['Neuromyelitis optica (NMO) is caused by binding of pathogenic autoantibodies (NMO-immunoglobulin G [IgG]) to aquaporin-4 (AQP4) on astrocytes, which initiates complement-dependent cytotoxicity (CDC) and inflammation. We recently introduced mutated antibody (aquaporumab) and small-molecule blocker strategies for therapy of NMO, based on prevention of NMO-IgG binding to AQP4. Here, we investigated an alternative strategy involving neutralization of NMO-IgG effector function by selective IgG heavy-chain deglycosylation with bacteria-derived endoglycosidase S (EndoS).', 'Cytotoxicity and NMO pathology were measured in cell and spinal cord slice cultures, and in mice exposed to control or EndoS-treated NMO-IgG.', 'EndoS treatment of NMO patient serum reduced by >95% CDC and antibody-dependent cell-mediated cytotoxicity, without impairment of NMO-IgG binding to AQP4. Cytotoxicity was also prevented by addition of EndoS after NMO-IgG binding to AQP4. The EndoS-treated, nonpathogenic NMO-IgG competitively displaced pathogenic NMO-IgG bound to AQP4, and prevented NMO pathology in spinal cord slice culture and mouse models of NMO.'] Does enzymatic deglycosylation convert pathogenic neuromyelitis optica anti-aquaporin-4 immunoglobulin G into therapeutic antibody?