Immune T cells can protect or induce fatal neurological disease in murine lymphocytic choriomeningitis

Adoptively transferred immune spleen cells induce fatal neurological disease in cyclophosphamide-suppressed recipients injected intracerebrally (ic) with a large, but not small, dose of neurotropic lymphocytic choriomeningitis (LCM) virus. The elimination of virus from brain in the latter group, which survives without developing symptoms, depends upon the presence of Lyt 2+ lymphocytes. However removal of Lyt 2+ subset which is cytotoxic in vitro does not diminish the severity of the inflammatory process in vivo, though the onset of clinical disease is delayed in mice given Lyt 2-depleted populations and a larger ic dose of virus. The present findings are consistent with the idea that fatal LCM results from acute, synchronous damage to key functional cells in the central nervous system by virus-immune Lyt 2+, lymphocytes. Even so, if the number of virus-infected CNS cells is still relatively small at the time of T cell invasion, neurological symptoms are not recognized and the mice survive.     

Lack of correlation between cytotoxic T lymphocytes and lethal murine lymphocytic choriomeningitis

Adoptive transfer of lymph node and spleen cells from mice infected with LCM virus to similarly infected immunocompromised recipients has been the classic way to demonstrate the lethal role of T cells in the CNS disease caused by this virus. Isolation and adoptive transfer techniques are presented here which show that Thy-1+ cells isolated from the meningeal infiltrates (MI) of LCM virus-infected mice possess this property. We compared various T cell functions of MI cells taken from mice infected with two strains of LCM virus differing markedly in their pathogenicities. One of these strains, termed aggressive, caused a typical, invariably fatal, CNS disease within 7 to 10 days after infection. The other virus, termed docile, killed few mice after the standard intracerebral inoculation, and could persist in the mice for 6 mo or more. The yields of MI leukocytes from mice infected with docile virus varied from 50 to 100% of those found in mice infected with aggressive virus (3 X 10(6) cells/brain). On a cell-to-cell basis, the CTL activity in the MI of mice infected with docile virus ranged from 50 to 100% of that found in the MI of mice infected with aggressive virus. MI cells from mice infected with aggressive virus consistently caused lethal disease by adoptive transfer into immunocompromised (irradiated) recipients infected with either strain of virus. All attempts to induce lethal disease by adoptive transfer of MI cells (or splenocytes) from mice infected with docile virus into irradiated recipients failed. The latter experiments with the docile-MI cells were performed with six times the number of aggressive-MI cells needed to kill irradiated recipients by adoptive transfer. The possible reasons for this discordance between CTL and in vivo killer function are discussed.     

Antibody is required for clearance of infectious murine hepatitis virus A59 from the central nervous system, but not the liver.

Intracerebral inoculation with mouse hepatitis virus strain A59 results in viral replication in the CNS and liver. To investigate whether B cells are important for controlling mouse hepatitis virus strain A59 infection, we infected muMT mice who lack membrane-bound IgM and therefore mature B lymphocytes. Infectious virus peaked and was cleared from the livers of muMT and wild-type mice. However, while virus was cleared from the CNS of wild-type mice, virus persisted in the CNS of muMT mice. To determine how B cells mediate viral clearance, we first assessed CD4(+) T cell activation in the absence of B cells as APC. CD4(+) T cells express wild-type levels of CD69 after infection in muMT mice. IFN-gamma production in response to viral Ag in muMT mice was also normal during acute infection, but was decreased 31 days postinfection compared with that in wild-type mice. The role of Ab in viral clearance was also assessed. In wild-type mice plasma cells appeared in the CNS around the time that virus is cleared. The muMT mice that received A59-specific Ab had decreased virus, while mice with B cells deficient in Ab secretion did not clear virus from the CNS. Viral persistence was not detected in FcR or complement knockout mice. These data suggest that clearance of infectious mouse hepatitis virus strain A59 from the CNS requires Ab production and perhaps B cell support of T cells; however, virus is cleared from the liver without the involvement of Abs or B cells.     

