Gnotobiotic IL-10-/-;NF-κBEGFP mice reveal the critical role of TLR/NF-κB signaling in commensal bacteria-induced colitis

Commensal bacteria and TLR signaling have been associated with the maintenance of intestinal homeostasis in dextran sodium sulfate-induced intestinal injury. The aim of this study was to determine the in vivo role of TLR/NF-kappa B activation in a model of commensal bacteria-induced T cell-mediated colitis. A NF-kappa B reporter gene mouse (NF-kappa B (EGFP)) (EGFP, enhanced GFP) was crossed to the colitogenic susceptible strain IL-10(-/-) and derived into germfree conditions using embryo-transfer technology. Gerinfree IL-10(wt/wt);NF-kappa B-EGFP and IL-10(-/-);NF-kappa B-EGFP mice (wt, wild type) were dual associated with the nonpathogenic commensal bacteria strains Enterococcus faecalis and Escherichia coli. EGFP was detected using macroimaging, confocal microscopy, and flow cytometry. IL-10(-/-);MyD88(-/-) mice were used to assess E.faecalis/E. coli-induced TLR-dependent signaling and IL-23 gene expression. Dual-associated IL-10(-/-);NF-kappa B (EGFP) mice developed severe inflammation by 7 wk. Macroscopic analysis showed elevated EGFP expression throughout the colon of bacteria-associated IL-10(-/-);NF-kappa B (EGFP) mice. Confocal microscopy analysis revealed EGFP-positive enterocytes during the early phase of bacterial colonization (1 wk) in both IL-10(wt/wt) and IL10(-/-) mice, while the signal shifted toward lamina propria T cells, dendritic cells, neutrophils, and macrophages in IL-10(-/-) mice during colitis (7 wk). The NF-kappa B inhibitor BAY 11-7085 attenuated E. faecalis/E. coli-induced EGFP expression and development of colitis. Additionally, E. faecalis/E. coli-induced NF-kappa B signaling and IL-23 gene expression were blocked in bone marrowderived dendritic cells derived from IL-10(-/-);MyD88(-/-) mice. We conclude that bacteria-induced experimental colitis involves the activation of TLR-induced NF-kappa B signaling derived mostly from mucosal immune cells. Blocking TLR-induced NF-kappa B activity may represent an attractive strategy to treat immune-mediated intestinal inflammation. The Journal of Immunology, 2007, 178: 6522-6532.