Identification of a major T-cell epitope within VP3 amino acid residues 24 to 37 of Theiler's virus in demyelination-susceptible SJL/J mice

Excessive Innate Immunity Steers Pathogenic Adaptive Immunity in the Development of Theiler's Virus-Induced Demyelinating Disease

Several virus-induced models were used to study the underlying mechanisms of multiple sclerosis (MS). The infection of susceptible mice with Theiler’s murine encephalomyelitis virus (TMEV) establishes persistent viral infections and induces chronic inflammatory demyelinating disease. In this review, the innate and adaptive immune responses to TMEV are discussed to better understand the pathogenic mechanisms of viral infections. Professional (dendritic cells (DCs), macrophages, and B cells) and non-professional (microglia, astrocytes, and oligodendrocytes) antigen-presenting cells (APCs) are the major cell populations permissive to viral infection and involved in cytokine production. The levels of viral loads and cytokine production in the APCs correspond to the degrees of susceptibility of the mice to the TMEV-induced demyelinating diseases. TMEV infection leads to the activation of cytokine production via TLRs and MDA-5 coupled with NF-κB activation, which is required for TMEV replication. These activation signals further amplify the cytokine production and viral loads, promote the differentiation of pathogenic Th17 responses, and prevent cellular apoptosis, enabling viral persistence. Among the many chemokines and cytokines induced after viral infection, IFN α/β plays an essential role in the downstream expression of costimulatory molecules in APCs. The excessive levels of cytokine production after viral infection facilitate the pathogenesis of TMEV-induced demyelinating disease. In particular, IL-6 and IL-1β play critical roles in the development of pathogenic Th17 responses to viral antigens and autoantigens. These cytokines, together with TLR2, may preferentially generate deficient FoxP3⁺CD25^- regulatory cells converting to Th17. These cytokines also inhibit the apoptosis of TMEV-infected cells and cytolytic function of CD8⁺ T lymphocytes (CTLs) and prolong the survival of B cells reactive to viral and self-antigens, which preferentially stimulate Th17 responses.

The VP3 protein of duck hepatitis A virus mediates host cell adsorption and apoptosis

Duck hepatitis A virus (DHAV) causes an infectious disease that mainly affects 1- to 4-week-old ducklings, resulting in considerable loss to the duck industry. Although there have been many studies on DHAV in recent years, the effects on host infection and pathogenesis of DHAV-1 remain largely unknown. This study investigated the effects of the DHAV-1 structural protein VP3 on DHAV-1 virus adsorption and apoptosis to explore the role of VP3 in the viral life cycle. The effects of DHAV-1 VP3 and an antibody against the protein on virion adsorption was analyzed by qRT-PCR. The results showed that the virus copy number for the rabbit anti-VP3 IgG-treated group was significantly lower than that for the negative control group but higher than that for the rabbit anti-DHAV-1 IgG-treated group. This result indicates that VP3 mediates DHAV-1 virus adsorption but that it is not the only protein that involved in this process. In addition, a eukaryotic recombinant plasmid, pCAGGS/VP3, was transfected into duck embryo fibroblasts (DEFs), and the apoptotic rate was determined by DAPI staining, the TUNEL assay and flow cytometry. DAPI staining showed nucleus fragmentation and nuclear edge shifting. TUNEL assay results revealed yellow nuclei, and flow cytometry indicated a significant increase in the apoptotic rate. In addition, qRT-PCR revealed increased in the transcriptional levels of the apoptotic caspase-3, −8 and −9, with the largest increase for caspase-3, followed by caspase-9 and caspase-8. Enzyme activity analysis confirmed these results. Furthermore, the VP3 protein decreased the mitochondrial membrane potential, and the transcriptional levels of the proapoptotic factors Bak, Cyt c and Apaf-1 in the mitochondrial apoptotic pathway were significantly upregulated. These data suggest that expression of VP3 in DEFs induces apoptosis and may primarily activate caspase-3-induced apoptosis through mitochondrion-mediated intrinsic pathways. The findings provide scientific data to clarify DHAV-1 infection and pathogenesis.

Molecular mimicry as an inducing trigger for CNS autoimmune demyelinating disease

Summary:  Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that affects about 0.1% of the worldwide population. This deleterious disease is marked by infiltration of myelin‐specific T cells that attack the protective myelin sheath that surrounds CNS nerve axons. Upon demyelination, saltatory nerve conduction is disrupted, and patients experience neurologic deficiencies. The exact cause for MS remains unknown, although most evidence supports the hypothesis that both genetic and environmental factors contribute to disease development. Epidemiologic evidence supports a role for environmental pathogens, such as viruses, as potentially key contributors to MS induction. Pathogens can induce autoimmunity via several well‐studied mechanisms with the most postulated being molecular mimicry. Molecular mimicry occurs when T cells specific for peptide epitopes derived from pathogens cross‐react with self‐epitopes, leading to autoimmune tissue destruction. In this review, we discuss an in vivo virus‐induced mouse model of MS developed in our laboratory, which has contributed greatly to our understanding of the mechanisms underlying molecular mimicry‐induced CNS autoimmunity.

Neuropathogenesis of Theiler's murine encephalomyelitis virus infection, an animal model for multiple sclerosis

Theiler's murine encephalomyelitis virus (TMEV) infection of mice is an experimental model for multiple sclerosis (MS). TMEV induces a biphasic disease in susceptible mouse strains. During the acute phase, 1 week after infection, TMEV causes polioencephalomyelitis characterized by infection and apoptosis of neurons in the gray matter of the brain. During the chronic phase, about 1 month after infection, virus infects glial cells and macrophages, and induces inflammatory demyelination with oligodendrocyte apoptosis and axonal degeneration in the white matter of the spinal cord. Although antibody, CD4(+), and CD8(+) T cell responses against TMEV capsid proteins play important roles in neuropathogenesis, infectious virus with persistence is necessary to induce demyelination; in general, adoptive transfer of antibody or T cells alone did not induce central nervous system (CNS) disease. The TMEV model can be useful for testing new therapeutic strategies specifically as a viral model for MS. Therapies targeting adhesion molecules, axonal degeneration, and immunosuppression can be beneficial for pure autoimmune CNS demyelinating diseases, such as experimental autoimmune encephalomyelitis, but could be detrimental in virus-induced demyelinating diseases, such as progressive multifocal leukoencephalopathy.

