Airway epithelial cells are equipped with a mucociliary clearance system to prevent the detrimental effect of microorganisms in the respiratory tract. The defence mechanism is based on mucus producing cells and ciliated cells. The latter cells are responsible for the transport of mucus out of the respiratory tract via ciliary activity.
In order to address the importance of the ciliary activity in preventing infection by microorganisms, porcine precision-cut lung slices were infected with a swine influenza A virus of the H3N2 subtype in the presence or absence of the ciliary activity for 20 min. The amount of virus released under ciliostatic conditions at 24 h or 48 h post-infection was around twofold or threefold higher compared to slices with ciliary activity. The results indicate that the protective function of the cilia beating is not restricted to the transport of mucus, The ciliary activity also impedes the infection by influenza A virus to some extent. Our protocol for analyzing influenza virus infection under ciliostatic conditions is applicable to infections by other viruses and by bacteria.
Pigs are an important host for influenza A viruses, and may play a role in the interspecies transmission. The influenza pandemic of 2009 was caused by a swine-origin H1N1 influenza A virus which was transmitted from a pig to humans. In order to characterize the 2009 pandemic virus and the viruses isolated in the following years, experimental infections in pigs and porcine air-liquid interface culture for differentiated airway epithelial cells were performed. In animal experiments, viruses isolated in 2009/2010 induced a higher dyspnea score, an increased rectal temperature, a higher viral lung load, and more lung lesions in infected pigs compared to viruses of 2014/2015. In the infection of air-liquid interface cultures, the loss of ciliated cells, the reduction of the epithelial thickness and the release of virus into the medium were more pronounced after infection by the viruses of 2009 /2010 than after infection by the 2014/2015 isolates. The effects of the viruses observed in animal experiments were paralleled by the effects of the viruses observed in in vitro infections. There are 20 amino acids changes shared by viruses of 2009/2010, which distinguish them from viruses of 2014/2015. Our results indicate that the virulence of pandemic H1N1 influenza A viruses has decreased from 2009 to 2015, which may be indicative of an
adaptation process.
Porcine precision-cut lung slices and air-liquid interface cultures are useful tools that can be used to analyze the interaction of airway cells and respiratory pathogens, to investigate the virulence as well as the effect of mutations on these properties of influenza A viruses.
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