Loss rather than downregulation of CD4+ T cells as a mechanism for remission from experimental allergic encephalomyelitis

Neurological Benefits, Clinical Challenges, and Neuropathologic Promise of Medical Marijuana: A Systematic Review of Cannabinoid Effects in Multiple Sclerosis and Experimental Models of Demyelination

Despite current therapeutic strategies for immunomodulation and relief of symptoms in multiple sclerosis (MS), remyelination falls short due to dynamic neuropathologic deterioration and relapses, leading to accrual of disability and associated patient dissatisfaction. The potential of cannabinoids includes add-on immunosuppressive, analgesic, neuroprotective, and remyelinative effects. This study evaluates the efficacy of medical marijuana in MS and its experimental animal models. A systematic review was conducted by a literature search through PubMed, ProQuest, and EBSCO electronic databases for studies reported since 2007 on the use of cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) in MS and in experimental autoimmune encephalomyelitis (EAE), Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), and toxin-induced demyelination models. Study selection and data extraction were performed by 3 reviewers, and 28 studies were selected for inclusion. The certainty of evidence was appraised using the Cochrane GRADE approach. In clinical studies, there was low- and moderate-quality evidence that treatment with ~1:1 CBD/THC mixtures as a nabiximols (Sativex®) oromucosal spray reduced numerical rating scale (NRS) scores for spasticity, pain, and sleep disturbance, diminished bladder overactivity, and decreased proinflammatory cytokine and transcription factor expression levels. Preclinical studies demonstrated decreases in disease severity, hindlimb stiffness, motor function, neuroinflammation, and demyelination. Other experimental systems showed the capacity of cannabinoids to promote remyelination in vitro and by electron microscopy. Modest short-term benefits were realized in MS responders to adjunctive therapy with CBD/THC mixtures. Future studies are recommended to investigate the cellular and molecular mechanisms of cannabinoid effects on MS lesions and to evaluate whether medical marijuana can accelerate remyelination and retard the accrual of disability over the long term.

Gut-licensed IFNγ+ NK cells drive LAMP1+TRAIL+ anti-inflammatory astrocytes

Astrocytes are glial cells that are abundant in the central nervous system (CNS) and that have important homeostatic and disease-promoting functions1. However, little is known about the homeostatic anti-inflammatory activities of astrocytes and their regulation. Here, using high-throughput flow cytometry screening, single-cell RNA sequencing and CRISPR-Cas9-based cell-specific in vivo genetic perturbations in mice, we identify a subset of astrocytes that expresses the lysosomal protein LAMP12 and the death receptor ligand TRAIL3. LAMP1+TRAIL+ astrocytes limit inflammation in the CNS by inducing T cell apoptosis through TRAIL-DR5 signalling. In homeostatic conditions, the expression of TRAIL in astrocytes is driven by interferon-γ (IFNγ) produced by meningeal natural killer (NK) cells, in which IFNγ expression is modulated by the gut microbiome. TRAIL expression in astrocytes is repressed by molecules produced by T cells and microglia in the context of inflammation. Altogether, we show that LAMP1+TRAIL+ astrocytes limit CNS inflammation by inducing T cell apoptosis, and that this astrocyte subset is maintained by meningeal IFNγ+ NK cells that are licensed by the microbiome.

Immunomodulatory effects of the ether phospholipid edelfosine in experimental autoimmune encephalomyelitis

The 2-lysophosphatidylcholine analog edelfosine induces apoptosis in highly proliferating cells, e.g. activated immune cells. We examined mechanisms of action of edelfosine on immune functions in experimental autoimmune encephalomyelitis, a well-accepted animal model for multiple sclerosis. We observed activated caspase-3 expression in lymphoid organs and the central nervous system; however, edelfosine did not induce global apoptosis. Edelfosine improved the disease course and led to reduced frequencies of CD4(+) T cells infiltrating into the central nervous system. Our data suggest edelfosine as an interesting treatment candidate for multiple sclerosis.