Theiler's virus infection induces a predominant pathogenic CD4+ T cell response to RNA polymerase in susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV)-induced immune-mediated demyelinating disease in susceptible mouse strains has been extensively investigated as a relevant model for human multiple sclerosis. Previous investigations of antiviral T-cell responses focus on immune responses to viral capsid proteins, while virtually nothing is reported on immune responses to nonstructural proteins. In this study, we have identified noncapsid regions recognized by CD4(+) T cells from TMEV-infected mice using an overlapping peptide library. Interestingly, a greater number of CD4(+) T cells recognizing an epitope (3D(21-36)) of the 3D viral RNA polymerase, in contrast to capsid epitopes, were detected in the CNS of TMEV-infected SJL mice, whereas only a minor population of CD4(+) T cells from infected C57BL/6 mice recognized this region. The effects of preimmunization and tolerization with these epitopes on the development of demyelinating disease indicated that capsid-specific CD4(+) T cells are protective during the early stages of viral infection, whereas 3D(21-36)-specific CD4(+) T cells exacerbate disease development. Therefore, protective versus pathogenic CD4(+) T-cell responses directed to TMEV appear to be epitope dependent, and the differences in CD4(+) T-cell responses to these epitopes between susceptible and resistant mice may play an important role in the resistance or susceptibility to virally induced demyelinating disease.

Phylogenetic analysis of the species Theilovirus: emerging murine and human pathogens

The Cardiovirus genus of the family Picornaviridae includes two distinct species, Encephalomyocarditis virus and Theilovirus. We now report the complete nucleotide sequences of three Theiler's murine encephalomyelitis virus (TMEV) strains (TO Yale, TOB15, and Vie 415HTR) and of Vilyuisk human encephalomyelitis virus (VHEV). This information, together with the recently reported sequences of divergent theiloviruses (Theiler's-like rat virus [TRV] and Saffold viruses 1 and 2 [SAFV-1 and SAFV-2]), enables an updated phylogenetic analysis as well as a reexamination of several gene products important in the pathogenesis of this emerging group of viruses. In the light of the known neurotropism of TMEV and the new human SAFV-1 and SAFV-2, the resulting data suggest the existence of theiloviruses that cause human central nervous system infections. Our phylogenetic analyses point to the classification of presently known theiloviruses into five types: TMEV, VHEV, TRV, SAFV-1, and SAFV-2.

Anticapsid immunity level, not viral persistence level, correlates with the progression of Theiler's virus-induced demyelinating disease in viral P1-transgenic mice

Intracranial infection of Theiler's murine encephalomyelitis virus (TMEV) induces demyelination and a neurological disease in susceptible SJL/J (SJL) mice that resembles multiple sclerosis. While the virus is cleared from the central nervous system (CNS) of resistant C57BL/6 (B6) mice, it persists in SJL mice. To investigate the role of viral persistence and its accompanying immune responses in the development of demyelinating disease, transgenic mice expressing the P1 region of the TMEV genome (P1-Tg) were employed. Interestingly, P1-Tg mice with the B6 background showed severe reductions in both CD4(+) and CD8(+) T-cell responses to capsid epitopes, while P1-Tg mice with the SJL background displayed transient reductions following viral infection. Reduced antiviral immune responses in P1-Tg mice led to >100- to 1,000-fold increases in viral persistence at 120 days postinfection in the CNS of mice with both backgrounds. Despite the increased CNS TMEV levels in these P1-Tg mice, B6 P1-Tg mice developed neither neuropathological symptoms nor demyelinating lesions, and SJL P1-Tg mice developed significantly less severe TMEV-induced demyelinating disease. These results strongly suggest that viral persistence alone is not sufficient to induce disease and that the level of T-cell immunity to viral capsid epitopes is critical for the development of demyelinating disease in SJL mice.

Differential virus replication, cytokine production, and antigen-presenting function by microglia from susceptible and resistant mice infected with Theiler's virus

Infection with Theiler's murine encephalomyelitis virus (TMEV) in the central nervous system (CNS) causes an immune system-mediated demyelinating disease similar to human multiple sclerosis in susceptible but not resistant strains of mice. To understand the underlying mechanisms of differential susceptibility, we analyzed viral replication, cytokine production, and costimulatory molecule expression levels in microglia and macrophages in the CNS of virus-infected resistant C57BL/6 (B6) and susceptible SJL/J (SJL) mice. Our results indicated that message levels of TMEV, tumor necrosis factor alpha, beta interferon, and interleukin-6 were consistently higher in microglia from virus-infected SJL mice than in those from B6 mice. However, the levels of costimulatory molecule expression, as well as the ability to stimulate allogeneic T cells, were significantly lower in TMEV-infected SJL mice than in B6 mice. In addition, microglia from uninfected naïve mice displayed differential viral replication, T-cell stimulation, and cytokine production, similar to those of microglia from infected mice. These results strongly suggest that different levels of intrinsic susceptibility to TMEV infection, cytokine production, and T-cell activation ability by microglia contribute to the levels of viral persistence and antiviral T-cell responses in the CNS, which are critical for the differential susceptibility to TMEV-induced demyelinating disease between SJL and B6 mice.

Genetic deletion of a single immunodominant T-cell response confers susceptibility to virus-induced demyelination

An important question in neuropathology involves determining the antigens that are targeted during demyelinating disease. Viral infection of the central nervous system (CNS) leads to T‐cell responses that can be protective as well as pathogenic. In the Theiler’s murine encephalomyelitis virus (TMEV) model of demyelination it is known that the immune response to the viral capsid protein 2 (VP2) is critical for disease pathogenesis. This study shows that expressing the whole viral capsid VP2 or the minimal CD8‐specific peptide VP2_121‐130 as “self” leads to a loss of VP2‐specific immune responses. Loss of responsiveness is caused by T cell‐specific tolerance, as VP2‐specific antibodies are generated in response to infection. More importantly, these mice lose the CD8 T‐cell response to the immunodominant peptide VP2_121‐130, which is critical for the development of demyelinating disease. The transgenic mice fail to clear the infection and develop chronic demyelinating disease in the spinal cord white matter. These findings demonstrate that T‐cell responses can be removed by transgenic expression and that lack of responsiveness alters viral clearance and CNS pathology. This model will be important for understanding the mechanisms involved in antigen‐specific T‐cell deletion and the contribution of this response to CNS pathology.

