Apoptotic elimination of V beta 8.2+ cells from the central nervous system during recovery from experimental autoimmune encephalomyelitis induced by the passive transfer of V beta 8.2+ encephalitogenic T cells

Herpesviruses and the hidden links to Multiple Sclerosis neuropathology

Herpesviruses like Epstein-Barr virus, human herpesvirus (HHV)-6, HHV-1, VZV, and human endogenous retroviruses, have an age-old clinical association with multiple sclerosis (MS). MS is an autoimmune disease of the nervous system wherein the myelin sheath deteriorates. The most popular mode of virus mediated immune system manipulation is molecular mimicry. Numerous herpesvirus antigens are similar to myelin proteins. Other mechanisms described here include the activity of cytokines and autoantibodies produced by the autoreactive T and B cells, respectively, viral déjà vu, epitope spreading, CD46 receptor engagement, impaired remyelination etc. Overall, this review addresses the host-parasite association of viruses with MS.

Hypothesis: bipolar disorder is an Epstein-Barr virus-driven chronic autoimmune disease - implications for immunotherapy

Bipolar disorder (BD) is a chronic disease characterised by episodes of major depression and episodes of mania or hypomania, with a worldwide prevalence of 2.4%. The cause of BD is unknown. Here, I propose the hypothesis that BD is a chronic autoimmune disease caused by Epstein–Barr virus (EBV) infection of autoreactive B cells. It is postulated that EBV‐infected autoreactive B cells accumulate in the brain where they provide costimulatory survival signals to autoreactive T cells and differentiate into plasma cells producing pathogenic autoantibodies targeting brain components such as the N‐methyl‐D‐aspartate receptor. It is also proposed that the accumulation of EBV‐infected autoreactive B cells in the brain is a consequence of a genetically determined defect in the ability of CD8⁺ T cells to control EBV infection. The theory is supported by studies indicating that autoimmunity, EBV infection and CD8⁺ T‐cell deficiency all have roles in the pathogenesis of BD. According to the hypothesis, BD should be able to be treated by EBV‐specific T‐cell therapy and to be prevented by vaccination against EBV in early childhood. Exposure to sunlight or appropriate artificial light should also be beneficial in BD by augmenting CD8⁺ T‐cell control of EBV infection.

Epstein-Barr virus and multiple sclerosis: potential opportunities for immunotherapy

Multiple sclerosis (MS) is a common chronic inflammatory demyelinating disease of the central nervous system (CNS) causing progressive disability. Many observations implicate Epstein–Barr virus (EBV) in the pathogenesis of MS, namely universal EBV seropositivity, high anti-EBV antibody levels, alterations in EBV-specific CD8⁺ T-cell immunity, increased spontaneous EBV-induced transformation of peripheral blood B cells, increased shedding of EBV from saliva and accumulation of EBV-infected B cells and plasma cells in the brain. Several mechanisms have been postulated to explain the role of EBV in the development of MS including cross-reactivity between EBV and CNS antigens, bystander damage to the CNS by EBV-specific CD8⁺ T cells, activation of innate immunity by EBV-encoded small RNA molecules in the CNS, expression of αB-crystallin in EBV-infected B cells leading to a CD4⁺ T-cell response against oligodendrocyte-derived αB-crystallin and EBV infection of autoreactive B cells, which produce pathogenic autoantibodies and provide costimulatory survival signals to autoreactive T cells in the CNS. The rapidly accumulating evidence for a pathogenic role of EBV in MS provides ground for optimism that it might be possible to prevent and cure MS by effectively controlling EBV infection through vaccination, antiviral drugs or treatment with EBV-specific cytotoxic CD8⁺ T cells. Adoptive immunotherapy with in vitro-expanded autologous EBV-specific CD8⁺ T cells directed against viral latent proteins was recently used to treat a patient with secondary progressive MS. Following the therapy, there was clinical improvement, decreased disease activity on magnetic resonance imaging and reduced intrathecal immunoglobulin production.

Astrocytic Fas ligand expression is required to induce T-cell apoptosis and recovery from experimental autoimmune encephalomyelitis

In T-cell-mediated autoimmune diseases of the CNS, apoptosis of Fas(+) T cells by FasL contributes to resolution of disease. However, the apoptosis-inducing cell population still remains to be identified. To address the role of astrocytic FasL in the regulation of T-cell apoptosis in experimental autoimmune encephalomyelitis, we immunized C57BL/6 glial fibrillary acid protein (GFAP)-Cre FasL(fl/fl) mice selectively lacking FasL in astrocytes with MOG(35-55) peptide. GFAP-Cre FasL(fl/fl) mice were unable to resolve EAE and suffered from persisting demyelination and paralysis, while FasL(fl/fl) control mice recovered. In contrast to FasL(fl/fl) mice, GFAP-Cre FasL(fl/fl) mice failed to induce apoptosis of Fas(+) activated CD4(+) T cells and to increase numbers of Foxp3(+) Treg cells beyond day 15 post immunization, the time point of maximal clinical disease in control mice. The persistence of activated and GM-CSF-producing CD4(+) T cells in GFAP-Cre FasL(fl/fl) mice also resulted in an increased IL-17, IFN-γ, TNF, and GM-CSF mRNA expression in the CNS. In vitro, FasL(+) but not FasL(-) astrocytes induced caspase-3 expression and apoptosis of activated T cells. In conclusion, FasL expression of astrocytes plays an important role in the control and elimination of autoimmune T cells from the CNS, thereby determining recovery from EAE.

CD8+ T-Cell Deficiency, Epstein-Barr Virus Infection, Vitamin D Deficiency, and Steps to Autoimmunity: A Unifying Hypothesis

CD8+ T-cell deficiency is a feature of many chronic autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's syndrome, systemic sclerosis, dermatomyositis, primary biliary cirrhosis, primary sclerosing cholangitis, ulcerative colitis, Crohn's disease, psoriasis, vitiligo, bullous pemphigoid, alopecia areata, idiopathic dilated cardiomyopathy, type 1 diabetes mellitus, Graves' disease, Hashimoto's thyroiditis, myasthenia gravis, IgA nephropathy, membranous nephropathy, and pernicious anaemia. It also occurs in healthy blood relatives of patients with autoimmune diseases, suggesting it is genetically determined. Here it is proposed that this CD8+ T-cell deficiency underlies the development of chronic autoimmune diseases by impairing CD8+ T-cell control of Epstein-Barr virus (EBV) infection, with the result that EBV-infected autoreactive B cells accumulate in the target organ where they produce pathogenic autoantibodies and provide costimulatory survival signals to autoreactive T cells which would otherwise die in the target organ by activation-induced apoptosis. Autoimmunity is postulated to evolve in the following steps: (1) CD8+ T-cell deficiency, (2) primary EBV infection, (3) decreased CD8+ T-cell control of EBV, (4) increased EBV load and increased anti-EBV antibodies, (5) EBV infection in the target organ, (6) clonal expansion of EBV-infected autoreactive B cells in the target organ, (7) infiltration of autoreactive T cells into the target organ, and (8) development of ectopic lymphoid follicles in the target organ. It is also proposed that deprivation of sunlight and vitamin D at higher latitudes facilitates the development of autoimmune diseases by aggravating the CD8+ T-cell deficiency and thereby further impairing control of EBV. The hypothesis makes predictions which can be tested, including the prevention and successful treatment of chronic autoimmune diseases by controlling EBV infection.

