The Role of Autoimmunity-Related Gene CLEC16A in the B Cell Receptor-Mediated HLA Class II Pathway.

C-type lectin CLEC16A is located next to CIITA, the master transcription factor of HLA class II (HLA-II), at a susceptibility locus for several autoimmune diseases, including multiple sclerosis (MS). We previously found that CLEC16A promotes the biogenesis of HLA-II peptide-loading compartments (MIICs) in myeloid cells. Given the emerging role of B cells as APCs in these diseases, in this study, we addressed whether and how CLEC16A is involved in the BCR-dependent HLA-II pathway. CLEC16A was coexpressed with surface class II-associated invariant chain peptides (CLIP) in human EBV-positive and not EBV-negative B cell lines. Stable knockdown of CLEC16A in EBV-positive Raji B cells resulted in an upregulation of surface HLA-DR and CD74 (invariant chain), whereas CLIP was slightly but significantly reduced. In addition, IgM-mediated Salmonella uptake was decreased, and MIICs were less clustered in CLEC16A-silenced Raji cells, implying that CLEC16A controls both HLA-DR/CD74 and BCR/Ag processing in MIICs. In primary B cells, CLEC16A was only induced under CLIP-stimulating conditions in vitro and was predominantly expressed in CLIPhigh naive populations. Finally, CLIP-loaded HLA-DR molecules were abnormally enriched, and coregulation with CLEC16A was abolished in blood B cells of patients who rapidly develop MS. These findings demonstrate that CLEC16A participates in the BCR-dependent HLA-II pathway in human B cells and that this regulation is impaired during MS disease onset. The abundance of CLIP already on naive B cells of MS patients may point to a chronically induced stage and a new mechanism underlying B cell-mediated autoimmune diseases such as MS.

Pediatric autoimmune encephalitis: Recognition and diagnosis.

OBJECTIVE: The aims of this study were (1) to describe the incidence of autoimmune encephalitis (AIE) and acute disseminated encephalomyelitis (ADEM) in children, (2) to validate the currently used clinical criteria to diagnose AIE, and (3) to describe pitfalls in the diagnosis of pediatric autoimmune (AI) and inflammatory neurologic disorders. METHODS: This study cohort consists of 3 patient categories: (1) children with antibody-mediated AIE (n = 21), (2) children with ADEM (n = 32), and (3) children with suspicion of an AI etiology of their neurologic symptoms (n = 60). Baseline and follow-up clinical data were used to validate the current guideline to diagnose AIE. In addition, patient files and final diagnoses were reviewed. RESULTS: One-hundred three of the 113 included patients fulfilled the criteria of possible AIE. Twenty-one children had antibody-mediated AIE, of whom 19 had anti-N-methyl-D-aspartate receptor (NMDAR), 1 had anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, and 1 had anti-leucine-rich glioma-inactivated protein 1 encephalitis. Finally, 34 children had ADEM, and 2 children had Hashimoto encephalopathy. Mean incidence rates were 1.54 children/million (95% CI 0.95-2.35) for antibody-mediated AIE and 2.49 children/million (95% CI 1.73-3.48) for ADEM. Of the other 48 children, treating physicians' diagnoses were reviewed. In 22% (n = 6) of children initially diagnosed as having an AI/inflammatory etiology (n = 27), no support for AI/inflammation was found. CONCLUSION: Besides anti-NMDAR encephalitis and ADEM, other AIEs are rare in children. The current guideline to diagnose AIE is also useful in children. However, in children with nonspecific symptoms, it is important to review data critically, to perform complete workup, and to consult specialized neuroinflammatory centers.

T-cell activation marker sCD27 is associated with clinically definite multiple sclerosis in childhood-acquired demyelinating syndromes.

