Astrocytes are a specific immunological target in Rasmussen's encephalitis

The immune system and metabolic products in epilepsy and glioma-associated epilepsy: emerging therapeutic directions

Epilepsy has a profound impact on quality of life. Despite the development of new antiseizure medications (ASMs), approximately one-third of affected patients have drug-refractory epilepsy and are nonresponsive to medical treatment. Nearly all currently approved ASMs target neuronal activity through ion channel modulation. Recent human and animal model studies have implicated new immunotherapeutic and metabolomic approaches that may benefit patients with epilepsy. In this Review, we detail the proinflammatory immune landscape of epilepsy and contrast this with the immunosuppressive microenvironment in patients with glioma-related epilepsy. In the tumor setting, excessive neuronal activity facilitates immunosuppression, thereby contributing to subsequent glioma progression. Metabolic modulation of the IDH1-mutant pathway provides a dual pathway for reversing immune suppression and dampening seizure activity. Elucidating the relationship between neurons and immunoreactivity is an area for the prioritization and development of the next era of ASMs.

Single-Cell Sequencing Combined with Transcriptome Sequencing Constructs a Predictive Model of Key Genes in Multiple Sclerosis and Explores Molecular Mechanisms Related to Cellular Communication

Background

Multiple sclerosis (MS) causes chronic inflammation and demyelination of the central nervous system and comprises a class of neurodegenerative diseases in which interactions between multiple immune cell types mediate the involvement of MS development. However, the early diagnosis and treatment of MS remain challenging.

Methods

Gene expression profiles of MS patients were obtained from the Gene Expression Omnibus (GEO) database. Single-cell and intercellular communication analyses were performed to identify candidate gene sets. Predictive models were constructed using LASSO regression. Relationships between genes and immune cells were analyzed by single sample gene set enrichment analysis (ssGSEA). The molecular mechanisms of key genes were explored using gene enrichment analysis. An miRNA network was constructed to search for target miRNAs related to key genes, and related transcription factors were searched by transcriptional regulation analysis. We utilized the GeneCard database to detect the correlations between disease-regulated genes and key genes. We verified the mRNA expression of 4 key genes by reverse transcription-quantitative PCR (RT‒qPCR).

Results

Monocyte marker genes were selected as candidate gene sets. CD3D, IL2RG, MS4A6A, and NCF2 were found to be the key genes by LASSO regression. We constructed a prediction model with AUC values of 0.7569 and 0.719. The key genes were closely related to immune factors and immune cells. We explored the signaling pathways and molecular mechanisms involving the key genes by gene enrichment analysis. We obtained and visualized the miRNAs associated with the key genes using the miRcode database. We also predicted the transcription factors involved. We used validated key genes in MS patients, several of which were confirmed by RT‒qPCR.

Conclusion

The prediction model constructed with the CD3D, IL2RG, MS4A6A, and NCF2 genes has good diagnostic efficacy and provides new ideas for the diagnosis and treatment of MS.

Myeloid cell iron uptake pathways and paramagnetic rim formation in multiple sclerosis

In multiple sclerosis (MS), sustained inflammatory activity can be visualized by iron-sensitive magnetic resonance imaging (MRI) at the edges of chronic lesions. These paramagnetic rim lesions (PRLs) are associated with clinical worsening, although the cell type-specific and molecular pathways of iron uptake and metabolism are not well known. We studied two postmortem cohorts: an exploratory formalin-fixed paraffin-embedded (FFPE) tissue cohort of 18 controls and 24 MS cases and a confirmatory snap-frozen cohort of 6 controls and 14 MS cases. Besides myelin and non-heme iron imaging, the haptoglobin-hemoglobin scavenger receptor CD163, the iron-metabolizing markers HMOX1 and HAMP as well as immune-related markers P2RY12, CD68, C1QA and IL10 were visualized in myeloid cell (MC) subtypes at RNA and protein levels across different MS lesion areas. In addition, we studied PRLs in vivo in a cohort of 98 people with MS (pwMS) via iron-sensitive 3 T MRI and haptoglobin genotyping by PCR. CSF samples were available from 38 pwMS for soluble CD163 (sCD163) protein level measurements by ELISA. In postmortem tissues, we observed that iron uptake was linked to rim-associated C1QA-expressing MC subtypes, characterized by upregulation of CD163, HMOX1, HAMP and, conversely, downregulation of P2RY12. We found that pwMS with [Formula: see text] 4 PRLs had higher sCD163 levels in the CSF than pwMS with [Formula: see text] 3 PRLs with sCD163 correlating with the number of PRLs. The number of PRLs was associated with clinical worsening but not with age, sex or haptoglobin genotype of pwMS. However, pwMS with Hp2-1/Hp2-2 haplotypes had higher clinical disability scores than pwMS with Hp1-1. In summary, we observed upregulation of the CD163-HMOX1-HAMP axis in MC subtypes at chronic active lesion rims, suggesting haptoglobin-bound hemoglobin but not transferrin-bound iron as a critical source for MC-associated iron uptake in MS. The correlation of CSF-associated sCD163 with PRL counts in MS highlights the relevance of CD163-mediated iron uptake via haptoglobin-bound hemoglobin. Also, while Hp haplotypes had no noticeable influence on PRL counts, pwMS carriers of a Hp2 allele might have a higher risk to experience clinical worsening.

Mechanisms and Emerging Therapies for Treatment of Seizures in Pediatric Autoimmune Encephalitis and Autoinflammatory/Autoimmune-Associated Epilepsy

There has been increasing understanding of the role of inflammation in seizures and epilepsy, as well as targeted immunomodulatory treatments. In children, immune-mediated seizures often present acutely in the setting of autoimmune encephalitis and are very responsive to immunotherapy with low rates of subsequent epilepsy. Conversely, seizures in autoimmune-associated epilepsies, such as Rasmussen syndrome, can remain refractory to multimodal therapy, including immunomodulation. In this review, the authors discuss the presentations of immune-mediated seizures in children, underlying mechanisms, and emerging therapies.

Rasmussen's Encephalitis: A Literary Review

Usually affecting one hemisphere of the brain, Rasmussen's encephalitis (RE) is a persistent inflammatory disease of unclear origin. Rasmussen and colleagues presumed a viral etiology of the sickness in their first description. Later, the condition was linked to autoantibodies that were in the blood. Recently, it was shown that the cause of RE was a cytotoxic T-cell reaction to neurons. RE may be identified histopathologically by cortical inflammation, neuronal degeneration, and cerebral hemispheric-specific gliosis. The hemisphere is affected by increasing multilocular inflammation. To diagnose patients sooner and to evaluate whether the aforementioned phenomena are primary or secondary, it is essential to continue the search for a primary immunological or viral component. This information is crucial for determining the effectiveness of immunotherapy. RE-related seizures can only now be managed surgically. The only procedure that works is complete hemispheric disconnection (hemidisconnection), which may be done as either a (functional) hemispherectomy or hemispherectomy. Although thalidomide has been anecdotally reported, its safety profile prevents it from being used as a first-line treatment despite having a noticeable effect on the frequency and severity of seizures. Finding the disease's root causes more quickly by combining descriptive clinical studies, genetic testing, and early histological evaluation of RE tissue specimens to check for viral and autoimmune pathogenesis. Creating appropriate in vitro or animal models will enable the study of causality, perhaps directing clinical trials.

