Mapping of antigenic sites on the nucleocapsid protein of the severe acute respiratory syndrome coronavirus

Antigenic sites on the nucleocapsid (N) protein of severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) were mapped by Pepscan analysis with overlapping peptides that span the N protein sequence. Two major immunodominant epitopes located in the C-terminal region (amino acids [aa] 362 to 412) and middle region (aa 153 to 178) reacted with more than 75% of sera from SARS patients. Several minor immunodominant epitopes were reactive with about 50% of the SARS sera. Antisera from mice immunized with inactivated SARS-CoV recognized the two major immunodominant epitopes and one antigenic site located adjacent to the N-terminal region (aa 76 to 101), which did not react with the sera from SARS patients. Several monoclonal antibodies against SARS-CoV bound to the N- or C-terminal antigenic sites. These results suggest that the above antigenic sites on the N protein are important in eliciting humoral immune response against SARS-CoV in humans and animals and can be used as antigens for developing diagnostic tests.