Apoptosis of T cells in peripheral blood and cerebrospinal fluid is associated with disease activity of multiple sclerosis

Apoptotic elimination of pathogenic T cells is considered to be one of regulatory mechanisms in multiple sclerosis (MS). To explore the potential relationship between Fas-mediated apoptosis and the disease course of MS, we examined apoptosis, defined by annexin V (AV) binding, and Fas (CD95) expression in CD4+ and in CD8+ T cells in MS patients by using five-color flow cytometry. The percentage of AV+CD4+CD3+ cells and CD95+AV+CD4+CD3+ cells in peripheral blood and cerebrospinal fluid (CSF) were significantly decreased in active MS patients compared with inactive MS patients. A significantly lower proportion of CD95+AV+CD8+CD3+ cells in CSF was observed in active MS patients compared with inactive MS patients, but not in peripheral blood. These results indicate that the resistance of T cells to Fas-mediated apoptosis is involved in exacerbation of MS and/or that Fas-mediated apoptosis of T cells is associated with remission of MS.

The suppression of T cell apoptosis influences the severity of disease during the chronic phase but not the recovery from the acute phase of experimental autoimmune encephalomyelitis in mice

The elimination of T cells by apoptosis is considered to be one of the regulatory factors in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. To address further the role of apoptotic T cell death in EAE, we investigated myelin oligodendrocyte glycoprotein (MOG)-induced EAE in transgenic mice overexpressing the anti-apoptotic gene, bcl-2, in T cells. During the acute phase of EAE, no significant difference was observed in the clinical course, pathology and T cell response to MOG between bcl-2 transgenic mice and wild-type littermates. While the recovery from the first attack of EAE was not impaired in the bcl-2 transgenic mice, a more severe disease was observed during the chronic phase of the disease even though T and B cell responses to MOG were comparable to those of wild-type littermates. A flow cytometric analysis by Annexin V showed a significant decrease of apoptotic T cells in the central nervous system (CNS) of the bcl-2 transgenic mice with EAE compared with controls during the chronic as well as the acute phase of disease. These results suggest that while T cell apoptosis in the CNS may play a regulatory role in EAE, the spontaneous recovery from acute EAE cannot solely be explained by T cell apoptosis.

Prolonged reversal of chronic experimental allergic encephalomyelitis using a small molecule inhibitor of alpha4 integrin

CNS leukocytic invasion in experimental allergic encephalomyelitis (EAE) depends on alpha4beta1 integrin/vascular cell adhesion molecule-1 (VCAM-1) interactions. A small molecule inhibitor of alpha4beta1 integrin (CT301) was administered to guinea pigs in the chronic phase (>d40) of EAE for 10, 20, 30 or 40 days. CT301 elicited a rapid, significant improvement in the clinical and pathological scores that was maintained throughout the treatment period. A progressive loss of cells in the spinal cord of treated animals confirmed the resolution of inflammation associated with clinical recovery. Therefore, prolonged inhibition of alpha4beta1 integrin caused a sustained reversal of disease pathology in chronic EAE and may be similarly useful in MS.

gammadelta T cells express activation markers in the central nervous system of mice with chronic-relapsing experimental autoimmune encephalomyelitis

In this study, we assessed the expression of activation markers on gammadelta T cells in central nervous system (CNS) lesions of SJL mice adoptively sensitized to develop experimental autoimmune encephalomyelitis (EAE) using myelin basic protein-reactive T cells. Although disease expression is known to be dependent upon T cells that express the alphabeta T cell receptor (TCR), a role for gammadelta T cells has been implicated in some studies but not in others. Using three-color flow cytometric analysis of both total and gammadelta T cells in spleen and CNS, the data showed that expression of CD69 (early activation marker), CD62L (lymphocyte homing receptor), CD25 (IL-2Ralpha), CD122 (IL-2Rbeta) and CD95/CD95L (Fas/FasL), fluctuated on gammadelta T cells in EAE lesions in a disease-related fashion. Furthermore, the pattern of expression for these markers on gammadelta T cells was distinct from that found on the total lymphocyte population. Cytokine analysis of gammadelta T cells in the CNS demonstrated a bias towards a Th1-like cytokine profile. From these data, we conclude that gammadelta T cells in EAE lesions display an activated phenotype and form a dynamic component of the total lymphocyte population in the CNS, supporting a contributory role for these cells.