Progress in pathogenesis and therapy of Rasmussen's encephalitis

Rasmussen's encephalitis (RE) is a rare condition of unknown etiology that causes a severe chronically neurological disorder with mostly affecting children. The main clinical feature of RE includes frequent seizures with drug-resistant, unilateral hemispheric atrophy, and progressive neurological deficits. In this review, we summarized five pathogenesis on the basis of the current research including virus infection, antibody-mediated degeneration, cell-mediated immunity, microglia-induced degeneration, and genetic mutations. So far, no exact virus in RE brain tissue or definite antigen in humoral immune system was confirmed as the determined etiology. The importance of cytotoxic CD8⁺ T lymphocytes and activated microglial and the role of their immune mechanism in RE development are gradually emerging with the deep study. Genetic researches support the notion that the pathogenesis of RE is probably associated with single nucleotide polymorphisms on immune-related genes, which is driven by affecting inherent antiretroviral innate immunity. Recent advances in treatment suggest immunotherapy could partially slows down the progression of RE according to the histopathology and clinical presentation, which aimed at the initial damage to the brain by T cells and microglia in the early stage. However, the cerebral hemispherectomy is an effective means to controlling the intractable seizure, which is accompanied by neurological complications inevitably. So, the optimal timing for surgical intervention is still a challenge for RE patient. On the contrary, exploration on other aspects of pathogenesis such as dysfunction of adenosine system may offer a new therapeutic option for the treatment of RE in future.

The role of astrocytes in neuropathic pain

Neuropathic pain, whose symptoms are characterized by spontaneous and irritation-induced painful sensations, is a condition that poses a global burden. Numerous neurotransmitters and other chemicals play a role in the emergence and maintenance of neuropathic pain, which is strongly correlated with common clinical challenges, such as chronic pain and depression. However, the mechanism underlying its occurrence and development has not yet been fully elucidated, thus rendering the use of traditional painkillers, such as non-steroidal anti-inflammatory medications and opioids, relatively ineffective in its treatment. Astrocytes, which are abundant and occupy the largest volume in the central nervous system, contribute to physiological and pathological situations. In recent years, an increasing number of researchers have claimed that astrocytes contribute indispensably to the occurrence and progression of neuropathic pain. The activation of reactive astrocytes involves a variety of signal transduction mechanisms and molecules. Signal molecules in cells, including intracellular kinases, channels, receptors, and transcription factors, tend to play a role in regulating post-injury pain once they exhibit pathological changes. In addition, astrocytes regulate neuropathic pain by releasing a series of mediators of different molecular weights, actively participating in the regulation of neurons and synapses, which are associated with the onset and general maintenance of neuropathic pain. This review summarizes the progress made in elucidating the mechanism underlying the involvement of astrocytes in neuropathic pain regulation.

Rasmussen's encephalitis: Early diagnostic criteria in children

Rasmussen's encephalitis (RE) is a rare chronic inflammatory brain disorder resulting in progressive neurodegeneration in one cerebral hemisphere. The inflammatory process is accompanied by progressive loss of function of the affected hemisphere, associated with drug-resistant partial epilepsy. The diagnosis is based on a range of clinical, electroencephalographic, radiological and biochemical arguments, without any specific formal marker, which makes the diagnosis of the disease complex, especially in its initial phase. Seizures are refractory to anti-seizures medication (ASM) and to classical immunomodulatory treatments. These treatments are also ineffective to stop the degenerative process. Only surgical treatment with hemispherotomy (surgical disconnection of a cerebral hemisphere) allows definitive cessation of seizures but this leads to definitive motor and cognitive deficits. The etiology of RE is not known, but there is strong evidence for an immunopathogenic mechanism involving T-cell mediated immunity. The emergence of biotherapies targeting against various cytokines offers potential therapeutic perspectives. This disease is currently a real challenge in terms of: (i) early diagnosis, before the constitution of marked hemispheric atrophy and the appearance of neurological and cognitive consequences; (ii) recognition of incomplete form; (iii) therapeutic management due to advances in the field of targeted treatment of inflammation; (iv) surgery and recovery possibilities.

Factors not considered in the study of drug-resistant epilepsy: Drug-resistant epilepsy: assessment of neuroinflammation

More than one‐third of people with epilepsy develop drug‐resistant epilepsy (DRE). Different hypotheses have been proposed to explain the origin of DRE. Accumulating evidence suggests the contribution of neuroinflammation, modifications in the integrity of the blood‐brain barrier (BBB), and altered immune responses in the pathophysiology of DRE. The inflammatory response is mainly due to the increase of cytokines and related molecules; these molecules have neuromodulatory effects that contribute to hyperexcitability in neural networks that cause seizure generation. Some patients with DRE display the presence of autoantibodies in the serum and mainly cerebrospinal fluid. These patients are refractory to the different treatments with standard antiseizure medications (ASMs), and they could be responding well to immunomodulatory therapies. This observation emphasizes that the etiopathogenesis of DRE is involved with immunology responses and associated long‐term events and chronic inflammation processes. Furthermore, multiple studies have shown that functional polymorphisms as risk factors are involved in inflammation processes. Several relevant polymorphisms could be considered risk factors involved in inflammation‐related DRE such as receptor for advanced glycation end products (RAGE) and interleukin 1β (IL‐1β). All these evidences sustained the hypothesis that the chronic inflammation process is associated with the DRE. However, the effect of the chronic inflammation process should be investigated in further clinical studies to promote the development of novel therapeutics useful in treatment of DRE.

The role of astrocytes in epileptic disorders

Epilepsy affects about 1% of the population and approximately 30% of epileptic patients are resistant to current antiepileptic drugs. As a hallmark in epileptic tissue, many of the epileptic patients show changes in glia morphology and function. There are characteristic changes in different types of glia in different epilepsy models. Some of these changes such as astrogliosis are enough to provoke epileptic seizures. Astrogliosis is well known in mesial temporal lobe epilepsy (MTLE), the most common form of refractory epilepsy. A better understanding of astrocytes alterations could lead to novel and efficient pharmacological approaches for epilepsy. In this review, we present the alterations of astrocyte morphology and function and present some instances of targeting astrocytes in seizure and epilepsy.

Neuronal Presentation of Antigen and Its Possible Role in Parkinson's Disease

Patients with Parkinson's disease (PD) and other synucleinopathies often exhibit autoimmune features, including CD4+ and some CD8+ T lymphocytes that recognize epitopes derived from alpha-synuclein. While neurons have long been considered to not present antigens, recent data indicate that they can be induced to do so, particularly in response to interferons and other forms of stress. Here, we review literature on neuronal antigen presentation and its potential role in PD. Although direct evidence for CD8+ T cell-mediated neuronal death is lacking in PD, neuronal antigen presentation appears central to the pathology of Rasmussen's encephalitis, a pediatric neurological disorder driven by cytotoxic T cell infiltration and neuroinflammation. Emerging data suggest that T cells enter the brain in PD and other synucleinopathies, where the majority of neuromelanin-containing substantia nigra and locus coeruleus neurons express MHC Class I molecules. In cell culture, CD8+ T cell recognition of antigen:MHC Class I complexes on neuronal membranes leads to cytotoxic responses and neuronal cell death. Recent animal models suggest the possibility of T cell autoreactivity to mitochondrial antigens in PD. It remains unclear if neuronal antigen presentation plays a role in PD or other neurodegenerative disorders, and efforts are underway to better elucidate the potential impact of autoimmune responses on neurodegeneration.

Increased inflammasome-activated pyroptosis mediated by caspase-1 in Rasmussen's encephalitis

BACKGROUND

Rasmussen's encephalitis (RE) is a rare, progressive disease characterized by unilateral cerebral hemisphere atrophy. Studies showed that inflammatory response and overexpressed chemokines were present in RE patients. The present study aims to determine whether caspase-1- mediated neuronal pyroptosis occurred in RE.

METHODS

Immunohistochemistry and Western blotting analysis were used to examine the expression of Gasdermin D (GSDMD), NOD-like receptor protein 1 (NLRP1), NOD-like receptor protein 3 (NLRP3), caspase-1, and pro-caspase-1 in RE and control cortical specimens (n = 14). Perilesional tissue specimens from six focal cortical dysplasia (FCD) cases were used as controls. Double staining showed the colocalization of GSDMD, NLRP1, NLRP3 and caspase-1. Enzyme-linked immunosorbent assay (ELISA) was used to quantify the amount of interleukin (IL)-1β and IL-18 in RE cortical specimens.

