6-months post-infection in <i>H. pylori</i>-infected <i>InsGAS</i>^<i>tg/tg</i><i>Il17ra</i>^<i>-/-</i> mice compared to <i>InsGAS</i>^<i>tg/tg</i> mice. Chronic inflammation was exacerbated with IL-17RA deficiency, characterized by elevated Th1/Th17 cytokines, increased B cell infiltration, and enhanced IgA production, despite reduced expression of the polymeric immunoglobulin receptor. Further, paragastric lymph nodes of <i>InsGAS</i>^<i>tg/tg</i><i>Il17ra</i>^<i>-/-</i> mice were enlarged relative to controls and displayed altered gene expression profiles. Increased inflammation was accompanied by a significant increase in <i>Cybb</i> expression, which encodes NADPH oxidase 2, suggesting that increased oxidative damage may occur in the absence of IL-17RA. Further, there is increased phosphorylation of histone 2AX in IL-17RA deficient mice, indicating that the DNA damage response is highly activated. These data suggest that IL-17RA signaling activates a protective pathway to prevent excessive inflammation which otherwise can lead to increased oxidative stress, DNA damage, and drive gastric carcinogenesis after <i>H. pylori</i> infection.