The adaptation of avian influenza viruses to the respiratory epithelium of pigs

Background Pigs are an important host for influenza A viruses and may play a crucial role in the interspecies transmission. To analyze the infection by influenza viruses, we have established precision-cut lung slices from the porcine lung as a culture system for differentiated respiratory epithelial cells. As differentiated repiratory epithelial cells are the primary target cells for influenza virus infections, precision-cut lung slices provide an interesting system to analyze the adaptation of avian influenza viruses to the respiratory epithelium of pigs. Avian influenza viruses H9N2 subtype have been circulating worldwide in multiple avian species and have repeatedly infected mammalian to cause typical disease. The continued avian-to-mammalian interspecies transmission of H9N2 viruses raises concerns about the possibility of viral adaption with increased virulence for humans and poses a potential health risk to the public. Methods Avian influenza viruses H9N2 subtype were subjected to several passages in precision-cut lung slices. Then the changes in the viral properties that are associated with the adaptation process were characterized by analyzing: (1) duration of the growth cycle; (2) amount of infectious virus released into the supernatant; (3) extent of the ciliostatic effect. Sequence analysis will reveal which amino acid changes occur during the different virus passages Results Adaptation of the avian viruses to growth in porcine cells was evident in a shortening of the growth cycle. Sequence analysis revealed that few amino acid changes occurred during the different virus passages. The importance of the individual mutations is currently analyzed by generating recombinant viruses that contain the respective mutated proteins. Conclusions Our study will help to understand the processes involved in the adaptation of H9N2 influenza viruses to new hosts.