Clinical usefulness of cell-based indirect immunofuorescence assay for the detection of aquaporin-4 antibodies in neuromyelitis optica spectrum disorder

Background: The presence of antibodies to aquaporin-4 (AQP4) has been identifed as a key characteristic of neuromyelitis optica spectrum disorder (NMOSD), an autoimmune infammatory demyelinating central nervous system (CNS) disorder. We evaluated the performance of a cell-based indirect immunofuorescence assay (CIIFA) for detecting AQP4 antibodies using antigen prepared with a recombinant AQP4 peptide transfection technique and assessed the usefulness of CIIFA for diagnosis of NMOSD in routine clinical practice. Methods: Forty-six serum samples from 36 patients as a comparison set and another 101 patients enrolled consecutively from a neurology clinic were included. CIIFA and fuorescence immunoprecipitation assays (FIPA) were performed. CIIFA was performed at 2 different institutions for comparison purposes. Results: CIIFA and FIPA sensitivity in the comparison set was 86% and 79% in neuromyelitis optica (NMO) patients and 55% and 36% in high-risk NMO patients, respectively. The semiquantitative titer measured by CIIFA correlated well with the arbitrary unit (fuorescence units [FU]) derived from FIPA (r=0.66). Titers measured by CIIFA and FIPA were elevated in NMO patients compared to high-risk NMO patients (1:240 vs. 1:180 and 8,390 vs. 4,059 FU, respectively). The frequency of AQP4 antibody detection by CIIFA in 101 consecutively enrolled patients was 100% in NMO and 23% in high-risk NMO patients, while only 4.6% in control patients, including those with multiple sclerosis. Conclusions: Detection of AQP4 antibodies by CIIFA provides sensitive and highly specifc diagnostic information for NMO and high-risk NMO patients, which can be used to differentiate these conditions from other demyelinating CNS diseases.