Viral mouse models used to study multiple sclerosis: past and present.

Multiple sclerosis (MS) is a common inflammatory demyelinating disease of the central nervous system. Although the etiology of MS is unknown, genetics and environmental factors, such as infections, play a role. Viral infections of mice have been used as model systems to study this demyelinating disease of humans. Three viruses that have long been studied in this capacity are Theiler's murine encephalomyelitis virus, mouse hepatitis virus, and Semliki Forest virus. This review describes the viruses themselves, the infection process, the disease caused by infection and its accompanying pathology, and the model systems and their usefulness in studying MS.

Theiler's murine encephalomyelitis virus contrasts with encephalomyocarditis and foot-and-mouth disease viruses in its functional utilization of the StopGo non-standard translation mechanism.

The picornaviruses' genome consists of a positive-sense ssRNA. Like many picornaviruses, cardioviruses synthesize two distinct polyprotein precursors from adjacent but non-overlapping genome segments. Both the [L-1ABCD-2A] and the [2BC-3ABCD] polyproteins are proteolytically processed to yield mature capsid and non-structural proteins, respectively. An unusual translational event, known as 'StopGo' or 'Stop-Carry on', is responsible for the release of the [L-1ABCD-2A] polyprotein from the ribosome and synthesis of the N-terminal amino acid of the [2BC-3ABCD] polyprotein. A common feature of these viruses is the presence of a highly conserved signature sequence for StopGo: -D(V/I)ExNPG(↓)P-, where -D(V/I)ExNPG are the last 7 aa of 2A, and the last P- is the first amino acid of 2B. Here, we report that, in contrast to encephalomyocarditis virus and foot-and-mouth disease virus, a functional StopGo does not appear to be essential for Theiler's murine encephalomyelitis virus viability when tested in vitro and in vivo.

Alteration of amino acid 101 within capsid protein VP-1 changes the pathogenicity of Theiler's murine encephalomyelitis virus.

Chronic Theiler's murine encephalomyelitis virus infection of susceptible mice is an animal model for human demyelinating diseases. Previously we described an altered and diminished pattern of central nervous system disease in immunocompetent SJL/J mice infected with a variant virus. This variant virus H7A6-2 was selected with a neutralizing mAb recognizing the capsid protein VP-1 of Theiler's virus. Here we characterize the variant virus by ELISA and neutralization assays and by sequencing selected regions of the viral RNA genome and relate the alteration to disease. The variant virus contains one single point mutation within a neutralizing epitope of VP-1. This nucleotide change lead to an amino acid replacement at amino acid 101 of VP-1, a threonine (wild type) to an isoleucine (variant). Model building based on sequence alignments and the known structure of the related Mengo virus indicates that the altered amino acid is located in an exposed loop on the surface of the virus at the periphery of a site that has been proposed to be the receptor binding site. The results of ELISA, neutralization assay, and direct RNA sequencing provide for the first time an opportunity to precisely map an important structural determinant of neurovirulence.

Monoclonal antibody to Theiler's murine encephalomyelitis virus defines a determinant on myelin and oligodendrocytes, and augments demyelination in experimental allergic encephalomyelitis.

Theiler's murine encephalomyelitis virus (TMEV) causes a chronic demyelinating disease in mice. The mechanisms underlying the demyelination have not been fully elucidated. We have raised a mAb to TMEV (DA strain), H8, that reacts both with TMEV VP-1 and galactocerebroside (GC). In mouse brain cultures, cells positive for the mAb H8 epitope were double labeled with antibody to myelin basic protein, indicating that those cells were oligodendrocytes. Further, mAb H8 could immunostain myelin structures in frozen sections from mouse brains. When injected intravenously into mice with acute allergic encephalomyelitis, mAb H8 increased by 10-fold the size of demyelinated areas within the spinal cords. This is the first report demonstrating that an antibody to virus can enhance demyelination of a central nervous system disease. Ig fractions from the sera of mice with chronic TMEV infection had antibody(s) to GC, as well as to TMEV, as determined by ELISA. Furthermore, a competition ELISA for TMEV or GC antigen revealed that sera from these infected mice contained antibody(s) with the same specificity as mAb H8. Our results indicate that antibodies generated by immune response to TMEV can react with myelin and oligodendrocytes, and contribute to demyelination through an immune process.

