title: [Antibody response of patients with severe acute respiratory syndrome (SARS) to nucleocapsid antigen of SARS-associated coronavirus].
abstract: 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.
authors.affiliation: Central Laboratory, Zhujiang Hospital, First Military Medical University, Guangzhou 510282, China. linche@pub.guangzhou.gd.cn
authors.forename: Xiao-yan
authors.initials: XY
authors.lastname: Che
authors.forename: Wei
authors.initials: W
authors.lastname: Hao
authors.forename: Li-wen
authors.initials: LW
authors.lastname: Qiu
authors.forename: Yu-xian
authors.initials: YX
authors.lastname: Pan
authors.forename: Zhi-yong
authors.initials: ZY
authors.lastname: Liao
authors.forename: Hua
authors.initials: H
authors.lastname: Xu
authors.forename: Jin-jun
authors.initials: JJ
authors.lastname: Chen
authors.forename: Jin-lin
authors.initials: JL
authors.lastname: Hou
authors.forename: Patrick C Y
authors.initials: PC
authors.lastname: Woo
authors.forename: Susanna K P
authors.initials: SK
authors.lastname: Lau
authors.forename: Yung Yuen
authors.initials: YY
authors.lastname: Kwok
authors.forename: Zhen
authors.initials: Z
authors.lastname: Huang
mesh_terms: 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*
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D019590:Nucleocapsid Proteins