Identification of a novel T cell epitope of human proteolipid protein (residues 40-60) recognized by proliferative and cytolytic CD4+ T cells from multiple sclerosis patients

Mimicking the brain: Epstein-Barr virus and foreign agents as drivers of neuroimmune attack in multiple sclerosis

T cells have an essential role in adaptive immunity against pathogens and cancer, but failure of thymic tolerance mechanisms can instead lead to escape of T cells with the ability to attack host tissues. Multiple sclerosis (MS) occurs when structures such as myelin and neurons in the central nervous system (CNS) are the target of autoreactive immune responses, resulting in lesions in the brain and spinal cord which cause varied and episodic neurological deficits. A role for autoreactive T cell and antibody responses in MS is likely, and mounting evidence implicates Epstein-Barr virus (EBV) in disease mechanisms. In this review we discuss antigen specificity of T cells involved in development and progression of MS. We examine the current evidence that these T cells can target multiple antigens such as those from pathogens including EBV and briefly describe other mechanisms through which viruses could affect disease. Unravelling the complexity of the autoantigen T cell repertoire is essential for understanding key events in the development and progression of MS, with wider implications for development of future therapies.

Autoimmunity in narcolepsy

PURPOSE OF REVIEW

Summarize the recent findings in narcolepsy focusing on the environmental and genetic risk factors in disease development.

RECENT FINDINGS

Both genetic and epidemiological evidence point towards an autoimmune mechanism in the destruction of orexin/hypocretin neurons. Recent studies suggest both humoral and cellular immune responses in the disease development.

SUMMARY

Narcolepsy is a severe sleep disorder, in which neurons producing orexin/hypocretin in the hypothalamus are destroyed. The core symptoms of narcolepsy are debilitating, extreme sleepiness, cataplexy, and abnormalities in the structure of sleep. Both genetic and epidemiological evidence point towards an autoimmune mechanism in the destruction of orexin/hypocretin neurons. Importantly, the highest environmental risk is seen with influenza-A infection and immunization. However, how the cells are destroyed is currently unknown. In this review we summarize the disease symptoms, and focus on the immunological findings in narcolepsy. We also discuss the environmental and genetic risk factors as well as propose a model for disease development.

In Silico Perspectives on the Prediction of the PLP's Epitopes involved in Multiple Sclerosis

BACKGROUND

Multiple sclerosis (MS) is the most common autoimmune disease of the central nervous system (CNS). The main cause of the MS is yet to be revealed, but the most probable theory is based on the molecular mimicry that concludes some infections in the activation of T cells against brain auto-antigens that initiate the disease cascade.

OBJECTIVES

The Purpose of this research is the prediction of the auto-antigen potency of the myelin proteolipid protein (PLP) in multiple sclerosis.

MATERIALS AND METHODS

As there wasn't any tertiary structure of PLP available in the Protein Data Bank (PDB) and in order to characterize the structural properties of the protein, we modeled this protein using prediction servers. Meta prediction method, as a new perspective in silico, was performed to fi nd PLPs epitopes. For this purpose, several T cell epitope prediction web servers were used to predict PLPs epitopes against Human Leukocyte Antigens (HLA). The overlap regions, as were predicted by most web servers were selected as immunogenic epitopes and were subjected to the BLASTP against microorganisms.

RESULTS

Three common regions, AA58-74, AA161-177, and AA238-254 were detected as immunodominant regions through meta-prediction. Investigating peptides with more than 50% similarity to that of candidate epitope AA58-74 in bacteria showed a similar peptide in bacteria (mainly consistent with that of clostridium and mycobacterium) and spike protein of Alphacoronavirus 1, Canine coronavirus, and Feline coronavirus. These results suggest that cross reaction of the immune system to PLP may have originated from a bacteria or viral infection, and therefore molecular mimicry might have an important role in the progression of MS.

CONCLUSIONS

Through reliable and accurate prediction of the consensus epitopes, it is not necessary to synthesize all PLP fragments and examine their immunogenicity experimentally (in vitro). In this study, the best encephalitogenic antigens were predicted based on bioinformatics tools that may provide reliable results for researches in a shorter time and at a lower cost.