BACKGROUND: Cerebrospinal fluid (CSF) levels of T-cell activation marker soluble CD27 (sCD27) are associated with subsequent disease activity after a first attack of suspected MS in adults. The predictive value for disease course in children with acquired demyelinating syndromes (ADS) is unknown. OBJECTIVES: To assess the predictive value of sCD27 levels for clinically definite multiple sclerosis (CDMS) diagnosis in childhood ADS. METHODS: Children <18 years with a first demyelinating event were prospectively included and followed. Soluble CD27 was determined in CSF using an enzyme-linked immunosorbent assay (ELISA). Cox regression analyses were used to calculate hazard ratios (HRs) for CDMS. RESULTS: A total of 94 ADS children were included (ADS with encephalopathy (ADS+) n = 33 and ADS without encephalopathy (ADS-) n = 61). Of the 61 ADS- children, 21 (48%) were diagnosed with CDMS during follow-up. At baseline, sCD27 levels were higher in patients with a future CDMS diagnosis ( n = 29) than in monophasic ADS+ ( n = 30), monophasic ADS- ( n = 28) and relapsing non-MS patients ( n = 7; p < 0.001). In ADS- patients, sCD27 was associated with CDMS (HR = 1.8 per 100 U/mL increase in sCD27 levels, p = 0.031), after adjustments for age, oligoclonal bands and the presence of dissemination in space on baseline magnetic resonance imaging (MRI). CONCLUSION: CSF sCD27 levels at first attack of demyelination were associated with CDMS diagnosis in children. This makes sCD27 a potential clinically relevant quantitative marker when performing routine CSF diagnostics.

Chemical and genetic control of IFNγ-induced MHCII expression.

The cytokine interferon-γ (IFNγ) can induce expression of MHC class II (MHCII) on many different cell types, leading to antigen presentation to CD4+ T cells and immune activation. This has also been linked to anti-tumour immunity and graft-versus-host disease. The extent of MHCII upregulation by IFNγ is cell type-dependent and under extensive control of epigenetic regulators and signalling pathways. Here, we identify novel genetic and chemical factors that control this form of MHCII expression. Loss of the oxidative stress sensor Keap1, autophagy adaptor p62/SQSTM1, ubiquitin E3-ligase Cullin-3 and chromatin remodeller BPTF impair IFNγ-mediated MHCII expression. A similar phenotype is observed for arsenite, an oxidative stressor. Effects of the latter can be reversed by the inhibition of HDAC1/2, linking oxidative stress conditions to epigenetic control of MHCII expression. Furthermore, dimethyl fumarate, an antioxidant used for the treatment of several autoimmune diseases, impairs the IFNγ response by manipulating transcriptional control of MHCII We describe novel pathways and drugs related to oxidative conditions in cells impacting on IFNγ-mediated MHCII expression, which provide a molecular basis for the understanding of MHCII-associated diseases.

Smoking at time of CIS increases the risk of clinically definite multiple sclerosis.

BACKGROUND: Cigarette smoking is a modifiable risk factor that influences the disease course of patients with multiple sclerosis (MS). However, in patients with a clinically isolated syndrome (CIS), there are conflicting results about the association between smoking and the risk of a subsequent MS diagnosis. The aim of this study was to determine the risk of clinically definite MS (CDMS) in smoking and non-smoking patients at time of a first demyelinating event. METHODS: Two hundred and fifty patients, aged 18-50 years, were included in our prospective CIS cohort. At time of the first neurological symptoms, patients completed a questionnaire about smoking habits. Cox regression analyses were performed to calculate univariate and multivariate hazard ratios for CDMS diagnosis in smoking and non-smoking CIS patients. RESULTS: One hundred and fourteen (46%) CIS patients were diagnosed with CDMS during a mean follow-up of 58 months. In total, 79 (32%) patients smoked at time of CIS. Sixty-seven % of the smoking CIS patients were diagnosed with CDMS during follow-up compared to 36% of the non-smoking CIS patients (p < 0.001). Smoking at time of CIS was an independent predictor for CDMS diagnosis (HR 2.3; p = 0.002). Non-smoking CIS patients who had a history of smoking did not have a higher risk for CDMS than those who had never smoked. CONCLUSIONS: Smoking at time of CIS was an independent risk factor for a future CDMS diagnosis. This is an additional argument to quit smoking at time of the first attack of suspected MS.

Soluble CD27 Levels in Cerebrospinal Fluid as a Prognostic Biomarker in Clinically Isolated Syndrome.

