Experimental autoimmune encephalomyelitis as a model of immune-mediated CNS disease

Gut-Brain Interactions and Their Impact on Astrocytes in the Context of Multiple Sclerosis and Beyond

Multiple Sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system (CNS) that leads to physical and cognitive impairment in young adults. The increasing prevalence of MS underscores the critical need for innovative therapeutic approaches. Recent advances in neuroimmunology have highlighted the significant role of the gut microbiome in MS pathology, unveiling distinct alterations in patients' gut microbiota. Dysbiosis not only impacts gut-intrinsic processes but also influences the production of bacterial metabolites and hormones, which can regulate processes in remote tissues, such as the CNS. Central to this paradigm is the gut-brain axis, a bidirectional communication network linking the gastrointestinal tract to the brain and spinal cord. Via specific routes, bacterial metabolites and hormones can influence CNS-resident cells and processes both directly and indirectly. Exploiting this axis, novel therapeutic interventions, including pro- and prebiotic treatments, have emerged as promising avenues with the aim of mitigating the severity of MS. This review delves into the complex interplay between the gut microbiome and the brain in the context of MS, summarizing current knowledge on the key signals of cross-organ crosstalk, routes of communication, and potential therapeutic relevance of the gut microbiome. Moreover, this review places particular emphasis on elucidating the influence of these interactions on astrocyte functions within the CNS, offering insights into their role in MS pathophysiology and potential therapeutic interventions.

NFE2L1/Nrf1 serves as a potential therapeutical target for neurodegenerative diseases

The failure of the proper protein turnover in the nervous system is mainly linked to a variety of neurodegenerative disorders. Therefore, a better understanding of key protein degradation through the ubiquitin-proteasome system is critical for effective prevention and treatment of those disorders. The proteasome expression is tightly regulated by a CNC (cap'n'collar) family of transcription factors, amongst which the nuclear factor-erythroid 2-like bZIP factor 1 (NFE2L1, also known as Nrf1, with its long isoform TCF11 and short isoform LCR-F1) has been identified as an indispensable regulator of the transcriptional expression of the ubiquitin-proteasome system. However, much less is known about how the pivotal role of NFE2L1/Nrf1, as compared to its homologous NFE2L2 (also called Nrf2), is translated to its physiological and pathophysiological functions in the nervous system insomuch as to yield its proper cytoprotective effects against neurodegenerative diseases. The potential of NFE2L1 to fulfill its unique neuronal function to serve as a novel therapeutic target for neurodegenerative diseases is explored by evaluating the hitherto established preclinical and clinical studies of Alzheimer's and Parkinson's diseases. In this review, we have also showcased a group of currently available activators of NFE2L1, along with an additional putative requirement of this CNC-bZIP factor for healthy longevity based on the experimental evidence obtained from its orthologous SKN1-A in Caenorhabditis elegans.

Tr1 cell-mediated protection against autoimmune disease by intranasal administration of a fusion protein targeting cDC1 cells

Curative therapies against autoimmune diseases are lacking. Indeed, most of the currently available treatments are only targeting symptoms. We have developed a novel strategy for a therapeutic vaccine against autoimmune diseases based on intranasal administration of a fusion protein tolerogen, which consists of a mutant, enzymatically inactive, cholera toxin A1 (CTA1)-subunit genetically fused to disease-relevant high-affinity peptides and a dimer of D-fragments from protein A (DD). The CTA1 R7K mutant - myelin oligodendrocyte glycoprotein (MOG), or proteolipid protein (PLP) - DD (CTA1R7K-MOG/PLP-DD) fusion proteins effectively reduced clinical symptoms in the experimental autoimmune encephalitis model of multiple sclerosis. The treatment induced Tr1 cells, in the draining lymph node, which produced interleukin (IL)-10 and suppressed effector clusters of differentiation 4+ T-cell responses. This effect was dependent on IL-27 signaling because treatment was ineffective in bone marrow chimeras lacking IL-27Ra within their hematopoietic compartment. Single-cell RNA sequencing of dendritic cells in draining lymph nodes demonstrated distinct gene transcriptional changes of classic dendritic cells 1, including enhanced lipid metabolic pathways, induced by the tolerogenic fusion protein. Thus, our results with the tolerogenic fusion protein demonstrate the possibility to vaccinate and protect against disease progression by reinstating tolerance in multiple sclerosis and other autoimmune diseases.

Gut immune cell trafficking: inter-organ communication and immune-mediated inflammation

Immune cell trafficking is a complex and tightly regulated process that is indispensable for the body's fight against pathogens. However, it is also increasingly acknowledged that dysregulation of cell trafficking contributes to the pathogenesis of immune-mediated inflammatory diseases (IMIDs) in gastroenterology and hepatology, such as inflammatory bowel disease and primary sclerosing cholangitis. Moreover, altered cell trafficking has also been implicated as a crucial step in the immunopathogenesis of other IMIDs, such as rheumatoid arthritis and multiple sclerosis. Over the past few years, a central role of the gut in mediating these disorders has progressively emerged, and the partly microbiota-driven imprinting of particular cell trafficking phenotypes in the intestine seems to be crucially involved. Therefore, this Review highlights achievements in understanding immune cell trafficking to, within and from the intestine and delineates its consequences for immune-mediated pathology along the gut-liver, gut-joint and gut-brain axes. We also discuss implications for current and future therapeutic approaches that specifically interfere with homing, retention, egress and recirculation of immune cells.

