AQP4 and neuromyelitis optica: Surprisingly, co-immunofluorescence experiments performed using those sera and AQP4 antibodies on AQP4+/+ and AQP4−/− mouse brain (Fig. 5 A) clearly demonstrated the presence of endothelial, NMO IgG-like but AQP4-independent, staining of some NMO sera demonstrating that TB-A, may have serious limitations especially due to false positive results.