Protection of SJL/J mice from demyelinating disease mediated by Theiler's murine encephalomyelitis virus

DA virus mutant H101 has altered CNS pathogenesis and causes immunosuppression

Viruses use various mechanisms to evade clearance by the host. Investigating how a few changes in the genome of a non-lethal virus can lead to altered disease, from survivable to immunosuppression/death, would provide valuable information into viral pathogenesis. The Daniels strain of Theiler's murine encephalomyelitis virus causes an asymptomatic infection or acute encephalitis followed by viral clearance. A mutant, H101, carries several alterations in the viral genome. H101 infection causes profound immunosuppression and death. Thus, a virus that is normally cleared by its natural host can become lethal due to just a few changes in the viral genome.

Protective and detrimental roles for regulatory T cells in a viral model for multiple sclerosis

Multiple sclerosis (MS) has been proposed to be an immune-mediated disease in the central nervous system (CNS) that can be triggered by virus infections. In Theiler's murine encephalomyelitis virus (TMEV) infection, during the first week (acute stage), mice develop polioencephalomyelitis. After 3 weeks (chronic stage), mice develop immune-mediated demyelination with virus persistence, which has been used as a viral model for MS. Regulatory T cells (Tregs) can suppress inflammation, and have been suggested to be protective in immune-mediated diseases, including MS. However, in virus-induced inflammatory demyelination, although Tregs can suppress inflammation, preventing immune-mediated pathology, Tregs may also suppress antiviral immune responses, leading to more active viral replication and/or persistence. To determine the role and potential translational usage of Tregs in MS, we treated TMEV-infected mice with ex vivo generated induced Tregs (iTregs) on day 0 (early) or during the chronic stage (therapeutic). Early treatment worsened clinical signs during acute disease. The exacerbation of acute disease was associated with increased virus titers and decreased immune cell recruitment in the CNS. Therapeutic iTreg treatment reduced inflammatory demyelination during chronic disease. Immunologically, iTreg treatment increased interleukin-10 production from B cells, CD4(+) T cells and dendritic cells, which may contribute to the decreased CNS inflammation.

Immunization with structural and non-structural proteins of Theiler's murine encephalomyelitis virus alters demyelinating disease

Theiler's murine encephalomyelitis virus (TMEV) causes a demyelinating disease similar to multiple sclerosis in the central nervous system (CNS) of susceptible SJL/J mice. Immune responses to TMEV contribute to viral clearance as well as to demyelination. We constructed recombinant vaccinia viruses (VV) that encode each or all of the capsid proteins (VV(VP1), VV(VP2), VV(VP3), VV(VP4), and VV(all)) or non-structural proteins (VV(P2), VV(P2P3), and VV(3'P3)) of the Daniels strain of TMEV. To determine the role of each of the coding regions of TMEV in vivo, we immunized SJL/J mice with each recombinant VV, with or without subsequent TMEV infection. The groups of mice were compared clinically, immunologically, and histologically. No mice immunized with any recombinant VV without subsequent TMEV infection developed demyelination. However, antibody responses to TMEV were detected in mice immunized with VV(all). In addition, in some mice, VV(P2) immunization induced mild meningitis. VV(VP3) or VV(VP4) immunization of mice prior to TMEV infection ameliorated TMEV-induced pathology or clinical signs of disease. The beneficial effect of VP4 immunization was also seen through DNA immunization with a plasmid encoding VP4 and leader prior to TMEV infection. Therefore, vaccination against not only surface capsid proteins (VV(VP3) and VV(all)) but also non-surface capsid protein (VV(VP4)), and non-structural proteins (VV(P2)) can elicit immune responses to virus or modulate subsequent viral-induced CNS disease.

The effect of FTY720 in the Theiler's virus model of multiple sclerosis

FTY720 (fingolimod) has demonstrated efficacy in multiple sclerosis (MS). We evaluated the effects of FTY720 on progressive disability, viral load, and antibody responses in mice infected with Theiler's murine encephalomyocarditis virus (TMEV). FTY720 and phosphorylated FTY720 (FTY720-P) were detected in the brain after intraperitoneal injection of the drug. Bioactivity of FTY720 was confirmed by reduced numbers of mononuclear cells in the spleen and blood after treatment. No significant differences were found in disability progression, viral load, and serum antibody responses between the FTY720-treated versus the PBS-treated mice. There was less production of IgG within the CNS in the FTY-treated group on some measures.

Infectious RNA isolated from the spinal cords of mice chronically infected with Theiler's murine encephalomyelitis virus

The DA strain of Theiler's murine encephalomyelitis virus (TMEV) persistently infects cells of the spinal cord during the chronic phase of infection. Although in situ hybridization and reverse transcription-PCR have demonstrated the presence of viral RNA in the spinal cord, it has not been determined whether this RNA is infectious and, if so, how many PFU equivalents of virus the RNA can yield. In this study, we demonstrated that TMEV RNA isolated from the spinal cords of chronically infected mice is infectious and that there is at least 30-fold more infectious RNA than infectious virus in the spinal cords of these mice.

