Testing for antibodies to human aquaporin-4 by ELISA: sensitivity, specificity, and direct comparison with immunohistochemistry.
BACKGROUND
Several assays have been developed to detect antibodies to aquaporin-4 (NMO-IgG/AQP4-Ab). However, many of these assays require sophisticated techniques and are thus only available at specialized laboratories. This is problematic since NMO-IgG/AQP4-Ab testing has important prognostic and therapeutic implications.


OBJECTIVE
To evaluate a newly developed, commercial, enzyme-linked immunosorbent assay (ELISA) for detecting NMO-IgG/AQP4-Ab.


METHODS
Serum samples from 261 patients with NMO spectrum disorders (NMOSD; n=108) and controls (n=153) were tested for AQP4-Ab by using ELISA. Of these patients, 207 were tested in parallel using a standard immunohistochemical (IHC) assay.


RESULTS
Fifty of 66 (75.8%) patients with NMO, 17/25 (68%) with LETM, 3/14 (21.4%) with ON, 2/3 (66.7%) with ON and non-extensive transverse myelitis, and 2/153 (1.3%) controls tested positive in the ELISA. Of those NMOSD patients tested by both ELISA and IHC, 10 were positive only in the ELISA and 3 exclusively in the IHC assay, suggesting that the overall sensitivity of the ELISA was higher than that of the standard IHC assay. The ELISA yielded very good intra- and inter-run reproducibility with regard to AQP4-Ab detection and good intrarun, but only moderate inter-run reproducibility with regard to AQP4-Ab quantification. Anti-AQP4 serum concentrations correlated with disease activity (p<0.00001), but did not differ between patients with NMO and patients with isolated LETM or ON.


CONCLUSIONS
The ELISA evaluated here provides a relatively sensitive and easy-to-use diagnostic tool for detecting antibodies to AQP4 and could make AQP4-Ab testing, which is of high clinical relevance, more widely available.
Division of Molecular Neuroimmunology, Department of Neurology, University of Heidelberg, Heidelberg, Germany.
S
S
Jarius
D
D
Franciotta
F
F
Paul
R
R
Bergamaschi
P S
PS
Rommer
K
K
Ruprecht
M
M
Ringelstein
O
O
Aktas
W
W
Kristoferitsch
B
B
Wildemann
D000293:Adolescent; D000328:Adult; D000368:Aged; D051401:Aquaporin 4 / Q000097:blood; D001323:Autoantibodies / Q000097:blood; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods* / Q000706:statistics & numerical data; D007223:Infant; D008297:Male; D008875:Middle Aged; D009188:Myelitis, Transverse / Q000097:blood / Q000175:diagnosis*; D009471:Neuromyelitis Optica / Q000097:blood / Q000175:diagnosis*; D009902:Optic Neuritis / Q000097:blood / Q000175:diagnosis*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D051401:Aquaporin 4; D001323:Autoantibodies; D015415:Biomarkers