title: Quantitative measurement of anti-aquaporin-4 antibodies by enzyme-linked immunosorbent assay using purified recombinant human aquaporin-4.
abstract: BACKGROUND
  Antibodies to aquaporin-4 (AQP4-Ab), known as NMO-IgG, are a sensitive and specific marker for neuromyelitis optica (NMO).
  
  
  METHODS
  To develop an enzyme-linked immunosorbent assay (ELISA) for AQP4-Ab, we expressed M23 isoform of human AQP4 in a baculovirus system, and used it as an antigen. We measured AQP4-Ab in the sera of 300 individuals: 64 with definite NMO, 31 with high-risk NMO, 105 with multiple sclerosis (MS), 57 with other neurological diseases (ONDs), and 43 healthy controls. We also performed longitudinal measurements of AQP4-Ab in 787 samples collected from 51 patients with definite or high-risk NMO.
  
  
  RESULTS
  AQP4-Abs were positive in 72% with definite NMO, 55% with high-risk NMO, and 4% with MS, but none of the OND patients and the healthy individuals. The longitudinal measurement showed AQP4-Ab levels correlating with disease activity. Out of 38 initially seropositive patients, 21 became seronegative under effective immunosuppressive therapy. During most relapses, the serum AQP4-Ab levels were either high or rising compared with the previous value, although rising AQP4-Ab levels did not always lead to acute exacerbation. Two of the 13 initially seronegative patients converted to seropositive following acute exacerbations.
  
  
  CONCLUSIONS
  We established an AQP4-Ab ELISA, which could be a potential monitoring tool of disease activity.
authors.affiliation: Department of Neurology, Research Institute and Hospital of National Cancer Center, Goyang, Korea.
authors.forename: Woojun
authors.initials: W
authors.lastname: Kim
authors.forename: Ji-Eun
authors.initials: JE
authors.lastname: Lee
authors.forename: Xue Feng
authors.initials: XF
authors.lastname: Li
authors.forename: Su-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Byeong-Gu
authors.initials: BG
authors.lastname: Han
authors.forename: Byung Il
authors.initials: BI
authors.lastname: Lee
authors.forename: Jong Kuk
authors.initials: JK
authors.lastname: Kim
authors.forename: Kyungho
authors.initials: K
authors.lastname: Choi
authors.forename: Ho Jin
authors.initials: HJ
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D051401:Aquaporin 4 / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D003937:Diagnosis, Differential; D018450:Disease Progression; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D009471:Neuromyelitis Optica / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy / Q000276:immunology; D011237:Predictive Value of Tests; D011994:Recombinant Proteins; D012008:Recurrence; D056910:Republic of Korea; D012680:Sensitivity and Specificity; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: C496030:AQP4 protein, human; D051401:Aquaporin 4; D001323:Autoantibodies; D015415:Biomarkers; D007166:Immunosuppressive Agents; D011994:Recombinant Proteins