Antigen Presentation, Autoantigens, and Immune Regulation in Multiple Sclerosis and Other Autoimmune Diseases

Antigen presentation is in the center of the immune system, both in host defense against pathogens, but also when the system is unbalanced and autoimmune diseases like multiple sclerosis (MS) develop. It is not just by chance that a major histocompatibility complex gene is the major genetic susceptibility locus in MS; a feature that MS shares with other autoimmune diseases. The exact etiology of the disease, however, has not been fully understood yet. T cells are regarded as the major players in the disease, but most probably a complex interplay of altered central and peripheral tolerance mechanisms, T-cell and B-cell functions, characteristics of putative autoantigens, and a possible interference of environmental factors like microorganisms are at work. In this review, new data on all these different aspects of antigen presentation and their role in MS will be discussed, probable autoantigens will be summarized, and comparisons to other autoimmune diseases will be drawn.

The role of fractalkine (CX3CL1) in regulation of CD4(+) cell migration to the central nervous system in patients with relapsing-remitting multiple sclerosis

Fractalkine (CX3CL1) levels are increased in the cerebrospinal fluid (CSF) of patients with clinically isolated syndrome (CIS), as well as in the CSF and serum samples from patients with relapsing-remitting multiple sclerosis (RRMS). A higher percentage of circulating CD4(+) T-cells expressed its surface receptor (CX3CR1) and intracellular adhesion molecule (ICAM-1) in RRMS patients in comparison to healthy controls (HCs). The CX3CR1(+)ICAM-1(+)CD4(+) T-cells are enriched in the CSF of the RRMS patients. In vitro migration studies revealed that CD4(+) T-cells, which migrated toward a CX3CL1 gradient, expressed higher levels of ICAM-1 than non-migrating cells. CX3CL1 significantly increased IFN-γ and TNF-α gene expression and IFN-γ secretion by CD4(+) T-cells derived from the RRMS patients. CX3CL1 upregulated ICAM-1 expression on the surface of RRMS patient-derived but not HC-derived CD4(+) T-cells. Thus, CX3CL1 induces recruitment of CX3CR1(+)ICAM-1(+)CD4(+) T-cells into the central nervous system (CNS) during the early inflammatory response in MS.

Autoimmune T-cell reactivity to myelin proteolipids and glycolipids in multiple sclerosis

Central nervous system (CNS) myelin, the likely major target of autoimmune attack in multiple sclerosis (MS), contains a number of unique components that are potential targets of the attack. Two classes of molecules that are greatly enriched in CNS myelin compared to other parts of the body are certain types of proteolipids and glycolipids. Due to the hydrophobic nature of both of these classes of molecules, they present challenges for use in immunological assays and have therefore been somewhat neglected in studies of T-cell reactivity in MS compared to more soluble molecules such as the myelin basic proteins and the extracellular domain of myelin oligodendrocyte glycoprotein. This review firstly looks at the makeup of CNS myelin, with an emphasis on proteolipids and glycolipids. Next, a retrospective of what is known of T-cell reactivity directed against proteolipids and glycolipids in patients with MS is presented, and the implications of the findings are discussed. Finally, this review considers the question of what would be required to prove a definite role for autoreactivity against proteolipids and glycolipids in the pathogenesis of MS.

Antigen processing and presentation in multiple sclerosis

CD4(+) T cells play a central role in the pathogenesis of multiple sclerosis (MS). Generation, activation and effector function of these cells crucially depends on their interaction with MHC II-peptide complexes displayed by antigen presenting cells (APC). Processing and presentation of self antigens by different APC therefore influences the disease course at all stages. Selection by thymic APC leads to the generation of autoreactive T cells, which can be activated by peripheral APC. Reactivation by central nervous system APC leads to the initiation of the inflammatory response resulting in demyelination. In this review we will focus on how MHC class II antigenic epitopes are created by different APC from the thymus, the periphery and from the brain, and will discuss the relevance of the balance between creation and destruction of such epitopes in the context of MS. A solid understanding of these processes offers the possibility for designing future therapeutic strategies.

Myelin peptides in multiple sclerosis

The development of specific therapies for organ-specific autoimmune diseases requires the identification of relevant immunogenic epitopes, recognized by both pathogenic T cells and autoantibodies. Here, we review the most relevant studies focused in the identification of peptides in multiple sclerosis (MS) and the distinct T cell reactivity induced in patients compared to controls. Only a few studies reported significant differences in terms of T cell reactivity to them. The current knowledge on this issue, and the diagnostic and therapeutic possibilities opened by the identification of pathogenic MS epitopes are discussed in this paper.

