A multicenter comparison of MOG-IgG cell-based assays

Abstract

Objectives: To compares 3 different myelin oligodendrocyte glycoprotein-immunoglobulin G (IgG) cell-based assays (CBAs) from 3 international centers.

Methods: Serum samples from 394 patients were as follows: acute disseminated encephalomyelitis (28), seronegative neuromyelitis optica (27), optic neuritis (21 single, 2 relapsing), and longitudinally extensive (10 single, 3 recurrent). The control samples were from patients with multiple sclerosis (244), hypergammaglobulinemia (42), and other (17). Seropositivity was determined by visual observation on a fluorescence microscope (Euroimmun fixed CBA, Oxford live cell CBA) or flow cytometry (Mayo live cell fluorescence-activated cell sorting assay).

Results: Of 25 samples positive by any methodology, 21 were concordant on all 3 assays, 2 were positive at Oxford and Euroimmun, and 2 were positive only at Oxford. Euroimmun, Mayo, and Oxford results were as follows: clinical specificity 98.1%, 99.6%, and 100%; positive predictive values (PPVs) 82.1%, 95.5%, and 100%; and negative predictive values 79.0%, 78.8%, and 79.8%. Of 5 false-positives, 1 was positive at both Euroimmun and Mayo and 4 were positive at Euroimmun alone.

Conclusions: Overall, a high degree of agreement was observed across 3 different MOG-IgG CBAs. Both live cell-based methodologies had superior PPVs to the fixed cell assays, indicating that positive results in these assays are more reliable indicators of MOG autoimmune spectrum disorders.

Figure. Comparison of positive and negative controls for Oxford, Euroimmun, and Mayo Clinic MOG-IgG assays

Oxford cell-based assay (CBA) (A.a) negative and (A.b) positive result; Euroimmun CBA (B.a) negative and (B.b) positive result; and Mayo fluorescence-activated cell sorting assay (FACS) (C.a) negative and (C.b) positive result. For the Mayo FACS assay, 2 cell populations are used to obtain a median fluorescent intensity. The green fluorescent protein (GFP)–negative population represents nontransfected cells, and the GFP-positive population represents cells that express both acetylated GFP and myelin oligodendrocyte glycoprotein (MOG) protein. The AlexaFluor-647 median intensity is an indicator of bound human serum antibodies. As shown in panel (C.b), the positive control has a median AlexaFluor-647 intensity of 40,593 for the GFP-positive population, and the GFP-negative population is 477. The negative control (C.a) has a median 647 intensity of 162 for the GFP-positive population, and the GFP-negative population is similar at 147. These statistical values are used to calculate the immunoglobulin G (IgG) binding index, which is a ratio of the GFP-positive value over the GFP-negative value.