Regulatory T Cell-Based Immunotherapy

CD4+CD25+ regulatory T (Treg) cells expressing the forkhead box transcription factor Foxp3 have a vital function in the maintenance of immune homeostasis and the prevention of fatal multi-organ autoimmunity throughout life. In the last decade, Foxp3+ Treg cells have raised the hope for novel cell-based therapies to achieve tolerance in clinical settings of unwanted immune responses such as autoimmunity and graft rejection. Conceptually, the antigen-specific enhancement of Treg cell function is of particular importance because such strategies will minimize the requirements for pharmaceutical immunosuppression, sparing desired protective host immune responses to infectious and malignant insults. This chapter discusses current concepts of Treg cell-based immunotherapy with particular emphasis on antigen-specific Treg cell induction from conventional CD4+ T cells to deal with organ-specific autoimmunity.

Targeted antigen delivery to DEC-205⁺ dendritic cells for tolerogenic vaccination

Dendritic cells (DCs) and Foxp3-expressing CD4⁺ regulatory T (Treg) cells play non-redundant roles in the maintenance of peripheral tolerance to self-antigens, thereby preventing fatal autoimmunity. A common hallmark of intra- and extra-thymic Treg cell lineage commitment is the induction of Foxp3 expression as a consequence of appropriate T cell receptor engagement with MHC class II:agonist ligand. It has now become increasingly clear that agonist ligand presentation by immature DCs in the steady state induces T cell tolerance by both recessive and dominant mechanisms, rather than promoting productive T helper cell responses. In this context, the ability of steady-state DCs to promote the extrathymic conversion of initially naïve CD4⁺Foxp3⁻ T cells into Foxp3⁺ Treg cells is of particular interest as it provides novel perspectives to enhance antigen-specific Treg cell function in clinical settings of unwanted immunity, such as β-cell autoimmunity.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.

Promoting tolerance to proteolipid protein-induced experimental autoimmune encephalomyelitis through targeting dendritic cells

In T cell-mediated autoimmune diseases, self-reactive T cells with known antigen specificity appear to be particularly promising targets for antigen-specific induction of tolerance without compromising desired protective host immune responses. Several lines of evidence suggest that delivery of antigens to antigen-presenting dendritic cells (DCs) in the steady state (i.e., to immature DCs) may represent a suitable approach to induce antigen-specific T-cell tolerance peripherally. Here, we report that anti-DEC205-mediated delivery of the self-peptide proteolipid protein (PLP)139-151 to DCs ameliorated clinical symptoms in the PLP-induced SJL model of experimental autoimmune encephalomyelitis. Splenocytes from treated mice were anergized to PLP139-151, and IL-17 secretion was markedly reduced. Moreover, we show directly, using transgenic CD4(+) Vβ6(+) TCR T cells specific for PLP139-151, that, under the conditions of the present experiments, these cells also became anergic. In addition, evidence for a CD4(+) T cell-mediated suppressor mechanism was obtained.

Carcinoembryonic antigen-related cell adhesion molecule 1 modulates experimental autoimmune encephalomyelitis via an iNKT cell-dependent mechanism

Carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) is a CEA family member that has been reported to have an important role in the regulation of Th1-mediated colitis. In this study, we examined the role of CEACAM1 in an animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Treatment of C57BL/6J mice with CEACAM1-Fc fusion protein, a homophilic ligand of CEACAM1, inhibited the severity of EAE and reduced myelin oligodendrocyte glycoprotein-derived peptide (MOG(35-55))-reactive interferon-gamma and interleukin-17 production. In contrast, treatment of these animals with AgB10, an anti-mouse CEACAM1 blocking monoclonal antibody, generated increased severity of EAE in association with increased MOG(35-55)-specific induction of both interferon-gamma and interleukin-17. These results indicated that the signal elicited through CEACAM1 ameliorated EAE disease severity. Furthermore, we found that there was both a rapid and enhanced expression of CEACAM1 on invariant natural killer T cells after activation. The effect of CEACAM1-Fc fusion protein and anti-CEACAM1 mAb on both EAE and MOG(35-55)-reactive cytokine responses were abolished in invariant natural killer T cell-deficient Jalpha18(-/-) mice. Taken together, the ligation of CEACAM1 negatively regulates the severity of EAE by reducing MOG(35-55)-specific induction of both interferon-gamma and interleukin-17 via invariant natural killer T cell-dependent mechanisms.

Clinical, pathological, and immunologic aspects of the multiple sclerosis model in common marmosets (Callithrix jacchus)

The efficacy of many new immunomodulatory therapies for multiple sclerosis (MS) patients has often been disappointing, reflecting our incomplete understanding of this enigmatic disease. There is a growing awareness that, at least in part, there may be limited applicability to the human disease of results obtained in the widely studied MS model experimental autoimmune encephalomyelitis in rodents. This review describes the experimental autoimmune encephalomyelitis model developed in a small neotropical primate, the common marmoset (Callithrix jacchus). The model has features including clinicopathologic correlation patterns, lesion heterogeneity, immunologic mechanisms, and disease markers that more closely mimic the human disease. Several unique features of experimental autoimmune encephalomyelitis in marmosets, together with their outbred nature and close genetic and immunologic similarities to humans, create an attractive experimental model for translational research into MS, particularly for the preclinical evaluation of new biologic therapeutic molecules that cannot be investigated in rodents because of their species specificity. Moreover, this model provides new insights into possible pathogenetic mechanisms in MS.