The essential role of Epstein-Barr virus in the pathogenesis of multiple sclerosis

There is increasing evidence that infection with the Epstein-Barr virus (EBV) plays a role in the development of multiple sclerosis (MS), a chronic inflammatory demyelinating disease of the CNS. This article provides a four-tier hypothesis proposing (1) EBV infection is essential for the development of MS; (2) EBV causes MS in genetically susceptible individuals by infecting autoreactive B cells, which seed the CNS where they produce pathogenic autoantibodies and provide costimulatory survival signals to autoreactive T cells that would otherwise die in the CNS by apoptosis; (3) the susceptibility to develop MS after EBV infection is dependent on a genetically determined quantitative deficiency of the cytotoxic CD8+ T cells that normally keep EBV infection under tight control; and (4) sunlight and vitamin D protect against MS by increasing the number of CD8+ T cells available to control EBV infection. The hypothesis makes predictions that can be tested, including the prevention and successful treatment of MS by controlling EBV infection.

Decreased production of TNF-alpha by lymph node cells indicates experimental autoimmune encephalomyelitis remission in Lewis rats

Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4+ Th1 cells that mainly secrete IFN-gamma and TNF-alpha, important cytokines in the pathophysiology of the disease. Spontaneous remission is, in part, attributed to the down regulation of IFN-gamma and TNF-alpha by TGF-beta. In the current paper, we compared weight, histopathology and immunological parameters during the acute and recovery phases of EAE to establish the best biomarker for clinical remission. Female Lewis rats were immunised with myelin basic protein (MBP) emulsified with complete Freund's adjuvant. Animals were evaluated daily for clinical score and weight prior to euthanisation. All immunised animals developed the expected characteristics of EAE during the acute phase, including significant weight loss and high clinical scores. Disease remission was associated with a significant reduction in clinical scores, although immunised rats did not regain their initial weight values. Brain inflammatory infiltrates were higher during the acute phase. During the remission phase, anti-myelin antibody levels increased, whereas TNF-alpha and IFN-gamma production by lymph node cells cultured with MBP or concanavalin A, respectively, decreased. The most significant difference observed between the acute and recovery phases was in the induction of TNF-alpha levels in MBP-stimulated cultures. Therefore, the in vitro production of this cytokine could be used as a biomarker for EAE remission.

Genetic deficiency of Irgm1 (LRG-47) suppresses induction of experimental autoimmune encephalomyelitis by promoting apoptosis of activated CD4+ T cells

The immunity-related GTPase Irgm1, also called LRG-47, is known to regulate host resistance to intracellular pathogens through multiple mechanisms that include controlling the survival of T lymphocytes. Here, we address whether Irgm1 also plays a role in the pathogenesis of experimental autoimmune encephalitis (EAE). We find that Irgm1/LRG-47 is a significant factor in the progression of EAE and multiple sclerosis (MS). Expression of Irgm1 was robustly elevated in MS-affected lesions and in the central nervous system (CNS) of myelin basic protein (MBP)-induced EAE mice, especially in cells of lymphoid and mononuclear phagocyte origin. Homozygous Irgm1 null mice were resistant to MBP-induced EAE, and CD4(+) T cells in spleen and CNS of these mice displayed decreased proliferative capacity, increased apoptosis, and up-regulated interferon (IFN)-gamma induction. Therefore, Irgm1-induced survival of autoreactive CD4(+) T cells contributes significantly to the pathogenesis of EAE. Blockade of Irgm1 may be a potential therapeutic strategy for halting multiple sclerosis.

The multiple roles of the innate immune system in the regulation of apoptosis and inflammation in the brain

Central nervous system (CNS) tissues contain cells (i.e. glia and neurons) that have innate immune functions. These cells express a range of receptors that are capable of detecting and clearing apoptotic cells and regulating inflammatory responses. Phagocytosis of apoptotic cells is a nonphlogistic (i.e. noninflammatory) process that provides immune regulation through anti-inflammatory cytokines andregulatory T cells. Neurons and glia express cellular death signals, including CD95Fas/CD95L, FasL, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and tumor necrosis factor receptor 1 (TNFR), through which they can trigger apoptosis in T cells and other infiltrating cells. Microglia, astrocytes, ependymal cells, and neurons express defense collagens and scavenger and phagocytic receptors that recognize apoptotic cells displaying apoptotic cell-associated molecular patterns, which serve as markers of "altered self." Glia also express pentraxins and complement proteins (C1q, C3b, and iC3b) that opsonize apoptotic cells, making them targets for the phagocytic receptors CR3 and CR4. Immunoregulatory molecules such as the complement regulator CD46 are lost from apoptotic cells and stimulate phagocytosis, whereas the expression of CD47 and CD200 is upregulated during apoptosis; this inhibits proinflammatory microglial cytokine expression, thereby reducing the severity of inflammation. This review outlines the cellular pathways used for the detection and phagocytosis of apoptotic cells in vitro and in experimental models of CNS inflammation.

Drak2 regulates the survival of activated T cells and is required for organ-specific autoimmune disease

Drak2 is a serine/threonine kinase expressed in T and B cells. The absence of Drak2 renders T cells hypersensitive to suboptimal stimulation, yet Drak2(-/-) mice are enigmatically resistant to experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. We show in this study that Drak2(-/-) mice were also completely resistant to type 1 diabetes when bred to the NOD strain of mice that spontaneously develop autoimmune diabetes. However, there was not a generalized suppression of the immune system, because Drak2(-/-) mice remained susceptible to other models of autoimmunity. Adoptive transfer experiments revealed that resistance to disease was intrinsic to the T cells and was due to a loss of T cell survival under conditions of chronic autoimmune stimulation. Importantly, the absence of Drak2 did not alter the survival of naive T cells, memory T cells, or T cells responding to an acute viral infection. These experiments reveal a distinction between the immune response to persistent self-encoded molecules and transiently present infectious agents. We present a model whereby T cell survival depends on a balance of TCR and costimulatory signals to explain how the absence of Drak2 affects autoimmune disease without generalized suppression of the immune system.

Treating autoimmune demyelination by augmenting lymphocyte apoptosis in the central nervous system

The elimination of autoreactive T cells from the central nervous system (CNS) by apoptosis plays an important role in switching off autoimmune attack. B-cell apoptosis in the CNS probably also has a key role in downregulating autoimmunity. Augmenting lymphocyte apoptosis in the CNS is a potential strategy for treating autoimmune CNS diseases such as multiple sclerosis. These strategies involve modulation of the physiological pro-apoptotic and anti-apoptotic pathways that control lymphocyte fate in the CNS. In the case of T cells, apoptosis can be augmented by enhancing activation-induced T-cell apoptosis through the CD95 (Fas) pathway and by inhibiting costimulation-induced anti-apoptotic pathways mediated through BCL-2 and BCL-X L.

