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 IFN¿R1
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 stem cells. The proposed research is significant because it is
expected to provide novel mechanisms by which T cells and IECs cooperate to protect the host from enteric
pathogens. Ultimately, such knowledge has the potential for innovative therapies for infectious colitis and IBD.