Alteration of the somatostatinergic system in the striatum of rats with acute experimental autoimmune encephalomyelitis

To date, the neurochemical basis underlying the motor and cognitive deficits described in patients with multiple sclerosis (MS) is unclear. Since the neuropeptide somatostatin (SRIF) and the striatum have been implicated in movement control and implicit memory, the aim of this study was to analyze the striatal somatostatinergic system in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). Female Lewis rats were immunized with an emulsion containing myelin basic protein (MBP) in complete Freund's adjuvant to induce the disease. The animals were decapitated when limp tail (grade 1) or severe hind limb paralysis (grade 3) was observed. Acute EAE in grade 3 did not modify striatal somatostatin-like immunoreactivity (SRIF-LI) content but decreased the overall SRIF receptor density, without affecting the apparent affinity, in the rat striatal membranes. A selective reduction in the protein levels of the SRIF receptor subtype sst2, analyzed by Western blotting, was detected in the EAE rats, which correlated with decreased sst2 mRNA levels. The expression of the receptor subtypes sst1, sst3 or sst4 was unaltered by the disease. The decrease in the SRIF receptor density was accompanied by an attenuated capacity of SRIF to inhibit both basal and forskolin-stimulated adenylyl cyclase activity. No significant changes, however, were found in the protein levels of Gi proteins (G(ialpha1), G(ialpha2) or G(ialpha3)) nor in those of the G-protein-coupled receptor kinase subtypes GRK2, GRK5 or GRK6. Acute EAE in grade 1 did not modify any of the parameters studied. In conclusion, these data demonstrate that acute EAE, in grade 3, disrupts the rat striatal SRIF receptor-effector system. These findings provide new insight into the molecular basis of EAE which might contribute to a better understanding of multiple sclerosis in humans.

T cells traffic from brain to cervical lymph nodes via the cribroid plate and the nasal mucosa

Although drainage pathways of soluble antigens from brain to cervical lymph nodes have been well established, there is no direct evidence for similar routes of leukocytes leaving the central nervous system. We developed a protocol allowing the cross-sectioning of an entire head-neck preparation while preserving the signal of the GFP. We monitored how GFP-expressing CD4 T lymphocytes injected into the entorhinal cortex after lesion or the lateral ventricle of unlesioned C57/bl6 mice reach cervical lymph nodes. Irrespective of the injection site, we demonstrate their passage through the cribroid plate, appearance in the nasal mucosa, and specific accumulation in one of the cervical lymph nodes.

Purely systemically active anti-inflammatory treatments are adequate to control multiple sclerosis

Collective evidence supports the notion that multiple sclerosis is principally an autoimmune disease. Much of it stems from models of experimental autoimmune encephalomyelitis, generated by inoculation of animals with central nervous system antigens such as MBP, PLP, S100 and MOG or peptides thereof. Different ways of immunization and different animal species and strains mirror different aspects of the neuropathology of multiple sclerosis, such as inflammation, demyelination or axonal damage, and reflect different clinical courses. In all these models, the first immune reactions take place in lymph nodes from which immune cells migrate into the circulation and then to the central nervous system. Adoptive transfer of myelin-reactive T cells from these animals produces pathology and disease in the central nervous system of naïve healthy recipients. In the human disease, autoreactive T and B cells specific for a variety of central antigens are present in the immune repertoire. These cells appear to be activated in the periphery through a number of mechanisms which causes them to home to the central nervous system. Contact with the local immune circuitry of the brain stimulates clonal expansion of autoreactive T cells, initiating a cascade of immuno-inflammatory events in situ. Numerous ways of disrupting this complex sequence of events, either by non-specific immunosuppression or by targeting specific checkpoints, abrogate or ameliorate disease in animal models. All approved disease-modifying drugs have an impact on components of the systemic immune compartment. All have been shown to reduce the number of gadolinium-enhancing T1 lesions observed with magnetic resonance imaging, an index of acute inflammatory invasion of the central nervous system.

Targeted overexpression of IL-18 binding protein at the central nervous system overrides flexibility in functional polarization of antigen-specific Th2 cells

The current study shows that functional polarization of Ag-specific CD4(+) Th2 cells entering the CNS during the accelerating phase of experimental autoimmune encephalomyelitis is flexible and dependent on the cytokine milieu there. Thus, targeted cell/gene therapy by Ag-specific T cells overexpressing IL-18 binding protein overrides this flexibility and induces infectious spread of T cell tolerance. Using a congenic system, we demonstrated that at this time, Ag-specific Th2 cells accumulate at the CNS but then arrest of IL-4 production. A manipulation of targeted cell/gene delivery was then used to detect whether this function is dependent on the cytokine milieu there. Targeted overexpression of IL-18 binding protein, a natural inhibitor of IL-18, restored the ability of these Ag-specific Th2 cells to produce IL-4 and subsequently induce protective spread of Th2 polarization. These findings not only suggest a novel way of therapy, but also explain why shifting the balance of Ag-specific T cells toward Th2 suppresses ongoing experimental autoimmune encephalomyelitis, whereas a direct transfer of these cells is ineffective.