Production of random classes of immunoglobulins in brain tissue during persistent viral infection paralleled by secretion of interleukin-6 (IL-6) but not IL-4, IL-5, and gamma interferon

The activities of cytokines were determined in cerebrospinal fluid (CSF) and serum of mice persistently or intracerebrally acutely infected with lymphocytic choriomeningitis (LCM) virus (LCMV). In contrast to CBA/J (LCMV carrier) mice that responded with low levels of LCMV-specific antibody, high-responder NMRI (carrier) mice showed antibody production by B cells outside of lymphoid organs. The B cells that had infiltrated the brains of LCMV carrier mice exhibited no preferential immunoglobulin isotype or subtype virus-specific antibody production. Phenotypic analysis of the brain infiltrates in virus carrier mice revealed dominance of CD4+ T cells in contrast to virtual absence of CD4+ and dominance of CD8+ in mice with acute LCM. In NMRI but not in CBA/J carrier mice, significant concentrations of interleukin-6 (IL-6) were detected in CSF and serum; IL-2, IL-4, IL-5, granulocyte-macrophage CSF (GM-CSF), and gamma interferon (IFN-gamma) were not elevated. In contrast, during acute, lethal LCM, IL-6 and IFN-gamma were found at high concentrations, and IL-4, IL-5, and GM-CSF were detectable in CSF and serum, but virus-specific antibody-producing cells were not (yet) detectable in the brain. Thus, distinct cytokine patterns are found in acute versus chronic LCMV infection of the brain: in LCM carrier mice, local random-class immunoglobulin production correlated with the absence of IL-2, IL-4, IL-5, and IFN-gamma but active secretion of IL-6.     

CNS expression of B7-H1 regulates pro-inflammatory cytokine production and alters severity of Theiler's virus-induced demyelinating disease

The CNS is a unique organ due to its limited capacity for immune surveillance. As macrophages of the CNS, microglia represent a population originally known for the ability to assist neuronal stability, are now appreciated for their role in initiating and regulating immune responses in the brain. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease is a mouse model of multiple sclerosis (MS). In response to TMEV infection in vitro, microglia produce high levels of inflammatory cytokines and chemokines, and are efficient antigen-presenting cells (APCs) for activating CD4(+) T cells. However, the regulatory function of microglia and other CNS-infiltrating APCs in response to TMEV in vivo remains unclear. Here we demonstrate that microglia increase expression of proliferating cell nuclear antigen (PCNA), and phenotypically express high levels of major histocompatibility complex (MHC)-Class I and II in response to acute infection with TMEV in SJL/J mice. Microglia increase expression of the inhibitory co-stimulatory molecule, B7-H1 as early as day 5 post-infection, while CNS-infiltrating CD11b(+)CD11c(-)CD45(HIGH) monocytes/macrophages and CD11b(+)CD11c(+)CD45(HIGH) dendritic cells upregulate expression of B7-H1 by day 3 post-infection. Utilizing a neutralizing antibody, we demonstrate that B7-H1 negatively regulates TMEV-specific ex vivo production of interferon (IFN)-γ, interleukin (IL)-17, IL-10, and IL-2 from CD4(+) and CD8(+) T cells. In vivo blockade of B7-H1 in SJL/J mice significantly exacerbates clinical disease symptoms during the chronic autoimmune stage of TMEV-IDD, but only has minimal effects on viral clearance. Collectively, these results suggest that CNS expression of B7-H1 regulates activation of TMEV-specific T cells, which affects protection against TMEV-IDD.     

