Differential expression of interferon-γ and chemokine genes distinguishes Rasmussen encephalitis from cortical dysplasia and provides evidence for an early Th1 immune response Owens et al. Owens et al. Journal of Neuroinflammation 2013, 10:56 http://www.jneuroinflammation.com/content/10/1/56 Owens et al. Journal of Neuroinflammation 2013, 10:56 JOURNAL OF http://www.jneuroinflammation.com/content/10/1/56 NEUROINFLAMMATION RESEARCH Open Access Differential expression of interferon-γ and chemokine genes distinguishes Rasmussen encephalitis from cortical dysplasia and provides evidence for an early Th1 immune response Geoffrey C Owens1,7*, My N Huynh1, Julia W Chang1, David L McArthur1, Michelle J Hickey2, Harry V Vinters2,3, Gary W Mathern1,4,5,6† and Carol A Kruse1,6† Abstract Background: Rasmussen encephalitis (RE) is a rare complex inflammatory disease, primarily seen in young children, that is characterized by severe partial seizures and brain atrophy. Surgery is currently the only effective treatment option. To identify genes specifically associated with the immunopathology in RE, RNA transcripts of genes involved in inflammation and autoimmunity were measured in brain tissue from RE surgeries and compared with those in surgical specimens of cortical dysplasia (CD), a major cause of intractable pediatric epilepsy. Methods: Quantitative polymerase chain reactions measured the relative expression of 84 genes related to inflammation and autoimmunity in 12 RE specimens and in the reference group of 12 CD surgical specimens. Data were analyzed by consensus clustering using the entire dataset, and by pairwise comparison of gene expression levels between the RE and CD cohorts using the Harrell-Davis distribution-free quantile estimator method. Results: Consensus clustering identified six RE cases that were clearly distinguished from the CD cases and from other RE cases. Pairwise comparison showed that seven mRNAs encoding interferon-γ, CCL5, CCL22, CCL23, CXCL9, CXCL10, and Fas ligand were higher in the RE specimens compared with the CD specimens, whereas the mRNA encoding hypoxanthine-guanine phosphoribosyltransferase was reduced. Interferon-γ, CXCL5, CXCL9 and CXCL10 mRNA levels negatively correlated with time from seizure onset to surgery (P <0.05), whereas CCL23 and Fas ligand transcript levels positively correlated with the degree of tissue destruction and inflammation, respectively (P <0.05), as determined from magnetic resonance imaging (MRI) T2 and FLAIR images. Accumulation of CD4+ lymphocytes in leptomeninges and perivascular spaces was a prominent feature in RE specimens resected within a year of seizure onset. Conclusions: Active disease is characterized by a Th1 immune response that appears to involve both CD8+ and CD4+ T cells. Our findings suggest therapeutic intervention targeting specific chemokine/chemokine receptors may be useful in early stage RE. Keywords: Inflammation, Rasmussen encephalitis, Cortical dysplasia, Epilepsy, Gene expression, T cells, Chemokines * Correspondence: [email protected] †Equal contributors 1Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, CA, USA 7UCLA Neurosurgery, Gonda Center, Room 1554, Box 951761, Los Angeles, CA 90095, USA Full list of author information is available at the end of the article © 2013 Owens et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Owens et al. Journal of Neuroinflammation 2013, 10:56 Page 3 of 13 http://www.jneuroinflammation.com/content/10/1/56 Background and surgical procedures for collection and processing of Rasmussen encephalitis (RE) is an inflammatory neuro- cortical specimens have been previously published [26,27]. degenerative disease primarily seen in young children. It Clinical variables included, age at seizure onset, age at sur- is clinically characterized by intense focal and genera- gery, and disease progression (age at seizure onset to age lized seizures with inflammation almost invariably at surgery). Magnetic resonance imaging (MRI) scans confined to one cerebral hemisphere [1-3]. Seizure fre- were assessed by one investigator (GWM). A semiquanti- quency may decrease over time, but patients are left tative score was assigned to the T2 and FLAIR signal with unilateral hemiparesis and significant cognitive changes (0 = none, 1 = slight; 2 = mild; 3 = moderate; 4 = deficits [4,5]. Histopathologic examination of RE brain extensive) to estimate the degree of tissue destruction and tissue, usually after years of seizures, reveals the pre- inflammation, respectively. sence of activated microglia and T lymphocytes [6-8]. CD8+ T cells containing granzymes are observed