الفهرس 
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Abstract
Avian infectious bronchitis virus (IBV) is the causing agent of a highly contagious disease with a major economic impact on the poultry industry. It is characterized clinically by respiratory, renal and reproductive manifestations. Despite various vaccination protocols, IBV still plays a role in poultry flocks, mostly because of the appearance of new variant strains which are not neutralized by antibodies induced by available vaccines. Viral entry into host cells is mediated by binding of the viral glycoprotein S to a receptor on the cell surface. Alpha 2,3 linked sialic acid has been reported to play an important role as a receptor determinant for IBV . Here, a comparative study of current field strains, 4/91, Italy 02 and QX has been carried out to investigate their dependence of sialic acid for infection in different primary cell culture systems. To reflect the main target organs of an IBV infection in chicken, the following tissue cultures were used in this study: a) primary chicken embryo kidney cells, b) chicken tracheal organ cell cultures (TOCs), c) chicken precision-cut lung slices (PCLS) and d) chicken oviduct explants (COE). Removal of sialic acids from the surface of the target cells by treating the cells with the enzyme neuraminidase affected the infection of all analyzed IBV strains. In primary chicken kidney cells, a plaque reduction test revealed that desialylation reduced the number of plaques with all strains. Infection of TOCs by different IBV isolates results in ciliostasis, which can be observed under a light microscope. In TOCs treated with neuramindase prior to infection, a prolonged ciliary activity was observed. These results indicate that sialic acids play an important role for the infection of all analyzed IBV strains. In addition to the dependence of the IBV strains on sialic acid, the primary target cells in the epithelium of trachea and bronchi were identified. Immunofluorescence analysis of infected TOCs and PCLS revealed that ciliated and goblet cells are sensitive to infection by all strains analyzed. No viral antigen was detected in cells of the parabronchi. Staining of the sensitive cells with the lectin MAAII, to detect alpha 2,3-linked sialic acids, showed that this linkage type of sialic acid is abundantly expressed on the target cells. Interestingly, the amount of sialic acids on the cell surface detectable by MAAII was reduced after infection by the different IBV strains in the trachea and also in the bronchi. First infection experiments in chicken oviduct explants show, that these tissue cultures can be infected by IBV and a lectin staining revealed, that alpha2,3-linked sialic acids are expressed on the oviduct epithelial cells. Future work will compare the infection by IBV in different parts of the oviduct and will analyze the expression of sialic acids. In this study, we have established two culture systems for well-differentiated epithelial cells, PCLS and COE, which promise to be valuable tools in the future to analyse the infection of the respiratory tract and oviduct by IBV and other avian viruses.