Importance: There is a growing number of therapies that could be administered after the first symptom of central nervous system demyelination. These drugs can delay multiple sclerosis (MS) diagnosis and slow down future disability. However, treatment of patients with benign course may not be needed; therefore, there is a need for biomarkers to predict long-term prognosis in patients with clinically isolated syndrome (CIS). Objective: To investigate whether the T-cell activation marker soluble CD27 (sCD27) measured in cerebrospinal fluid of patients at time of a first attack is associated with a subsequent diagnosis of MS and a higher relapse rate. Design, Setting, and Participants: This prospective study included 77 patients with CIS between March 2002 and May 2015 in a tertiary referral center for multiple sclerosis, in collaboration with several regional hospitals. Patients with CIS underwent a lumbar puncture and magnetic resonance imaging scan within 6 months after first onset of symptoms. Main Outcomes and Measures: Soluble CD27 levels were determined in cerebrospinal fluid using a commercially available enzyme-linked immunosorbent assay. Cox regression analyses was used to calculate univariate and multivariate hazard ratios for MS diagnosis. Association between sCD27 levels and relapse rate was assessed using a negative binomial regression model. Results: Among 77 patients with CIS, 50 were female (79.5%), and mean (SD) age was 32.7 (7.4) years. Mean (SD) age in the control individuals was 33.4 (9.5) years, and 20 were female (66.7%).Patients with CIS had higher cerebrospinal fluid sCD27 levels than control individuals (geometric mean, 31.3 U/mL; 95% CI, 24.0-40.9 vs mean, 4.67 U/mL; 95% CI, 2.9-7.5; P < .001). During a mean (SD) follow-up of 54.8 (35.1) months, 39 of 77 patients (50.6%) were diagnosed as having MS. In a model adjusted for magnetic resonance imaging and cerebrospinal fluid measurements, sCD27 levels were associated with a diagnosis of MS (hazard ratio, 2.4 per 100 U/mL increase in sCD27 levels; 95% CI, 1.27-4.53; P = .007). Additionally, patients with MS with high sCD27 levels (median, >31.4 U/mL) at the time of CIS had a 5.5 times higher annualized relapse rate than patients with low sCD27 levels (annualized relapse rate, 0.06 vs 0.33; P = .02). Conclusions and Relevance: Soluble CD27 in cerebrospinal fluid of patients with CIS was associated with MS diagnosis and a high relapse rate. Therefore, sCD27 is an activation molecule directly related to the immunopathology of the disease and is a potential clinical marker to help in treatment decisions after a first attack of suspected MS.

Environmental and genetic factors in pediatric inflammatory demyelinating diseases.

The onset of multiple sclerosis (MS) occurs in childhood in about 5% of all patients with MS. The disease in adults has a complex genetic and environmental inheritability. One of the main risk factors, also confirmed in pediatric MS, is HLA DRB1*1501 In addition to genetic factors, a large part of disease susceptibility in adults is conferred by environmental risk factors such as low vitamin D status, exposure to cigarette smoking, and remote Epstein-Barr virus (EBV) infection. In children, both exposure to cigarette smoking and prior EBV infection have been reported consistently as risk factors for MS. The role of vitamin D remains to be confirmed in this age category. Finally, although very likely critical in disease processes, few gene-environment interactions and epigenetic changes have been reported for adult and pediatric MS susceptibility. Of interest, some of the risk factors for MS have also been associated with disease course modification, such as low 25(OH) vitamin D serum levels in pediatric and adult MS. Age is also a clear disease modifier of clinical, CSF, and MRI phenotype in children with the disease. Finally, although much has yet to be unraveled regarding molecular processes at play in MS, there is a larger gap in our knowledge of genetic and environmental risk factors for pediatric neuromyelitis optica spectrum disorders and acute disseminated encephalomyelitis and only collaborative studies will answer those questions.

Intrathecal CD4(+) and CD8(+) T-cell responses to endogenously synthesized candidate disease-associated human autoantigens in multiple sclerosis patients.

MS pathology is potentially orchestrated by autoreactive T cells, but the antigens recognized remain unknown. A novel APC/T-cell platform was developed to determine intrathecal CD4(+) and CD8(+) T-cell responses to candidate MS-associated autoantigens (cMSAg) in clinically isolated syndrome (CIS, n = 7) and MS (n = 6) patients. Human cMSAg encoding open reading frames (n = 8) were cloned into an Epstein-Barr virus (EBV)-based vector to express cMSAg at high levels in EBV-transformed B-cells (BLCLs). Human cMSAg cloned were myelin-associated and -oligodendrocyte glycoprotein, myelin basic protein, proteolipid protein, ATP-dependent potassium channel ATP-dependent inwards rectifying potassium channel 4.1, S100 calcium-binding protein B, contactin-2, and neurofascin. Transduced BLCLs were used as autologous APC in functional T-cell assays to determine cMSAg-specific T-cell frequencies in cerebrospinal fluid derived T-cell lines (CSF-TCLs) by intracellular IFN-γ flow cytometry. Whereas all CSF-TCL responded strongly to mitogenic stimulation, no substantial T-cell reactivity to cMSAg was observed. Contrastingly, measles virus fusion protein-specific CD4(+) and CD8(+) T-cell clones, used as control of the APC/T-cell platform, efficiently recognized transduced BLCL expressing their cognate antigen. The inability to detect substantial T-cell reactivity to eight human endogenously synthesized cMSAg in autologous APC do not support their role as prominent intrathecal T-cell target antigens in CIS and MS patients early after onset of disease.

Intrathecal CD8 T-cells of multiple sclerosis patients recognize lytic Epstein-Barr virus proteins.

BACKGROUND: The association between Epstein-Barr virus (EBV) and multiple sclerosis (MS) may involve intrathecal EBV-specific T-cell responses targeting the virus or indirectly, autoantigens. OBJECTIVE: Compare the prevalence and fine-specificity of EBV-specific T-cells in the cerebrospinal fluid (CSF) of patients with MS (n = 12), clinically-isolated syndrome (CIS) (n = 17) and other neurological diseases (OND) (n = 13). METHODS: Intrathecal EBV-specific T-cell reactivity was assayed using CSF-derived T-cell lines (CSF-TCL) and autologous EBV-transformed B-cells (autoBLCL) as antigen-presenting cells (APC). EBV proteins recognized by autoBLCL-specific CD8 T-cells were identified using human leukocyte antigen class I (HLA-I)-negative monkey cells as artificial APC, co-transfected with 59 different EBV genes and the corresponding patient's HLA-I alleles that were involved in autoBLCL T-cell reactivity. Reactivity towards the MS-associated autoantigen αB-crystallin (CRYAB) was determined analogously. RESULTS: CSF-TCL from CIS and MS patients had significantly higher frequencies of autoBLCL-reactive CD4 T-cells, compared to the OND patients. CIS patients also had significantly higher autoBLCL-reactive CD8 T cells, which correlated with reactive CD4 T-cell frequencies. AutoBLCL-specific CD8 T-cell responses of four CSF-TCL analyzed in detail were oligoclonal and directed to lytic EBV proteins, but not CRYAB endogenously expressed by autoBLCL. CONCLUSIONS: Enhanced intrathecal autoBLCL-specific T-cell reactivity, selectively directed towards lytic EBV proteins in two CSF-TCL, suggested a localized T-cell response to EBV in patients with MS. Our data warrant further characterization of the magnitude and breadth of intrathecal EBV-specific T-cell responses in larger patient cohorts.

Proteomics urine analysis of pregnant women suffering from multiple sclerosis.

Multiple sclerosis (MScl) frequently is remitted during the third trimester of pregnancy but exacerbated in the first postpartum period. In this context, we investigated protein identification, its abundance, and its change in urine related to these two periods. Using mass spectrometry (LTQ Orbitrap), we identified 1699 tryptic peptides (related to 402 proteins) in urine from 31 MScl and 8 control at these two periods. Pregnancy-related peptides were significantly elevated (p < 0.01) in MScl patients compared with controls (Analysis 1: 531 peptides in MScl and 36 peptides in controls higher abundant in the third trimester compared to postpartum). When comparing the longitudinal differences (Analysis 2), we identified 43 (related to 35 proteins) MScl disease-associated peptides (p < 0.01) with increased or decreased difference ratio in MScl compared with controls. The most discriminating peptides identified were trefoil factor 3 and lysosomal-associated membrane protein 2. Both proteins have a role in the innate immune system. Three proteins with a significant decreased ratio were plasma glutamate carboxypeptidase, Ig mu chain C region, and osteoclast associated immune like receptor. Our results indicate that the protein expression pattern in urine of MScl patients contains information about remote CNS and brain disease processes.

Anti-MOG antibodies plead against MS diagnosis in an Acquired Demyelinating Syndromes cohort.

BACKGROUND: Acquired demyelinating syndromes (ADS) in children are a group of distinct first immune-mediated demyelinating events of the central nervous system (CNS). Predictive biomarkers for future diagnosis are lacking. A putative target antigen is myelin oligodendrocyte glycoprotein (MOG). We analyzed the presence of MOG antibodies in a cohort of ADS patients in The Netherlands. METHODS: Using a cell-based assay, we analyzed 117 children with ADS from a nationwide cohort, whom were divided into five groups: optic neuritis (ON; n = 20), transverse myelitis (TM; n = 7), other monofocal ADS (n = 22), polyfocal ADS without encephalopathy (n = 44) and polyfocal ADS with encephalopathy (n = 24). Additionally, we tested children with other neurological diseases (OND; n = 13), healthy children (n = 31) and adult polyfocal ADS plus encephalopathy (ADEM) patients (n = 29). RESULTS: We found that 21 of the 117 children with ADS tested anti-MOG seropositive (18%). The group of patients with ADEM had the highest prevalence of anti-MOG seropositivity (42% versus 18% in the non-encephalopathic polyfocal ADS patients). Although 47 ADS children had a final diagnosis of multiple sclerosis (MS), in only one of them were MOG antibodies detected (2%), with only borderline positivity. Only 1 out of the 29 adult ADEM patients tested anti-MOG seropositive. CONCLUSIONS: MOG antibodies are strongly skewed towards ADS children that present with an ADEM-like disease onset. The presence of such antibodies pleads against a future diagnosis of MS.

