Final Progress Report

Proposal No. IBD-0157R2
Principal Investigator:  Jean-Pierre Hugot, M.D., Ph.D.
Applicant Organization:  Naturalia et Biologia (Paris, France)
Project Title:  Role of psychotrophic bacteria in Crohn's disease
Period of Award:  May 1, 2006 – October 31, 2007

Summary of project aims:

The aim of the project was to test the hypothesis that the host response to Yersinia is modulated by CARD15/NOD2, a susceptibility gene for Crohn’s Disease (CD).

Accomplishments towards meeting those aims: 

NOD2 invalidated mice have been developed in collaboration with Marco Giovanini (CEPH) and studied in tha laboratory (Université Paris Diderot/INSERM).

List of significant results: 

We have shown that mice invalidated for NOD2 are more ressistant to Yersinia pseudotuberculosis infection when the bacteria are inoculated intragastrically. There is no difference when the bacteria are injected intraperitoneally. The observation was made on two genetic backgrounds and also for a model of mice carrying the homolous mutation to the human Crohn’s disease mutation. Thus, even if the reported differences are modest, they look robust.
 
The resistance is linked with a lower dissemination of the bacteria from the intestine to the spleen and liver. In the intestine, the bacteria are in a lower number and the immune response of the host was increased with a higher concentration of phagocytic cells and KC (an IL8 like molecule) production.
 
The phenotype seems to be relatively specific to Yersinia considering that the same mice are more sensitive to Listeria infection (previously published data) and Salmonella typhymurium (personal data published in PLOS One). 

Because these results were encouraging we added to the previously proposed work a project on Peyer's patches. Peyer’s patches are specialised places of interaction between Yersinia pseudotuberculosis and its host. We have shown a dysfunction of Peyer’s patches in mice invalidated for NOD2.
 
Peyer's patches from invalidated mice are more numerous and larger than the Peyer’s patches of wild-type controls. Isolated lymphoid follicles are also more numerous in the intestine. There is thus a hyperplasia and hypertrophia of the gut-associated lymphoid tissue. This finding is not present at birth and appears to regress after antiotherapy suggesting that it is driven by the normal ileal flora. 

In addition, we have shown that Peyer patches are characterised by an increased number of CD4+ T-cells which produce IFNγ. IFNγ is able induces an overexpression of the long isoform of MLCK and by consequence higher permeability and bacterial translocation rates through the epithelium. This phenomenoms are reversed after oral antibiotics. As a result, NOD2 modulates the complex cross-talk between the epithelial and the immune cells present in the Peyer's patches in response to the gut flora.