Thesis (M.P.A.)--University of Hong Kong, 2005.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 119-130).

Avian influenza A viruses pose threats to public health and agriculture stability. Historically, each of the four influenza A viruses responsible for pandemics in the last century contained at least one gene segment of avian origin. Migratory waterfowl are natural reservoirs of influenza A viruses and are capable of widespread dissemination. In this study, we aim to characterize the antigenic profiles of H3 and H7 avian influenza A viruses currently circulating in migratory waterfowl within North America. By understanding the antigenic diversity of these subtypes, we can understand the natural history of influenza evolution and develop potential disease preventive strategies.

No description available.

Thesis (M. Med. Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 63-70).

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 116-132).

published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

Because diagnostic tests for highly pathogenic avian influenza (HPAI) viruses require the use of replication-competent viruses in a biosafety level 3 containment, numerous studies have looked at ways to develop alternative tests. Lentiviral particles pseudotyped with H5 hemagglutinin (HA), the surface glycoprotein of influenza virus, have been described as useful and safe tools for research and serological surveillance on the HPAI viruses. However, not all H5 HA give rise to efficient H5 pseudotyped lentiviral particles (H5pp) production. HA from A/Cambodia/408008/05 H5N1 (H5Cam) and HA from A/Anhui/1/05 H5N1 (H5Anh) exhibit a dramatic difference in their ability to pseudotype lentiviral particles. H5Cam gives the highest H5pp production among all HAs tested, whereas the lowest has been observed with H5Anh. The objective of this study was to investigate the molecular determinants that govern efficient H5pp production. Based on the amino acid differences between H5Cam and H5Anh, H5Anh mutants were generated by site-directed mutagenesis. Strikingly, a single amino acid change, A134V, in the 130-loop receptor-binding domain of HA, significantly increased H5pp production with H5Anh. The finding that valine 134 is crucial for H5pp production was confirmed by reciprocal H5Cam and H5Anh mutants, which displayed either a dramatic decrease or increase in H5pp production, respectively. Influenza virus and H5pp bud at the plasma membrane, therefore changes in HA cell surface expression could affect the production of H5pp. Thus, cell surface expressions of H5Cam and H5Anh were compared by flow cytometry. Intriguingly, H5Cam displayed a higher plasma membrane expression than H5Anh, suggesting that transport is important for H5pp production. Introduction of V134A mutation in H5Cam reduced its surface expression to that of H5Anh; by contrast, H5Anh mutant harboring A134V mutation largely restored its expression. Next the effect of A134V mutation on the binding of HA to sialic acid receptors was investigated. A cell-based Enzyme-linked Immunosorbent Assay was developed to measure binding of wild-type and mutated HA. Soluble recombinant proteins were produced by mammalian cells stably transfected with HA gene ectodomain and were mostly trimeric as indicated by discontinuous native gel electrophoresis. Interestingly, H5Anh proteins exhibited a stronger binding to MDCK cells than H5Cam proteins, and introduction of A134V mutation in H5Anh proteins reduced the binding. By contrast, as predicted, the reciprocal V134A mutation induced a major increase in binding to cellular receptors. It is likely that stronger binding of H5Anh to sialic acids could hinder the release of H5pp. Consistent with this notion, the ability of H5Anh to generate H5pp was significantly increased in a sialylation deficient Lec2 cell, a CHO mutant cell line. In conclusion, H5Cam allows efficient H5pp production whereas H5Anh does not. With several lines of evidence, it is likely that the behavior of H5Anh can be explained by a stronger binding to sialic acid receptors that is dependent on a single amino acid residue at position 134. Since A134V is a naturally occurring mutation observed occasionally in human host, these results may have implications for the understanding of human host adaptations of H5N1 viruses. / published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy