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PLOS ONE logoLink to PLOS ONE
. 2016 Feb 5;11(2):e0147567. doi: 10.1371/journal.pone.0147567

Identifying Patient-Specific Epstein-Barr Nuclear Antigen-1 Genetic Variation and Potential Autoreactive Targets Relevant to Multiple Sclerosis Pathogenesis

Monika Tschochner 1,*, Shay Leary 1, Don Cooper 1, Kaija Strautins 1, Abha Chopra 1, Hayley Clark 1, Linda Choo 1, David Dunn 1, Ian James 1, William M Carroll 2,3, Allan G Kermode 1,2,3, David Nolan 1,4
Editor: Alison J Sinclair5
PMCID: PMC4744032  PMID: 26849221

Abstract

Background

Epstein-Barr virus (EBV) infection represents a major environmental risk factor for multiple sclerosis (MS), with evidence of selective expansion of Epstein-Barr Nuclear Antigen-1 (EBNA1)-specific CD4+ T cells that cross-recognize MS-associated myelin antigens in MS patients. HLA-DRB1*15-restricted antigen presentation also appears to determine susceptibility given its role as a dominant risk allele. In this study, we have utilised standard and next-generation sequencing techniques to investigate EBNA-1 sequence variation and its relationship to HLA-DR15 binding affinity, as well as examining potential cross-reactive immune targets within the central nervous system proteome.

Methods

Sanger sequencing was performed on DNA isolated from peripheral blood samples from 73 Western Australian MS cases, without requirement for primary culture, with additional FLX 454 Roche sequencing in 23 samples to identify low-frequency variants. Patient-derived viral sequences were used to predict HLA-DRB1*1501 epitopes (NetMHCII, NetMHCIIpan) and candidates were evaluated for cross recognition with human brain proteins.

Results

EBNA-1 sequence variation was limited, with no evidence of multiple viral strains and only low levels of variation identified by FLX technology (8.3% nucleotide positions at a 1% cut-off). In silico epitope mapping revealed two known HLA-DRB1*1501-restricted epitopes (‘AEG’: aa 481–496 and ‘MVF’: aa 562–577), and two putative epitopes between positions 502–543. We identified potential cross-reactive targets involving a number of major myelin antigens including experimentally confirmed HLA-DRB1*15-restricted epitopes as well as novel candidate antigens within myelin and paranodal assembly proteins that may be relevant to MS pathogenesis.

Conclusions

This study demonstrates the feasibility of obtaining autologous EBNA-1 sequences directly from buffy coat samples, and confirms divergence of these sequences from standard laboratory strains. This approach has identified a number of immunogenic regions of EBNA-1 as well as known and novel targets for autoreactive HLA-DRB1*15-restricted T cells within the central nervous system that could arise as a result of cross-reactivity with EBNA-1-specific immune responses.

Introduction

Epstein-Barr virus (EBV) is the only human-adapted member of the Lymphocryptovirus genus, belonging to a lineage of Old World primate gamma-1 herpesviruses that was transferred to a hominid ancestor approximately twelve million years ago, and which is now responsible for near-universal and lifelong human infection [1,2]. Viral transmission is generally via saliva, with evidence that age of infection is associated with cultural and socioeconomic factors [3]. Uniquely, chronic infection is established within ‘immortalised’ B-lymphocytes that are transformed by an array of viral proteins that functionally mimic host proteins to create long-lived memory cells [4,5]. Viral persistence is then promoted through mechanisms that reduce antigen presentation to the adaptive immune system [6], including the involvement of latency programs that limit viral protein expression to a minimal subset critical for replication; most notably Epstein-Barr Nuclear Antigen-1 (EBNA-1), which maintains host chromosomal attachment of viral episomal DNA thus linking viral and cellular replication cycles [7].

These mechanisms of viral persistence would predict limited viral sequence diversity, in keeping with the relatively slow evolutionary rate of EBV and other gamma-1 herpesviruses [2] and evidence of geographically-defined viral subtypes [8]. Nevertheless, evidence of diversifying selection involving latency genes including EBNA-1 has been identified [9], including preferential variation within human leukocyte antigen (HLA) binding sites (viral epitopes) suggesting that antigen presentation can promote HLA-specific viral escape mutations [10,11]. Thus, EBNA-1 is not immunologically ‘silent’ as once thought [12] but is an antigenic target for both CD4 and CD8 T-cell responses [1214] as well as antibodies [15], in keeping with finely tuned immune surveillance mechanisms that generally maintain persistent but stable cycles of EBV infection involving both epithelial and B-lymphocyte compartments [5]. Within this paradigm, mechanisms of viral antigen display [13,14] and the general hierarchy of EBV-specific immune responses including regulatory as well as effector T cell responses are being examined [14,1618]. These have particular relevance to the therapeutic application of EBV-specific T-cell adoptive immunotherapy against EBV-related malignancies including Burkitt’s and Hodgkin’s lymphoma and nasopharyngeal carcinoma [19], now supported by positive findings in clinical trials [20,21]. This strategy is underpinned by knowledge of EBV sequence diversity in tissue samples [9,22,23] and its utilisation to predict viral epitope targets [24].

Our own investigations have focused on multiple sclerosis, an inflammatory demyelinating disease of the central nervous system that often leads to neurodegeneration and long-term disability despite current treatment strategies [25]. While a comprehensive explanation of multiple sclerosis pathogenesis remains incomplete, it is clear that the major component of genetic risk is associated with the HLA-DR locus [2629], thus implicating HLA-restricted antigen binding and presentation [30], as well as genetic determinants that predominantly relate to T-cell activation [29]. Several lines of evidence link Epstein-Barr virus-specific immunity to multiple sclerosis risk. Both serological [27,31,32] and CD4 T cell responses [33] directed against EBNA-1 have been associated with multiple sclerosis, with further evidence that EBNA-1-specific antibodies differentiate disease-discordant identical twins [34]. Several groups have demonstrated higher EBV seroprevalence in MS patients compared to controls and it has further been demonstrated that EBV infection late in life, in particular if manifested as infectious mononucleosis, increases a person’s MS risk [27, 35, 36]. A recent study has also explored the use of Epstein-Barr virus-specific adoptive immunotherapy for progressive multiple sclerosis, with promising preliminary results [37]. Further observations include that cerebrospinal fluid oligoclonal bands that are a hallmark of MS specifically can target EBNA-1 [38] and one group has additionally identified the presence of EBV-infected B cells within white matter MS lesions at all disease stages [39], although this result has not been replicated in other studies [40].

In this study, we have utilised DNA obtained from buffy coat samples of patients with multiple sclerosis to analyse EBNA-1 sequence variation using both Sanger and FLX ‘next-generation’ sequencing technologies, without any requirement for primary culture techniques or the creation of cell lines through ex vivo EBV transformation. We have then sought to identify potential HLA-DRB1*1501-restricted viral epitopes within the EBNA-1 protein sequence using standard HLA binding algorithms [41], and investigated potential homology with similarly HLA-restricted antigens in a dataset of human central nervous system proteins [42]. The results of this study, which follow from our previous investigations of the contributions made by HLA alleles and Epstein-Barr virus immunity to multiple sclerosis risk [27,28], highlight the divergence of autologous ‘wild-type’ EBNA-1 sequences from those of laboratory strains commonly used for experimental purposes, and suggest possible avenues of investigation that acknowledge both host and viral genetic diversity in higher-resolution analyses of the role of host-pathogenic interactions in autoimmunity [30,43,44].

Materials and Methods

Research participants

A total of 79 study participants in the Perth Demyelinating Disease Database (PDDD) were included in the study. The study protocol was approved by the Sir Charles Gairdner Hospital Human Research Ethics Committee, and written informed consent was obtained from all participants.

DNA extraction

DNA was isolated from buffy coats (stored at -80°C) using an automated robotic setup using Genfind according to the manufacturer’s instructions. Briefly, 100ul of buffy coat were lysed and Proteinase K added to rupture cell membranes and digest protein. DNA was then immobilized on magnetic particles by the addition of a magnetic bead binding reagent. DNA was separated from contaminants using a magnetic field and washing steps. DNA was eluted in 125μl from the magnetic particles. A minority of samples were manually extracted using Qiagen with the provided protocol. 200μl of buffy coat were lysed and Proteinase K added to remove protein and other contaminants. DNA was absorbed on to the silica-gel membrane during centrifugation of columns and then washed twice to ensure complete removal of any residual contaminants. Finally, samples are recovered from the membrane using 200μL elution buffer. Concentration of all eluted samples was determined using Nanodrop and 1 μl of each sample was loaded on a 1% agarose gel to test for presence and integrity of DNA. All samples were stored at 4°C until further use.

HLA typing

PCR and sequencing based HLA genotyping of the MS cohort resolved to at least the 4-digit level was performed as previously described using heterozygous ambiguity resolving primers where applicable [27,28].

EBV amplification

The N- and C-terminal ends excluding the glycine-alanine rich regions of the EBNA-1 gene were amplified using semi-nested PCRs and fully automated setup utilising Biomek FX robots. EBV reference strain B95-8 was extracted from a B95-8 transformed cell line and was diluted and used as a control in each EBV PCR. All PCR reactions were performed using Roche High Fidelity Taq in 25μl reactions with forward and reverse primers at a concentration of 25pmol/μl. All primers used for amplification have been previously published and named according to the position in the reference strain B95-8 [11,45,46], as summarised below:

  • 107754F: TCCGGGCTGCGAGTAATTGG

  • 107881F: GTCTGCACTCCCTGTATTCA

  • 109111F: TCATCATCATCCGGGTCTCCACCGC

  • 108160R: GGACACCATCTCTATGTCTTGGCC

  • 109135R: GCGGTGGAGACCCGGATGATGATGA

  • 109459R: CCCAAGTTCCTTCGTCGGTAGTCC

  • 109759R: CTCCATCGTCAAAGCTGCA

  • 109869R: CTGCCCTTCCTCACCCTCAT

  • 109970R: CAACAGCACGCATGATGTCT

For amplification of the N-terminal end the first round primer pair 107754F-109135R (PCR1) resulting in a 1381 base pair fragment (bp) was used. Detailed information about size and location of EBNA-1 PCRs with reference to the EBV strain B95-8 can be found in S1 Fig. Second round amplification was then performed using either 107881F-109135R (PCR2) or 107754F-108160R (PCR3), resulting in 1254bp or 406bp fragments respectively. C-terminal EBNA-1 PCR was performed as described previously [27]. Briefly, first round amplification with the primer pair EBV109111F-EBV109970R (PCR 4) resulted in an 859bp fragment. A semi-nested PCR was followed using the primer combination 109111F-109869R (PCR5) resulting in a final 758 base pair product. Alternatively, shorter semi-nested PCRs were performed using the primer combinations 109111F-109759R (PCR6, 648bp) and 109111F-109459R (PCR7, 348bp) respectively. In some cases PCRs with alternative primers have been performed. For an overview of primer pairs used in each PCR, nucleotide coordinates of primers within the B95-8 reference strain as well as primer melting temperatures, elongation times and product sizessee S1 Table. Successful PCR samples were purified using magnetic particles with AMPure (Beckman Coulter) on Biomek FX robots and stored at 4°C until further use.

Sanger sequencing and analysis

Samples were directly sequenced on an automated 96 capillary ABI 373 DNA Sequencer, followed by purification of sequencing products with magnetic particles using CleanSEQ (Beckman Coulter) on Biomek FX robots. Analysis of electropherograms was performed using the ASSIGN V4.0.1.36 software (Conexio Genomics). Threshold for mixture detection in Sanger sequencing has been established to be ~30%. For construction of the Phylogenetic tree, 53 MS sequences and reference strains B95-8, AG876, GD1 and HKNPC1 covering the majority of nucleotide positions B95-8: 109135–109815 (EBNA-1: 1186–1866) were included. Genetic distance was visualized using the Neighbour-joining method based on the p-distance model with pairwise deletion within the PHYLIP (Phylogeny Inference Package) version 3.695 [47].

454 FLX sequencing

For the 454 FLX sequencing strategy, 24 samples were pooled in a single FLX lane. 20 MS samples were selected based on successful Sanger sequencing for three epitopes of interest (EBNA-1 aa PPP: 401–416, AEG: 482–496 and MVF: 563–577). Three additional MS samples were included that displayed a band of correct size on a 1% agarose gel but were not successfully sequenced by Sanger methods. The B95-8 strain of EBV was used as a control in each EBV PCR and was also selected as a control for FLX sequencing.

First round C-terminal EBV PCRs products with the primer combination EBV109111F-EBV109970R (PCR4) were used as templates to generate shorter second round PCRs for the selected deep sequencing samples. For PCR length and location please refer to S1 Fig. This nested PCR was performed with molecular barcoded primers. These tags consisted of eleven nucleotides unique extension to the 5’ end of the second round primers EBV109111F and EBV109869R (PCR5b) resulting in 780bp amplicons. This method facilitates sample multiplexing while also increasing the ability to accurately assign reads back to the sample. Resulting PCR amplicons were pooled at equimolar ratios (3x1011 copies each) to achieve similar number of reads. Standard Library was constructed using 454 Roche Titanium Chemistry protocol. The denatured DNA library was immobilized onto beads and emulsified with the amplification reagents in a water-in-oil mixture and clonally amplified (emPCR). Following emPCR, the capture beads with bound DNA were enriched according to the 454FLX titanium manual and used for pyrosequencing on one lane of an eight lane 454 FLX sequencing run according to the 454 sequencing manual.

The reads obtained from the sequencing were separated according to the unique tags and linked back to the original samples, using the NextGENe software package from SoftGenetics, Inc (State College, PA, USA). Further analysis was performed with inhouse software.

FLX data analysis

The NextGENe software package version 2.3.0 (SoftGenetics, Inc, USA) was used to create a consensus sequence present at >45% for each sample based on the B95-8 EBV reference strain (GenBank accession number: V01555.2). For each sample, all reads were aligned to the consensus using a pairwise alignment. The pairwise alignments were combined into a multiple alignment by matching the reference positions for all aligned pairs. The aligned files were used to detect homopolymers, which are known to occur in FLX sequencing as artefacts. During analysis, all homopolymers not present in the respective consensus sequence have been excluded. Minorities present at <1% were not taken into consideration and insertion deletions were also excluded except for a strain specific in-frame insertion of three amino acids (glycine (GGA), aspartic acid (GAT), aspartic acid (GAC)) at position 2367 of EBNA-1 position (109818/109819 of reference strain B95-8) in several samples, which has been described previously [11]. All mutations detected were additionally manually analysed in the raw FLX data file of each sample to exclude any contribution of homopolymer errors. A nucleotide change was considered a real mutation if the mutation could not have been caused by a nucleotide insertion/deletion before or after the mutation. Additionally, mutations were only taken into consideration if they were present in at least three sequences, independent of the total number of individual reads per sample. Mutations within three nucleotides from the beginning or end of a read were excluded. Furthermore, unresolved nucleotide mixtures within reads were few, but indicated low signal quality in this position and were not taken into consideration.

Epitope predictions

HLA binding algorithms (NetMHCII, NetMHCIIpan) were utilized to identify potential HLA-DRB1*1501 class II HLA epitopes within the EBNA-1 Sanger derived sequences. Additionally, predictions were performed for two known HLA-DRB1*1501 class II EBNA-1 epitopes (denoted AEG and MVF) using all FLX consensus and Sanger sequences generated. All predicted 15mer peptides which resulted in HLA-DRB1*1501 strong (<50 nM) and weak binders (50–500 nM) were selected and tested for potential cross-reactivity on a dataset of CNS proteins enriched for axoglial proteins (human protein reference database (HPRD.org) and [42], as well as a selection of brain proteins derived from NCBI (S2 Table). Amongst these potential cross-reactive epitopes, a subset of epitopes sharing the majority of peptide amino acid residues within the epitope core HLA-binding sequence of nine amino acids, were identified.

Statistical analysis

We assessed whether EBNA-1 nucleotide polymorphism at each position was significantly associated with MS risk alleles by grouping alleles according to previous genetic analysis by our group [27]. Samples were categorized as carrying high MS risk, low MS risk or neutral risk alleles, respectively, if they carried at least one risk allele (HLA-DR1*08, *15, *16); at least one protective allele (HLA-DR1*04, *07, *09) and no risk allele; or two neutral risk alleles. Tables of nucleotide frequencies by risk groups were created at each nucleotide position and associations assessed by Fisher exact tests. We assessed clustering based on all 62 C-terminal Sanger sequences using the “partitioning around medoids” (PAM) method [48]. All nucleotide positions demonstrating some nucleotide variation were included and clusters displayed via a plot of the first two principal components [48]. Associations of HLA risk groups with viral clusters found in the cluster analysis were also assessed using Fisher exact tests. Analyses were carried out using TIBCO Spotfire S+ 8.2 (Somerville, MA).

Results

Epstein Barr Nuclear Antigen-1 (EBNA-1) was successfully amplified for bulk (Sanger) sequencing in 76 MS samples from DNA extracted buffy coats without any requirement for primary culture to enrich for EBV episomes. All samples were obtained from participants in the Perth Demyelinating Disease Database (PDDD) with confirmed MS, reflecting a wide range of age and disease severity (Fig 1). Females were more prevalent (73%) than males (27%) in the study population, with a slightly higher age (median: 53) compared to males (median: 49). Within this dataset, 62 samples were successfully sequenced across the EBNA-1 C-terminal region, which is known to contain the majority of MHC Class II-restricted T-cell epitopes [4951], and a subset of 37 samples was sequenced in the N-terminal EBNA-1 region additionally. Sequences for both the N- and C-terminal end were obtained from 23 samples.

Fig 1. Age and gender distribution of patients recruited from the Perth Demyelinating Disease Database.

Fig 1

Wild-type EBNA-1 sequence variation

The C-terminal region of EBNA-1 demonstrated sequence variation within four major clusters with additional minor variation (Fig 2). In keeping with previous analyses of wild-type EBNA-1 sequences [9,11], wild-type sequences showed strong similarity to the EBV reference strain B95-8 in only a minority of cases (9/53, 16.9%) and none clustered with the type 2 AG876 strain. No nucleotide mixtures were identified by Sanger sequencing methods that would indicate the presence of multiple EBNA-1 populations, either as a result of mutation or superinfection with multiple strains. N-terminal sequence analysis showed high conservation and identified only three different variants: 19 samples demonstrated 100% sequence similarity with the N terminal sequence of the EBV reference strain B95-8, while 12 sequences matched the previously identified type 2 EBV strain AG876 which differs to B95-8 in the positions: Q16E, E18G, D24E, S27G and A85T [52]. Three of these positions (Q16E, E18G, S27G) have previously been described to occur in combination (44). The third variant occurred in seven samples and aligned well with AG876 but contained two mismatches to it: EBNA-1 amino acid positions: V70A), (Q74P.

Fig 2. Phylogenetic tree of C-terminal EBNA-1 Sanger sequences including the reference strains B95-8, AG876, GD1 and HKNPC1.

Fig 2

Phylogenetic tree covering nucleotide positions B95-8: 109135–109815; EBNA-1: 1186–1866; blue triangles: EBV reference strains; red dots: MS cases (n = 53).

Association of HLA and viral sequence variation

Association analysis of MS risk group with EBNA-1 sequence variation revealed nine positions at which individuals in the high risk group had nucleotide frequencies significantly differing from the other risk groups with p<0.05 –namely positions 1428 (P476), 1460 (A487), 1475, (S492), 1498 (D499), 1690 (M563), 1722 (V574), 1754 (T585), 1782 (R594) and 1785 (V595). Cluster analysis based on the C-terminal Sanger sequences described in Methods revealed two distinct populations (Fig 3), a main cluster (A) of 47 cases and a smaller cluster (B) of 15 cases. Across the nine positions with significant HLA association there were 373 consensus nucleotides and seven non-consensus among the 47 cases in cluster A and just 10 consensus nucleotides and 109 non-consensus in cluster B. Hence at these nine positions the two clusters were almost mutually exclusive.

Fig 3.

Fig 3

Principal Component plot (Component 1 vs Component 2) for cluster analysis based on the C-terminal EBNA-1 Sanger sequences revealed two distinct populations of 47 (A) and 15 (B) cases.

When assessed for HLA MS risk group, cluster A contained 5, 9 and 33 individuals classified as MS risk neutral, protective and high, respectively, compared with the smaller cluster (B) which contained 4, 6 and 5 individuals with neutral, protective and high MS risk. The high MS risk group was thus significantly over-represented in the large cluster (p = 0.016).

454 deep sequencing

Additional sequencing of the C-terminal EBNA-1 fragment (EBNA-1 nucleotide positions 1160–1906) was then undertaken utilising FLX technology for 23 samples and a B95-8 control. Among these, 14 samples and the B95-8 control had coverage of all positions between 80–1632 reads, while 10 samples had very low coverage of reads per position (average reads <15) and were not included in subsequent sequence minority analysis. As shown in Table 1, low-level EBNA-1 sequence variation could be detected although only two samples (samples 1 and 5) showed the presence of minor sequence variants at a level of ≥10%. Mixtures occurred at nucleotide positions 1190 (R397) and 1588 (P529) in sample 1 and at 14 different positions in sample 5: 1286 (V429), 1420 (G473), 1421 (S474), 1428 (P476), 1460 (A487), 1475 (S492), 1498 (D499), 1561 (L520), 1572 (T524), 1660 (P553), 1690 (M563), 1722 (V574), 1754 (T585), 1782 (R594) and 1785 (V595). Silent mutations occurred at amino acid positions G473, D499, L520, P529 and P553, whereas the other mutations lead to a mixture of wild type and variant amino acids: R397R/G, V429V/M, S474S/T, P476P/Q, A487A/T, S492S/C, T524/TI, M563M/I, V574V/G, T585T/P, R594R/K and V595V/A. Lowering this threshold to 5% revealed minority variants in 3.6% positions (27/749 nucleotides sequenced); increasing to 5.0% at a 2% cut-off (37/749 nucleotides) and 8.3% at a 1% cut-off (62/749 nucleotides). As noted in Table 1, most of the mutations that defined minority variants were unique to individual samples (42 individual positions) (Table 1).

Table 1. EBNA-1 quasispecies detected with FLX sequencing.

Minority EBV sequence variants at a level of ≥10% were detected in two samples only. Sequence mixtures present at a ≥5% threshold revealed minority variants in 3.6% of investigated nucleotide positions (27/749 nucleotides sequenced,), increasing to 5.0% at a ≥2% cut-off (37/749 nucleotides,) and 8.3% at a ≥1% cut-off (62/749 nucleotides,). Samples 7, 8 and 13 did not have minority species present at ≥1%.

EBNA-1 aa pos 397 410 411 422 425 429 431 432 435 435 459 459 460 469 473 474 476 484 487 492 499 507 508 520 524 525 525 528 528 529 533 534 536 539 549 550 553 559 561 563 574 585 594 595 595
B95-8 aa R G E G G V P G E E R R K R G S P G A S D V F L T A A I I P L T L L P Q P V Y M V T R V V
B95-8 codon AGG GGG GAA GGC GGT GTG CCG GGA GAG GAG CGC CGC AAA CGT GGT TCC CCG GGT GCT AGT GAC GTG TTC CTA ACT GCC GCC ATT ATT CCA CTT ACA TTG CTC CCA CAA CCG GTC TAT ATG GTT ACA AGG GTG GTG
EBNA-1 pos 1190 1231 1232 1265 1275 1286 1292 1296 1304 1305 1377 1378 1379 1406 1420 1421 1428 1453 1460 1475 1498 1520 1525 1561 1572 1574 1575 1583 1584 1588 1598 1603 1608 1616 1648 1651 1660 1678 1684 1690 1722 1754 1782 1785 1786
variant aa G G Q S S M T V stop G H R Q S G T Q G T C D M L L I $ $ $ T P I T S I P Q P V Y I G P K A A
variant codon GGG GGA CAA AGC GAT ATG ACG GTA TAG GGG CAC CGA CAA AGT GGC ACC CAG GGC ACT TGT GAT ATG TTA CTC ATT SSC SSC RYT ACT CCG ATT ACG TCG ATC CCG CAG CCA GTA TAC ATT GGT CCA AAG GCG GCT
sample 1, 1% AG                   AG                                     AG                 AT         CT  
sample 1, 2% AG                                                         AG                 AT            
sample 1, 5% AG                                                         AG                              
sample 1, 10% AG                                                         AG                              
sample 2, 1%                                                   CG CG         AG CT                        
sample 3, 1%                   AG   AC AC                                             AG                  
sample 3, 2%                         AC                                                                
sample 3, 5%                         AC                                                                
sample 4, 1%                                   CT                                                      
sample 4, 2%                                   CT                                                      
sample 5, 1%     CG     AG                 CT AT AC   AG AT CT     AC CT     AG     AC           AG     GT GT AC AG CT  
sample 5, 2%     CG     AG                 CT AT AC   AG AT CT     AC CT     AG     AC           AG     GT GT AC AG CT  
sample 5, 5%     CG     AG                 CT AT AC   AG AT CT     AC CT     AG     AC           AG     GT GT AC AG CT  
sample 5, 10%           AG                 CT AT AC   AG AT CT     AC CT                       AG     GT GT AC AG CT  
sample 6, 1%                                                                     AG                    
sample 10, 1%                             CT                                                            
sample 11, 1%                             CT                                                            
sample 12, 1%   AG       AG                     AC   AG AT CT     AC CT                       AG     GT GT AC AG CT  
sample 12, 2%   AG       AG                     AC   AG AT CT     AC CT                       AG     GT GT AC AG CT  

Subsequent capital letters indicate both nucleotide mixtures detected. Single capital letters indicate amino acids present. Amino acid positions representing silent mutations have been indicated in bold. EBNA-1 = Epstein-Barr virus nuclear antigen-1, aa = amino acid, pos = position

Sequence conservation and relevance to HLA-DRB1*15 binding

As shown in Fig 3, EBNA-1 sequences were mapped against the standard reference strain B95-8 in order to illustrate known and putative HLA-DRB1*15-restricted epitopes and their relationship with EBNA-1 sequence conservation at the amino acid level. This approach, which utilises the ConSeq server [53], reflects amino acid conservation in terms of the influence of physicochemical properties of amino acid substitution as well as the frequency of sequence variation. Hence, ‘dips’ in the conservation plot (highlighted in red) reflect sites of variation that are likely to influence protein structure. Above these plots, predicted HLA-DRB1*15 binding sites are denoted along with the core binding regions, derived from NetMHCIIPan analysis [41]. As shown, this approach revealed two known HLA-DRB1*1501 restricted epitopes (AEGLRALLARSHVER (‘AEG’: aa 481–496) and MVFLQTHIFAEVLKD (‘MVF’: aa 562–577), as well as two overlapping putative epitopes covering a region between positions 502–543. In contrast, no HLA-DRB1*15 epitopes were identified within the N-terminal region of EBNA-1. The most frequent sequences at these epitope sites were AEGLRTLLARCHVER and IVFLQTHIFAEGLKD (differences to B95-8 reference underlined). Variant sequences within these epitope regions are described in Table 2, along with comparisons of HLA-DRB1*15 binding affinity. As noted, there are no wild-type EBNA-1 variants within these known epitopes that would be predicted to abrogate HLA-DRB1*15 binding completely, although further studies will be required to establish if minor variations in binding affinity could influence the nature of the T cell response, noting that a previous study has demonstrated both regulatory and effector EBNA-1-specific CD4+ T cells with identical epitope specificity [18]. Interestingly, eight of the nine polymorphic sites from the cluster analysis fell within our predicted HLA-DRB1 epitopes including two changes in the previously described ‘AEG’ and ‘MVF’ epitopes, respectively.

Table 2. EBNA-1 sequence variation identified with next-generation sequencing technology, and impact on HLA-DRB1*15 binding affinity within known epitopes.

The two most frequent variants for the A) AEG epitope and B) MVF epitope are printed in bold, the most frequent variant is underlined. All epitopes are predicted to be weak binders (affinity 50nM-500nM).

Table 2A                                 NetMHCII NetMHCIIpan
nt B95-8 gca gaa ggt tta aga gct ctc ctg gct agg agt cac gta gaa agg peptide core affinity(nM) core affinity(nM)
aa B95-8 A E G L R A L L A R S H V E R AEGLRALLARSHVER RALLARSHV 197 LRALLARSH 63
  - - - - - - - - - - - - - - - AEGLRALLARSHVER RALLARSHV 197 LRALLARSH 63
  - - - - - V - - - - - - - - - AEGLRVLLARSHVER RVLLARSHV 87 LRVLLARSH 61
  - - - - K - - - - - - - - - - AEGLKALLARSHVER KALLARSHV 165 LKALLARSH 88
  - - - - - T - - - - C - - - - AEGLRTLLARCHVER LRTLLARCH 267 LRTLLARCH 91
  - - - - - A - - - - S - - - - AEGLRALLARSHVER RALLARSHV 197 LRALLARSH 63
pos B95-8 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496          
Table 2B                                 NetMHCII NetMHCIIpan
nt B95-8 atg gtc ttt tta caa act cat ata ttt gct gag gtt ttg aag gat peptide core affinity(nM) Core affinity(nM)
aa B95-8 M V F L Q T H I F A E V L K D MVFLQTHIFAEVLKD MVFLQTHIF 303 VFLQTHIFA 257
  - - - - - - - - - - - - - - - MVFLQTHIFAEVLKD MVFLQTHIF 303 VFLQTHIFA 257
  I - - - - - - - - - - G - - - IVFLQTHIFAEGLKD IVFLQTHIF 261 IVFLQTHIF 259
  - - - - - - - - - - - - F - - MVFLQTHIFAEVFKD VFLQTHIFA 281 VFLQTHIFA 270
  I - - - - - - - - - - V - - - IVFLQTHIFAEVLKD IVFLQTHIF 275 IVFLQTHIF 181
  M - - - - - - - - - - G - - - MVFLQTHIFAEGLKD VFLQTHIFA 272 MVFLQTHIF 386
  M - - - - - - - - - - V - - - MVFLQTHIFAEVLKD MVFLQTHIF 303 VFLQTHIFA 257
pos B95-8 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577          

nt: nucleotides, aa: amino acid, pos: amino acid position, B95-8: wildtype EBV reference strain

Identification of HLA-DRB1*15 epitopes within brain proteins homologous to EBNA-1

For this analysis we utilised three datasets enriched for CNS proteins [42], to identify candidate cross-reactive proteins that shared a propensity for HLA-DRB1*15 binding as well as homology to natural EBNA-1 sequences at these sites. This analysis was predicated on the hypothesis that (1) EBNA-1-specific T cell immunity reflects a standard model of HLA-restricted binding and antigen presentation, providing a long-term stimulus for T cell responses that could then (2) cross-react with CNS-specific antigens in a manner that requires HLA-restricted presentation but which may be less predictably associated with HLA binding affinity given the constraints of negative selection against high-affinity autoantigens, and the known altered topology of many autoreactive HLA-peptide-TCR interactions [54]. This approach is also informed by the previous demonstration of EBNA-1-specific CD4+ T cells capable of producing pro-inflammatory responses against myelin antigens in a seminal study by Lunemann and colleagues [33].

Thus, we initially selected EBNA-1 epitopes of interest based on HLA binding affinity, and then identified candidate CNS protein epitopes that would be predicted to bind HLA-DRB1*15 with sufficient affinity to allow antigen presentation (strong and weak binders with affinity threshold 500 nM) and which exhibited homology with the EBNA-1 epitope (threshold ≥3 residues within the 9 amino acid core binding region identified by NetMHCII and NetMHCIIPan analysis). Applying this approach to myelin proteins of known interest in MS research in the first instance reviewed in [55], we identified potential cross-reactive responses involving a number of major myelin antigens (Table 3) including experimentally confirmed HLA-DRB1*15-restricted epitopes associated with encephalitogenic T cell responses (asterisked) including 2',3'-cyclic-nucleotide 3'-phosphodiesterase, alpha B crystallin, myelin basic protein and oligodendrocyte-specific protein. Additionally, we identified several novel candidate antigens within glial fabrillary acidic protein, myelin proteolipid protein, neurofilament heavy polypeptide and myelin-oligodendrocyte glycoprotein.

Table 3. Putative HLA-DRB1*15 binders within autologous EBNA-1 peptide sequences and candidate myelin antigens.

Brain Peptides EBNA-1 Peptides Peptide Match Count Brain Binding Scores EBNA-1 Binding Scores EBNA-1 Protein Position Brain Protein Position Brain Protein Accession No(s)
GKLYSLGNGRWMLTL GSKTSLYNLRRGTTL X…XX.X.X…XX 66 267 512 370 P09543
RGKLYSLGNGRWMLT GGSKTSLYNLRRGVA .X…XX.X.X.... 41 347 511 369 P09543
LYSLGNGRWMLTLAK * KTSLYNLRRGVALAI ..XX.X.X....XX. 306 45 514 372 P09543
SRGKLYSLGNGRWML * SKTSLYNLRRGVALA X…XX.X..X.... 41 90 513 368 P09543
LSPFYLRPPSFLRAP ** TSLYNLRRGVALAIP .X…XX....X..X 47 52 514 44 ACP18852
LSPFYLRPPSFLRAP ** TSLYNLRRGTALAIP .X…XX....X..X 135 16 515 44 ACP18852
SPFYLRPPSFLRAPS SLYNLRRGVALAIPQ X…XX....X..X. 59 54 515 45 AAB23453
KTKEGVLYVGSKTRE WVAGVFVYGGSKTSL .......X.XXXX.. 54 8 503 32 Q16143
EKTKEGVLYVGSKTR NWVAGVLVYGGSKTS ........X.XXXX. 67 48 502 31 Q16143
TRLSLARMPPPLPTR LRVLLARSHVERTTE .X..XXX......X. 468 32 485 35 P14136
KLALDIEIATYRKLL NLRRGIGLAIPQCLL .X…X..X....XX 176 323 518 356 P14136
GKGRGLSLSRFSWGA PQCRITPLSRLPFGM …X…XXX…X. 287 384 528 131 AAC41944
EFAPVLLLESHCAAA *** GLRVLLARSHVERTT XX......XX....X 410 125 483 79 AAC41944
PGVLVLLAVLPVLLL EGLRVLLARSHVERT .X..XXXX…X… 301 8 483 153 Q16653
GPLVALIICYNWLHR GPLRESIVCYFIVFL XXX…X.XX..... 26 373 551 219 Q16653
GEGKVTLRIRNVRFS AEGLRTLLARCHVXR .XX..XX..X..... 89 16 482 106 Q16653
DPFYWVSPGVLVLLA QKFENIAXGLRTLLA ..X.....X…XXX 134 202 475 146 Q16653
DPFYWVSPGVLVLLA PKFENIAEGLKLLLA ..X.....X…XXX 185 438 475 146 Q16653
CSAVPVYIYFNTWTT VAGVFVYGGXNTSLY …X.XX…XX… 31 8 504 169 AAA59565
ATYNFAVLKLMGRGT GTWVAGVLVYGGSKT .X....XX…X..X 219 8 501 261 AAA59565
LLTFMIAATYNFAVL LVMTKPAPTCNIKVT X.....X.X.X..X. 70 32 582 254 AAA59565
EEITEYRRQLQARTT ENIAEGLRVLLARSH X.X.X..X.X.XX.. 376 239 479 316 P12036
EMRGAVLRLGAARGQ ENIAEGLRLLLARCH X.....XXX..XX.. 138 154 479 152 P12036
GAVLRLGAARGQLRL AEGLRLLLARCHVER …XXX..XX..... 67 88 482 155 P12036
TRLSFTSVGSITSGY VAGVFVYGGSRTSLY ....X…XX.XX.X 206 71 504 398 P07196
KVVLIKNTLRSLEVL KFENIAEGLRLLLAR X…X…XX.X… 74 336 477 137 P23515
SLEVLNLSSNKLWTV GLRVLLARSHVERTT .X.XX…X....X. 62 125 484 147 P23515
PGTLINLTNLTHLYL KTSLYNLRRGTALAI …X.XX…X.X.. 102 77 514 184 P23515
ENVSTTLRALAPRLM ENIAEGLRALLARSH XX....XXXX..X.. 39 32 479 187 AAC25187
AGVLLILLALCALVA AEGLRTLLARCHVER X..X..XXX.X.... 389 32 482 123 AAC25187
NVSTTLRALAPRLMR NIAEGLRALLARSHV X....XXXX..X… 25 16 480 188 AAC25187
CKPLVDILILPGYVQ †† IKDLVMIKPAPTCNI .X.XX.X…X.... 48 120 578 65 AAC25187
ELEKAMVALIDVFHQ EGLKALLARSHVERT X..XX..X…X… 376 16 483 3 NP_006263
AFVAMVTTACHEFFE VCYFMVFLQTHIFAE ....XX....X.X.X 457 71 558 76 NP_006263
FGAEILKKIPGRVST NIAEGLKALLARSHV ..XX.XX....X… 51 16 480 91 NP_006746
GIRKFAADAVKLERM NLRRGIALAVQQCRL ..X…X.XX…X. 387 32 519 311 NP_006746
PILAVLLFSSLVLSP EGLRVLLARSHVERT ..X.XXX..X.X… 66 8 483 12 P25189
ILAVLLFSSLVLSPA GLRVLLARSHVERTT .X.XXX..X.X.... 65 16 484 13 P25189
EFAPVLLLESHCAAA EGLRVLLARSHVERT X…XXX..XX.... 177 8 483 410 P20916
VEFAPVLLLESHCAA AEGLRVLLARSHVER .X…XXX..XX… 250 16 482 409 P20916
PGVLVLLAVLPVLLL EGLRVLLARSHVERT .X..XXXX…X… 301 8 483 153 Q16653
VLGPLVALIICYNWL NLRRGVALAIPQCRL .X…XXX.X....X 148 32 519 217 Q16653
GAEIRHVLVTLGEKM GTWVAGVLVYGGSKT X.....XXX..X.X. 358 8 501 106 P60660
KLRRGDLPFVVPRRM NLRRGIALAVQQCRL .XXXX....X…X. 498 32 519 1920 P35579
AEELRARLTAKKQEL AEGLRALLARSHVER XX.XXX.X.....X. 466 115 482 899 P35579