The role of antibodies in multiple sclerosis

B cells, plasma cells, and antibodies are commonly found in active central nervous system (CNS) lesions in patients with multiple sclerosis (MS). B cells isolated from CNS lesions as well as from the cerebrospinal fluid (CSF) show signs of clonal expansion and hypermutation, suggesting their local activation. Plasma blasts and plasma cells maturating from these B cells were recently identified to contribute to the development of oligoclonal antibodies produced within the CSF, which remain a diagnostic hallmark finding in MS. Within the CNS, antibody deposition is associated with complement activation and demyelination, indicating antigen recognition-associated effector function. While some studies indeed implied a disease-intrinsic and possibly pathogenic role of antibodies directed against components of the myelin sheath, no unequivocal results on a decisive target antigen within the CNS persisted to date. The notion of a pathogenic role for antibodies in MS is nevertheless empirically supported by the clinical benefit of plasma exchange in patients with histologic signs of antibody deposition within the CNS. Further, such evidence derives from the animal model of MS, experimental autoimmune encephalomyelitis (EAE). In transgenic mice endogenously producing myelin-specific antibodies, EAE severity was substantially increased accompanied by enhanced CNS demyelination. Further, genetic engineering in mice adding T cells that recognize the same myelin antigen resulted in spontaneous EAE development, indicating that the coexistence of myelin-specific B cells, T cells, and antibodies was sufficient to trigger CNS autoimmune disease. In conclusion, various pathological, clinical, immunological, and experimental findings collectively indicate a pathogenic role of antibodies in MS, whereas several conceptual challenges, above all uncovering potential target antigens of the antibody response within the CNS, remain to be overcome.     

Predisposition to EAE induction in resistant mice by prior infection with Semliki Forest virus

The premise that acute non-fatal viral infections of the central nervous system (CNS) predispose to the subsequent development of chronic immune-mediated neurologic disease was investigated. Adult C57Bl/6 mice inoculated peripherally with 10(4) PFU of the A774 strain of Semliki Forest virus (SFV) develop a transient encephalomyelitis and sporadic (less than 20%) mild symptoms of paralysis with demyelination in the cerebellum from which they recover. Such recovered mice were found to develop signs characteristic of experimental allergic encephalomyelitis (EAE) 2 to 8 wk after either immunization with myelin basic protein (MBP) or receipt of 1 to 2 X 10(7) lymph node cells from MBP-primed syngeneic donors. These two methods of disease induction were unsuccessful when applied to normal B6 mice or those previously inoculated with noninfectious SFV. These findings suggest the possibility that virus-induced damage to CNS tissue may facilitate subsequent priming or clonal expansion of pre-existing myelin-reactive lymphoid cells.     

Mechanisms of central nervous system viral persistence: the critical role of antibody and B cells.

Contributions of humoral and cellular immunity in controlling neurotropic mouse hepatitis virus persistence within the CNS were determined in B cell-deficient J(H)D and syngeneic H-2(d) B cell+ Ab-deficient mice. Virus clearance followed similar kinetics in all mice, confirming initial control of virus replication by cellular immunity. Nevertheless, virus reemerged within the CNS of all Ab-deficient mice. In contrast to diminished T cell responses in H-2(b) B cell-deficient muMT mice, the absence of B cells or Ab in the H-2(d) mice did not compromise expansion, recruitment into the CNS, or function of virus-specific CD4+ and CD8+ T cells. The lack of B cells and lymphoid architecture thus appears to manifest itself on T cell responses in a genetically biased manner. Increasing viral load did not enhance frequencies or effector function of virus-specific T cells within the CNS, indicating down-regulation of T cell responses. Although an Ab-independent antiviral function of B cells was not evident during acute infection, the presence of B cells altered CNS cellular tropism during viral recrudescence. Reemerging virus localized almost exclusively to oligodendroglia in B cell+ Ab-deficient mice, whereas it also replicated in astrocytes in B cell-deficient mice. Altered tropism coincided with distinct regulation of CNS virus-specific CD4+ T cells. These data conclusively demonstrate that the Ab component of humoral immunity is critical in preventing virus reactivation within CNS glial cells. B cells themselves may also play a subtle role in modulating pathogenesis by influencing tropism.     

