Enzootic Abortion of Ewes (EAE) is an economically important disease of ewes, caused by the gram negative, intracellular bacterium, <i>Chlamydia psittaci</i>. The disease results in lamb loss from abortion and the perinatal death of weak lambs. Vaccines have controlled EAE for more than thirty years, however in the last decade vaccine efficacy has been poor. The primary aim of this project was to examine the cell mediated immune responses to <i>C.psittaci</i> in sheep and to identify potentially immunoprotective antigens for future vaccine studies, by their ability to stimulate both T-cell proliferation and cytokine production. Preliminary studies determined the parameters of an antigen driven, ovine lymphocyte transformation assay for <i>C.psittaci</i>, employing whole chlamydial elementary bodies (EB) as antigen. It was shown that peripheral blood mononuclear cells (PMBC) from post abortion animals would proliferate in response to chlamydial EB, although lymphocytes from naive ewes also proliferated to a lesser degree. Further studies in mice showed this latter response could be caused by a cross reaction with harmless, enteric bacteria. The development of proliferative responses of the PMBC to both EB and mitogens was also measured during gestation. Infection at this time led to the development of lasting T-cell responses and a transient suppression of the response to the T-cell mitogen, Con A. In addition, both mitogen and antigen specific responses were disrupted in the immediate pre-parturition period. These responses returned to control levels soon after lambing. The T-cell proliferative response was further characterised by probing chlamydial EB which had been separated by SDS page electrophoresis and blotted onto nitrocellulose. Individual antigens were then added to cultures of PBMC and T-cell lines generates from post abortion animals. Four antigens were identified with approximate weights of 70, 50, 38 and 30kDa which stimulated proliferation. The ability of individual chlamydial proteins to stimulate cytokine production in these cultures was also tested. The four antigens above also stimulated the production of γ-IFN in the PBMC and T-cell lines from all sheep tested. Finally, the importance of γ-IFN in a chlamydial infection was investigted in an <i>in vivo</i> mouse model, where neutralising γ-IFN with a monoclonal antibody resulted in an increase in the severity of infection in both thymic and athymic mice, when compared with control animals. Increased numbers of viable chlamydiae were isolated from tissues and increased pathological changes and serum interferon levels were demonstrated. The results presented in this thesis provide evidence for the involvement of cell mediated responses in ovine immunity to <i>C.psittaci</i>. Both T-cell proliferation and γ-IFN production can be measured, although how the responses interact with B-cells and antibody has yet to be elucidated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657531 |
| Date | January 1992 |
| Creators | McCafferty, Michael Campbell |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/20002 |
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