Dissertation

Characterization of the Host Response to Salmonella Typhimurium in AcB61 and AcB60 Recombinant Congenic Mice: The Genetic Foundations of Susceptibility and Resistance to Infection

Beatty, Sean Christopher

2016

Overview

Salmonella species are globally relevant human pathogens that present a significant challenge to human health in low and middle-income nations, and an economic challenge in high-income nations. Where Salmonella infection is a significant source of mortality and morbidity, risk is primarily associated with inadequate water and sanitation infrastructure, or compromised immunity. The outcome of infection is the product of complex interactions between factors that are both environmental and genetic. A panel of recombinant congenic strains (RCS) derived from the reciprocal double backcross of the Salmonella resistant A/J inbred mouse strain, and susceptible C57BL/6J strain has revealed a number of congenic strains demonstrating survival phenotypes of unknown aetiology. In the case of the highly susceptible AcB61 strain two susceptibility loci, Ity4 (Immunity to Typhimurium locus 4) and Ity5 have been identified. While the Ity4 susceptibility trait has been previously demonstrated to be the product of a de novo mutation in the AcB61 Pklr variant, the genetic origin of the Ity5 survival phenotype remained unstudied. In the thesis that follows we report on the further characterization of AcB61, including the tissue iron loading, dysregulated iron homeostasis, and chronic erythrophagocytosis that predispose the strain to infection. Observations of AcB61 transcription and protein expression, as well as microscopy and experiments using knock-out mice, reveal the pathogenic downregulaton of AcB61 FPN during infection, novel in its hepcidin independence. We also report the validation of the other susceptibility locus of AcB61 Ity5, in a genetic environment free of the impact of Ity4, using a cross between A/J and 129S6. Using a time-series analysis of genome-wide transcription during infection, comparing A/J mice to AcB60 control mice having a C57BL/6J derived Ity5 interval, we have identified the differential expression of the Ity5 positional candidate gene Cd40, Cd40 associated canonical signaling pathways, and the differential expression of numerous genes involved in neutrophil function. Our study of RCS derived from A/J and C57BL/6J has included the study of the AcB60 RCS, the most resistant to infection of all of the studied RCS. Using a combination of linkage analysis, transcriptional profiling, and protein expression we have identified Ity5 to be the likely source of much of the resistance of AcB60 mice to infection. In addition, through the use of a genome-scan between the highly resistant AcB60 strain, and the intermediately resistant strain DBA/2J, we report the identification of Ity8, a QTL associated with the survival phenotype of AcB60xDBA/2J F2 mice. Through the integration of interval mapping, genome-wide transcriptional profiling and canonical pathway analysis we further report the identification of likely protective signaling though the Ccr7 and Mapk11 in AcB60xDBA/2J F2 mice resistant to Salmonella infection. Collectively the work collected herein further demonstrates the utility of mice as models of human infection, and of Salmonella as a model pathogen. Observations of AcB61 provide novel insight into iron homeostasis and hepcidin independent regulation of FPN while the study of AcB60 and AcB64 has provided new insight into the immune response of the seminally important A/J and C56BL/6J inbred strains, popular and enduringly relevant tools for medical research.

• Publisher: ProQuest Dissertations & Theses
• Subject: Acids / Binding sites / Bioinformatics / Biology / Bone marrow / Chemokines / Dendritic cells / Gene expression / Genetics / Immunology / Infections / Microbiology / Neutrophils / Salmonella / Survival analysis / Tumor necrosis factor-TNF / Typhoid
• ISBN: 9798582598466