Binding of human mAbs to GABA_AR and other CNS targets. (A and B) Immunofluorescence stainings of human GABA_AR mAb #113-115 (green) on unfixed murine brain tissue, with binding to hippocampal neuropil. (B) Higher magnification of the hippocampal CA3 area showing the colocalization with a commercial anti-GABA_AR antibody (red; nuclei in blue). (C) Live-cell staining of GABA_AR mAb #113-115 on cultured cortical rat neurons. (D and E) Immunofluorescence staining on fixed cultured cortical rat neurons, with GABA_AR mAb #113-115 (green) in D with clustered binding pattern along MAP2⁺ (red) dendrites and in E colocalization with commercial antibodies against GABA_AR (red) and the presynaptic marker vGAT (blue). (F–J) Immunofluorescence staining of human GABA_AR-negative mAbs (green; nuclei in blue) from encephalitis patient’s CSF repertoire with reactivity in variable distribution patterns on unfixed murine brain sections, including binding to blood vessels (F), hippocampal neuropil (G), cell soma in corpus callosum (H), and cells of different cerebellar layers (J and I). F shows a tile scan of a whole sagittal brain section. Inserts in H–J show mAb staining on fixed cultured neurons. All stainings were replicated at least twice on tissue or neurons from two different animals. Scale bars indicate 100 µm in A and B, 20 µm in C–E, 100 µm in F–J, and 20 µm in inserts of F–J. GCL, granule cell layer; MCL, molecular cell layer; MoDG, molecular layer of the dentate gyrus; neg. ctrl., negative control; PCL, Purkinje cell layer; rb, rabbit.