RESULTS

Compared with the control cortex, we found higher GSDMD expression in the cytoplasm of neurons in RE cortex but no detectable expression in astrocytes and microglia. Further analysis revealed that NLRP1, NLRP3, caspase-1 and its precursor pro-caspase-1 were also upregulated in the RE, and predominantly localized in the cytoplasm of the neurons. In addition, significantly higher levels of IL-1β and IL-18 were present in the RE group compared with the control group.

CONCLUSION

Our results suggest that pyroptosis represents an important pathway for neuronal loss in the pathological processes associated with RE, and that targeting the canonical inflammasome pathway of pyroptosis may provide potential therapeutic value for RE.

Impact of T cells on neurodegeneration in anti-GAD65 limbic encephalitis

Objective

Direct pathogenic effects of autoantibodies to the 65 kDa isoform of glutamic acid decarboxylase (GAD65) in autoimmune limbic encephalitis (LE) have been questioned due to its intracellular localization. We therefore hypothesized a pathogenic role for T cells.

Methods

We assessed magnet resonance imaging, neuropsychological and peripheral blood, and CSF flow cytometry data of 10 patients with long‐standing GAD65‐LE compared to controls in a cross‐sectional manner. These data were related to each other within the GAD65‐LE group and linked to neuropathological findings in selective hippocampectomy specimen from another two patients. In addition, full‐resolution human leukocyte antigen (HLA) genotyping of all patients was performed.

Results

Compared to controls, no alteration in hippocampal volume but impaired memory function and elevated fractions of activated HLADR⁺ CD4⁺ and CD8⁺ T cells in peripheral blood and cerebrospinal fluid were found. Intrathecal fractions of CD8⁺ T cells negatively correlated with hippocampal volume and memory function, whereas the opposite was true for CD4⁺ T cells. Consistently, antigen‐experienced CD8⁺ T cells expressed increased levels of the cytotoxic effector molecule perforin in peripheral blood, and perforin‐expressing CD8⁺ T cells were found attached mainly to small interneurons but also to large principal neurons together with wide‐spread hippocampal neurodegeneration. 6/10 LE patients harbored the HLA‐A*02:01 allele known to present the immunodominant GAD65_114–123 peptide in humans.

Interpretation

Our data suggest a pathogenic effect of CD8⁺ T cells and a regulatory effect of CD4⁺ T cells in patients with long‐standing GAD65‐LE.

Rasmussen encephalitis: Predisposing factors and their potential role in unilaterality

OBJECTIVE

Rasmussen encephalitis (RE) is a progressive and destructive inflammatory disease of one hemisphere. Its cause is unknown. We investigated comorbidity and laterality factors that might predispose to RE.

METHODS

We retrospectively compared the histories of 160 RE patients to those with genetic generalized epilepsy (n = 154) and those with focal cortical dysplasia Type II (FCD II; n = 148).

RESULTS

The median/mean age at symptom onset in RE was 7/10 years (range = 1-53 years), and 58.1% of the patients were female. The female sex predominated in RE patients, with age > 7 years at disease manifestation. The left hemisphere was affected in 65.6%. Perinatal complications (preterm birth, twin pregnancies, early acquired brain lesions) were more frequent in RE than in control patients. Ipsilateral facial autoimmune conditions (scleroderma en coup de sabre, uveitis, or chorioretinitis) were only observed in RE patients (6.9%). Onset of RE was more frequently associated with fever than that of FCD II. In 33.1% of RE patients, ≥1 potential risk factor was found. Interestingly, 11.9% of patients had one-sided early brain lesions or facial autoimmune lesions ipsilateral to subsequent RE; none had such a lesion contralaterally.

SIGNIFICANCE

Perinatal complications and facial autoimmune conditions may act as predisposing factors for RE. Fever might trigger RE manifestation. Further genetic or infectious contributors may be identified in the future. Single or combined hits may be required to elicit or facilitate the start of the disease. Ipsilateral early comorbid lesions or facial autoimmune processes might in part explain the enigmatic unilaterality of RE.

Glia and extracellular matrix molecules: What are their importance for the electrographic and MRI changes in the epileptogenic zone?

Glial cells and extracellular matrix (ECM) molecules are crucial for the maintenance of brain homeostasis. Especially because of their actions regarding neurotransmitter and ionic control, and synaptic function, these cells can potentially contribute to the hyperexcitability seen in the epileptogenic, while ECM changes are linked to synaptic reorganization. The present review will explore glial and ECM homeostatic roles and their potential contribution to tissue plasticity. Finally, we will address how glial, and ECM changes in the epileptogenic zone can be seen in magnetic resonance imaging (MRI), pointing out their importance as markers for the extension of the epileptogenic area. This article is part of the Special Issue "NEWroscience 2018".

The CD8 T Cell-Epstein-Barr Virus-B Cell Trialogue: A Central Issue in Multiple Sclerosis Pathogenesis

The cause and the pathogenic mechanisms leading to multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system (CNS), are still under scrutiny. During the last decade, awareness has increased that multiple genetic and environmental factors act in concert to modulate MS risk. Likewise, the landscape of cells of the adaptive immune system that are believed to play a role in MS immunopathogenesis has expanded by including not only CD4 T helper cells but also cytotoxic CD8 T cells and B cells. Once the key cellular players are identified, the main challenge is to define precisely how they act and interact to induce neuroinflammation and the neurodegenerative cascade in MS. CD8 T cells have been implicated in MS pathogenesis since the 80's when it was shown that CD8 T cells predominate in MS brain lesions. Interest in the role of CD8 T cells in MS was revived in 2000 and the years thereafter by studies showing that CNS-recruited CD8 T cells are clonally expanded and have a memory effector phenotype indicating in situ antigen-driven reactivation. The association of certain MHC class I alleles with MS genetic risk implicates CD8 T cells in disease pathogenesis. Moreover, experimental studies have highlighted the detrimental effects of CD8 T cell activation on neural cells. While the antigens responsible for T cell recruitment and activation in the CNS remain elusive, the high efficacy of B-cell depleting drugs in MS and a growing number of studies implicate B cells and Epstein-Barr virus (EBV), a B-lymphotropic herpesvirus that is strongly associated with MS, in the activation of pathogenic T cells. This article reviews the results of human studies that have contributed to elucidate the role of CD8 T cells in MS immunopathogenesis, and discusses them in light of current understanding of autoreactivity, B-cell and EBV involvement in MS, and mechanism of action of different MS treatments. Based on the available evidences, an immunopathological model of MS is proposed that entails a persistent EBV infection of CNS-infiltrating B cells as the target of a dysregulated cytotoxic CD8 T cell response causing CNS tissue damage.

Fundamental mechanistic insights from rare but paradigmatic neuroimmunological diseases

The pathophysiology of complex neuroimmunological diseases, such as multiple sclerosis and autoimmune encephalitis, remains puzzling - various mechanisms that are difficult to dissect seem to contribute, hampering the understanding of the processes involved. Some rare neuroimmunological diseases are easier to study because their presentation and pathogenesis are more homogeneous. The investigation of these diseases can provide fundamental insights into neuroimmunological pathomechanisms that can in turn be applied to more complex diseases. In this Review, we summarize key mechanistic insights into three such rare but paradigmatic neuroimmunological diseases - Susac syndrome, Rasmussen encephalitis and narcolepsy type 1 - and consider the implications of these insights for the study of other neuroimmunological diseases. In these diseases, the combination of findings in humans, different modalities of investigation and animal models has enabled the triangulation of evidence to validate and consolidate the pathomechanistic features and to develop diagnostic and therapeutic strategies; this approach has provided insights that are directly relevant to other neuroimmunological diseases and applicable in other contexts. We also outline how next-generation technologies and refined animal models can further improve our understanding of pathomechanisms, including cell-specific and antigen-specific CNS immune responses, thereby paving the way for the development of targeted therapeutic approaches.