A public T cell clonotype within a heterogeneous autoreactive repertoire is dominant in driving EAE

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis. Immunization of B10.PL mice with the Ac1-9 peptide, the immunodominant determinant of myelin basic protein (MBP), produced a single episode of EAE followed by recovery and resistance to reinduction of disease. Using the CDR3 length spectratyping technique, we characterized the clonal composition of the Ac1-9-specific T cell repertoire from induction through onset and resolution of disease. Two clonally restricted subsets within a heterogeneous self-reactive repertoire were found in mouse lymph nodes, spleen, and spinal cord soon after immunization, before any sign of EAE. These clonotypes, designated BV8S2/BJ2S7 and BV16/BJ2S5, were present in all mice examined and thus considered public. BV8S2/BJ2S7 was found in far greater excess; was exclusively Th1 polarized; disappeared from the spinal cord, spleen, and lymph nodes concomitantly with recovery; and transferred disease to naive recipients. In contrast, BV16/BJ2S5 and numerous private clonotypes were either Th1 or Th2 and persisted following recovery. These results are consistent with the hypothesis that the public clonotype BV8S2/BJ2S7 is a driver of disease and necessary for its propagation.

Glucocorticoids in the control of neuroinflammation

Glucocorticoids are a class of steroid hormones that are endowed with profound anti-inflammatory and immunosuppressive activities. Endogenous glucocorticoids are key players in the modulation of the immune system and establish an endocrine basis of many inflammatory diseases. In addition, synthetic glucocorticoids are amongst the most commonly prescribed drugs worldwide for the treatment of autoimmune disorders. In this review we summarize our present knowledge on the mechanisms by which glucocorticoids impact on multiple sclerosis (MS), a highly prevalent neuroinflammatory disease, and its animal model experimental autoimmune encephalomyelitis (EAE). In spite of the new methodologies that have become available during recent years, we are still far from a comprehensive picture of the mechanism by which glucocorticoids control neuroinflammation.

Termination of inflammation in the nervous system

T cell apoptosis has been studied in animal models for human autoimmune disorders of the nervous system and in other tissues devoid of specialized immune-defense mechanisms. Our data suggest that the central nervous system has a high potential to eliminate T cell inflammation, whereas this mechanism is less effective in the peripheral nervous system, and even more in muscle and skin. In-vitro experiments indicate different scenarios how specific cellular and humoral elements in the nervous system may synergize and sensitize T cells for apoptosis in-vivo. Probably release of TNF-alpha in the nervous system is a central mechanism to limit inflammation in the brain. This is further substantiated since neutralization of TNF-alpha in MS patients increased cellular inflammation and relapses. Therapeutically several conventional and novel approaches like glucocorticosteroids and high-dose antigen therapy induce T cell apoptosis in-situ. We also discuss regulatory, proapoptotic mechanisms such as the Fas/FasL system and counterregulatory mechanisms that have been utilized to limit tissue damage.

Immunology of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) leading to demyelination, axonal damage, and progressive neurologic disability. The development of MS is influenced by environmental factors, particularly the Epstein-Barr virus (EBV), and genetic factors, which include specific HLA types, particularly DRB1*1501-DQA1*0102-DQB1*0602, and a predisposition to autoimmunity in general. MS patients have increased circulating T-cell and antibody reactivity to myelin proteins and gangliosides. It is proposed that the role of EBV is to infect autoreactive B cells that then seed the CNS and promote the survival of autoreactive T cells there. It is also proposed that the clinical attacks of relapsing-remitting MS are orchestrated by myelin-reactive T cells entering the white matter of the CNS from the blood, and that the progressive disability in primary and secondary progressive MS is caused by the action of autoantibodies produced in the CNS by -meningeal lymphoid follicles with germinal centers.

Major histocompatibility complex molecules on parenchymal cells of the target organ protect against autoimmune disease

Parenchymal cells of the autoimmune organ may only express major histocompatibility complex (MHC) molecules during the disease process. In this paper, we hypothesize that the appearance of MHC molecules on parenchymal cells may augment the activation of invading autoreactive T cells and either exacerbate or suppress local inflammation. It is speculated that like many biological responses this is a two-edge sword - namely, the expression of modest levels of MHC molecules may inhibit the activation of invading T cells, whereas overexpression of these molecules may promote activation of autoimmune T cells, enhancing the inflammatory cascade, thus leading to tissue damage.

Osteopontin-induced relapse and progression of autoimmune brain disease through enhanced survival of activated T cells

Relapses and disease exacerbations are vexing features of multiple sclerosis. Osteopontin (Opn), which is expressed in multiple sclerosis lesions, is increased in patients' plasma during relapses. Here, in models of multiple sclerosis including relapsing, progressive and multifocal experimental autoimmune encephalomyelitis (EAE), Opn triggered recurrent relapses, promoted worsening paralysis and induced neurological deficits, including optic neuritis. Increased inflammation followed Opn administration, whereas its absence resulted in more cell death of brain-infiltrating lymphocytes. Opn promoted the survival of activated T cells by inhibiting the transcription factor Foxo3a, by activating the transcription factor NF-kappaB through induction of phosphorylation of the kinase IKKbeta and by altering expression of the proapoptotic proteins Bim, Bak and Bax. Those mechanisms collectively suppressed the death of myelin-reactive T cells, linking Opn to the relapses and insidious progression characterizing multiple sclerosis.

T-cell apoptosis in human glioblastoma multiforme: Implications for immunotherapy

We used immunohistochemistry and flow cytometry to assess apoptosis in human glioblastoma multiforme (GBM). Our immunohistochemical study revealed apoptosis of glioma cells expressing glial fibrillary acidic protein and of CD3(+) T cells infiltrating GBM. To quantify and phenotype the apoptotic T cells, we performed flow cytometry on lymphocytes separated from GBM. The cells were stained with annexin-V-FLUOS/propidium iodide to identify apoptosis. We found that high proportions of both the CD4(+) and CD8(+) T cells were apoptotic. In particular, we found that T cells expressing Fas ligand (Fas-L, CD95L) were eight times more vulnerable to apoptosis than those not expressing Fas-L, which suggests that the T-cell apoptosis is induced by overactivation of the T-cell receptor, possibly in the absence of appropriate costimulation. Our results have implications for the design of immunotherapies for GBM.