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.

Role of MOG-stimulated Th1 type "light up" (GFP+) CD4+ T cells for the development of experimental autoimmune encephalomyelitis (EAE)

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis in humans. EAE can be passively transferred into naive syngeneic animals by administration of MOG-specific T cell clones. Lymphocytes isolated from green fluorescent protein (GFP)-transgenic (Tg) mice can light up by emitting green fluorescence, thus making it feasible to use such animals in a passive transfer model for EAE. When MOG-sensitized splenic lymphocytes from GFP-Tg mice were adoptively transferred to irradiated, syngeneic C57BL/6 and RAG-1(-/-)mice, typical symptoms of EAE developed. Analysis of the reconstituted mice with EAE revealed prominent infiltration of fluorescing (GFP+), CD4+ T cells into the central nervous system (CNS). Real-time confocal imaging revealed these cells in the spinal cords and brains of recipient mice. This infiltration was also confirmed by anti-GFP monoclonal antibodies. Furthermore, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) evaluation indicated that the infiltrating GFP+, CD4+ T cells exclusively produced T helper type 1 (Th1) cytokines, especially interferon-gamma (IFN-gamma). These results clearly show that MOG-specific CD4+ T cells preferentially invade into the CNS and mediate the development of EAE by producing Th1-biased cytokines.

The role of costimulation in autoimmune demyelination

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated, autoimmune disorder characterized by central nervous system (CNS) inflammation and demyelination, features reminiscent of the human disease, multiple sclerosis (MS). In addition to the signal the encephalitogenic T cell receives through the T cell receptor (TCR), a second signal, termed costimulation, is required for complete T cell activation. The B7 family of cell surface molecules expressed on antigen presenting cells (APC) is capable of providing this second signal to T cells via two receptors, CD28 and CTLA-4. Our studies have shown that costimulation provided by B7 molecules to its ligand CD28 is important in the initiation of the autoimmune response in EAE. Further, it appears the costimulation provided by B7-1 is important in disease development, while B7-2 may play an important regulatory role. We and others later showed that B7/CTLA-4 interaction plays a critical role in down-regulating the immune response. Previous work has shown that activated T cells and T cells of a memory phenotype are less dependent on costimulation than naive T cells. T cells reactive with myelin components that are involved in the pathogenesis of EAE and possibly MS would be expected to have been activated as part of the disease process. Building upon our prior work in the EAE model, we have tested the hypothesis that myelin-reactive T cells, which are relevant to the pathogenesis of CNS inflammatory demyelination, can be distinguished from naive myelin-reactive T cells by a lack of dependence upon costimulation for activation and that the costimulatory requirements of these myelin-reactive T cells change during the course of disease. Our studies in the EAE model have also addressed the mechanisms of extrathymic (peripheral) T cell tolerance following intravenous (i.v. ) administration of high dose antigen. It is believed that TCR signaling in the absence of costimulation is a vital component of peripheral tolerance mechanisms. However, recent evidence suggests that peripheral tolerance of antigen-specific T cells induced in vivo may require CTLA-4 engagement of the tolerized T cells. We have begun to examine the molecular mechanisms of tolerance induction following intravenous and intraperitoneal administration of myelin antigens in the EAE model and test the hypothesis that tolerance induction is dependent on the B7:CD28/CTLA-4 pathway. The results from our studies will enhance our understanding of the role that myelin-reactive T cells may play in the pathogenesis of MS. We have determined that MBP-reactive T cells in MS patients are less dependent upon CD28 costimulation than in normal controls, suggesting that these T cells were previously primed in vivo. Characterization of these CD28-independent myelin-specific T cells will have broad implications for a variety of immunologically based therapies in diseases such as MS.

Role of Fas--FasL interactions in the pathogenesis and regulation of autoimmune demyelinating disease

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) represent complex processes that lead to destruction of oligodendrocytes (ODCs) and myelin. T cells are integral to the development of these diseases, but whether T cell-mediated cytolytic mechanisms are involved in the destruction of MHC Class II-negative targets, such as oligodendroglia and myelin, in the CNS is unclear. The primary lytic mechanism employed by CD4+ T cells is Fas-dependent, but can be MHC-unrestricted. Thus, T cell-mediated Fas-FasL interactions could directly contribute to the pathology of EAE and MS. This review summarizes studies from our laboratory and others that implicate Fas-FasL interactions in both the pathogenesis and regulation of demyelinating diseases.