Brain astrocytes and microglia express functional MR1 molecules that present microbial antigens to mucosal-associated invariant T (MAIT) cells

It is unknown whether brain astrocytes and microglia have the capacity to present microbial antigens via the innate immune MR1/MAIT cell axis. We have detected MAIT cells in the normal mouse brain and found that both astrocytes and microglia are MR1⁺. When we stimulated brain astrocytes and microglia with E. coli, and then co-cultured them with MAIT cells, MR1 surface expression was upregulated and MAIT cells were activated in an antigen-dependent manner. Considering the association of MAIT cells with inflammatory conditions, including those in the CNS, the MR1/MAIT cell axis could be a novel therapeutic target in neuroinflammatory disorders.

Rasmussen's encephalitis: mechanisms update and potential therapy target

Rasmussen’s encephalitis (RE) is rare neurological diseases characterized as epilepsia partialis continua, invariably hemiparesis, and cognitive impairment. This disease is encountered frequently in childhood and presents with progressive atrophy of the unilateral hemisphere, and there are also sustained neurological complications. Owing to uncertain pathogenesis, the most effective way to limit the influence of seizures currently is cerebral hemispherectomy. In this review, we focus on four main lines of pathogenesis: virus infection, antibody-mediated, cell-mediated immunity, and microglia activation. Although one or more antigenic epitopes may give rise to infiltrating T cell responses in RE brain tissue, no exact antigen was confirmed as the definite cause of the disease. On the other hand, the appearance of antibodies related with RE seem to be a secondary pathological process. Synthetic studies have suggested an adaptive immune mechanism mediated by CD8⁺ T cells and an innate immune mechanism mediated by activated microglia and neuroglia. Accordingly, opinions have been raised that immunomodulatory treatments aimed at initial damage to the brain that are induced by cytotoxic CD8⁺ T cell lymphocytes and microglia in the early stage of RE slow down disease progression. However, systematic exploration of the theory behind these therapeutic effects based on multicenter and large sample studies are needed. In addition, dysfunction of the adenosine system, including the main adenosine removing enzyme adenosine kinase and adenosine receptors, has been demonstrated in RE, which might provide a novel therapeutic target for treatment of RE in future.

Immunomodulation With Azathioprine Therapy in Rasmussen Syndrome: A Multimodal Evaluation

OBJECTIVE

To verify safety and efficacy of the corticosteroid-sparing drug azathioprine (AZA) in Rasmussen syndrome (RS), we retrospectively analyzed a cohort of patients with RS recruited in a single pediatric neuroscience center.

METHODS

We compared outcomes in 30 patients with RS who received AZA with 23 patients who were not treated with this drug. We used a multimodal approach to correlate therapy with clinical features (seizures, epilepsia partialis continua [EPC], hemiparesis) and neuroimaging markers of progressive brain atrophy.

RESULTS

AZA was well tolerated; only 1 patient discontinued treatment due to pancytopenia. In 27 of 30 patients receiving AZA, all of whom were corticosteroid responders, corticosteroid therapy could be weaned or reduced without worsening of seizures in 89%. Patients receiving AZA had a lower prevalence of EPC (42% vs 67% in controls) and hemiparesis (64% vs 92%, respectively). Cox regression showed for the AZA group compared to controls a delayed time to (1) EPC (≈2 years, exp[B] = 0.295, 95% confidence interval [CI] 0.108-0.807; p = 0.017), (2) hemiparesis (≈1 year, exp[B] = 0.315, 95% CI 0.137-0.724; p = 0.007), and (3) surgery (≈2 years, exp[B] = 2.068, 95% CI 1.012-4.227; p = 0.046). However, there were no group differences in cognitive decline over time (IQ change per year) or in hemispheric gray matter atrophy on serial MRI scans.

CONCLUSION

AZA treatment appears to slow clinical progression of RS in steroid responders; this will give the greatest advantage in patients in the early stages of the disease in whom surgical decision-making may require further time.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that for pediatric patients with RS AZA is well tolerated and slows hemiparesis and appearance of EPC.

An immunotherapy effect analysis in Rasmussen encephalitis

Background

Immune-mediated mechanisms substantially contribute to the Rasmussen encephalitis (RE) pathology, but for unknown reasons, immunotherapy is generally ineffective in patients who have already developed intractable epilepsy; overall laboratory data regarding the effect of immunotherapy on patients with RE are limited. We analyzed multiple samples from seven differently treated children with RE and evaluated the effects of immunotherapies on neuroinflammation. Immunotherapy was introduced to all patients at the time of intractable epilepsy and they all had to undergo hemispherothomy.

Methods

Immunohistochemistry, flow cytometry, Luminex multiplex bead and enzyme-linked immunosorbent assay techniques were combined to determine: 1) inflammatory changes and lymphocyte subpopulations in 45 brain tissues; 2) lymphocyte subpopulations and the levels of 12 chemokines/cytokines in 24 cerebrospinal fluid (CSF) samples and 30 blood samples; and 3) the dynamics of these parameters in four RE patients from whom multiple samples were collected.

Results

Sustained T cell-targeted therapy with cyclophosphamide, natalizumab, alemtuzumab, and intrathecal methotrexate (ITMTX), but not with azathioprine, substantially reduced inflammation in brain tissues. Despite the therapy, the distributions of CD8⁺ T cells and the levels of C-X-C motif ligand (CXCL) 10, CXCL13, and B cell activating factor (BAFF) in patients’ CSF remained increased compared to controls. A therapeutic approach combining alemtuzumab and ITMTX was the most effective in producing simultaneous reductions in histopathological inflammatory findings and in the numbers of activated CD8⁺ T cells in the brain tissue, as well as in the overall CD8⁺ T cell population and chemokine/cytokine production in the CSF.

Conclusions

We provide evidence that various T cell-targeted immunotherapies reduced inflammation in the brains of RE patients. The observation that intractable epilepsy persisted in all of the patients suggests a relative independence of seizure activity on the presence of T cells in the brain later in the disease course. Thus, new therapeutic targets must be identified. CXCL10, CXCL13 and BAFF levels were substantially increased in CSF from all patients and their significance in RE pathology remains to be addressed.

Interleukin 4 Affects Epilepsy by Regulating Glial Cells: Potential and Possible Mechanism

Epilepsy is a chronic brain dysfunction induced by an abnormal neuronal discharge that is caused by complicated psychopathologies. Recently, accumulating studies have revealed a close relationship between inflammation and epilepsy. Specifically, microglia and astrocytes are important inflammatory cells in the central nervous system (CNS) that have been proven to be related to the pathogenesis and development of epilepsy. Additionally, interleukin 4 (IL-4) is an anti-inflammatory factor that can regulate microglia and astrocytes in many aspects. This review article focuses on the regulatory role of IL-4 in the pathological changes of glial cells related to epilepsy. We additionally propose that IL-4 may play a protective role in epileptogenesis and suggest that IL-4 may be a novel therapeutic target for the treatment of epilepsy.

Autoimmune seizures and epilepsy

The rapid expansion in the number of encephalitis disorders associated with autoantibodies against neuronal proteins has led to an incremental increase in use of the term "autoimmune epilepsy," yet has occurred with limited attention to the physiopathology of each disease and genuine propensity to develop epilepsy. Indeed, most autoimmune encephalitides present with seizures, but the probability of evolving to epilepsy is relatively small. The risk of epilepsy is higher for disorders in which the antigens are intracellular (often T cell-mediated) compared with disorders in which the antigens are on the cell surface (antibody-mediated). Most autoantibodies against neuronal surface antigens show robust effects on the target proteins, resulting in hyperexcitability and impairment of synaptic function and plasticity. Here, we trace the evolution of the concept of autoimmune epilepsy and examine common inflammatory pathways that might lead to epilepsy. Then, we focus on several antibody-mediated encephalitis disorders that associate with seizures and review the synaptic alterations caused by patients' antibodies, with emphasis on those that have been modeled in animals (e.g., antibodies against NMDA, AMPA receptors, LGI1 protein) or in cultured neurons (e.g., antibodies against the GABAb receptor).