Microglial expression of the B7 family member B7 homolog 1 confers strong immune inhibition: implications for immune responses and autoimmunity in the CNS

Inflammation of the CNS is usually locally limited to avoid devastating consequences. Critical players involved in this immune regulatory process are the resident immune cells of the brain, the microglia. Interactions between the growing family of B7 costimulatory ligands and their receptors are increasingly recognized as important pathways for costimulation and/or inhibition of immune responses. Human and mouse microglial cells constitutively express B7 homolog 1 (B7-H1) in vitro. However, under inflammatory conditions [presence of interferon-gamma (IFN-gamma) or T-helper 1 supernatants], a significant upregulation of B7-H1 was detectable. Expression levels of B7-H1 protein on microglial cells were substantially higher compared with astrocytes or splenocytes. Coculture experiments of major histocompatibility complex class II-positive antigen-presenting cells (APC) with syngeneic T cells in the presence of antigen demonstrated the functional consequences of B7-H1 expression on T-cell activation. In the presence of a neutralizing anti-B7-H1 antibody, both the production of inflammatory cytokines (IFN-gamma and interleukin-2) and the upregulation of activation markers (inducible costimulatory signal) by T cells were markedly enhanced. Interestingly, this effect was clearly more pronounced when microglial cells were used as APC, compared with astrocytes or splenocytes. Furthermore, B7-H1 was highly upregulated during the course of myelin oligodendrocyte glycoprotein-induced and proteolipid protein-induced experimental allergic encephalomyelitis in vivo. Expression was predominantly localized to areas of strongest inflammation and could be colocalized with microglial cells/macrophages as well as T cells. Together, our data propose microglial B7-H1 as an important immune inhibitory molecule capable of downregulating T-cell activation in the CNS and thus confining immunopathological damage.

Apoptotic Cell Death in Experimental Autoimmune Encephalomyelitis

Particularly in the vulnerable CNS with a low capacity for regeneration specialized mechanisms must be active for the fast and gentle elimination of dysregulated autoaggressive immune cells. In EAE, local apoptosis of autoimmune T-cells has been identified as a safe means for the removal of these unwanted cells. T-cell apoptosis in situ followed by phagocytic clearance of apoptotic remnants by glia assures a minimum of detrimental bystander damage to the local parenchyma and down-regulates the local inflammatory reaction. The pharmacological augmentation of local apoptosis of inflammatory effector cells might gain therapeutic importance also in human neuroimmunological diseases such as multiple sclerosis.

Nitric-oxide-dependent and independent mechanisms of protection from CNS inflammation during Th1-mediated autoimmunity: evidence from EAE in iNOS KO mice

Experimental autoimmune encephalomyelitis (EAE) disease was accelerated iNOS-deficient (KO) mice: coinciding with greatly increased numbers of Ag-specific Th1 cells in the periphery that appeared to rapidly shift from the spleen to the CNS during onset of disease symptoms. iNOS KO mice had significantly increased Th1 cells in the CNS versus wild-type mice. Apoptosis of CNS-infiltrating CD4(+) T cells was impaired in iNOS KO mice at peak of disease; consequently, these mice had more CNS-infiltrating CD4(+) T cells. Subsequently, iNOS KO mice up-regulated apoptosis of CNS-CD4(+) T cells. During chronic EAE, CNS macrophages were greatly decreased, suggesting elimination of CNS-infiltrating CD4(+) T cells and activated macrophages by iNOS-independent mechanisms. INOS is not only required for apoptosis of CNS-CD4(+) T cells but also prevents overexpansion of autoreactive Th1 cells in the periphery and the CNS.

Chronically stimulated microglial cells do no longer alter their immune functions in response to the phagocytosis of apoptotic cells

In an autoimmune inflammatory setting, ingestion of apoptotic T cells leads to a down-regulation of microglial immune functions. Recent studies have indicated that microglia can be matured by exposure to GM-CSF. GM-CSF stimulation led to a differentiated microglial phenotype and enhanced antigen-presenting capabilities. The secretion of TNF-alpha was significantly decreased by the uptake of apoptotic cells in unstimulated microglia, but not in GM-CSF-differentiated microglia. IL-10 secretion was unaffected. After ingestion of apoptotic cells, only previously unstimulated, but not GM-CSF-differentiated microglial cells decreased their T cell-activating potential as measured by IFN-gamma secretion in antigen-activated MBP-specific T cells. Thus, GM-CSF stimulation reduces the immunomodulatory functions of microglial cells.

Fas ligand-mediated apoptosis in degenerative disorders of the brain

While defective apoptosis predisposes to neoplasia, inappropriate apoptosis in the brain leads to permanent neurological deficits. Disregulated apoptosis has been implicated in several neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Recent reports have suggested that the key apoptosis regulator Fas ligand (FasL) may participate in both neuronal and immune cell apoptosis in Alzheimer's disease. FasL has also been implicated as a negative regulator for the inflammatory component of the demyelinating brain disorder multiple sclerosis (MS). Here we discuss how FasL-mediated apoptosis may balance immune cell access to the brain with Alzheimer's disease and MS representing extremes of too little and too much immune access, respectively.

Fas ligand-mediated apoptosis in degenerative disorders of the brain

While defective apoptosis predisposes to neoplasia, inappropriate apoptosis in the brain leads to permanent neurological deficits. Disregulated apoptosis has been implicated in several neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Recent reports have suggested that the key apoptosis regulator Fas ligand (FasL) may participate in both neuronal and immune cell apoptosis in Alzheimer's disease. FasL has also been implicated as a negative regulator for the inflammatory component of the demyelinating brain disorder multiple sclerosis (MS). Here, we discuss how FasL-mediated apoptosis may balance immune cell access to the brain with Alzheimer's disease and MS representing extremes of too little and too much immune access, respectively.

A protective effect of early pregnancy factor on experimental autoimmune encephalomyelitis induced in Lewis rats by inoculation with myelin basic protein

Experimental autoimmune encephalomyelitis (EAE) is an organ-specific autoimmune disease characterised by inflammation and demyelination of the central nervous system and is the best available animal model of multiple sclerosis (MS). Since previous studies have shown that EAE is less severe or is delayed in onset during pregnancy and that administration of the pregnancy hormone early pregnancy factor (EPF) down-regulates EAE, experiments in the present study were designed to explore further the role of EPF in EAE. By using the rosette inhibition test, the standard bioassay for EPF and, by semi-quantitative RT-PCR techniques, we have now shown that inflammatory cells from the spinal cord of rats with EAE can produce and secrete EPF, with production being greatest during recovery from disease. Administration of EPF to rats with EAE resulted in a significant increase in the expression of IL-4 and IL-10 mRNA and a significant decrease in IFN-gamma mRNA expression in spinal cord inflammatory cells. Encephalitogenic MBP-specific T cell lines were prepared from popliteal lymph nodes of rats with EAE. Proliferation assays using these cells demonstrated the ability of exogenous EPF to down-regulate the responses of T lymphocytes to MBP.

Early pregnancy factor suppresses the infiltration of lymphocytes and macrophages in the spinal cord of rats during experimental autoimmune encephalomyelitis but has no effect on apoptosis

Early pregnancy factor (EPF) is a secreted protein with immunosuppressive and growth factor properties that has been shown to suppress acute experimental autoimmune encephalomyelitis (EAE) induced with myelin basic protein (MBP) in Lewis rats. EAE is associated with infiltration of the central nervous system (CNS) with inflammatory cells. Spontaneous recovery involves the loss of T lymphocytes from the CNS and the selective apoptosis of Vbeta8.2+ cells. In the present study, T cell, macrophage (CD11b/c+) and B cell (CD45RA+) populations in spinal cord and popliteal lymph nodes (LN) of Lewis rats with EAE were quantitated and apoptosis was studied. Rats were treated with EPF or vehicle. Following treatment on day 14 after inoculation with MBP, neither 1 x 100 microg nor 2 x 100 microg doses of EPF affected the total number of cells infiltrating the spinal cord on day 15, although the higher dose caused a decrease in the number of CD5+ and CD11b/c+ cells. Treatment with 2 x 100 microg/day from days 10 to 14 decreased the total number of infiltrating cells, and the numbers of CD5+, CD11b/c+ and CD45RA+ cells. Apoptosis was unaffected. No alteration on the number or type of inflammatory cells in the popliteal LN was observed after treatment on days 10-14. However, treatment with EPF from days 0 to 11 increased the total number of T and B cells and CD5+ T cells found on day 12 in the LN. Similarly, there was an increase in the frequency of MBP-reactive cells in the LN as determined by limiting dilution analysis. These results suggest that EPF treatment reduces the numbers of lymphocytes and macrophages in the CNS, possibly through an effect on cell trafficking.

