Peptides with 16R in S2 protein showed broad reactions with sera against different types of infectious bronchitis viruses

Vaccination plays a vital role in controlling diseases caused by chicken infectious bronchitis virus (IBV). The continuously variant antigenicity of IBV limits the application of current vaccine strategies and serological diagnostic systems. S2 protein is an invariant that harbors broad neutralizing epitopes. However, little is known about the key amino acids that contribute to the broad-spectrum S2 epitopes. In this study, we aimed to elucidate the specific amino acids contributing to S2 epitopes. Site mutagenesis and peptide-based enzyme-linked immunosorbent assays (ELISAs) showed that 16R in S2 protein was a key amino acid mediating the antigenicity of S2 protein. S2-derived peptides with 16R, but not those with 16 K, could react with sera against different types of IBVs. Notably, a commercial ELISA kit for detection of antibodies against IBV did not react with sera against all types of IBVs. Taken together, these data demonstrated that S2-derived peptides with 16R could be used as novel marker-based antigens for developing both broad-spectrum vaccines and serological diagnostic kits to control IBV.