Endogenous gamma interferon produced in central nervous system by systemic infection with Theiler's virus in mice

Neuroimmune interactions in a model of multiple sclerosis

Psychological stress has been implicated in both the onset and exacerbation of multiple sclerosis (MS). Our research has focused on the role of stress at the onset of MS, using the mouse model Theiler's murine encephalomyelitis virus-induced demyelination. Theiler's virus is a natural pathogen of mice that causes a persistent infection of the central nervous system (CNS) and inflammatory immune-mediated demyelination that is very similar to MS. Our research has shown that restraint stress sufficiently increases corticosterone secretion to cause immunosuppression. Stressed mice develop decreased innate and adaptive immune responses, including decreased chemokine and cytokine responses, to virus, which leads to increased viral replication within the CNS. Higher levels of virus then cause increased later demyelinating disease. These findings may have important implications in our understanding of the interactions between stress and the development of autoimmune diseases induced by infectious agents.

Sex steroids, APOE genotype and the innate immune system

Microglia are a primary cellular component of the CNS innate immune system. Their response to conserved pathogen motifs is inherent and leads to the release of cytoactive factors that impact surrounding neurons and glia. The microglial response is modified by the local tissue environment and by "global" factors such as gender. Exposure to estrogen and testosterone, in general, down regulate microglia and peripheral macrophage function, promoting an anti-inflammatory phenotype. Other global factors, however, can "override" the gender-based effects demonstrated by estrogen or testosterone. Apolipoprotein E (APOE) genotype and the expression of specific isoforms of apolipoprotein E differentially regulate microglial and peripheral macrophage function. Our studies have shown that the presence of the APOE4 gene, a known risk factor for AD and other neurodegenerative diseases, promotes a pro-inflammatory macrophage phenotype in neonatal microglia. However, in adult mice, the APOE genotype-specific effect depends on gender. Peritoneal macrophages from female adult APOE3 and APOE4 targeted replacement mice do not demonstrate an APOE genotype-specific response, whereas adult male APOE4 targeted replacement mice show enhanced macrophage responsiveness compared to adult male APOE3 mice. At least part of the altered macrophage response in APOE4 male mice may be due to differences in androgen receptor sensitivity to testosterone. These data re-enforce the concept that classical activation in macrophages has multiple levels of regulation, dictated by competing or synergistic factors and genotype.

Dexamethasone regulation of interleukin-1-receptors in the hippocampus of Theiler's virus-infected mice: effects on virus-mediated demyelination

Intracerebral (i.c.) inoculation of susceptible strains of mice with Theiler's murine encephalomyelitis virus (TMEV) results in immune-mediated demyelinating disease. Interleukin-1 receptors are expressed in the brain of mice, in particular in the hippocampus, and have been implicated in neuroimmunoendocrine interactions. In the present study we investigated the regulation of interleukin-1 receptors in the hippocampus of a susceptible (SJL/J) and a resistant (BALB/c) strain of mice infected with TMEV, at different time intervals of the disease. Our results show that interleukin-1 receptors in the hippocampus were decreased in TMEV-infected mice at early times post-infection (10 and 14 days p.i.). The reduction in interleukin-1 receptors only occurred in the susceptible strain of mice (SJL/J), whereas interleukin-1 binding in the hippocampus of TMEV-infected resistant mice (BALB/c) showed values similar to those in control animals. The TMEV-induced down-regulation of interleukin-1 receptors was secondary to a marked decrease in the affinity of the receptor (control: Kd = 10.5 pM; TMEV: Kd = 1.30 pM) accompanied by a decrease in receptor number (control: Bmax = 2.189 fmol/mg protein; TMEV: B max = 0.84 fmol/mg protein). We also investigated the effects of glucocorticoid treatment on the regulation of hippocampal interleukin-1 receptors of TMEV-infected mice. Dexamethasone treatment in the early phase (500 microg/kg or 1 mg/kg during days 5-10 p.i.) of the disease significantly reversed the deficits in hippocampal interleukin-1 receptors observed at 10 days p.i. in SJL/J mice, and suppressed neurological signs of demyelination. These results suggest that: (i) the reduction of interleukin-1 receptors may be a consequence, at least in part, of local production of interleukin-1 at early times during TMEV infection; (ii) interleukin-1 seems to be a critical factor for the susceptibility to TMEV-induced demyelination and (iii) the protective effect of dexamethasone appears to be related to its ability to reverse the reduction in interleukin-1 receptors during the early disease. These results suggest that interleukin-1 is a pivotal mediator in TMEV-induced demyelination.

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.

Macrophage antigen-1 positive cells are essential in the defense against Theiler's virus strain GD VII infection in the spinal cord

Acute encephalomyelitis caused by Theiler's virus strain GD VII resembles human poliomyelitis, and T cells are essential in eliminating the virus from the brain, though not from the spinal cord. We speculated that macrophage-lineage cells might play a crucial role in eliminating the virus from the spinal cord. To analyse the role of macrophage-lineage cells in the infection, antibodies specific for beta2 integrin, as well as an anti-leukocyte function antigen 1 (LFA-1) monoclonal antibody (MAb) and an anti-complement receptor type 3 (CR3) MAb were used to deplete the corresponding cell populations in Theiler's virus-infected mice. Infiltration of CD8+ T cells into the brain and spinal cord was inhibited by the administration of the anti-LFA-1 MAb, and viral replication was augmented only in the brain. The number of CD4+ T cells and macrophage antigen-1 (Mac-1[+]) cells in the brain and spinal cord were not decreased by anti-LFA-1 MAb treatment. Anti-CR3 MAb treatment led to decrease of Mac-1(+) cells in the brain and spinal cord. The viral replication in the spinal cord of anti-CR3 MAb treated mice was augmented, but not that in the brain. These results indicate that the defense mechanism against Theiler's virus strain GD VII is dependent on Mac-1(+) cells in the spinal cord.

