Since the discoveries of T cells in NMO lesions [21], and of NMO-IgG containing pathogenic AQP4-specific antibodies with the T cell-dependent immunoglobulin subclass IgG1 [19, 20], the question arose whether AQP4 specific T cells are only responsible for T cell help in antibody formation, or whether they can also participate in directing lesions to NMO-typical sites, and induce there astrocyte-destructive lesions in the presence of NMO-IgG. The gene discussed is AQP4; the disease is neuromyelitis optica.