B cells and multiple sclerosis

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B cells and multiple sclerosis Diego Franciotta, Marco Salvetti, Francesco Lolli, Barbara Serafini, Francesca Aloisi Lancet Neurol 2008; 7: 852–58 See Reflection and Reaction page 766 Laboratory of Neuroimmunology, IRCCS Neurological Institute ‘C Mondino’, via Mondino 2, 27100, Pavia, Italy (D Franciotta MD); Department of Neurology and Centro Neurologico Terapia Sperimentale (CENTERS), Ospedale S. Andrea, University of Rome ‘La Sapienza’, via di Grottarossa 1035, 00189, Rome, Italy (M Salvetti MD); Department of Neurological and Psychiatric Sciences, University of Florence, viale Morgagni 85, 50134, Florence, Italy (F Lolli MD); Department of Cell Biology and Neuroscience, Istituto Superiore di Sanità, viale Regina Elena 299, 00161, Rome, Italy (B Serafini PhD, F Aloisi PhD) Correspondence to: Dr Diego Franciotta, Neurological Institute ‘C. Mondino’, via Mondino 2, 27100 Pavia, Italy [email protected]

Clonal expansion of B cells and the production of oligoclonal IgG in the brain and cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) have long been interpreted as circumstantial evidence of the immune-mediated pathogenesis of the disease and suggest a possible infectious cause. Extensive work on intrathecally produced antibodies has not yet clarified whether they are pathogenetically relevant. Irrespective of antibody specificity, however, the processes of antibody synthesis in the CNS of patients with MS are becoming increasingly clear. Likewise, targeting B cells might be therapeutically relevant in MS and other autoimmune diseases that are deemed to be driven predominantly by T cells. Accumulating evidence indicates that in MS, similar to rheumatoid arthritis, B cells aggregate into lymphoid-like structures in the target organ. The process of aggregation is mediated through the expression of lymphoid-homing chemokines. In the brain of a patient with MS, ectopic B-cell follicles preferentially adjoin the pial membrane within the subarachnoid space. Recent findings indicate that substantial numbers of B cells that are infected with Epstein-Barr virus (EBV) accumulate in these intrameningeal follicles and in white matter lesions and are probably the target of a cytotoxic immune response. These findings, which await confirmation, could be an explanation for the continuous B-cell and T-cell activation in MS, but leave open concerns about the possible pathogenicity of autoantibodies. Going beyond the antimyelin-antibody dogma, the above data warrant further work on various B-cell-related mechanisms, including investigation of B-cell effector and regulatory functions, definition of the consistency of CNS colonisation by Epstein-Barr virus-infected B cells, and understanding of the mechanisms that underlie the formation and persistence of tertiary lymphoid tissues in patients with MS and other chronic autoimmune diseases (ectopic follicle syndromes). This work will stimulate new and unconventional ways of reasoning about MS pathogenesis.

Introduction Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS that is characterised by persistent intrathecal synthesis of immunoglobulins— mainly oligoclonal IgG—and recruitment of activated T cells and macrophages into the CNS. The antigenic stimuli that initiate or perpetuate this abnormal immune reactivity are still a matter of intense research and debate. In the past few years, the concept of MS as an autoimmune disease that is mediated by myelinreactive T cells has been challenged, and reassessment of the role of B cells in the pathogenesis of the disease is ongoing.1,2 Three sets of new data—the characterisation of B-cell follicle-like structures in the brain meninges of patients with MS,3–5 which extends the earlier description of lymphoid tissue in MS lesions;6 the finding that a substantial proportion of the B cells or plasma cells that accumulate in these follicles and in white-matter lesions are infected with Epstein-Barr virus (EBV);7 and the results of a trial with the B-celldepleting antibody rituximab8—now provide reciprocal conceptual support for the prominent role of B cells in the pathogenesis of MS and disclose a possible scenario that links abnormal B-cell activation to T-cell-mediated immunopathology.

Recent developments Triggers of B-cell activation Traditionally, B cells have been implicated in MS through their ability to produce pathogenic antibodies or autoantibodies, which can destroy tissue by recruiting macrophages that express the Fc receptor and by activation of the complement pathway. The results of 852

histopathological analyses indicate that antibodies might have an important role in plaque initiation9 and in demyelination in patients with established MS.10 The list of candidate pathogenic antigens in MS has recently grown longer; in addition to myelin antigens, for which no conclusive evidence is available,11 some non-myelin antigens have come into focus. Interest in the small heat-shock protein αβ-crystallin was revived by the findings that this protein has anti-inflammatory activity and that anti-αβ-crystallin antibodies have been detected in the CSF of patients with MS.12 In the proposed pathogenic model, B-cell responses that target αβ-crystallin could exacerbate inflammation by abrogating the immunosuppressive role of this protein.12 Adding to previous data on the presence of antibodies to axonal proteins (mainly neurofilaments) in patients with MS,13,14 Mathey and co-workers15 found increased concentrations of antibodies to neurofascin—a neuronal protein that is concentrated at the nodes of Ranvier in myelinated fibres—in the serum of patients with secondary-progressive MS. Injecting anti-neurofascin antibodies into mice with experimental autoimmune encephalomyelitis inhibited axonal conduction in a complement-dependent manner.15 Although the notion that autoantibodies can exacerbate inflammation and neurodegeneration in patients with MS is attractive, which antigens intrathecal oligoclonal IgG recognise and how the autoimmune response is induced are still unknown. Infectious organisms have long been regarded as candidate triggers of autoimmunity in MS, possibly through molecular mimicry or bystander activation.16 This idea has received new impetus from the results of www.thelancet.com/neurology Vol 7 September 2008

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Panel 1: Glossary of terms Epstein–Barr virus (EBV) is a γ-herpes virus that persistently infects more than 90% of individuals worldwide. B lymphocytes are the main cellular reservoir of the virus: in the peripheral blood of healthy individuals, between 1 and 50 per 1 000 000 B cells are infected with EBV. Because EBV can transform or immortalise B cells, stringent immunological control is needed to prevent EBV-associated malignancies, mainly nasopharyngeal carcinoma, Burkitt lymphoma, and Hodgkin’s disease. Infectious mononucleosis, a symptomatic primary EBV infection, is associated with a high risk of MS;17 the two diseases have striking epidemiological similarities, and EBV seropositivity and EBV antibody titres are higher in patients with MS than they are in healthy individuals.17 EBV-positive serology is increasingly associated with many autoimmune diseases.18 Autoimmunity could be triggered by several EBV-specific biological features: latent and lytic EBV proteins are potent immunogens that elicit strong B-cell and T-cell responses; EBV-specific immune responses might cross-recognise self antigens; the EBV latent membrane protein 1 (LMP1) induces expression of the B-cell activation factor of the TNF family (BAFF) and a proliferation-induced ligand (APRIL), which stimulate B-cell survival and T-cell-independent antibody production; experimental evidence was also provided that BAFF might rescue self-reactive B cells.19 Ectopic lymphoid follicles develop from immune cells that infiltrate chronically inflamed tissues and organise into structures that are reminiscent of lymphoid tissue; they show several features of germinal centres, including proliferating B cells and a core network of stromal/follicular dendritic cells. The germinal centres support humoral immune responses towards infectious organisms by promoting B-cell homing, expansion, and differentiation into plasma cells that produce high-affinity antibodies. CXCL13–CXCR5 system is a receptor–ligand association. CXCL13, a chemokine produced by stromal/follicular dendritic cells, has a vital role in the formation and maintenance of B-cell follicles in secondary and tertiary lymphoid organs. The chemokine acts by binding to the receptor CXCR5, which is expressed on B cells and subsets of T cells, and attracting these cells into the follicles. Oligoclonal IgG are the products of oligoclonal plasma cells that secrete immunoglobulins, which migrate as discrete bands after electrophoretic separation. These bands can be detected in the cerebrospinal fluid (CSF) of most (>95%) patients with MS, persist throughout the course of the disease, and are a diagnostic hallmark of the disease; however, their antigenic specificity is largely unknown. Oligoclonal IgG are also found in the CSF of patients with other neurological diseases. In acute and chronic infections of the CNS, intrathecal oligoclonal IgG are transient and are mainly directed against the causative pathogen, whereas in paraneoplastic neurological syndromes they recognise onconeural antigens. By matching the immunoglobulin transcriptomes of B cells with the corresponding immunoglobulin transcriptomes in samples of CSF from patients with MS, Obermeier and co-workers43 have provided direct evidence that CSF B cells are the source of oligoclonal immunoglobulin in patients with MS. MRZ reaction takes into account the intrathecal production of antibodies to measles, rubella, and varicella zoster virus, calculated by the respective virus-specific antibody indices. A positive MRZ reaction, defined as a combination of at least two of the three positive antibody indices, is present in about 90% of patients with MS, without active replication of the three viruses. However, intrathecal production of antibodies to a specific infectious organsism usually follows a active replication of that pathogen in the CNS. Rituximab was approved by the FDA in 1997 for some B-cell lymphomas and treatment-resistant rheumatoid arthritis and has been used off-label to treat the severe forms of other autoantibody-mediated diseases. The drug is a humanised monoclonal antibody that targets CD20 antigen on circulating and, possibly, lymphoid tissue-associated B cells through cell-mediated, complement-dependent cytotoxicity and pro-apoptotic effects. Because plasma cells do not express CD20, they are not depleted by rituximab; this implies that serum antibody concentrations and CSF oligoclonal IgG might not be affected by the drug in patients with MS.