Regulatory T cells control autoimmunity in vivo by inducing apoptotic depletion of activated pathogenic lymphocytes

Clinical autoimmunity requires both activation of self-reactive T cells as well as a failure of peripheral tolerance mechanisms. We previously identified one such mechanism that involves regulatory T cells recognizing TCR V beta 8.2 chain-derived peptides in the context of MHC. How this regulation affects the fate of target V beta 8.2(+) T lymphocytes in vivo that mediate experimental autoimmune encephalomyelitis has remained unknown. The present study using immunoscope and CFSE-labeling analysis demonstrates that the expansion of regulatory CD4 and CD8 T cells in vivo results in apoptotic depletion of the dominant, myelin basic protein-reactive V beta 8.2(+) T cells, but not subdominant V beta 13(+) T cells. The elimination of only activated T cells by this negative feedback mechanism preserves the remainder of the naive V beta 8.2(+) T cell repertoire and at the same time results in protection from disease. These studies are the first in clearly elucidating the fate of myelin basic protein-specific encephalitogenic T cells in vivo following regulation.

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.

Regulatory role of p53 in experimental autoimmune encephalomyelitis

The role of p53, a pro-apoptotic protein, in experimental autoimmune encephalomyelitis (EAE) was investigated using p53-deficient C57BL/6J mice. p53-deficient mice immunised with myelin oligodendrocyte glycoprotein (MOG) exhibited a more severe clinical course of EAE with more severe inflammation in the central nervous system (CNS) compared to wild-type littermates. While T and B cell responses of p53-deficient mice to MOG were comparable to those of wild-type littermates, significantly higher production of IL-6, granulocyte macrophage colony-stimulating factor and IL-10 was observed in lymphocytes exposed to MOG from p53-deficient mice than those from wild-type littermates. Furthermore, a flow cytometric analysis of Annexin V staining showed that apoptosis of CNS-infiltrating cells was less in p53-deficient mice with EAE compared to wild-type littermates. These results suggest that p53 may be involved in the regulatory process of EAE through the control of cytokine production and/or the apoptotic elimination of inflammatory cells.

Prevention of autoimmune attack and disease progression in multiple sclerosis: current therapies and future prospects

Multiple sclerosis (MS) is an important cause of progressive neurological disability, typically commencing in early adulthood. There is a need for safe and effective therapy to prevent the progressive central nervous system (CNS) damage and resultant disability that characterize the disease course. Increasing evidence supports a chronic autoimmune basis for CNS damage in MS. In the present study, we review current concepts of autoimmune pathogenesis in MS, assess current therapies aimed at countering autoimmune attack and discuss potential therapeutic strategies. Among currently available therapies, beta-interferon and glatiramer acetate have a modest effect on reducing relapses and slowing the accumulation of disability in relapsing-remitting MS. Beta-interferon is of doubtful efficacy in secondary progressive MS and appears to aggravate primary progressive MS, possibly by increasing antibody-mediated CNS damage through inhibition of B-cell apoptosis. Mitoxantrone may reduce relapses and slow disability progression in relapsing-remitting and secondary progressive MS, but its use is limited by the risk of cardiomyopathy. There are currently no effective treatments for primary progressive MS. Many therapies that are effective in the animal model, experimental autoimmune encephalomyelitis (EAE), are either ineffective in MS or--in the case of gamma-interferon, lenercept and altered peptide ligands--actually make MS worse. This discrepancy may be explained by the occurrence in MS of defects in immunoregulatory mechanisms, the integrity of which is essential for the efficacy of these treatments in EAE. It is likely that the development of safe, effective therapy for MS will depend on a better understanding of immunoregulatory defects in MS.

Astrocyte-induced T cell elimination is CD95 ligand dependent

The brain has an intrinsic capacity to remove infiltrating T cells by inducing apoptosis. However, the pathways and cellular components driving this process are still under debate. Astrocytes seem to play an important role because they colocalize with apoptotic lymphocytes in vivo and induce apoptosis of transformed T cells in vitro. Since we previously demonstrated the expression of the death ligand CD95L (APO-1L/FasL) on astrocytes in the brain, we wanted to know whether nontransformed astrocytes induce cell death in nontransformed T cells, reflecting the in vivo situation and, if so, whether CD95/CD95 ligand interaction is important. T cell apoptosis measured by Annexin V binding and DNA fragmentation was significantly lower using CD95 ligand-deficient (gld) astrocytes compared to nondeficient controls. Moreover, neutralizing anti-CD95 ligand antibody reduced astrocyte-induced T cell apoptosis. Thus, adult astrocytes are capable of inducing the apoptotic death of T cells by involving the CD95/CD95 ligand pathway without undergoing cell death in vitro. Since astrocytic end-feet contribute to the formation of the blood-brain barrier, this depletion mechanism may play an important role as the first line of defense in the brain.

Astrocytes are less efficient in the removal of apoptotic lymphocytes than microglia cells: implications for the role of glial cells in the inflamed central nervous system

Apoptosis of T lymphocytes is a common pathway to terminate autoimmune inflammation in the brain as shown in experimental autoimmune encephalomyelitis (EAE) and in the autoimmune inflamed human brain. To date it is unclear to what extent different glial cells are involved in the removal of apoptotic cells. In an in vitro phagocytosis assay we compared the phagocytic capacity of rat microglia cells to remove apoptotic lymphocytes with that of astrocytes. Apoptosis was induced in autologous thymocytes and myelin basic protein (MBP)-specific T-cells by methylprednisolone (MP) or by irradiation. Apoptotic cells were then added to glial cells that were untreated or prestimulated with interferon-gamma (IFN-gamma), interleukin-4 (IL-4), transforming growth factor-beta (TGF-beta), or tumor necrosis factor-a (TNF-a). Supernatants were collected from cell cultures to measure their cytokine secretion. Surface antigen expression was analyzed by flow cytometry. Both cell types significantly increased their phagocytic activity in response to the addition of apoptotic lymphocytes when compared to non-apoptotic cells (p < 0.0001). Astrocytes removed only up to one third of the number of apoptotic lymphocytes ingested by microglia cells (p < 0.0001). Microglia cells significantly increased their phagocytosis rate after IFN-gamma stimulation and decreased it in response to IL-4. In contrast, astrocyte phagocytosis was almost unresponsive to cytokine stimulation. After interaction with apoptotic cells, microglia secreted significantly less TNF-alpha. Astrocytic TNF-alpha production was also decreased but not to a statistically significant extent. MHC-class II expression after phagocytosis was increased on microglia cells but not on astrocytes. Both microglia cells and astrocytes are capable of ingesting apoptotic cells, but microglia cells are much more efficient phagocytes. Their phagocytic capacity is modulated by the local microenvironment and microglial immune function is downregulated after phagocytosis. We suggest that in vivo astrocytes might be activated as phagocytes once the limit of microglial phagocytic capacity has been reached.

