AQP4 and neuromyelitis optica: Binding of NMO-IgG to water channel aquaporin-4 (AQP4), primarily expressed at the end-feet of astrocytes, initiates complement-dependent cell cytotoxicity (CDCC) on astrocytes, followed by blood–brain barrier breakdown, recruitment of granulocytes and macrophages and cytokine secretion, which result in secondary oligodendrocyte injury, demyelination, and neuronal injury (3–6).