Underlined is the core of the peptide. Binding score (nM) prediction using NetMHCII and NetMHCIIpan. Binding score <50: strong binder, binding score 50–500 weak binder.

*Known CNP epitope [56]

**Known aB-crystallin epitope [57]

***Known MBP epitope [58]

†Known MOG epitope [59]

††Known OSP epitope [60].

We then extended this analysis to a larger set of central nervous system antigens enriched for axoglial proteins that maintain myelinated nerves and nodes of Ranvier critical for saltatory conduction reviewed in [61], noting recent evidence that the axoglial apparatus may be targeted in the earliest phases of multiple sclerosis lesion development [62,63]. As described in Table 4, which presents a subset of results based on optimal EBNA-1 epitope binding and core match values ≥3, this analysis identified a larger set of potentially cross-reactive CNS proteins including neurofascin [62] as well as a number of other proteins involved in actin organisation and paranodal assembly like ankyrins, contactin-associated proteins as well as gelsolin [64].

Table 4. Extended axoglial brain protein dataset with HLA-DRB1*1501 predicted brain epitopes overlapping with predicted EBV binders.

Brain Peptides EBNA-1 Peptides Peptide Match Count Brain Binding Scores EBNA-1 Binding Scores EBNA-1 Protein Position Brain Protein Position Brain Protein Accession No(s) Brain Protein Genbank Description(s)
TGQFVYCGKKAQLNI AGVFVYGGSKTSLYN .X.XXX.X.X..X.. 203 8 505 84 P62917 60S ribosomal protein L8
GQFVYCGKKAQLNIG GVFVYGGSKTSLYNL X.XXX.X.X..X… 237 8 506 85 P62917  
QFVYCGKKAQLNIGN VFVYGGSKTSLYNLR .XXX.X.X..X.... 302 16 507 86 P62917  
GDRGKLARASGNYAT GLRTLLARCHVERTT X.X..XXX......X 329 32 484 121 P62917  
REEIHEYRRQLQART FENIAEGLRVLLARS .X.X.X..X.X.XX. 231 32 478 309 Q16352 Alpha-internexin
EEIHEYRRQLQARTI ENIAEGLRTLLARCH X.X.X..X.X.XX.. 189 32 479 310 Q16352  
VAELLATLQASSQAA IAEGLRTLLARSHVE .XX.X.XX.X.X… 348 280 480 235 Q16352  
VASVLLEAGAAHSLA VAGVLVYGGSKTSLY XX.XX…X…XX. 140 22 504 545 Q01484 Ankyrin-2
DVASVLLEAGAAHSL WVAGVLVYGGSKTSL .XX.XX…X…XX 178 29 503 544 Q01484  
ELLLERGAPLLARTK ENIAEGLRPLLARCH X…X…XXXXX.. 112 408 479 316 Q01484  
RITCRLVKPQKLSTP RRGIGLAIPQCLLTP X....X..XX.X.XX 227 369 520 948 AAA51732  
DIVKLLLPRGGSPHS NWVAGVLVYGGSKTS ..X…X..XXX..X 74 48 502 583 AAA51732  
GAYVKLLSKTPELNL GVLVYGGSKTSLYNL X..X…XXX…XX 283 30 506 162 P27824 Calnexin
TAEAIKALGAKHCVK IAEGLKALLARSHVE .XX..XXX.X…X. 69 16 481 209 P30042 ES1 protein homolog, mitochondrial
AEAIKALGAKHCVKE AEGLKALLARSHVER XX..XXX.X…X.. 73 16 482 210 P30042  
LSGESLGHLRSLGAL GSKTSLYNLRRGVAL .X..XX..XX…XX 406 16 512 189 P0C6S8 Leucine-rich repeat and immunoglobulin-like
SGESLGHLRSLGALR SKTSLYNLRRGVALA X..XX..XX…XX. 54 16 513 190 P0C6S8  
LSGESLGHLRSLGAL GSKTSLYNLRRGIAL .X..XX..XX…XX 406 16 512 189 P0C6S8  
AFLGLRQIRLLNLSN VALAIPQCRLTPLSR ..X…X.XX..XX. 34 32 524 313 P0C6S8  
LGLRQIRLLNLSNNL LAVQQCRLTPLSRLP X…X.XX..XX… 26 32 526 315 P0C6S8  
AGVLLILLALCALVA AEGLRTLLARCHVXR X..X..XXX.X.... 389 16 482 123 NP_005593 claudin-11 isoform 1
VLLILLALCALVATI GLRTLLARCHVERTT .X..XXX.X....X. 349 32 484 125 NP_005593  
LYCIYVAIGQKRSTV RRGIALAIPQCRLTP …X..XX.X.X.X. 124 32 521 242 P25705 ATP synthase subunit alpha, mitochondrial
SPGWLADGSVRYPIV QPGPLRESIVCYFIV .XX.X....X.X.XX 398 361 550 302 Q96GW7 Brevican core protein
LLGRWKALLIPPSSP NLRRGIALAIPQCXL .X.X..XX.XX.... 78 32 519 893 Q96GW7  
EDSLECLRAMLSANI ENIAEGLRALLARSH X…X.XXX.X.... 105 32 479 661 Q00610 Clathrin heavy chain 1
SLECLRAMLSANIRQ SLYNLRRGISLAIPQ XX..XX…X..X.X 38 77 516 663 Q00610  
GVLLILLALCALVAT EGLRTLLARCHVERT ..X..XXX.X....X 387 32 483 124 O75508 Claudin-11
VLLILLALCALVATI GLRTLLARCHVERTT .X..XXX.X....X. 349 32 484 125 O75508  
ENLIVPGGVKTIEAN AGVFVYGGSKTSLYN ....X.XX.XX…X 318 8 505 47 Q14194 Dihydropyrimidinase-related protein 1
DNLIVPGGVKTIEAN AGVLVYGGSKTSLYN ....X.XX.XX…X 351 24 505 47 Q14195  
ELRREISYAIKNIHG NLRRGIALAIPQCXL .XXX.X..XX..... 74 32 519 383 Q05193 Dynamin-1
KELRREISYAIKNIH YNLRRGISLAIPQCR ..XXX.XX.XX.... 116 237 518 382 Q05193  