Impaired T cell immunity in B cell-deficient mice following viral central nervous system infection

CD8(+) T cells are required to control acute viral replication in the CNS following infection with neurotropic coronavirus. By contrast, studies in B cell-deficient (muMT) mice revealed Abs as key effectors in suppressing virus recrudescence. The apparent loss of initial T cell-mediated immune control in the absence of B cells was investigated by comparing T cell populations in CNS mononuclear cells from infected muMT and wild-type mice. Following viral recrudescence in muMT mice, total CD8(+) T cell numbers were similar to those of wild-type mice that had cleared infectious virus; however, virus-specific T cells were reduced at least 3-fold by class I tetramer and IFN-gamma ELISPOT analysis. Although overall T cell recruitment into the CNS of muMT mice was not impaired, discrepancies in frequencies of virus-specific CD8(+) T cells were most severe during acute infection. Impaired ex vivo cytolytic activity of muMT CNS mononuclear cells, concomitant with reduced frequencies, implicated IFN-gamma as the primary anti viral factor early in infection. Reduced virus-specific CD8(+) T cell responses in the CNS coincided with poor peripheral expansion and diminished CD4(+) T cell help. Thus, in addition to the lack of Ab, limited CD8(+) and CD4(+) T cell responses in muMT mice contribute to the ultimate loss of control of CNS infection. Using a model of virus infection restricted to the CNS, the results provide novel evidence for a role of B cells in regulating T cell expansion and differentiation into effector cells.     

Resident and infiltrating central nervous system APCs regulate the emergence and resolution of experimental autoimmune encephalomyelitis

During experimental autoimmune encephalomyelitis (EAE), autoreactive Th1 T cells invade the CNS. Before performing their effector functions in the target organ, T cells must recognize Ag presented by CNS APCs. Here, we investigate the nature and activity of the cells that present Ag within the CNS during myelin oligodendrocyte glycoprotein-induced EAE, with the goal of understanding their role in regulating inflammation. Both infiltrating macrophages (Mac-1(+)CD45(high)) and resident microglia (Mac-1(+)CD45(int)) expressed MHC-II, B7-1, and B7-2. Macrophages and microglia presented exogenous and endogenous CNS Ags to T cell lines and CNS T cells, resulting in IFN-gamma production. In contrast, Mac-1(-) cells were inefficient APCs during EAE. Late in disease, after mice had partially recovered from clinical signs of disease, there was a reduction in Ag-presenting capability that correlated with decreased MHC-II and B7-1 expression. Interestingly, although CNS APCs induced T cell cytokine production, they did not induce proliferation of either T cell lines or CNS T cells. This was attributable to production by CNS cells (mainly by macrophages) of NO. T cell proliferation was restored with an NO inhibitor, or if the APCs were obtained from inducible NO synthase-deficient mice. Thus, CNS APCs, though essential for the initiation of disease, also play a down-regulatory role. The mechanisms by which CNS APCs limit the expansion of autoreactive T cells in the target organ include their production of NO, which inhibits T cell proliferation, and their decline in Ag presentation late in disease.     

Gamma delta T cells regulate the extent and duration of inflammation in the central nervous system by a Fas ligand-dependent mechanism

Gamma delta T cells have been shown to regulate immune responses associated with inflammation, but the mechanism of this regulation is largely unknown. Using the experimental autoimmune encephalomyelitis (EAE) model of the human CNS autoimmune disease multiple sclerosis, we demonstrate that gamma delta T cells are important regulators of CNS inflammation. This was shown using gamma delta T cell-deficient mice that were unable to recover from EAE. The chronic disease was accompanied by a prolonged presence of both macrophages and lymphocytes in the CNS. This extended inflammatory response was due to alterations in both cell proliferation and death. In mice lacking gamma delta T cells, proliferation of encephalitogenic T cells was 3-fold higher, and caspase activity, indicating apoptosis, was 2-fold lower compared with those in control mice recovering from EAE. gamma delta T cell-deficient mice reconstituted with wild-type gamma delta T cells recovered from EAE and resolved inflammation in the CNS, whereas mice reconstituted with Fas ligand-dysfunctional gamma delta T cells did not. Thus, gamma delta T cells regulate both inflammation in the CNS and disease recovery via Fas/Fas ligand-induced apoptosis of encephalitogenic T cells, and a quick resolution of inflammation in the CNS is essential to prevent permanent damage to the CNS resulting in chronic disease.     

