Pathology of neuromyelitis optica

Understanding of the pathogenesis of neuromyelitis optica (NMO) is rapidly growing. In our immunohistochemical studies from 2006, the loss of AQP4 was evident in about 90% of NMO lesions, especially in perivascular areas of acute inflammatory lesions where immunoglobulins and complements were deposited. Glial fibrillary acidic protein (GFAP) was also weak or lost in those lesions. In contrast, myelin basic protein (MBP)-stained myelinated fibers were relatively preserved in those lesions where AQP4 was completely lost. In contrast to NMO lesions, AQP4 and GFAP were preserved or increased in demyelinating MS lesions. The loss of AQP4 in acute inflammatory lesions was evident in the largest areas compared with GFAP or MBP, which probably suggested the primary loss of AQP4 on astrocytes and the secondarily demyelination. In contrast, the immunostaining patterns in more chronic lesions of NMO mostly lacked AQP4 but were necrotic heterogeneously with demyelination and gliosis, or completely burn-out. Swelling and regressive changes of astrocytes were easily evident. In addition, the lesions lacking AQP4 was appeared by passive-transferred Lewis rats with human purified IgG from NMO patients. Accordingly, these evidences strongly suggest its humoral autoimmune astrocytopathy in the pathomechanism of NMO.