IFA in testing specific antibody of SARS coronavirus

Objective To develop testing method for SARS coronavirus (SARS CoV) through IFA. Methods SARS CoVs were isolated from the Vero E6 cells inoculated with throat washings from 44 SARS patients. Antigen slides were prepared from infected cells in order to react with fluorescence labeled goat anti human IgM and IgG antibodies for further observation through fluorescence microscope. The procedure was controlled with 97 serum samples collected from healthy people. Results 31 of 44 patients were IgG positive through this approach, with coincident rate of 70.45% with clinical diagnosis. 38.70% of the IgG positives could be test positively of IgM in the acute phase, with the highest title of 1:80 presented during the 12-15 days of the course of the disease. The earliest time when the IgM could be detected was at 3 days after the onset and IgG in the convalescent sera could be firstly detected on 8 days of the course, with the highest title of 1:320-1:640 presented during 15-20 days of the course. However, the IgM was negative in all of the 97 control samples with only 3 IgG positive. Conclusion Specific IgM and IgG antibodies could be generated in the bodies after SARS CoV infection. The high coincident rate with clinic diagnosis showed the method can be applied in serologic test of SARS CoV infection to assist the clinic diagnosis.