Mycobacterium marinum infection in zebrafish has become a well-established model of tuberculosis. Both embryonic and adult zebrafish infection studies have contributed to our knowledge of the... Show moreMycobacterium marinum infection in zebrafish has become a well-established model of tuberculosis. Both embryonic and adult zebrafish infection studies have contributed to our knowledge of the development and function of tuberculous granulomas, which are typical of mycobacterial pathogenesis. In this review we discuss how transcriptome profiling studies have helped to characterize this infection process. We illustrate this using new RNA sequencing (RNA-Seq) data that reveals three main phases in the host response to M. marinum during the early stages of granuloma development in zebrafish embryos and larvae. The early phase shows induction of complement and transcription factors, followed by a relatively minor induction of pro-inflammatory cytokines within hours following phagocytosis of M. marinum. A minimal response is observed in the mid-phase, between 6 hours and 1day post infection, when the tissue dissemination of M. marinum begins. During subsequent larval development the granulomas expand and a late-phase response is apparent, which is characterized by progressively increasing induction of complement, transcription factors, pro-inflammatory cytokines, matrix metalloproteinases, and other defense and inflammation-related gene groups. This late-phase response shares common components with the strong and acute host transcriptome response that has previously been reported for Salmonella typhimurium infection in zebrafish embryos. In contrast, the early/mid-phase response to M. marinum infection, characterized by suppressed pro-inflammatory signaling, is strikingly different from the acute response to S. typhimurium infection. Furthermore, M. marinum infection shows a collective and strongly fluctuating regulation of lipoproteins, while S. typhimurium infection has pronounced effects on amino acid metabolism and glycolysis. Show less
This thesis is focused on the innate immune defence mechanisms responsible for controlling mycobacterial growth after infection. To provide a detailed description of the host__s innate immune... Show moreThis thesis is focused on the innate immune defence mechanisms responsible for controlling mycobacterial growth after infection. To provide a detailed description of the host__s innate immune response to M. marinum infection, zebrafish gene expression levels were analysed by RNA sequencing at various time points during infection and correlated with imaging data of the process of pathogenesis. We demonstrate that the scavenger receptor Marco (macrophage receptor with collagenous structure) is a key player in the rapid phagocytosis of M. marinum and we use gene expression analysis in combination with gene knockdown studies to show that it is also essential in the establishment of an initial transient pro-inflammatory response to M. marinum infection. Once phagocytosed, M. marinum is capable of avoiding killing mechanisms of the host cell and can continue to grow within macrophages. This is the period when Membrane Attack Complex/Perforin proteins are involved in killing intracellular bacteria by their pore-forming activities. We reveal the regulatory mechanisms and function of two macrophage specific genes, mpeg1 and mpeg1.2 (macrophage expressed gene 1.2). The results from this thesis complement knowledge obtained from other model organisms by providing new insights into both counteracting and supporting mechanisms underlying the innate immune response. Show less
The major cell types of the innate immune system, macrophages and neutrophils, develop during the first two days of zebrafish embryogenesis. The interaction of these immune cells with pathogenic... Show moreThe major cell types of the innate immune system, macrophages and neutrophils, develop during the first two days of zebrafish embryogenesis. The interaction of these immune cells with pathogenic microbes can excellently be traced in the optically transparent zebrafish embryos. Various tools and methods have recently been developed for visualizing and isolating the zebrafish embryonic innate immune cells, for establishing infections by different micro-injection techniques, and for analyzing the host innate immune response following microbial recognition. Here we provide practical guidelines for the application of these methodologies and review the current state of the art in zebrafish infectious disease research. Show less