Role of NK cells and invariant NKT cells in multiple sclerosis

Natural killer (NK) cells and invariant natural killer T (iNKT) cells are two distinctive lymphocyte populations, each possessing its own unique features. Although NK cells are innate lymphocytes with cytotoxic property, they play an immunoregulatory role in the pathogenesis of autoimmune diseases. NKT cells are T cells expressing invariant TCR a-chains, which are known to bridge innate and adaptive arms of the immune system. Accumulating data now support active involvement of these cells in multiple sclerosis (MS). However, unlike professionally committed regulatory cells such as Foxp3(+) regulatory T cells, NK, and iNKT cells have dual potential of acting as either protective or pathogenic lymphocytes depending on the disease setting, adding complexity to the interpretation of data obtained from human and rodent studies. They are potential therapeutic targets in MS, and further in-depth understanding of these cells will lead to designing new strategies to overcome the disabling disease MS.

Multiple sclerosis patients show sexual dimorphism in cytokine responses to myelin antigens

Multiple sclerosis affects more women than men. The reasons for this are unknown. Previously, we have shown significant differences in women versus men in inflammatory cytokine responses to the major protein component of myelin, proteolipid protein (PLP), which is thought to be a target in MS patients. Here, using the ELISPOT assay, we examined sex differences in single-cell secretion of Th1 and Th2 cytokines from freshly isolated PBMC between relapsing remitting (RR) MS patients and healthy individuals. Cells were stimulated with MS-associated antigens including proteolipid protein (PLP), myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), and non-disease related antigens. Our data show a sex bias in the cytokine responses to multiple MS-relevant myelin antigens: Women with MS show IFNgamma-skewed responses and men with MS show IL-5-skewed responses. These data extend our previous findings [Pelfrey, C.M., Cotleur, A.C., Lee, J.C., Rudick, R.A. 2002. Sex differences in cytokine responses to myelin peptides in multiple sclerosis. J. Neuroimmunol. 130, 211-223.]: (1) by demonstrating gender skewing in cytokine responses to an expanded myelin antigen repertoire, which includes MBP, MOG and PLP; (2) by showing TNFalpha and IL-10 do not display comparable gender skewing compared to IFNgamma and IL5; (3) by defining the patient population as early, untreated RRMS patients to avoid confounding factors, such as different disease stages/disability and immunomodulatory therapy; and (4) by showing HLA type does not appear to underlie the gender differences. These findings may explain increased susceptibility to MS in women and could contribute to the differences in disease severity between men and women.

Longitudinal single-cell cytokine responses reveal recurrent autoimmune myelin reactivity in relapsing--remitting multiple sclerosis patients

The relationship between multiple sclerosis (MS) disease activity and myelin protein-induced cytokine responses over time is not elucidated. We addressed this relationship by examining longitudinal cytokine responses to myelin proteins every three months for one year, in the context of gadolinium (gad)-enhancing brain lesions and of clinical relapses. The ELISPOT assay was used to determine the ex vivo cytokine production in response to nine amino acid long peptides spanning the entire proteolipid protein (PLP) and myelin basic protein (MBP) molecules in relapsing-remitting (RR) MS patients and matched healthy controls. We identified three longitudinal levels of myelin-induced cytokine secretion by adding up the positive responses for all PLP or MBP peptides obtained for five timepoints, at three-month intervals: low reactivity (< 200 cumulative cytokine-secreting cells), isolated peptide reactivity (201-450 cumulative cytokine-secreting cells) and recurrent protein-wide bursts of cytokine reactivity (> 451 cumulative cytokine-secreting cells). The majority of MS patients showed recurrent bursts to PLP and MBP. In contrast, controls showed a more even distribution between all levels of cytokine reactivity. The majority of patients with gad-enhancing lesions showed PLP/IFN gamma and MBP/IFN gamma recurrent burst responses. This is the first longitudinal study on MS patients in which nine amino acid long myelin peptides are used to reveal the broad range of PLP- and MBP-peptide cytokine reactivity across the whole molecule of these two major myelin proteins. This study also reveals the extremely dynamic nature of the immune reactivity to numerous regions of myelin, which can fluctuate dramatically over time. Such fluctuation could hamper the efficacy of antigen-based therapies for MS.

Immunology of multiple sclerosis

Multiple sclerosis (MS) develops in young adults with a complex predisposing genetic trait and probably requires an inciting environmental insult such as a viral infection to trigger the disease. The activation of CD4+ autoreactive T cells and their differentiation into a Th1 phenotype are a crucial events in the initial steps, and these cells are probably also important players in the long-term evolution of the disease. Damage of the target tissue, the central nervous system, is, however, most likely mediated by other components of the immune system, such as antibodies, complement, CD8+ T cells, and factors produced by innate immune cells. Perturbations in immunomodulatory networks that include Th2 cells, regulatory CD4+ T cells, NK cells, and others may in part be responsible for the relapsing-remitting or chronic progressive nature of the disease. However, an important paradigmatic shift in the study of MS has occurred in the past decade. It is now clear that MS is not just a disease of the immune system, but that factors contributed by the central nervous system are equally important and must be considered in the future.

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.

Delineation of the minimal encephalitogenic epitope of proteolipid protein peptide(91-110) and critical residues required for induction of EAE in HLA-DR3 transgenic mice

Previously, we have reported that proteolipid protein (PLP) peptide 91-110 can induce experimental autoimmune encephalomyelitis (EAE) in HLA-DR3 transgenic (tg) mice. Here we, report that residues spanning 97-108 are the minimal epitope required for induction of EAE in DR3 mice. Utilizing a series of alanine-substituted peptides, positions 99, 101, 102, 103, 104, and 106 are identified as residues necessary for an immune response. Further analysis indicated that amino acid isoleucine (99), aspartate (102) and lysine (104) are anchor residues facilitating binding to HLA-DR3 molecules. These results may have applications in the future design of peptide based immunotherapy.

Multiple sclerosis and hepatitis B vaccination: Could minute contamination of the vaccine by partial Hepatitis B virus polymerase play a role through molecular mimicry?

Reports of multiple sclerosis developing after hepatitis B vaccination have led to the concern that this vaccine might be a cause of multiple sclerosis in previously healthy subjects. Some articles evidenced that minor Hepatitis B virus (HBV) polymerase proteins could be produced by alternative transcriptional or translational strategies. Their detection is very difficult because they are in minute concentration and probably enzymatically inactive, however, it was shown that they could be exposed on the outside of the virus particles and also be immunogenic. In addition, HBV polymerase shares significant amino acid similarities with the human myelin basic protein. We hypothesise that some of the apparent adverse reactions to the vaccine could be due to a process called of molecular mimicry, the HBV polymerase, which could be a contaminant in the recombinant or plasma-derived vaccines, could act as autoantigens and induce autoimmune demyelinating diseases such as multiple sclerosis.

Sidechain biology and the immunogenicity of PDC-E2, the major autoantigen of primary biliary cirrhosis

The E2 component of mitochondrial pyruvate dehydrogenase complex (PDC-E2) is the immunodominant autoantigen of primary biliary cirrhosis. Whereas lipoylation of PDC-E2 is essential for enzymatic activity and predominates under normal conditions, other biochemical systems exist that also target the lysine residue, including acylation of fatty acids or xenobiotics and ubiquitinylation. More importantly, the immunogenicity can be affected by derivatization of the lysine residue, as the recognition of lipoylated PDC-E2 by patient autoantibodies is enhanced compared with octanoylated PDC-E2. Furthermore, our laboratory has shown that various xenobiotic modifications of a peptide representing the immunodominant region of PDC-E2 are immunoreactive against patient sera. The only purported regulatory system that prevents the accumulation of potentially autoreactive PDC-E2 is glutathionylation, in which the lysine-lipoic acid moiety is further modified with glutathione during apoptosis. Interestingly, this system is found in several cell lines, including HeLa, Jurkat, and Caco-2 cells, but not in cholangiocytes and salivary gland epithelial cells, both of which are targets for destruction in primary biliary cirrhosis. Hence, the failure of this or other regulatory system(s) may overwhelm the immune system with immunogenic PDC-E2 that can initiate the breakdown of tolerance in a genetically susceptible individual. In this review the authors survey the data available on the biochemical life of PDC-E2, with particular emphasis on the lysine residue and its known interactions with machinery involved in various posttranslational modifications.

Diazepam-binding inhibitor-related protein 1: a candidate autoantigen in acquired aplastic anemia patients harboring a minor population of paroxysmal nocturnal hemoglobinuria-type cells

To identify candidate antigens in aplastic anemia (AA), we screened proteins derived from a leukemia cell line with serum of an AA patient and identified diazepam-binding inhibitor-related protein 1 (DRS-1). Enzyme-linked immunosorbent assay (ELISA) revealed high titers of anti-DRS-1 antibodies (DRS-1 Abs) in 27 (38.0%) of 71 AA patients displaying increased paroxysmal nocturnal hemoglobinuria (PNH)-type cells (PNH(+)), 2 (6.3%) of 32 PNH(-) AA patients, 5 (38.5%) of 13 PNH(+) myelodysplastic syndrome (MDS) patients, and none of 42 PNH(-) MDS patients. DRS-1 gene was abundantly expressed in myeloid leukemia cell lines and in CD34(+) cells derived from healthy individuals. Stimulation of T cells from an AA patient displaying high DRS-1 Abs with a putative CD4(+) T-cell epitope (amino acid residues [aa's] 191-204) presented by HLA-DR15, which overlapped with a hot spot (aa's 173-198) of DRS-1 Ab epitopes, gave rise to T cells cytotoxic for L cells (murine fibroblasts) that were transfected with DRB1*1501 and DRS-1. Enzyme-linked immunospot assay demonstrated increased frequency of T-cell precursors specific to the DRS-1 peptide in other HLA-DR15(+) AA patients displaying high DRS-1 Ab titers. These findings indicate that DRS-1 may serve as an autoantigen eliciting immune attack against hematopoietic stem cells in a subset of AA patients characterized by increased PNH-type cells.

Expansion and Functional Relevance of High-Avidity Myelin-Specific CD4+T Cells in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease in which myelin-specific T cells are believed to play a crucial pathogenic role. Nevertheless, so far it has been extremely difficult to demonstrate differences in T cell reactivity to myelin Ag between MS patients and controls. We believe that by using unphysiologically high Ag concentrations previous studies have missed a highly relevant aspect of autoimmune responses, i.e., T cells recognizing Ag with high functional avidity. Therefore, we focused on the characterization of high-avidity myelin-specific CD4+ T cells in a large cohort of MS patients and controls that was matched demographically and with respect to expression of MHC class II alleles. We demonstrated that their frequency is significantly higher in MS patients while the numbers of control T cells specific for influenza hemagglutinin are virtually identical between the two cohorts; that high-avidity T cells are enriched for previously in vivo-activated cells and are significantly skewed toward a proinflammatory phenotype. Moreover, the immunodominant epitopes that were most discriminatory between MS patients and controls differed from those described previously and were clearly biased toward epitopes with lower predicted binding affinities to HLA-DR molecules, pointing at the importance of thymic selection for the generation of the autoimmune T cell repertoire. Correlations between selected immunological parameters and magnetic resonance imaging markers indicate that the specificity and function of these cells influences phenotypic disease expression. These data have important implications for autoimmunity research and should be considered in the development of Ag-specific therapies in MS.

Interferon gamma responses to myelin peptides in multiple sclerosis correlate with a new clinical measure of disease progression

The relationship between autoreactivity to myelin antigens and disease progression in multiple sclerosis (MS) is not fully understood. We addressed this relationship by cross-sectionally comparing an objective measure of MS disability with immune cytokine responses to myelin proteins. The ELISPOT assay was used to determine the ex vivo interferon gamma (IFNgamma) and interleukin-10 (IL-10) production by peripheral blood mononuclear cells (PBMCs) in response to peptides spanning the entire proteolipid protein (PLP) and myelin basic protein (MBP) molecules in 20 patients with relapsing-remitting (RR) MS and 27 age- and sex-matched healthy controls. MS patients showed significantly higher MBP-induced IFNgamma responses and PLP-induced IL-10 responses compared with healthy controls. Using the Multiple Sclerosis Functional Composite (MSFC), a new multifactorial measure of disability, MS patients showed a significant correlation between the IFNgamma response to PLP peptides and MBP peptides, and disability. In contrast, in MS patients, there was no correlation between the MSFC and the response to unrelated control antigens or mitogens. These data show that myelin-specific T lymphocytes secreting the inflammatory cytokine IFNgamma correlate with functional impairment in MS, supporting an antigen-specific link between the immune response to myelin and disability in MS.

