Overcoming the airway epithelium barrier in the early phase of bovine viral diarrhea virus (BVDV) infection

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Bovine Viral Diarrhea/ Mucosal Disease (BVD/ MD) is an economically important notifiable disease of cattle. The causative agent, BVD virus (BVDV), is a plus strand RNA virus of the family Flaviviridae, genus Pestivirus. BVDV is known to enter oronasally and through the respiratory tract, from where it spreads to various organs and tissues. The initial stage of infection is poorly understood. In the context of preliminary work for the proposed research project it was shown that non-differentiated polarized respiratory epithelial cells are highly susceptible to apical and basolateral infection with BVDV, but virus release occurs only via the apical side of the cells. Thus, it remains unknown how pestiviruses cross the barrier of the airway epithelium. However, it is well established that BVDV and other pestiviruses have a strong tropism for immune cells. Therefore, an important goal of this project is to explore the pathway by which BVDV crosses the barrier of the respiratory epithelium and spreads from there to immune cells.In the first part of the project, the infection of airway epithelial cells (tracheal/bronchial epithelial cells) will be investigated. Two cell culture systems established at the Institute of Virology are available for the analysis of end-differentiated cells: Air-liquid-interface (ALI) cultures and precision lung slices (PCLS). Subsequently, cells that have not yet completed differentiation or cells that are in the regeneration phase after epithelial injury will be examined. Finally, we will analyze whether BVDV can overcome the epithelial barrier in a paracellular manner by exploiting leaky junctions between cells. To find out whether the different infection characteristics in the different culture systems and under the various infection conditions depending on the degree of differentiation can be correlated or explained with the presence of the cellular receptor, the expression of the receptor for BVDV, CD46, will be analyzed. For the detection of CD46 a monoclonal antibody is available, which was produced at the Institute of Virology. Another focus will be studies on the infection of macrophages. First, the infection of macrophage monocultures will be investigated. Subsequently, co-cultures of macrophages and airway epithelial cells will be established to find out whether macrophage infection can be used to overcome the epithelial barrier. Other interesting perspectives for future projects include the role of cellular innate immunity for respiratory epithelial infection with BVDV, and viral-viral or viral-bacterial co-infections.