Immunopathology of Inflammatory Bowel Disease

Abstract: Inflammatory bowel disease (IBD) is a chronic inflammatory condition affecting the gastrointestinal tract, with a remitting and relapsing course. There are two main forms of IBD: Crohn’s disease (CD) and ulcerative colitis (UC). The etiology of IBD is not fully understood, however both CD and UC thought to be closely associated with dysregulated innate and adaptive immune responses. The aim of this thesis was to investigate the immunopathology of CD and UC with particular focus on T cell subsets, the cellular and molecular effects of anti-TNFα treatment in CD; and to develop a tool to monitor the disease activity in both CD and UC based on immunological alterations.In the first paper, we described an optimized method for isolating immune cells separately from epithelium and lamina propria of human intestinal biopsies. We identified the distinct T cell compartments of epithelium and lamina propria in the normal gut, and showed that the T cell compartment of the small bowel differed from the colon in healthy gut. Importantly, we demonstrated that intestinal T cell profile changed in patients with CD and UC compared to healthy controls, in which the intestinal T cell compartment of CD and UC patients differed. These data might be used for in- depth IBD phenotyping, potentially defining new subgroups of the two diseases, and for differentiating between aggressive versus mild disease phenotypes. Finally, it could be used for prognosis of responders and non-responders to various therapies.In the second paper we identified a novel, distinct, and functionally active γδ T cell subpopulation in human expressing CD8αβ heterodimer. Only two subsets of γδ T cells have been previously characterized based on the expression of co- receptors. We showed that CD8αβ+ γδ T cells were enriched in the gut particularly in the epithelial layer. Moreover, we showed that the frequency of CD8αβ+ γδ T cells were reduced in the gut of patients with active IBD, correlated negatively with disease activity, and their frequency normalized after IBD therapy, suggesting a protective role for this subset in IBD. By improved subset delineation these results could contribute to the development of immunotherapy strategies.In the third paper, we performed a comprehensive evaluation of the cellular and molecular effects of anti-TNFα treatment in CD patients. Results from the study allow us to propose the following model that both molecular and cellular proinflammatory/harming and anti-inflammatory/repair components are present and upregulated during active inflammation, but tissue-destructive forces overpower the anti-inflammatory and repairing efforts. Interestingly, anti- TNFα treatment downregulated both of these arms, especially with an emphasis on the proinflammatory/tissue- destruction mediators. This allows the anti-inflammatory/healing mechanisms to become fully effective, imparting mucosal healing. Thus, it could be beneficial to administrate selected growth factors and repair mediators for a limited time during the induction phase of anti-TNFα therapy, to further enhance the healing process, which also would help to seal a leaky barrier that allows loss of drug into the lumen and penetration of microbes into the gut tissues.In the forth paper, we developed a new validated and unbiased immunohistological index to assess the disease activity uniformly in both CD and UC, Quantitative Immunohistochemical Computerized Crohn’s and Colitis (QiC3) index. We formulated this objective index based on the number of some immune cells to achieve the best sensitivity and specificity for separating normal and inflamed tissues. Our results showed that the QiC3 index correlated strongly with histopathological scores and gene expression levels of proinflammatory mediators in IBD patients. The QiC3 index works for both ileal and colonic mucosal samples and can be used in clinical management and clinical trials for IBD, in human and animals’ basic researches, and in intestinal infectious diseases.

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