S2 subunit plays a critical role in pathogenesis of TW-like avian coronavirus infectious bronchitis virus.

To investigate the critical role of the S gene in determining pathogenesis of TW-like avian infectious bronchitis virus (IBV), we generated two recombinant IBVs (rGDaGD-S1 and rGDaGD-S2) by replacing either the S1 or S2 region of GD strain with the corresponding regions from an attenuated vaccine candidate aGD strain. The virulence and pathogenicity of these recombinant viruses was assessed both in vitro and in vivo. Our results indicated the mutations in the S2 region led to decreased virulence, as evidenced by reduced virus replication in embryonated chicken eggs and chicken embryonic kidney cells as well as observed clinical symptoms, gross lesions, microscopic lesions, tracheal ciliary activity, and viral distribution in SPF chickens challenged with recombinant IBVs. These findings highlight that the S2 subunit is a key determinant of TW-like IBV pathogenicity. Our study established a foundation for future investigations into the molecular mechanisms underlying IBV virulence.