Project Summary The goal of this proposal is to investigate the role of the gut microbiota and microbiota-specific immune responses in health and disease. The gut microbiota has been associated with a number of immune-based diseases, including cancer, autoimmunity, IBD and infections; however, specific mechanisms remain unclear. Our recent findings have shown that select members of the gut microbiota drive lymphatic development and formation of tertiary lymphoid structures. Specifically, addition of an adherent colonic-residing bacteria, Helicobacter hepaticus, supports lymphangiogenesis and tertiary lymphoid structure formation within the colon of colorectal tumor-bearing mice. Ultimately, this led to an increase in immune infiltration by T cells into the tumor core. However, how select colonic bacteria drive lymphangiogenesis and support tertiary lymphoid structure formation and maturation remains unknown. Project 1 of this proposal will identify the key signals responsible for bacteria-drive lymphangiogenesis using spatio-temporal analysis. Part 2 will investigate the cell subsets responsible for tertiary lymphoid structure formation due to lymphangiogenesis and Part 3 will assess the direct and indirect roles of gut microbes in lymphangiogenesis in health and disease. Our overall hypothesis is that colonization with Helicobacter hepaticus drives lymphangiogenesis and tertiary lymphoid structure maturation through upregulation of VEGF-driven reprogrammed Lyve1+ macrophages. Completion of these aims will lead to a completely new field of study and understanding of lymphangiogenesis in the adult host and will also establish the necessary foundation for my career as an independent investigator.