AQP4 and neuromyelitis optica: The aim of the current study was to determine the sensitivity and specificity of the IHC-o to detect NMO-IgG/AQP4-antibodies, and compare them with those of conventional tissue-based assays, including IIF and IHC-c, and two CBA, an in-house assay (CBA-ih) with the AQP4-M23 isoform and a commercial assay (CBA-c) [15].