Prevalence of human Herpesviridae in cerebrospinal fluid of patients with multiple sclerosis and noninfectious neurological disease in the Netherlands.

Prevalence of eight human herpesviruses (HHV1-8) was determined by real-time PCR in cell-rich cerebrospinal fluid (CSF) samples, obtained early after disease symptoms, of Dutch patients with multiple sclerosis (MS) and other noninfectious central nervous system diseases (NIND). Whereas HHV1-8 DNA was undetectable in CSF samples of MS patients, HHV6 DNA was detected in a plexus neuritis case and HHV7 DNA in an ependymoma and a Behçets' disease patient. However, intrathecal HHV infection was not detected. Data indicate that HHV1-8 are rarely detected in CSF of Dutch NIND patients and do not support the role of intrathecal HHV infection early after onset of disease symptoms in MS.

Fine-mapping the genetic association of the major histocompatibility complex in multiple sclerosis: HLA and non-HLA effects.

The major histocompatibility complex (MHC) region is strongly associated with multiple sclerosis (MS) susceptibility. HLA-DRB1*15:01 has the strongest effect, and several other alleles have been reported at different levels of validation. Using SNP data from genome-wide studies, we imputed and tested classical alleles and amino acid polymorphisms in 8 classical human leukocyte antigen (HLA) genes in 5,091 cases and 9,595 controls. We identified 11 statistically independent effects overall: 6 HLA-DRB1 and one DPB1 alleles in class II, one HLA-A and two B alleles in class I, and one signal in a region spanning from MICB to LST1. This genomic segment does not contain any HLA class I or II genes and provides robust evidence for the involvement of a non-HLA risk allele within the MHC. Interestingly, this region contains the TNF gene, the cognate ligand of the well-validated TNFRSF1A MS susceptibility gene. The classical HLA effects can be explained to some extent by polymorphic amino acid positions in the peptide-binding grooves. This study dissects the independent effects in the MHC, a critical region for MS susceptibility that harbors multiple risk alleles.

Endotoxin- and ATP-neutralizing activity of alkaline phosphatase as a strategy to limit neuroinflammation.

BACKGROUND: Alkaline phosphatase (AP) is a ubiquitously expressed enzyme which can neutralize endotoxin as well as adenosine triphosphate (ATP), an endogenous danger signal released during brain injury. In this study we assessed a potential therapeutic role for AP in inhibiting neuroinflammation using three complementary approaches. METHODS: Mice were immunized to induce experimental autoimmune encephalomyelitis (EAE) and treated with AP for seven days during different phases of disease. In addition, serological assays to determine AP activity, endotoxin levels and endotoxin-reactive antibodies were performed in a cohort of multiple sclerosis (MS) patients and controls. Finally, the expression of AP and related enzymes CD39 and CD73 was investigated in brain tissue from MS patients and control subjects. RESULTS: AP administration during the priming phase, but not during later stages, of EAE significantly reduced neurological signs. This was accompanied by reduced proliferation of splenocytes to the immunogen, myelin oligodendrocyte glycoprotein peptide. In MS patients, AP activity and isoenzyme distribution were similar to controls. Although endotoxin-reactive IgM was reduced in primary-progressive MS patients, plasma endotoxin levels were not different between groups. Finally, unlike AP and CD73, CD39 was highly upregulated on microglia in white matter lesions of patients with MS. CONCLUSIONS: Our findings demonstrate that: 1) pre-symptomatic AP treatment reduces neurological signs of EAE; 2) MS patients do not have altered circulating levels of AP or endotoxin; and 3) the expression of the AP-like enzyme CD39 is increased on microglia in white matter lesions of MS patients.

The association between cigarette smoking and multiple sclerosis.

