AQP4 and neuromyelitis optica: Complement-mediated cytotoxicity plays a central role in the pathogenesis of seropositive neuromyelitis optica spectrum disorders (herein called NMO), in which immunoglobulin G autoantibodies against water channel aquaporin-4 (AQP4), called AQP4-IgG, bind to astrocytes in brain, spinal cord and optic nerve [9, 10].