Encephalitis patient derived monoclonal GABA_Areceptor antibodies cause catatonia and epileptic seizures

Abstract

Autoantibodies targeting the GABAA receptor (GABAAR) hallmark an autoimmune encephalitis presenting with frequent seizures and psychomotor abnormalities. Their pathogenic role is still not well-defined, given the common overlap with further autoantibodies and the lack of patient derived monoclonal antibodies (mAbs). We cloned and recombinantly produced five affinity-maturated GABAAR IgG1 mAbs from cerebrospinal fluid cells, which bound to various epitopes involving α1 and γ2 receptor subunits, with variable binding strength and partial competition. mAbs selectively reduced GABAergic currents in neuronal cultures without causing receptor internalization. Cerebroventricular infusion of GABAAR mAbs and Fab fragments into rodents induced a severe phenotype with catatonia, seizures and increased mortality, reminiscent of encephalitis patients’ symptoms. Our results prove direct functional effects of autoantibodies on GABAARs and provide an animal model for GABAAR encephalitis. They further provide the scientific rationale for clinical treatments using antibody depletion and pave the way for future antibody-selective immunotherapies.

GABAA Receptor Autoantibodies Decrease GABAergic Synaptic Transmission in the Hippocampal CA3 Network

“…This finding is important because CA3 neurons are involved in the generation of epileptic discharges [ 15 , 16 , 17 , 18 , 19 ]. In another study, the cerebroventricular infusion of GABA A R mAb in Wistar rats caused spontaneous seizures in vivo [ 12 ]. Moreover, increased spontaneous epileptic activity was detected from electrodes placed in the hippocampal areas CA1 and CA3 of the rats ex vivo [ 12 ].…”

“…Moreover, a severe form of autoimmune encephalitis with refractory seizures, status epilepticus, and antibodies (Abs) against α1, β3, and γ2 subunits of GABA A R has been reported as a new form of central nervous system (CNS) autoimmunity [ 5 , 6 , 7 , 8 ]. Several studies have demonstrated the pathogenic effects of these antibodies on GABA A R function [ 5 , 9 , 10 , 11 , 12 , 13 ]. These Abs led to the reduction in synaptic GABA A R complexes, presumably via cross-linking and the subsequent internalization of the Ab-receptor complex [ 5 , 9 , 10 ].…”

“…This caused selective reduction in the postsynaptic GABA A R clusters at inhibitory GABAergic synapses that was linked to the hyperexcitability and dysfunction of neuronal networks [ 5 , 9 , 10 ]. In contrast, a recent study showed that recombinant human monoclonal Abs (mAbs) with GABA A R reactivity, which were derived from a patient with GABA A R encephalitis and generated using single-cell cloning, reduced inhibitory postsynaptic signaling in neuronal cultures without causing receptor internalization [ 12 ]. Subsequently, a severe clinical phenotype with epileptic seizures was induced by cerebroventricular infusion of GABA A R mAbs into rodents [ 12 ].…”

“…In contrast, a recent study showed that recombinant human monoclonal Abs (mAbs) with GABA A R reactivity, which were derived from a patient with GABA A R encephalitis and generated using single-cell cloning, reduced inhibitory postsynaptic signaling in neuronal cultures without causing receptor internalization [ 12 ]. Subsequently, a severe clinical phenotype with epileptic seizures was induced by cerebroventricular infusion of GABA A R mAbs into rodents [ 12 ]. In another study, a recombinantly expressed pathogenic antibody from the cerebrospinal fluid (CSF) B cells of a patient with autoimmune GABA A R encephalitis, previously described and termed “index patient 2” (IP2), led to the reduction in phasic GABAergic inhibitory synaptic activity and the increase in excitability in hippocampal CA1 pyramidal neurons, most probably contributing to clinical disease symptoms [ 13 ].…”

Impaired functional connectivity of the hippocampus in murine models of NMDA-receptor antibody associated pathology

“…1). These C57BL/6J mice (age of 10 weeks) received bilateral infusion of 200 µg human monoclonal IgG1 antibody (high-affinity NR1-reactive [amino-terminal domain] IgG1 clone: #003-102 [n=10, "NR1"]) 12,19 in PBS for 14 days into the lateral ventricles using implanted catheters connected to osmotics pumps following established protocols [20][21][22] . Ten mice received human monoclonal IgG1 antibody that is non-reactive to brain tissue (control clone: #mGO53) 12,23 into the lateral ventricles via implanted catheters and served as NR1-controls.…”