Castration of male C57L/J mice increases susceptibility and estrogen treatment restores resistance to Theiler's virus-induced demyelinating disease

Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) results in immune-mediated demyelination in selective mouse strains. We have previously demonstrated that the males of C57L mice are significantly more susceptible to TMEV-induced demyelinating disease. To assess further the hormonal influence for this gender-associated differential susceptibility, estrogen-treated, castrated C57L mice were infected with TMEV and compared with sham-operated and/or placebo-treated mice. Interestingly, castration further elevated the susceptibility to virally induced demyelinating disease compared with sham-castrated control mice, and prolonged treatment of castrated mice with estrogen restored the resistance to the level of control mice. These results strongly suggest that sex hormone levels contribute to the gender-biased susceptibility to TMEV-induced demyelinating disease. Mice treated with estrogen showed a significantly decreased level of virus-specific Th1 responses both in the periphery and in the CNS. In addition, in vitro estrogen treatment was able to inhibit viral replication directly in macrophages, consistent with the lower level of viral RNA in microglia/macrophages in the CNS from castrated estrogen-treated mice compared with controls. Also, estrogen treatment inhibited VCAM-1 expression induced by tumor necrosis factor-alpha in cerebral vascular endothelial (CVE) cells via inhibition of nuclear factor-kappaB (NFkappaB), which is produced in various glial cells upon TMEV infection. Overall, estrogen treatment appears to exert its effects on viral replication, induction of immune responses, as well as infiltration of activated immune cells into the CNS via inhibition of NFkappaB function.

Initial capsid-specific CD4(+) T cell responses protect against Theiler's murine encephalomyelitisvirus-induced demyelinating disease

Central nervous system (CNS) infection by Theiler's murine encephalomyelitis virus (TMEV) causes an immune-mediated demyelinating disease similar to human multiple sclerosis in susceptible mice. To understand the pathogenic mechanisms, we analyzed the level, specificity, and function of CD4(+) Th cells in susceptible SJL/J and resistant C57BL/6 mice. Compared to resistant mice, susceptible mice have three- to fourfold higher levels of overall CNS-infiltrating CD4(+) T cells during acute infection. CD4(+) T cells in the CNS of both strains display various activation markers and produce high levels of IFN-gamma upon stimulation with anti-CD3 antibody. However, susceptible mice display significantly fewer (tenfold) IFN-gamma-producing Th1 cells specific for viral capsid epitopes as compared to resistant mice. Furthermore, preimmunization with capsid-epitope peptides significantly increased capsid-specific CD4(+) T cells in the CNS during the early stages of viral infection and delayed the development of demyelinating disease in SJL/J mice. This suggests a protective role of capsid-reactive Th cells during early viral infection. Therefore, a low level of the protective Th1 response to viral capsid proteins, in conjunction with Th1 responses to unknown epitopes may delay viral clearance in susceptible mice leading to pathogenesis of demyelination during acute infection, as compared to resistant mice.

Effects of the major histocompatibility complex loci and T-cell receptor beta-chain repertoire on Theiler's virus-induced demyelinating disease

We have investigated the potential effects of H-2 and T-cell receptor (TCR) V beta family genes on induction of T-cell immunity and susceptibility to virally induced demyelinating disease by using BALB.S (H-2K(s)A(s)D(s)) and BALB.S 3 R (H-2K(s)A(s)D(d)/L(d)) mice. These parameters were compared with those of highly susceptible SJL/J (H-2K(s)A(s)D(s)) mice that contain only one-half of TCR V beta family genes compared with the above-mentioned strains. Our results demonstrate that BALB.S but not BALB.S 3 R mice are susceptible similar to SJL/J mice. Although the level of CD4(+) T-cell infiltration to the CNS was elevated in susceptible mice, virus-specific immune responses restricted with H-2(s) were similar in these mice. No preferential use of V beta families associated with differences in the major histocompatibility complex (MHC) components was apparent. However, the pattern and sequence of CDR 3 distribution shows T-cell clonal accumulation in the CNS associated with the H-2 components. Further anti-CD8 antibody treatment of resistant BALB.S 3 R mice abrogated resistance to demyelinating disease, indicating that CD8(+) T cells restricted with H-2D(d)/L(d) are most likely to exert resistance in BALB.S 3 R mice. These studies indicated that TCR V beta and MHC class II genes are the secondary to a particular MHC class I gene expression in susceptibility to virally induced demyelinating disease.

Gender bias in Theiler's virus-induced demyelinating disease correlates with the level of antiviral immune responses

Multiple sclerosis is an immune-mediated disease of the CNS and shows a sex-biased distribution in which 60-75% of all cases are female. A mouse model of multiple sclerosis, Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, also displays a gender bias. However, in the C57L/J strain of mice, males are susceptible to disease whereas females are completely resistant. In this study we determined the gender differences in the TMEV-specific immune response, which may be responsible for the gender bias in clinical disease. Our data clearly demonstrate that female C57L/J mice induce significantly higher levels of TMEV-specific neutralizing Ab as well as a stronger peripheral T cell response throughout the course of viral infection. In contrast, male mice have a higher level of TMEV-specific CD4(+) and CD8(+) T cell infiltration into the CNS as well as viral persistence. These results suggest that a higher level of the initial antiviral immune response in female mice may be able to effectively clear virus from the periphery and CNS and therefore prevent further disease manifestations. Male mice in contrast do not mount as effective an immune response, thereby allowing for eventual viral persistence in the CNS and continuous T cell expansion leading to clinical symptoms.

