Evaluation of a recombinant nucleocapsid protein-based assay for anti-SARS-CoV IgG detection

A high throughput accurate assay for anti-SARS-CoV IgG detection is needed for large-scale epidemiological studies. The evaluation of a commercial recombinant nucleocapsid protein-based microtitre plate enzyme immunoassay, ELISARS is described. The results on 150 sera from SARS patients and 450 sera from non-SARS controls showed that this assay had a high level of sensitivity (96.2% for late serum samples) and specificity (97.8%). The performance and setup of this assay fulfills the requirement as a screening test for large-scale studies. A vast majority of SARS patients developed antibodies against the nucleocapsid protein. In some patients (10/45), a high level of anti-nucleocapsid antibody appeared very early in the course of the illness. In contrast, a minority (4 of 105 patients) never developed these antibodies. The implication of differences in antibody response to the nucleocapsid protein deserves further investigation.