To identify differentially expressed genes in multiple sclerosis, microarrays were used in a stringent experimental setting-leukapheresis from disease-discordant monozygotic twins and gene expression profiling in CD4(+) and CD8(+) T-cell subsets. Disease-related differences emerged only in the CD8(+) T-cell subset. The five differentially expressed genes identified included killer cell lectin-like receptor subfamily B, member 1, also known as natural killer receptor protein 1a/CD161, presented by the International Multiple Sclerosis Genetics Consortium as one of the non-MHC candidate loci. Flow cytometric analysis on peripheral blood of healthy donors and patients with multiple sclerosis and rheumatoid arthritis confirmed an upregulation of CD161 at the protein level, showing also a significant excess of CD161(high)CD8(+) T cells in multiple sclerosis. This subset prevalently included chemokine (C-C motif) receptor 6(+), cytokine-producing, effector-memory T cells with proinflammatory profiles. It also included all circulating interleukin-17(+)CD8(+) T cells. In the CD161(high)CD8(+) subset, interleukin-12 facilitated proliferation and interferon-γ production, with CD161 acting as a co-stimulatory receptor. CD161(+)CD8(+)CD3(+) T cells producing interferon-γ were part of intralesional immune infiltrates and ectopic B cell follicles in autopsy multiple sclerosis brains. Variations of CD161 expression on CD8(+) T cells identify a subset of lymphocytes with proinflammatory characteristics that have not been previously reported in multiple sclerosis and are likely to contribute to disease immunopathology.

It has long been known that multiple sclerosis (MS) is associated with an increased Epstein-Barr virus (EBV) seroprevalence and high immune reactivity to EBV and that infectious mononucleosis increases MS risk. This evidence led to postulate that EBV infection plays a role in MS etiopathogenesis, although the mechanisms are debated. This study was designed to assess the prevalence and magnitude of CD8+ T-cell responses to EBV latent (EBNA-3A, LMP-2A) and lytic (BZLF-1, BMLF-1) antigens in relapsing-remitting MS patients (n = 113) and healthy donors (HD) (n = 43) and to investigate whether the EBV-specific CD8+ T cell response correlates with disease activity, as defined by clinical evaluation and gadolinium-enhanced magnetic resonance imaging. Using HLA class I pentamers, lytic antigen-specific CD8+ T cell responses were detected in fewer untreated inactive MS patients than in active MS patients and HD while the frequency of CD8+ T cells specific for EBV lytic and latent antigens was higher in active and inactive MS patients, respectively. In contrast, the CD8+ T cell response to cytomegalovirus did not differ between HD and MS patients, irrespective of the disease phase. Marked differences in the prevalence of EBV-specific CD8+ T cell responses were observed in patients treated with interferon-β and natalizumab, two licensed drugs for relapsing-remitting MS. Longitudinal studies revealed expansion of CD8+ T cells specific for EBV lytic antigens during active disease in untreated MS patients but not in relapse-free, natalizumab-treated patients. Analysis of post-mortem MS brain samples showed expression of the EBV lytic protein BZLF-1 and interactions between cytotoxic CD8+ T cells and EBV lytically infected plasma cells in inflammatory white matter lesions and meninges. We therefore propose that inability to control EBV infection during inactive MS could set the stage for intracerebral viral reactivation and disease relapse.

The relatively high proportion of IP changes in RR-MS patients seems to confirm our work hypothesis and warrants more work to confirm the result on a larger sample, and to understand the implications for related immunological disturbances and intestinal microbiota alterations. Our finding may also have relevance for oral treatments, recently introduced in clinical practice.

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Growing evidences put B lymphocytes on a central stage in multiple sclerosis (MS) immunopathology. While investigating the effects of interferon-β (IFN-β) therapy, one of the most used first-line disease-modifying drugs for the treatment of relapsing-remitting MS, in circulating B-cell sub-populations, we found a specific and marked decrease of CD27 memory B cells. Interestingly, memory B cells are considered a population with a great disease-driving relevance in MS and resulted to be also target of B-cell depleting therapies. In addition, Epstein-Barr virus (EBV), associated with MS etiopathogenesis, harbors in this cell type and an IFN-β-induced reduction of the memory B-cell compartment, in turn, resulted in a decreased expression of the EBV gene latent membrane protein 2A in treated patients. We found that in vivo IFN-β therapy specifically and highly induced apoptosis in memory B cells, in accordance with a strong increase of the apoptotic markers Annexin-V and active caspase-3, via a mechanism requiring the FAS-receptor/TACI (transmembrane activator and CAML interactor) signaling. Thus, efficacy of IFN-β therapy in MS may rely not only on its recognized anti-inflammatory activities but also on the specific depletion of memory B cells, considered to be a pathogenic cell subset, reducing their inflammatory impact in target organs.

Epstein-Barr virus (EBV) is a non-heritable factor that associates with multiple sclerosis (MS). However its causal relationship with the disease is still unclear. The virus establishes a complex co-existence with the host that includes regulatory influences on gene expression. Hence, if EBV contributes to the pathogenesis of MS it may do so by interacting with disease predisposing genes. To verify this hypothesis we evaluated EBV nuclear antigen 2 (EBNA2, a protein that recent works by our and other groups have implicated in disease development) binding inside MS associated genomic intervals. We found that EBNA2 binding occurs within MS susceptibility sites more than expected by chance (factor of observed vs expected overlap [O/E] = 5.392-fold, p < 2.0e-05). This remains significant after controlling for multiple genomic confounders. We then asked whether this observation is significant per se or should also be viewed in the context of other disease relevant gene-environment interactions, such as those attributable to vitamin D. We therefore verified the overlap between EBNA2 genomic occupancy and vitamin D receptor (VDR) binding sites. EBNA2 shows a striking overlap with VDR binding sites (O/E = 96.16-fold, p < 2.0e-05), even after controlling for the chromatin accessibility state of shared regions (p <0.001). Furthermore, MS susceptibility regions are preferentially targeted by both EBNA2 and VDR than by EBNA2 alone (enrichment difference = 1.722-fold, p = 0.0267). Taken together, these findings demonstrate that EBV participates in the gene-environment interactions that predispose to MS.

Defective regulation of PAD2 in the periphery, without the immunological shelter of the blood-brain barrier, may contribute to the development of the autoimmune responses in MS.