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Epstein–Barr virus and multiple sclerosis
Journal of the Neurological Sciences 286 (2009) 62–64
Contents lists available at ScienceDirect
Journal of the Neurological Sciences j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n s
Epstein–Barr virus and multiple sclerosis Daniela Pohl ⁎ Faculty of Medicine, University of Ottawa, Canada Department of Neurology, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, K1H8L1, Ontario, Canada
a r t i c l e
i n f o
Article history: Received 11 February 2009 Accepted 19 March 2009 Available online 10 April 2009 Keywords: Multiple sclerosis Epstein–Barr virus Infectious mononucleosis CNS infection Autoimmunity Chronic infection Demyelination
a b s t r a c t Epstein–Barr virus (EBV) is a human DNA herpesvirus infecting more than 90% of the world's population. EBV is the etiological agent of infectious mononucleosis (Pfeiffer's disease). Furthermore, diverse malignancies such as Burkitt and Hodgkin lymphoma have been associated with EBV. More recently, a possible role for EBV has been suggested in chronic inflammatory/autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus as well as in multiple sclerosis (MS). MS is currently regarded as a disease with multifactorial etiology, EBV being one possible factor in MS manifestation: Infectious mononucleosis has been shown to increase the risk of developing MS later in life. EBV seroprevalence rates are higher in MS as compared to controls, in adult as well as in pediatric MS patients. Moreover, EBV antibody titres and EBV specific T-cells are increased in MS patients as compared to healthy individuals. Recently, CNS B-cells of MS patients have been reported to harbour EBV. However, there is still controversy whether EBV could be a causative agent as opposed to an innocent bystander in the pathogenesis of MS. This review summarizes current knowledge on the association of EBV and MS including a critical discussion of equivocal findings. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Multiple sclerosis (MS) is presently regarded as a disease with multifactorial etiology, comprising genetic as well as environmental influences. Already more than a century ago, Pierre Marie did state that “the cause of insular (multiple) sclerosis is intimately connected with infectious diseases” [1]. Since that time, a multitude of germs, including bacteria as well as diverse viruses, have been suspected to cause MS. For most of them inconsistent results have been obtained, and nearly all suspicious candidates of the past are now considered unrelated to the disease (e.g. measles virus). So far, no single agent has been identified as the “MS-pathogen”, but current leading candidates comprise human herpesvirus type 6 (HHV6), multiple sclerosis associated human endogenous retrovirus (HERV) and Epstein–Barr virus (EBV). EBV is a B-lymphotropic human DNA herpesvirus. It is one of the most common human viruses and infects more than 90% of the world's population, with a life-long viral persistence in the host. Infection occurs via the saliva, and is often asymptomatic, especially in early childhood. If infection happens in adolescence or later in life, it is more frequently symptomatic, causing the clinical picture of infectious mononucleosis in up to 50% of cases. The acute illness usually resolves within weeks, but EBV remains dormant in memory B cells
⁎ Tel.: +1 613 737 7600x3504; fax: +1 613 738 4886. E-mail address: [email protected]. 0022-510X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2009.03.028
throughout life. It can periodically reactivate and then be shed into the saliva, thereby enabling transmission to other individuals [2]. Already in 1889, Emil Pfeiffer described the clinical picture of infectious mononucleosis (Pfeiffer's disease). However, it was only in 1964 that Epstein–Barr virus was discovered by Michael Epstein and Yvonne Barr in cells cultured from a lymphoma specimen sent to them from Uganda by Dennis Burkitt. The virus was soon identified to be associated with B cell malignancies (Burkitt lymphoma and Hodgkin lymphoma), T cell malignancies (extranodal NK/T cell lymphoma and hemophagocytic syndrome T cell lymphoma), and epithelial cell malignancies (nasopharyngeal carcinoma and lymphoepitheliomalike carcinoma). Furthermore, there now is increasing evidence that EBV may play a role in the pathogenesis of chronic inflammatory/ autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus (SLE) as well as in MS. However, there is still considerable controversy whether EBV could be a causative agent as opposed to an innocent bystander in the pathogenesis of MS. This review summarizes current knowledge on the association of EBV and MS including a discussion of equivocal findings. 2. EBV seroprevalence and EBV antibody titres in MS In 1976, increased EBV-viral capsid antigen (VCA) antibody titres have been reported in a higher percentage of MS patients than healthy controls. However, this study was not able to show significantly higher EBV seroprevalence rates (98.5% of MS patients versus 95.8% of controls), maybe due to the rather small sample size [3]. In 1980, the
D. Pohl / Journal of the Neurological Sciences 286 (2009) 62–64
same group found significantly higher EBV–VCA seroprevalence rates in MS patients (98.7%) as compared to controls (93.8%) in an enlarged study with 157 MS patients and 81 control subjects. Furthermore, significantly higher geometric mean titres of EBV–VCA antibodies were demonstrated in the MS patient cohort [4]. In the following decades, these findings have been reproduced by many other groups, and higher titres have been reported for EBV nuclear antigen (EBNA) antibodies as well [5–21]. An increase in EBNA antibodies may precede the clinical onset of MS by 5–20 years [9,11,13,16]. MS-associated differences of the humoral immune response to EBV appear to be even more pronounced in paediatric than in adult patients, presumably because the rate of seronegative individuals is higher in that age group, and potentially also because of the closer proximity to the true onset of the disease [18–20]. Taken together, robust serological data consistently demonstrate a close to 100% EBV seropositivity rate in adult patients with MS. However, a very high seroprevalence for EBV antibodies has also been reported for other autoimmune diseases such as systemic lupus erythematosus [22]. Thus, EBV does not seem to be associated specifically with MS, but might act as a general trigger for autoimmune processes leading to various different chronic inflammatory diseases. An argument against a pivotal role of EBV in the etiology of MS is the fact that 100% of children with SLE [23], but only 83–99% of pediatric MS patients have been reported to be EBV seropositive [18–20]. Therefore, EBV might not be a conditio sine qua non for the development of MS. The finding that MS patients have elevated titres of EBV antibodies even before disease manifestation has been reproduced in independent studies. However, elevated antibody concentrations in MS patients have also been reported for measles, herpes simplex, varicella zoster virus and HHV6 [11,24]. Hence, as opposed to a unique pathognomonic immune response to EBV, raised EBV antibody titres might merely be representative of an increased propensity for viral reactivation in patients with MS. 3. Infectious mononucleosis and MS Infectious mononucleosis is the clinical manifestation of acute EBV infection. It is more common in adolescents and adults as compared to younger children, in whom primary EBV infection is more often clinically silent. MS and infectious mononucleosis share a similar prevalence distribution, following a latitude gradient: prevalence generally rises with increasing distance to the equator, on both the southern and the northern hemisphere. Late infection with EBV, evidenced by occurrence of infectious mononucleosis, is therefore considered as a possible risk factor for MS. A metaanalysis of all published studies on the association of MS and infectious mononucleosis revealed a combined relative MS risk of 2.3 for individuals with infectious mononucleosis as compared to EBVpositive individuals with a clinically silent primary infection [25]. A longitudinal study including 25,234 Danish patients with mononucleosis exactly confirmed these data: 104 patients (4.1‰) developed MS, representing a 2.3-fold increase in MS incidence as compared to the general population. The MS risk increased within 5 years of the infectious mononucleosis illness, and remained elevated for more than 3 decades [26]. Combining the results of the metaanalysis with those from other investigations on EBV, a model for the relation between EBV infection and MS has been proposed: the risk for MS is close to zero among EBV-negative individuals, intermediate among those infected with EBV in early childhood and highest among persons infected in adolescence or later in life [25]. The crucial question all these epidemiological studies cannot answer is whether a (late) EBV infection really predisposes to contract MS, or whether there might be a shared immunogenetic susceptibility towards a symptomatic EBV infection and MS or common environmental factors triggering both, the occurrence of infectious mononucleosis and MS.
