Early events in Aspergillus fumigatus infection: A chronicle of host-pathogen interactions

Abstract

Host-pathogen interactions have critical implications for the establishment of disease and for determining adaptive immune responses of the host. This study has conducted global Aspergillus fumigatus transcriptional analyses throughout the initiation of murine infection using a wild-type and an attenuated ΔlaeA isolate. A novel data analysis protocol was applied from which three time-series datasets were generated between 4, 8 and 14 hours post infection. This approach identified distinct temporal gene expression profiles during disease initiation whereby numerous secreted enzymes, including proteases and antigens, were upregulated between 4 and 8 hours, while a striking upregulation of genes in secondary metabolism clusters and subtelomeric loci was observed between 8 and 14 hours. In order to test the role of several upregulated secondary metabolite genes on host-pathogen interactions and virulence, two isolates mutated in non-ribosomal peptide synthetase encoding genes (ΔftmA, Δpes3), and mutants of a hybrid non-ribosomal-polyketide synthase (ΔpsoA) and a putative secondary metabolite transcription factor (ΔregA) were analysed in murine models of infection. These analyses suggest fumitremorgin C, pseurotin A and, putatively, a pigment augment A. fumigatus virulence. In contrast, the pes3 gene product favours pathogen clearance, possibly by facilitating recognition of host innate immunity. There was no evidence to support the view that defective secondary metabolism is causative of the attenuated virulence phenotype observed for the LaeA mutant. Alternative hypotheses regarding the attenuation of ΔlaeA include upregulation and downregulation of Th1 and Th2 associated antigens respectively, and deficiencies in plasma membrane transport relative to wild-type isolates. A hypothesised deficiency in maintenance of genome stability, due to LINE-1 mobilisation in the ΔlaeA isolate was tested, and subsequently discredited by a discovered lack of isogenicity among the tested strains. Work presented in this thesis also assesses the use of a mass-spectrometric method for detection of epitope tagged A. fumigatus protein in the host.