Exacerbation of viral and autoimmune animal models for multiple sclerosis by bacterial DNA

Theiler's murine encephalomyelitis virus (TMEV) infection and relapsing-remitting experimental allergic encephalomyelitis (R-EAE) have been used to investigate the viral and autoimmune etiology of multiple sclerosis (MS), a possible Th1-type mediated disease. DNA immunization is a novel vaccination strategy in which few harmful effects have been reported. Bacterial DNA and oligodeoxynucleotides, which contain CpG motifs, have been reported to enhance immunostimulation. Our objectives were two-fold: first, to ascertain whether plasmid DNA, pCMV, which is widely used as a vector in DNA immunization studies, could exert immunostimulation in vitro; and second, to test if pCMV injection could modulate animal models for MS in vivo. We demonstrated that this bacterially derived DNA could induce interleukin (IL)-12, interferon (IFN)gamma, (Th1-promoting cytokines), and IL-6 production as well as activate NK cells. Following pCMV injections, SJL/J mice were infected with TMEV or challenged with encephalitogenic myelin proteolipid protein (PLP) peptides. pCMV injection exacerbated TMEV-induced demyelinating disease in a dose-dependent manner. Exacerbation of the disease did not correlate with the number of TMEV-antigen positive cells but did with an increase in anti-TMEV antibody. pCMV injection also enhanced R-EAE with increased IFNgamma and IL-6 responses. These results caution the use of DNA vaccination in MS patients and other possible Th1-mediated diseases.

Infection-dependent phenotypes in MHC-congenic mice are not due to MHC: can we trust congenic animals?

Background

Congenic strains of mice are assumed to differ only at a single gene or region of the genome. These mice have great importance in evaluating the function of genes. However, their utility depends on the maintenance of this true congenic nature. Although, accumulating evidence suggests that congenic strains suffer genetic divergence that could compromise interpretation of experimental results, this problem is usually ignored. During coinfection studies with Salmonella typhimurium and Theiler's murine encephalomyelitis virus (TMEV) in major histocompatibility complex (MHC)-congenic mice, we conducted the proper F₂ controls and discovered significant differences between these F₂ animals and MHC-genotype-matched P₀ and F₁ animals in weight gain and pathogen load. To systematically evaluate the apparent non-MHC differences in these mice, we infected all three generations (P₀, F₁ and F₂) for 5 MHC genotypes (b/b, b/q and q/q as well as d/d, d/q, and q/q) with Salmonella and TMEV.

Results

Infected P₀ MHC q/q congenic homozygotes lost significantly more weight (p = 0.02) and had significantly higher Salmonella (p < 0.01) and TMEV (p = 0.02) titers than the infected F₂ q/q homozygotes. Neither weight nor pathogen load differences were present in sham-infected controls.

Conclusions

These data suggest that these strains differ for genes other than those in the MHC congenic region. The most likely explanation is that deleterious recessive mutations affecting response to infection have accumulated in the more than 40 years that this B10.Q-H-2^q MHC-congenic strain has been separated from its B10-H-2^b parental strain. During typical experiments with congenic strains, the phenotypes of these accumulated mutations will be falsely ascribed to the congenic gene(s). This problem likely affects any strains separated for appreciable time and while usually ignored, can be avoided with the use of F₂ segregants.

Axonal injury heralds virus-induced demyelination

Axonal pathology has been highlighted as a cause of neurological disability in multiple sclerosis. The Daniels (DA) strain of Theiler's murine encephalomyelitis virus infects the gray matter of the central nervous system of mice during the acute phase and persistently infects the white matter of the spinal cord during the chronic phase, leading to demyelination. This experimental infection has been used as an animal model for multiple sclerosis. The GDVII strain causes an acute fatal polioencephalomyelitis without demyelination. Injured axons were detected in normal appearing white matter at 1 week after infection with DA virus by immunohistochemistry using antibodies specific for neurofilament protein. The number of damaged axons increased throughout time. By 2 and 3 weeks after infection, injured axons were accompanied by parenchymal infiltration of Ricinus communis agglutinin I(+) microglia/macrophages, but never associated with perivascular T-cell infiltration or obvious demyelination until the chronic phase. GDVII virus infection resulted in severe axonal injury in normal appearing white matter at 1 week after infection, without the presence of macrophages, T cells, or viral antigen-positive cells. The distribution of axonal injury observed during the early phase corresponded to regions where subsequent demyelination occurs during the chronic phase. The results suggest that axonal injury might herald or trigger demyelination.

Major histocompatibility complex heterozygote superiority during coinfection

Genes of the major histocompatibility complex (MHC) play a critical role in immune recognition, and many alleles confer susceptibility to infectious and autoimmune diseases. How these deleterious alleles persist in populations is controversial. One hypothesis postulates that MHC heterozygote superiority emerges over multiple infections because MHC-mediated resistance is generally dominant and many allele-specific susceptibilities to pathogens will be masked by the resistant allele in heterozygotes. We tested this hypothesis by using experimental coinfections with Salmonella enterica (serovar Typhimurium C5TS) and Theiler's murine encephalomyelitis virus (TMEV) in MHC-congenic mouse strains where one haplotype was resistant to Salmonella and the other was resistant to TMEV. MHC heterozygotes were superior to both homozygotes in 7 out of 8 comparisons (P = 0.0024), and the mean standardized pathogen load of heterozygotes was reduced by 41% over that of homozygotes (P = 0.01). In contrast, no heterozygote superiority was observed when the MHC haplotype combinations had similar susceptibility profiles to the two pathogens. This is the first experimental evidence for MHC heterozygote superiority against multiple pathogens, a mechanism that would contribute to the evolution of MHC diversity and explain the persistence of alleles conferring susceptibility to disease.

