Overview of patient cohort, antibody status, and anti-MOG antibody levels. (A) Patient cohort and antibody status: The study comprised a total of 135 participants including patients with NMO/NMOSD (n = 48), relapsing-remitting multiple sclerosis (RR-MS) (n = 48), and healthy donors (n = 39). Of the NMO/NMOSD patients, 31 were positive for anti-AQP4 antibodies (AQP4+) with the cell-based assay (CBA) while only 22 patients tested positive with indirect immunofluorescence (iIF). All of the AQP4-seropositive patients were negative for anti-MOG antibodies (MOG−). Of the AQP4-seronegative patients (AQP4−), four patients had anti-MOG antibodies (MOG+) (CBA), while 13 patients had no detectable antibodies against either AQP4 or MOG. (B) Anti-MOG antibody levels: Anti-MOG reactivity was analyzed with the CBA and is expressed as the geometric mean channel fluorescence (GMCF) ratio of the MOG-transfected cell line divided by the empty vector-transfected cell line. Values shown represent the (mean) GMCF ratio of one to four experiments. The cutoff used (dotted line) is the mean GMCF ratio of the healthy donor group measured in parallel (n = 39) plus two standard deviations (cutoff = 1.45). Using this cutoff, 4 of the 17 (23.5%) NMO/NMOSD sera were positive for anti-MOG antibodies (empty red squares), all of which were AQP4-seronegative (filled red squares). None of the AQP4-seropositive NMO/NMOSD patients (filled red circles) and none of the RR-MS patients (filled light red triangles) were positive for anti-MOG antibodies.