Cytotoxic effect of neuromyelitis optica antibody (NMO-IgG) to astrocytes: An in vitro study

NMO-IgG is a disease-specific autoantibody for neuromyelitis optica (NMO) that binds selectively to aquaporin-4 (AQ4), an astrocytic water channel. The normal distribution of AQP4 coincides with the sites of immunoglobulin and complement deposits in lesions found in autopsy studies. The underlying mechanisms of cytotoxicity by NMO-IgG on astrocytes are not well known. In this study we show that serum samples from seropositive NMO patients (21) induce a higher rate of cell death compared with sera from seronegative NMO (16), relapsing–remitting MS (20) patients, and healthy controls (24) on primary cultures of astrocytes. Similar results were obtained by two different techniques: lactate dehydrogenase release and tetrazolium-based viability assay. Cell death was only observed in the presence of active complement. The complement-dependent cytotoxicity was not accompanied by caspase-3/7 activation or increase in the percentage of apoptotic cells. Our data show that NMO-IgG induces a complement-dependent cytotoxicity of astrocytes in vitro, and suggest that a mechanism of cellular death by necrosis might be implicated in the pathophysiology of NMO.