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Breithaupt, Ute (2011): Genexpressionsanalysen der frühen angeborenen Immunantwort des Haushuhns induziert durch eine Infektion mit Salmonella enteritidis mit Hilfe der Microarray Technologie. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

Salmonella infections in humans arise through chicken-based food such as eggs, egg-products, or chicken meat. The most common cause for these infections is Salmonella enteritidis, and the aim of this study has been to analyze the early innate immune response of chickens induced via this pathogen. Note that S. enteritidis is a host-adapted serovar, which only causes clinical findings in young chickens during their first week of life; adult chickens do not get sick, but may nevertheless act as inapparent infected carriers. We studied the reaction from the chicken immune system on S. enteritidis, using macrophage cultures as well as tissue samples of infected adult chickens. The gene expression studies were carried out by an “Agilent 4x44K chicken microarray” method. In our in vitro studies, we infected primary macrophages with S. enteritidis for 4 hours, using a MOI of 10. The gene expression studies resulted in the inductions of interleukins (IL1β, IL6, IL12p40, IL18), of chemokines (CCL1, CCL4 (K203), CCL20, CXCL8 (IL8), CXCL13), of some members of the tumor-nekrose-factor-superfamily (TNFSF), and of some toll-like receptors (TLR). Hence the cells have an inflammatory reaction. Particularly prominent were the expression changes of K60 (IL8 homolog), K203 (chCCLi2, MIP-1β), CCL20, and TL1a (TNFSF15). Finally, infected macrophages expressed a group of typical Th1-cytokines, including IL12p40, IL18, and IFN-γ. In further analysis of our data, we focused on cytokines, chemokines, and members of the TNF-superfamily. In the ceca we found similar expression patterns within these three groups as was previously found for them in the macrophages study. In our in vivo studies, we infected chickens that were 8 weeks old and already had a well developed immune system. They were infected in the crop using a dose of 107 salmonella. At 5, 12, 24, and 48 hours of infection, we sampled the ceca and cecal tonsils for the bacterial, histological, and gene expression analyses. Already at 5 hours p.i., we were (for all but one animal) able to isolate bacteria from the ceca-tissue. The bacterial load reached its maximum at 12 hours p.i.. The infection of the cecal-tissues was confirmed in the histology, both by the detection of bacteria and by the occurrence of inflammatory cells. However, using histology, we could not detect any bacteria in cecal tonsils, which suggests that no infection was present in these organs. This suggestion was confirmed in gene expression analyses. When comparing the gene expression studies of cecal tonsils and ceca, the former showed lower counts of differential regulated genes (Tab. 11). Both their count maxima occurred at 12 hour p.i though. Moreover, at this time 41 significant regulated pathways had been identified.. In summary, the in vitro and the in vivo experiment both resulted in an initial inflammatory reaction, as well as in a typical Th1-cytokines reaction. To investigate functional characterisation of named candidate genes, in the first instance CCL20, CXCL8, K60, K203, and TL1a, future analyses of the innate immune response should involve them. This may contribute to a better understanding of the successful defense mechanisms against S. enteritidis in chicken, which may help to contain the amount of salmonellosis in humans.