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Title: Neutral evolution of antigenic variation and variant-specific epitopes in GII-4 norovirus variants selected through immunological pressure
Author: Allen, David James
ISNI:       0000 0004 2702 5689
Awarding Body: London School of Hygiene and Tropical Medicine (University of London)
Current Institution: London School of Hygiene and Tropical Medicine (University of London)
Date of Award: 2009
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The caliciviruses are a family of small single-stranded RNA viruses that infect humans and animals, and comprise four genera: lagovirus, vesivirus, sapovirus and norovirus. Human noroviruses are a genetically diverse group of pathogens that cause gastroenteritis in persons of all ages, and the genogroup II-genotype 4 (GII-4) noroviruses are the predominant circulating strain worldwide. GII-4 noroviruses are epidemiologically significant because of their association with epidemics and seasonal outbreaks of gastroenteritis, particularly in semi-closed environments such as cruse ships, hospitals and nursing homes. The work presented in this thesis analyses the diversity of GII-4 norovirus variants, and identifies variant-specific epitopes on the virus capsid. The genetic diversity was analysed among GII-4 norovirus variant strains collected during outbreaks of gastroenteritis in the UK over a 10 year period. It was found that amino acid diversity in the hypervariable region of the capsid protein could be used to model the evolution of these viruses through a neutral network model. This analysis of sequence diversity coupled with protein homology modelling data revealed two putative epitopes on the virus surface. To evaluate the functionality of these sites as epitopes, baculovirus-expressed virus-like particles (VLPs) representing epidemiologically significant variants were constructed and used to generate monoclonal antibodies (mAbs). The VLPs were also systematically mutated at the sites of the putative epitopes to generate antigenically hybrid particles. Using the VLPs and mAbs in immunoassays, it was shown that the identified sites function as a conformational variant-specific surface epitope. These data show that GII-4 norovirus variants evolve through neutral evolution and that variant strains are selected through immunological pressure form the host exerted on surface-exposed variant-specific epitopes.
Supervisor: Iturriza-Gomara, M ; Roy, Polly Sponsor: European Commission & Health Protection Agency
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available