GoTLR7 but not GoTLR21 mediated antiviral immune responses against low pathogenic H9N2 AIV and Newcastle disease virus infection

- goTLR7 but not goTLR21 could respond to LPAIV H9N2, resulting in differential regulation of IFN-stimulated genes in vivo and in vitro.
- goTLR7 overexpression significantly inhibited NDV infection in DF-1 cells.
- goTLR7 localized in the cytoplasm similar to chTLR7 and mammalian TLR7, and goTLR21 exhibited localization similar to mammalian TLR9.
- The localization of goTLR7 and goTLR21 changed in a time-dependent and cell type-dependent manner.

Aquatic birds are considered the biological and genetic reservoirs of avian influenza virus and play a critical role in the transmission and dissemination of Newcastle Disease Virus (NDV). Both TLR7 and TLR21 are important for the host antiviral immune response. In an in vivo study, goTLR7, not goTLR21, was significantly up-regulated in the lungs of geese at 3 to 7 d after challenge with H9N2. And goOASL expression was induced in the bursa of fabricius, harderian glands and lungs. An increase in goRIG-I was detected in the lung and small intestine, whereas goPKR was increased in the lung but decreased in the thymus. In the in vitro study, goTLR7 and goRIG-I but not goTLR21 were highly induced by H9N2. Moreover, goOASL and goPKR were significantly induced in H9N2-treated PBMCs, whereas goMx was suppressed. The over-expression of goTLR7, not goTLR21, controlled NDV replication in DF-1 cells, resulting in a decrease in viral copies and the viral titres. Furthermore, we explored the cellular localization of goTLR7 and goTLR21 in heterologous (DF-1 and BHK21) and homologous cells (GEF) through ectopic expression of goTLRs. The antiviral functions of goTLR7 and goTLR21 during H9N2 and NDV infection and their cellular locations were reported here for the first time. These results will contribute to better understand the TLR-dependent antiviral immune responses of waterfowl.