Defining receptor-ligand interactions in gastric epithelial immunosurveillance

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SUMMARY Stomach infections with H. pylori are a significant cause of morbidity and mortality, leading to chronic gastritis, peptic ulcer disease and gastric cancer. While significant research efforts have been devoted to studying H. pylori-induced gastric pathogenesis and inflammation, the immune mechanisms specific to the gastric mucosa are still not very well understood. Importantly, how mononuclear phagocytes (MNPs) in the stomach access the luminal H. pylori bacteria for stimulation and regulation of T cell responses is unclear. Unlike the intestine, the stomach lacks M cells that are specialized for antigen transport from the lumen to the lamina propria. However, a large proportion of gastric MNPs are positioned in direct contact with the gastric epithelial layer, which likely supports efficient epithelial immunosurveillance including transepithelial dendrite formation by the MNPs. The receptors and ligands that control these functionally important adhesive interactions between the gastric epithelium and the MNPs are unknown. In preliminary studies, we have identified homotypic interactions between E-cadherin (E-cad) expressed on the epithelial cells and E-cad expressed by a subset of gastric MNPs as a potential candidate mechanism for MNP binding to the gastric epithelium. The overarching goal of the current proposal is to identify the receptor-ligand (R-L) interactions that MNPs in the stomach utilize to adhere to the gastric epithelium and to define the functional outcome of these interactions for gastric immunity. In Specific Aim 1, we will determine the role of E-cad-mediated MNP- epithelial cell engagement for MNP function in H. pylori infection. To achieve this aim, we will perform H. pylori infection experiments in MNP-organoid co-cultures with and without E-cad inhibition and in two novel transgenic mouse models with MNP-specific E-cad deletions, and we will map the distribution of E-cad+ MNPs in the stomach of healthy and H. pylori-infected individuals. In Specific Aim 2, we will utilize single cell RNA sequencing in gastric epithelial cell and MNP preparations to identify and evaluate additional receptors and ligands that mediate cell-cell interactions between gastric MNPs and epithelial cells. Identified candidate receptor-ligand pairs will be validated by analyzing gastric tissue sections and in functional experiments. Our research is conceptually innovative, because it addresses the role of MNP E-cad expression in the stomach and because it will identify receptor-ligand interactions that MNPs in the gastrointestinal tract utilize to interact with the epithelial layer. The proposed research is significant, because understanding the mechanisms of gastric epithelial immunosurveillance and adhesion by MNPs may ultimately inform the development of novel strategies to modulate the gastric response to H. pylori and combat infection.