Loss of T-bet, but not STAT1, prevents the development of experimental autoimmune encephalomyelitis

The transcription factors signal transducer and activator of transcription (STAT)1 and T-bet control the differentiation of interferon (IFN)-γ–producing T helper type (Th)1 cells. Here we compare the role of T-bet and STAT1 in the initiation and regulation of experimental autoimmune encephalomyelitis (EAE), a disease initiated by Th1 cells. T-bet–deficient mice immunized with myelin oligodendrocyte glycoprotein (MOG) were resistant to the development of EAE. This protection was also observed when T-bet^−/− mice were crossed to the MOG-specific 2D2 T cell receptor transgenic strain. In contrast, although T-bet is downstream of STAT1, STAT1^−/− mice were highly susceptible to EAE and developed more severe and accelerated disease with atypical neuropathologic features. The function of T-bet was dominant as mice deficient in both T-bet and STAT1 were also protected from EAE. CD4⁺ CD25⁺ regulatory T cells from these two mice strains were fully competent and do not explain the difference in disease susceptibility. However, enhanced EAE in STAT1^−/− mice was associated with continued generation of IFN-γ–producing Th1 cells and up-regulation of selective chemokines responsible for the increased recruitment of macrophages and neutrophils in the central nervous system. Although the two transcription factors, STAT1 and T-bet, both induce IFN-γ gene transcription, our results demonstrate marked differences in their function in regulating pathogenic Th1 cell responses.

Modulation of experimental autoimmune encephalomyelitis by administration of cells expressing antigenic peptide covalently linked to MHC class II

The MHC class II molecule RT1Bl covalently linked with gpMBP-71-90 was expressed in P80 cells (mouse mastocytoma P815 expressing rat-CD80) and i.v. injection ameleriorated active and adoptive transfer (AT) experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Spinal cord of animals with AT-EAE showed significant increase of apoptotic T-cells at maximum of disease after injection of P80-RT1Bl-MBP-71-90 but not of P80RT1Bl or P80 cells. The data demonstrate a possible therapeutic effect on EAE by provision of T-cell receptor (TCR) and costimulatory signals by genetically engineered antigen presenting cells (APC) and suggest induction of T-cell apoptosis as important mechanism of action.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Neuropeptide Y (NPY) suppresses experimental autoimmune encephalomyelitis: NPY1 receptor-specific inhibition of autoreactive Th1 responses in vivo

Prior studies have revealed that the sympathetic nervous system regulates the clinical and pathological manifestations of experimental autoimmune encephalomyelitis (EAE), an autoimmune disease model mediated by Th1 T cells. Although the regulatory role of catecholamines has been indicated in the previous works, it remained possible that other sympathetic neurotransmitters like neuropeptide Y (NPY) may also be involved in the regulation of EAE. Here we examined the effect of NPY and NPY receptor subtype-specific compounds on EAE, actively induced with myelin oligodendrocyte glycoprotein 35-55 in C57BL/6 mice. Our results revealed that exogenous NPY as well as NPY Y(1) receptor agonists significantly inhibited the induction of EAE, whereas a Y(5) receptor agonist or a combined treatment of NPY with a Y(1) receptor antagonist did not inhibit signs of EAE. These results indicate that the suppression of EAE by NPY is mediated via Y(1) receptors. Furthermore, treatment with the Y(1) receptor antagonist induced a significantly earlier onset of EAE, indicating a protective role of endogenous NPY in the induction phase of EAE. We also revealed a significant inhibition of myelin oligodendrocyte glycoprotein 35-55-specific Th1 response as well as a Th2 bias of the autoimmune T cells in mice treated with the Y(1) receptor agonist. Ex vivo analysis further demonstrated that autoimmune T cells are directly affected by NPY via Y(1) receptors. Taken together, we conclude that NPY is a potent immunomodulator involved in the regulation of the Th1-mediated autoimmune disease EAE.

Microglia are activated to become competent antigen presenting and effector cells in the inflammatory environment of the Theiler's virus model of multiple sclerosis

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is a well-characterized murine model of the chronic-progressive form of human multiple sclerosis (MS) characterized by the activation of myelin-specific autoreactive CD4 Th1 cells via epitope spreading. To gain an understanding of the potential role of central nervous system (CNS)-resident cells in the presentation of endogenous myelin epitopes, we determined the individual antigen presentation and effector potential of resident microglia vs. infiltrating macrophages in the CNS of mice with ongoing TMEV-IDD by performing functional analysis of these populations separated to high purity by flow cytometric sorting based on their level of CD45 expression. Unlike microglia from nai;ve mice, peptide-pulsed CD45(lo) microglia isolated at the onset of clinical disease were as efficient as CNS-infiltrating CD45(hi) macrophages in activating proliferation and IFN-gamma production by myelin-peptide specific Th1 cells. In contrast, during the chronic stages of TMEV-IDD, CNS-infiltrating macrophages were more highly activated than the resident microglia as reflected both by higher expression of cell surface molecules associated with APC function and enhanced functional ability of spinal cord-infiltrating macrophages to stimulate T cell proliferation in vitro. Interestingly, both microglia and infiltrating macrophages expressed similar profiles of effector molecules such as IL-1, IL-6, IL-12 p40, TNF-alpha, and iNOS. Collectively, this is the first report comparing the antigen-presenting phenotype and function of microglia and infiltrating macrophages in a virus-induced model of CNS demyelination demonstrating that the resident microglia are capable APCs and may play an important role in antigen presentation at the onset of clinical disease and contribute to effector myelin destruction.