seroepidemiological and immunological studies that have expanded the evidence on altered immune reactivity to EBV17–19 (see glossary, panel 1) in patients with MS.16,20 The results of longitudinal studies showed that increases in anti-EBV antibody titres occur long before the onset of MS, which indicates that increased immune reactivity to EBV is an early event in MS, rather than a consequence of the disease.21 Cepok and co-workers22 isolated oligoclonal IgG that recognised EBV antigens from the CSF of patients with MS,22 and increased T-cell responses to EBV antigens, particularly EBNA1, in the patients’ blood were reported in different studies.22–24 Despite the revived interest for EBV as an aetiological mediator of MS, the mechanisms that link infection with EBV to MS pathology were unknown. Clues to elucidate this problem come from the analysis of inflammatory cell infiltrates in the brains of people with MS. www.thelancet.com/neurology Vol 7 September 2008

While searching for the molecular mechanisms of B-cell attraction and survival in post-mortem brain tissues, Serafini and co-workers3 identified ectopic lymphoid follicles (panel 1) that were enriched with B cells and plasma cells in the meninges of a subset of patients with secondary-progressive MS. Although apparently restricted to late disease phases, the establishment of lymphoid-like structures in the brains of patients with MS could provide a microenvironment in which B-cell expansion and maturation, and hence local immunoglobulin production, can occur. Magliozzi and co-workers5 highlighted the preferential localisation of ectopic follicles to the subarachnoid space in the cerebral sulci (figure 1) and correlated their presence with severe cortical pathology and an aggressive clinical course. These findings raise the possibility that some cell types that are part of the ectopic follicles could release 853

