NEUROLOGICAL REVIEW Epilepsy and the Immune System Johan A. Aarli, MD Objective: To discuss evidence that immune mecha- data to prove that immune mechanisms are involved in nisms are involved in the pathogenesis of some forms of the pathogenesis of intractable childhood epilepsies other epilepsy. than Rasmussen encephalitis. Epilepsy is more com- mon in patients with systemic lupus erythematosus who Data Sources: Computerized data sources and pub- have antiphospholipid antibodies, and it is possible that lished indexes and articles. these antibodies can lead to immune-mediated cortical damage. Immune defects in patients with epilepsy may Study Selection: Published reports showing disor- occur as a consequence of long-term antiepileptic treat- ders of the immune system in patients with epilepsy and ment or may represent a genetic coupling to the convul- in animals with experimental epilepsy. sive disorder. Data Synthesis: Rasmussen encephalitis is an ex- Conclusion: The finding of an immunological basis may ample of an autoimmune disorder of the central ner- offer new modalities for the treatment of selected cases vous system. Serum samples of patients with this dis- of intractable partial epilepsies. ease contain antibodies to the glutamate receptor GluR3, and immunization of animals with GluR3 induces a dis- order resembling the human disease. There are still few Arch Neurol. 2000;57:1689-1692 HE FINDING of immune sys- Rogers and coworkers3 demonstrated in tem activation in patients 1994 that immunization of rabbits with the with a seizure disorder has glutamate receptor GluR3 produces a con- lead to the suggestion that dition resembling Rasmussen encephali- immune mechanisms may tis. They also showed that serum samples play a role in the pathogenesis of some of patients with this disease indeed con- T 1 forms of epilepsy. For a long time, such tain antibodies to GluR3 and postulated theories lacked an experimental basis. The that Rasmussen encephalitis is an auto- results of recent studies, especially in pa- immune disorder.3 tients with Rasmussen encephalitis, have To establish that a disease has an au- given new information about the pos- toimmune etiology, Witebsky postulates sible relation between epileptic disorders require that an autoimmune response be and the immune system. recognized in the form of an autoanti- body or cell-mediated immunity, that the RASMUSSEN ENCEPHALITIS—AN corresponding antigen be identified, and AUTOIMMUNE DISORDER? that an analogous autoimmune response be induced in experimental animals. Fi- The clinical setting in Rasmussen encepha- nally, the immunized animals must de- litis is an apparently healthy child or young velop a similar disease.4 adult developing focal seizures that ini- The most straightforward evidence tially appear to be benign, but that gradu- for an autoimmune etiology of a disease ally develop into epilepsia partialis con- is to reproduce it in a normal recipient tinua with hemiparesis and mental by direct transfer of autoantibodies or From the Department retardation. A neuropathological exami- sensitized cells. This is seen as nature’s of Neurology, University nation reveals the typical picture of en- own experiment in neonatal myasthenia of Bergen, Haukeland Hospital, cephalitis with perivascular lymphocyte gravis, where placental transfer of mater- Bergen, Norway. cuffs and scattered microglial nodules.2 nal IgG anti–acetylcholine receptor anti- (REPRINTED) ARCH NEUROL / VOL 57, DEC 2000 WWW.ARCHNEUROL.COM 1689 ©2000 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/02/2021 bodies produces muscular weakness in the newborn. effect. Surprisingly, intraventricular infusion of inter- However, the blood-brain barrier represents an impedi- feron alfa reduced the seizure frequency dramatically in ment for antibodies to reach target antigens in the cen- a child with intractable Rasmussen encephalitis.11 This, tral nervous system. Opportunities for direct transfer of however, may relate to the demonstration that GluR3 an- autoimmune central nervous system disease are, there- tibodies exhibit greater immunoreactivity toward the fore, limited. interferon alfa receptor than toward GluR3.12 The classic strategy for documenting an autoim- These new data on Rasmussen encephalitis confirm mune etiology has been to identify and isolate the of- that immune factors may be central in the pathogenesis fending antigen and reproduce the essential features of of an epileptic disorder and may lead to an increased un- the disease by experimental immunization. This has been derstanding of the basis of other seizure disorders with im- accomplished with Rasmussen encephalitis. In raising an- munological concomitants. tibodies to glutamate receptors, Rogers et