Scanning electron microscopy of serum AQP4-IgG mediated complement activation. Following incubation of AQP4 transfected HEK-293A cells with an NMO serum (AQP4-IgG titer: 1:10,240) and either active or inactive complement, the cells were investigated via scanning electron microscopy (1,000 × magnification). NMO serum supplemented with active complement resulted in increased apoptosis (shown by the detached cells, left panel). In contrast, the cell layer of NMO serum supplemented with inactive complement remained largely preserved (right panel). Images are representative of similar observations in independent complement activation assays.