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The specific objectives of the project are:
1. To define the nature and extent of antigenic diversity in field populations of T. parva
Antigenic diversity will be evaluated by sequencing genes encoding CD8 T cell target antigens in a collection of field isolates of T. parva. These studies will include a comparison of parasites from cattle grazing in the presence or absence of buffalo to determine whether contact with buffalo gives rise to greater antigenic diversity. Genotyping the parasites will allow comparison of genotypes and antigenic types to determine whether there is any selection for antigenic structuring of the populations. The gene sequences will also be subjected to analysis for evidence of selection for amino acid changes. |
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2. To determine the extent of antigenic diversity within the live T. parva vaccine
Similar methods will be used to analyse large sets of clones from the three components of the live vaccine, in order to compare the antigenic diversity within the vaccine to that of the field parasite populations. These data will be used to assess whether there is scope for modifying the content of the vaccine to provide more robust immunity.
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3. To determine how variation in the amino sequences of antigens impacts on CD8 T cell recognition and the capacity of CD8 T cell responses to cross-react with different antigen alleles
Allelic variants of defined epitopes will be analysed to determine whether the amino acid substitutions result in complete or partial loss of recognition by specific CD8 T cells. Further analyses with mutated peptides will allow identification of the residues involved in MHC binding and TCR recognition by the CD8 T cells. This information together with the nucleotide sequence data will be used to determine whether the sites recognised by CD8 T cells are under immune selection pressure. |
4. To understand the basis the broad strain specificity of immunity induced by mixtures of parasite strains
Responses of cattle following immunisation with single clones or mixtures of antigenically different clones of live T. parva parasites, administered simultaneously or sequentially, will be analysed to determine whether the specificity of the responses following exposure to multiple strains represents a summation of responses normally induced by the single strains or is preferentially directed to conserved antigens.
5. To determine whether Friesian cattle expressing the most frequent MHC haplotypes in this breed recognise the currently defined parasite antigens
T. parva-specific CD8 T cell lines from Friesian cattle of different MHC I genotypes will be screened to determine how many of the genotypes recognise one or more of the parasite antigens, as a means of targeting priorities for further antigen screening. |
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