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Figure 1: Inflammatory cell infiltrates in the brain of a patient with MS (A) Immune cells mainly accumulate in perivascular regions (Virchow–Robin spaces) in white matter lesions. (B) Ectopic lymphoid follicles are usually located close to meningeal venules and adjoin the pial membrane inside the cerebral sulci. Myeloid dendritic cells and plasmacytoid dendritic cells also infiltrate the MS brain. Myeloid dendritic cells have a major role in antigen presentation and T-cell activation, whereas plasmacytoid dendritic cells produce large amounts of the antiviral cytokine type-1 interferon. Adhesion molecules, such as lymphocyte function-associated antigen-1 (LFA-1) and very-late antigen 4 (VLA-4 [α4β1-integrin]) enable lymphocyte extravasation at both sites. Stromal/follicular dendritic cells, which form a network within the follicles, secrete the B-cell homing chemokine CXCL13. The presence of proliferating B cells in the follicles is suggestive of the formation of a germinal centre.4 In perivenular and meningeal areas, B cells or plasma cells that are infected with Epstein–Barr virus might become the target of cytotoxic CD8+ T cells.7 PC=plasma cell. T=T cell. B=B cell. Mφ=macrophage. e=erythrocyte. mDC=myeloid dendritic cell. pDC=plasmacytoid dendritic cell. PM=pial membrane. S/FDC=stromal/follicular dendritic cell. PB=plasmablast. LLP=long-lived plasma cell.

pathogenic antibodies or other cytotoxic factors. Taken together with previous observations that the ratio of immunoglobulin-producing plasma cells to T cells is lower in early MS lesions compared with late lesions,25,26 the above findings suggest that overt B-cell infiltration and lymphoid organisation in the MS brain could have a role in augmenting brain tissue injury. B-cell accumulation and the formation of ectopic lymphoid tissue with distinct T-cell areas and B-cell follicles (lymphoid neogenesis) are also characteristic of other autoimmune diseases, such as myasthenia gravis,27 autoimmune thyroiditis, and rheumatoid arthritis.4,28 Strong immune activation is common to all these diseases and it produces lymphoid neogenesis in inflamed target organs, although the precise role of this process in disease development and its relation with disease activity are largely unknown. The results of recent studies in patients with rheumatoid arthritis support the association of synovial ectopic lymphoid tissue with disease severity and a lower response to therapy.29 CXCL13 (panel 1), a chemokine that is involved in lymphoid organogenesis through regulation of B-cell homing to lymphoid tissues, is an important molecule in the development of ectopic lymphoid tissue in various inflammatory diseases.4,30,31 In patients with MS, CXCL13 expression was detected in intrameningeal follicles3,5 and active lesions,32 and a high concentration of the chemokine was seen in the CSF,32 associated with B-cell follicles.33 Other chemokines (eg, CCL19, CCL21, and CXCL12) and adhesion molecules (eg, VCAM1 and PNAd) that are constitutively expressed in secondary lymphoid organs and are induced during inflammation have been implicated in B-cell migration and organisation 854

into B-cell follicles in target organs, particularly in patients with rheumatoid arthritis.4 The identification of ectopic B-cell follicles in patients with MS led to the suggestion that their formation could be the manifestation of an EBV-associated disease. The rationale behind this hypothesis was that EBV is unique in its ability to establish a latent infection in B cells, which drives their proliferation and maturation, and to reactivate, which elicits a potent cytotoxic immune response.34 With in situ hybridisation for EBV-encoded small nuclear mRNAs and immunohistochemical techniques with antibodies against latent and lytic viral proteins, Serafini and co-workers7 found an abnormal accumulation of EBV-infected cells in post-mortem brain tissues from 21 of 22 patients with MS. Perturbed EBV infection in the brain was independent of the disease stage or form (early-acute, late-chronic, relapsingremitting, secondary-progressive, or primary-progressive), unrelated to chronic immunosuppressive or immunomodulatory therapy (only 4 of 22 patients with MS received these therapies), and MS-specific, because it was not found in patients with other inflammatory diseases of the CNS that have substantial intracerebral accumulation of B-cells (eg, viral and mycotic infections or primary vasculitis). The inability to detect EBV-infected B cells in the brains of patients with MS in two previous studies35,36 could be the result of methodological differences, tissue degradation, or both. Serafini and coworkers7 found that markers of latent EBV infection were consistently expressed in a substantial proportion of the B cells or plasma cells that accumulated in the meninges, particularly inside ectopic follicles, and in the perivascular cuffs of acute and chronic demyelinated lesions. The www.thelancet.com/neurology Vol 7 September 2008

