Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

published_or_final_version / Microbiology / Master / Master of Philosophy

Vaccination against Marek's disease (MD) is greatly enhanced by host genetic resistance. Genes of the growth hormone (GH) axis have been reported to affect the ontogeny and effector functions of cells of the immune system. Two strains of White Leghorn chickens bred for contrasting homozygous markers in the GH and GH receptor (GHR) genes were challenged with MDV. Contrasts for the significant interaction between marker genotype and tissue indicated that the GH/GHR marker genotype caused a shift in the distribution of the viral load in lymphoid tissues in the two strains. The analysis suggests that genetic variations in genes of the GH axis may differentially affect the host response to MDV replication in lymphoid tissues. Regarding the early time course of infection, at day 6 the viral load was highest in the thymus, while at day 10, it was highest in the spleen, indicating that the virus may have accumulated in the spleen or was continuing to replicate in this tissue. (Abstract shortened by UMI.)

Marek's disease (MD) is a highly contagious and economically important disease in the poultry industry. It is caused by an oncogenic avian herpes virus. The ability of the virus to evolve into new strains is a continual threat. Vaccination, proper management and genetic resistance are required to completely eliminate the pathogen. The discovery of several markers associated with MD resistance shows that genetic selection for resistance is feasible. Our objective was to identify markers in QTL regions that are associated with MD viraemia. The markers analysed were in the ODC gene, the GH gene and two chemokine genes, all of which are candidate genes for immune responsiveness. A database in a commercial strain of White Leghorn chickens was created. Heterozygous males and homozygous females were identified. The offspring were challenged with MD virus and spleen and thymus samples were collected six days after infection. The viral titre was quantified using competitive PCR. The data was analysed using non-parametric statistics. We found that the paternal alleles of a Hindlll RFLP in the ODC gene were associated with differences in MD viraemia in one of the six sire families analysed. In addition, a Sacl RFLP located in the GH gene also segregated for alleles, which affected MD viraemia. The analysis of the ODC gene was extended to include a second RFLP at a Msp\ site. Together with the Hindlll RFLP it defines three different haplotypes. One genotypic class AB (Hindlll (+/-), Mspl (+/+)) was associated with low vireamia in the thymus and the genotype BB (Hindlll (-/-), Mspl (+/+)) with high viraemia in the spleen. The result suggests that genetic variations in the ODC and GH gene affect MD viraemia. However, we cannot exclude that the observed effects might be due to linkage disequilibrium with adjacent genes. In the latter case, chromosome 3 and chromosome 1, which harbour the ODC and GH gene respectively, must segregate for regions that affect viraemia. The markers identified in this analysis can be used in marker assisted selection.

Diapedesis, phagocytosis and microbicidal activity are important parameters of neutrophil functionality and thus outcome of mastitis. An in vitro model of an "alveolar pavement" using the MAC-T3 bovine mammary epithelial cell line was developed to assess neutrophil diapedesis. Features of this biologically-meaningful barrier include: characteristic transepithelial resistance, tight junction complexes and polarity. Continuous transepithelial resistance measurements showed no significant changes throughout the assay period. Neither a Staphylococcus aureus challenge ($1 times10 sp7$ and $2 times10 sp9$ cfu/ml), or the presence of neutrophils, both resting and challenged had any deleterious effects on monolayer integrity over a short term (1-2 h) exposure. Neutrophils, both resting and challenged gave no indication of causing damage to the epithelium over the short term. Neutrophils isolated from proven sires and evaluated for phagocytic activity were found to differ significantly (p $<$ 0.05) in activity, rate and capacity to uptake particles. Correlations between phagocytic parameters and production traits were negative and small in magnitude. Microbicidal activity of neutrophils isolated from proven sires showed a highly significant variation between animals due to test day (p $<$ 0.001), however variation due to source of cells (i.e. animal) was not significant. in vitro analysis of diapedesis and phagocytosis is promising as a tool for the assessment of resistance or susceptibility to mastitis.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1997. / Includes bibliographical references (leaves 82-111).

Thesis (Ph.D.)--University of Western Sydney, Macarthur, Faculty of Business, 1999. / Bibliography: p. 230-312.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 143-164).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1939. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 100-109).