DEKELRREISYAIKN SLYNLRRGISLAIPQ ....XXX.XX.XX.. 246 77 516 380 Q05193  
EDLRRGLVMVKPGSI KDAIKDLVMTKPAPT .X....XXX.XX… 162 32 576 332 P49411 Elongation factor Tu, mitochondrial
DLRRGLVMVKPGSIK DGIKDLVMTKPAPTC X....XXX.XX.... 93 32 577 333 P49411  
IVFRGEHGFIGCRKV IVFLQTHIFAEGLKX XXX…X.X....X. 233 16 563 386 Q16658 Fascin
IVFRGEHGFIGCRKV IVFLQTHIFXEGLKD XXX…X.X....X. 233 32 563 386 Q16658  
TGAQELLRVLRAQPV ENIAEGLRVLLARSH ....X.XXXX.X… 52 32 479 616 P06396 Gelsolin
GDSYIILYNYRHGGR GGSKTSLYNLRRGVA X.X…XXX.X.X.. 11 347 511 471 P06396  
KVKAHGKKVLGAFSD ENIAEGLRVLLARSH …X.X..XX.X.X. 498 32 479 60 P68871 Hemoglobin subunit beta
AFLGLRQIRLLNLSN VALAIPQCRLTPLSR ..X…X.XX..XX. 34 32 524 313 P0C6S8 Leucine-rich repeat and immunoglobulin-like
LGLRQIRLLNLSNNL LAVQQCRLTPLSRLP X…X.XX..XX… 26 32 526 315 P0C6S8  
YSWGMAVNVYSTSIT GNWVAGVLVYGGSKT ..X…X.XX..X.X 239 8 501 40 Q15555 Microtubule-associated protein RP/EB family member 2
WGMAVNVYSTSITQE WVAGVFVYGGSKTSL X…X.XX..X.X.. 252 8 503 42 Q15555  
LPRWQLALAVGAPLL NLRRGIALAVQQCRL ..X…XXXX....X 97 32 519 36 O94826 Mitochondrial import receptor subunit TOM70
IFQKLMFKNAPTPQE IKDLVMTKPAPTCNI X....X.X.XXX… 90 16 579 114 P13591 Neural cell adhesion molecule 1
VKIFQKLMFKNAPTP DAIKDLVMTKPAPTC ..X....X.X.XXX. 40 32 577 112 P13591  
SLLVTRLQKALGVRQ SLYNLRRGIALAVQQ XX…X…XX.X.X 121 57 516 5 Q99798 Aconitate hydratase, mitochondrial
SLLVTRLQKALGVRQ SLYNLRRGIALAVSQ XX…X…XX.X.X 121 58 516 5 Q99798  
SLLVTRLQKALGVRQ SLYNLRRGIALAVPQ XX…X…XX.X.X 121 72 516 5 Q99798 Aconitate hydratase, mitochondrial
NKGIGLAIVRDLCRL RRGIGLAIPQCLLTP ..XXXXXX…X… 436 369 521 14 P16152 Carbonyl reductase NADPH 1
RRGRLAVSFRFRTWD LRALLARSHVERTTD .X..XX.X…XX.X 77 407 485 379 P78357 Contactin-associated protein 1
LGAALRRCAVAATTR LRLLLARCHVERTTE X…X.XX.X..XX. 401 277 485 2 P20674 Cytochrome c oxidase subunit 5A, mitochondrial
LGAALRRCAVAATTR LRTLLXRCHVERTTX X…X.XX.X..XX. 401 248 484 2 P20674  
GTRLSLARMPPPLPT GLRLLLARCHVERTT X.XX.XXX......X 326 139 484 34 P14136 Glial fibrillary acidic protein
VVFFNVPEKLRLPDA QKFENIAEGLRLLLA ..X.X..X.XXX..X 416 382 476 134 P78559 Microtubule-associated protein 1A
TAYARLRGIEQAVQS SLYNLRRGIALAVQQ ..X…XXX..XXX. 482 57 516 541 Q16891 Mitochondrial inner membrane protein
NTAYARLRGIEQAVQ TSLYNLRRGIALAVQ …X…XXX..XXX 349 63 515 540 Q16891  
FTLKVLTTRGVAERT EGLRVLLARSHVERT ..X.XX..X…XXX 209 113 483 229 O94856 Neurofascin
TLKVLTTRGVAERTP GLKLLLARSHVERTT .XX.X..X…XXX. 368 96 484 230 O94856  
FTLKVLTTRGVAERT EGLKLLLARSHVERT ..XX.X..X…XXX 209 87 483 229 O94856  
PTEIIAFSNRAEDFR KFENIADSLRALLAR ..X.XX.X.XX…X 83 436 477 52 P32119 Peroxiredoxin-2
EIIAFSNRAEDFRKL ENIADSLRALLARSH X.XX.X.XX…X.. 233 194 479 54 P32119  
GSVILLENLRFHVEE GSKTSLYNLRRGVAL XX…X.XXX..X.. 33 119 512 114 P00558 Phosphoglycerate kinase 1
AGSVILLENLRFHVE GGSKTSLYNLRRGVA .XX…X.XXX..X. 26 347 511 113 P00558  
ASLQRVRRPVAMVMP TSLYNLRRGVALAIP .XX…XX.XX…X 268 52 515 95 Q15149 Plectin
LKKGLLSAEVARLLL SQKFENIAEGLRLLL ..X....XX..XXXX 70 465 475 3847 Q15149  
VRVFRIFKLSRHSKG VPQCRITPLSRLPFG X…XX..XXX…X 13 475 528 299 P16389 Potassium voltage-gated channel subfamily A member 2
VRVFRIFKLSRHSKG VSQCRITPLSRLPFG X…XX..XXX…X 13 427 528 299 P16389  
LFPGVALLLAAARLA LRRGVALAIPQCRLT X..XXXX.....XX. 131 413 520 8 P30101 Protein disulfide-isomerase A3
ALFPGVALLLAAARL NLRRGVALAIPQCRL .X..XXXX.....XX 242 333 519 7 P30101  
PAIRLLYAKRPGIGL GSRTSLYNLRRGIGL .....XX..X.XXXX 40 250 512 190 O75061 Putative tyrosine-protein phosphatase auxilin
RLLYAKRPGIGLSPS TSLYNLRRGIALAVS ..XX..X.XX.X..X 466 64 515 193 O75061  
SFASDPILYRPVAVA SKTSLYNLRRGVALA X..X…X.X.XX.X 253 90 513 97 P14618 Pyruvate kinase PKM
VEGSFVYKGGKIYKV VAGVFVYGGSKTSLY X.X.XXX.X.X.... 120 100 504 105 P31150 Rab GDP dissociation inhibitor alpha
ARKKKLLEAQSHFRK AEGLKLLLARSHVER X…XXX.X.XX… 212 86 482 2074 Q13813 Spectrin alpha chain, non-erythrocytic 1
TTCIELGKSLLARKH ENIAEGLKLLLARSH ....X..X.XXXX.X 62 254 479 1968 Q01082  

Underlined is the core of the peptide. Binding score (nM) prediction using NetMHCII and NetMHCIIpan. Binding score <50: strong binder, binding score 50–500 weak binder.

