Accumulating evidences reveal that NMO-IgG localizes to blood-brain barrier (BBB) [54]: an indirect immunofluorescence study with dual immunolabeling of mouse brain sections with NMO patient’ sera and antibodies specific for the endothelial marker factor VIII, the reactive-astrocyte marker glial fibrillary acidic protein (GFAP) or the extracellular matrix protein laminin, has suggested that the main target antigen is in astrocytes located adjacent to the BBB [54]. This evidence concerns the gene GFAP and neuromyelitis optica.