Dual-association of gnotobiotic IL-10-/- mice vith 2 nonpathogenic commensal bacteria induces aggressive pancolitis

Background: Monoassociating gnotobiotic IL-10-deficient (-/-) mice with either nonpathogenic Enterococcus faecalis or a nonpathogenic Escherichia coli strain induces T-cell-mediated colitis with different kinetics and anatomical location (E. fiaecalis: late onset, distal colonic; E. coli: early onset, cecal). Hypothesis: E. faecalis and E. coli act in an additive manner to induce more aggressive colitis than disease induced by each bacteria] species independently. Methods: Germ-free (GF) inbred 129S6/SvEv IL-10-/- and wildtype (WT) mice inoculated with nonpathogenic E. faecalis and/or E. coli were killed 3-7 weeks later. Colonic segments were scored histologically for inflammation (0 to 4) or incubated in media overnight to measure spontaneous IL-12/IL-23p40 secretion. Bacterial species were quantified by serial dilution and plated on culture media. Mesenteric lymph node (MLN) CD4(+) cells were stimulated with antigen-presenting cells pulsed with bacterial lysate (E. faecalis, E. coli, Bacteroides vulgatus) or KLH (unrelated antigen control). IFN-gamma and IL-17 levels were measured in the supernatants. Results: Dual-associated IL-10-/- (but not WT) mice developed mild-to-moderate pancolitis by 3 weeks that progressed to severe distal colonic-predominant pancolitis with reactive atypia and duodenal inflammation by 7 weeks. NF-kappa B\ was activated in the duodenum and colon in dual-associated IL-10-/- x NF-kappa B-EGFP mice. The aggressiveness of intestinal inflammation and the degree of antigen-specific CD4(+) cell activation were greater in dual- versus monoassociated IL-10-/- mice. Conclusion: Two commensal bacteria that individually induce phenotypically distinct colitis in gnotobiotic IL-10-/- mice act additively to induce aggressive pancolitis and duodenal inflammation.