Project Summary: Chronic inflammation and metaplasia are precursors to gastrointestinal diseases, including gastric cancer. Although the increased risk of gastric cancer in individuals with chronic inflammation in the stomach has been known for many years, there is still a fundamental gap in our knowledge of the molecular and cellular processes by which inflammation influences the progression from chronic atrophic gastritis to gastric cancer. A more mechanistic understanding of these processes is likely to improve strategies to identify those at risk of gastric cancer, to diagnoses individuals at an earlier stage of disease, and/or to develop new immune-based treatments. Cytokines play a critical role in carcinogenesis by acting on immune cells to regulate severity of inflammation and the release of DNA-damaging chemicals, and by acting on epithelial cells and regulating proliferation and differentiation. This is especially relevant to gastritis and gastric cancer because >90% of all gastric cancers are adenocarcinomas, which are derived from epithelial cells, and most develop in a setting of chronic inflammation (e.g. Helicobacter infection). We recently discovered, using a mouse model of inflammation- induced gastric cancer, that expression of the Ebi3 gene is critical for slowing the progression of gastric carcinogenesis. The EBI3 protein is a component of two cytokines, IL-27 and IL-35. The goal of this proposal is to identify how EBI3 (IL-27/IL-35) regulates the progression of gastric carcinogenesis. Our central hypothesis, based on strong preliminary data, is that IL-27 and/or IL-35 slow the progression of gastritis and gastric cancer by two novel mechanisms: 1) by regulating cytokine production by CD4+ T cells, and 2) regulating epithelial cell injury and repair mechanisms. The specific aims of this proposal are to: 1) Determine whether IL-27 regulates gastritis severity by inhibiting Th17 and Th22 cells; 2) Test the direct effects of EBI3 on gastric epithelial cells homeostasis and/or metaplasia-repair; and 3) Determine whether EBI3 expressed by immune cells, epithelial cells, or both types regulate inflammation and epithelial changes during gastric cancer progression. Studies will be performed in tissue from mice and in human biopsies, and in mouse and human gastroids. The proposed research is innovative because it identifies a novel functions for EBI3 in regulating the biology of immune cells and epithelial cells in the gastric mucosa and uses innovative approaches. The proposed research is significant because it is expected to expand our mechanistic understanding of the cellular and molecular processes that regulate both inflammation and metaplasia in the gastric mucosa.