Detrimental and beneficial effects of injury-induced inflammation and cytokine expression in the nervous system

Lesions in the nervous system induce rapid activation of glial cells and under certain conditions additional recruitment of granulocytes, T-cells and monocytes/macrophages from the blood stream triggered by upregulation of cell adhesion molecules, chemokines and cytokines. Hematogenous cell infiltration is not restricted to infectious or autoimmune disorders of the nervous system, but also occurs in response to cerebral ischemia and traumatic lesions. Neuroinflammation can cause neuronal damage, but also confers neuroprotection. Granulocytes occlude vessels during reperfusion after transient focal ischemia, while the functional role of T-cells and macrophages in stroke development awaits further clarification. After focal cerebral ischemia neurotoxic mediators released by microglia such as the inducible nitric oxide synthase (leading to NO synthesis) and the cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are upregulated prior to cellular inflammation in the evolving lesion and functionally contribute to secondary infarct growth as revealed by numerous pharmacological experiments and by use of transgenic animals. On the other hand, cytokine induction remote from ischemic lesions involves NMDA-mediated signalling pathways and confers neuroprotection. After nerve injury T cells can rescue CNS neurons. In the peripheral nervous system neuroinflammation is a prerequisite for successful regeneration that is impeded in the CNS. In conclusion, there is increasing evidence that neuroinflammation represents a double edged sword. The opposing neurotoxic and neuroprotective properties of neuroinflammation during CNS injury provide arich and currently unexplored set of research problems.

Analysis of immunoregulatory T-helper cell subsets in patients with multiple sclerosis: relapsing-progressive course correlates with enhanced T H1, relapsing-remitting course with enhanced T H0 reactivity

In this study, we analysed the recall antigen-induced cytokine production by peripheral blood mononuclear cells (PBMC) from 31 patients with multiple sclerosis (MS) with a relapsing-remitting (rr) and a relapsing-progressive (rp) course and from 40 healthy controls. Cells were stimulated with purified protein derivative (PPD; type 1 response) and tetanus toxoid (TT; type 2 response). Cytokines were determined in the supernatants by ELISA. One of the interesting findings was that healthy controls showed more frequently an IL-5 production after incubation with TT than MS-patients (68% vs.37%; p<0.01), while the type 1 reactivity was only slightly enhanced in MS patients as compared to the controls. However, within the MS patients, there was a significant difference in the incidence of the type 1 reactivity comparing patients with an rp and an rr course (60% vs. 24%; p<0.05). Furthermore, the frequency of a type 0 profile (simultaneous PPD-induced IFN-gamma and TT-induced IL-5 production) was fourfold higher in rr than in the rp patients (43% vs. 10%, p<0.05). In vitro analysis of cytokine profiles in MS could therefore be an interesting approach to evaluate the prognosis of MS (rr vs. rp) already at the beginning of the disease. Thus, it seems that the presence of a type 0 profile is a valid indicator for a favorable course, while a type 1 profile is rather associated with rp MS.

Tr1 cell-dependent active tolerance blunts the pathogenic effects of determinant spreading

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease of the CNS. The current study shows that even in an acute episode of disease the autoimmune response spreads from one determinant on myelin basic protein (MBP) to the other linked determinant and that this spread plays a functional role in the pathogenesis of disease. The soluble form of each determinant could be used to induce Ag-specific T cell tolerance and reverse an ongoing disease. We show that the rapid effect of soluble peptide therapy is due to repolarization of autoimmune T cells undergoing activation. We suggest that at least two different types of regulatory T cells participate in the induction of active tolerance. The first, yet to be fully characterized, functions in an IL-4-dependent manner. The second produces high levels of IL-10 and low levels of IL-4 (Tr1). We bring about completing evidence showing that these Tr1 cells play a pivotal role in the regulation of T cell tolerance during determinant spread and that soluble peptide therapy with the determinant to which the autoimmune response spreads amplifies a de novo regulatory mechanism aimed to reduce the pathological consequences of determinant spreading.

Marmoset fine B cell and T cell epitope specificities mapped onto a homology model of the extracellular domain of human myelin oligodendrocyte glycoprotein

Aberrant association of autoantibodies with myelin oligodendrocyte glycoprotein (MOG), an integral membrane protein of the central nervous system (CNS) myelin, has been implicated in the pathogenesis of multiple sclerosis (MS). Sensitization of nonhuman primates (Callithrix jacchus marmosets) against the nonglycosylated, recombinant N-terminal domain of rat MOG (residues 1-125) reproduces an MS-like disease in which MOG-specific autoantibodies directly mediate demyelination. To assess the interrelationship between MOG structure and the induction of autoimmune CNS diseases and to enable structure-based rational design of therapeutics, a homology model of human MOG(2-120) was constructed based on consensus residues found in immunoglobulin superfamily variable-type proteins having known structures. Possible sites for posttranslational modifications and dimerization have also been identified and analyzed. The B cell and T cell epitopes have been identified in rat MOG-immunized marmosets, and these sequences are observed to map primarily onto accessible regions in the model, which may explain their ability to generate potent antibody responses.

Functional role of epitope spreading in the chronic pathogenesis of autoimmune and virus-induced demyelinating diseases

These results support a model of epitope spreading (Figure 4) wherein localized virus-specific T cell-mediated inflammatory processes lead to the recruitment/activation of CNS-resident APCs which can serve both as effector cells for myelin destruction and as APCs which efficiently process/present endogenous self epitopes to autoreactive T cells. Thus, inflammatory responses induced by viruses which trigger pro-inflammatory Th1 responses and have the ability to persist in genetically susceptible hosts, may lead to chronic organ-specific autoimmune disease via epitope spreading. Regardless of the specificity of the T cells (myelin peptides in R-EAE or TMEV epitopes in TMEV-IDD) responsible for initiating myelin destruction, epitope spreading plays an important contributory role in the chronic disease process in genetically susceptible SJL mice. Epitope spreading has obvious important implications to the design of antigen-specific therapies for the potential treatment of MS and other autoimmune diseases. This process indicates that autoimmune diseases are evolving pathologies and that the specificity of the effector autoantigen-specific T cells varies during the chronic disease process.