al3 demon- strated that 2 animals immunized with GluR3 devel- EPILEPSY IN PATIENTS WITH SYSTEMIC oped behavior typical of seizures and histopathological LUPUS ERYTHEMATOSUS (SLE) features mimicking Rasmussen encephalitis. This obser- vation has since been confirmed in other species.5,6 Between 10% and 20% of patients with SLE develop epi- Additional support that the autoantibodies are patho- leptic seizures at some stage of their disease. This is genic comes from the demonstration that IgG from rab- nearly 8 times the prevalence of epilepsy in the general bit antiserum to GluR3 binds to and activates a subpopu- population; epilepsy is, therefore, much more common lation of fetal murine cortical neurons in culture and that in patients with SLE than would be expected. Between this binding could be blocked by a competitive antago- 5% and 10% have onset of seizures several years before nist, CNQX.7 the clinical onset of SLE.13-15 This may mean that long- The experimental disease in these animals mirrors term treatment with antiepileptic drugs may precipitate several features of the human disease, such as the epi- SLE, or that epilepsy and SLE occur together as manifes- leptic seizures, the histopathological findings, and the se- tations of a genetically determined predisposition. lectivity of the immune response to GluR3. It differs, how- According to Mackworth-Young and Hughes,14 epilepsy ever, from Rasmussen encephalitis in humans in that the developing in patients before the other manifestations of latter is unilateral while the experimental disease in- SLE differs from that developing after the other manifes- volves both hemispheres. tations of SLE. Epileptic seizures occurring before the The neuronal cell death observed in vitro appears onset of other manifestations of SLE were more often not to be caused by excitotoxicity. IgG antibodies to GluR3 primary generalized, but seizures that occurred after the isolated from immunized animals (both ill and healthy) clinical onset of SLE were either focal or generalized- promote death of cultured cortical cells by a complement- tonic.14 dependent mechanism. IgG and complement factors of Seizures may occur in patients with SLE based on the membrane attack complex were found on neurons immune-mediated neuronal damage, because of throm- and their processes in the cortex of brains from patients botic events in cortical blood vessels, or they may be with Rasmussen encephalitis. Antibodies seem, there- secondary to hypertensive encephalopathy or renal fail- fore, to gain access to the central nervous system and trig- ure. Antibodies to transmitter receptors such as GluR3 ger complement-mediated neuronal damage. This pro- have never been convincingly demonstrated in patients cess may be of special importance in the initial, active with SLE. Epilepsy in patients with SLE is significantly phase of the disease.8,9 Genetic and species differences associated with antiphospholipid antibodies (aPLs).16 may exist, as Levite et al5 recently reported that murine Chapman et al17 reported recently that purified IgG GluR3 antibodies can mimic excess glutamate effect and containing aPLs depolarized synaptoneurosomes from induce neuronal death via activation of the receptor ion rat brainstem and suggested this as an additional channel, apparently independent of complement. mechanism in nonthromboembolic central nervous There is additional circumstantial evidence that au- system manifestations. toimmune mechanisms operate in Rasmussen encepha- Patients with aPLs are at risk of thromboembolic litis. Li et al10 have demonstrated restricted T-lymph- manifestations, intrauterine fetal loss, and thrombocy- ocyte populations in the brains of patients with Rasmussen topenia (antiphospholipid syndrome). Such antibodies encephalitis. Removal of antibodies by plasma ex- are commonly found in serum samples of patients with change transiently reduces the seizure frequency and im- SLE and are generally heterogeneous, and the different proves the neurologic function as the serum concentra- specificities may play causal roles in different clinical mani- 3 18,19 b tions of GluR3 antibodies decrease. As antibodies to festations. For example, anti– 2-glycoprotein I anti- GluR3 are found in serum samples from immunized ani- bodies may have a direct pathogenic role in thrombosis. b mals without apparent disease, a focal or a general dis- They recognize a 2-glycoprotein I structure on cellular ruption of the blood-brain barrier is essential for serum structures and are also significantly elevated in patients antibodies to reach the brain.1 with epilepsy.20,21 IgG antibodies to cardiolipin have been The finding of an immunological background for an found in 30% to 60% of unselected patients