The work presented in this thesis has provided new insights into the mechanisms involved in the regulation of innate immune responses in zebrafish embryos. Furthermore, cell-specific transcriptome... Show moreThe work presented in this thesis has provided new insights into the mechanisms involved in the regulation of innate immune responses in zebrafish embryos. Furthermore, cell-specific transcriptome profiling studies identified novel marker genes for distinguishing immune cell types, which is highly useful information to fulfill the demand for new fluorescent reporter lines and lineage-specific antibodies in the zebrafish model. We have shown that Ptpn6, a protein tyrosine phosphatase homolog of human SHP1, functions as a critical negative regulator, required for a properly balanced innate immune response and for controlling infections with bacterial pathogens. In Salmonella typhimurium infection, ptpn6 deficiency caused a general hyperinduction of pro-inflammatory genes, which was contraproductive as it impaired the infection control. In Mycobacterium marinum infection, a more specific effect of ptpn6 deficiency on matrix metalloproteinase gene expression was found as a major underlying cause of increased bacterial burden. We further concluded that Ptpn6 functions as a much stronger negative regulator than infection-inducible miRNAs of the miR-146 family, which may be involved in more subtle fine-tuning of the innate immune response. Knowledge about the distinct roles of Ptpn6 and miR-146 miRNAs has practical applicability in regard to their potential as therapeutic targets for inflammatory diseases and cancer. Show less
In the last decade the study of the innate immune system has gained renewed scientific momentum as a result of the discovery of essential receptor families, such as the Toll-like receptor (TLR)... Show moreIn the last decade the study of the innate immune system has gained renewed scientific momentum as a result of the discovery of essential receptor families, such as the Toll-like receptor (TLR) family, that are required for pathogen recognition. These receptors detect specific molecular structures of microorganisms and in turn are able to trigger host immune responses. The work described in this thesis focuses on the use of the zebrafish embryo as a model to study the vertebrate immune system in order to gain new insights into the mechanisms of innate immune defence against bacterial infections and TLR signalling. Making use of a Salmonella infection model in combination with microarray technology and gene knock-down studies we were able to thoroughly characterize the embryonic host transcriptome response to a bacterial infection. Furthermore, we have demonstrated important functions for key signalling molecules in the innate immune response, including Tlr5, MyD88 and Traf6 and discovered new downstream targets of the TLR signalling pathway. The data presented here will enable in-depth functional follow-up studies that will provide new insights into the mechanisms of innate immune defence systems. This, in combination with future applications of zebrafish embryo infection models in high-throughput compound screens, holds much promise for the discovery of novel anti-microbial and anti-inflammatory drugs. Show less
