Longitudinal profile of antibodies against SARS‐coronavirus in SARS patients and their clinical significance

MO, Hongying; ZENG, Guangqiao; REN, Xiaolan; LI, Hui; KE, Changwen; TAN, Yaxia; CAI, Chaoda; LAI, Kefang; CHEN, Rongchang; CHAN‐YEUNG, Moira; ZHONG, Nanshan

Background: Severe acute respiratory syndrome (SARS) is a newly discovered disease caused by a novel coronavirus. The present study studied the longitudinal profile of antibodies against SARS‐coronavirus (SARS‐CoV) in SARS patients and evaluated the clinical significance of these antibodies. Methods: Two methods, ELISA and indirect immunofluorescent assay, were used for the detection of the anti‐SARS‐CoV IgG and IgM in 335 serial sera from 98 SARS patients. In 18 patients, serum antibody profiles were investigated and antibody neutralization tests were performed from 7 to 720 days after the onset of symptoms. Results: The ratios of positive IgG/IgM by ELISA were 0/0, 45.4/39.4, 88.6/71.4, 96/88, 100/48.6, 100/30.9, 100/17.1, 100/0 per cent, respectively, on 1–7, 8–14, 15–21, 22–28, 29–60, 61–90, 91–180 and 181–720 days after the onset of symptoms. Antibodies were not detected within the first 7 days of illness, but IgG titre increased dramatically on day 15, reaching a peak on day 60, and remained high until day 180 from when it declined gradually until day 720. IgM was detected on day 15 and rapidly reached a peak, then declined gradually until it was undetectable on day 180. Neutralizing viral antibodies were demonstrated in the convalescence sera from SARS patients. Conclusion: The persistence of detectable IgG antibodies and neutralizing viral antibodies for up to 720 days suggest that SARS patients may be protected from recurrent SARS‐CoV infection for up to 2 years.