2023-01-032024-07-01https://boris-portal.unibe.ch/handle/20.500.12422/31153Background: Influenza viruses are notorious pathogens that frequently cross the species barrier with often severe consequences for both animal and human health. In 2011, a novel member of the Orthomyxoviridae family, Influenza D virus (IDV), was identified in the respiratory tract of pigs with influenza-like symptoms and subsequently also in cattle, a species that previously never was considered to be susceptible to influenza virus infection. Epidemiological surveys among livestock demonstrated that Influenza D virus is worldwide distributed among cattle, swine, goat and sheep, but the most striking is the detection of influenza D virus directed antibodies among humans with occupational exposure to livestock. Influenza D virus is phylogenetic closely related to the human influenza C virus that utilize the same cellular receptor determinant, however, influenza C virus infections are predominantly restricted to humans, whereas the novel influenza D virus has a promiscuous host tropism. The underlying molecular viral and host determinants affecting the broad host tropism of influenza D virus remain elusive, and considering the zoonotic potential, interspecies transmission and the important veterinary and public health significance of influenza viruses, the molecular characterization of influenza D virus – host interactions is warranted. Working hypothesis and aims: In cattle and swine the respiratory epithelium has shown to be the main entry port of IDV and is an important barrier to infection. Herein the innate immune system has a major protective role as the first line of defence in the barrier function. My hypothesis is that the receptor determinant (9-O-Ac-Neu5Ac) of IDV is distributed in a cell-type specific fashion and that this influences the dynamics of the host innate immune response, and that this may differ among host species. In addition, I hypothesize that the non-structural 1 (NS1) protein of IDV is a potent virulence factor that plays an important role in antagonising the innate immune response and, like other influenza viruses, influences the host range. As a first step toward identifying viral traits involved in the broad host tropism of the newly emerging influenza D virus we will determine the (i) cell and host tropism and (ii) innate immune response at the primary site of replication using in vitro respiratory epithelium models of cattle, swine, and human. Furthermore, we will (iii) molecular characterize the NS1 protein on its role in innate immune response antagonism in those different species. In combination, with the other aims we will perform a (iv) novel complementary genome-wide CRISPR-based screen to identify host determinants impeding influenza D virus replication. Expected significance: The proposed studies will provide detailed knowledge on the host tropism of influenza D virus and innate immune response during viral infections among different species and will reveal whether IDV possess zoonotic potential. Moreover, it provides a comprehensive overview on the innate immune system among livestock and the role of IDV NS1 protein as an important antagonist of this system. This knowledge is indispensable to understand the basic parameters of the successful establishment of IVD among different livestock species and will be highly instructive when assessing the risk of other influenza virus family members in animals and humans.enDewey Decimal Classification::500 - Science::570 - Life sciences; biologyInfluenza virusInnate immunityHost - pathogen interaction