Anti-AQP4 antibodies were also detected by ELISA in most IVIg preparations in titers seen in AQP4-seropositive NMO-SD; these antibodies were not however detected with CBA and immunohistochemistry, indicating that they are directed against linear, rather than structural, epitopes, as part of the natural immune repertoire [16, 18]. The gene discussed is AQP4; the disease is neuromyelitis optica.