Background There is increasing recognition of antibody-mediated immunotherapy-
responsive neurologic diseases and a need for appropriate immunoassays. Objectives To
develop a clinically applicable quantitative assay to detect the presence of aquaporin-4
(AQP4) antibodies in patients with neuromyelitis optica and to characterize the anti-AQP4
antibodies. Design We compared a simple new quantitative fluorescence
immunoprecipitation assay (FIPA) with both indirect immunofluorescence and an AQP4 …