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4. Intrathecal production of EBV-antibodies in MS An intrathecal IgG production is a key feature of both MS and CNS infections. In neuroinfectious diseases like herpes simplex virus encephalitis, neuroborreliosis, subacute sclerosing panencephalitis, varicella zoster virus vasculitis and ganglionitis, a significant part of the intrathecally produced IgG is directed against the causative agent [27–29]. This specific intrathecal immune response is long-lasting and can still be detected several years after an infection [28]. There are several reports pointing towards a possibly increased EBV-targeted humoral immune response in the CNS of MS patients. The first of these studies analyzed the CSF-to-serum antibody ratios of EBV and adenovirus in MS patients: 32 of 39 MS patients (82%) showed an increased CSF-to-serum EBV–VCA antibody ratio, whereas only 4 of 20 MS patients (20%) showed an increased adenovirus antibody ratio. The authors interpreted these findings as an indication for a raised CNS antibody production against EBV in patients with MS [6]. Similar conclusions were drawn from another survey, in which 10 of 15 MS patients showed intrathecal IgG antibody synthesis against EBNA-1. In 5 of these patients, a distinctive oligoclonal antigen specific banding pattern for EBNA-1 was observed [30]. More recently, an intrathecal antibody response to the EBV protein BRRF2 has been reported, as well as an oligoclonal binding pattern of CSF IgG to EBNA1 and BRRF2 proteins in individual MS patients. In 3 MS patients with high EBNA-1 antibody titres in CSF, part of their CSF oligoclonal bands were absorbed by preincubation of CSF with EBNA-1 [21]. However, it is a well-known phenomenon that MS patients may present an intrathecal antibody synthesis against various germs like measles, rubella, varicella zoster, herpes simplex, mumps virus, HHV6 and Chlamydia pneumoniae [27,28,31–33]. In a cohort of 177 MS patients, as many as 78% showed intrathecally produced antibodies against rubella, 60% against measles and 55% against varicella zoster virus [31]. Furthermore, Chlamydia pneumoniae specific oligoclonal bands have been detected in 5 of 56 MS patients, similar to the observations reported for EBV [34]. These findings indicate the possibility that intrathecally produced antibodies against EBV antigens might merely be part of the MS-typical polyspecific CNS antibody production, directed against diverse common pathogens. 5. EBV specific T-cells in MS Cell mediated immune mechanisms, involving T and NK cells, are of pivotal importance in controlling the proliferation of EBV-infected B cells. The frequency of EBNA-1 specific CD4+ memory T cells was found to be strikingly elevated in MS patients as compared to healthy EBV carriers. Furthermore, these EBNA-1 specific T cells showed increased proliferative capacity and enhanced interferon-gamma production [35]. A strong EBV-specific CD8+ T cell response in patients with clinically isolated syndrome has been reported recently [36]. T cell crossrecognition between EBV peptides and myelin proteins including myelin basic protein (MBP) has been demonstrated, supporting a concept of possible autoimmune mechanisms by cross-reactivity towards EBV and autoantigens (molecular mimicry) [37–40]. Still, it is to be noted that EBV–MBP cross-reactive T cells have been found in similar frequencies in MS patients and healthy controls [38]. The mechanisms leading to tolerance in the majority of individuals versus the induction of autoimmunity and disease in others are not even rudimentarily understood. 6. EBV in the CNS of MS patients Several independent groups have analyzed the presence of EBV genome in the CSF of MS patients by PCR. They have either not detected any EBV DNA at all [41] or demonstrated EBV DNA in only a small percentage of MS patients without significant difference as compared to controls [42,43]. One study of postmortem brain samples detected EBV in 27% of MS cases as opposed to 38% of controls [44].
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D. Pohl / Journal of the Neurological Sciences 286 (2009) 62–64
Interestingly, a recent study investigating the expression of markers of EBV latent and lytic infection in postmortem brain specimens showed evidence of EBV infection in brain-infiltrating B cells and plasma cells in 21 of 22 MS patients and none of 11 controls [45]. However, only 2 of the 11 controls were suffering from chronic inflammatory CNS diseases, and their treatment status is not reported. Furthermore, 11 of 12 MS patients with information on therapy received long-term immunosuppressive treatment, 7 of them with ACTH. Thus, the results of this study await confirmation by an independent analysis of MS patients without immunosuppressive treatment combined with a larger number of control patients with other chronic inflammatory CNS diseases. 7. Conclusions EBV represents, due to its life-long latent infection of B cells, promoting their proliferation and activation, and due to its periodical reactivation with consecutive repetitive antigenic challenge to the immune system, a plausible candidate to trigger a chronic inflammatory immune response of the type seen in MS. Diverse studies have shown an association of EBV with MS, however, most of them lack the combination of appropriate control groups of other chronic inflammatory autoimmune CNS diseases with the evaluation of a control panel of neurotropic and EBV-related viruses in parallel. Further investigations designed with adequate controls will be necessary to better define the role of EBV in MS pathogenesis. Assuming EBV really acts as a cofactor in the pathogenesis of MS, there might be an opportunity for preventive strategies such as vaccinations. Hopefully one day, the following statement of Pierre Marie will become a reality: “I have little doubt in fact, gentlemen, that in the employment of such a substance as the vaccine of Pasteur or lymph of Koch the evolution of insular (multiple) sclerosis will someday be rendered absolutely impossible.” [1]. References [1] Murray TJ. Multiple sclerosis: the history of a disease. New York: Demos Medical Publishing; 2005. p. 179. [2] Lünemann JD, Muenz C. Epstein–Barr virus and multiple sclerosis. Curr Neurol Neurosci Rep 2007;7:253–8. [3] Sumaya CV, Myers L, Ellison GW. Epstein–Barr virus antibodies in multiple sclerosis. Trans Am Neurol Ass 1976;101:300–2. [4] Sumaya CV, Myers LW, Ellison GW. Epstein–Barr virus antibodies in multiple sclerosis. Arch Neurol 1980;37:94–6. [5] Bray PF, Bloomer LC, Salmon VC. Epstein–Barr virus infection and antibody synthesis in patients with multiple sclerosis. Arch Neurol 1983;40:406–8. [6] Sumaya CV, Myers LW, Ellison GW, Ench Y. Increased prevalence and titer of Epstein–Barr virus antibodies in patients with multiple sclerosis. Ann Neurol 1985;17:371–7. [7] Larsen PD, Bloomer LC, Bray PF. Epstein–Barr nuclear antigen and viral capsid antigen antibody titers in multiple sclerosis. Neurology 1985;35:435–8. [8] Shirodaria PV, Haire M, Fleming E, Merrett JD, Hawkins Sa, Roberts SD. Viral antibody titers. Comparison in patients with multiple sclerosis and rheumatoid arthritis. Arch Neurol 1987;44:1237–41. [9] Ascherio A, Munger KL, Lennette ET, Spiegelman D, Hernán MA, Olek MJ, et al. Epstein–Barr virus antibodies and risk of multiple sclerosis: a prospective study. JAMA 2001;26:3083–8. [10] Villoslada P, Juste C, Tintore M, Llorenç V, Codina G, Pozo-Rosich P, et al. The immune response against herpesvirus is more prominent in the early stages of MS. Neurology 2003;60:1944–8. [11] Sundström P, Juto P, Wadell G, Hallmans G, Svenningsson A, Nyström L, et al. An altered immune response to Epstein–Barr virus in multiple sclerosis: a prospective study. Neurology 2004;62:2277–82. [12] Haahr S, Plesner Am, Vestergaard BF, Höllsberg P. A role of late Epstein–Barr virus infection in multiple sclerosis. Acta Neurol Scand 2004;109:270–5. [13] Levin LI, Munger KL, Rubertone MV, Peck CA, Lennette ET, Spiegelman D, et al. Temporal relationship between elevation of Epstein–Barr virus antibody titers and initial onset of neurological symptoms in multiple sclerosis. JAMA 2005;293:2496–500. [14] Myhr KM, Riise T, Barrett-Connor E, Myrmel H, Vedeler C, Gronning M, et al. Altered antibody pattern to Epstein–Barr virus but not to other herpesviruses in multiple sclerosis: a population based case-control study from western Norway. J Neurol Neurosurg Psychiatry 1998;64:539–42. [15] Buljevac D, van Doornum GJJ, Flach HZ, Groen J, Osterhaus AD, Hop W, et al. Epstein–Barr virus and disease activity in multiple sclerosis. J Neurol Neurosurg Psychiatry 2005;76:1377–81.
[16] DeLorenze GN, Munger KL, Lennette ET, Orentreich N, Vogelman JH, Ascherio A. Epstein–Barr virus and multiple sclerosis: evidence of an association from a prospective study with long-term follow-up. Arch Neurol 2006;63:839–44. [17] De Jager PL, Simon KC, Munger KL, Rioux JD, Hafler DA, Ascherio A. Integrating risk factors: HLA-DRB1⁎1501 and Epstein–Barr virus in multiple sclerosis. Neurology 2008;70:1113–8. [18] Banwell B, Krupp L, Kennedy J, Tellier R, Tenembaum S, Ness J, et al. Clinical features and viral serologies in children with multiple sclerosis: a multinational observational study. Lancet Neurol 2007;6:773–81. [19] Pohl D, Krone B, Rostasy K, Kahler E, Brunner E, Lehnert M, et al. High seroprevalence of Epstein–Barr virus in children with multiple sclerosis. Neurology 2006;67:2063–5. [20] Alotaibi S, Kennedy J, Tellier R, Stephens D, Banwell B. Epstein–Barr virus in pediatric multiple sclerosis. JAMA 2004;291:1875–9. [21] Cepok S, Zhou D, Srivastava R, Nessler S, Stei S, Büssow K, et al. Identification of Epstein–Barr virus proteins as putative targets of the immune response in multiple sclerosis. J