Positivity of fluorescence labeling with serum from natalizumab-treated patients. A: Shows fluorescence microphotographs from HEK cells expressing AQP4-EGFP (left column), or the fluorescent signal after the immunoassay (middle column) with patients serum, and the merged image of both fluorescent signals (right column). Serum from three types of patient was used in the analysis: C-, in which NMO-IgG was absent; NMO+, in which NMO-IgG antibodies had been confirmed previously; and “Nat”, in which serum from a patient treated with natalizumab was used. Immunofluorescence signals (red) were observed both in NMO + and Nat, although the merged image confirms exclusive co-localization of red and green labels only in the NMO + case. All HEK cells (DAPI stained) independently of whether they express AQP4 or not show some red fluorescence signal with Nat serum, thereby producing a signal that, though low, was above background (C-) level. B: Summarizes the quantitative analysis. Significant statistical differences (** p < 0.01, *** p < 0.001) were observed when signals were compared to C + serum or comparing Nat and NMO- samples (**p < 0.01). Error bars are ± SEM (n = 6-7).