Accuracy of the Fluorescence-Activated Cell Sorting Assay for the Aquaporin-4 Antibody (AQP4-Ab): Comparison with the Commercial AQP4-Ab Assay Kit

Jiwon Yang; Sung Min Kim; Yoo-Jin Kim; So Young Cheon; Boram Kim; Kyeong Cheon Jung; Kyung Seok Park

doi:10.1371/journal.pone.0162900

Accuracy of the Fluorescence-Activated Cell Sorting Assay for the Aquaporin-4 Antibody (AQP4-Ab): Comparison with the Commercial AQP4-Ab Assay Kit

PLoS One. 2016 Sep 22;11(9):e0162900. doi: 10.1371/journal.pone.0162900. eCollection 2016.

Authors

Jiwon Yang¹, Sung Min Kim², Yoo-Jin Kim², So Young Cheon², Boram Kim², Kyeong Cheon Jung³, Kyung Seok Park¹

Affiliations

¹ Department of Neurology, Gachon University, Gil Medical Center, Incheon, Korea.
² Department of Neurology, Seoul National University, College of Medicine, Seoul, Korea.
³ Department of Pathology, Seoul National University, College of Medicine, Seoul, Korea.

Abstract

Background: The aquaporin-4 antibody (AQP4-Ab) is a disease-specific autoantibody to neuromyelitis optica (NMO). We aimed to evaluate the accuracy of the FACS assay in detecting the AQP4-Ab compared with the commercial cell-based assay (C-CBA) kit.

Methods: Human embryonic kidney-293 cells were transfected with human aquaporin-4 (M23) cDNA. The optimal cut off values of FACS assay was tested using 1123 serum samples from patients with clinically definite NMO, those at high risk for NMO, patients with multiple sclerosis, patients with other idiopathic inflammatory demyelinating diseases, and negative controls. The accuracy of FACS assay and C-CBA were compared in consecutive 225 samples that were collected between January 2014 and June 2014.

Results: With a cut-off value of MFIi of 3.5 and MFIr of 2.0, the receiver operating characteristic curve for the FACS assay showed an area under the curve of 0.876. Among 225 consecutive sera, the FACS assay and C-CBA had a sensitivity of 77.3% and 69.7%, respectively, in differentiating the sera of definite NMO patients from sera of controls without IDD or of MS. Both assay had a good specificity of 100% in it. The overall positivity of the C-CBA among FACS-positive sera was 81.5%; moreover, its positivity was low as 50% among FACS-positive sera with relatively low MFIis.

Conclusions: Both the FACS assay and C-CBA are sensitive and highly specific assays in detecting AQP4-Ab. However, in some sera with relatively low antibody titer, FACS-assay can be a more sensitive assay option. In real practice, complementary use of FACS assay and C-CBA will benefit the diagnosis of NMO patients, because the former can be more sensitive among low titer sera and the latter are easier to use therefore can be widely used.

Grants and funding

This work was supported by (1) Grant no. 02-2013-020 from the Seoul National University Bundang Hospital Research Fund (2) Grant no. A121118 from the Korea Health Industry Development Institute Research fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.