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expression of EBV proteins associated with the early lytic cycle was instead confined to ectopic follicles and acute lesions in the brains with the most infiltration, linking viral reactivation to inflammatory activity.7 These findings suggest that ectopic B-cell follicles could arise from the uncontrolled expansion of EBV-infected B-cell clones and might be major occult sites of EBV persistence and reactivation during late disease stages. The altered immune reactivity to EBV18–24 and the absence of a notable increase in EBV DNA titres in the patients’ blood and CSF,7,24,37 strongly support a persistently dysregulated and predominantly CNS-restricted EBV infection in MS pathogenesis. Cross-reactivity between EBV and myelin antigens38,39 and immortalisation of autoantibody-producing B-cell clones40 have been proposed as plausible mechanisms for EBV to trigger autoimmunity. Alternatively, or in addition to, the brain could be the innocent bystander, rather than the direct target of a virus-triggered immunopathological response; in other EBV-associated diseases this is known to be highly detrimental.41 Consistent with this view, activated CD8+ T cells, which showed signs of cytotoxicity towards B cells or plasma cells, and plasmacytoid dendritic cells, which have a role in antiviral immunity, were identified at the main sites of EBV infection in the brains of people with MS.7 This suggests an attempt by the immune system to eradicate EBV-infected cells from the CNS. Abnormal deposits of EBV and EBV-specific CD8+ T cells have been found in the synovial tissue and fluid of patients with rheumatoid arthritis but their pathological relevance is uncertain.42 Therefore, in genetically predisposed individuals, and probably with the contribution of additional environmental factors, including other viruses, EBV infection could not be optimally controlled by the host’s immune system, resulting in expansion of infected B cells in extralymphatic niches. EBV-infected B cells and plasma cells in the subarachnoid space and in Virchow-Robin spaces that are contiguous with the subarachnoid–ventricular compartment suggests that in patients with MS, oligoclonal IgG43 (panel 1) could be mostly the by-product of a dysregulated EBV infection that causes chronic Bcell activation, rather than the result of an antigen-driven process. Intrathecally synthesised IgG could be produced by memory B cells that have been randomly infected by EBV and, consequently, would be heterogeneous and not MS-specific, in accordance with historical data.44 The possibility that EBV-infected B cells produce nonsense antibodies fits well with the data reported by Mattson and co-workers45 that IgG from individual MS plaques have distinct patterns, whereas IgG eluted from separate brain areas of patients with subacute sclerosing panencephalitis have identical IgG patterns. Because subacute sclerosing panencephalitis is a complication of infection with the measles virus, namely a disease caused by a single pathogen, the authors suspected that the patterns in the www.thelancet.com/neurology Vol 7 September 2008

MS plaques could be derived from nonsense antibodies that are pathogenetically irrelevant.45 Owens and coworkers46 used single-cell RT-PCR to find further evidence of somatically mutated and expanded IgG clonotypes in the CSF of patients with MS. They also showed preferential enrichment of plasma blast cells with functionally rearranged VH4 gene segments, which encode the variable parts of immunoglobulin heavy chains. These findings have been interpreted as evidence that a highly restricted B-cell response occurs in the brain of patients with MS, which is probably driven by a limited set of antigens. The possibility that the hypothesised intrathecal expansion of EBV-infected B cells fits with the data from Owens and co-workers46 (B-cell clonal restriction) and the findings of Mattson and co-workers45 (different oligoclonal IgG patterns in different plaques from single patients) needs to be investigated. There are new data on the polyclonal, intrathecal B-cell response in idiopathic inflammatory demyelinating CNS diseases. The so-called MRZ reaction (panel 1)—the intrathecal synthesis of antimeasles, antirubella, and antivaricella zoster IgG—is seen in most patients with MS but is uncommon in patients with acute disseminated encephalomyelitis47 or Devic’s disease.48 These findings indicate that the MRZ reaction helps to discriminate between MS and two inflammatory demyelinating CNS diseases that can be clinically indistinguishable from MS at onset. From the EBV perspective, the phenomenon could be interpreted as evidence that when the peripheral B-cell pool is targeted, the virus has more chances of infecting memory B cells that have been activated by common neurotropic viruses compared with memory B cells that are activated by other antigens. Because few patients with MS are oligoclonal-IgGnegative raises the possibility that disease development in these patients might depend on the persistence of fewer polyclonal B cells in the CNS and no or undetectable oligoclonal expansion. Indeed, true oligoclonal-IgGnegative patients are rare and have a better prognosis.49 Hypothetically, the immune systems of these patients could face an infection with EBV in the brain more efficiently than could those patients with oligoclonal IgG. In the context of a dynamic host–EBV interplay, as the disease progresses new B-cell clones could expand, whereas others could disappear; this phenomenon could explain the changes in oligoclonal IgG pattern seen in patients with MS who underwent repeated CSF analyses over time.50

