Citrobacter rodentium-induced colitis: A robust model to study mucosal immune responses in the gut.

Citrobacter rodentium is a natural mouse pathogen which reproducibly infects mice and causes intestinal disease. The C. rodentium model of infection is very useful for investigating host-pathogen immune interactions in the gut, and can also be used to understand the pathogenesis of several important human intestinal disorders, including Crohn's disease, ulcerative colitis, dysbiosis and colon tumorigenesis. Both innate and adaptive immune responses play a critical role in protection against C. rodentium. Here, we summarize the role of immune components in protection against C. rodentium and describe techniques for the analysis of innate and adaptive mucosal immune responses, including setting up the infection, analysis of colonic hyperplasia and bacterial dissemination, evaluation of antibody responses, and purification and analysis of intestinal epithelial and lymphoid cells.

Beneficial effect of probiotics in IBD: are peptidogycan and NOD2 the molecular key effectors?

Although the beneficial capacities of probiotics are more and more substantiated, their effects clearly depend on the strains used and their mechanisms of action remain poorly understood. Recent evidences have highlighted the potential role of cell-wall components in the anti-inflammatory capacity of selected lactobacilli. In this addendum, we summarize our recent results concerning the role of peptidoglycan (PGN) and NOD2 signaling in the regulation of intestinal inflammation. We showed that the protective effect of Lactobacillus PGN is strain-specific and linked to the induction of diverse immune regulatory pathways. Moreover the beneficial effect of Lactobacillus PGN correlated with the release of a specific muropeptide sensed by NOD2. These findings allow for a better understanding of how probiotic lactobacilli exert their beneficial effect and will help guide for more successful strain selection.

Anti-inflammatory capacity of selected lactobacilli in experimental colitis is driven by NOD2-mediated recognition of a specific peptidoglycan-derived muropeptide.

BACKGROUND AND AIMS: Inflammatory bowel disease (IBD) has been linked to a loss of tolerance towards the resident microflora. Therapeutic use of probiotics is known to be strain specific, but precise mechanisms remain unclear. The role of NOD2 signalling and the protective effect of Lactobacillus peptidoglycan (PGN) and derived muropeptides in experimental colitis were evaluated. METHODS: The anti-inflammatory capacity of lactobacilli and derived bacterial compounds was evaluated using the 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis model. The role of NOD2, MyD88 and interleukin 10 (IL-10) in this protection was studied using Nod2(-/-), MyD88(-/-) and Il10-deficient mice, while induction of regulatory dendritic cells (DCs) was monitored through the expansion of CD103(+) DCs in mesenteric lymph nodes or after adoptive transfer of bone marrow-derived DCs. The development of regulatory T cells was investigated by following the expansion of CD4(+)FoxP3(+) cells. High-performance liquid chromatography and mass spectrometry were used to analyse the PGN structural differences. RESULTS: The protective capacity of strain Lactobacillus salivarius Ls33 was correlated with a local IL-10 production and was abolished in Nod2-deficient mice. PGN purified from Ls33 rescued mice from colitis in an IL-10-dependent manner and favoured the development of CD103(+) DCs and CD4(+)Foxp3(+) regulatory T cells. In vitro Ls33 PGN induced IL-10-producing DCs able to achieve in vivo protection after adoptive transfer in a NOD2-dependent way. This protection was also correlated with an upregulation of the indoleamine 2,3-dioxygenase immunosuppressive pathway. The protective capacity was not obtained with PGN purified from a non-anti-inflammatory strain. Structural analysis of PGNs highlighted in Ls33 the presence of an additional muropeptide, M-tri-Lys. The synthesised ligand protected mice from colitis in a NOD2-dependent but MyD88-independent manner. CONCLUSIONS: The results indicated that PGN and derived muropeptides are active compounds in probiotic functionality and might represent a useful therapeutic strategy in IBD.