Discussion

In this study we have proven the feasibility of obtaining EBNA-1 sequences directly from buffy coat samples, without any requirement for primary cultures that could theoretically be associated with preferential selection of viral sequence variants through ex vivo expansion. In this regard our findings are in keeping with those of Burrows and colleagues [11], who demonstrated similar patterns of EBNA-1 sequence variation predominantly within the C-terminal region in both MS cases and controls, in a study that did involve primary B lymphocyte cultures. Both studies, as well as a more recent analysis of spontaneously outgrown human lymphoblastoid cell lines [65] are in agreement in demonstrating that the majority of autologous sequences do not align closely with the widely used B95-8 laboratory strain–a result that is perhaps not surprising given that this strain was originally identified following transfusion-associated EBV in an elderly woman and subsequently selected for its ability to efficiently immortalise B lymphocytes [66].

Our results are also in agreement with other studies that have identified similar patterns of EBNA-1 [67] and EBNA-2 [68] sequence variation when comparing MS cases and controls, albeit at low resolution in these cases, suggesting that MS susceptibility is not likely to be readily explained by an ‘encephalitogenic strain’ of EBV. We have also explored sequence variation within individual samples using next-generation sequencing techniques, to investigate if the presence of multiple viral sequence variants could indicate sites of immune selection pressure–as has been suggested previously for EBNA-1 [11]–and/or that infection with multiple EBV strains could represent a risk factor for MS disease as has been previously proposed [69]. We identified nucleotide mixtures present at 10 percent in two samples. Mixtures were primarily caused by point mutations leading to amino acid changes in 12 different positions compared to silent mutations in five positions only. This could indicate EBV superinfection or viral immune escape. While we were able to identify low-level EBNA-1 sequence variation in these samples (involving 8.3% of nucleotides at a 1% threshold), our results do not support a strong influence of intraindividual EBV sequence variation in MS disease risk and we cannot exclude that some of these point mutations are due to technical artefacts. It is however interesting to note that EBNA-1 sequence conservation described in Fig 4 (reflecting genetic variation as well as the impact this has on amino acid properties), does appear to map to HLA-DRB1 binding regions, although we were unable to identify natural sequence variants that were associated with abrogation of HLA binding using the NetMHCIIPan prediction algorithm. However, in the HLA-viral sequence variation association analyses, we could identify eight out of nine EBNA-1 polymorphic nucleotide positions significantly associated with MS risk alleles within these HLA-DRB1 binding regions, including two in the previously described HLA-DRB1*15 ‘AEG’ and ‘MVF’ epitopes respectively, noting in each case that the more common (wild-type) viral sequence was favoured in the presence of disease-associated HLA-DR alleles. These differences will be explored further in terms of their impact on epitope-specific CD4+ T-cell immune responses, acknowledging in relation to MS pathogenesis that important differences may relate to the selection of regulatory versus effector EBNA-1-specific CD4+ T cells [18], rather than simply reflecting immune evasion.

Fig 4. EBNA-1 sequence conservation and relationship to NetMHCII predicted HLA-DRB1*DR15-restricted epitopes derived from patient MS sequences.

Fig 4

Shown are EBNA-1 amino acid positions 473–593. Predicted epitopes: blue boxes, known epitopes: black underlined, predicted epitope core: grey shade.

We have also explored the potential for autoantigens to be selected by cross-reactive EBNA-1-specific T cells, according to a shared propensity for HLA-DRB1*15-restricted antigen presentation as well as evidence of sequence homology. This concept is in keeping with previous experimentally-proven examples of this phenomenon (albeit without identification of specific epitopes involved) [35], with additional support from observations that HLA-DRB1*15-restricted immune responses are characterised by a relatively high level of TCR degeneracy that would favour cross-reactivity [70]. These results are preliminary and require experimental confirmation of their functional validity.The main purpose of this analysis was to create a platform for experimental design that acknowledges natural patient derived EBNA-1 sequence variants as the basis for epitope selection, while also expanding the possibilities of identifying novel candidate CNS antigens that may have a role in MS pathogenesis. As noted by Ben-Nun and colleagues [55] and Lassmann and colleagues [71], MS research is increasingly moving away from reductionist experimental models towards an interest in a wide array of myelin and axoglial antigen targets, which would be in keeping with a model of MS pathogenesis that allows for cross-reactive T cell (as well as humoral) responses that are initially driven by viral-specific responses–with EBNA-1 representing a legitimate candidate target based on previous work [27, 3139].

These observations, along with continuing evidence of patient-specific heterogeneity of MS lesion pathology [72] and oligoclonal TCR repertoire [73] would support a model of MS disease pathogenesis in which virus-specific immunity, which is oligoclonal in nature as determined by viral sequence variation seen in this and other studies [911] as well as by polymorphic HLA-restricted antigen presentation, could then trigger cross-reactive autoimmune responses. We now hope to investigate these possibilities further, with a particular focus on the roles of both antigen-presenting B cells as well as antigen-specific T cells in provoking inflammatory immune responses. In this respect, we would anticipate that targeted T-cell immunotherapy is likely to require a patient-specific approach as recently performed by Pender and colleagues [37], while targeting EBV-infected B cells may have the potential to provide a more universal treatment strategy, particularly in light of recent evidence that antigen-experienced B cells within the central nervous system in MS cases are likely to be derived from the peripheral blood and lymph nodes [74,75].

Supporting Information

S1 Fig. Location of EBNA-1 PCR primers given with reference to nucleotide position of the B95-8 strain and PCR size given as base pairs (bp).

Start and stop indicate the EBNA-1 gene. Purple indicates position of known epitopes.

(TIF)

S1 Table. Primers used for EBV amplification.

(DOC)

S2 Table. Human brain proteins included in the analysis from NCBI database.

(DOC)

S3 Table. Sanger sequence Genbank Accession numbers.

(DOC)

Acknowledgments

We would like to thank all participants in the Perth Demyelinating Disease cohort for their participation, as well as all doctors and nurses involved in sample collection.

We gratefully acknowledge the McCusker Charitable Foundation that enabled this project to be realised.

Data Availability

All relevant data are within the paper and its Supporting Information files.

Funding Statement

This project was funded by the McCusker Charitable Foundation; URL: http://www.mccuskercharitable.com.au (MT, KS, DN) and Multiple Sclerosis Research Australia (MSRA)—Grant number 12040; URL: http://www.msra.org.au (MT, WMC, AGK, DN). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Fig. Location of EBNA-1 PCR primers given with reference to nucleotide position of the B95-8 strain and PCR size given as base pairs (bp).

Start and stop indicate the EBNA-1 gene. Purple indicates position of known epitopes.

(TIF)

S1 Table. Primers used for EBV amplification.

(DOC)

S2 Table. Human brain proteins included in the analysis from NCBI database.

(DOC)

S3 Table. Sanger sequence Genbank Accession numbers.

(DOC)

Data Availability Statement

All relevant data are within the paper and its Supporting Information files.


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