Host-pathogen interactions at the sino-nasal surface of dogs

Abstract

Non-invasive aspergillosis in the sino-nasal area (area of the nose and sinus cavities) of dogs (SNA) is similar to nasal sinus inflammation in humans that can be caused by various types of fungi. Knowledge about SNA is limited and most research focuses on diagnostics, treatment and the local immune response. In this dissertation, I analysed the genomes, gene expression and phenotypes of A. fumigatus isolates from dogs with SNA. In Chapter 2 it is described that each dog with SNA was infected with a single A. fumigatus genotype while multiple genotypes were found in the lungs in human patients. The isolates from the same dog were found to show a large variation in phenotypes such as reduced sporulation and / or pigmentation of the spores. I explain this phenomenon by adapting the fungus during growth in the host. Chapter 3 describes gene expression of A. fumigatus in SNA. Results showed that 6% (514) of the A. fumigatus genes are expressed in a very variable way. This variation may be due to differences in environmental factors in the host, but also due to epigenetic changes and genomic mutations. Genes encoding secondary metabolites, host-pathogen interactions were found to have highly variable gene expression. The results indicate that A. fumigatus adapts in the host. In Chapter 4 the gene expression of the tissue of the dog is described. The analysis confirms earlier observations that both the innate immunity and the Th1 response are involved in the mucosal defense. Most notably, the absence of a Th17 response was evidenced by the absence of IL-17, IL-21 and IL-22 cytokines. The results described in this chapter point to a disruption of the T-cell response which can lead to a chronic fungal infection. Chapter 5 describes the large genetic and phenotypic variability between fungal isolates from the same dogs. Mutations were found in genes related to copper transport, adaptation to pH and oxidative stress. Some of the isolates from dogs had a remarkably high number of single nucleotide polymorphisms (SNPs) that are probably caused by mutations in genes encoding the DNA repair system. The high number of SNPs was not observed in isolates that originate in the indoor environment of houses. This indicates a positive selection for these SNPs, probably during the early stages of infection in the dog. High-impact mutations were mainly found in gene clusters encoding secondary metabolites and in genes involved in oxidative stress, hypoxia and pH response. Stress assays also indicated a high variability of fungal growth, even between isolates from the same biofilm. More research is needed to analyse the relationships between SNPs and growth