Differential expression of neurotrophic factors and inflammatory cytokines by myelin basic protein-specific and other recruited T cells infiltrating the central nervous system during experimental autoimmune encephalomyelitis

Recent evidence suggests that autoimmune reactions in the central nervous system (CNS) not only have detrimental consequences but can also be neuroprotective, and that this effect is mediated by the expression of neuronal growth factors by infiltrating leucocytes. Here we dissect these two phenomena in guinea pig myelin basic protein peptide (gpMBP 63-88)-induced experimental autoimmune encephalomyelitis (EAE) in the Lewis rat. Real-time TaqMan polymerase chain reaction (PCR) was used to measure mRNA for the nerve growth factors, brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3. As reference, the well-known proinflammatory mediator molecules interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha were quantified. In whole lumbar cord tissue, both the nerve growth factors and the proinflammatory cytokines, IFN-gamma and TNF-alpha, displayed similar expression patterns, peaking at the height of the disease. Among the infiltrating inflammatory cells isolated and sorted from the CNS, alphabeta+/T-cell receptor (TCR)BV8S2+, but not alphabeta+/TCRBV8S2-, recognized the encephalitogenic MBP peptide. Interestingly, these two populations displayed contrasting expression patterns of nerve growth factors and proinflammatory cytokines with higher inflammatory cytokine mRNA levels in alphabeta+/TCRBV8S2+ cells at all time intervals, whereas the levels of BDNF and NT3 were higher in alphabeta+/TCRBV8S2- cells. We conclude that a potentially important neuroprotective facet of CNS inflammation dominantly prevails within other non-MBP peptide-specific lymphoid cells and that there are independent regulatory mechanisms for neurotrophin and inflammatory cytokine expression during EAE.

Expression and regulation of Fas and Fas ligand on thyrocytes and infiltrating cells during induction and resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized spleen cells activated in vitro with mouse thyroglobulin, anti-IL-2R, and IL-12. G-EAT lesions reach maximal severity 19-21 days after cell transfer, and lesions almost completely resolve by day 35. Depletion of CD8+ cells delays resolution and reduces Fas ligand (FasL) mRNA expression in thyroids. This study was undertaken to analyze Fas and FasL protein expression in the thyroid during induction and resolution of G-EAT and to determine whether CD8+ cells might regulate Fas or FasL expression in the thyroid. Fas and FasL expression was analyzed by immunohistochemical staining or in situ hybridization in thyroids of mice with or without depletion of CD8+ cells. Fas and FasL proteins were not detectable in normal thyroids, but expression of both proteins increased during development of G-EAT. Fas was expressed primarily by inflammatory cells; some enlarged thyrocytes were also Fas+. Thyrocytes had intense FasL immunoreactvity, and many CD8+ cells were also FasL positive. Depletion of CD8+ cells resulted in decreased FasL expression by thyrocytes and inflammatory cells, but had no effect on Fas expression. TUNEL assay detected many apoptotic inflammatory cells in proximity to thyrocytes. CD8-depleted thyroids had ongoing inflammation with fewer apoptotic infiltrating cells at day 35. Administration of a neutralizing anti-FasL mAb had no apparent effects on development of G-EAT, but anti-FasL was as effective as anti-CD8 in preventing G-EAT resolution. These results suggested that CD8+ T cells and thyrocytes may kill inflammatory cells through the Fas pathway, contributing to G-EAT resolution.

Possible role of organ-specific autoantigen for Fas ligand-mediated activation-induced cell death in murine Sjögren's syndrome

Activation-induced cell death (AICD) is a well-known mechanism of peripheral T cell tolerance that depends upon an interaction between Fas and Fas ligand (FasL). In this study, we demonstrate that the administration of a soluble form of anti-FasL Ab, FLIM58, results in severe destructive autoimmune exocrinopathy in the murine model of human Sjögren's syndrome (SS), and we found that an organ-specific autoantigen may play an important role on down-modulation of AICD. A high titer of serum autoantibodies against 120-kDa alpha-fodrin autoantigen was detected in the FLIM58-treated mice, and splenic T cell culture supernatants contained high levels of IFN-gamma. In vitro T cell apoptosis assay indicated that FasL-mediated AICD is down-regulated by autoantigen stimulation in spleen cells from the murine SS model, but not from Fas-deficient MRL/lpr mice and FasL-deficient MRL/gld mice. FasL undergo metalloproteinase-mediated proteolytic processing in their extracellular domains, resulting in the release of soluble trimeric ligands (soluble FasL). We showed that the processing of soluble FasL occurs in autoantigen-specific CD4(+) T cells, and that a significant increase in expressions of metalloproteinase-9 mRNA was observed in spleen cells from SS model mice. These findings indicate that the increased generation of soluble FasL inhibits the normal AICD process, leading to the proliferation of effector CD4(+) T cells in the murine SS model.

Apoptosis of inflammatory cells in immune control of the nervous system: role of glia

The elimination of inflammatory cells within the central nervous system (CNS) by apoptosis plays an important role in protecting the CNS from immune-mediated damage. T cells, B cells, macrophages, and microglia all undergo apoptosis in the CNS. The apoptotic elimination of CNS-reactive T cells is particularly important, as these cells can recruit and activate other inflammatory cells. T-cell apoptosis contributes to the resolution of CNS inflammation and clinical recovery from attacks of experimental autoimmune encephalomyelitis (EAE), an animal model of the demyelinating disease multiple sclerosis (MS). T-cell apoptosis in the CNS in EAE occurs in both an antigen-specific and an antigen-nonspecific manner. In antigen-specific T-cell apoptosis, it is proposed that T cells that recognize their antigen in the CNS, such as CNS-reactive T cells, are deleted by the process of activation-induced apoptosis after activation of the T-cell receptor. This may result from the ligation of T-cell death receptors (such as CD95 (Fas) or tumor necrosis factor (TNF) receptor 1) by CD95 ligand (CD95L) or TNF expressed by the same T cell or possibly by microglia, astrocytes or neurons. Inadequate costimulation of the T cell by antigen-presenting glial cells may render T cells susceptible to activation-induced apoptosis. T cells expressing CD95 may also die in an antigen-nonspecific manner after interacting with glial cells expressing CD95L. Other mechanisms for antigen-nonspecific T-cell apoptosis include the endogenous release of glucocorticosteroids, deprivation of interleukin-2, and the release of nitric oxide by macrophages or glia. Apoptosis of autoreactive T cells in the CNS is likely to be important in preventing the development of autoimmune CNS diseases such as MS.