Understanding Childhood Neuroimmune Diseases of the Central Nervous System

Immune-mediated diseases of the central nervous system (CNS) in childhood are a heterogeneous group of rare conditions sharing the inflammatory involvement of the CNS. This review highlights the growing knowledge of childhood neuroimmune diseases that primarily affect the CNS, outlining the clinical and diagnostic features, the pathobiological mechanisms and genetics, current treatment options, and emerging challenges. The clinical spectrum of these conditions is increasingly expanded, and the underlying mechanisms of dysregulation of the immune system could vary widely. Cell-mediated and antibody-mediated disorders, infection-triggered and paraneoplastic conditions, and genetically defined mechanisms can occur in previously healthy children and can contribute to different stages of the disease. The careful evaluation of the clinical presentation and temporal course of symptoms, the specific neuroimaging and immunological findings, and the exclusion of alternative causes are mandatory in clinical practice for the syndromic diagnosis. A common feature of these conditions is that immunotherapeutic agents could modulate the clinical course and outcomes of the disease. Furthermore, specific symptomatic treatments and comprehensive multidisciplinary care are needed in the overall management. We focus on recent advances on immune-mediated demyelinating CNS disorders, autoimmune encephalitis, interferonopathies, and possible neuroimmune disorders as Rasmussen encephalitis. Better knowledge of these conditions could allow prompt diagnosis and targeted immunotherapy, to decrease morbidity and mortality as well as to improve clinical outcomes, reducing the burden of the disease due to possible long-term neuropsychiatric sequelae. Persisting controversies remain in the rigorous characterization of each specific clinical entity because of the relative rarity in children; moreover, in a large proportion of suspected neuroimmune diseases, the immune "signature" remains unidentified; treatment guidelines are mostly based on retrospective cohort studies and expert opinions; then advances in specific molecular therapies are required. In the future, a better characterization of specific immunological biomarkers may provide a useful understanding of the underlying pathobiological mechanisms of these conditions in order to individualize more tailored therapeutic options and paradigms. Multicenter collaborative research on homogeneous groups of patients who may undergo immunological studies and therapeutic trials could improve the characterization of the underlying mechanisms, the specific phenotypes, and tailored management.

Proliferative hippocampal activity in a group of patients with Rasmussen's encephalitis: Neuronal, glial, and BDNF tissue expression correlations

Rasmussen's encephalitis (RE) is a rare and devastating unilateral inflammatory brain disease that causes severe and intractable partial epilepsy. It has been shown that epilepsy and subsequent inflammation have deleterious influence on hippocampal cell survival and neurogenesis, but this still has not been systematically explored in human tissue. In this study, we investigated the correlation between inflammation and epilepsy as well as the rates of hippocampal gliogenesis and neurogenesis in a pediatric group of six patients with RE and six control cases. The dentate gyrus (DG) samples were obtained from patients who underwent surgery for intractable RE. Sections were processed for immunohistochemistry using antibodies against sex determining region Y-box 2 (Sox2), nestin, human protein encoded by MKI67 gen (Ki67), and brain-derived neurotrophic factor (BDNF). There was an increase in the number of Ki67-positive granule cells in the DG of patients with RE in comparison with the autopsy control group, but no statistical difference for Sox2-positive cells was observed between these groups. Nestin immunolabeling was less intense in the RE group while BDNF expression was increased. Neurons that were BDNF-positive were found in DG from patients with RE but not in the control group. In patients with RE, few nestin-positive cells in DG were also positive for BDNF, unlike in controls which showed no colocalization for these two markers. These results suggest a proliferation activity in the DG subfield of patients with RE, and also future studies are necessary to address the role of new cells in the hippocampus of patients with RE.

Humanized mouse model of Rasmussen's encephalitis supports the immune-mediated hypothesis

Rasmussen's encephalitis (RE) is a chronic inflammatory brain disorder that causes frequent seizures and unilateral hemispheric atrophy with progressive neurological deficits. Hemispherectomy remains the only treatment that leads to seizure freedom for this refractory epileptic syndrome. The absence of an animal model of disease has been a major obstacle hampering the development of effective therapies. Here, we describe an experimental mouse model that shares several clinical and pathological features with the human disease. Immunodeficient mice injected with peripheral blood mononuclear cells from RE patients and monitored by video electroencephalography developed severe seizures of cortical origin and showed intense astrogliosis and accumulation of human IFN-γ- and granzyme B-expressing T lymphocytes in the brain compared with mice injected with immune cells from control subjects. We also provide evidence for the efficacy of α4 integrin blockade, an approved therapy for the treatment of multiple sclerosis and Crohn's disease, in reducing inflammatory markers associated with RE in the CNS. This model holds promise as a valuable tool for understanding the pathology of RE and for developing patient-tailored experimental therapeutics.

Phenotypic and functional complexity of brain-infiltrating T cells in Rasmussen encephalitis

Objective:

To characterize the brain-infiltrating immune cell repertoire in Rasmussen encephalitis (RE) with special focus on the subsets, clonality, and their cytokine profile.

Methods:

The immune cell infiltrate of freshly isolated brain tissue from RE was phenotypically and functionally characterized using immunohistology, flow cytometry, and T-cell receptor (TCR) deep sequencing. Identification of clonally expanded T-cell clones (TCCs) was achieved by combining flow cytometry sorting of CD4⁺ and CD8⁺ T cells and high-throughput TCR Vβ-chain sequencing. The most abundant brain-infiltrating TCCs were isolated and functionally characterized.

Results:

We found that CD4⁺, CD8⁺, and also γδ T cells infiltrate the brain tissue in RE. Further analysis surprisingly revealed that not only brain-infiltrating CD8⁺ but also CD4⁺ T cells are clonally expanded in RE. All 3 subsets exhibited a Tc1/Th1 phenotype characterized by the production of interferon (IFN)-γ and TNF. Broad cytokine profiling at the clonal level showed strong production of IFN-γ and TNF and also secretion of interleukin (IL)-5, IL-13, and granzyme B, both in CD4⁺ and CD8⁺ T cells.

Conclusions:

CD8⁺ T cells were until now considered the central players in the immunopathogenesis of RE. Our study adds to previous findings and highlights that CD4⁺ TCCs and γδ T cells that secrete IFN-γ and TNF are also involved. These findings underline the complexity of T-cell immunity in RE and suggest a specific role for CD4⁺ T cells in orchestrating the CD8⁺ T-cell effector immune response.

Mycophenolate mofetil prevents the delayed T cell response after pilocarpine-induced status epilepticus in mice

Growing clinical and laboratory evidence corroborates a role for the immune system in the pathophysiology of epilepsy. In order to delineate the immune response following pilocarpine-induced status epilepticus (SE) in the mouse, we monitored the kinetics of leukocyte presence in the hippocampus over the period of four weeks. SE was induced following a ramping protocol of pilocarpine injection into 4–5 weeks old C57BL/6 mice. Brains were removed at days 1–4, 14 or 28 after SE, and the hippocampi were analyzed via flow cytometry, via quantitative reverse transcriptase PCR (qRT-PCR) and via immunohistochemistry. Epileptogenesis was confirmed by Timm staining of mossy fiber sprouting in the inner molecular layer of the dentate gyrus. The flow cytometry data revealed a biphasic immune response following pilocarpine-induced SE with a transient increase in activated CD11b⁺ and F4/80⁺ macrophages within the first four days replaced by an increase in CD3⁺ T-lymphocytes around day 28. This delayed T cell response was confirmed via qRT-PCR and via immunohistochemistry. In addition, qRT-PCR data could show that the delayed T cell response was associated with an increased CD8/CD4 ratio indicating a cytotoxic T cell response after SE. Intriguingly, early intervention with mycophenolate mofetil administration on days 0–3 after SE prevented this delayed T cell response. These results show an orchestrated immunological sequela and provide evidence that the delayed T cell response is sensitive to early immunomodulatory intervention.