Regulation of immune response and inflammatory reactions against viral infection by VCAM-1

The migration of activated antigen-specific immune cells to the target tissues of virus replication is controlled by the expression of adhesion molecules on the vascular endothelium that bind to ligands on circulating lymphocytes. Here, we demonstrate that the adhesion pathway mediated by vascular cell adhesion molecule 1 (VCAM-1) plays a role in regulating T-cell-mediated inflammation and pathology in nonlymphoid tissues, including the central nervous system (CNS) during viral infection. The ablation of VCAM-1 expression from endothelial and hematopoietic cells using a loxP-Cre recombination strategy had no major effect on the induction or overall tissue distribution of antigen-specific T cells during a systemic infection with lymphocytic choriomeningitis virus (LCMV), except in the case of lung tissue. However, enhanced resistance to lethal LCM and the significantly reduced magnitude and duration of footpad swelling observed in VCAM-1 mutant mice compared to B6 controls suggest a significant role for VCAM-1 in promoting successful local inflammatory reactions associated with efficient viral clearance and even life-threatening immunopathology under particular infection conditions. Interestingly, analysis of the infiltrating populations in the brains of intracerebrally infected mice revealed that VCAM-1 deletion significantly delayed migration into the CNS of antigen-presenting cells (macrophages and dendritic cells), which are critical for optimal stimulation of migrating virus-specific CD8⁺ T cells initiating a pathological cascade. We propose that the impaired migration of these accessory cells in the brain may explain the improved clinical outcome of infection in VCAM-1 mutant mice. Thus, these results underscore the potential role of VCAM-1 in regulating the immune response and inflammatory reactions against viral infections.     

Antiviral immune responses of fully allogeneic irradiation bone marrow mouse chimeras

In (B10.BR----B10) chimeras infected with lymphocytic choriomeningitis (LCM) virus higher titers were attained in spleens and livers than in organs of the mice used for their construction, and the subsequent elimination was retarded, but eventually the virus was cleared. The numbers of LCM virus-specific CTL and their precursors as quantitated with chromium-release assay and limiting dilution method, respectively, were lower in chimeras than in B10.BR or C57BL/10J mice, and fewer were restricted for the haplotypes of the donors than of the recipients. The same was true with regard to antiviral effector cells, which were determined by adoptive immunization. The numbers of spleen cells releasing IgM and IgG antiviral antibodies were virtually as high in chimeras as they were in C57BL/10J and B10.BR mice. Transfer of immune splenocytes from either B10.BR or C57BL/10J mice resulted in incomplete virus elimination from the spleens of infected chimeras, whereas injection of a mixture of the two types of immune cells led to efficient clearance. We conclude that in the chimeras cells of both donor and recipient haplotypes participate in the infection, which is terminated by H-2k- and H-2b-restricted T lymphocytes that these animals are capable of generating. We conclude, furthermore, that clearance of the LCM virus from the tissues requires contact between effector and target cells.     

Effect of Bordetella pertussis vaccine on the course of lymphocytic choriomeningitis (LCM) virus infection in suckling mice pretreated with dianhydrodulcitol (DAD)

In earlier experiments Bordetella pertussis vaccine was found to enhance and dianhydrodulcitol (DAD) to weaken cellular immune response to intracerebral LCM virus infection in suckling mice. B. pertussis vaccine proved to inhibit the restrictive effect of DAD produced on the immune response in mice when 2-to-4-days-old animals were pretreated with DAD and subsequently, at the age of 16 to 18 days of life, treated with B. pertussis vaccine then infected with LCM virus. Consequently, B. pertussis vaccine enhanced the immune response previously affected by DAD.     

Antibody prevents virus reactivation within the central nervous system.

