PROJECT SUMMARY Although much progress has been made in the treatment and prevention of diarrheal illness over the last century, the developing world is still plagued by diarrheal pathogens, with young children being particularly susceptible to diarrhea-related deaths. The long-term goal is to better understand how the coordinated responses of both immune and non-immune cells contribute to intestinal barrier protection during enteric infection. Our group recently discovered that Th17/22 cells are uniquely charged with protection of the intestinal crypts from enteric pathogens; however, the mechanisms by which these T cells are recruited to and sustain activation of crypt intestinal epithelial cells (cIECs) are unknown. The overall objectives in this application are to (i) elucidate the molecular mechanisms involved in recruiting T cells to cIECs and (ii) determine how recruited T cells interact with cIECs to deliver protective IL-22 signals. The central hypothesis is that IFN–induced upregulation of IEC- derived T cell-recruiting chemokines and MHCII expression promotes T cell recruitment to colonic crypts and targets pathogen-specific T cell-derived IL-22 signals to cIECs, respectively. The rationale for this project is that molecules involved in both recruitment and localized delivery of IL-22 to IECs will likely yield novel targets for therapies in diarrheal illnesses and inflammatory bowel disease (IBD), since responses to enteric pathogens and etiology of IBD share overlapping immune mechanisms. The central hypothesis will be tested by pursuing two specific aims: 1) IFN signaling in Lgr5+ IECs is critical for recruiting host-protective Cxcr3+ Th1 and Th17/22 cells to the colonic crypts; and 2) pathogen-specific T cells protect intestinal crypts via MHCII-dependent, sustained IL-22 delivery to IECs. The Citrobacter rodentium (C.r) model of infectious colitis, which closely models human E. coli infections, will be used to test both aims in this proposal. In Aim I, mice with deletion of the IFNR1 in Lgr5+ IECs will be used to to test the hypothesis that IFN signaling in Lgr5+ IECs is required for upregulation of T cell-recruiting chemokines Cxcl9 and Cxcl10 and adoptive transfer of Cxcr3-deficient T cells will be used to determine if the Cxcl9/10-Cxcr3 axis is involved in recruiting CD4+ T cells to cIECs. In Aim II, mice deficient for MHCII expression on IECs will be utilized to test the requirement of antigen presentation by IECs for IL-22- mediated protection of the intestinal crypts. In addition, mice that report TCR stimulation and adoptive transfer of C.r-specific T cells will be used to test the hypothesis that antigen-specific T cell–IEC interactions are important for protection from C.r infection. The research proposed in this application is innovative because it utilizes a newly engineered C.r strain to track antigen-specific T cells in the colon, and it offers unique insights into previously unrecognized roles of Lgr5+ intestinal ...