Immunogenicity difference between the SARS coronavirus and the bat SARS-like coronavirus spike (S) proteins

SARS-like coronavirus (SL-CoV) in bats have a similar genomic organization to the human SARS-CoV. Their cognate gene products are highly conserved with the exception of the N-terminal region of the S proteins, which have only 63–64% sequence identity. The N-terminal region of coronavirus S protein is responsible for virus–receptor interaction. In this study, the immunogenicity of the SL-CoV S protein (SSL) was studied and compared with that of SARS-CoV (SSARS). DNA immunization in mice with SSL elicited a high titer of antibodies against HIV-pseudotyped SSL. The sera had low cross-reactivity, but no neutralization activity, for the HIV-pseudotyped SSARS. Studies using wild bat sera revealed that it is highly likely that the immunodominant epitopes overlap with the major neutralizing sites of the SL-CoV S protein. These results demonstrated that SL-CoV and SARS-CoV shared only a limited number of immunogenic epitopes in their S proteins and the major neutralization epitopes are substantially different. This work provides useful information for future development of differential serologic diagnosis and vaccines for coronaviruses with different S protein sequences.