Microglial phagocytosis of apoptotic inflammatory T cells leads to down-regulation of microglial immune activation

Apoptotic cell death is an established mechanism to terminate an inflammatory response in rodent or human brains. Microglia, as the resident phagocyte, is a strong candidate for the clearance of apoptotic lymphocytes. Apoptosis was induced in cultured autologous thymocytes and in myelin basic protein (MBP)-specific, encephalitogenic T cells from Lewis rats by the addition of 0.1 microg/ml methylprednisolone. The amount of phagocytosis of apoptotic cells was assessed using an in vitro phagocytosis assay. Supernatants were collected to measure microglial cytokine secretion. The state of immune activation in microglia was investigated by a T cell proliferation assay and by flow cytometric analysis of microglial surface expression of immune molecules. Microglia ingested specifically apoptotic cells (apoptotic thymocytes as well as MBP-specific T cells) in contrast to nonapoptotic control cells (p < 0.0001). Subsequent secretion of the proinflammatory cytokines TNF-alpha and IL-12 was significantly decreased, while the secretion of IL-10 and TGF-beta was not affected. Furthermore, ingestion of apoptotic cells led to increased microglial MHC class II expression without concomitant increase in MHC class I, costimulatory molecules, and ICAM expression. The Ag-specific activation of MBP-specific T cells in cocultures with microglia that had ingested apoptotic cells was significantly less than that of identical T cells that interacted with nonphagocytosing microglia. Together with negative results obtained in a trans-well system, this is in support of a cell contact-mediated effect. Microglia might play an important role in the clearance of apoptotic cells. The uptake of apoptotic cells by microglia is tolerogenic and results in a reduced proinflammatory cytokine production and a reduced activation of encephalitogenic T cells. This might help to restrict an autoimmune inflammation and minimize damage in the inflamed brain.

Cyclosporin A treatment modulates cytokine mRNA expression by inflammatory cells extracted from the spinal cord of rats with experimental autoimmune encephalomyelitis induced by inoculation with myelin basic protein

In Lewis rats, treatment with high doses of cyclosporin A (CsA) suppresses clinical signs of experimental autoimmune encephalomyelitis (EAE), although disease occurs when treatment is ceased. Treatment with low doses of CsA causes EAE to take a chronic relapsing course. We have previously shown that CsA treatment causes a decline in the number of T cells and increased inflammatory cell apoptosis in the spinal cord. The present study was undertaken to assess whether CsA therapy also modulates cytokine mRNA expression by inflammatory cells in the spinal cord of rats with EAE, looking for changes that might contribute to the observed effects of CsA on the course of EAE. EAE was induced in Lewis rats by inoculation with myelin basic protein and adjuvants. At the peak of neurological signs, on day 14 after inoculation, rats were given a single intraperitoneal injection of saline, or CsA at a dose of 8, 16, 32 or 64 mg/kg. The next day, rats were sacrificed, the spinal cords removed, inflammatory cells were extracted from the cords, and mRNA isolated from these cells. Expression of cytokine mRNA was assessed by semi-quantitative reverse transcription polymerase chain reaction (PCR) and by quantitative real-time PCR. With both techniques, we found that CsA suppressed the expression of interferon-gamma mRNA and interleukin-2 (IL-2) mRNA. With real-time PCR, we found that CsA caused significantly increased expression of transforming growth factor-beta mRNA. With the different techniques, we observed no consistent pattern of alteration of expression of interleukin-10 or interleukin-4 mRNA. It is possible that these changes in cytokine mRNA expression contribute to the modulation of the clinical course of EAE that is produced by CsA treatment.

Migratory Activity and Functional Changes of Green Fluorescent Effector Cells before and during Experimental Autoimmune Encephalomyelitis

Homing behavior and function of autoimmune CD4+ T cells in vivo was analyzed before and during EAE, using MBP-specific T cells retrovirally engineered to express the gene of green fluorescent protein. The cells migrate from parathymic lymph nodes to blood and to the spleen. Preceding disease onset, large numbers of effector cells invade the CNS, with only negligible numbers left in the periphery. In early EAE, most (>90%) infiltrating CD4+ cells were effector cells. Migratory effector cells downregulate activation markers (CD25, OX-40) but upregulate several chemokine receptors and adsorb MHC class II on their membranes. Within the CNS, the effector cells are reactivated, with upregulated proinflammatory cytokines and downmodulated T cell receptor-associated structures, presumably reflecting autoantigen recognition in situ.

Rapid entry and downregulation of T cells in the central nervous system during the reinduction of experimental autoimmune encephalomyelitis

We investigated the mechanisms whereby a previous attack of experimental autoimmune encephalomyelitis (EAE) modifies a subsequent attack in the Lewis rat. Active immunization with myelin basic protein (MBP) and complete Freund's adjuvant 28 days after the passive transfer of MBP-sensitized spleen cells induced a second episode of EAE, which occurred earlier than in naive control animals, but was less severe overall. The pattern of neurological signs was also different in rechallenged rats, which had less severe tail and hindlimb weakness but more severe forelimb weakness. In rechallenged rats, inflammation was more severe in the cervical spinal cord, cerebellum, brainstem and cerebrum, but less severe in the lumbar spinal cord, than in controls. The early onset of EAE in rechallenged rats was explained by a memory T cell response to MBP(72-89) in the draining lymph node and spleen, and by the enhanced entry of T cells into the central nervous system (CNS). However, the number of alphabeta T cells in the spinal cord of rechallenged rats declined faster than in controls, especially in the lumbosacral cord, where the number of Vbeta8.2(+) T cells and the frequency of T cells reactive to MBP(72-89) rapidly decreased, indicating rapid downregulation of the immune response in the previously inflamed spinal cord. Apoptosis of inflammatory cells in the CNS was increased in the rechallenged rats and is likely to contribute to this downregulation. Furthermore, during the disease course the generation of encephalitogenic T cells in the peripheral lymphoid organs was limited compared with controls. Thus, a previous attack of EAE modifies a subsequent attack through the interaction of the following processes: a memory T cell response to MBP; facilitated T cell entry into the CNS; downregulation of the immune response in the CNS, including increased apoptosis of inflammatory cells; and a limited generation of encephalitogenic T cells in the peripheral lymphoid organs.

Surges of increased T cell reactivity to an encephalitogenic region of myelin proteolipid protein occur more often in patients with multiple sclerosis than in healthy subjects

We have previously shown that patients with multiple sclerosis (MS) have increased T cell responses to the immunodominant region (residues 184-209) of myelin proteolipid protein (PLP). The present study investigated whether this reactivity fluctuates over time and correlates with disease activity. We performed monthly limiting dilution assays for 12-16 mo in four healthy subjects and five patients with relapsing-remitting MS to quantify the frequencies of circulating T cells proliferating in response to PLP(41-58), PLP(184-199), PLP(190-209), myelin basic protein (MBP), MBP(82-100), and tetanus toxoid. Disease activity was monitored by clinical assessment and gadolinium-enhanced magnetic resonance imaging of the brain. There were fluctuations in the frequencies of autoreactive T cells in all subjects. Compared with healthy controls, MS patients had significantly more frequent surges of T cells reactive to the 184-209 region of PLP, but infrequent surges of T cell reactivity to MBP(82-100). There was temporal clustering of the surges of T cell reactivity to MBP(82-100) and MBP, suggesting T cell activation by environmental stimuli. Some clinical relapses were preceded by surges of T cell reactivity to PLP(184-209), and in one patient there was significant correlation between the frequency of T cells reactive to PLP(184-199) and the total number of gadolinium-enhancing magnetic resonance imaging lesions. However, other relapses were not associated with surges of T cell reactivity to the Ags tested. T cells reactive to PLP(184-209) may contribute to the development of some of the CNS lesions in MS.

