Inflammatory bowel disease (including Crohn’s disease and ulcerative colitis) and coeliac disease are debilitating gastrointestinal diseases that seriously affect the quality of life of those affected. Under normal circumstances, the intestinal immune system is maintained in a state of controlled inflammation, whereby balance exists between protective immunity, mediated by effector cells, and tolerance mediated by cells with regulatory function. However, an aberrant immune response is believed to contribute to the intestinal inflammation present in individuals afflicted by these diseases. This thesis investigated the involvement of CD4⁺ CD25[superscript]high Foxp3⁺ Regulatory T cells (Treg) and Th17 Effector cells in both inflammatory bowel disease (IBD) and coeliac disease. The reciprocal relationship between Treg and Th17 cells under certain cytokine conditions, has prompted the exploration of these two cell types in IBD and coeliac disease. Previous studies have examined these factors individually in a range of diseases, however, to our knowledge the study of both Treg and Th17 in IBD and coeliac disease subjects represents a novel area of research. Crohn’s disease (CD), ulcerative colitis (UC) and coeliac disease subjects were recruited through the Department of Gastroenterology and Hepatology at The Queen Elizabeth Hospital (QEH) in Adelaide, South Australia. In total, one-hundred and seventeen subjects were enlisted in this study to donate blood samples. In addtion, intestinal biopsy samples were collected from fifty-six subjects undergoing colonoscopy at the QEH Department of Gastroenterology and Hepatology. All subjects participated, with informed consent and ethics approval. Treg and Th17 cell numbers were investigated in the peripheral blood of Crohn’s disease, ulcerative colitis, coeliac disease and control subjects using multi-colour, intracellular flow cytometry. A decrease in Treg cell numbers and an increase in Th17 cell numbers was observed in IBD, but not in coeliac disease. Closer investigation into the ratio of Treg and Th17 cells within patients identified a near 1:1 Treg/Th17 ratio in control subjects, but a lower Treg/Th17 ratio in IBD patients. This suggested a disturbance in regulatory and effector cell equilibrium. Furthermore, the excess of Th17 cells and deficiency of Tregs could contribute to the pathologies observed in IBD. The discovery of an imbalance in Treg and Th17 cell numbers in IBD prompted further investigation of these cells in intestinal biopsies collected from IBD, coeliac and control subjects. Real time RT-PCR of intestinal biopsy samples demonstrated increased expression of the Th17 cytokine, IL-17a, in both IBD and coeliac disease. Elevated levels of the Treg transcription factor Foxp3 were also identified in intestinal biopsies from IBD subjects. It was therefore hypothesised that Treg cells may have been actively recruited from the periphery in an attempt to control inflammation in the gut; however, the intestinal cytokine microenvironment may have restricted the regulatory function of these cells. Cytokines known to promote human Th17 differentiation, namely IL-1β, IL-6, TGF-β, IL-21 and IL-23, were explored in intestinal biopsy samples from IBD, coeliac and control subjects. High levels of IL-1β and IL-6 were detected in IBD patient samples, however, no change in levels of IL-21 or IL-23 were observed in IBD or coeliac disease subjects. Elevated levels of TGF-β were only identified in UC. No changes in cytokine expression were observed between control and coeliac subjects, except a significant decrease in IL-6 levels was identified in coeliac disease sufferers. The pro-inflammatory microenvironment identified in intestinal biopsies from IBD subjects may have promoted the continual differentiation and development of Th17 cells, whilst restricting Treg activity. Moreover, the observed deficiency of Treg in IBD patients may have impaired the ability of the immune system to limit excessive pathogenic Th17 driven immune responses in the intestinal mucosa. Therefore, therapeutic approaches that aim to re-establish regulatory and effector cell homeostasis by increasing Treg numbers in IBD patients, and specifically targeting Th17 cells, may prove effective in the treatment of IBD. Approaches such as these could provide greater focus to treatment strategies for IBD management compared to current broad-spectrum immunosuppressive therapies that could increase susceptibility to cancer or infection in IBD patients. In addition, the imbalance of regulatory and effector cells demonstrated in the peripheral blood of IBD patients may potentially provide new options for a noninvasive diagnostic tool. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1457580 / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2009
| Identifer | oai:union.ndltd.org:ADTP/288237 |
| Date | January 2009 |
| Creators | Eastaff-Leung, Nicola |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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