Edwards, L.A.; (2008) Crohn's disease: in vitro and ex vivo innate epithelial responses to bacterial stimulation. Doctoral thesis , University of London.

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Abstract

Evidence in the literature suggests that Crohn's disease involves an abnormal, innate immune response to the "commensal microbiota". It is hypothesised that when symbiosis between the residential microbiota and the epithelial cells of the gastrointestinal tract is broken, secretion of potent inflammatory mediators initiates a chronic adaptive immune response, which leads to the pathology seen in Crohn's disease. The aims of the studentship were to a) characterise and compare the innate mucosal signals generated in vitro in response to the presence of "commensal", "probiotic" and "pathogenic bacteria" and b) to establish the typical ex vivo mucosal response in order to ascertain if the immunological responses to bacterial stimuli in Crohn's disease is abnormal. On investigation of a range of bacterial species it was found that bacterial "properties" that influence host responses are not necessarily linked to pathogenicity and bacteria did not segregate into good (commensal / probiotic) and bad (pathogenic) bacteria. Bacterial phenotype was assessed by electron microscopy and both pathogenic and non pathogenic bacteria expressed external structures associated with virulence. Virulence gene deletion mutants of pathogenic bacterial strains were used to determine what bacterial epitopes drove the in vitro responses. Epithelial responses to the whole organism were found to be complex, with a range of responses to soluble and/or external microbial structures. In addition, bacterial supernatants had minimal effect, implying that bacterial contact was an essential part of the process. Evidence was found to suggest that the host recognises the bacterium by combinations of microbial products and may also require co-stimulatory signals to confirm "danger" before responding. The influence of the maturity of the epithelium was studied using Caco-2 cells and immature primary crypt cells (HIEC). Evidence was found to support a hypothesis that the abnormal response in Crohn's disease could originate from the inappropriate stimulus of immature epithelial cells. In vitro organ culture was used to assess the mucosal response to bacterial stimulus ex vivo. Regional and bacterial specific differences were observed in biopsies from Crohn's disease, and evidence was found to support the hypothesis of abnormal innate immune responses to bacterial stimuli.

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