Identification of capsid epitopes of Theiler's virus recognized by CNS-infiltrating CD4+ T cells from virus-infected C57BL/6 mice

Intracerebral infection of Theiler's murine encephalomyelitis virus (TMEV) induces immune-mediated demyelinating disease in some mouse strains but not in others. We report here for the first time two new predominant capsid epitopes (VP4(21-40) and VP2(201-220)) recognized by CD4+ T cells from virus-infected resistant C57BL/6 mice based on IFNgamma ELISPOT assay utilizing a 20-mer peptide library covering the entire capsid proteins. Further experiments by IFNgamma ELISPOT and flow cytometry for intracellular IFNgamma production using truncated peptides indicated that the epitope regions recognized by CNS-infiltrating CD4+ T cells are VP4(25-38) and VP2(206-220), respectively. No apparent reduction in the T cell response to these viral epitopes is seen in the CNS of IL-12- and ICAM-1-deficient C57BL/6 mice compared to those in control C57BL/6 mice, suggesting that T cell response to TMEV in the CNS is largely insensitive to the absence of these proinflammatory cytokine and adhesion molecules. Therefore, these newly defined CD4+ T cell epitopes are likely to provide an important tool to investigate the role of CD4+ T cell responses in H-2b-bearing congenic strains.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Differences in avidity and epitope recognition of CD8(+) T cells infiltrating the central nervous systems of SJL/J mice infected with BeAn and DA strains of Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus (TMEV) infection induces immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infectious model for human multiple sclerosis. To investigate the pathogenic mechanisms, two strains of TMEV (DA and BeAn), capable of inducing chronic demyelination in the central nervous system (CNS), have primarily been used. Here, we have compared the T-cell responses induced after infection with DA and BeAn strains in highly susceptible SJL/J mice. CD4(+) T-cell responses to known epitopes induced by these two strains were virtually identical. However, the CD8(+) T-cell response induced following DA infection in susceptible SJL/J mice was unable to recognize two of three H-2K(s)-restricted epitope regions of BeAn, due to single-amino-acid substitutions. Interestingly, T cells specific for the H-2K(s)-restricted epitope (VP1(11-20)) recognized by both strains showed a drastic increase in frequency as well as avidity after infection with DA virus. These results strongly suggest that the level and avidity of virus-specific CD8(+) T cells infiltrating the CNS could be drastically different after infection with these two strains of TMEV and may differentially influence the pathogenic and/or protective outcome.

Avian encephalomyelitis virus induces apoptosis via major structural protein VP3

Avian encephalomyelitis virus (AEV) strain L(2)Z was investigated for its apoptotic activity in specific-pathogen-free chick embryo brain tissue. DNA fragmentation analysis and electron microscopy observation demonstrated that AEV could induce apoptosis in chick embryo brain tissues characterized by chromatin condensation, plasma membrane blebbing, cell shrinkage, and nucleosomal DNA fragmentation after 4 days postinfection. AEV structural protein genes VP1, VP2, and VP3 were transfected into Cos-7 and chick embryo brain (CEB) cells, respectively. The results showed that only VP3 protein was an apoptotic inducer, as demonstrated by DNA fragmentation analysis and TUNEL assay at 24 and 48 h posttransfection. Furthermore, expression of VP3 protein resulted in the activation of caspase-3-like proteases in both cells, which could be inhibited by a caspase-3-like protease-specific inhibitor Ac-DEVD-CHO peptide, suggesting that AEV VP3 protein induces apoptosis through a caspase-3-like protease pathway. In addition, VP3 protein localized to mitochondria in the Cos-7 and CEB cells at 24 h posttransfection observed by confocal microscopy, indicating that mitochondria may play an important role in VP3-induced apoptosis. Taken together, our results show that AEV could induce apoptosis in chick embryo brain tissue, structural protein VP3 could serve as an apoptotic inducer resulting in apoptosis in cell culture through a caspase-3-like protease pathway, which may be related to its localization to mitochondria.

The majority of infiltrating CD8+ T cells in the central nervous system of susceptible SJL/J mice infected with Theiler's virus are virus specific and fully functional

Theiler's virus infection of the central nervous system (CNS) induces an immune-mediated demyelinating disease in susceptible mouse strains, such as SJL/J, and serves as a relevant infectious model for human multiple sclerosis. It has been previously suggested that susceptible SJL/J mice do not mount an efficient cytotoxic T-lymphocyte (CTL) response to the virus. In addition, genetic studies have shown that resistance to Theiler's virus-induced demyelinating disease is linked to the H-2D major histocompatibility complex class I locus, suggesting that a compromised CTL response may contribute to the susceptibility of SJL/J mice. Here we show that SJL/J mice do, in fact, generate a CD8(+) T-cell response in the CNS that is directed against one dominant (VP3(159-166)) and two subdominant (VP1(11-20) and VP3(173-181)) capsid protein epitopes. These virus-specific CD8(+) T cells produce gamma interferon (IFN-gamma) and lyse target cells in the presence of the epitope peptides, indicating that these CNS-infiltrating CD8(+) T cells are fully functional effector cells. Intracellular IFN-gamma staining analysis indicates that greater than 50% of CNS-infiltrating CD8(+) T cells are specific for these viral epitopes at 7 days postinfection. Therefore, the susceptibility of SJL/J mice is not due to the lack of an early functional Theiler's murine encephalomyelitis virus-specific CTL response. Interestingly, T-cell responses to all three epitopes are restricted by the H-2K(s) molecule, and this skewed class I restriction may be associated with susceptibility to demyelinating disease.

Preferential induction of IL-10 in APC correlates with a switch from Th1 to Th2 response following infection with a low pathogenic variant of Theiler's virus

Theiler's murine encephalomyelitis virus induces immune-mediated demyelination in susceptible mice after intracerebral inoculation. A naturally occurring, low pathogenic Theiler's murine encephalomyelitis virus variant showed a single amino acid change within a predominant Th epitope from lysine to arginine at position 244 of VP1. This substitution is the only one present in the entire viral capsid proteins. In this paper, we demonstrate that the majority of T cells specific for VP1(233-250) and VP2(74-86) from wild-type virus-infected mice are Th1 type and these VP1-specific cells poorly recognize the variant VP1 epitope (VP1(K244R)) containing the substituted arginine. In contrast, the Th2-type T cell population specific for these epitopes predominates in variant virus-infected mice. Immunization with UV-inactivated virus or VP1 epitope peptides could not duplicate the preferential Th1/Th2 responses following viral infection. Interestingly, the major APC populations, such as dendritic cells and macrophages, produce IL-12 on exposure to the pathogenic wild-type virus, whereas they preferentially produce IL-10 in response to the low pathogenic variant virus. Thus, such a spontaneous mutant virus may have a profoundly different capability to induce Th-type responses via selective production of cytokines involved in T cell differentiation and the consequent pathogenicity of virally induced immune-mediated inflammatory diseases.

Capsid-specific cytotoxic T lymphocytes recognize three distinct H-2D(b)-restricted regions of the BeAn strain of Theiler's virus and exhibit different cytokine profiles

The role of virus-specific cytotoxic T lymphocytes (CTL) in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, a viral model for multiple sclerosis, is not yet clear. To investigate the specificity and function of CTL generated in response to TMEV infection, we generated a panel of overlapping 20-mer peptides encompassing the entire capsid and leader protein region of the BeAn strain of TMEV. Binding of these peptides to H-2K(b) and H-2D(b) class I molecules of resistant mice was assessed using RMA-S cells. Several peptides displayed significant binding to H-2K(b), H-2D(b), or both. However, infiltrating cytotoxic T cells in the central nervous system of virus-infected mice preferentially lysed target cells pulsed with VP2(111-130/121-140) or VP2(121-130), a previously defined CTL epitope shared by the DA strain of TMEV and other closely related cardioviruses. In addition, at a high effector-to-target cell ratio, two additional peptides (VP2(161-180) and VP3(101-120)) sensitized target cells for cytolysis by infiltrating T cells or splenic T cells from virus-infected mice. The minimal epitopes within these peptides were defined as VP2(165-173) and VP3(110-120). Based on cytokine profiles, CTL specific for these subdominant epitopes are Tc2, in contrast to CTL for the immunodominant epitope, which are of the Tc1 type. Interestingly, CTL function towards both of these subdominant epitopes is restricted by the H-2D molecule, despite the fact that these epitopes bind both H-2K and H-2D molecules. This skewing toward an H-2D(b)-restricted response may confer resistance to TMEV-induced demyelinating disease, which is known to be associated with the H-2D genetic locus.

Virus-induced autoimmunity: epitope spreading to myelin autoepitopes in Theiler's virus infection of the central nervous system

Epidemiological studies indicate that host immunogenetics and history of infection, particularly by viruses, may be a necessary cofactor for the induction of a variety of autoimmune diseases. To date, however, there is no clear-cut evidence, either in experimental animal models or in human autoimmune disease, that supports either molecular mimicry (Wucherpfennig and Strominger, 1995; Fujinami and Oldstone, 1985) or a role for superantigens (Scherer et al., 1993) in the initiation of T cell-mediated autoimmunity. In contrast, the current data provide compelling evidence in support of a major role for epitope spreading in the induction of myelin-specific autoimmunity in mice persistently infected with TMEV. It is significant that two picornaviruses closely related to TMEV, coxsackievirus (Rose and Hill, 1996) and encephalomyocarditis virus (EMCV) (Kyu et al., 1992), have been similarly shown to persist (either the viral RNA or the infectious virus) in their target organs and have been associated with the development of chronic autoimmune diseases, including myocarditis and diabetes. Thus, inflammatory responses induced by viruses that trigger proinflammatory Th1 responses, and have the ability to persist in genetically susceptible hosts, may lead to chronic organ-specific autoimmune disease via epitope spreading. Epitope spreading has important implications for the design of antigen-specific therapies for the potential treatment of MS and other autoimmune diseases. This process indicates that autoimmune diseases are evolving entities and that the specificity of the effector autoantigen-specific T cells varies during the chronic disease process. Our experiments employing tolerance in R-EAE clearly indicate that antigen-specific treatment of ongoing disease is possible for preventing disease relapses, provided the proper relapse-associated epitope is targeted (Vanderlugt et al., 1999). However, the ability to identify relapse-associated epitopes in humans will be a difficult task because immunodominance will vary in every individual. The use of costimulatory antagonists that can induce anergy without requiring prior knowledge of the exact epitopes (Miller et al., 1995b), or the use of therapies that induce bystander suppression (Nicholson et al., 1997; Brocke et al., 1996), may thus be more practical current alternative therapies for the treatment of human autoimmune disease.

Myelin-specific tolerance attenuates the progression of a virus-induced demyelinating disease: implications for the treatment of MS

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a multiple sclerosis (MS) model, is a central nervous system (CNS) demyelinating disease characterized by early peripheral T cell responses to virus epitopes which spreads to myelin epitopes during chronic disease. We show that CD4(+) T cells isolated from the spinal cords of chronically infected SJL mice proliferate and secrete pro-inflammatory cytokines upon in vitro challenge with both TMEV epitopes and proteolipid protein (PLP(139-151)). Importantly, myelin-specific tolerance induced by intravenous administration of MP4, a fusion of the myelin proteins myelin basic protein (MBP) and PLP, to SJL mice with ongoing TMEV-IDD attenuated disease progression and resulted in significantly less demyelination and decreased inflammatory cell infiltration in the CNS. Paradoxically, peptide-specific splenic T cell proliferative and IFN-gamma responses were enhanced in the tolerized mice. Collectively, these results indicate that myelin-specific T cell responses contribute to chronic disease progression in this virus-induced model of MS, and suggest caution in the use of antigen-specific tolerance for treatment of ongoing autoimmune disease.

Direct activation of innate and antigen-presenting functions of microglia following infection with Theiler's virus

Microglia are resident central nervous system (CNS) macrophages. Theiler's murine encephalomyelitis virus (TMEV) infection of SJL/J mice causes persistent infection of CNS microglia, leading to the development of a chronic-progressive CD4(+) T-cell-mediated autoimmune demyelinating disease. We asked if TMEV infection of microglia activates their innate immune functions and/or activates their ability to serve as antigen-presenting cells for activation of T-cell responses to virus and endogenous myelin epitopes. The results indicate that microglia lines can be persistently infected with TMEV and that infection significantly upregulates the expression of cytokines involved in innate immunity (tumor necrosis factor alpha, interleukin-6 [IL-6], IL-18, and, most importantly, type I interferons) along with upregulation of major histocompatibility complex class II, IL-12, and various costimulatory molecules (B7-1, B7-2, CD40, and ICAM-1). Most significantly, TMEV-infected microglia were able to efficiently process and present both endogenous virus epitopes and exogenous myelin epitopes to inflammatory CD4(+) Th1 cells. Thus, TMEV infection of microglia activates these cells to initiate an innate immune response which may lead to the activation of naive and memory virus- and myelin-specific adaptive immune responses within the CNS.

Enhanced susceptibility to Theiler's virus-induced demyelinating disease in perforin-deficient mice

Theiler's virus induces immune-mediated demyelinating disease similar to human MS in susceptible mice. Though the MHC class II-restricted T cell response is critical, susceptibility/resistance is also associated with a MHC class I haplotype. Here we report that perforin-deficient C57BL/6 mice (pKO) are susceptible to demyelination and develop clinical disease. The levels of primary demyelination, proliferation, Th1 responses, and viral load were also markedly enhanced. In addition, immunization of pKO mice with UV-inactivated virus further enhanced clinical incidence and accelerated the disease course. Thus, perforin is most likely involved in viral clearance, hence protection from the disease.