Clin Invest 2005;115:1352–60. [22] James JA, Neas BR, Moser KL, Hall T, Bruner GR, Sestak AL, et al. Systemic lupus erythematosus in adults is associated with previous Epstein–Barr virus exposure. Arthritis Rheum 2001;44:1122–6. [23] McClain MT, Poole BD, Bruner BF, Kaufman KM, Harley JB, James JA. An altered immune response to Epstein–Barr nuclear antigen 1 in pediatric systemic lupus erythematosus. Arthritis Rheum 2006;54:360–8. [24] Krone B, Pohl D, Rostasy K, Kahler E, Brunner E, Oeffner F, et al. Common infectious agents in multiple sclerosis: a case control study in children. Mult Scler 2008;14:136–9. [25] Thacker EL, Mirzaei F, Ascherio A. Infectious mononucleosis and risk for multiple sclerosis: a meta-analysis. Ann Neurol 2006;59:499–503. [26] Nielsen TR, Rostgaard K, Nielsen NM, Frisch M, Hjalgrim H. Multiple sclerosis after infectious mononucleosis. Arch Neurol 2007;64:72–5. [27] Derfuss T, Gürkov R, Then Bergh F, Goebels N, Hartmann M, Barz C, et al. Intrathecal antibody production against Chlamydia pneumoniae in multiple sclerosis is part of a polyspecific immune response. Brain 2001;124:1325–35. [28] Reiber H, Peter JB. Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs. J Neurol Sci 2001;184:101–22. [29] Burgoon MP, Hammack BN, Owens GP, Maybach AL, Eikelenboom MJ, Gilden DH. Oligoclonal immunoglobulins in cerebrospinal fluid during varicella zoster virus (VZV) vasculopathy are directed against VZV. Ann Neurol 2003;54:459–63. [30] Rand KH, Houck H, Denslow ND, Heilman KM. Epstein–Barr virus nuclear antigen1 (EBNA-1) associated oligoclonal bands in patients with multiple sclerosis. J Neurol Sci 2000;173:32–9. [31] Reiber H, Ungefehr S, Jacobi C. The intrathecal, polyspecific and oligoclonal immune response in multiple sclerosis. Mult Scler 1998;4:111–7. [32] Derfuss T, Hohlfeld R, Meinl E. Intrathecal antibody (IgG) production against human herpesvirus type 6 occurs in about 20% of multiple sclerosis patients and might be linked to a polyspecific B-cell response. J Neurol 2005;252:968–71. [33] Rostasy K, Reiber H, Pohl D, Lange P, Ohlenbusch A, Eiffert H, et al. Chlamydia pneumoniae in children with MS: frequency and quantity of intrathecal antibodies. Neurology 2003;61:125–8. [34] Franciotta D, Yardini E, Bergamaschi R, Grimaldi LM, Andreoni L, Cosi V. Analysis of Chlamydia pneumoniae-specific oligoclonal bands in multiple sclerosis and other neurological diseases. Acta Neurol Scand 2005;112:238–41. [35] Lünemann JD, Edwards N, Muraro PA, Hayashi S, Cohen JI, Munz C, et al. Increased frequency and broadened specificity of latent EBV nuclear antigen-I-specific Tcells in multiple sclerosis. Brain 2006;129:1493–506. [36] Jilek S, Schluep M, Meylan P, Vingerhoets F, Guignard L, Monney A, et al. Strong EBV-specific CD8+ T-cell response in patients with early multiple sclerosis. Brain 2008;131:1712–21. [37] Holmoy T, Kvale EO, Vartdal F. Cerebrospinal fluid CD4+ T cells from a multiple sclerosis patient cross-recognize Epstein–Barr virus and myelin basic protein. J Neurovirology 2004;10:278–83. [38] Lünemann JD, Jelcic I, Roberts S, Lutterotti A, Tackenberg B, Martin R, et al. EBNA1specific T cells from patients with multiple sclerosis cross react with myelin antigens and co-produce IFN-gamma and IL-2. J Exp Med 2008;205:1763–73. [39] Wucherpfennig KW, Strominger JL. Molecular mimicry in T cell-mediated autoimmunity: viral peptides activate human T cell clones specific for myelin basic protein. Cell 1995;80:695–705. [40] Lang HLE, Jacobsen H, Ikemizu S, Andersson C, Harlos K, Madsen L, et al. A functional and structural basis for TCR cross-reactivity in multiple sclerosis. Nat Immunol 2002;3:940–3. [41] Martin C, Enbom M, Söderström M, Fredrikson S, Dahl H, Lycke J, et al. Absence of seven human herpesviruses, including HHV-6, by polymerase chain reaction in CSF and blood from patients with multiple sclerosis and optic neuritis. Acta Neurol Scand 1997;95:280–3. [42] Mancuso R, Delbue S, Borghi E, Pagani E, Calvo MG, Caputo D, et al. Increased prevalence of varicella zoster virus DNA in cerebrospinal fluid from patients with multiple sclerosis. J Med Virol 2007;79:192–9. [43] Alvarez-Lafuente R, García-Montojo M, De Las Heras V, Domínguez-Mozo MI, Bartolome M, Benito-Martin MS, et al. Herpesviruses and human endogenous retroviral sequences in the cerebrospinal fluid of multiple sclerosis patients. Mult Scler 2008;14:595–601. [44] Sanders VJ, Felisan S, Waddell A, Tourtellotte WW. Detection of herpesviridae in postmortem multiple sclerosis brain tissue and controls by polymerase chain reaction. J Neurovirol 1996;2:249–58. [45] Serafini B, Rosicarelli B, Franciotta D, Magliozzi R, Reynolds R, Cinque P, et al. Dysregulated Epstein–Barr infection in the multiple sclerosis brain. J Exp Med 2007;204:2899–912.
Contents lists available at ScienceDirect
Journal of the Neurological Sciences j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n s
Epstein–Barr virus and multiple sclerosis Daniela Pohl ⁎ Faculty of Medicine, University of Ottawa, Canada Department of Neurology, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, K1H8L1, Ontario, Canada
a r t i c l e
i n f o
Article history: Received 11 February 2009 Accepted 19 March 2009 Available online 10 April 2009 Keywords: Multiple sclerosis Epstein–Barr virus Infectious mononucleosis CNS infection Autoimmunity Chronic infection Demyelination
a b s t r a c t Epstein–Barr virus (EBV) is a human DNA herpesvirus infecting more than 90% of the world's population. EBV is the etiological agent of infectious mononucleosis (Pfeiffer's disease). Furthermore, diverse malignancies such as Burkitt and Hodgkin lymphoma have been associated with EBV. More recently, a possible role for EBV has been suggested in chronic inflammatory/autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus as well as in multiple sclerosis (MS). MS is currently regarded as a disease with multifactorial etiology, EBV being one possible factor in MS manifestation: Infectious mononucleosis has been shown to increase the risk of developing MS later in life. EBV seroprevalence rates are higher in MS as compared to controls, in adult as well as in pediatric MS patients. Moreover, EBV antibody titres and EBV specific T-cells are increased in MS patients as compared to healthy individuals. Recently, CNS B-cells of MS patients have been reported to harbour EBV. However, there is still controversy whether EBV could be a causative agent as opposed to an innocent bystander in the pathogenesis of MS. This review summarizes current knowledge on the association of EBV and MS including a critical discussion of equivocal findings. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Multiple sclerosis (MS) is presently regarded as a disease with multifactorial etiology, comprising genetic as well as environmental influences. Already more than a century ago, Pierre Marie did state that “the cause of insular (multiple) sclerosis is intimately connected with infectious diseases” [1]. Since that time, a multitude of germs, including bacteria as well as diverse viruses, have been suspected to cause MS. For most of them inconsistent results have been obtained, and nearly all suspicious candidates of the past are now considered unrelated to the disease (e.g. measles virus). So far, no single agent has been identified as the “MS-pathogen”, but current leading candidates comprise human herpesvirus type 6 (HHV6), multiple sclerosis associated human endogenous retrovirus (HERV) and Epstein–Barr virus (EBV). EBV is a B-lymphotropic human DNA herpesvirus. It is one of the most common human viruses and infects more than 90% of the world's population, with a life-long viral persistence in the host. Infection occurs via the saliva, and is often asymptomatic, especially in early childhood. If infection happens in adolescence or later in life, it is more frequently symptomatic, causing the clinical picture of infectious mononucleosis in up to 50% of cases. The acute illness usually resolves within weeks, but EBV remains dormant in memory B cells
⁎ Tel.: +1 613 737 7600x3504; fax: +1 613 738 4886. E-mail address: [email protected]. 0022-510X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2009.03.028
throughout life. It can periodically reactivate and then be shed into the saliva, thereby enabling transmission to other individuals [2]. Already in 1889, Emil Pfeiffer described the clinical picture of infectious mononucleosis (Pfeiffer's disease). However, it was only in 1964 that Epstein–Barr virus was discovered by Michael Epstein and Yvonne Barr in cells cultured from a lymphoma specimen sent to them from Uganda by Dennis Burkitt. The virus was soon identified to be associated with B cell malignancies (Burkitt lymphoma and Hodgkin lymphoma), T cell malignancies (extranodal NK/T cell lymphoma and hemophagocytic syndrome T cell lymphoma), and epithelial cell malignancies (nasopharyngeal carcinoma and lymphoepitheliomalike carcinoma). Furthermore, there now is increasing evidence that EBV may play a role in the pathogenesis of chronic inflammatory/ autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus (SLE) as well as in MS. However, there is still considerable controversy whether EBV could be a causative agent as opposed to an innocent bystander in the pathogenesis of MS. This review summarizes current knowledge on the association of EBV and MS including a discussion of equivocal findings. 2. EBV seroprevalence and EBV antibody titres in MS In 1976, increased EBV-viral capsid antigen (VCA) antibody titres have been reported in a higher percentage of MS patients than healthy controls. However, this study was not able to show significantly higher EBV seroprevalence rates (98.5% of MS patients versus 95.8% of controls), maybe due to the rather small sample size [3]. In 1980, the
D. Pohl / Journal of the Neurological Sciences 286 (2009) 62–64
same group found significantly higher EBV–VCA seroprevalence rates in MS patients (98.7%) as compared to controls (93.8%) in an enlarged study with 157 MS patients and 81 control subjects. Furthermore, significantly higher geometric mean titres of EBV–VCA antibodies were demonstrated in the MS patient cohort [4]. In the following decades, these findings have been reproduced by many other groups, and higher titres have been reported for EBV nuclear antigen (EBNA) antibodies as well [5–21]. An increase in EBNA antibodies may precede the clinical onset of MS by 5–20 years [9,11,13,16]. MS-associated differences of the humoral immune response to EBV appear to be even more pronounced in paediatric than in adult patients, presumably because the rate of seronegative individuals is higher in that age group, and potentially also because of the closer proximity to the true onset of the disease [18–20]. Taken together, robust serological data consistently demonstrate a close to 100% EBV seropositivity rate in adult patients with MS. However, a very high seroprevalence for EBV antibodies has also been reported for other autoimmune diseases such as systemic lupus erythematosus [22]. Thus, EBV does not seem to be associated specifically with MS, but might act as a general trigger for autoimmune processes leading to various different chronic inflammatory diseases. An argument against a pivotal role of EBV in the etiology of MS is the fact that 100% of children with SLE [23], but only 83–99% of pediatric