AQP4 and neuromyelitis optica: The authors studied time-matched serum and CSF samples (defined as being drawn no more than 30 days apart) from cases classified as NMO by 2006 Wingerchuk criteria.8 Each sample and a variety of controls were tested with a commercially available M1-AQP4-transfected, fixed cell-based assay (CBA), and in-house live cell flow cytometry.