The neurotropic JHM strain of mouse hepatitis virus (JHMV) produces an acute CNS infection characterized by encephalomyelitis and demyelination. The immune response cannot completely eliminate virus, resulting in persistence associated with chronic ongoing CNS demyelination. The contribution of humoral immunity to viral clearance and persistent infection was investigated in mice homozygous for disruption of the Ig mu gene (IgM-/-). Acute disease developed with equal kinetics and severity in IgM-/- and syngeneic C57BL/6 (wt) mice. However, clinical disease progressed in IgM-/- mice, while wt mice recovered. Viral clearance during acute infection was similar in both groups, supporting a primary role of cell-mediated immunity in viral clearance. In contrast to wt mice, in which infectious virus was reduced to below detection following acute infection, increasing infectious virus was recovered from the CNS of the IgM-/- mice following initial clearance. No evidence was obtained for selection of variant viruses nor was there an apparent loss of cell-mediated immunity in the absence of Ab. Passive transfer of anti-JHMV Ab following initial clearance prevented reactivation of infectious virus within the CNS of IgM-/- mice. These data demonstrate the clearance of infectious virus during acute disease by cell-mediated immunity. However, immunologic control is not maintained in the absence of anti-viral Ab, resulting in recrudescence of infectious virus. These data suggest that humoral immunity plays no role in controlling virus during acute infection, but plays an important role in establishing and maintaining CNS viral persistence.     

A monoclonal antibody against a myelin oligodendrocyte glycoprotein induces relapses and demyelination in central nervous system autoimmune disease

The factors contributing to chronic relapsing inflammatory disease processes of the central nervous system (CNS) and demyelination are poorly understood. In addition to cellular immune reactions, humoral factors such as antibodies might quantitatively or qualitatively influence the disease process. We therefore investigated the effects of administration of a monoclonal antibody specific for a CNS autoantigen on both acute and chronic experimental autoimmune encephalomyelitis (EAE) in mice and rats. This monoclonal antibody, 8-18C5, specific for a myelin/oligodendrocyte glycoprotein, was observed to accelerate clinical and pathologic changes of CNS autoimmune disease. In SJL mice with chronic relapsing EAE, injection of antibody into animals recovering from an attack induced fatal relapses; in Lewis rats, acute EAE was enhanced and associated with a hyperacute inflammatory response with demyelination, a feature not commonly seen in acute EAE. The demonstration that relapses and demyelination can be induced by administration of a white matter-reactive monoclonal antibody offers new possibilities to study processes resulting in CNS damage during autoimmune disease. Furthermore, these findings support the immunopathogenic potential of antibody to myelin components in inflammatory CNS disease processes and, specifically, in causing demyelination.     

Expression of the long form of human FLIP by retroviral gene transfer of hemopoietic stem cells exacerbates experimental autoimmune encephalomyelitis

Subsidence of inflammation and clinical recovery in experimental autoimmune encephalomyelitis (EAE) is postulated to involve apoptosis of inflammatory cells. To test this concept, we examined the effects of overexpressing the long form of human FLICE-inhibitory protein, a potent inhibitor of death receptor-mediated apoptosis, in myelin oligodendrocyte glycoprotein-induced EAE in DBA/1 mice. We found that overexpression of the long form of human FLICE-inhibitory protein by retroviral gene transfer of hemopoietic stem cells led to a clinically more severe EAE in these mice compared with control mice receiving the retroviral vector alone. The exacerbated disease was evident by an enhanced and prolonged inflammatory reaction in the CNS of these animals compared with control mice. The acute phase of EAE was characterized by a massive infiltration of macrophages and granulocytes and a simultaneous increase in TNF-alpha production in the CNS. In the chronic phase of the disease, there was a prolonged inflammatory response in the form of persistent CD4(+) T and B cells in the CNS and a peripheral Th1 cytokine bias caused by elevated levels of IFN-gamma and reduced levels of IL-4 in the spleen. Our findings demonstrate that death receptor-mediated apoptosis can be important in the pathogenesis of EAE and further emphasize the need for effective apoptotic elimination of inflammatory cells to achieve disease remission.     