Prolonged gray matter disease without demyelination caused by Theiler's murine encephalomyelitis virus with a mutation in VP2 puff B

Theiler's murine encephalomyelitis virus (TMEV) is divided into two subgroups based on neurovirulence. During the acute phase, DA virus infects cells in the gray matter of the central nervous system (CNS). Throughout the chronic phase, DA virus infects glial cells in the white matter, causing demyelinating disease. Although GDVII virus also infects neurons in the gray matter, infected mice developed a severe polioencephalomyelitis, and no virus is detected in the white matter or other areas in the CNS in rare survivors. Several sequence differences between the two viruses are located in VP2 puff B and VP1 loop II, which are located near each other, close to the proposed receptor binding site. We constructed a DA virus mutant, DApBL2M, which has the VP1 loop II of GDVII virus and a mutation at position 171 in VP2 puff B. While DApBL2M virus replicated less efficiently than DA virus during the acute phase, DApBL2M-induced acute polioencephalitis was comparable to that in DA virus infection. Interestingly, during the chronic phase, DApBL2M caused prolonged gray matter disease in the brain without white matter involvement in the spinal cord. This is opposite what is observed during wild-type DA virus infection. Our study is the first to demonstrate that conformational differences via interaction of VP2 puff B and VP1 loop II between GDVII and DA viruses can play an important role in making the transition of infection from the gray matter in the brain to the spinal cord white matter during TMEV infection.

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.

The infection of mouse by Theiler's virus: from genetics to immunology

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter of the spinal cord with chronic inflammation and demyelination. This late disease is studied as a model for multiple sclerosis. Inbred strains of mice differ in their susceptibility to persistent infection and demyelination. Resistant strains clear the infection after the acute encephalomyelitis. This observation is the basis of genetic studies which we used as a thread for this review. The H-2D locus has a major effect on susceptibility. The H-2Db gene is involved in a fast and intense CTL response which confers resistance. The Tcrb locus is also implicated, although there is no proof that the susceptibility gene in this region codes for the T-cell receptor. A complete screen of the genome uncovered the role of the Ifng locus and led to the demonstration that IFN-gamma limits viral spread in the white matter. The roles of NK cells and B cells in limiting the infection are discussed. CD4+ T cells participate both in protection against the infection and in demyelination. Finally, the effect of non-immune factors in resistance is illustrated by mice with mutations in the MBP or PLP gene.

Enhancement of EAE and induction of autoantibodies to T-cell epitopes in mice infected with a recombinant vaccinia virus encoding myelin proteolipid protein

SJL/J mice were infected with a recombinant vaccinia virus encoding myelin proteolipid protein (PLP) (VVplp). Antibody responses to whole PLP and to encephalitogenic peptides, p139-151, p178-191 or p104-117 were measured after vaccination and following challenge with these three PLP peptides. Competitive ELISAs showed that antibodies to p139-151 and p178-191 represented the majority of antibodies in the anti-PLP antibody response following VVplp vaccination, since the antibodies to intact PLP could be inhibited 56, 35 and 1%, respectively, by p139-151, p178-191 and p104-117. After peptide challenge, epitope specific anti-peptide antibodies were enhanced. These anti-peptide antibodies also reacted with the intact PLP molecule. Interestingly, the mean titer of anti-p139-151 antibody in p139-151 challenged mice was significantly higher than that observed for anti-p178-191 in p178-191 and for anti-p104-117 in p104-117 challenged mice. Following peptide challenge, the anti-PLP IgG response shifted from an IgG1 to an IgG2a and 2b phenotype. In these mice, both the clinical disease and histological pattern of experimental allergic encephalomyelitis (EAE) were enhanced. The enhancement was most pronounced in the pathologic scores in the p139-151 challenged group followed by p104-117 challenged mice. Thus, humoral immune responses to PLP encephalitogenic peptides can be generated with virus encoding a self central nervous system (CNS) protein.

B-lymphocyte requirement for vaccine-mediated protection from Theiler's murine encephalomyelitis virus-induced central nervous system disease

The role of humoral immunity in the protection of vaccinated SJL/J mice from central nervous system disease induced by the DA strain (DAV) of Theiler's murine encephalomyelitis virus was investigated in B-cell-deficient mice. Mice were depleted of B cells by treatment with a mouse monoclonal antibody specific for immunoglobulin M. DAV-vaccinated, B-cell-deficient mice failed to clear viral infection and were no longer protected from Theiler's murine encephalomyelitis virus-mediated central nervous system disease. CD4+ T cells are required in this model of protection to provide help for the development of an antiviral antibody response in the central nervous system.