Murray, Paul D.

Abstract Intracranial infection of susceptible mice with Theiler’s virus results in persistent infection and spinal cord demyelination similar to human multiple sclerosis. While central nervous system infiltrating lymphocytes (CNS-ILs) in these mice display no virus-specific CTL activity, the cells were found to be activated killers using a specificity-independent assay. We previously demonstrated that the depletion of T cells in persistently infected mice significantly decreases demyelinating disease. Consequently, we have investigated the killing pathways employed by CNS-ILs that are isolated from persistently infected animals, the relative contribution of CD4 and CD8 cells in the generation of these CTLs, and the reactivity of this cell population to two putative autoantigens in the CNS. In vitro or in vivo manipulation of T cell populations using Abs or genetic knockout strategies demonstrate that the cytotoxic activity is primarily mediated by CD8+ T cells, and that perforin is an important molecule in the effector pathway. Since effector functions in infected mice were not inhibited by the depletion of CD4 cells with mAb but was blocked genetically in CD4 knockout mice, CD4+ T cells appear to play a helper role in the generation of CD8+ CTLs. We found no evidence of autoimmune-mediated demyelination, as the CD8+ CTLs were not reactive to two major myelin autoantigens, myelin basic protein and proteolipid protein. Our finding that CNS-ILs that are isolated from mice susceptible to persistent virus infection are neither specific for virus or myelin autoantigens is consistent with the possibility that CD8+ CTLs mediate CNS damage as a result of nonspecific activation by virus.

ABSTRACTFollowing intracerebral infection with Theiler’s murine encephalomyelitis virus (TMEV), susceptible strains of mice (SJL and PLJ) develop virus persistence and demyelination similar to that found in human multiple sclerosis. Resistant strains of mice (C57BL/6) clear virus and do not develop demyelination. To resolve the controversy about the role of CD4+and CD8+T cells in the development of demyelination and neurologic deficits in diseases of the central nervous system, we analyzed TMEV infection in CD4- and CD8-deficient B6, PLJ, and SJL mice. Genetic deletion of either CD4 or CD8 from resistant B6 mice resulted in viral persistence and demyelination during the chronic stage of disease. Viral persistence and demyelination were detected in all strains of susceptible background. Although genetic deletion of CD8 had no effect on the extent of demyelination in susceptible strains, deletion of CD4 dramatically increased the degree of demyelination observed. Whereas strains with deletions of CD4 showed severe neurologic deficits, mice with deletions of CD8 showed minimal or no deficits despite demyelination. In all strains, deletion of CD4 but not CD8 resulted in a decreased delayed-type hypersensitivity response to viral antigen. We conclude that each T-cell subset makes a discrete and nonredundant contribution to protection from viral persistence and demyelination in resistant strains. In contrast, in susceptible strains, CD8+T cells do not provide protection against chronic demyelinating disease. Furthermore, in persistent TMEV infection of the central nervous system, neurologic deficits appear to result either from the absence of a protective class II-restricted immune response or from the presence of a pathogenic class I-restricted response.

Abstract TGF-β2 is a potent immunoregulatory mediator that influences B cell, T cell, and macrophage function. To test whether this cytokine alters pathology in a model of virus-induced demyelinating disease, we treated SJL/J mice with TGF-β2 either before or after infection with Theiler’s murine encephalomyelitis virus. Treatment continued three times weekly through day 35 postinfection. TGF-β2 administration resulted in significantly smaller lesions and fewer virus Ag-positive cells in the spinal cords of infected SJL/J mice. Mice treated with TGF-β2 had similar levels of virus-specific IgG as infected, control-treated mice. TGF-β2 administration significantly increased the level of non-virus-specific activated CTLs, but had no effect on virus-specific CTLs. TUNEL revealed a decrease in the number of apoptotic nuclei in the spinal cord white matter of mice treated in vivo with TGF-β2. Immunostaining with an Ab to F4/80 revealed that TGF-β2-treated mice had significantly fewer F4/80-positive cells in the white matter of the spinal cord as compared with infected control-treated mice. These data suggest that TGF-β2 may control virus-induced demyelination via an immunomodulatory mechanism that reduces macrophage infiltration.

ABSTRACTDuring the first 45 days after intracerebral infection with Theiler's murine encephalomyelitis virus (TMEV), the levels of mRNAs encoding chemokines MCP-1/CCL2, RANTES/CCL5, and IP-10/CXCL10 in the central nervous system (CNS) are closely related to the sites of virus gene expression and tissue inflammation. In the present study, these chemokines were monitored during the latter 135 days of a 6-month course of TMEV-induced disease in susceptible (PLJ) or resistant (C57BL/6) mice that possessed or lacked either CD4+or CD8+T cells. These data were additionally correlated to mouse genotype, virus persistence in the CNS, antiviral antibody titers, mortality, and the severity of neurological disease. Surprisingly, the major determinant of chemokine expression was virus persistence: the factors of susceptible or resistant genotype, severity of neuropathology, and presence or absence of regulatory T cells exerted minimal effects. Our observations indicated that chemokine expression in the CNS in this chronic viral disorder was intrinsic to the CNS innate immune response to infection and was not governed by elements of the adaptive immune system.