Specificity of autoantibodies to epitopes of myelin proteins in multiple sclerosis

An autoimmune response to one or more myelin-protein components is thought to be part of the pathogenesis of multiple sclerosis (MS). The immunodominant-autoantibody epitope may be localized on a linear peptide segment, on a conformation-sensitive epitope, or on an epitope resulting from post-translational modifications. Primary, secondary, and tertiary structures of myelin proteins may determine the specific site for binding of autoantibodies. A myelin protein-specific autoantibody can bind to either a linear or conformational epitope, whereas all of the T cell epitopes are linear. At present, the conformational epitopes of myelin proteins have not been identified; most of the methods used to identify the myelin-protein epitopes corresponding to the pathogenesis of multiple sclerosis are involved in the linear epitope mapping. Polymorphism or mutations may cause inappropriate expression of the myelin proteins with alterations to their linear and/or conformational epitopes, and make them susceptible to autoantibody binding, especially if these changes occur at the surface of the protein. This review focuses on the specificity of autoantibodies to the epitopes of myelin proteins and correlates this to the structures of proteins. Factors that influence the expression of myelin-protein epitopes such as the alpha-helical or beta-sheet structure of the protein, the tri-proline site, and the post-translational modifications as well as physicochemical properties of amino acid changed are included.

Comprehensive mapping of HLA-A0201-restricted CD8 T-cell epitopes on PDC-E2 in primary biliary cirrhosis

Growing evidence has implicated the involvement of autoreactive T lymphocytes in the pathogenesis of primary biliary cirrhosis (PBC). We have recently taken advantage of motif prediction analysis of HLA-A*0201 and identified the first major histocompatibility complex (MHC) class I restricted epitope, amino acids 159 to 167 on E2 components of pyruvate dehydrogenase complexes (PDC-E2), the major mitochondrial antigens in PBC. The mechanisms involved in the selection of epitope peptide(s) that comprise the PDC-E2-specific autoreactive cytotoxic T lymphocytes (CTLs) are unknown and likely involve other epitopes on PDC-E2 restricted by MHC class I molecules. To address this issue, a comprehensive mapping of the CTL epitope repertoire on the PDC-E2 molecule that binds HLA-A*0201 was performed to provide further clues regarding the role of CTLs. We used the T2 cell line to screen 79 overlapping 15mer peptides, spanning the entire PDC-E2 molecule. Six of the 79 peptides exhibited significantly higher binding activity to HLA-A*0201 than the other 15mer peptides. Two of these 6 peptides induced CTL lines from patients with PBC. Fine mapping with N-terminus or C-terminus truncated peptides identified 10mer peptide, PDC-E2 amino acids 165 to 174, which is a novel CD8 epitope restricted by HLA-A*0201. In conclusion, using a combination of the 15mer peptide library screening with the T2 binding assay and also the induction of CTL lines with candidate peptides, we have defined a novel HLA-A*0201-restricted epitope PDC-E2 165 to 174 in patients with PBC. These data will become important in the development of altered peptide ligands to modulate disease activity.

Insights into the immunopathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). Significant progress has been made in our understanding of the etiology of MS. MS is widely believed to be an autoimmune disease that results from aberrant immune responses to CNS antigens. T cells are considered to be crucial in orchestrating an immunopathological cascade that results in damage to the myelin sheath. This review summarizes the currently available data supporting the idea that myelin reactive T cells are actively involved in the immunopathogenesis of MS. Some of the therapeutic strategies for MS are discussed with a focus on immunotherapies that aim to specifically target the myelin reactive T cells.

