Distinct features of immunoglobulin G2 aquaporin-4 antibody carriers with neuromyelitis optica

Objective Neuromyelitis optica (NMO) is an inflammatory disease in which NMO-immunoglobulin G (IgG) targeting aquaporin-4 (AQP4) is specifically detected. Although the main subclass of AQP4 antibody was reported to be in the IgG1 subclass, other subclasses have also been described, including IgG2 AQP4 antibody, as a second common subclass. NMO patients were analyzed to clarify the clinical features of NMO patients with IgG2 AQP4 antibody. Methods Serum samples from 58 NMO patients, who met the revised 2006 criteria for NMO, were analyzed for AQP4 antibody subclass expression using an established flow cytometric assay, and clinical features were compared according to the main AQP4 antibody subclasses. Results A total of 50 patients (86.2%) had IgG1 AQP4 antibodies, while eight (13.8%) expressed IgG2 AQP4 antibody as the main subclass. Those eight individuals exhibited younger age of onset (P = 0.0089), lower AQP4 antibody titers (P = 0.0024) and a more common fulfillment of Barkhof's criteria (P = 0.0466) than patients with IgG1 AQP4 antibody expression. Conclusions Results from the present study suggest that the characteristics of individuals with IgG2 AQP4 antibody as a main subclass are more similar to multiple sclerosis and somewhat distinct from NMO patients with IgG1 AQP4 antibody.