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A Complex Environment Involving Constant Interaction

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The GIT is a complex environment involving constant interaction between microbiota (infectious & commensal), mucus layer, epithelial cell layer (made of diverse secretory cells), mucosal immune system (innate & adaptive cells), and lymphatic system (Peyer’s patches). Mucus layer and epithelial barrier prevent the direct interaction of the contents with underlying layers, but regulate/modulate the passage of contents across the intestinal barrier. IBD is characterized by intestinal inflammation of unknown etiology. Various theories have been proposed to identify the immune cells, microbiome and elucidate pathways leading to chronic intestinal inflammation. Three main theories35 were proposed & investigated as underlying causes for IBD inflammation - 1.Reaction to persistent inflammation in intestine, 2.Defective intestinal barrier to luminal antigens and 3.Dysregulated host immune responses to normal GIT contents. The mucosal immune system of GIT has co-evolved with several layers to maintain the fine balance between tolerance and vigilance.36 Mucosal immune system and microbial flora of GIT have co-evolved36 and development of mucosal immune cells is dependent upon the presence of specific microbial species without which differentiation & functioning of immune cells is affected. For example differentiation of Th17 cells is dependent upon presence of single species of segmented filamentous bacteria Candidatus arthromitus.38,39 in mice studies. Animal model studies have also

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