Treatment of murine experimental autoimmune encephalomyelitis with a myelin basic protein peptide analog alters the cellular composition of leukocytes infiltrating the cerebrospinal fluid

Experimental autoimmune encephalomyelitis (EAE) can be effectively treated during disease exacerbation by administration of a peptide corresponding to the major T cell epitope of myelin basic protein (MBP), but the mechanism by which T cell tolerance leads to clinical improvement is not well-defined. Acute exacerbations of EAE are accompanied by an infiltration of blood-borne leukocytes into the brain and spinal cord, where they mediate inflammation and demyelination. To investigate peptide effects on infiltrating cells, we collected cerebrospinal fluid (CSF) from (PL/JxSJL)F1 mice with MBP-induced EAE. Pleiocytosis by lymphocytes, neutrophils, and macrophages was seen throughout the course of relapsing-remitting disease. A single administration of the MBP peptide analog, Ac1-11[4Y], reduced disease severity, accompanied by a dramatic and selective loss of neutrophil pleiocytosis. A longer course of peptide therapy resulted in complete recovery from clinical signs of disease, and decreased pleiocytosis by all cell types. Clinical severity throughout the course of disease and therapy was directly related to the degree of infiltration by neutrophils and macrophages, and the clinical improvement following peptide therapy was accompanied by decreased central nervous system (CNS) expression of chemoattractants for these cell types. These observations support a model of disease exacerbation mediated by phagocytic cellular infiltration under the ultimate control of T cell-derived factors, amenable to treatment by down-regulation of the T cell activation state.

The case against epitope spread in experimental allergic encephalomyelitis

Epitope spread has been proposed as a possible mechanism for diversification of the autoimmune T-cell response during disease. Specifically, it offers a plausible mechanism for the previously obscure cyclical nature of autoimmune demyelination whereby the sequence of attack, quiescence and reactivation may recur over a long period of time. However, we were concerned that previous studies of epitope spread have not necessarily shown it to be well correlated with disease severity or relapse. Furthermore, we had studied two transgenic models of exacerbated experimental allergic encephalomyelitis (EAE) in which no indication of spread away from the initial disease-inducing peptide could be observed. We conducted a systematic, longitudinal study in SJL mice to look for determinant spread during relapsing and remitting EAE, correlating epitope recognition and cytokine production with disease severity. When T cells from spleen, lymph node and central nervous system (CNS) were analysed, little or no determinant spread was found. The best immunological correlate of relapse was the reappearance after remission of CNS-infiltrating T cells mounting a strong proliferative and interferon (IFN)-gamma response to the original disease-inducing epitope. Our data do not support a general role for determinant spread in EAE relapse. Rather, they indicate the importance of a focused proliferative and IFN-gamma response to the disease-inducing peptide.

IFN-gamma production of adult rat astrocytes triggered by TNF-alpha

IFN-gamma plays an important role in modulating inflammatory responses within the CNS. The cell type responsible for IFN-gamma production within the CNS is less well defined. We examined the production and regulation of IFN-gamma by adult rat astrocytes. IFN-gamma was hardly detectable in cultured astrocytes, while addition of TNF-alpha dose-dependently induced IFN-gamma production by astrocytes. No IFN-gamma production by astrocytes could be induced by LPS, IL-10 or TGF-beta 1. TNF-alpha-induced IFN-gamma production by astrocytes was inhibited by treatment of astrocytes with TGF-beta 1, but not IL-10. TNF-alpha induced IFN-gamma production by astrocytes was confirmed by using immunocytochemical staining. The data suggest that astrocyte-derived IFN-gamma induced by TNF-alpha may participate in local immune reactions of the brain in an autocrine and paracrine fashion.

