[Antibody response of patients with severe acute respiratory syndrome (SARS) to nucleocapsid antigen of SARS-associated coronavirus].
OBJECTIVE
To assess serum antibody responses of patients with severe acute respiratory syndrome (SARS) to nucleocapsid (N) antigen of SARS-associated coronavirus.


METHODS
The serum levels of IgM and IgG antibodies to N antigen were measured in 200 healthy blood donors and 13 SARS patients at different time points of acute and convalescent phases using indirect enzyme-linked immunosorbent assay (ELISA) with N fusion proteins of SARS-associated coronaviruses.


RESULTS
The IgM positive critical value of 0.233 and IgG of 0.239 were selected as the threshold value for positive results that equals the product of 2.1 and the mean IgM and IgG levels of 200 healthy blood donors. In 13 patients with SARS, the antibody responses to N antigen were not detectable in the first week after the onset of symptoms. The IgM and IgG seroprotection rates were 83.3% and 66.7% respectively in the second week, both reaching 100% at the third week. IgM seroprotection rates was 61.5% in the second month, and 38.5% at third month. The IgG peaked one month after the onset and remained at high levels in the following 2 months.


CONCLUSIONS
The antibody responses suggest that N protein of SARS is immunodominant and plays an important role in viral pathogenesis. This ELISA-based test for detecting anti- N antigen may be of significant value for SARS diagnosis.
Che
Xiao-yan
XY
Central Laboratory, Zhujiang Hospital, First Military Medical University, Guangzhou 510282, China. linche@pub.guangzhou.gd.cn
Hao
Wei
W
Qiu
Li-wen
LW
Pan
Yu-xian
YX
Liao
Zhi-yong
ZY
Xu
Hua
H
Chen
Jin-jun
JJ
Hou
Jin-lin
JL
Woo
Patrick C Y
PC
Lau
Susanna K P
SK
Kwok
Yung Yuen
YY
Huang
Zhen
Z
D000914:Antibodies, Viral / Q000097:blood*; D000956:Antigens, Viral / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D019590:Nucleocapsid Proteins / Q000276:immunology*; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology*; D012698:Serologic Tests; D045169:Severe Acute Respiratory Syndrome / Q000175:diagnosis / Q000276:immunology*
D000914:Antibodies, Viral; D000956:Antigens, Viral; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D019590:Nucleocapsid Proteins