Ballany, Catherine Miriam Dixon

2018-05-14T10:13:53Z

2018-05-14T10:13:53Z

2007

Viral encephalitis is a serious and important human and animal health problem, as exemplified by West Nile encephalitis and HIV-related dementia. There is a need for better understanding of the pathogenesis of virus encephalitis. Experimentally, Semliki Forest virus (SFV) is an excellent mouse model of viral encephalitis and virus-induced demyelination. SFV is an alphavirus of the Togaviridae. In mice it is neuroinvasive and neurotropic. Following infection of susceptible mouse strains, clearance of infectious brain virus is coincident with inflammatory cell infiltration and is followed by demyelination. There is some existing evidence to suggest that CNS demyelination observed following SFV infection has an immune aetiology and based on transient depletion studies that CD8+ T-cells are likely to be the main effectors of this.

This thesis examines the role of acquired immune responses in SFV encephalitis. The role of components of the acquired immune response in mediating clearance of infectious virus and virus RNA and in the pathogenesis of demyelination was examined using mice with genetic deletions affecting components of acquired immune responses. This included mice deficient in CD4⁺ and CD8⁺ T-cell responses and in specific T-cell mediators IFNγ, perforin and Fas. Infectious virus was determined by plaque assay, the presence of virus RNA by quantitative, real-time PCR and the neuropathology by standard histopathology and immunohistochemistry.

Analysis of inflammatory infiltrates in the SFV infected CNS demonstrated a rapid influx of macrophages and NK cells and a >40-fold increase in T-lymphocytes, predominantly CD8+ cells. Mice lacking CD8+ T-cells showed no difference in their ability to clear infectious virus from the brain, but had a slower clearance of virus RNA. Adoptive transfer of CD8+ T-cells to SFV infected SCID mice demonstrated that CD8+ T-cells mediated the demyelinating lesions. Mice lacking CD4⁺ T-cells were unable to generate good antibody responses and were unable to clear infectious virus. Transfer of anti-SFV hyperimmune (HI) serum to SFV infected SCID mice lowered virus RNA to levels comparable to those in immunocompetent (BALB/c) mice. However, antibody alone was not sufficient to eliminate virus RNA and infectious virus reappeared once antibody levels dropped.

IFNγR⁻/⁻ mice were found to have slower clearance of virus RNA compared to wildtype mice but IFNγ was not necessary for the development of demyelinating lesions. A protective role for IFNγ was demonstrated in SFV infection; recombinant IFNγ transiently protected SFV infected IFNa/ßR⁻/⁻ mice. Neither perforin nor Fas was necessary for clearance of infectious virus or viral RNA. SFV infected Fas knock-out mice had increased CNS demyelination.

In summary this thesis demonstrates that in SFV infection, CD8⁺ T-cells are the main component of the CNS inflammatory response; CD8⁺ T-cells mediate the lesions of demyelination; clearance of infectious virus is mediated by antibody but antibody alone is insufficient to clear all virus RNA; CD8⁺ T-cells and the IFN-γ system contribute to the elimination of virus RNA. It is likely that both antibody and CD8⁺ T-cells are required to eliminate SFV infection.

http://hdl.handle.net/1842/29837

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 18

Already catalogued

Role of the acquired immune response in virus clearance and neuropathology in Semliki Forest virus infection

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy