Abstracts

Rationale: The hypothesis linking autoimmunity to the etiology of epilepsies has gained support over the past decade. Autoimmune epilepsies can be characterized by autoantibodies against membrane-bound, intracellular or secreted proteins. Recently, we demonstrated that histone- and chromatin-specific gamma immunoglobulins (IgGs) are found in the nuclei of cortical neurons and in serum from patients with epilepsy. The mechanism of IgG extravasation is blood-brain barrier (BBB) disruption; however, the trigger of nuclear IgG uptake is unknown. We tested the hypothesis that acute seizures may cause IgG extravasation and neuronal uptake. To study the effect of a single seizure we used a genetic mouse model of lupus displaying high levels of anti-histone, anti-chromatin and anti-dsDNA IgGs in female compared to male animals.Methods: Mice chosen for these experiments were NZBWF1/J from Jackson Laboratories. Mice were given pilocarpine at 170 or 340 mg/kg i.p. Seizures were monitored and quantified using the Racine scale. After two hours, mice were sacrificed and brains processed for immunochemistry. Sections were incubated with a donkey anti-mouse secondary (FITC) to probe for IgG and DAPI to identify nuclei. Sections were analyzed using a fluorescent microscope and a fluorescent slide scanner. Results: Mice could be segregated in three groups based on seizure severity: control (no seizures), low pilocarpine dose and high pilocarpine dose. Control mice (no pilocarpine, lupus background; 4-24 weeks, male and female, n=20) displayed no extravasation of IgG, suggesting that at these disease stages the BBB is intact. In contrast, NZBWF1/J lupus mice receiving high doses of pilocarpine and experiencing a lethal Racine IV seizure (male and female, lupus background; 15 weeks, n=6), displayed hippocampal BBB leakage with prominent ingress of IgG in hilar and CA3 neurons. In morphological sections, the pattern of IgG accumulation in neurons followed the mossy fiber territory. NZBWF1/J mice treated with low doses of pilocarpine displayed minimal IgG extravasation and intracellular accumulation (male and female, lupus background; 15 weeks, n = 12)Conclusions: Our results show that a single severe seizure allows intracellular accumulation of IgGs which extravasated across a leaky BBB. Nuclear accumulation of IgGs in NZBWF1/J mice was comparable to what was observed in human epileptic brain. In mice, nuclear IgG accumulation was prominent in regions of the hippocampus that are most susceptible to neuronal cell death following epileptiform discharges (CA3 and hilus). Our results support the use of NZBWF1/J lupus mice to study nuclear autoimmunity and its role in epileptogenesis. In summary, intranuclear immunoglobulin accumulation may be a mechanism of seizure-induced hippocampal sclerosis.