Anti-NMDA Receptor Encephalitis Antibody Binding Is Dependent on Amino Acid Identity of a Small Region within the GluN1 Amino Terminal Domain

Abstract

Anti-NMDA receptor (NMDAR) encephalitis is a newly identified autoimmune disorder that targets NMDARs, causing severe neurological symptoms including hallucinations, psychosis, and seizures, and may result in death (Dalmau et al., 2008). However, the exact epitope to which these antibodies bind is unknown. A clearly defined antigenic region could provide more precise testing, allow for comparison of immunogenicity between patients to explore potential clinically relevant variations, elucidate the functional effects of antibodies, and make patients’ antibodies a more effective tool with which to study NMDAR function. Here, we use human cerebrospinal fluid to explore the antigenic region of the NMDAR. We created a series of mutants within the amino terminal domain of GluN1 that change patient antibody binding in transfected cells in stereotyped ways. These mutants demonstrate that the N368/G369 region of GluN1 is crucial for the creation of immunoreactivity. Mass spectrometry experiments show that N368 is glycosylated in transfected cells and rat brain regions; however, this glycosylation is not directly required for epitope formation. Mutations of residues N368/G369 change the closed time of the receptor in single channel recordings; more frequent channel openings correlates with the degree of antibody staining, and acute antibody exposure prolongs open time of the receptor. The staining pattern of mutant receptors is similar across subgroups of patients, indicating consistent immunogenicity, although we have identified one region that has a variable role in epitope formation. These findings provide tools for detailed comparison of antibodies across patients and suggest an interaction between antibody binding and channel function.

NMDAR encephalitis: passive transfer from man to mouse by a recombinant antibody

“…4A–C) as previously described 29. Patient‐derived rhuMab SSM5, but not isotype control rhuMab 12D7, specifically stained HEK293 cells cotransfected with wild‐type GluN1/GluN2b in a similar pattern as CSF from a patient with anti‐NMDAR encephalitis (green, Fig.…”

“…Moreover, this recombinant antibody competed with patients' CSF antibodies for the same restricted epitope on the extracellular amino terminal domain of the GluN1 subunit of the NMDA receptor,29 decreased the density of cell surface and synaptic NMDAR in cultured neurons, and significantly reduced NMDAR mediated currents in Xenopus oocytes expressing GluN1/GluN2B. Importantly, continuous infusion of rhuMab SSM5 into the cerebroventricular system of mice for 14 days resulted in progressive impairment of memory paralleled by accumulation of brain‐bound antibody and specific reduction of the density of synaptic NMDAR clusters, as previously reported in a similar model of infusion of patients' CSF 11, 15.…”

Induction of Memory Deficit in Mice with Chronic Exposure to Cerebrospinal Fluid from Patients with Anti-<i>N</i>-Methyl-D-Aspartate Receptor Encephalitis

“…The epitope targeted by anti-NMDAR antibodies is located in the extracellular domain of the GluN1 subunit (Dalmau et al 2008;Gleichman et al 2012). Following the binding of anti-NMDAR antibodies, the receptor becomes cross-linked and internalized at the postsynaptic site, thereby suppressing NMDAR-mediated transmission (Hughes et al 2010).…”

Identification of the <i>N</i>-Methyl-D-Aspartate Receptor (NMDAR)-Related Epitope, NR2B, in the Normal Human Ovary: Implication for the Pathogenesis of Anti-NMDAR Encephalitis

“…It is now controversial which of NR1 and NR2 subunits are targeted by patient anti-NMDAR IgGs. Gleichman et al (2012) emphasized that NR1 epitope was crucial for the creation of immunoreactivity, while Mikasova et al (2012) reported that the surface dynamics of synaptic NR2A and extrasynaptic NR2B subunits were significantly impaired by patient anti-NMDAR IgGs. The pathogenic process of anti-NMDAR encephalitis is considered to be more complicated than previously recognized.…”