Nod1 and Nod2 are intracellular pattern recognition receptors that detect specific moieties of peptidoglycan, a critical component of the bacterial cell wall, to initiate host innate immune responses. Importantly, mutations in the human NOD2 gene have been associated with increased risk to develop mucosal auto-inflammatory disorders such as Crohn’s Disease. However, how Nod1 and Nod2 mediate mucosal homeostasis still remains unclear.
In Chapter 2, I determined that mice deficient for both Nod1 and Nod2 (Nod1-/-Nod2-/-) exhibited delayed induction of intestinal inflammation at early timepoints after infection with Citrobacter rodentium compared to wild-type mice, which correlated with compromised control of the pathogen at later timepoints. Notably, I determined that induction of the cytokines IL-17 and IL-22 in the cecal lamina propria (LP) was blunted in Nod1-/-Nod2-/- mice after infection with either C. rodentium or Salmonella enterica serovar Typhimurium. Importantly, I found that Th17 cells were the principal producers of IL-17 and IL-22 after infection. Due to the rapid kinetics of activation and the regulation by Nod1 and Nod2, I termed this early mucosal response the innate Th17 (iTh17) response.
The iTh17 cells exhibited an effector memory phenotype and required priming from the enteric microbiota for full induction. Therefore, in Chapter 3, I next determined that major histocompatibility complex (MHC) class II expression in hematopoietic cells was required for the induction of LP Th17 responses after infection. Interestingly, I found that the percentage IL-17+CD8+ T cells was strongly upregulated when MHCII signaling was ablated, suggesting a dynamic compensatory mechanism of IL-17-producing T cell responses in the mucosa.
In Chapter 4, I identified MDP(D-Glu2)-OCH3 as a synthetic Nod2 agonist that exhibited increased stimulatory ability of Nod2-dependent NF-B activation compared to MDP in an unbiased screen. Moreover, I determined that MDP(D-Glu2)-OCH3 induced more potent inflammatory responses both in vitro and in vivo and was a better adjuvant than MDP.
Together, the data presented in this thesis expand our current understanding of the roles of Nod1 and Nod2 in the intestinal LP, the regulation of IL-17 producing T cells in the gut and the therapeutic potential of novel Nod2 agonists.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/44135 |
| Date | 02 April 2014 |
| Creators | Rubino, Stephen |
| Contributors | Girardin, Stephen |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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