Genetic factors partially explain the susceptibility of multiple sclerosis (MS) and might even relate to the clinical course. Still, many epidemiological studies point at an important role for environmental factors in MS. Smoking is one of the major candidates. In this review we provide an overview of the epidemiological studies on cigarette smoking and the association on MS risk and MS clinical course. In addition, we discuss the possible biological pathways that may influence neurological damage in MS. Moreover, the relation of smoking with other environmental MS risk factors will be addressed.

No evidence for intrathecal IgG synthesis to Epstein Barr virus nuclear antigen-1 in multiple sclerosis.

BACKGROUND: Recent studies suggest an intrathecal IgG response against Epstein Barr virus (EBV) in multiple sclerosis (MS), implicating a pathogenic role for the virus in MS. OBJECTIVES: To determine the spectrum of anti-EBV antibodies and B-cell epitopes within EBV nuclear antigen-1 (EBNA-1). Furthermore, to determine whether EBNA-1-specific IgG is produced intrathecally. STUDY DESIGN: Immunoblot analysis was used to study the anti-EBV IgG response in serum and cerebral spinal fluid (CSF) in MS and controls. EBNA-1 B-cell epitopes were identified by immunoscreening of 12 residue long peptides, with 11 residue overlap, spanning EBNA-1. Thirteen peptides containing all immunoreactive regions were constructed and used in paired serum and CSF of MS patients (n=17) and controls (n=18). Subsequently, reactivity to the identified immunodominant peptide was analysed in a large cohort of serum and CSF of MS patients (n=114) and disease controls (n=62). RESULTS: No difference was observed in the overall anti-EBV antibody diversity, but EBNA-1 reactivity was increased in MS patients versus controls for immunoblot and ELISA (p<0.0001). Epitope analysis on EBNA-1 revealed one immunodominant region covering residues 394-451: EBNA-1(394-451). Anti-EBNA-1(394-451) IgG levels in serum and CSF were significantly higher in MS patients compared to controls. However, normalization for total IgG content of paired serum and CSF samples abrogated this disease association. CONCLUSIONS: MS patients have normal overall anti-EBV antibody responses with increased reactivity to EBNA-1(394-451). No evidence was found for intrathecal EBNA-1-specific IgG synthesis in MS.

Cigarette smoking and risk of MS in multiplex families.

Recent studies suggest that a history of cigarette smoking is a risk factor for multiple sclerosis (MS). We aimed to test the smoking effect in multiplex families, matching for both environmental and genetic factors. In a matched case-control study, 136 MS patients from 106 multiplex MS families were compared with their 204 healthy siblings as controls. Participants completed self-report questionnaires. Conditional logistic regression was used to analyse smoking and MS risk association while controlling for confounding by age and sex. Smoking history was classified in different variables. Within our survey the smoking history of MS patients and the controls did not differ. The odds of MS were comparable for different smoking levels. However, more intense exposure and women showed higher odds ratios, although non-significant. Association studies in families with relatively high genetic loading are unlikely to be confounded by smoking history.

T-cell responses to neurofilament light protein are part of the normal immune repertoire.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system in which axonal damage and degeneration contribute significantly to the progressive irreversible neurological disability. Similar to pathogenic myelin autoimmunity, autoimmune responses to neuronal antigens may contribute to axonal damage and irreversible disability in MS. Auto-antibodies to the axonal cytoskeletal protein neurofilament light (NF-L) are associated with cerebral atrophy in MS and we have recently reported that NF-L autoimmunity is pathogenic in mice. However, the T-cell response to NF-L in MS patients has not been examined. Here, we identify and characterize T-cell proliferative responses to NF-L as compared with myelin oligodendrocyte glycoprotein (MOG) in MS patients and healthy controls. Using a carboxyfluorescein succinimidyl ester dilution assay, we show that while responses to MOG are dominated by CD3(+)CD4(+) T cells, responses to NF-L were observed in both CD3(+)CD4(+) and CD3(+)CD8(+) T-cell populations. Both MOG- and NF-L-reactive cells expressed CD45RO(+), indicative of a memory phenotype. Moreover, in contrast to MOG stimulation which predominantly induced IFN-gamma, both T(h)1- and T(h)2-type T-cell responses to NF-L were observed as indicated by the induction of IFN-gamma, tumor necrosis factor-alpha as well as IL-4. The finding of T-cell responses to NF-L in MS patients may reflect transient activation of pathogenic potential but their presence also in healthy controls indicates that these cells are part of the normal immune repertoire.