Failure to cleave measles virus fusion protein in lymphoid cells.

The host-directed cleavage of measles virus fusion protein on infected lymphoid cells was studied to understand the mechanism of viral persistence in lymphoid cells in vivo. Several lymphoblastoid cell lines were infected with measles virus, and the viral glycoproteins expressed on the cell's surface were radiolabeled and analyzed for cleavage of fusion (F(0)) to F(1) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Daudi and Ramos lymphoblastoid cells were deficient in their ability to cleave measles virus fusion protein and correspondingly produced low titers of infectious measles virus, Daudi cells being more defective than Ramos cells. In contrast, other lymphoblastoid cells studied, Victor, Raji, Wi-L2, RPMI 8866, and Seraphine, cleaved the fusion polypeptide and made significantly more infectious virus. Despite their defect in cleaving F protein, Daudi cells were able to assemble and release (noninfectious) measles virus particles into the fluid phase. The deficit in Daudi cells was corrected by fusing infected Daudi cells with cleavage-competent cells such as Victor or Raji. Furthermore, the cleavage event performed by competent cells could be mimicked at the plasma membrane by treating infected Daudi cells with trypsin, implicating the role of a plasma membrane enzyme in cleaving F(0) to F(1) during measles virus infection. Hence, lymphoid cells deficient in the plasma membrane enzyme required to cleave F protein are permissive for measles virus, maintain viral gene products, produce mostly noninfectious virus, and fail to place the biologic activity F(1) protein on their surfaces.

Myelin basic protein serum factor. An endogenous neuroantigen influencing development of experimental allergic encephalomyelitis in Lewis rats.

Age-related concentrations of myelin basic protein serum factor (MBP-SF), an endogenous neuroantigen detected and quantitated by inhibition of binding of rat myelin basic protein (RMBP) antibody with 125I-RMBP reagent antigen and immunochemically indistinguishable from native RMBP in this respect, reach peak levels as high as 21 ng/microliter among 2-3-wk-old normal suckling Lewis rats. Levels then progressively decline to low, usually undetectable levels of less than or equal to 0.6 ng/microliter MBP-equivalents in adult animals by 7 wk of age. MBP-SF levels are inversely related to the age-related increasing capacity of maturing Lewis rats to develop experimental allergic encephalomyelitis (EAE) after sensitization to MBP of syngeneic, but not xenogeneic, origin. MBP-SF appears to be an endogenous neuroimmunoregulatory product of potential importance for immunologic tolerance to autologous RMBP in Lewis rats.

Viruses disrupt functions of human lymphocytes. II. Measles virus suppresses antibody production by acting on B lymphocytes.

Measles virus infection is associated with suppression of immune functions both in vivo and in vitro. The virus infects T lymphocytes, B lymphocytes, and monocytes, but does not produce cytolysis. One consequence of infection in vitro is the failure of T and B lymphocyte mixtures to cooperate in secreting Ig in a PWM-driven system. Here we report that this defect in Ig secretion resides in the infected B lymphocyte, but not in the T lymphocyte or monocyte. Further, NK cells are not involved, since neither their depletion nor reconstitution abrogates suppression of B cell function. Proliferation of B cells in the early culture period is suppressed, suggesting that measles virus suppresses B cell development at the activation or proliferation stages, but does not affect terminal differentiation into Ig secreting cells.

Modulation of experimental autoimmune encephalomyelitis through colonisation of the gut with Escherichia coli.