MS patients have been reported to be EBV seropositive [18–20]. Therefore, EBV might not be a conditio sine qua non for the development of MS. The finding that MS patients have elevated titres of EBV antibodies even before disease manifestation has been reproduced in independent studies. However, elevated antibody concentrations in MS patients have also been reported for measles, herpes simplex, varicella zoster virus and HHV6 [11,24]. Hence, as opposed to a unique pathognomonic immune response to EBV, raised EBV antibody titres might merely be representative of an increased propensity for viral reactivation in patients with MS. 3. Infectious mononucleosis and MS Infectious mononucleosis is the clinical manifestation of acute EBV infection. It is more common in adolescents and adults as compared to younger children, in whom primary EBV infection is more often clinically silent. MS and infectious mononucleosis share a similar prevalence distribution, following a latitude gradient: prevalence generally rises with increasing distance to the equator, on both the southern and the northern hemisphere. Late infection with EBV, evidenced by occurrence of infectious mononucleosis, is therefore considered as a possible risk factor for MS. A metaanalysis of all published studies on the association of MS and infectious mononucleosis revealed a combined relative MS risk of 2.3 for individuals with infectious mononucleosis as compared to EBVpositive individuals with a clinically silent primary infection [25]. A longitudinal study including 25,234 Danish patients with mononucleosis exactly confirmed these data: 104 patients (4.1‰) developed MS, representing a 2.3-fold increase in MS incidence as compared to the general population. The MS risk increased within 5 years of the infectious mononucleosis illness, and remained elevated for more than 3 decades [26]. Combining the results of the metaanalysis with those from other investigations on EBV, a model for the relation between EBV infection and MS has been proposed: the risk for MS is close to zero among EBV-negative individuals, intermediate among those infected with EBV in early childhood and highest among persons infected in adolescence or later in life [25]. The crucial question all these epidemiological studies cannot answer is whether a (late) EBV infection really predisposes to contract MS, or whether there might be a shared immunogenetic susceptibility towards a symptomatic EBV infection and MS or common environmental factors triggering both, the occurrence of infectious mononucleosis and MS.
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4. Intrathecal production of EBV-antibodies in MS An intrathecal IgG production is a key feature of both MS and CNS infections. In neuroinfectious diseases like herpes simplex virus encephalitis, neuroborreliosis, subacute sclerosing panencephalitis, varicella zoster virus vasculitis and ganglionitis, a significant part of the intrathecally produced IgG is directed against the causative agent [27–29]. This specific intrathecal immune response is long-lasting and can still be detected several years after an infection [28]. There are several reports pointing towards a possibly increased EBV-targeted humoral immune response in the CNS of MS patients. The first of these studies analyzed the CSF-to-serum antibody ratios of EBV and adenovirus in MS patients: 32 of 39 MS patients (82%) showed an increased CSF-to-serum EBV–VCA antibody ratio, whereas only 4 of 20 MS patients (20%) showed an increased adenovirus antibody ratio. The authors interpreted these findings as an indication for a raised CNS antibody production against EBV in patients with MS [6]. Similar conclusions were drawn from another survey, in which 10 of 15 MS patients showed intrathecal IgG antibody synthesis against EBNA-1. In 5 of these patients, a distinctive oligoclonal antigen specific banding pattern for EBNA-1 was observed [30]. More recently, an intrathecal antibody response to the EBV protein BRRF2 has been reported, as well as an oligoclonal binding pattern of CSF IgG to EBNA1 and BRRF2 proteins in individual MS patients. In 3 MS patients with high EBNA-1 antibody titres in CSF, part of their CSF oligoclonal bands were absorbed by preincubation of CSF with EBNA-1 [21]. However, it is a well-known phenomenon that MS patients may present an intrathecal antibody synthesis against various germs like measles, rubella, varicella zoster, herpes simplex, mumps virus, HHV6 and Chlamydia pneumoniae [27,28,31–33]. In a cohort of 177 MS patients, as many as 78% showed intrathecally produced antibodies against rubella, 60% against measles and 55% against varicella zoster virus [31]. Furthermore, Chlamydia pneumoniae specific oligoclonal bands have been detected in 5 of 56 MS patients, similar to the observations reported for EBV [34]. These findings indicate the possibility that intrathecally produced antibodies against EBV antigens might merely be part of the MS-typical polyspecific CNS antibody production, directed against diverse common pathogens. 5. EBV specific T-cells in MS Cell mediated immune mechanisms, involving T and NK cells, are of pivotal importance in controlling the proliferation of EBV-infected B cells. The frequency of EBNA-1 specific CD4+ memory T cells was found to be strikingly elevated in MS patients as compared to healthy EBV carriers. Furthermore, these EBNA-1 specific T cells showed increased proliferative capacity and enhanced interferon-gamma production [35]. A strong EBV-specific CD8+ T cell response in patients with clinically isolated syndrome has been reported recently [36]. T cell crossrecognition between EBV peptides and myelin proteins including myelin basic protein (MBP) has been demonstrated, supporting a concept of possible autoimmune mechanisms by cross-reactivity towards EBV and autoantigens (molecular mimicry) [37–40]. Still, it is to be noted that EBV–MBP cross-reactive T cells have been found in similar frequencies in MS patients and healthy controls [38]. The mechanisms leading to tolerance in the majority of individuals versus the induction of autoimmunity and disease in others are not even rudimentarily understood. 6. EBV in the CNS of MS patients Several independent groups have analyzed the presence of EBV genome in the CSF of MS patients by PCR. They have either not detected any EBV DNA at all [41] or demonstrated EBV DNA in only a small percentage of MS patients without significant difference as compared to controls [42,43]. One study of postmortem brain samples detected EBV in 27% of MS cases as opposed to 38% of controls [44].
