Comparison of potentials of structural proteins of SARS--associated coronavirus for serological diagnosis
To identify the sensitive antigens which are suitable for serological diagnostic tests of severe acute respiratory syndrome (SARS),we compared the reactivity of the main structural proteins of SARS-associated coronavirus (SARS-CoV) with the sera from SARS patients. The cDNAs encoding structural proteins M, N, E and 3 truncated forms of S protein (S1, S2 and S3) of SARS-CoV were respectively amplified by RT-PCR using the total RNA extracted from the lung tissue of a dead SARS case and expressed in Escherichia coli (E.coli).By using the recombinant proteins as antigens, the relevant IgG antibodies were detected in 54 serum samples of 11 SARS patients by Western blot. The results showed that the recombinant proteins N, S1, S2 and S3 were strong antigens, but the antigenicity of the three truncated S proteins was different. The positive rate of IgG antibody to S3 protein was the highest, whereras that to S2 was the lowest in the Western blot analysis. The positive rates of IgG antibody against recombinant proteins N and S3 were both 40% in the first week of disease onset, 65.2% and 61% in the second week, 100% and 76.2% in the third week, respectively, and both were 100% after 3 weeks. These results imply that the recombinant proteins N and S3 are the potentially useful antigens in serological diagnosis of SARS.