Is B-cell activation pathogenetically relevant? Increasing evidence for a pathogenetic role for B-cells in many autoimmune diseases means that drugs that target humoral immunity, such as rituximab (panel 1), could be useful. In a phase II trial, patients with relapsingremitting MS received 1 g intravenous rituximab or placebo on day one and day 15.8 The patients treated with rituximab had a substantial reduction in the number of 855

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Figure 2: B-cell lineages in different body compartments. Rituximab targets the CD20 antigen, which is absent on B cell precursors, plasma blasts, and plasma cells; therefore, these cells can resist rituximab in bone marrow and ectopic lymphoid tissues. In particular, plasma cells generated (or recruited) in ectopic follicles and MS lesions could sustain production of intrathecal oligoclonal immunoglobulins, producing potentially detrimental mechanisms. Owing to its rapid efficacy, rituximab could deplete the pool of memory B cells that can secrete proinflammatory molecules such as TNF, and are expanded in patients with MS.53 The pool of naive B cells predominantly secretes the anti-inflammatory cytokine IL-10 and could be reduced in patients with MS.53 Rituximab might also deplete the pool of EBV-infected B cells, reducing the detrimental effects of EBV-specific T-cell immunity. B=B cell. PC=plasma cell. IL-10=interleukin 10. Ag=antigen. TNF=tumour necrosis factor. Th=T-helper cell. APC=antigen-presenting cell. pCD=plasmacytoid dendritic cell. S/FDC=stromal/follicular dendritic cell. PB=plasma blast cell. Green shape=CD20. Red shape=rituximab.

total gadolinium-enhancing lesions, which was still evident at 48 weeks follow-up, half the number of clinical relapses of the patients treated with placebo, and frequent infusion-related, mild-to-moderate adverse events (78%) but no increased incidence of any infection.8 The results of another large trial of rituximab in patients with active rheumatoid arthritis51 showed its efficacy in improving quality of life. Hence, the efficacy of rituximab in patients with MS or rheumatoid arthritis indirectly supports the involvement of humoral immunity in both disorders. However, the absence of a reduction in total antibody concentrations in patients with MS who were treated with rituximab suggests that a decrease in potentially pathogenic antibodies cannot account for the rapid effects of the drug.8 Furthermore, if antibody depletion was crucial for the treatment of MS, plasmapheresis would be more effective in ameliorating the symptoms of the disease than is currently reported.52 However, these studies tended to be underpowered and were done when MS trial methodology was in its infancy. Hence, B-cell functions other than those involved in immunoglobulin synthesis, such as antigen presentation and the production of proinflammatory cytokines,53 might be inhibited by rituximab (figure 2). Rituximab, which is used in EBV-associated, B-cell lymphoproliferative disorders,54 could effectively deplete EBV-infected cells in the blood and CSF, although it is not yet known whether it targets the pool of CNS tissue-infiltrating B cells. Niino and co-workers55 found that memory B cells can express high concentrations of the adhesion molecule 856

very-late antigen (VLA)-4, which binds to vascular-cell adhesion molecule-1 on the endothelial cells (figure 1). The α4-integrin component of VLA-4 is the target of natalizumab, another drug that is able to reduce disease activity and relapse rate in patients with MS.56 Natalizumab reduces the expression of VLA-4 on circulating immune cells,55 and inhibits B-cell and T-cell entry into the CNS, which might explain its beneficial effects in patients with MS. However, even total immune ablation does not eradicate lymphocytes from the brains of patients with MS; 88% of patients who had bone marrow transplants showed the persistence of CSF oligoclonal bands and clinical deterioration.57

