Ikuo Tsunoda

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), Theilers 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. Thl 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.

Exacerbation of Viral and Autoimmune Animal Models for Multiple Sclerosis by Bacterial DNA

Theilers 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 possibleTh1‐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 vitro. We demonstrated that this bacterially derived DNA could induce interleukin (IL)‐12, interferon (IFN)γ (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 IFNγ and IL‐6 responses. These results caution the use of DNA vaccination in MS patients and other possible Th1‐mediated diseases.

Inside-Out versus Outside-In models for virus induced demyelination: axonal damage triggering demyelination.

Abstract.The primary target in multiple sclerosis (MS) is believed to be either myelin itself (myelinopathy) or the myelin-forming cell, the oligodendrocyte (oligodendrogliopathy). Although axonal injury occurs in MS, it is regarded as a secondary event to the myelin damage. Here, the lesion develops from myelin (outside) to the axon (inside) (Outside-In model). Recently, gray matter lesions and axonal injury in normal-appearing white matter have also been reported in MS. This raises two questions. 1) Is axonal injury exclusively secondary to myelin damage or from a direct insult to the axon or neurons (axonopathy)? (2) Is the injured axon regarded as only an end result of pathology or disease, or can axonal injury contribute to the spread of secondary damage, including demyelination? The former is raised from the fact that axonal damage has been reported in several virus infections, including human immunodeficiency virus, human T-lymphotropic virus 1, herpes simplex virus and coronavirus, which also cause demyelination. The latter possibility where axonal injury leads to other changes is raised from the rather unexpected similarity between spinal cord injury (SCI) and MS where axonal injury, oligodendrocyte apoptosis and demyelination are all present. In SCI, transection of axons leads to delayed oligodendrocyte apoptosis with secondary demyelination. Neurofilament immunostaining of spinal cord sections demonstrates that axonal injury with oligodendrocyte apoptosis also precedes demyelination in an animal model for MS, Theiler’s murine encephalomyelitis virus infection. This implies that axonal injury could trigger demyelination. In this instance, lesions develop from the axon (inside) to the myelin (outside) (Inside-Out model).

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.

Multiple sclerosis and virus induced immune responses: Autoimmunity can be primed by molecular mimicry and augmented by bystander activation

Polymicrobial infections have been associated with plausible immune mediated diseases, including multiple sclerosis (MS). Virus infection can prime autoimmune T cells specific for central nervous system (CNS) antigens, if virus has molecular mimicry with CNS proteins. On the other hand, infection of irrelevant viruses will induce two types of cytokine responses. Infection with a virus such as lymphocytic choriomeningitis virus (LCMV), can induce interferon (IFN)-α/β production and suppress autoimmunity, while infection with a virus, such as murine cytomegalovirus (MCMV), can activate natural killer (NK), NKT and dendritic cells, resulting in interleukin (IL)-12 and IFN-γ production. These cytokines can cause bystander activation of autoreactive T cells. We established an animal model, where mice infected with vaccinia virus encoding myelin protein can mount autoimmune responses. However, the mice develop clinical disease only after irrelevant immune activation either with complete Freunds adjuvant or MCMV infection. In this review, we propose that a combination of two mechanisms, molecular mimicry and bystander activation, induced by virus infection, can lead to CNS demyelinating diseases, including MS. Viral proteins having molecular mimicry with self-proteins in the CNS can prime genetically susceptible individuals. Once this priming has occurred, an immunologic challenge could result in disease through bystander activation by cytokines.

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 Theilers 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.

Distinct roles for IP-10/CXCL10 in three animal models, Theiler's virus infection, EAE, and MHV infection, for multiple sclerosis: implication of differing roles for IP-10.

Theiler’s murine encephalomyelitis virus (TMEV) causes demyelination with inflammation of the central nervous system (C NS) in mice and is used as an animal model for multiple sclerosis (MS). Interferon-g inducible protein-10 kDa (IP-10) is a C XC chemokine and a chemoattractant for C XC R3+ T cells. IP-10 mRNA is expressed in the C NS during TMEV infection. However, administration of anti-IP- 10 serum caused no difference in clinical signs, inflammation, demyelination, virus persistence or anti-virus antibody response in TMEV infection, while levels of virus specific and autoreactive lymphoproliferation increased. This likely reflects a difference in the pathogenesis of TMEV infection from that of two other animal models for MS, mouse hepatitis virus infection and experimental allergic encephalomyelitis (EAE), where blocking of IP-10 resulted in clinical and histological improvement with suppression of antigen specific lymphoproliferation. In this review, we compare and contrast the roles of IP-10 between the three animal models for MS, and discuss the relevance to MS patients with different clinical courses.

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 (pPLPalt) or encephalitogenic epitopes PLP139-151 (pPLP139-151) and PLP178-191 (pPLP178-191). Following DNA injection, we induced R-EAE in SJL/J mice using PLP138-151 or PLP178-191 peptides in adjuvant. All 3 plasmid constructs enhanced R-EAE induced with PLP178-191 and injection of mice with pPLPalt increased R-EAE induced with PLP178-191 DNA immunization induced higher PLP peptidc-spccific lymphoproliferative responses than did vector alone following R-EAE induction with IgGl or IgG2b antibody responses. These data suggest that DNA immunization of PLP can modulate immune responses, leading to enhancement of R-EAE.

Alterations in cytokine but not chemokine mRNA expression during three distinct Theiler's virus infections

DA, GDVII and H101 are neurovirulent strains of Theilers murine encephalomyelitis virus that cause very different neuropathology and CNS disease when inoculated into SJL/J mice. DA virus causes a chronic demyelinating disease, GDVII virus causes an acute fatal polioencephalomyelitis, and H101 virus causes an acute pachymeningitis with hydrocephalus. Performing RNase protection assays, we detected the same pattern of chemokine (RANTES, MCP-1, IP-10, MIP-1beta, MIP-1alpha and MIP-2) mRNA expression in brain and spinal cord during all three infections. In contrast, IFN-beta and IL-6 mRNA were highly expressed only in GDVII virus infection, whereas high levels of LT-alpha mRNA were only found during DA virus infection. Our study demonstrates that proinflammatory cytokines are involved in the neuropathogenesis of CNS disease and modulate the acute and chronic process underlying different pathologic features of disease.

Viruses can silently prime for and trigger central nervous system autoimmune disease.

Although many viruses have been isolated from patients with multiple sclerosis (MS), as yet, no one agent has been demonstrated to cause MS. In contrast, epidemiological data indicate that viral infections are associated with exacerbations of MS. Here, we present data showing that virus infections can subclinically prime animals for central nervous system (CNS) autoimmune disease; long after the original infection has been eradicated, a nonspecific challenge/infection can trigger an exacerbation. The priming infectious agent must show molecular mimicry with self-CNS antigens such as glial fibrillary acidic protein (GFAP), myelin associated glycoprotein (MAG) or myelin proteolipid protein (PLP). The subsequent challenge, however, may be nonspecific; complete Freund’s adjuvant (CFA), or infection with a recombinant vaccinia virus encoding an irrelevant protein, could trigger CNS disease. In the CNS, we could detect a mononuclear cell infiltration, but no demyelination was found. However, if the pathogenesis of MS is similar to that of this novel animal model for CNS autoimmune disease, our findings could help explain why exacerbations of MS are often associated with a variety of different viral infections.