The major histocompatibility complex influences the ethiopathogenesis of MS-like disease in primates at multiple levels

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease primarily affecting the central nervous system. Of the many candidate polymorphic major histocompatibility complex (MHC) and non-MHC genes contributing to disease susceptibility, including those encoding effector (cytokines and chemokines) or receptor molecules within the immune system (MHC, TCR, Ig or FcR), human leukocyte antigen (HLA) class II genes have the most significant influence. In this article we put forward the hypothesis that the influence of HLA genes on the risk to develop MS is actually the sum of multiple antigen presenting cell (APC) and T-cell interactions involving HLA class I and class II molecules. This article will also discuss that, because of the genetic and immunologic similarity to humans, autoimmune models of MS in non-human primates are the experimental models "par excellence" to test this hypothesis.

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.

Direct activation of innate and antigen-presenting functions of microglia following infection with Theiler's virus

Microglia are resident central nervous system (CNS) macrophages. Theiler's murine encephalomyelitis virus (TMEV) infection of SJL/J mice causes persistent infection of CNS microglia, leading to the development of a chronic-progressive CD4(+) T-cell-mediated autoimmune demyelinating disease. We asked if TMEV infection of microglia activates their innate immune functions and/or activates their ability to serve as antigen-presenting cells for activation of T-cell responses to virus and endogenous myelin epitopes. The results indicate that microglia lines can be persistently infected with TMEV and that infection significantly upregulates the expression of cytokines involved in innate immunity (tumor necrosis factor alpha, interleukin-6 [IL-6], IL-18, and, most importantly, type I interferons) along with upregulation of major histocompatibility complex class II, IL-12, and various costimulatory molecules (B7-1, B7-2, CD40, and ICAM-1). Most significantly, TMEV-infected microglia were able to efficiently process and present both endogenous virus epitopes and exogenous myelin epitopes to inflammatory CD4(+) Th1 cells. Thus, TMEV infection of microglia activates these cells to initiate an innate immune response which may lead to the activation of naive and memory virus- and myelin-specific adaptive immune responses within the CNS.

Cell surface expression of the 300 kDa mannose-6-phosphate receptor by activated T lymphocytes

Phosphosugars, such as mannose-6-phosphate (M6P), have been shown previously to display anti-inflammatory properties, notably inhibition of experimental autoimmune encephalomyelitis (EAE) and adjuvant-induced arthritis in rats. It has been proposed that M6P exerts its anti-inflammatory effect by displacing lysosomal enzymes, which are involved in T-cell extravasation into inflammatory sites, from the 300 kDa mannose-6- phosphate receptor (MPR-300) on the surface of T cells. If this model is correct MPR-300 should be selectively expressed on the surface of activated T cells, as T cell entry into the central nervous system in EAE depends on the T cells being in an activated state. Thus, the present study examines whether cell surface expression of MPR-300 by T lymphocytes correlates with their state of activation and whether T cells in inflammatory sites express the receptor. Flow cytometric studies showed MPR-300 to be absent from the surface of unstimulated rat T cells isolated from peripheral blood and lymphoid tissues, and T cells resident within the peritoneal cavity. In contrast, MPR-300 was expressed on activated T cells derived from an inflammatory peritoneal exudate. In vitro studies demonstrated transient expression of MPR-300 on the surface of splenic T cells following stimulation with Con A. MPR-300 was also induced on T-cell lines by antigen stimulation. These data demonstrate that T cells in inflammatory sites express MPR-300 on their surface and activation of T lymphocytes induces cell surface expression of MPR-300. Such findings are consistent with the hypothesis that cell surface MPR-300 is required for the entry of T cells into inflammatory sites.

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.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Toxic effector molecules in the pathogenesis of immune-mediated disorders of the central nervous system

A growing body of evidence supports the notion that inflammatory reactions in the central nervous system (CNS) are not only restricted to established immune mediated disorders, such as multiple sclerosis, but also contribute to the pathogenesis of Alzheimer's disease and other types of neurodegenerative disorders. The biological roles of toxic mediators, such as nitric oxide, reactive oxygen species, as well as complement and proteases in the genesis of inflammatory reactions in the CNS are reviewed within the context of demyelination and neuronal damage.

Molecular mechanisms of high-dose antigen therapy in experimental autoimmune encephalomyelitis: rapid induction of Th1-type cytokines and inducible nitric oxide synthase