Adoptively transferred EAE in gamma delta T cell-knockout mice

Recently there has been evidence suggesting that gamma delta receptor-bearing T cells may play a role in both multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). We have recently described approaches for the generation of encephalitogenic T-cell populations from EAE-resistant strains of mice. Using encephalitogenic T-cell lines and clones generated from wild-type C57BL/6 mice we have studied adoptively transferred EAE in C57BL/6-TCR delta-knockout mice. We now report that the adoptive transfer of encephalitogenic T cells into TCR delta T-knockout mice leads to clinical EAE that is not significantly different in severity or time course than that seen after transfer into wild-type C57BL/6 mice. We conclude that gamma delta T cells do not play an integral role in the mediation or regulation of the effector-phase mechanisms in EAE.

Relapsing and remitting experimental allergic encephalomyelitis: a focused response to the encephalitogenic peptide rather than epitope spread

The progression of experimental allergic encephalomyelitis (EAE) in certain mouse strains has been reported to involve a broadening of the response to myelin antigens, apparently resulting from priming to endogenous determinants of the myelin sheath. The phenomenon has been termed determinant spread. Interest in this effect has centered on the mechanism it offers to explain the progressive, relapsing and remitting course of EAE and indeed of multiple sclerosis. We have conducted a systematic, longitudinal study in SJL mice to look for determinant spread during relapsing and remitting EAE, correlating epitope recognition and cytokine production with disease severity. Disease was induced using three of the four encephalitogenic proteolipid protein or myelin basic protein epitopes, and responses to each of four epitopes recognized by SJL T cells were tracked through acute disease, remission and relapse. The responses of lymph node cells, splenocytes and central nervous system (CNS)-infiltrating T cells were analyzed. While marginal, transient responses to secondary epitopes were detectable in splenocytes, CNS-infiltrating cells showed a dominant response to the original disease-inducing epitope without evidence of a shift to other determinants during relapse. Disease relapse was correlated with an increase in CNS-infiltrating cells and a high proliferative and interferon (IFN)-gamma response to the disease-inducing peptide. During remission, there was a decrease in numbers of cells infiltrating the CNS. These cells were down-regulated, showing low if any response to the myelin peptides tested as measured by proliferation, production of IFN-gamma or production of IL-4. Our findings argue strongly against a causal role for determinant spread in disease relapse as observed in these models of EAE.

Modulation of experimental allergic encephalomyelitis in mice by immunization with a peptide specific for the gamma delta T cell receptor

This study investigated the role of gamma delta T cells in experimental allergic encephalomyelitis (EAE), a chronic inflammatory disease of the central nervous system (CNS) that resembles multiple sclerosis. The strategy was to assess the effect on EAE of TCR peptide immunization directed against V gamma 6 T cells, shown recently to predominate in the CNS of mice during the early stages of EAE. The data show that TCR peptide immunization specific for V gamma 6 chains does not induce protection against EAE, since the incidence of EAE in TCR treated animals was similar to control mice, and therefore does not affect disease susceptibility per se, but rather alters the development of the disease. Specifically, there was a delay in the onset of EAE and a reduction in disease severity in TCR treated animals, although the effects were not highly significant. These findings suggest a role for gamma delta T cells in the development of EAE; however, further studies are necessary to confirm the specificity of TCR peptide immunization.

Corticosteroid treatment of experimental autoimmune encephalomyelitis in the Lewis rat results in loss of V beta 8.2+ and myelin basic protein-reactive cells from the spinal cord, with increased total T-cell apoptosis but reduced apoptosis of V beta 8.2+ cells

