PROJECT SUMMARY More than 1.5 billion people are infected with helminths worldwide, predominantly distributed in tropical and subtropical areas. On the other hand, in developed countries with markedly reduced infectious diseases, there is a continuing increase in the incidences of allergic, inflammatory, and autoimmune diseases. The hygiene hypothesis proposes that an under-stimulated immune system resulting from the absence of exposure to helminths, predisposes to autoimmune and allergic inflammation. There is an urgent need for new preventive and therapeutic medicines for mucosal infection and inflammation. The research in my laboratory has been focused on the pathophysiological role of O-linked N-Acetylglucosamine (O-GlcNAc) modification on intracellular proteins at serine and threonine residues. The long-term goal is to elucidate the regulatory mechanisms and physiological functions of O-GlcNAc signaling in intestinal homeostasis and mucosal host defense. In the proposed study, we will test the hypothesis that O-GlcNAc transferase (OGT), by activating STAT6 signaling, promotes the differentiation of IL-25-producing tuft cells and facilitates IL-33 secretion from goblet cells, thus evoking type 2 immune responses for tissue repair and inflammation control. In Aim 1, we seek to define the functional impact, upstream activating signals, and downstream targets of STAT6 O-GlcNAcylation in tuft cell differentiation, type 2 immune activation, and helminth expulsion. In Aim 2, we identify a novel, common target of OGT and STAT6 that colocalizes with IL-33 in goblet cells and mediates the unconventional secretion of IL- 33 to initiate type 2 immune responses. In Aim 3, using pharmacological and genetic approaches to increase global protein O-GlcNAcylation in the intestinal epithelium, we expect to establish that the OGT-STAT6 pathway is required for intestinal homeostasis and mediates the therapeutic effect of helminths in colitis. The proposed study will provide valuable insights into the development of new intervention strategies to eradicate parasitic worms in areas of poverty in the developing world and to treat inflammatory bowel disease in industrialized countries.