Viral co-infection of differentiated airway cells pre-infected by influenza viruses

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After infection of the airways, in both human and animal specimen, often more than one infectious agent is detected. Secondary infections may result in a more severe course of the disease. The molecular interactions between the pathogens and the host during co-infection are not well characterized. To apply an in vitro model which mimics the in vivo situation as closely as possible, we have established an air-liquid interface culture system for porcine airway epithelial cells and used it to analyze the infection of differentiated respiratory epithelial cells by influenza viruses. Infection resulted in the loss of ciliated cells. The loss was compensated by basal cells that differentiated into specialized cells. These cells maintain the barrier function of the epithelium; however, for a longer time period they do not contain cilia and during this time, they cannot contribute to the mucociliary clearance system. Furhermore, these cells differ from ciliated cells in the expression pattern of surface proteins. Based on these findings we hypothesize that during the regeneration, the foci of infection have an increased susceptibility to infection by secondary pathogens. In the proposed project we will analyse whether airway eptihelial cells infected by influenza viruses show an increased susceptibility to infection by secondary pathogens. With respect to secondary pathogens, we will focus on viruses. In the first stage of the project, we will apply different methods to characterize changes in the expression pattern of surface proteins during regeneration after an infection by influenza viruses. Our special focus will be on a virus receptor, porcine amonopeptidase N (pAPN), the cellular receptor for porcine respiratory coronavirus (PRCoV). In the following chapter, we will analyse how a prior infection by influenza viruses affects the subsequent infection by PRCoV. The second model virus is porcine reproductive and respiratory syndrome virus (PRRSV). This virus uses macrophages as primary target cells. We will determine to what extent the adherence of PRRSV-infected macrophages to the airway epithelium is increased after an infection by influenza viruses; furthermore, we will analyse whether the adhering macrophages are able to transmit the PRRSV infection across the barrier of the airway epithelium. Finally, we will determine whether the results obtained with porcine airway cells are valid also for human respiratory epithelial cells. The results of this project will reveal to what extent prior infection by influenza viruses facilitates infection by secondary viral infection. In this way, we will increase the knowledge about the interactions between pathogens and the host during co-infections.