Identification of HLA-A2-restricted CD8(+) cytotoxic T cell responses in primary biliary cirrhosis: T cell activation is augmented by immune complexes cross-presented by dendritic cells

Primary biliary cirrhosis (PBC) is characterized by an intense biliary inflammatory CD4(+) and CD8(+) T cell response. Very limited information on autoantigen-specific cytotoxic T lymphocyte (CTL) responses is available compared with autoreactive CD4(+) T cell responses. Using peripheral blood mononuclear cells (PBMCs) from PBC, we identified an HLA-A2-restricted CTL epitope of the E2 component of pyruvate dehydrogenase (PDC-E2), the immunodominant mitochondrial autoantigen. This peptide, amino acids 159-167 of PDC-E2, induces specific MHC class I-restricted CD8(+) CTL lines from 10/12 HLA-A2(+) PBC patients, but not controls, after in vitro stimulation with antigen-pulsed dendritic cells (DCs). PDC-E2-specific CTLs could also be generated by pulsing DCs with full-length recombinant PDC-E2 protein. Furthermore, using soluble PDC-E2 complexed with either PDC-E2-specific human monoclonal antibody or affinity-purified autoantibodies against PDC-E2, the generation of PDC-E2-specific CTLs, occurred at 100-fold and 10-fold less concentration, respectively, compared with soluble antigen alone. Collectively, these data demonstrate that autoantibody, helper, and CTL epitopes all contain a shared peptide sequence. The finding that autoantigen-immune complexes can not only cross-present but also that presentation of the autoantigen is of a higher relative efficiency, for the first time defines a unique role for autoantibodies in the pathogenesis of an autoimmune disease.

Lessons from studies of antigen-specific T cell responses in Multiple Sclerosis

Multiple Sclerosis (MS) is considered a T cell-mediated autoimmune disease of central nervous system myelin. Based on elegant experiments in an animal model of MS, experimental allergic encephalomyelitis (EAE), a number of myelin proteins and peptides derived from these can induce inflammatory demyelinating lesions. Recent studies with transgenic mice expressing human HLA-DR molecules and a myelin basic protein (MBP)-specific T cell receptor as well as data from a phase II clinical trial with an altered peptide ligand based on MBP peptide (83-99) provide convincing evidence that the pathogenetic concepts which largely stem from the above EAE studies are valid in MS, too.

T lymphocytes promote the development of bone marrow-derived APC in the central nervous system

Certain cells within the CNS, microglial cells and perivascular macrophages, develop from hemopoietic myelomonocytic lineage progenitors in the bone marrow (BM). Such BM-derived cells function as CNS APC during the development of T cell-mediated paralytic inflammation in diseases such as experimental autoimmune encephalomyelitis and multiple sclerosis. We used a novel, interspecies, rat-into-mouse T cell and/or BM cell-transfer method to examine the development and function of BM-derived APC in the CNS. Activated rat T cells, specific for either myelin or nonmyelin Ag, entered the SCID mouse CNS within 3-5 days of cell transfer and caused an accelerated recruitment of BM-derived APC into the CNS. Rat APC in the mouse CNS developed from transferred rat BM within an 8-day period and were entirely sufficient for induction of CNS inflammation and paralysis mediated by myelin-specific rat T cells. The results demonstrate that T cells modulate the development of BM-derived CNS APC in an Ag-independent fashion. This previously unrecognized regulatory pathway, governing the presence of functional APC in the CNS, may be relevant to pathogenesis in experimental autoimmune encephalomyelitis, multiple sclerosis, and/or other CNS diseases involving myelomonocytic lineage cells.

Kinetic profiles of cerebrospinal fluid anti-MBP in response to intravenous MBP synthetic peptide DENP(85)VVHFFKNIVTP(96)RT in multiple sclerosis patients

Multiple sclerosis [MS], a demyelinating disease of the central nervous system associated with inflammation and gliosis, may be an autoimmune disease with T lymphocytes and autoantibodies to myelin protein(s). This study deals exclusively with B cell autoimmunity to myelin basic protein (MBP). T lymphocytes and anti-MBP share a common MBP epitope located between P(85) and P(96) which contains the essential contact residues H(88)FFK(91) for the trimolecular complex. The purpose of this Phase I open label clinical study was to monitor CSF anti-MBP in patients with chronic progressive MS subsequent to IV administration of synthetic peptide (sp) MBP82-98 namely DEN(85)VVHFFKNIVTP(96)RT. Fifty-six patients who participated in this project were assigned to two groups: a 'control group' of 15 patients who received IV saline injections every 6 months for the first 2 years of the study and a 'peptide group' of 41 patients who received IV spMBP82-98 from the beginning of the study and then infrequently subsequent to a rise of their CSF anti-MBP. In the control group antibody levels remained persistently elevated during the 2 year period. Patients in the 'peptide group' segregated into four kinetic profiles: Cohort A (15 patients) illustrated prolonged anti-BMP suppression into the normal range. Cohort B (10 patients) illustrated significant anti-MBP suppression into the normal range for shorter durations. Cohort C (eight patients) showed significant CSF anti-MBP suppression after the initial injection but lost the ability to suppress the autoantibody titer following subsequent injections. Cohort D (eight patients) failed to show significant CSF anti-MBP suppression. In conclusion the B cell tolerizing effect of spMBP82-98 segregated into four kinetic profiles; this molecular variability should be considered in attempts to develop specific 'peptide therapies' for the broad range of clinical profiles currently diagnosed as 'multiple sclerosis'. Multiple Sclerosis (2000) 6 300 - 311