Antigens to viral capsid and non-capsid proteins are present in brain tissues and antibodies in sera of Theiler's virus-infected mice

Recombinant proteins to the LP, VP1, VP2, VP3, VP4, 2A, 2B, 2C, 3A, and 3D genes of Theiler's murine encephalomyelitis virus (TMEV) were generated and antibodies were produced against them for use in analysis of the TMEV epitopes responsible for eliciting the antibody responses observed during acute and chronic disease. Antibodies against recombinant VP1, VP2, and VP3 recognized the corresponding proteins from purified TMEV particles. In immunohistochemical analysis, antibodies against recombinant capsid (VP1, VP2, and VP3), and non-capsid (2A, 2C, 3A) proteins were reactive with PO-2D cells (astrocytes) infected with TMEV in vitro and with brain tissues of acutely infected mice. Antibodies against VP4, 2B, and 3D antigens were not reactive with corresponding viral proteins in infected astrocytes cells or brain tissues, but they reacted with TMEV precursor proteins produced during the early viral replication phase. Sera from SJL/J mice infected with TMEV acutely (14 days) and chronically (45 days) reacted with VP1, VP2, VP4, 2A, and 2C proteins. In an in vitro assay for neutralization, only anti-VP1 antibodies neutralized TMEV infection. These findings suggest that both capsid and non-capsid proteins of TMEV play a role in the immunopathology of the TMEV disease in the central nervous system.

Pathogenesis of virus-induced immune-mediated demyelination

Theiler's murine encephalomyelitis virus-induced demyelinating disease has been extensively studied as an attractive infectious model for human multiple sclerosis. Virus-specific inflammatory Th1 cell responses followed by autoimmune responses to myelin antigens play a crucial role in the pathogenic processes leading to demyelination. Antibody and cytotoxic T cells (CTL) responses to virus appears to be primarily protective from demyelinating disease. Although the role of Th1 and CTL responses in the induction of demyelinating disease is controversial, assessment of cytokines produced locally in the central nervous system (CNS) during the course of disease and the effects of altered inflammatory cytokine levels strongly support the importance of Th1 responses in this virus-induced demyelinating disease. Induction of various chemokines and cytokines in different glial and antigen presenting cells upon viral infection appears to be an important initiation mechanism for inflammatory Th1 responses in the CNS. Coupled with the initial inflammatory responses, viral persistence in the CNS may be a critical factor for sustaining inflammatory responses and consequent immune-mediated demyelinating disease.

CD28 costimulatory blockade exacerbates disease severity and accelerates epitope spreading in a virus-induced autoimmune disease

Theiler's murine encephalomyelitis virus (TMEV) is a natural mouse pathogen which causes a lifelong persistent infection of the central nervous system (CNS) accompanied by T-cell-mediated myelin destruction leading to chronic, progressive hind limb paralysis. TMEV-induced demyelinating disease (TMEV-IDD) is considered to be a highly relevant animal model for the human autoimmune disease multiple sclerosis (MS), which is thought to be initiated as a secondary consequence of a virus infection. Although TMEV-IDD is initiated by virus-specific CD4(+) T cells targeting CNS-persistent virus, CD4(+) T-cell responses against self myelin protein epitopes activated via epitope spreading contribute to chronic disease pathogenesis. We thus examined the ability of antibodies directed against B7 costimulatory molecules to regulate this chronic virus-induced immunopathologic process. Contrary to previous studies showing that blockade of B7-CD28 costimulatory interactions inhibit the initiation of experimental autoimmune encephalomyelitis, treatment of SJL mice at the time of TMEV infection with murine CTLA-4 immunoglobulin or a combination of anti-B7-1 and anti-B7-2 antibodies significantly enhanced clinical disease severity. Costimulatory blockade inhibited early TMEV-specific T-cell and antibody responses critical in clearing peripheral virus infection. The inhibition of virus-specific immune responses led to significantly increased CNS viral titers resulting in increased damage to myelin-producing oligodendrocytes. Following clearance of the costimulatory antagonists, epitope spreading to myelin epitopes was accelerated as a result of the increased availability of myelin epitopes leading to a more severe chronic disease course. Our results raise concern about the potential use of B7-CD28 costimulatory blockade to treat human autoimmune diseases potentially associated with acute or persistent virus infections.

RT-PCR, nucleotide, amino acid and phylogenetic analyses of enterovirus type 71 strains from Asia

A specific and sensitive method based on RT-PCR was developed to detect enterovirus 71 (EV71) from patients with hand, foot and mouth disease, myocarditis, aseptic meningitis and acute flaccid paralysis. RT-PCR primers from conserved parts of the VP1 capsid gene were designed on the basis of good correlation with sequences of EV71 strains. These primers successfully amplified 44 strains of EV71 including 34 strains isolated from Singapore in 1997 and 1998, eight strains from Malaysia isolated in 1997 and 1998, one Japanese strain and the neurovirulent strain EV71/7423/MS/87. RT-PCR of 30 strains of other enteroviruses including coxsackievirus A and B, and echoviruses failed to give any positive amplicons. Hence, RT-PCR with these primers showed 100% correlation with serotyping. Direct sequencing of the RT-PCR products of 20 EV71 strains revealed a distinct cluster with two major subgroups, thus enabling genetic typing of the viruses. The genetic heterogeneity of these strains culminated in amino acid substitutions within the VP1, VP2 and VP3 regions. The sequencing of a 2.9 kb fragment comprising the capsid region and the major part of 5' UTR of two Singapore strains revealed that they belonged to a group distinct from the prototype EV71/BrCr strain and the EV71/7423/MS/87 strain. The dendrogram generated from 341 bp fragments within the VP1 region revealed that the strains of Singapore, Malaysia and Taiwan belong to two entirely different EV71 genogroups, distinct from the three genogroups identified in another recent study.