Gamma interferon is critical for resistance to Theiler's virus-induced demyelination

Administration of neutralizing monoclonal antibody to gamma interferon increased Theiler's virus-induced demyelination and virus antigen persistence in the spinal cord in susceptible SJL/J mice and completely abrogated resistance such that all C57BL/10SNJ mice developed demyelination. These experiments support the hypothesis that gamma interferon is critically important for resistance to Theiler's virus-induced disease but is not required for myelin destruction.

Characteristics of cloned cerebrovascular endothelial cells following infection with Theiler's virus. I. Acute infection

The present study describes the replication of Theiler's virus in cloned cerebrovascular endothelial cells (CVE) isolated from strains of mice that are either susceptible or resistant to Theiler's virus-induced demyelination (TVID). CVE isolated from all strains of mice were equally permissive to Theiler's virus infection. Interferon-gamma and tumor necrosis factor-alpha were found to inhibit the replication of Theiler's virus in CVE. A correlation between susceptibility to demyelination and the ability of Theiler's virus to induce MHC Class I on CVE was demonstrated.

Immunology of Theiler's murine encephalomyelitis virus infection

Theiler's murine encephalomyelitis virus (TMEV) is a single-stranded RNA virus that belongs to the family of picornaviruses. Intracranial inoculation of susceptible mouse strains with TMEV results in biphasic disease, consisting of early acute disease that resembles poliomyelitis, followed by late chronic demyelinating disease that is characterized by the appearance of chronic inflammatory demyelinating lesions. Susceptibility to TMEV infection is genetically controlled by three loci: one that maps to the H-2D region of the major histocompatibility complex, one to the beta-chain constant region of the T-cell antigen receptor, and one located on chromosome 3. Both early acute and chronic late demyelinating diseases are immunologically mediated. T cells appear to play an important role in the pathogenesis of the disease. TMEV-induced demyelinating disease in mice has extensive similarities with multiple sclerosis, and it is considered one of the best experimental animal models for multiple sclerosis.

CD3+/TCR-alpha beta- cells are important in protecting spinal cord tissues against Theiler's virus strain GD VII infection

Intravenous infection with Theiler's virus strain GD VII causes acute encephalomyelitis in mice. Endogenous IFN-gamma produced in the spinal cord is important to protect the tissue in mice infected with this virus. Neither CD4+ cells nor CD8+ cells infiltrated the spinal cords of infected mice until Day 9 postinfection. However, the number of CD3+/TCR-gamma delta+ cells increased in the spinal cords of mice infected with the virus. These cells resided in the spinal cords of normal mice, and produced IFN-gamma as a result of stimulation by immobilized anti-CD3 mAb. Elimination of CD3+ cells by the administration of a specific mAb augmented viral replication and suppressed production of endogenous IFN-gamma. Depletion of TCR-alpha beta+ cells and ASGM1+ cells did not affect the viral replication, and did not alter the production of IFN-gamma. Therefore, CD3+/TCR-alpha beta- cells producing IFN-gamma play an important role in the protection of the spinal cord against Theiler's virus infection. These results suggest that CD3+/TCR-alpha beta- cells might be identical to TCR-gamma delta+ cells.

Theiler's virus is eliminated by a gamma-interferon-independent mechanism in the brain

The intravenous infection of Theiler's virus GD VII strain causes acute encephalomyelitis in infected mice. To determine the cellular mechanism of resistance and interferon (IFN)-gamma-producing cell populations, mononuclear cells isolated from tissues of the brain were analyzed by the flow cytometry method. Antibodies specific for CD3, CD4, CD8, T cell receptor (TCR)-alpha beta, and Asialo GM1 were used to deplete the corresponding cell populations in Theiler's virus-infected mice. CD4+ lymphocytes and CD8+ lymphocytes infiltrated in the brains of infected mice from 5 days postinfection (p.i.). The number of CD3+/TCR-gamma delta+ lymphocytes increased in the brains on Day 6 p.i. The elimination of CD3+ lymphocytes or CD4+ lymphocytes augmented viral replication and suppressed the production of IFN-gamma. The suppression of IFN-gamma production by anti-CD3 monoclonal antibody (mAb) persisted, although the suppression by anti-CD4 mAb was observed only on Day 6 p.i. The depletion of CD8+ lymphocytes as well as TCR-alpha beta+ lymphocytes also augmented the viral replication; however, it did not alter the production of IFN-gamma. Anti-Asialo GM1 antibody had no effect on viral replication and IFN-gamma production. These results indicate that T lymphocytes are important for eliminating Theiler's virus from the brain, CD3+/CD4+/CD8- lymphocytes and CD3+/TCR alpha beta-/CD4-/CD8- lymphocytes would produce IFN-gamma in brain. However, from the result on the experiment of the depletion of TCR-alpha beta+ lymphocytes, the defence mechanisms by T lymphocytes against Theiler's virus would be independent of endogenous IFN-gamma production.