Multiple sclerosis (MS) is a neuro-inflammatory autoimmune disease of the central nervous system (CNS) that affects young adults. It is characterised by the development of demyelinating lesions and inflammation within the CNS. Although the causes of MS are still elusive, recent work using patient samples and experimental animal models has demonstrated a strong relationship between the gut microbiota and its contribution to CNS inflammation and MS. While there is no cure for MS, alteration of the gut microbiota composition through the use of probiotics is a very promising treatment. However, while most recent works have focused on the use of probiotics to modify pre-existing disease, little is known about its role in protecting from the establishment of MS. In this study, we determined whether colonisation with the probiotic bacterium Escherichia coli strain Nissle 1917 (EcN) could be used as a prophylactic strategy to prevent or alter the development of experimental autoimmune encephalomyelitis (EAE), a preclinical model of MS. We found that double gavage (two doses) of EcN before induction of EAE delayed disease onset and decreased disease severity. We also found that EcN-treated mice had decreased amounts of perivascular cuffing, CD4+ T cell infiltration into the CNS, together with significantly decreased absolute numbers of Th1 cells, and reduced activation of microglia. Although further studies are necessary to comprehend the exact protective mechanisms induced, our study supports a promising use of EcN as a probiotic for the prevention of MS.

Amino acid homology between the encephalitogenic site of myelin basic protein and virus: mechanism for autoimmunity.

Amino acid sequence homology was found between viral and host encephalitogenic protein. Immune responses were then generated in rabbits by using the viral peptide that cross-reacts with the self protein. Mononuclear cell infiltration was observed in the central nervous systems of animals immunized with the viral peptide. Myelin basic protein (MBP) is a host protein whose encephalitogenic site of ten amino acids induces experimental allergic encephalomyelitis. By computer analysis, hepatitis B virus polymerase (HBVP) was found to share six consecutive amino acids with the encephalitogenic site of rabbit MBP. Rabbits given injections of a selected eight- or ten-amino acid peptide from HBVP made antibody that reacted with the predetermined sequences of HBVP and also with native MBP. Peripheral blood mononuclear cells from the immunized rabbits proliferated when incubated with either MBP or HBVP. Central nervous system tissue taken from these rabbits had a histologic picture reminiscent of experimental allergic encephalomyelitis. Thus, viral infection may trigger the production of antibodies and mononuclear cells that cross-react with self proteins by a mechanism termed molecular mimicry. Tissue injury from the resultant autoallergic event can take place in the absence of the infectious virus that initiated the immune response.

Variations in diet cause alterations in microbiota and metabolites that follow changes in disease severity in a multiple sclerosis model.

Multiple sclerosis (MS) is a metabolically demanding disease involving immune-mediated destruction of myelin in the central nervous system. We previously demonstrated a significant alteration in disease course in the experimental autoimmune encephalomyelitis (EAE) preclinical model of MS due to diet. Based on the established crosstalk between metabolism and gut microbiota, we took an unbiased sampling of microbiota, in the stool, and metabolites, in the serum and stool, from mice (Mus musculus) on the two different diets, the Teklad global soy protein-free extruded rodent diet (irradiated diet) and the Teklad sterilisable rodent diet (autoclaved diet). Within the microbiota, the genus Lactobacillus was found to be inversely correlated with EAE severity. Therapeutic treatment with Lactobacillus paracasei resulted in a significant reduction in the incidence of disease, clinical scores and the amount of weight loss in EAE mice. Within the metabolites, we identified shifts in glycolysis and the tricarboxylic acid cycle that may explain the differences in disease severity between the different diets in EAE. This work begins to elucidate the relationship between diet, microbiota and metabolism in the EAE preclinical model of MS and identifies targets for further study with the goal to more specifically probe the complex metabolic interaction at play in EAE that may have translational relevance to MS patients.

Viruses as triggers of autoimmunity: facts and fantasies.

Autoimmunity has been proposed as the cause of several human chronic inflammatory diseases, and recent animal studies show that viruses can induce autoimmune disease. These studies demonstrate how viruses might misdirect the immune system, and here we discuss critically the evidence that similar phenomena may lead to human disease.

Viruses and autoimmune disease--two sides of the same coin?

Some viruses have the ability to modulate the development of autoimmune diseases. Virus infections have long been associated with the exacerbation of autoimmune disease, however, there is also evidence that viruses can actually protect against autoimmune disease. Several experimental models have been developed to investigate how some virus infections can prime for and trigger autoimmunity whereas others ameliorate the pathway leading to clinical disease. It is possible that the type I interferons, via interleukin 12, provide the link between viruses and autoimmunity.

