In human cases, there is an elevated level of IL-17 and IFNγ in the gastric mucosa of H. pylori patients, and upregulation of Th17-related gene expression (IL-6, IL-23 p19, IL-12/IL-23 p40, TGF-β1) [7] has been found to progressively increase from gastritis to peptic ulcers [75]. Here, IL17A is linked to peptic ulcer disease.