A Case Series of Adult-Onset Rasmussen's Encephalitis: Diagnostic and Therapeutic Challenges

Rasmussen’s encephalitis (RE) is a rare neurologic disorder characterized by progressive cerebral hemiatrophy and medically refractory epilepsy. The majority of current literature on this topic is focused on the pediatric population. In this case series, we will review three cases of adult-onset RE, as defined by fulfillment of the 2005 Bien criteria. The diagnostic challenge of characterizing this rare disease will be highlighted by the extensive serum, CSF, and pathologic sampling in all three patients. MR imaging and EEG data will be examined over time to characterize hallmark findings as well as progression. In addition, we will review the various forms of therapy attempted in these three patients, namely anti-epileptic drug therapy and immunomodulatory therapy. We will also utilize this case series to critically evaluate the broader context of atypical presentations of this disease and the value of current diagnostic criteria.

Differences in T cell cytotoxicity and cell death mechanisms between progressive multifocal leukoencephalopathy, herpes simplex virus encephalitis and cytomegalovirus encephalitis

During the appearance of human immunodeficiency virus infection in the 1980 and the 1990s, progressive multifocal leukoencephalopathy (PML), a viral encephalitis induced by the JC virus, was the leading opportunistic brain infection. As a result of the use of modern immunomodulatory compounds such as Natalizumab and Rituximab, the number of patients with PML is once again increasing. Despite the presence of PML over decades, little is known regarding the mechanisms leading to death of infected cells and the role the immune system plays in this process. Here we compared the presence of inflammatory T cells and the targeting of infected cells by cytotoxic T cells in PML, herpes simplex virus encephalitis (HSVE) and cytomegalovirus encephalitis (CMVE). In addition, we analyzed cell death mechanisms in infected cells in these encephalitides. Our results show that large numbers of inflammatory cytotoxic T cells are present in PML lesions. Whereas in HSVE and CMVE, single or multiple appositions of CD8⁺ or granzyme-B⁺ T cells to infected cells are found, in PML such appositions are significantly less apparent. Analysis of apoptotic pathways by markers such as activated caspase-3, caspase-6, poly(ADP-ribose) polymerase-1 (PARP-1) and apoptosis-inducing factor (AIF) showed upregulation of caspase-3 and loss of caspase-6 from mitochondria in CMVE and HSVE infected cells. Infected oligodendrocytes in PML did not upregulate activated caspase-3 but instead showed translocation of PARP-1 from nucleus to cytoplasm and AIF from mitochondria to nucleus. These findings suggest that in HSVE and CMVE, cells die by caspase-mediated apoptosis induced by cytotoxic T cells. In PML, on the other hand, infected cells are not eliminated by the immune system but seem to die by virus-induced PARP and AIF translocation in a type of cell death defined as parthanatos.

Neuropathology of epilepsy

Epilepsy is one of the most common neurologic disorders, affecting about 50 million people worldwide. The disease is characterized by recurrent seizures, which are due to aberrant neuronal networks resulting in synchronous discharges. The term epilepsy encompasses a large spectrum of syndromes and diseases with different etiopathogenesis. The recent development of imaging and epilepsy surgery techniques is now enabling the identification of structural abnormalities that are part of the epileptic network, and the removal of these lesions may result in control of seizures. Access of this clinically well-characterized neurosurgical material has provided neuropathologists with the opportunity to study a variety of structural brain abnormalities associated with epilepsy, by combining traditional routine histopathologic methods with molecular genetics and functional analysis of the resected tissue. This approach has contributed greatly to a better diagnosis and classification of these structural lesions, and has provided important new insights into their pathogenesis and epileptogenesis. The present chapter provides a detailed description of the large spectrum of histopathologic findings encountered in epilepsy surgery patients, addressing in particular the nonneoplastic pathologies, including hippocampal sclerosis, malformations of cortical development, Sturge-Weber syndrome, and Rasmussen encephalitis, and reviews current knowledge regarding the underlying molecular pathomechanisms and cellular mechanisms mediating hyperexcitability.

Shared HLA Class I and II Alleles and Clonally Restricted Public and Private Brain-Infiltrating αβ T Cells in a Cohort of Rasmussen Encephalitis Surgery Patients

Rasmussen encephalitis (RE) is a rare pediatric neuroinflammatory disease characterized by intractable seizures and unilateral brain atrophy. T cell infiltrates in affected brain tissue and the presence of circulating autoantibodies in some RE patients have indicated that RE may be an autoimmune disease. The strongest genetic links to autoimmunity reside in the MHC locus, therefore, we determined the human leukocyte antigen (HLA) class I and class II alleles carried by a cohort of 24 RE surgery cases by targeted in-depth genomic sequencing. Compared with a reference population the allelic frequency of three alleles, DQA1*04:01:01, DQB1*04:02:01, and HLA-C*07:02:01:01 indicated that they might confer susceptibility to the disease. It has been reported that HLA-C*07:02 is a risk factor for Graves disease. Further, eight patients in the study cohort carried HLA-A*03:01:01:01, which has been linked to susceptibility to multiple sclerosis. Four patients carried a combination of three HLA class II alleles that has been linked to type 1 diabetes (DQA1*05:01:01:01~DQB1*02:01:01~DRB1*03:01:01:01), and five patients carried a combination of HLA class II alleles that has been linked to the risk of contracting multiple sclerosis (DQA1*01:02:01:01, DQB1*06:02:01, DRB1*15:01:01:01). We also analyzed the diversity of αβ T cells in brain and blood specimens from 14 of these RE surgery cases by sequencing the third complementarity regions (CDR3s) of rearranged T cell receptor β genes. A total of 31 unique CDR3 sequences accounted for the top 5% of all CDR3 sequences in the 14 brain specimens. Thirteen of these sequences were found in sequencing data from healthy blood donors; the remaining 18 sequences were patient specific. These observations provide evidence for the clonal expansion of public and private T cells in the brain, which might be influenced by the RE patient’s HLA haplotype.

Autoimmune Encephalitis

Antibodies to brain cell-surface proteins have recently been identified in patients whose symptoms cross the boundary between neurology and psychiatry and are associated with syndromes that are responsive to treatment with immunosuppression-based treatments. This has led to an expansion in the field of autoimmune encephalitis. The common syndromes, with particular relevance to psychiatry, are discussed, in particular the N-methyl-d-aspartate receptor antibody encephalitis syndrome, which is most often associated with a psychosis and cognitive prodrome resembling acute or first-episode psychosis. The recognition, clinical diagnosis and associations, and evidence for disease mechanisms are discussed in this brief review.

Automated MRI Volumetric Analysis in Patients with Rasmussen Syndrome

BACKGROUND AND PURPOSE

Rasmussen syndrome, also known as Rasmussen encephalitis, is typically associated with volume loss of the affected hemisphere of the brain. Our aim was to apply automated quantitative volumetric MR imaging analyses to patients diagnosed with Rasmussen encephalitis, to determine the predictive value of lobar volumetric measures and to assess regional atrophy differences as well as monitor disease progression by using these measures.

MATERIALS AND METHODS

Nineteen patients (42 scans) with diagnosed Rasmussen encephalitis were studied. We used 2 control groups: one with 42 age- and sex-matched healthy subjects and the other with 42 epileptic patients without Rasmussen encephalitis with the same disease duration as patients with Rasmussen encephalitis. Volumetric analysis was performed on T1-weighted images by using BrainSuite. Ratios of volumes from the affected hemisphere divided by those from the unaffected hemisphere were used as input to a logistic regression classifier, which was trained to discriminate patients from controls. Using the classifier, we compared the predictive accuracy of all the volumetric measures. These ratios were used to further assess regional atrophy differences and correlate with epilepsy duration.