in Real-time PCR and analysis close apposition to neurons and astrocytes, but not Total RNA was purified from flash frozen blocks of in- oligodendrocytes [6,9]. Auto-antibodies against the volved tissue consisting of mostly cortical gray matter glutamate receptor GluR3, once considered a possible (approximately 50 mg) using Trizol™ (Life Technologies, cause of RE [10], are not present in all RE cases and are Carlsbad, CA, USA) and reverse transcribed (Qiagen, not specific to the disease [11-13]. Circulating anti- Valencia, CA, USA). PCR reactions were carried out in bodies to other neuronal proteins are found in other RE an ABI 7300 thermocycler using SYBR™ green chemistry cases [14-16], leading to the view that a humoral im- (SABiosciences, Valencia, CA, USA). The 96-well format mune response may be a secondary event to T cell im- qPCR array contained primers for 84 genes of interest munity [6,17]. Thus, RE resembles an autoimmune and 5 reference genes (SABiosciences inflammation and disease although the histopathology is also consistent autoimmunity qPCR array, cat no. PAHS-0077Z). Stand- with an immune response to a virus or other infectious ard cycling parameters were used as follows: 1 cycle: 95°C agent [1,17]. Cytomegalovirus, herpes simplex virus, 10 min, 40 cycles: 95°C 15 sec, 60°C 1 min. As part of the and Epstein Barr virus sequences have been detected in cycling program, all PCR products were thermally dena- some RE brain specimens, but have not been reprodu- tured and dissociation curves were obtained. Two of the cibly identified in all cases [18-22]. Neither autoimmunity primer sets resulted in dissociation curves with multiple nor infection can easily explain the unilateral hemispheric peaks (CCL16 and CCL24) and were eliminated from the involvement. analysis. To calculate relative transcript levels, baseline- To gain further insight into the immunopathology of subtracted fluorescence values per cycle for each primer RE, we measured the relative expression of 84 mRNA set were entered into LinRegPCR [28] and PCR efficien- transcripts associated with inflammation and autoimmu- cies (E) and Ct values were determined. The relative nity in brain tissue from 12 RE and 12 cortical dysplasia expression of each gene (X0) [29] in each array was calcu- (CD) epilepsy patients. The CD cases constituted a refe- lated from: rence group against which to compare gene expression levels. Inflammation is associated with CD, but is less X ¼ E−Ct severe than in RE, and T cell involvement is limited 0 [23,24]. Quantitative differences in transcript levels be- tween RE and CD specimens were found for several genes NormalFinder [30] was used to identify the least variable involved in the activation and recruitment of effector T housekeeping gene across the 24 arrays. ACTB encoding cells. The highest levels of expression were found in early β-actin was found to be the most stable reference gene, stage RE cases. and was used to normalize all of the data including the four other reference genes (HPRT1, RPL13A, GAPDH, Methods B2M). Samples were grouped by consensus clustering [31] Cohort recruitment and clinical variables using the non-negative matrix factorization algorithm [32] Under University of California, Los Angeles, (UCLA) In- found in the GENE-E bioinformatics package (www. stitutional Review Board (IRB) approval, brain tissue was broadinstitute.org). Statistical analyses utilized R-project collected at surgery as part of UCLA’s Pediatric Epilepsy programs (www.r-project.org). Plots were generated Surgery program. Informed consent to use the surgically by the Deducer graphical user interface and exported resected tissue for research was obtained through the into CorelDRAW X6 (Corel Corporation, Ottawa, ON, parents or legal guardians. The 12 RE and 12 CD cases Canada). Significant differences (P <0.05) in gene expres- used in the study were selected with similar ages at sur- sion between RE and CD cases were determined by pair- gery. Seven CD cases were classified as CDI, and five as wise comparison of the distribution of transcript levels for CDII [25]. The clinical protocols for patient evaluation each gene using Harrell-Davis quantile estimators [33,34]. Owens et al. Journal of Neuroinflammation 2013, 10:56 Page 4 of 13 http://www.jneuroinflammation.com/content/10/1/56 Table 1 Summary of clinical variables for Rasmussen encephalitis (RE) and cortical dysplasia (CD) cohorts Clinical variable RE (n = 12) CD (n = 12) P value Age at surgery (years) 9.9 ± 3.1 9.2 ± 3.6 P = 0.621a Age at seizure onset (years) 6.4 ± 3.1 2.8 ± 2.4 P = 0.005a Time from onset to surgery