Divergent roles for p55 and p75 tumor necrosis factor receptors in the pathogenesis of MOG(35-55)-induced experimental autoimmune encephalomyelitis

To clarify the role of tumor necrosis factor (TNF) in the inflammatory aspects of autoimmunity vs its potential role in the apoptotic elimination of autoreactive effector cells, we assessed the roles of the p55 (TNFR1/Tnfrsf1a/CD120a) and p75 (TNFR2/Tnfrsf1b/CD120b) TNF receptors in the pathogenesis of MOG(35-55)-induced experimental autoimmune encephalomyelitis (EAE). TNFR p55/p75(-/-) double knockout mice were completely resistant to clinical disease. TNFR p55(-/-) single knockout mice were also totally resistant to EAE, exhibiting reduced MOG(35-55)- specific proliferative responses and Th1 cytokine production, despite displaying equivalent DTH responses. Importantly, IL-5 was significantly increased in p55(-/-) mice. In contrast, p75(-/-) knockout mice exhibited exacerbated EAE, enhanced Th1 cytokine production, and enhanced CD4(+) and F4/80(+) CNS infiltration. Thus, p55/TNFR1 is required for the initiation of pathologic disease, whereas p75/TNFR2 may be important in regulating the immune response. These results have important implications for therapies targeting p55 and p75 receptors for treating autoimmune diseases.

Aminoguanidine reduces apoptosis of circulating V Beta 8.2 T lymphocytes in Lewis rats with actively induced experimental autoimmune encephalomyelitis. Association with persistent inflammation of the central nervous system and lack of recovery

Aminoguanidine therapy delayed the onset of actively induced EAE in Lewis rats, but recovery was impaired in most animals. In the central nervous system this was correlated with persistent inflammation and production of proinflammatory cytokines. In the periphery of aminoguanidine-treated animals, T lymphocytes showed increased proliferation against myelin basic protein, and the percentage of Vbeta 8.2(+) T lymphocytes undergoing early apoptosis was markedly decreased, although it was unchanged in Vbeta 8.2(+) T cells isolated from the spinal cord. These results suggest that the prolonged survival of circulating encephalitogenic cells achieved by aminoguanidine would favor a longer lasting entry of these cells into the nervous system resulting in persistent inflammation and lack of recovery.

Alterations in the spinal cord T cell repertoire during relapsing experimental autoimmune encephalomyelitis

The CNS T cell repertoire was analyzed by RT-PCR, spectratyping, and nucleotide sequencing of the amplified products at different times following adoptive transfer of a CD4+, Th1, VB2+ encephalitogenic SJL/J proteolipid protein peptide 139-151-specific T cell clone. The third complementarity-determining region of TCR B chains in the spinal cord was used as an indicator of T cell heterogeneity. Spectratypic analysis revealed that a single peak corresponding to the third complementarity-determining region of the initiating T cell clone predominated during the acute phase. During recovery and relapse the complexity of the spectratype increased. DNA sequence analysis revealed that the donor clone predominated at the acute phase. By the first relapse the donor clone, although represented most frequently, was a minority of the total. Spectratypic analysis of the same samples for several other VB families revealed their presence during acute disease or relapses but, with the exception of VB17, their absence during the recovery stage.

B cell apoptosis in the central nervous system in experimental autoimmune encephalomyelitis: roles of B cell CD95, CD95L and Bcl-2 expression

The role and fate of B cells in the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE) are unknown. Using enzyme-linked immunospot assays we now show that B cells reactive to myelin basic protein (MBP) accumulate in the CNS of Lewis rats with acute EAE induced by immunization with MBP and adjuvants. We also report that B cells are eliminated from the CNS by apoptosis during spontaneous recovery from this disease. Apoptotic B cells were identified by flow cytometry of inflammatory cells extracted from the spinal cord and by histological sections of the spinal cord using light and electron microscopic immunocytochemistry. B cell apoptosis occurred preferentially in the CNS rather than in the peripheral lymphoid organs and was maximal just prior to the onset of spontaneous clinical recovery. Three colour flow cytometry indicated that B cells expressing CD95 (Fas) or CD95 ligand (CD95L) were highly vulnerable to apoptosis, whereas B cells expressing Bcl-2 were relatively protected from apoptosis. We propose that B cells are eliminated from the CNS by the interaction of CD95L and CD95 on the same B cell and that this contributes to the spontaneous resolution of CNS inflammation and clinical recovery in acute EAE.

The effect of apoptosis inhibitors on experimental autoimmune encephalomyelitis: apoptosis as a regulatory factor

The effect of apoptosis inhibitors on experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, was investigated by intraperitoneal or intracisternal administration of apoptosis inhibitors Ac-YVAD-cmk and zVAD-fmk. After onset of the disease, these agents had no suppressive effect on EAE and resulted in impaired recovery or earlier relapse. Histological examination revealed that administration of zVAD-fmk suppressed the apoptotic death of inflammatory cells in the central nervous system (CNS) of mice with EAE. The results indicated that the apoptotic elimination of infiltrated cells in the CNS might be one of the recovery mechanisms in EAE.

Fas-mediated apoptosis in clinical remissions of relapsing experimental autoimmune encephalomyelitis

PLP139-51-induced experimental autoimmune encephalomyelitis (R-EAE) displays a relapsing-remitting paralytic course in female SJL mice. We investigated the role of apoptosis/activation-induced cell death (AICD) in the spontaneous recovery from acute disease. Clinical EAE was significantly enhanced in Fas (CD95/APO-1)-deficient SJL lpr/lpr mice, which displayed significantly increased mean peak clinical scores, reduced remission rates, and increased mortality when compared with their SJL +/lpr littermates. PLP139-151-specific proliferative responses were fairly equivalent in the 2 groups, but draining lymph node T cells from SJL lpr/lpr mice produced dramatically increased levels of IFN-gamma. Central nervous system (CNS) Fas and FasL mRNA levels in wild-type SJL (H-2(s)) mice peaked just before spontaneous disease remission and gradually declined as disease remitted. We applied the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay to detect apoptosis in situ in spinal cords of mice at various clinical stages of EAE. Most TUNEL(+) cells were found during active periods of inflammation: the acute, peak, and relapse time points. Significantly fewer apoptotic cells were observed at preclinical and remission time points. Collectively, these findings indicate that Fas-mediated apoptosis/AICD plays a major role in the spontaneous remission after the initial acute inflammatory episode and represents an important intrinsic mechanism in regulation of autoimmune responses.