RESULTS

Interhemispheric and frontal lobe ratios had the best prediction accuracy for separating patients with Rasmussen encephalitis from healthy controls and patient controls without Rasmussen encephalitis. The insula showed significantly more atrophy compared with all the other cortical regions. Patients with longitudinal scans showed progressive volume loss in the affected hemisphere. Atrophy of the frontal lobe and insula correlated significantly with epilepsy duration.

CONCLUSIONS

Automated quantitative volumetric analysis provides accurate separation of patients with Rasmussen encephalitis from healthy controls and epileptic patients without Rasmussen encephalitis, and thus may assist the diagnosis of Rasmussen encephalitis. Volumetric analysis could also be included as part of follow-up for patients with Rasmussen encephalitis to assess disease progression.

TSPO PIGA Ligands Promote Neurosteroidogenesis and Human Astrocyte Well-Being

The steroidogenic 18 kDa translocator protein (TSPO) is an emerging, attractive therapeutic tool for several pathological conditions of the nervous system. Here, 13 high affinity TSPO ligands belonging to our previously described N,N-dialkyl-2-phenylindol-3-ylglyoxylamide (PIGA) class were evaluated for their potential ability to affect the cellular Oxidative Metabolism Activity/Proliferation index, which is used as a measure of astrocyte well-being. The most active PIGA ligands were also assessed for steroidogenic activity in terms of pregnenolone production, and the values were related to the metabolic index in rat and human models. The results showed a positive correlation between the increase in the Oxidative Metabolism Activity/Proliferation index and the pharmacologically induced stimulation of steroidogenesis. The specific involvement of steroid molecules in mediating the metabolic effects of the PIGA ligands was demonstrated using aminoglutethimide, a specific inhibitor of the first step of steroid biosynthesis. The most promising steroidogenic PIGA ligands were the 2-naphthyl derivatives that showed a long residence time to the target, in agreement with our previous data. In conclusion, TSPO ligand-induced neurosteroidogenesis was involved in astrocyte well-being.

Metabolic Changes Following Perinatal Asphyxia: Role of Astrocytes and Their Interaction with Neurons

Perinatal Asphyxia (PA) represents an important cause of severe neurological deficits including delayed mental and motor development, epilepsy, major cognitive deficits and blindness. The interaction between neurons, astrocytes and endothelial cells plays a central role coupling energy supply with changes in neuronal activity. Traditionally, experimental research focused on neurons, whereas astrocytes have been more related to the damage mechanisms of PA. Astrocytes carry out a number of functions that are critical to normal nervous system function, including uptake of neurotransmitters, regulation of pH and ion concentrations, and metabolic support for neurons. In this work, we aim to review metabolic neuron-astrocyte interactions with the purpose of encourage further research in this area in the context of PA, which is highly complex and its mechanisms and pathways have not been fully elucidated to this day.

Sprouty2 and -4 hypomorphism promotes neuronal survival and astrocytosis in a mouse model of kainic acid induced neuronal damage

Sprouty (Spry) proteins play a key role as negative feedback inhibitors of the Ras/Raf/MAPK/ERK pathway downstream of various receptor tyrosine kinases. Among the four Sprouty isoforms, Spry2 and Spry4 are expressed in the hippocampus. In this study, possible effects of Spry2 and Spry4 hypomorphism on neurodegeneration and seizure thresholds in a mouse model of epileptogenesis was analyzed. The Spry2/4 hypomorphs exhibited stronger ERK activation which was limited to the CA3 pyramidal cell layer and to the hilar region. The seizure threshold of Spry2/4(+/-) mice was significantly reduced at naive state but no difference to wildtype mice was observed 1 month following KA treatment. Histomorphological analysis revealed that dentate granule cell dispersion (GCD) was diminished in Spry2/4(+/-) mice in the subchronic phase after KA injection. Neuronal degeneration was reduced in CA1 and CA3 principal neuron layers as well as in scattered neurons of the contralateral CA1 and hilar regions. Moreover, Spry2/4 reduction resulted in enhanced survival of somatostatin and neuropeptide Y expressing interneurons. GFAP staining intensity and number of reactive astrocytes markedly increased in lesioned areas of Spry2/4(+/-) mice as compared with wildtype mice. Taken together, although the seizure threshold is reduced in naive Spry2/4(+/-) mice, neurodegeneration and GCD is mitigated following KA induced hippocampal lesions, identifying Spry proteins as possible pharmacological targets in brain injuries resulting in neurodegeneration. The present data are consistent with the established functions of the ERK pathway in astrocyte proliferation as well as protection from neuronal cell death and suggest a novel role of Spry proteins in the migration of differentiated neurons.

CD8(+) T-cell pathogenicity in Rasmussen encephalitis elucidated by large-scale T-cell receptor sequencing

Rasmussen encephalitis (RE) is a rare paediatric epilepsy with uni-hemispheric inflammation and progressive neurological deficits. To elucidate RE immunopathology, we applied T-cell receptor (TCR) sequencing to blood (n=23), cerebrospinal fluid (n=2) and brain biopsies (n=5) of RE patients, and paediatric controls. RE patients present with peripheral CD8⁺ T-cell expansion and its strength correlates with disease severity. In addition, RE is the only paediatric epilepsy with prominent T-cell expansions in the CNS. Consistently, common clones are shared between RE patients, who also share MHC-I alleles. Public RE clones share Vβ genes and length of the CDR3. Rituximab/natalizumab/basiliximab treatment does not change TCR diversity, stem cell transplantation replaces the TCR repertoire with minimal overlap between donor and recipient, as observed in individual cases. Our study supports the hypothesis of an antigen-specific attack of peripherally expanded CD8⁺ lymphocytes against CNS structures in RE, which might be ameliorated by restricting access to the CNS.

Rasmussen Encephalitis is a rare neurological disease accompanied by inflammation and T cell infiltration in the brain. Here the authors show that the severity of this disease correlates with clonal CD8 T cell expansion.

Peripheral leukocyte profile in people with temporal lobe epilepsy reflects the associated proinflammatory state

INTRODUCTION

Markers of low-grade peripheral inflammation have been reported amongst people with epilepsy. The mechanisms underlying this phenomenon are unknown. We attempted to characterize peripheral immune cells and their activation status in people with temporal lobe epilepsy (TLE) and healthy controls.

METHODS AND RESULTS

Twenty people with TLE and 19 controls were recruited, and peripheral blood lymphocyte and monocyte subsets evaluated ex vivo by multi-color flow cytometry. People with TLE had higher expression of HLA-DR, CD69, CTLA-4, CD25, IL-23R, IFN-γ, TNF and IL-17 in CD4(+) lymphocytes than controls. Granzyme A, CTLA-4, IL-23R and IL-17 expression was also elevated in CD8(+) T cells from people with TLE. Frequency of HLA-DR in CD19(+) B cells and regulatory T cells CD4(+)CD25(+)Foxp3(+) producing IL-10 was higher in TLE when compared with controls. A negative correlation between CD4(+) expressing co-stimulatory molecules (CD69, CD25 and CTLA-4) with age at onset of seizures was found. The frequency of CD4(+)CD25(+)Foxp3(+) cells was also positively correlated with age at onset of seizures.

CONCLUSION

Immune cells of people with TLE show an activation profile, mainly in effector T cells, in line with the low-grade peripheral inflammation.

Neuropathological Techniques to Investigate Central Nervous System Sections in Multiple Sclerosis

Immunohistochemical techniques (IHC) and in situ hybridization (ISH) are widely used techniques to study the expression of proteins and messenger RNAs in tissues and are extremely important to confirm and interpret biochemical and molecular results from the same tissues. Investigation of human brain by IHC and ISH therefore still plays an important role in the elucidation of pathogenetic mechanisms in diseases such as multiple sclerosis. In this review we describe the processing of human brain tissues as well as basic and advanced immunohistochemical staining and ISH techniques used for neuropathological analysis of such pathological brains.