We have studied the effects of corticosteroid treatment on the numbers of lymphocytes obtained from the spinal cords of Lewis rats with acute experimental autoimmune encephalomyelitis (EAE) induced by inoculation with myelin basic protein (MBP) and adjuvants. Flow cytometric studies showed that treatment with dexamethasone (4 mg/kg) 8-12 h prior to study on day 14 after inoculation resulted in a reduction in the numbers of CD5+, TCR alpha beta + and V beta 8.2+ cells in the spinal cord. Limiting dilution analysis indicated that dexamethasone treatment 12 h prior to study on day 12 after inoculation reduced the frequencies of MBP-reactive and interleukin-2-responsive lymphocytes in the spinal cord to low levels, but reduced the frequency of concanavalin-A-responsive lymphocytes to a lesser extent. Using propidium iodide staining of nuclear chromatin we also studied lymphocyte apoptosis. Greater numbers of apoptotic cells were found in the cells extracted from the spinal cords of rats, examined on day 14, that had been treated 1-12 h previously with dexamethasone, than in saline-treated controls. This increased level of apoptosis was observed in the CD5+ and TCR alpha beta + cell populations. At 1-4 h after dexamethasone treatment there was a reduction in the selective apoptosis of V beta 8.2+ cells that normally occurs during spontaneous recovery from EAE. Therefore apoptosis of V beta 8.2+ cells cannot explain the reduction in the numbers of V beta 8.2+ cells and MBP-reactive cells in the CNS after dexamethasone treatment. By 8-12 h after dexamethasone treatment the selectivity of the apoptotic process was restored. These studies suggest that a reduction in the number of T-lymphocytes in the central nervous system contributes to the beneficial effects of corticosteroids in EAE.

Interferon-gamma confers resistance to experimental allergic encephalomyelitis

In experimental allergic encephalomyelitis (EAE), T cells infiltrate the central nervous system (CNS) and induce inflammation. These CD4+ T cells secrete interferon (IFN)-gamma, levels of which correlate with disease severity, and which is proposed to play a key role in disease induction. Many strains of mice are resistant to EAE. We have studied the effect of deletion of IFN-gamma on the ability to induce EAE in resistant BALB/c-backcrossed mice. As expected, only 0-6% of BALB/c or BALB/c-backcrossed mice developed EAE when immunized with myelin basic protein in adjuvant. Strikingly, abrogation of IFN-gamma expression by targeted disruption of the IFN-gamma gene (GKO mice) converted them to a susceptible phenotype. As many as 71% of these IFN-gamma-deficient mice developed EAE, a frequency comparable to that seen with the susceptible SJL/J strain. In addition, EAE was of unusually high severity in mice lacking IFN-gamma. Immunological characteristics of disease in IFN-gamma-deficient mice were comparable to those seen in susceptible (SJL/J) mice with EAE, including perivascular infiltration in the CNS and order-of-magnitude increases for both CD3 gamma chain and TNF-alpha mRNA levels in the spinal cord. We thus demonstrate that lack of IFN-gamma converts an otherwise EAE-resistant mouse strain to become susceptible to disease. Therefore, in BALB/c mice, IFN-gamma confers resistance to EAE.

Gamma delta T cell receptor variable region usage during the development of experimental allergic encephalomyelitis

The molecular diversity of gamma delta T cells has not previously been investigated in experimental allergic encephalomyelitis (EAE). This study characterised the gamma delta T cell receptor (TCR) variable (V) region repertoires of T cells infiltrating the brains of EAE mice during development of the disease. TCR gamma- and delta-specific cDNAs were synthesised from total RNA prepared from brain samples and transcription of rearranged V genes was assessed by polymerase chain reaction amplification of TCR V-C transcripts and Southern blot analysis. In the early stages of EAE, the TCR gamma-chain repertoire consisted of V gamma 1-3 and V gamma 6 transcripts and, similarly, a few V delta transcripts that used primarily V delta 1, V delta 4 and V delta 5 gene segments were detected. During the progression of EAE, however, most V gamma and V delta TCR transcripts were observed in the brain. These results indicate that in the course of murine EAE there is an initial infiltration into the brain of a restricted population of gamma delta T cells followed by a heterogeneous gamma delta TCR repertoire as the disease develops. Moreover, the data suggest that gamma delta T cells may play a role in the pathogenesis of demyelinating autoimmune disease.

