Project Summary Although coronavirus disease 2019 (COVID-19) is primarily defined as a respiratory illness, patients often experience clinical gastrointestinal symptoms, including abdominal pain and diarrhea. We recently found that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, infects and replicates in human small bowel intestinal epithelial cells (IECs). However, the molecular mechanisms of SARS- CoV-2 driving gastrointestinal pathology, particularly in vulnerable populations with preexisting diseases remain unclear. In this proposal, our overall objectives are to better define the cellular signaling of SARS-CoV-2 interactions with IECs, enteric immune responses, and microbiome in the context of health or inflammatory bowel disease (IBD). Our preliminary data suggest that compared to normal COVID-19 patients, those with IBD have higher expression of cathepsin L in IECs, which correlated with higher viral loads. Our central hypothesis is that SARS- CoV-2 induces a distinctive intestinal pathology and mucosal immune response that is shaped by host factors (IBD), luminal factors (secretions, bile salts, and microbiome), and therapeutics (mesalamine). Specifically, using healthy and IBD-derived organoids, COVID-19 patient fecal samples, and K18-hACE2 mice, we aim to (1) define the host factors and cellular mechanisms involved in SARS-CoV-2 infection of normal and IBD epithelium, (2) determine the impact of intestinal SARS-CoV-2 infection on intestinal immune response and colitis, and (3) define the environmental factors that influence intestinal infection with SARS-CoV-2. With extensive and collaborative expertise in IBD, virology, and host-microbial interactions, we expect to address mechanistically interesting and clinically important questions like “What is the intestinal pathogenicity of SARS-CoV-2 and how is it impacted by IBD?”, “What is the interaction of SARS-CoV-2/COVID-19 with intestinal inflammation and IBD therapies?”, and “What is the impact of intestinal contents and IBD diagnosis/microbiome on intestinal SARS-CoV-2?”. We anticipate that this pathology will further our understanding of SARS-CoV-2 interactions with the epithelial and immune cells to explain COVID-19 GI symptoms with or without IBD. We also expect the new information gained from this project will expand our understanding of acute gastrointestinal pathology and symptoms of COVID-19, provide mechanistic context to existing clinical and translational literature, and create a foundational knowledge and tool set for deeper investigations into COVID-19 and potentially pathogenic and emerging coronaviruses of the future.