Fig 1: Immunolabeling of the patient's cerebrospinal fluid (CSF) sample with in-house tissue-based assay (TBA) (A–C) and cell-based assay (CBA) (D–I). Control CSF did not react with in-house TBA (A), whereas the initial patient's CSF immunolabeled neuropil on the rat hippocampus in the TBA (B). The patient's CSF showed reactivity [green, (D)], with human embryonic kidney (HEK) cells expressing the N-methyl-d-aspartate receptor (NMDAR). The commercial antibody against NMDAR1 (clone EPR2480Y, ab68144, Abcam) [red, (E)] colocalizes with that of the patient's CSF [yellow, (F)], whereas a control CSF is negative (G). Anti-NMDAR antibody titers (1:32) were confirmed using the fluorescent reactivity of CBA on the initial patient's CSF (H). Following tumor removal and whole-brain irradiation therapy, immunosignals in TBA (C) and CBA decreased, as did antibody titers of anti-NMDAR antibody (titers 1:4) (I). Nuclei were counterstained with 4', 6-diamino-2-phenylindole. Bars = 1000 µm (A–C), 50 µm (D–G), and 100 µm (H, I).