Interestingly, IFN-β, an approved MS therapy that alters cellular immune responses and may influence proinflammatory Th17 activity,46 has provoked NMO exacerbations.47–49 Our observation that T cells specific for the immunodominant AQP4 epitope exhibit Th17 polarization support testing of agents that target the IL-17 axis in NMO. This evidence concerns the gene IL17A and neuromyelitis optica.