Immunity and Inflammation in Epilepsy

This review reports the available evidence on the activation of the innate and adaptive branches of the immune system and the related inflammatory processes in epileptic disorders and the putative pathogenic role of inflammatory processes developing in the brain, as indicated by evidence from experimental and clinical research. Indeed, there is increasing knowledge supporting a role of specific inflammatory mediators and immune cells in the generation and recurrence of epileptic seizures, as well as in the associated neuropathology and comorbidities. Major challenges in this field remain: a better understanding of the key inflammatory pathogenic pathways activated in chronic epilepsy and during epileptogenesis, and how to counteract them efficiently without altering the homeostatic tissue repair function of inflammation. The relevance of this information for developing novel therapies will be highlighted.

Cell type-specific Nrf2 expression in multiple sclerosis lesions

Oxidative injury appears to play a major role in the propagation of demyelination and neurodegeneration in multiple sclerosis (MS). It has been suggested that endogenous anti-oxidant defense mechanisms within MS lesions are insufficient to prevent spreading of damage. Thus, current therapeutic approaches (e.g., fumarate treatment) target to up-regulate the expression of a key regulator of anti-oxidative defense, the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In this study, we show that Nrf2 is already strongly up-regulated in active MS lesions. Nuclear Nrf2 expression was particularly observed in oligodendrocytes and its functional activity is indicated by the expression of one of its downstream targets (heme oxygenase 1) in the same cells. In contrast, only a minor number of Nrf2-positive neurons were detected, even in highly inflammatory cortical lesions presenting with extensive oxidative injury. Overall, the most pronounced Nrf2 expression was found in degenerating cells, which showed signs of apoptotic or necrotic cell death. Via whole-genome microarray analyses of MS lesions, we observed a differential expression of numerous Nrf2-responsive genes, also involved in the defense against oxidative stress, predominantly in areas of initial myelin destruction within actively demyelinating white matter lesions. Furthermore, the expression patterns of Nrf2-induced genes differed between the white matter and cortical gray matter. Our study shows that in the MS brain, Nrf2 expression varies in different cell types and is associated with active demyelination in the lesions.

CD8(+) T Cell-Mediated Neuronal Dysfunction and Degeneration in Limbic Encephalitis

Autoimmune inflammation of the limbic gray matter structures of the human brain has recently been identified as major cause of mesial temporal lobe epilepsy with interictal temporal epileptiform activity and slowing of the electroencephalogram, progressive memory disturbances, as well as a variety of other behavioral, emotional, and cognitive changes. Magnetic resonance imaging exhibits volume and signal changes of the amygdala and hippocampus, and specific anti-neuronal antibodies binding to either intracellular or plasma membrane neuronal antigens can be detected in serum and cerebrospinal fluid. While effects of plasma cell-derived antibodies on neuronal function and integrity are increasingly becoming characterized, potentially contributing effects of T cell-mediated immune mechanisms remain poorly understood. CD8⁺ T cells are known to directly interact with major histocompatibility complex class I-expressing neurons in an antigen-specific manner. Here, we summarize current knowledge on how such direct CD8⁺ T cell–neuron interactions may impact neuronal excitability, plasticity, and integrity on a single cell and network level and provide an overview on methods to further corroborate the in vivo relevance of these mechanisms mainly obtained from in vitro studies.

Semi-quantitative analyses of antibodies to N-methyl-d-aspartate type glutamate receptor subunits (GluN2B & GluN1) in the clinical course of Rasmussen syndrome

OBJECTIVE

In Rasmussen syndrome (RS), in addition to the predominant involvement of cytotoxic T cells, heterogeneous autoantibodies against neural molecules are also found, but their function has not been elucidated. We examined antibodies to N-methyl-d-aspartate (NMDA) type glutamate receptor (GluR) subunits (GluN2B & GluN1) semi-quantitatively in cerebrospinal fluid (CSF) samples from RS patients, and evaluated their changes over time and their roles in immunopathogenesis.

METHODS

Autoantibodies against N-terminal and C-terminal of GluN2B and GluN1 were examined in 40 CSF samples collected from 18 RS patients 5 to 180 months after the onset of RS. Epileptic patients without infectious etiology or progressive clinical course served as disease controls (n=23). Synthesized peptides encoding the extracellular and intracellular domains of human GluN2B and GluN1 subunits were used as antigens in ELISA. We defined the cut-off for these antibodies as mean +2 standard deviations (optimal density) of the disease controls. MRI were evaluated according to the MRI staging proposed by Bien et al. (2002b, Neurology 58, 250).

RESULTS

CSF levels of antibodies against N-terminal and C-terminal of GluN2B were higher in RS patients than in disease controls (p<0.01). Likewise, CSF levels of antibodies against N-terminal and C-terminal of GluN1 were also higher in RS patients than in disease controls (p<0.01). All four antibodies tested were below cut-off levels in almost all CSF samples collected within one year from epilepsy onset. The proportions of CSF samples with these antibodies above cut-off levels were highest from 12 to 23 months after epilepsy onset, and declined after 24 months. CSF levels of these antibodies were higher when seizure occurred daily than when seizure occurred less frequently (p<0.01), and were higher at MRI stage 3 than at MRI stages 0, 2 and 4 (p<0.05), except for anti-GluN1-CT antibody at stage 2.

CONCLUSIONS

Broad epitope recognition spectrum and delayed production of autoantibodies to NMDA type GluR in CSF of RS patients suggest that the autoantibodies are produced against NMDA type GluR antigens derived from cytotoxic T cell-mediated neuronal damages. These antibodies may impact the pathophysiology of RS in the most active stage, and could be a marker for active inflammation in the clinical course of RS. Further studies including passive transfer of the antibodies to mice may reveal the pivotal roles of the antibodies in RS.

In Rasmussen encephalitis, hemichannels associated with microglial activation are linked to cortical pyramidal neuron coupling: a possible mechanism for cellular hyperexcitability

AIMS

Rasmussen encephalitis (RE) is a rare but devastating condition, mainly in children, characterized by sustained brain inflammation, atrophy of one cerebral hemisphere, epilepsy, and progressive cognitive deterioration. The etiology of RE-induced seizures associated with the inflammatory process remains unknown.

METHODS

Cortical tissue samples from children undergoing surgical resections for the treatment of RE (n = 16) and non-RE (n = 12) were compared using electrophysiological, morphological, and immunohistochemical techniques to examine neuronal properties and the relationship with microglial activation using the specific microglia/macrophage calcium-binding protein, IBA1 in conjunction with connexins and pannexin expression.

RESULTS

Compared with non-RE cases, pyramidal neurons from RE cases displayed increased cell capacitance and reduced input resistance. However, neuronal somatic areas were not increased in size. Instead, intracellular injection of biocytin led to increased dye coupling between neurons from RE cases. By Western blot, expression of IBA1 and pannexin was increased while connexin 32 was decreased in RE cases compared with non-RE cases. IBA1 immunostaining overlapped with pannexin and connexin 36 in RE cases.

CONCLUSIONS

In RE, these results support the notion that a possible mechanism for cellular hyperexcitability may be related to increased intercellular coupling from pannexin linked to increased microglial activation. Such findings suggest that a possible antiseizure treatment for RE may involve the use of gap junction blockers.

Focal epilepsies: immunologic and inflammatory mechanisms

There is increasing evidence documenting activation of inflammatory processes in focal epilepsies. This review article summarizes current data regarding immune mediated inflammatory processes in patients with symptomatic partial epilepsies such as mesial temporal sclerosis, focal cortical dysplasia, and Rasmussen's encephalitis. We have also reviewed several neuronal surface antibody-associated syndromes, which have been recently described with focal seizures as an important part of clinical presentation, such as antibody-associated limbic encephalitis and N-methyl-D-aspartic acid receptor antibody syndrome. An autoimmune mechanism may be one pathogenic factor in some symptomatic epilepsies acting as a triggering event in the process leading to the development of epilepsy.