N-linked glycosylation at site 158 of the HA protein of H5N6 highly pathogenic avian influenza virus is important for viral biological properties and host immune responses

Since 2014, clade 2.3.4.4 has become the dominant epidemic branch of the Asian lineage H5 subtype highly pathogenic avian influenza virus (HPAIV) in southern and eastern China, while the H5N6 subtype is the most prevalent. We have shown earlier that lack of glycosylation at position 158 of the hemagglutinin (HA) glycoprotein due to the T160A mutation is a key determinant of the dual receptor binding property of clade 2.3.4.4 H5NX subtypes. Our present study aims to explore other effects of this site among H5N6 viruses. Here we report that N-linked glycosylation at site 158 facilitated the assembly of virus-like particles and enhanced virus replication in A549, MDCK, and chicken embryonic fibroblast (CEF) cells. Consistently, the HA-glycosylated H5N6 virus induced higher levels of inflammatory factors and resulted in stronger pathogenicity in mice than the virus without glycosylation at site 158. However, H5N6 viruses without glycosylation at site 158 were more resistant to heat and bound host cells better than the HA-glycosylated viruses. H5N6 virus without glycosylation at this site triggered the host immune response mechanism to antagonize the viral infection, making viral pathogenicity milder and favoring virus spread. These findings highlight the importance of glycosylation at site 158 of HA for the pathogenicity of the H5N6 viruses.