Considering the facts that AQP4-specific T cells provide help to the formation of AQP4-specific antibodies, and that AQP4-specific T cells are clonally expanded in NMO patients [23, 38], it is tempting to speculate that the antigen leading to T cell activation within the CNS of NMO patients is AQP4 as well. The gene discussed is AQP4; the disease is neuromyelitis optica.