[A follow up study of total IgM, IgG, nucleoprotein and spike protein antibodies against severe acute respiratory syndrome (SARS) coronavirus in patients with SARS].

Objective To survey the dynamic changing and persistence of the special antibodies,including total IgM,IgG,nucleocapsid protein and spike protein antibodies,against severe acute respiratory syndrome coronavirus(SARS-CoV)in patients with SARS.Methods 146 cases,all clinically diagnosed as SARS with positive SARS-CoV IgG,were followed up.362 serum samples were collected from the onset of the disease to 660 days afterward.Total IgM and IgG against SARS-CoV were tested with commercial ELISA kits.For recombinant nucleoprotein and spike protein,we developed an ELISA to test these two antibodies.Results Within 20 days of the onset,the positive rate of anti-SARS-CoV IgM was 46.5%(20/43);it reached a peak after 21-40 days(80.6%,25/31).Then,the positive rate of IgM went down gradually to 8.2%(6/73)until 550 days after the onset.The patient's IgG positive rate was lower(34.9%,15/43)than that of IgM within 20 days of the onset.Then it went up rapidly to 100%.It remained positive(98.6%,70/71)until 600-660 days after the onset.When N-IgG and S-IgG were tested 40 days after the onset of the disease at three different times,the positive rate of N-IgG(92.5%,37/40)was higher than that of S-IgG(67.5%,27/40),but the two structure protein antibodies were always lower than the total IgG.Conclusions In SARS patients with definite clinical and etiological diagnosis,the highest positive rate of the antibodies against SARS-CoV was found at 21-40 days after the onset.IgM disappeared almost 500 days(91.8%)after the onset.Total IgG positive rate could reach 100% and 98.6% and the positivity might persist nearly two years.So it is speculated that the total IgG antibody may be positive 3 to 5 years after infection,but it seems that N-IgG and S-IgG keep positive shorter in time than total IgG antibody.