Spreading of the immune response to different myelin basic protein peptides in chronic experimental autoimmune encephalomyelitis in B10.RIII mice

B10.RIII mice develop chronic and relapsing experimental autoimmune encephalomyelitis (EAE) after immunization with the myelin basic protein (MBP) peptide 89-101 (VHFFKNIVTPRTP). To investigate the basis for the chronicity of the disease, the subsequent development of an immune responses to other parts of the MBP protein were investigated. Onset of disease occurs 9-25 days after immunization with MBP89-101. T cell responses towards a series of MBP peptides were assessed in an enzyme-linked immunospot assay detecting single cells secreting IFN-gamma. There were responses not only to MBP89-101, but also towards peptides derived from sequences outside of MBP89-101. These peptides were of two kinds: those with sequences completely outside the 89-101 stretch of MBP; and those sharing a short sequence with MBP89-101 depending on alternative splicing of MBP mRNA. Immunization with these peptides also produced chronic EAE and a spreading of the immune response to other MBP peptides. Immunization with stepped peptides around the relevant region (MBP87-110) showed that peptides sharing a 6-amino-acid motif induced EAE after immunization. After MBP89-101 peptide immunization, T cells isolated from lymph nodes did not cross-react in vitro to the other peptides sharing this motif. We suggest that one mechanism for the development of relapses during the disease course is the recruitment of new T cells with specificity for MBP peptides not derived from the peptide used for immunization. This is the first time such a mechanism has been demonstrated in a chronic autoimmune disease model.

Regulation of autoimmune response

Recent work on such apparently disparate fields as T-cell receptor peptide-induced regulation, superantigens, antigen-induced tolerance, models of peripheral tolerance, apoptosis, and T-cell receptor antagonists demonstrates a similarity in immune response from a regulatory perspective. In many systems, a 'tolerance' pathway is observed, characterized broadly as an initial disturbance in the immune system, with a resulting predominance of effector cells, followed by a homeostatic response (often requiring CD8+ cells) which leads the effector population into T-cell receptor downregulation, T-cell inactivation, anergy and, often, eventual apoptotic death. In the regulated immune response, mixed populations of anergized and apoptosing T cells can be found. In some cases, anergy appears to lead to death while, in other instances, cells revert to a functional state. This review focuses on recent papers examining each of these topics in an attempt to obtain a preliminary integrated picture of immune regulation in autoimmune diseases.

Inflammatory cytokines in the brain: does the CNS shape immune responses?

Immune responses in the central nervous system (CNS) have traditionally been regarded as representing the intrusion of an unruly, ill-behaved mob of leukocytes into the well-ordered and organized domain of thought and reason. However, results accumulated over the past few years suggest that, far from being an immunologically privileged organ, T lymphocytes may be regular and frequent visitors to the CNS, for purposes of immune surveillance. Here, Trevor Owens and colleagues propose that the brain itself can regulate or shape immune responses therein. Furthermore, given that the immune cells may be subverted to autoimmunity, they suggest that the study of inflammatory autoimmune disease in the brain may shed light on the ability of the local environment to regulate immune responses.

Inflammatory cells, microglia and MHC class II antigen-positive cells in the spinal cord of Lewis rats with acute and chronic relapsing experimental autoimmune encephalomyelitis

Chronic relapsing experimental autoimmune encephalomyelitis (CR-EAE) was induced in Lewis rats by inoculation with guinea pig spinal cord and adjuvants and treatment with low dose cyclosporin A (CsA). Acute EAE was induced by the same method without CsA treatment. Immunocytochemistry and flow cytometry were used to assess inflammatory cells and MHC class II (Ia) antigen expression in the central nervous system of these rats. The inflammatory infiltrate was composed mainly of CD4+ T cells and macrophages, and alpha beta T cells constituted about 65% of the CD2+ T cells. After recovery from acute EAE and during the first remission of CR-EAE, the number of T cells was significantly less than in the preceding episodes. The number of T cells was higher in the second episode of CR-EAE than in the first remission. Throughout the course of CR-EAE, the majority of the CD2+ T cells were CD45RC-. The ratio of IL-2R+ cells to CD2+ cells ranged from 10.5 to 24.0%. The ratio of CD4+ T cells to B cells was lower in the later episodes of CR-EAE than in the first episode. Ia antigen was expressed on infiltrating round cells at all stages of CR-EAE and on microglial cells (identified by dendritic morphology) with increasing intensity throughout the course of CR-EAE. With flow cytometry, the number of Ia+ cells obtained from the spinal cord rose throughout the course of CR-EAE. The number of FSClowOX1low cells, which we consider represent microglia, also increased during the course of CR-EAE.