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Title: T cell antigens and immune evasion genes from the parasitic nematode Brugia malayi
Author: Zang, Xingxing
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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The majority of this thesis deals with the identification, gene cloning, protein expression, molecular function and vaccine development of major T cell antigens in B. malayi. Immunization of microfilariae (Mf) proteins with different adjuvants selectively induced antigen-specific Th1 and Th2 responses in vivo. Mf-specific T cells, including Th1 and Th2 cells, were used to identify Mf protein fractions separated by fast protein liquid chromatography and SDS-polyacrylamide gel electrophoresis elution. This revealed a restricted number of major T cell antigens from Mf, a minority of which were insoluble. A novel serine proteinase inhibitor (serpin) gene (Bm-spn-2) was cloned by screening an Mf cDNA library with antisera against one Mf protein fraction which was highly potent at inducing antigen-specific T cell proliferation and cytokine production, while only the paramyosin gene was cloned using antisera against whole Mf proteins. Bm-spn-2, a single copy gene consisting of seven exons, was abundantly (>2% of total mRNA) and exclusively expressed by the Mf stage. This sequence analysis has been broadened into a genome data bank-based review of intron and exon sequences in B. malayi, which revealed an extended and conserved 3' splice site in all recorded B. malayi genes and relatively large introns compared with Caenorhabditis elegans. Bm-spn-2 contains 428 amino acids with a putative signal peptide and native protein was 47.5 kDa, one of the largest of the 93 known serpins. The recombinant Bm-SPN-2 protein was expressed in bacteria and purified to determine biological function. A panel of mammalian serine proteinases, which are involved in a wide range of biological processes, were screened and Bm-SPN-2 protein found to specifically inhibit enzymatic activities of human neutrophil cathepsin G and human neutrophil elastase, but not a range of other serine proteinases. This suggests that Bm-SPN-2 may directly interfere with human immune function. Human neutrophil cathepsin G and elastase mediate multiple host defence functions such as interleukin processing, chemokinetic stimulation for T lymphocytes and chemoattraction for monocytes. We hypothesize that neutrophils, which represent 55% of human blood leukocytes, would be the primary cell type to interact with B. malayi Mf, and that release of Bm-SPN-2 neutralizes the immune-stimulating properties of neutrophil serine proteinases.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available