Detection of anti-aquaporin 4 antibody

Abstract

Background: Neuromyelitis optica (NMO) has clinical features in common with optic spinal multiple sclerosis (OSMS), which is predominant among patients with multiple sclerosis (MS) in Asian countries, but it has certain traits distinct from classical MS, which is common in western countries. An antibody specific to a water channel protein, aquaporin 4 (AQP4), has recently allowed us to differentiate NMO from MS. We made an assay to detect anti-AQP4 antibody in our hospital and confirmed the value of this assay. Method: We used indirect immunohistochemistry with HEK293 cells expressing human AQP4 conjugated with green fluorescent protein (GFP). We incubated these cells with sera of two patients, one clinically defined as NMO and the other as classical MS; then we stained with red fluorescence-labeled anti-human IgG. Results: The AQP4-expressing cells incubated with the serum obtained from the NMO patient showed red dotted fluorescence on their surface, indicating positivity of the serum, while the cells incubated with the serum from the MS patient did not. In addition, the serum from the NMO patient did not bind to HEK293 cells not expressing AQP4, suggesting that the serum specifically recognized AQP4 molecules. Conclusion: These results confirm the value of our assay in diagnosing NMO.