Inappropriate responses to normal commensal bacteria trigger immune activation in both inflammatory bowel disease and experimental colitis. How gut flora contribute to the pathogenesis of inflammatory bowel disease is unclear, but may involve entrapment of leukocytes and remodeling of the vascular system. Here we evaluated how the progression and tissue remodeling in experimental colitis differ in a germ- free model of mouse colitis. Four treatment groups were used: control, antibiotic-treated (ABX), dextran sulfate colitis (DSS) and DSS pre- and co-treated with antibiotics (DSS + ABX). In days 0 - 3 of the study, germ-free mice received antibiotics (vancomycin, neomycin, and metronidazole). During the next 11 days, antibiotics were continued and DSS (3%) added to “colitis” groups. Disease activity, weight, stool form and blood were monitored daily. Mice were sacrificed and tissue samples harvested. Histopathological scores in controls (0.00) and in ABX (1.0+/ – 0.81) were significantly (p < 0.001) lower than DSS (12+/ – 0). Extents of injury, inflammation and crypt damage were all improved in DSS + ABX. The Disease Activity Index score (day 11) was significantly worse in the DSS group compared to the DSS + ABX group. Stool blood and form scores were also significantly improved among these groups. Importantly, myeloper- oxidase was significantly reduced in DSS + ABX, indicating that neutrophil infiltration was blocked. Colitis was associated with an increase in blood and lymphatic vessels; both of these events were also significantly reduced by gut sterilization. Our experiment shows that clinical and histopathological severity of colitis was significantly worse in the DSS colitis group compared to the DSS + ABX group, supporting the hypothesis that development of IBD is likely to be less severe with appropriate antibiotic treatment. In particular, gut sterilization effectively reduces leuko- cyte-dependent (PMN) injury to improve outcomes and may be an important target for therapy.
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