Clonal expansion of infiltrating T cells in the spinal cords of SJL/J mice infected with Theiler's virus

Intracerebral infection of susceptible mice with Theiler's murine encephalomyelitis virus results in immune-mediated inflammatory demyelination in the white matter and consequent clinical symptoms. This system has been utilized as an important virus model for human multiple sclerosis. Although the potential involvement of virus-specific Th cells has been studied extensively, very little is known about the nature of T cells infiltrating the CNS during viral infection and their role in the development of demyelinating disease. In this study, the clonal nature of T cells in the spinal cord during the disease course was analyzed using size spectratyping and sequencing of the TCR beta-chain CDR3 region. These studies clearly indicate that T cells are clonally expanded in the CNS after viral infection, although the overall TCR repertoire appears to be diverse. The clonal expansion appears to be Ag-driven in that it includes Th cells specific for known viral epitopes. Interestingly, such restricted accumulation of T cells was not detectable in the infiltrates of mice with proteolipid protein peptide-induced experimental autoimmune encephalomyelitis. The initial T cell repertoire (7-9 days postinfection) seems to be more diverse than that observed in the later stage (65 days) of virally induced demyelination, despite the more restricted utilization of Vbeta subfamilies. These results strongly suggest continuous stimulation and clonal expansion of virus-specific T cells in the CNS of Theiler's murine encephalomyelitis virus-infected mice during the entire course of demyelinating disease.

Diverse Fine Specificity and Receptor Repertoire of T Cells Reactive to the Major VP1 Epitope (VP1230–250) of Theiler’s Virus: Vβ Restriction Correlates with T Cell Recognition of the C-Terminal Residue

Theiler’s murine encephalomyelitis virus induces chronic demyelinating disease in genetically susceptible mice. The histopathological and immunological manifestation of the disease closely resembles human multiple sclerosis, and, thus, this system serves as a relevant infectious model for multiple sclerosis. The pathogenesis of demyelination appears to be mediated by the inflammatory Th1 response to viral epitopes. In this study, T cell repertoire reactive to the major pathogenic VP1 epitope region (VP1233–250) was analyzed. Diverse minimal T cell epitopes were found within this region, and yet close to 50% of the VP1-reactive T cell hybridomas used Vβ16. The majority (8/11) of the Vβ16+ T cells required the C-terminal amino acid residue on the epitope, valine at position 245, and every T cell hybridoma recognizing this C-terminal residue expressed Vβ16. However, the complementarity-determining region 3 sequences of the Vβ16+ T cell hybridomas were markedly heterogeneous. In contrast, such a restriction was not found in the Vα usage. Only restricted residues at this C-terminal position allowed for T cell activation, suggesting that Vβ16 may recognize this terminal residue. Further functional competition analysis for TCR and MHC class II-contacting residues indicate that many different residues can be involved in the class II and/or TCR binding depending on the T cell population, even if they recognize the identical minimal epitope region. Thus, recognition of the C-terminal residue of a minimal T cell epitope may associate with a particular Vβ (but not Vα) subfamily-specific sequence, resulting in a highly restricted Vβ repertoire of the epitope-specific T cells.

Potential Role of CD4+ T Cell-Mediated Apoptosis of Activated Astrocytes in Theiler’s Virus-Induced Demyelination

Intracerebral inoculation of Theiler’s murine encephalomyelitis virus (TMEV) into susceptible mouse strains results in a chronic, immune-mediated demyelinating disease similar to human multiple sclerosis. Here, we examined the role of astrocytes as an APC population in TMEV-induced demyelination and assessed the potential consequences of T cell activation following Ag presentation. IFN-γ-pretreated astrocytes were able to process and present all the predominant T cell epitopes of TMEV to virus-specific T cell hybridomas, clones, as well as bulk T cells. Despite low levels of proliferation of T cells due to prostaglandins produced by astrocytes, such Ag presentation by activated astrocytes induced the production of IFN-γ, a representative proinflammatory cytokine, in TMEV-specific Th cell clones derived from the CNS of virus-infected mice. Furthermore, these Th cell clones mediate lysis of the astrocytes in vitro in a Fas-dependent mechanism. TUNEL staining of CNS tissue demonstrates the presence of apoptotic GFAP+ cells in the white matter of TMEV-infected mice. These results strongly suggest that astrocytes could play an important role in the pathogenesis of TMEV-induced demyelination by activating T cells, subsequently leading to T cell-mediated apoptosis of astrocytes and thereby compromising the blood-brain barrier.

Theiler's viruses with mutations in loop I of VP1 lead to altered tropism and pathogenesis

Theiler's murine encephalomyelitis viruses are picornaviruses that can infect the central nervous system. The DA strain produces an acute polioencephalomyelitis followed by a chronic demyelinating disease in its natural host, the mouse. The ability of DA virus to induce a demyelinating disease renders this virus infection a model for human demyelinating diseases such as multiple sclerosis. Here we describe the generation and characterization of DA virus mutants that contain specific mutations in the viral capsid protein VP1 at sites believed to be important contact regions for the cellular receptor(s). A mutant virus with a threonine-to-aspartate (T81D) substitution in VP1 loop I adjacent to the putative virus receptor binding site exhibited a large-plaque phenotype but had a slower replication cycle in vitro. When this mutant virus was injected into susceptible mice, an altered tropism was seen during the acute stage of the disease and the chronic demyelinating disease was not produced. A virus with a threonine-to-valine substitution (T81V) did not cause any changes in the pattern or extent of disease seen in mice, whereas a virus with a tryptophan substitution at this position (T81W) produced a similar acute disease but was attenuated for the development of the chronic disease. A change in amino acids in a hydrophobic patch located in the wall of the pit, VP1 position 91, to a hydrophilic threonine (V91T) resulted in a profound attenuation of the acute and chronic disease without persistence of virus. This report illustrates the importance of the loop I of VP1 and a site in the wall of the pit in pathogenesis and that amino acid substitutions at these sites result in altered virus-host interactions.

