A13 PROTEOLYTIC BACTERIA PROMOTE INNATE IMMUNE ACTIVATION AND GLUTEN-INDUCED PATHOLOGY IN MICE.

Celiac disease (CeD) is an immune-mediated enteropathy triggered by gluten in genetically susceptible individuals expressing the HLA-DQ2 or DQ8 genes. Only 2–4% of genetically susceptible individuals develop CeD, suggesting additional environmental triggers contribute to disease pathogenesis. Duodenal dysbiosis has been described in CeD, but no causative mechanisms been described. We have previously isolated Pseudomonas aeruginosa (Psa), an elastase-producing opportunistic pathogen, from the duodenum of active CeD patients that increases gluten peptide immunogenicity through its gluten metabolism. Here we determined whether microbial-derived elastolytic activity induces innate immune activation, a key step for enteropathy development in CeD. Altered-Schaedler flora (ASF)-colonized C57BL/6 (non-susceptible) and NOD/DQ8 (genetically susceptible) mice were supplemented with Psa prior to gliadin sensitization and challenge. Non-sensitized mice and mice supplemented with a Psa mutant lacking elastase activity (LasB) were used as controls. Small intestinal proteolytic activity, intraepithelial lymphocyte (IEL) counts and villus-to-crypt (V/C) ratios were measured following gluten challenge. ASF-colonized C57BL/6 and NOD/DQ8 mice had low proteolytic activity in small intestinal washes and were protected from gluten-induced pathology following gluten sensitization and challenge. In ASF-colonized mice supplemented with Psa (ASF-Psa), gluten exposure increased small intestinal Psa load, which paralleled increased elastase activity in small intestinal washes. ASF-Psa colonization led to increased small intestinal IELs, independent of gluten exposure, in both the non-susceptible C57BL/6 and the genetically susceptible NOD/DQ8 mice. However, reduction in small intestinal V/C ratios was only observed in ASF-Psa-colonized NOD/DQ8 mice exposed to gluten. No increase in IELs or enteropathy were observed in ASF mice supplemented with the LasB mutant. These results suggest that bacterial-derived elastase from opportunistic pathogens, such as P. aeruginosa, may directly promote IEL proliferation contributing to gluten-induced pathology in genetically susceptible hosts. Microbial-derived elastolytic activity constitutes a mechanism, in addition to its gluten metabolic activity, through which tolerance to this common dietary protein may be broken. It also opens the road to adjuvant therapies to the gluten-free diet based on protease inhibitory therapy. CIHR