Gene expression of cytokines in lung and spleen of chickens vac- cinated with irradiated avian pathogenic Escherichia coli and challenged with the virulent strain

Avian colibacillosis is responsible for significant economic losses in the poultry industry world- wide. Due to the use of antibiotics against the disease, the development of multidrug resistance strains is increasing. Vaccination is a proper tool to avoid such negative effects of these chemo- therapeutics in preventing colibacillosis in poultry. The immune response against the causative pathogen Avian Pathogenic Escherichia coli (APEC) is still not fully understood. Especially, the effect of irradiated APEC on cytokine ex- pression has not been investigated at all. In this thesis, the expression of six cytokines (IL-1ß, IL-6, IL-10, IL-13, IL-17A and IFN-γ) was determined to identify regulatory and adaptive path- ways activated during vaccination and/or challenge with APEC. For this, birds were divided in four groups: negative control, challenged, vaccinated as well as vaccinated and challenged. Following challenge changes in organs and histopathological lesions as well as cytokine ex- pression using RT-qPCR were investigated at 3, 7, 14, and 21 dpc. Histopathology and im- munohistochemistry for the specific detection of bacterial infiltration in lung, spleen, heart and liver confirmed inflammation and bacterial spread. Significant changes in gene expression of the cytokines IL-1ß, IL-6, IL-10, IL-17A were observed in challenged and/or vaccinated and challenged pullets. Furthermore, the results showed significant upregulation of the cytokines IL-1ß (lung and spleen) and IL-6 (lung) in only vaccinated birds which shows a pro-inflamma- tory immune stimulatory effect of irradiated APEC. In conclusion, vaccination reduced macroscopical as well as histopathological lesions com- pared to only challenged birds which is an indicator of the effectiveness for the limitation of bacteria in vaccinated birds. The lung was identified as the primary effected organ and the first barrier to systemic migration for APEC. It could be confirmed, that vaccination with irradiated APEC via aerosol stimulates the immune system in lung and spleen, mostly obvious by the expression of pro-inflammatory cytokines