Detection of Anti-Aquaporin-4 Antibodies in Neuromyelitis Optica: Comparison of Tissue-Based and Cell-Based Indirect Immunofluorescence Assays and ELISA

NMO-IgGagainst aquaporin-4 (AQP4) is a specific marker for neuromyelitis optica (NMO). We evaluated the performance of different NMO-IgG detecting methods. In 124 sera (from 54 with NMO spectrum disorders including nine with NMO, ten with multiple sclerosis including two with OSMS, and 60 with other neurological diseases), NMO-IgG was measured with tissue-based indirect immunofluorescence (IIF-tissue) using mouse cerebellum, cell-based IIF (IIF-AQP4) using transfected HEK293 cells which express human AQP4, and AQP4 autoantibody detecting enzyme linked immunosorbent assay (ELISA-AQP4). The sensitivities and specificities of three assays were 44.4-55.6% and 87.0-92.2% for detecting NMO, and 11.1-20.4% and 95.7-97.1% for detecting NMO spectrum disorders. Although there was no significant difference, the patients with NMO or NMO spectrum disorders showed higher rates of seropositivity in the ELISA-AQP4 vs. IIF assays. Out of the 19 sera with NMO-IgG, in at least one test, only six (31.6%) were found to be positive by all three assays. Among the three methods, the ranges of co-negativities, co-positivities, and agreement were 77.4-97.4%, 42.9-75.0%, and 91.1-95.2% (kappa 0.475-0.641), respectively. In patients who had positive ELISA-AQP4 results, IIF-AQP4 positivity was associated with NMO (P = 0.01). In summary, we observed an increased prevalence of NMO-IgG in patients with NMO and NMO spectrum disorders. ELISA-AQP4 may be more sensitive and specific when confirmed by IIF-AQP4.