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076 IL-10 PREVENTS COLITIS DESPITE EPITHELIAL INVASION BY ENTEROBACTER CLOACAE BC Sydora1, A Swidsinski2, M Lupicki1, SM Martin1, T Churchill1, K Madsen1, RN Fedorak1, LA Dieleman1 BACKGROUND: Intestinal microflora is essential for the development of colitis in Interleukin-10 gene-deficient (IL-10 KO) mice. Monoassociation of germ free IL-10 KO mice has revealed that some bacteria, such as Escherichia coli and Enterobacter faecalis, are able to induce colitis in these mice, whereas other bacteria such as Bacteroides vulgatus, Streptococcus viridans, or Lactobacillus species have no effect.
1Centre of Excellence for Gastrointestinal Inflammation and Research, University of Alberta, Edmonton, Alberta; 2Division of Gastroenterology, Charité Universitätsmedizin Berlin, Berlin, Germany
PURPOSE: Enterobacter cloacae (E. cloacae) is another commensal bacterium found in the intestinal tract of humans and rodents. To investigate the effect of E. cloacae on the development of chronic intestinal inflammation we fed this organism to germ free IL-10 129 SvEv KO mice and their wild type littermates.
METHODS: Germ free IL-10 KO and wild type 129 SvEv mice were orally gavaged with 5x107 CFU of E. cloacae. Five and 10 weeks post feeding the mice were sacrificed and various parts of the intestine were collected for histology, cytokine release in colonic explant cultures and in situ hybridization (FISH) to study the location of E. cloacae in these tissues. Splenocytes and mesenteric lymph nodes (MLN) were stimulated with sonicates prepared from pure cultures of E. cloacae or various other commensal bacteria as well as fecal lysates derived from germ free, E. cloacae-monoassociated, or SPF littermates to measure proliferative responses and cytokine production.
RESULTS: In wild type mice monoassociated with E. cloacae the highest numbers of bacteria were observed in the proximal colon. E. cloacae entered crypts and goblet cells in high numbers and invaded epithelial cells at the crypt bottom, but did not induce colitis. E. cloacae induced rapid onset in the cecum with a vigorous bacterial-specific Th-1 cytokine response in IL-10 KO mice, but in contrast to wild type mice single bacteria were only sporadically observed in crypts and never in the cecal or colonic epithelium.
CONCLUSIONS: E. cloacae had a profound pro-inflammatory effect on the intestinal and systemic immune system of IL-10 KO mice as determined by a Th-1 cytokine response specific for its disease-inducing organism, resulting in early onset cecal inflammation in these mice. Despite epithelial penetration by E. cloacae IL-10 prevented the development of colitis in wild type mice.