Autoantibodies to the N-methyl-D-aspartate receptor and seizure susceptibility in mice

Abstract

BackgroundAutoantibodies to neuronal surface proteins are found in adult seizure-related disorders such as anti-N-methyl-D-aspartate receptor antibody (NMDAR-Ab) encephalitis and limbic encephalitis. We have previously shown, in new-onset childhood epilepsy, that CNS autoantibodies are also found in a proportion of these patients. We aimed to determine whether these antibodies are pathogenic and epileptogenic in vivo. MethodsIgG from three patients with NMDAR-Ab encephalitis and two healthy controls was purified for passive transfer. Wireless electroencephalogram (EEG) transmitters were implanted into 15 mice. Nine of these mice were injected intracerebroventricularly with IgG from NMDAR-Ab positive patients and six mice with IgG from controls. 5 days of continuous electrophysiology recordings were used to detect spontaneous and induced epileptiform activity. A library of signature events was created to analyse the EEG recordings of all mice. Seizure susceptibility was tested 48 h after injection with a subthreshold dose of the proconvulsant pentylenetetrazole. Seizures were scored according to a modified Racine scale: 1 non-epileptic behavioural change, 2 partial clonus, 3 generalised clonus, and 4 lethal seizure. FindingsMice injected with NMDAR-Ab positive IgG had increased seizure susceptibility, with all having stage 3 seizures compared with only half of the control-IgG injected group (p=0·04). The number of stage 3 seizures was also significantly higher (mean 7·7 [SD 8·4] vs 0·8 [1·0], p=0·003), as was the total seizure score calculated at the end of 60 min of observation (38 [29·5] vs 7·5 [4·1], p=0·003). Preliminary analysis of the post-mortem tissue showed human IgG in the hippocampi of NMDAR-Ab injected but not in control-IgG injected mice. InterpretationSuccessful passive transfer of NMDAR-Ab positive IgG shows the epileptogenic potential of these antibodies. EEG analysis and investigation of the underlying pathogenic mechanism in ex-vivo slices is in progress. FundingWellcome Trust.