Critical roles of CXC chemokine ligand 16/scavenger receptor that binds phosphatidylserine and oxidized lipoprotein in the pathogenesis of both acute and adoptive transfer experimental autoimmune encephalomyelitis

The scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX)/CXCL16 is a chemokine expressed on macrophages and dendritic cells, while its receptor expresses on T and NK T cells. We investigated the role of SR-PSOX/CXCL16 on acute and adoptive experimental autoimmune encephalomyelitis (EAE), which is Th1-polarized T cell-mediated autoimmune disease of the CNS. Administration of mAb against SR-PSOX/CXCL16 around the primary immunization decreased disease incidence of acute EAE with associated reduced infiltration of mononuclear cells into the CNS. Its administration was also shown to inhibit elevation of serum IFN-gamma level at primary immune response, as well as subsequent generation of Ag-specific T cells. In adoptive transfer EAE, treatment of recipient mice with anti-SR-PSOX/CXCL16 mAb also induced not only decreased clinical disease incidence, but also diminished traffic of mononuclear cells into the CNS. In addition, histopathological analyses showed that clinical development of EAE correlates well with expression of SR-PSOX/CXCL16 in the CNS. All the results show that SR-PSOX/CXCL16 plays important roles in EAE by supporting generation of Ag-specific T cells, as well as recruitment of inflammatory mononuclear cells into the CNS.     

Cytotoxic T cells isolated from the central nervous systems of mice infected with Theiler''s virus.

Intracerebral inoculation of resistant mice (C57BL/10SNJ) with Theiler's murine encephalomyelitis virus (TMEV) results in acute encephalitis followed by subsequent clearance of virus from the central nervous system (CNS). In contrast, infection of susceptible mice (SJL/J) results in virus persistence and chronic immune-mediated demyelination. Both resistance and susceptibility to TMEV-induced disease appear to be immune mediated, since immunosuppression results in enhanced encephalitis in resistant mice but diminished demyelination in susceptible mice. The purpose of these experiments was to determine whether anti-TMEV cytotoxic T lymphocytes (CTLs) are generated during acute and chronic TMEV infection. Nonspecific lectin-dependent cellular cytotoxicity was used initially to detect the cytolytic potential of lymphocytes infiltrating the CNS irrespective of antigen specificity. Using TMEV-infected targets, H-2-restricted TMEV-specific CTLs of the CD8+ phenotype were demonstrated in lymphocytes from the CNS of susceptible and resistant mice, arguing against the hypothesis that the ability to generate CD8+ CTLs mediates resistance. In chronically infected SJL/J mice, TMEV-specific CTL activity was detected in the CNS as late as 226 days postinfection. These experiments demonstrate that virus-specific CTLs are present in the CNS during both acute and chronic TMEV infection. Anti-TMEV CTLs in the CNS of chronically infected SJL/J mice may play a role in demyelination through their ability to lyse TMEV-infected glial cells.     

Chronic relapsing experimental allergic encephalomyelitis: Identification and dynamics of T and B cells within the central nervous system

Using a monoclonal antibody against guinea pig T cells and anti-guinea pig immunoglobulins, T- and B-cell dynamics were studied by immunofluorescence in situ in the central nervous system (CNS) of animals with untreated and treated chronic relapsing experimental allergic encephalomyelitis (EAE). Treated animals were given a series of injections of either myelin basic protein (MBP) in incomplete Freund's adjuvant (IFA) or MBP and galactocerebroside in IFA. Within the CNS, T and B cells showed distinct distribution patterns in untreated chronic relapsing EAE, similar to that recently described in acute EAE. T cells were predominantly localized within the CNS parenchyma and B cells were mainly found in perivascular areas. B-cell infiltrates were more extensive than in acute EAE and, although most were centered around blood vessels, some were also detectable in the parenchyma. IgG, C₃, and albumin deposits were common. These observations suggest an age-dependent difference in the immune response. In treated chronic EAE, the disease process was apparently arrested and T- and B-cell infiltrates in the white matter were negligible. Therefore, it appears that the present treatment protocol prevents lymphocytes from entering the CNS parenchyma.