The significance of an AQP4‐specific T‐cell response in experimental NMO, and by analogy also in NMO patients, has been discussed in the context of T‐cell help required to generate pathogenic anti‐AQP4 antibodies 34 and in the context of the potential of AQP4‐specific T cells to induce an inflammatory milieu at the blood–brain barrier, which may be the prerequisite for anti‐AQP4 antibodies to efficiently reach their target in astrocytic end feet and trigger complement‐mediated tissue destruction 35. Here, AQP4 is linked to neuromyelitis optica.