AQP4 and neuromyelitis optica: Saganet al. investigated the relevance of AQP4 as an autoantigen in neuromyelitis optica, recognized by T lymphocytes, in an animal model.25 This aquaporin is a water channel expressed in astrocytes in areas in contact with the blood-brain barrier, and 75% of patients with neuromyelitis have antibodies capable of recognizing AQP4.