High-dose Ag administration induces apoptotic death of autoreactive T cells and is an effective therapy of experimental autoimmune diseases of the nervous system. To explore the role of cytokines in Ag-specific immunotherapy, we analyzed mRNA induction and protein expression for the proinflammatory cytokines TNF-alpha and IFN-gamma, the anti-inflammatory cytokine IL-10, and the cytokine-inducible NO synthase (iNOS) during high-dose Ag therapy of adoptive transfer experimental autoimmune encephalomyelitis (AT-EAE) in the Lewis rat. Using semiquantitative and competitive RT-PCR, we found 5- to 6-fold induction of TNF-alpha mRNA and 3-fold induction of IFN-gamma mRNA in the spinal cord that occurred within 1 h after i.v. injection of Ag and was accompanied by a 2-fold increase of iNOS mRNA. Both IFN-gamma and iNOS mRNA remained elevated for at least 6 h, whereas TNF-alpha mRNA was already down-regulated 6 h after Ag injection. A comparable time course was found for circulating serum levels of TNF-alpha and IFN-gamma. IL-10 mRNA levels did not change significantly following Ag injection. Neutralization of TNF-alpha by anti-TNF-alpha antiserum in vivo led to a significant decrease in the rate of T cell and oligodendrocyte apoptosis induced by high-dose Ag administration, but did not change the beneficial clinical effect of Ag therapy. Our data suggest profound activation of proinflammatory but not of anti-inflammatory cytokine gene expression by high-dose Ag injection. Functionally, TNF-alpha contributes to increased apoptosis of both autoaggressive T cells and oligodendrocytes in the target organ and may thereby play a dual role in this model of Ag-specific therapy of CNS autoimmune diseases.

Temporal development of autoreactive Th1 responses and endogenous presentation of self myelin epitopes by central nervous system-resident APCs in Theiler's virus-infected mice

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease is a chronic-progressive, immune-mediated CNS demyelinating disease and a relevant model of multiple sclerosis. Myelin destruction is initiated by TMEV-specific CD4(+) T cells targeting persistently infected CNS-resident APCs leading to activation of myelin epitope-specific CD4(+) T cells via epitope spreading. We examined the temporal development of virus- and myelin-specific T cell responses and acquisition of virus and myelin epitopes by CNS-resident APCs during the chronic disease course. CD4(+) T cell responses to virus epitopes arise within 1 wk after infection and persist over a >300-day period. In contrast, myelin-specific T cell responses are first apparent approximately 50-60 days postinfection, appear in an ordered progression associated with their relative encephalitogenic dominance, and also persist. Consistent with disease initiation by virus-specific CD4(+) T cells, CNS mononuclear cells from TMEV-infected SJL mice endogenously process and present virus epitopes throughout the disease course, while myelin epitopes are presented only after initiation of myelin damage (>50-60 days postinfection). Activated F4/80(+) APCs expressing high levels of MHC class II and B7 costimulatory molecules and ingested myelin debris chronically accumulate in the CNS. These results suggest a process of autoimmune induction in which virus-specific T cell-mediated bystander myelin destruction leads to the recruitment and activation of infiltrating and CNS-resident APCs that process and present endogenous myelin epitopes to autoreactive T cells in a hierarchical order.

Combined TUNEL and double immunofluorescent labeling for detection of apoptotic mononuclear phagocytes in autoimmune demyelinating disease

Apoptosis is usually associated with genomic DNA fragmentation which can be detected in situ by the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) assay. We describe a combined TUNEL and double immunofluorescent labeling technique to determine the fate of inflammatory infiltrates and resident glial cells in the central nervous system following the onset of an autoimmune demyelinating disease such as experimental allergic encephalomyelitis (EAE) in rats. Anti-digoxigenin (anti-DIG) antibody conjugated with 7-amino-4-methylcoumarin-3-acetic acid (AMCA) emitting blue fluorescence was used to detect apoptotic cell DNA, which was already labeled by modified TUNEL using alkali-stable DIG-11-dUTP. Anti-mouse IgG secondary antibody conjugated with Texas Red emitting red fluorescence was used to detect anti-rat CD11b primary antibody (clone OX-42) directed to the surface antigen of mononuclear phagocytes including microglia. Using this technique, we detected apoptotic mononuclear phagocytes (co-labeled with blue and red fluorescences) in the spinal cord sections of rats with EAE.

Shaping of the autoreactive T-cell repertoire by a splice variant of self protein expressed in thymic epithelial cells

Intrathymic expression of tissue-specific self antigens may be involved in immunological tolerance and protection from autoimmune disease. We have analyzed the role of T-cell tolerance to proteolipid protein (PLP), the main protein of the myelin sheath, in susceptibility to experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. Intrathymic expression of PLP was largely restricted to the shorter splice variant, DM20. Expression of DM20 by thymic epithelium was sufficient to confer T-cell tolerance to all epitopes of PLP in EAE-resistant C57BL/6 mice. In contrast, the major T-cell epitope in SJL/J mice was only encoded by the central nervous system-specific exon of PLP, but not by thymic DM20. Thus, lack of tolerance to this epitope offers an explanation for the exquisite susceptibility of SJL/J mice to EAE. As PLP expression in the human thymus is also restricted to the DM20 isoform, these findings have implications for selection of the autoimmune T-cell repertoire in multiple sclerosis.

Autoimmune maintenance and neuroprotection of the central nervous system

The genesis of immune privilege high in the evolutionary tree suggests that immune privilege is necessary, if not advantageous for the progressive development of the CNS. Upon reaching a certain degree of complexity, it seems as if the CNS was obliged to restrain the immune system from penetrating the blood-brain barrier. CNS autoimmunity against myelin proteins is known to be a contributory factor in the pathophysiology of multiple sclerosis and in the animal model of experimental autoimmune encephalomyelitis (EAE) (Wekerle, 1993). Such autoimmunity has therefore been regarded as detrimental and hence obviously undesirable. However, recent findings in our laboratory suggest that T-cell autoimmunity to CNS self-antigens (Moalem et al., 1999), if expressed at the right time and the right place, can do much good in the CNS. We shall review the experiments briefly, and then discuss their implications for our understanding of immune privilege and CNS maintenance after injury.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood-brain barrier disruption: implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood-brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor alpha and IFN-gamma mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.