DNA vaccination against Theiler's murine encephalomyelitis virus leads to alterations in demyelinating disease

Although the etiology of multiple sclerosis (MS) is not known, several factors play a role in this disease: genetic contributions, immunologic elements, and environmental factors. Viruses and virus infections have been associated with the initiation and/or enhancement of exacerbations in MS. Theiler's murine encephalomyelitis virus (TMEV) infection of mice is one of the animal models used to mimic MS. In other animal model systems, DNA vaccination has been used to protect animals against a variety of virus infections. To explore the utility of DNA vaccination, we have constructed eukaryotic expression vectors encoding the TMEV capsid proteins VP1, VP2, and VP3. SJL/J mice were vaccinated intramuscularly once, twice, or three times with the different capsid protein cDNAs. This was followed by intracerebral TMEV infection to determine the effects of DNA vaccination on the course of TMEV-induced central nervous system (CNS) demyelinating disease. We found that vaccination of mice three times with cDNA encoding VP2 led to partial protection of mice from CNS demyelinating disease as determined by a decrease in clinical symptoms and histopathology. Vaccination of mice with cDNA encoding VP3 also led to a decrease in clinical symptoms. In contrast, mice vaccinated with cDNA encoding VP1 experienced a more severe disease with an earlier onset of clinical signs and enhanced histopathology compared with control mice. There was no correlation between anti-TMEV antibody titers and disease course. These results indicate that DNA immunization can modify chronic virus-induced demyelinating disease and may eventually lead to potential treatments for illnesses such as MS.

Role of individual T-cell epitopes of Theiler's virus in the pathogenesis of demyelination correlates with the ability to induce a Th1 response

Intracerebral inoculation of susceptible strains of mice with Theiler's murine encephalomyelitis virus (TMEV) results in immune-mediated demyelination. Three major T-cell epitopes have previously been identified within the VP1 (VP1233-250), VP2 (VP274-86), and VP3 (VP324-37) capsid proteins in virus-infected SJL/J mice. These epitopes appear to account for the majority ( approximately 90%) of major histocompatibility complex class II-restricted T-cell responses to TMEV. Interestingly, the effect of immunization with synthetic peptides bearing the predominant T-cell epitopes on the course of TMEV-induced demyelination indicates that T cells reactive to the VP1 and VP2 epitopes, but not VP3, accelerate the pathogenesis of demyelination. The predominant pathogenic role of the T cells is verified by similar immunization with the fusion proteins containing the entire individual capsid proteins. The order of appearance and level of T cells specific for the individual epitopes during the course of demyelination are similar to each other. However, cytokine profiles of T cells from virus-infected mice indicate that T cells specific for the VP1 (and perhaps the VP2) epitope are Th1, whereas T cells reactive to VP3 are primarily Th2. These results suggest that Th1-type cells specific for VP1 and VP2 are involved in the pathogenesis of viral demyelination induced by TMEV. Thus, a predominance of Th1-inducing viral epitopes is likely critical for the pathogenesis of demyelination.

A spontaneous low-pathogenic variant of Theiler's virus contains an amino acid substitution within the predominant VP1(233-250) T-cell epitope

Theiler's murine encephalomyelitis virus (TMEV) induces immune-mediated demyelination after intracerebral inoculation of the virus into susceptible mouse strains. We isolated from a TMEV BeAn 8386 viral stock, a low-pathogenic variant which requires greater than a 10,000-fold increase in viral inoculation for the manifestation of detectable clinical signs. Intracerebral inoculation of this variant virus induced a strong, long-lasting, protective immunity from the demyelinating disease caused by pathogenic TMEV. The levels of antibodies to the whole virus as well as to the major linear epitopes were similar in mice infected with either the variant or wild-type virus. However, persistence of the variant virus in the central nervous system (CNS) of mice was significantly lower than that of the pathogenic virus. In addition, the T-cell response to the predominant VP1 (VP1(233-250)) epitope in mice infected with the variant virus was significantly weaker than that in mice infected with the parent virus, while similar T-cell responses were induced against another predominant epitope (VP2(74-86)). Further analyses indicated that a change of lysine to arginine at position 244 of VP1, which is the only amino acid difference in the P1 region, is responsible for such differential T-cell recognition. Thus, the difference in the T-cell reactivity to this VP1 region as well as the low level of viral persistence in the CNS may account for the low pathogenicity of this spontaneous variant virus.

Association between susceptibility to Theiler's virus-induced demyelination and T-cell receptor Jbeta1-Cbeta1 polymorphism rather than Vbeta deletion

Theiler's murine encephalomyelitis virus (TMEV) induces demyelinating disease in susceptible mouse strains after intracerebral inoculation. The clinical symptoms and histopathology of the central nervous system appear to be similar to those of human multiple sclerosis (MS), and thus, this system provides an excellent infectious animal model for studying MS. The virus-induced demyelination is immune mediated, and the genes involved in the immune response such as those for the T-cell receptor beta-chain and major histocompatibility complex (MHC) haplotypes are known to influence disease susceptibility. To define whether the T-cell receptor Jbeta-Cbeta or Vbeta genes are associated with susceptibility, we have analyzed F2 mice from crosses of susceptible SJL/J (Vbeta(a)-JCbeta(b)) mice and resistant C57L (Vbeta(a)-JCbeta(a)) mice. Our results indicate that susceptibility to TMEV-induced demyelination is associated with restriction fragment length polymorphism reflecting the T-cell receptor Jbeta1-Cbeta1 region rather than the Vbeta polymorphism. This association becomes stronger when the MHC haplotype is considered in the linkage analysis. However, differences in the T-cell receptor alpha-chain haplotype have no significant influence on the pathogenesis of TMEV-induced demyelination.

Major linear antibody epitopes and capsid proteins differentially induce protective immunity against Theiler's virus-induced demyelinating disease

Theiler's murine encephalomyelitis virus-induced immunologically mediated demyelinating disease (TMEV-IDD) in susceptible mice provides a relevant infectious model for multiple sclerosis. Previously, we have identified six major linear antibody epitopes on the viral capsid proteins. In this study, we utilized fusion proteins containing individual capsid proteins and synthetic peptides containing the linear antibody epitopes to determine the potential role of antibody response in the course of virus-induced demyelination. Preimmunization of susceptible mice with VPI and VP2 fusion proteins, but not VP3, resulted in the protection from subsequent development of TMEV-IDD. Mice free of clinical symptoms following preimmunizations with fusion proteins displayed high levels of antibodies to the capsid proteins corresponding to the immunogens. In contrast, the level of antibodies to a particular linear epitope, A1C (VP1(262-276)), capable of efficiently neutralizing virus in vitro increased with the progression of disease. Further immunization with synthetic peptides containing individual antibody epitopes indicated that antibodies to the epitopes are differentially effective in protecting from virus-induced demyelination. Taken together, these results suggest that antibodies to only certain linear epitopes are protective and such protection may be restricted during the early stages of viral infection.