Specificity, magnitude, and kinetics of MOG-specific CD8+ T?cell responses during experimental autoimmune encephalomyelitis

A Pathogenic Role for CD8+ T Cells in a Spontaneous Model of Demyelinating Disease

Transgenic (Tg) mice that overexpress the costimulatory ligand B7.2/CD86 on microglia spontaneously develop a T cell-mediated demyelinating disease. Characterization of the inflammatory infiltrates in the nervous tissue revealed a predominance of CD8+ T cells, suggesting a prominent role of this T cell subset in the pathology. In this study, we show that the same neurological disease occurred in Tg mice deficient in the generation of CD4+ T cells, with an earlier time of onset. Analysis of the CD8+ T cell repertoire at early stage of disease revealed the presence of selected clonal expansions in the CNS but not in peripheral lymphoid organs. We further show that Tg animals deficient in IFN-gamma receptor expression were completely resistant to disease development. Microglia activation that is an early event in disease development is IFN-gamma dependent and thus appears as a key element in disease pathogenesis. Collectively, our data indicate that the spontaneous demyelinating disease in this animal model occurs as a consequence of an inflammatory response initiated through the activation of CNS-specific CD8+ T cells by Tg expression of B7.2 within the target organ. Thus, autoreactive CD8+ T cells can contribute directly to the pathogenesis of neuroinflammatory diseases such as multiple sclerosis.

Mast cells are required for optimal autoreactive T cell responses in a murine model of multiple sclerosis

Once considered to be of sole importance in allergy and parasitic infections, the role of mast cells in other pathologic and protective immune responses is becoming increasingly evident. We previously demonstrated that mast cells contribute to the severity of EAE, the rodent model of multiple sclerosis. Here we show that one mode of mast cell action is through effects on the autoreactive T cell response. Early indices of both peripheral CD4 and CD8 T cell activation, including IFN-gamma production and increases in CD44 and CD11a expression, are attenuated in mast cell-deficient (W/Wv) mice after myelin oligodendrocyte glycoprotein(35-55) priming when compared to WT animals. Reduced infiltrates of activated T cells in the central nervous system are also observed. Importantly, selective repletion of the mast cell compartment restores most T cell responses in the lymph nodes and the central nervous system, correlating with reconstitution of severe disease. The adoptive transfer of WT-derived encephalitogenic T cells results in significantly less severe disease in W/Wv recipients, indicating that mast cells also exert potent effects after the initial T cell response is generated. Our data provide the first in vivo evidence that mast cells can significantly influence T cell responses and suggest that mast cells exacerbate disease during both the inductive and effector phases.

The role of CD8+ T-cells in lesion formation and axonal dysfunction in multiple sclerosis

The etiology of multiple sclerosis (MS) remains unknown. However, both genetic and environmental factors play important roles in its pathogenesis. While demyelination of axons is a hallmark histological feature of MS, axonal and neuronal dysfunction may correlate better with clinical disability. All major immune cell types have been implicated in the pathogenesis of MS, with the CD4+ T-cells being the most commonly studied. In this review, we discuss the involvement of CD8+ T-cells in MS. In addition, we review the contribution of CD8+ T-cells to the pathogenesis of experimental autoimmune encephalitis (EAE) and Theiler's murine encephalomyelitis virus (TMEV) mouse models of MS, including the concept of CD8+ T-cell mediated axonal damage.

Antigen presentation in autoimmunity and CNS inflammation: how T lymphocytes recognize the brain

