Project Summary The objective of this research proposal is to define the role of polyamines in modulating intestinal innate lymphoid cell homeostasis. Innate lymphoid cells (ILC) play a crucial role in mucosal barrier integrity and resistance to pathogenic insult through the integration of environmental signals and rapid secretion of immunoregulatory cytokines. In the intestine, group 3 ILC (ILC3) are crucial in defense against pathogenic bacterial colonization. They play significant roles in promoting the barrier function of the epithelium, regulating intestinal myeloid cells, and inducing the formation of lymphoid tissue within the mucosa to orchestrate intestinal homeostasis. However, dysregulation of ILC3 drives intestinal autoimmunity and has been associated with chronic inflammatory bowel diseases (IBD). Although it is known that intestinal lymphocytes make numerous metabolic adaptations in order to function in the tissue, little is understood about the relationship between cellular metabolism and the various functions of ILC3. We have integrated single-cell RNA-sequencing data and untargeted metabolomics of intestinal ILC to identify a significant enrichment of polyamines and polyamine metabolic enzymes in ILC3. Furthermore, our preliminary data demonstrate a positive role for polyamines in supporting ILC3 proliferation and function. We propose to 1) evaluate the impact of intracellular polyamines on ILC3 function at steady state and 2) assess the contribution of ILC3-intrinsic polyamine metabolism in a preclinical model of colitis. We hypothesize that polyamines positively regulate ILC3 function and thus contribute to the immunopathological role of ILC3 in colitis. The proposed research plan will define an ILC3-intrinsic contribution of polyamines in enhancing their activity and potentiating colitis. If this is the case, these results will further our understanding of the metabolic adaptations of ILC3 as well as the potential role for targeting these metabolic pathways to treat IBD.