Two models for multiple sclerosis: experimental allergic encephalomyelitis and Theiler's murine encephalomyelitis virus.

In this review, we compare and contrast two popular models for multiple sclerosis (MS), Theiler's murine encephalomyelitis virus (TMEV) disease and experimental allergic encephalomyelitis (EAE). These models are used to investigate the viral and autoimmune etiology of MS, respectively. Infection with live TMEV is an essential component of TMEV demyelinating disease. TMEV-specific cellular and humoral immunity and apoptosis of infected cells eliminate virus from the gray matter of the central nervous system (CNS) during the acute phase of TMEV disease. In contrast, during the chronic phase, TMEV persistently infects glial cells and/or macrophages in the white matter. During the chronic phase, recruitment of macrophages, TMEV-specific T cells and antibody, with the induction of apoptosis are harmful to the host, leading to inflammation and demyelination. In EAE, induction of encephalitogenic CD4+ T cells is an important component for disease. After stimulation and activation, these T cells upregulate adhesion molecules and are able to enter the CNS. Th1 cytokines augment the recruitment of mononuclear cells in the CNS. Macrophages and/or glial cells secrete cytotoxic factors leading to demyelination in conjunction with B cells secreting anti-myelin antibody. Although immunopathological pathways during the course of the demyelination in TMEV infection and EAE are not always the same, oligodendroglial apoptosis is observed in both models, suggesting that their demyelinating processes share a common terminal pathway and finally lead to quite a similar clinical and pathological picture.

Hydrocephalus in mice infected with a Theiler's murine encephalomyelitis virus variant.

The etiology of hydrocephalus is never established in the majority of clinical cases, while various agents, nutritional deficiencies, and genetic factors have been shown to play a role. Viral infection has been recognized as one of the causative factors in the development of hydrocephalus. The wild-type DA strain of Theiler's murine encephalomyelitis virus (TMEV), which belongs to the family Picornaviridae, causes a chronic demyelinating disease in mice with viral persistence that resembles multiple sclerosis. We found that a DA virus variant, hydrocephalus 101 virus (H101 virus), caused hydrocephalus in mice, a condition previously never described for TMEV. To clarify the relationship between DA virus infection and hydrocephalus, we compared H101 virus and wild-type DA virus infection in mice. Using immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL), we found that during the acute phase of infection, H101 virus caused macrocephaly and meningitis with the presence of apoptosis, while parenchymal involvement was not evident. In contrast, wild-type DA virus caused an acute polioencephalomyelitis with parenchymal infection and apoptosis. During the chronic phase, H101 virus infection caused communicating hydrocephalus without viral persistence. No demyelination and little or no anti-TMEV antibodies were observed in H101 virus-infected mice. Sequence analysis revealed that H101 virus had mutations in the 5'UTR and capsid protein coding region. Characterization of this new hydrocephalus model gives insight into the possible viral involvement in human hydrocephalus cases of obscure etiology.

Enhancement of experimental allergic encephalomyelitis (EAE) by DNA immunization with myelin proteolipid protein (PLP) plasmid DNA.

Relapsing-remitting experimental allergic encephalomyelitis (R-EAE) is an animal model for multiple sclerosis (MS). Many potential immunomodulatory strategies for MS have been used first in EAE to assess their effectiveness. Recently, the injection of plasmid DNA has been shown to induce potent humoral and cellular immune responses. The primary aim of our experiments reported here was to determine if vaccination with cDNAs encoding myelin proteolipid protein (PLP) could prime for a PLP-specific immune response and affect subsequent R-EAE. We constructed cDNAs encoding whole PLP (pPLP(all)) or encephalitogenic epitopes PLP(139-151) (pPLP(139-151)) and PLP(178-191) (pPLP(178-191)). Following DNA injection, we induced R-EAE in SJL/J mice using PLP(139-151) or PLP(178-191) peptides in adjuvant. All 3 plasmid constructs enhanced R-EAE induced with PLP(139-151), and injection of mice with pPLP(all) increased R-EAE induced with PLP(178-191). DNA immunization induced higher PLP peptide-specific lymphoproliferative responses than did vector alone following R-EAE induction with IgG1 or IgG2b antibody responses. These data suggest that DNA immunization of PLP can modulate immune responses, leading to enhancement of R-EAE.