Where next and conclusions After years of impasse, new data on B cells are stimulating unconventional ways of reasoning about MS pathogenesis. The identification of antibodies to neuronal antigens provides clues about the mechanisms that underlie damage to brain tissue and deserve further investigation. The identification of ectopic B-cell follicles as a niche for the generation of B cells and plasma cells in the brain of patients with MS reinforces the concept that humoral immunity has a role in the pathological changes and raises important questions about the absence of efficacy of current therapies to abrogate intrathecal IgG synthesis in patients with MS. These data warrant further exploration through independent studies of B-cell effector and regulatory functions beyond the antimyelin-antibody dogma and www.thelancet.com/neurology Vol 7 September 2008

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Search strategy and selection criteria References were found by searching PubMed, between Jan, 2006, and March, 2008, with the terms “B cells”, “rituximab”, “natalizumab”, and “multiple sclerosis”. Articles identified from searches of the authors’ own files were also included. Only papers written in English were included, which were further selected on the basis of originality and importance to the topic of the Personal View.

confirmation of the consistency of CNS colonisation by EBV-infected B cells. An understanding of the mechanisms that underlie the formation, correlation with disease activity or outcome, and modulation by therapy of tertiary lymphoid tissues in patients with MS and other chronic autoimmune diseases (collectively, such diseases might be classified as “ectopic follicle syndromes”) could lead to the generation of more specific and effective drugs. Whether EBV has a primary or secondary role in this scenario is not known. Because most adults are EBVseropositive and carry latent EBV genomes, the puzzle is what could convert a usually well-tolerated infection into a tissue-specific disease. The possibility that a dysregulated EBV infection might be associated with the development of autoimmune features is only an initial step in a knowledgeimproving process that should integrate current understanding of genetics, immunology, and environmental factors in various autoimmune diseases. Working along these lines, further research has to be done to fully understand the role of B cells and antibodies in MS. Contributors DF coordinated the work, drew the figures, and wrote the first draft of this Personal View. DF and FL did the literature search. FA, MS, FL, and BS contributed substantially to the content and writing of the Personal View. All authors have seen and approved the final version. Conflicts of interest DF received an honorarium from Merck Serono for a handbook of laboratory neuroimmunology. MS has received research grant support from Bayer Schering, SanofiAventis, and Merck Serono. FL, BS, and FA have no conflicts of interest. Acknowledgments MS, FA, and DF are supported by FISM—Fondazione Italiana Sclerosi Multipla—Cod. 2007/R/17/C3. FA is supported by the 6th Framework Program of the European Union NeuroproMiSe LSHM-CT-2005-01863. FL is supported by PRIN 2006, MIUR, protocol 2006064219 (“Humoral immunity in multiple sclerosis: B lymphocyte activation and demyelination”). DF received grant RC2007 from the Italian Ministry of Health to Mondino Foundation. DF thanks Sara Pizzi for historical iconography. References 1 Meinl E, Krumbholz M, Hohlfeld R. B-lineage cells in the inflammatory central nervous system environment: migration, maintenance, local antibody production, and therapeutic modulation. Ann Neurol 2006; 59: 880–92. 2 Owens GP, Bennett JL, Gilden DH, Burgoon MP. The B cell response in multiple sclerosis. Neurol Res 2006; 28: 236–44. 3 Serafini B, Rosicarelli B, Magliozzi R, Stigliano E, Aloisi F. Detection of ectopic B-cell follicles with germinal centers in the meninges of patients with secondary progresive multiple sclerosis. Brain Pathol 2004; 14: 164–74.

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