Peptide-Purified Anti-N-methyl-D-aspartate Receptor (NMDAR) Autoantibodies Have Inhibitory Effect on Long-Term...

Background/Objectives: Recent studies, typically using patient cerebrospinal fluid (CSF), have suggested that different autoantibodies (Aabs) acting on their respective receptors, may underlie neuropsychiatric disorders. The GluN1 (NR1) subunit of the N-methyl-D-aspartate receptor (NMDAR) has been identified as a target of anti-NMDAR Aabs in a number of central nervous system (CNS) diseases, including encephalitis and autoimmune epilepsy. However, the role or the nature of Aabs responsible for effects on neuronal excitability and synaptic plasticity is yet to be established fully. Methods: Peptide immunisation was used to generate Aabs against selected specific GluN1 extracellular sequences based on patient-derived anti-NMDAR Aabs that have been shown to bind to specific regions within the GluN1 subunit. 'Protein A' purification was used to obtain the total IgG, and further peptide purification was used to obtain a greater percentage of NMDAR-target specific IgG Aabs. The binding and specificity of these anti-NMDAR Aabs were determined using a range of methodologies including enzyme-linked immunosorbent assays, immunocytochemistry and immunoblotting. Functional effects were determined using different in vitro electrophysiology techniques: two-electrode voltage-clamps in Xenopus oocytes and measures of long-term potentiation (LTP) in ex vivo hippocampal brain slices using multi-electrode arrays (MEAs). Results: We show that anti-NMDAR Aabs generated from peptide immunisation had specificity for GluN1 immunisation peptides as well as target-specific binding to the native protein. Anti-NMDAR Aabs had no clear effect on isolated NMDARs in an oocyte expression system. However, peptide-purified anti-NMDAR Aabs prevented the induction of LTP at Schaffer collateral-CA1 synapses in ex vivo brain slices, consistent with causing synaptic NMDAR hypofunction at a network level. Conclusions: This work provides a solid basis to address outstanding questions regarding anti-NMDAR Aab mechanisms of action and, potentially, the development of therapies against CNS diseases.