Antibody association with a novel model for primary progressive multiple sclerosis: induction of relapsing-remitting and progressive forms of EAE in H2s mouse strains.

Multiple sclerosis (MS) can be divided into 4 clinical forms: relapsing-remitting (RR), primary progressive (PP), secondary progressive (SP), and progressive relapsing (PR). Since PP-MS is notably different from the other forms of MS, both clinically and pathologically, the question arises whether PP-MS is immunologically similar to the other forms. The pathogenesis of the PP-MS remains unclear, partly due to a lack of highly relevant animal models. Using an encephalitogenic peptide from myelin oligodendrocyte glycoprotein (MOG)92-106, we have established animal models that mimic different forms of MS in 2 strains of H-2s mice, SJL/J and A.SW. We induced experimental allergic encephalomyelitis (EAE) using MOG92-106 in the presence or absence of supplemental Bordetella pertussis (BP). Although, SJL/J mice developed RR-EAE whether BP was given or not, A.SW mice developed PP-EAE without BP and SP-EAE with BP. Histologically, SJL/J mice developed mild demyelinating disease with T cell infiltration, while A.SW mice developed large areas of plaque-like demyelination with immunoglobulin deposition and neutrophil infiltration, but with minimal T cell infiltration. In A.SW mice without BP, high titer serum anti-MOG antibody was detected and the anti-MOG IgG2a/IgG1 ratio correlated with survival times of mice. We hypothesized that, in A.SW mice, a Th2 response favors production of myelinotoxic antibodies, leading to progressive forms with early death. Our new models indicate that a single encephalitogen could induce either RR-, PP-, or SP- forms of demyelinating disease in hosts with immunologically different humoral immune responses.

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.

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.

Monoclonal antibody defines determinant between Theiler's virus and lipid-like structures.

Theiler's murine encephalomyelitis virus is known to cause a chronic demyelinating disease in mice. The contributions of immunologic factors, i.e. humoral and cellular responses to virus and/or myelin components, and direct virus-cell interactions leading to demyelination are still unclear. One important factor could be antibody initiation of myelin destruction. Here we describe four monoclonal antibodies that react with Theiler's murine encephalomyelitis virus. Three of these neutralize the virus and one of these three could also bind to various lipid-like structures including galactocerebroside, a myelin component. Further, this monoclonal antibody reacted with oligodendrocyte-like cells in vitro. All four monoclonal antibodies reacted with VP-1 by Western blot analysis. Thus, an immune response generated by virus that cross-reacts with a myelin element such as galactocerebroside could play a role in directing autoimmune processes toward myelin destruction.

Enhancement of autoimmune disease using recombinant vaccinia virus encoding myelin proteolipid protein.

Viral infections have been associated with the initiation and exacerbations often observed with autoimmune disease. Mechanisms by which viruses may play a role in the development of autoreactive immune responses include polyclonal activation of B and T cells, molecular mimicry, viral infection of immune cells, exposure of sequestered antigens, or altered host cell expression (neoantigen or altered self) in virus infected host cells. We have been studying the immune response generated to self proteins in association with viral infection. Here we evaluate the effects of viral infection on the development of an autoimmune disease of the central nervous system, experimental allergic encephalomyelitis. A vaccinia virus construct, VVplp was made containing the coding region for rat myelin proteolipid protein (PLP). Cells infected with VVplp were found to express PLP protein in vitro. Central nervous system disease was not detectable in mice vaccinated with VVplp. However, mice vaccinated with VVplp and later challenged with encephalitogenic peptides derived from PLP were found to have enhanced disease with earlier onset of symptoms when compared to mice treated with a control vaccinia virus construct. This enhancement of disease was found to peak at 10 days post challenge with the encephalitogenic PLP peptide. Clinical disease and an inflammatory response in the central nervous system was evident in mice previously vaccinated with VVplp but not in control vaccinated mice at this time. These results indicate that prior infection with a virus capable of coding for self protein can predispose the host to an accentuated autoimmune response.