Oligoclonal IgG bands revealed to be constituted with NMDAR autoantibodies in a patient with anti-NMDA receptor encephalitis

•Oligoclonal IgG bands (OCBs) in cerebrospinal fluid (CSF) are markers of central nervous system (CNS) inflammation, though their specific components remain unidentified.•We identified the constituents of OCBs in the CSF of a patient with NMDAR encephalitis through antibody absorption using specific antigen-expressing cells, marking the first report to do so.•While the origin of NMDAR antibodies was not directly shown, our findings indicate that these antibodies are produced within the CNS.