Endogenous presentation of self myelin epitopes by CNS-resident APCs in Theiler's virus-infected mice

The mechanisms underlying the initiation of virus-induced autoimmune disease are not well understood. Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a mouse model of multiple sclerosis, is initiated by TMEV-specific CD4(+) T cells targeting virally infected central nervous system-resident (CNS-resident) antigen-presenting cells (APCs), leading to chronic activation of myelin epitope-specific CD4(+) T cells via epitope spreading. Here we show that F4/80(+), I-A(s+), CD45(+) macrophages/microglia isolated from the CNS of TMEV-infected SJL mice have the ability to endogenously process and present virus epitopes at both acute and chronic stages of the disease. Relevant to the initiation of virus-induced autoimmune disease, only CNS APCs isolated from TMEV-infected mice with preexisting myelin damage, not those isolated from naive mice or mice with acute disease, were able to endogenously present a variety of proteolipid protein epitopes to specific Th1 lines. These results offer a mechanism by which localized virus-induced, T cell-mediated inflammatory myelin destruction leads to the recruitment/activation of CNS-resident APCs that can process and present endogenous self epitopes to autoantigen-specific T cells, and thus provide a mechanistic basis by which epitope spreading occurs.

The role of microglia and macrophages in the pathophysiology of the CNS

Microglia are a major ghal component of the central nervous system (CNS) and are extremely sessile. Only a subtype, the perivascular microglia, are regularly replaced from the bone marrow in adult animals. Microglia respond to virtually any, even minor pathological events in the CNS. In most pathological settings microglia are aided by infiltrating hematogenous macrophages. Upon activation microglia and macrophages share most phenotypical markers and can exert similar effector functions. After transection of a CNS fibre tract microglia are insufficiently activated and hematogenous macrophages do not significantly enter the degenerating nerve stump. Thereby myelin debris that contains neurite outgrowth inhibiting activity persists for long time. This is in sharp contrast to the peripheral nervous system in which hematogenous macrophages are rapidly recruited in response to axotomy and clear myelin debris allowing regrowth of axons from the proximal stump. However, CNS lesion paradigms with breakdown of the blood-brain barrier such as cerebral ischemia, brain abscesses and stab wounds elicit prompt microglial activation, macrophage recruitment and debris clearance. There is increasing evidence that microglia play an active part in degenerative CNS diseases. In Alzheimer's disease activated microglia appear to be involved in plaque formation. In experimental globoid cell dystrophy T-cell independent induction of major histocompatibility complex class II molecules on microglia accelerates demyelination. In autoimmune diseases microglia probably have dual functions. Microglia present antigen to infiltrating T cells and exert effector functions thereby locally augmenting immune responses. On the other hand, microglia have the capacity to downregulate T cell responses. In the human acquired immunodeficiency syndrome (AIDS) virus infected macrophages probably introduce the virus to the CNS and in concert with microglia are involved in the pathophysiology of the AIDS dementia complex.

Differential induction of interleukin-12, interleukin-18, and interleukin-1beta converting enzyme mRNA in experimental autoimmune encephalomyelitis of the Lewis rat

Experimental autoimmune encephalomyelitis (EAE) is a model of autoimmune central nervous system (CNS) disease that is mediated by autoreactive Th1 cells secreting the proinflammatory cytokine interferon (IFN)-gamma. Interleukin (IL)-12 in its heterodimeric p35/p40 isoform and the recently described cytokine IL-18 potently induce T cell production of IFN-gamma. Interleukin-1beta converting enzyme (ICE) is required to convert IL-18 precursor protein into its biologically active mature form. In this study, we used semiquantitative reverse transciptase-polymerase chain reaction to determine steady state levels of IL-12, IL-18, and ICE mRNA in the spinal cord of Lewis rats at different stages of EAE. In control rats, we found significant IL-18, ICE, and IL-12p35, but not IL-12p40 mRNA expression. IL-18 mRNA increased during the acute stage of EAE together with a marked induction of ICE mRNA. IL-12p35 mRNA levels did not change significantly throughout the course of EAE. Surprisingly, the peak expression of IL-12p40 mRNA was delayed by several days relative to the peak of T cell infiltration and IFN-gamma mRNA synthesis. Our data implicate the IL-18/ICE pathway in the amplification of Th1-mediated immune responses in the CNS but suggest a different, so far undefined role of endogenous IL-12 in the late effector phase of EAE.

Accumulation of passively transferred primed T cells independently of their antigen specificity following central nervous system trauma

The central nervous system (CNS) enjoys a unique relationship with the immune system. Under non-pathological conditions, T cells move through the CNS but do not accumulate there. CNS trauma has been shown to trigger a response to CNS self-antigens such as myelin basic protein (MBP). Here, we examined whether the injured CNS tissue undergoes changes that permit T cell accumulation. We found that injury to CNS white matter, such as the optic nerve, led to a transiently increased accumulation of T cells (between days 3 and 21). In Lewis rats with unilaterally injured optic nerves, systemic administration of passively transferred T cells recognizing either self-antigen (MBP) or non-self-antigen (ovalbumin) resulted in accumulation of the T cells in injured optic nerve, irrespective of their antigenic specificity. The effect of the T cells on the damaged nerve, the lack of selectivity in T cell accumulation and the mechanism underlying non-selective accumulation are discussed.