The central nervous system (CNS) is traditionally viewed as an immune privileged site in which overzealous immune cells are prevented from doing irreparable damage. It was believed that immune responses occurring within the CNS could potentially do more damage than the initial pathogenic insult itself. However, virtually every aspect of CNS tissue damage, including degeneration, tumors, infection, and of course autoimmunity, involves a significant cellular inflammatory component. While the blood-brain barrier (BBB) inhibits diffusion of hydrophilic (immune) molecules across brain capillaries, activated lymphocytes readily pass the endothelial layer of postcapillary venules without difficulty. In classic neuro-immune diseases such as multiple sclerosis or acute disseminated encephalomyelitis, it is thought that neuroantigen-reactive lymphocytes, which have escaped immune tolerance, now invade the CNS and are responsible for tissue damage, demyelination, and axonal degeneration. The developed animal model for these disorders, experimental autoimmune encephalomyelitis (EAE), reflects many aspects of the human conditions. Studies in EAE proved that auto-reactive encephalitogenic T helper (Th) cells are responsible for the onset of the disease. Th cells recognize their cognate antigen (Ag) only when presented by professional Ag-presenting cells in the context of major histocompatibility complex class II molecules. The apparent target structures of EAE immunity are myelinating oligodendrocytes, which are not capable of presenting Ag to invading encephalitogenic T cells. A compulsory third party is thus required to mediate between the attacking T cells and the myelin-expressing target. This review will discuss the recent advances in this field of research and we will discuss the journey of an auto-reactive T cell from its site of activation into perivascular spaces and further into the target tissue.

Deficient p75 low-affinity neurotrophin receptor expression does alter the composition of cellular infiltrate in experimental autoimmune encephalomyelitis in C57BL/6 mice

We have shown earlier that induction of experimental autoimmune encephalomyelitis (EAE)-a model for the human disease multiple sclerosis-in C57BL/6 wild-type mice resulted in the expression of the p75 low-affinity neurotrophin receptor (p75NTR) in endothelial cells in the CNS. In comparison to the clinical manifestation of EAE observed in wild-type C57BL/6 mice, C57BL/6 mice deficient for p75NTR (p75NTR knockout mice) developed a more severe or even lethal disease and concomitant increased levels of inflammation in the CNS. In order to elucidate the role of endothelial p75NTR in cellular infiltration under these pathological circumstances, we have performed a more detailed, quantitative examination of the composition of the cellular infiltrate invading the CNS in EAE wild-type and EAE p75NTR knockout mice. We compared spinal cords of EAE wild-type with those of EAE p75NTR knockout mice of the same clinical score (3.5) using immunohistochemical markers for the cell types present in the infiltratory cuffs in EAE: T-cells, B-cells, monocytes, microglia, resident and infiltrating macrophages and polymorphonuclear cells. Interestingly, we detected that the proportion of B-cells, cells of the monocyte-macrophage lineage and polymorphonuclear cells in the infiltratory cuff of EAE-p75NTR knockout mice was decreased at the account of the proportion of T-cells which appeared to be almost doubled in comparison to the EAE wild-type mice. The altered composition of the infiltrate in p75NTR deficient mice argues for an involvement of endothelial p75NTR in the interaction between the inflamed endothelium and the activated cells of the immune system, in particular the T-cells, in EAE.

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.

Autoreactive CD8+ T cells in multiple sclerosis: a new target for therapy?

Multiple sclerosis afflicts more than 1 million individuals worldwide and is widely considered to be an autoimmune disease. Traditionally, CD4(+) T helper cells have almost exclusively been held responsible for its immunopathogenesis, partly because certain MHC class II alleles clearly predispose for developing multiple sclerosis and also, because of their importance in inducing experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. However, several strategies that target CD4(+) T cells beneficially in EAE have failed to ameliorate disease activity in multiple sclerosis, and some have even triggered exacerbations. Recently, the potential importance of CD8(+) T cells has begun to emerge. Physiologically, CD8(+) T cells are essential for detecting and eliminating abnormal cells, whether infected or neoplastic. In multiple sclerosis, genetic associations with MHC class I alleles have now been established, and CD8(+) as well as CD4(+) T cells have been found to invade and clonally expand in inflammatory central nervous system plaques. Recent animal models induced by CD8(+) T cells show interesting similarities to multiple sclerosis, in particular, in lesion distribution (more inflammation in the brain relative to the spinal cord), although not all of the features of the human disease are recapitulated. Here we outline the arguments for a possible role for CD8(+) T cells, a lymphocyte subset that has long been underrated in multiple sclerosis and should now be considered in new therapeutic approaches.