Passive transfer of AQP4-specific antibodies alone did not produce CNS pathology, but did promote development of NMO-like lesions in recipient animals when CNS inflammation was induced by myelin-specific T cells.4, 5 T cells are detected within active NMO lesions.6 Further, NMO lesions are characterized by an abundance of eosinophils and neutrophils, and elevated levels of IL-17 have been associated with NMO,7 suggesting involvement of Th17 cells. Here, IL17A is linked to neuromyelitis optica.