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Interestingly, a recent study investigating the expression of markers of EBV latent and lytic infection in postmortem brain specimens showed evidence of EBV infection in brain-infiltrating B cells and plasma cells in 21 of 22 MS patients and none of 11 controls [45]. However, only 2 of the 11 controls were suffering from chronic inflammatory CNS diseases, and their treatment status is not reported. Furthermore, 11 of 12 MS patients with information on therapy received long-term immunosuppressive treatment, 7 of them with ACTH. Thus, the results of this study await confirmation by an independent analysis of MS patients without immunosuppressive treatment combined with a larger number of control patients with other chronic inflammatory CNS diseases. 7. Conclusions EBV represents, due to its life-long latent infection of B cells, promoting their proliferation and activation, and due to its periodical reactivation with consecutive repetitive antigenic challenge to the immune system, a plausible candidate to trigger a chronic inflammatory immune response of the type seen in MS. Diverse studies have shown an association of EBV with MS, however, most of them lack the combination of appropriate control groups of other chronic inflammatory autoimmune CNS diseases with the evaluation of a control panel of neurotropic and EBV-related viruses in parallel. Further investigations designed with adequate controls will be necessary to better define the role of EBV in MS pathogenesis. Assuming EBV really acts as a cofactor in the pathogenesis of MS, there might be an opportunity for preventive strategies such as vaccinations. Hopefully one day, the following statement of Pierre Marie will become a reality: “I have little doubt in fact, gentlemen, that in the employment of such a substance as the vaccine of Pasteur or lymph of Koch the evolution of insular (multiple) sclerosis will someday be rendered absolutely impossible.” [1]. References [1] Murray TJ. Multiple sclerosis: the history of a disease. New York: Demos Medical Publishing; 2005. p. 179. [2] Lünemann JD, Muenz C. Epstein–Barr virus and multiple sclerosis. Curr Neurol Neurosci Rep 2007;7:253–8. [3] Sumaya CV, Myers L, Ellison GW. Epstein–Barr virus antibodies in multiple sclerosis. Trans Am Neurol Ass 1976;101:300–2. [4] Sumaya CV, Myers LW, Ellison GW. Epstein–Barr virus antibodies in multiple sclerosis. Arch Neurol 1980;37:94–6. [5] Bray PF, Bloomer LC, Salmon VC. Epstein–Barr virus infection and antibody synthesis in patients with multiple sclerosis. Arch Neurol 1983;40:406–8. [6] Sumaya CV, Myers LW, Ellison GW, Ench Y. Increased prevalence and titer of Epstein–Barr virus antibodies in patients with multiple sclerosis. Ann Neurol 1985;17:371–7. [7] Larsen PD, Bloomer LC, Bray PF. Epstein–Barr nuclear antigen and viral capsid antigen antibody titers in multiple sclerosis. Neurology 1985;35:435–8. [8] Shirodaria PV, Haire M, Fleming E, Merrett JD, Hawkins Sa, Roberts SD. Viral antibody titers. Comparison in patients with multiple sclerosis and rheumatoid arthritis. Arch Neurol 1987;44:1237–41. [9] Ascherio A, Munger KL, Lennette ET, Spiegelman D, Hernán MA, Olek MJ, et al. Epstein–Barr virus antibodies and risk of multiple sclerosis: a prospective study. JAMA 2001;26:3083–8. [10] Villoslada P, Juste C, Tintore M, Llorenç V, Codina G, Pozo-Rosich P, et al. The immune response against herpesvirus is more prominent in the early stages of MS. Neurology 2003;60:1944–8. [11] Sundström P, Juto P, Wadell G, Hallmans G, Svenningsson A, Nyström L, et al. An altered immune response to Epstein–Barr virus in multiple sclerosis: a prospective study. Neurology 2004;62:2277–82. [12] Haahr S, Plesner Am, Vestergaard BF, Höllsberg P. A role of late Epstein–Barr virus infection in multiple sclerosis. Acta Neurol Scand 2004;109:270–5. [13] Levin LI, Munger KL, Rubertone MV, Peck CA, Lennette ET, Spiegelman D, et al. Temporal relationship between elevation of Epstein–Barr virus antibody titers and initial onset of neurological symptoms in multiple sclerosis. JAMA 2005;293:2496–500. [14] Myhr KM, Riise T, Barrett-Connor E, Myrmel H, Vedeler C, Gronning M, et al. Altered antibody pattern to Epstein–Barr virus but not to other herpesviruses in multiple sclerosis: a population based case-control study from western Norway. J Neurol Neurosurg Psychiatry 1998;64:539–42. [15] Buljevac D, van Doornum GJJ, Flach HZ, Groen J, Osterhaus AD, Hop W, et al. Epstein–Barr virus and disease activity in multiple sclerosis. J Neurol Neurosurg Psychiatry 2005;76:1377–81.
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