Prior swine influenza virus infection of differentiated airway epithelial cells enhances secondary infection by avian influenza virus and facilitates the generation of reassortant viruses

• Applicant: Dr. Nai-Huei Wu
• Subject Area: Veterinary Medical Science
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 394776438

Pigs play an important role in the epidemiology of influenza A viruses (IAV), especially in the generation of pandemic viruses that spread all over the world and are associated with increased morbidity and mortality. Such viruses are usually reassortants containing gene segments from swine, avian, and/or human IAV. The respective reassortment events require the co-infection of airway cells by viruses from different species. Pigs are considered the most likely host for generating reassortant viruses that are able to infect human airway cells. Because of this role in the interspecies transmission of avian IAV to humans, pigs have been designated as "mixing vessel". Previously, porcine cells have been thought to contain binding sites for both swine/human IAV (alpha2,6-linked sialic acids) and avian IAV (alpha2,3-linked sialic acids) and therefore to be more suited than human cells for co-infection by avian and human/swine viruses. However, the sialic acid distributions in the human and swine airways have been shown to be very similar. We hypothesize, that swine airway cells recovering from a swine IAV infection are most promising candidate cells for co-infection by IAV. During the regeneration phase, when basal cells are differentiating into specialized cells, these cells lack for some time cilia and therefore are impaired in their mucociliary clearance function. Furthermore, the sialic acid expression is intermediate between that of basal cells (alpha2,3-linkeage type) and well-differentiated epithelial cells (alpha2,6-linkage type), i.e, they contain both linkage types.To confirm this hypothesis, I will apply air-liquid interface cultures to compare the mono-infection of well-differentiated swine airway epithelial cells by swine (sw) and avian IAV. In a second step, respiratory epithelial cells recovering from a swIAV infection will be characterized, with a special focus on the sialic acids. In addition to lectin staining, binding assays with different IAV will be performed to find out whether cells in the regeneration phase differ from well-differentiated cells with respect to binding sites for human, swine and avian IAV. In the third section, co-infection of swine airway cells by swine and avian IAV will be analyzed. We will compare two co-infection scenarios: (i) the swine and the avian virus partners are added at the same time to well-differentiated airway epithelial cells; (ii) co-infection by avian IAV occurs with airway cells recocvering from a swIAV infection. In the final part of the project, I will determine the reassortment rates of the two co-infection scenarios. Furthermore, selected reassortant viruses will be analyzed for their ability to infect human differentiated airway epithelial cells. The results of this project will provide new insights into the co-infection of airway epithelial cells by avian and swine/human viruses and thus provide a better understanding of the generation of pandemic influenza viruses.

• DFG Programme: Research Grants