Quantification of self-recognition in multiple sclerosis by single-cell analysis of cytokine production

Identifying and quantifying autoaggressive responses in multiple sclerosis (MS) has been difficult in the past due to the low frequency of autoantigen-specific T cells, the high number of putative determinants on the autoantigens, and the different cytokine signatures of the autoreactive T cells. We used single-cell resolution enzyme-linked immunospot (ELISPOT) assays to study, directly ex vivo, proteolipid protein (PLP)-specific memory cell reactivity from MS patients and controls. Overlapping 9-aa-long peptides, spanning the entire PLP molecule in single amino acid steps, were used to determine the frequency and fine specificity of PLP-specific lymphocytes as measured by their IFN-gamma and IL-5 production. MS patients (n = 22) responded to 4 times as many PLP peptides as did healthy controls (n = 22). The epitopes recognized in individual patients, up to 22 peptides, were scattered throughout the PLP molecule, showing considerable heterogeneity among MS patients. Frequency measurements showed that the number of PLP peptide-specific IFN-gamma-producing cells averaged 11 times higher in MS patients than in controls. PLP peptide-induced IL-5-producing T cells occurred in very low frequencies in both MS patients and controls. This first comprehensive assessment of the anti-PLP-Th1/Th2 response in MS shows a greatly increased Th1 effector cell mass in MS patients. Moreover, the highly IFN-gamma-polarized, IL-5-negative cytokine profile of the PLP-reactive T cells suggests that these cells are committed Th1 cells. The essential absence of uncommitted Th0 cells producing both cytokines may explain why therapeutic strategies that aim at the induction of immune deviation show little efficacy in the established disease.

Myelin-associated oligodendrocytic basic protein: identification of an encephalitogenic epitope and association with multiple sclerosis

Myelin-associated oligodendrocytic basic protein (MOBP) is an abundant myelin constituent expressed exclusively by oligodendrocytes, the myelin-forming cells of the CNS. We report that MOBP causes experimental allergic encephalomyelitis and is associated with multiple sclerosis. First, we note that purified recombinant MOBP inoculated into SJL/J mice produces CNS disease. Tests of overlapping peptides spanning the murine MOBP molecule map the encephalitogenic site to amino acids 37-60. MOBP-induced experimental allergic encephalomyelitis shows a severe clinical course and is characterized by a prominent CD4+ T lymphocyte infiltration and a lesser presence of CD8+ T cells and microglia/macrophages around vessels and in the white matter of the CNS. Second, PBL obtained from patients with relapsing/remitting multiple sclerosis mount a proliferative response to human MOBP, especially at amino acids 21-39. This response equals or exceeds the response to myelin basic protein and an influenza virus hemagglutinin peptide, both serving as internal controls. Thus, a novel myelin Ag, MOBP aa 37-60, plays a role in rodent autoimmune CNS disease, and its human MOBP counterpart is associated with the human demyelinating disease multiple sclerosis.

Oligodendrocyte-Specific Protein Peptides Induce Experimental Autoimmune Encephalomyelitis in SJL/J Mice

Oligodendrocyte-specific protein (OSP) is a recently isolated and cloned, 207-aa, hydrophobic, four-transmembrane protein found in CNS myelin. It represents ∼7% of total myelin protein. The OSP cDNA sequence has no significant homology with previously reported genes, but the predicted protein structure suggests that OSP is a CNS homologue of peripheral myelin protein-22. We previously reported the presence of anti-OSP Abs in the cerebrospinal fluid of relapsing-remitting multiple sclerosis (MS) patients, but not control patient groups. In this study, we tested the ability of a panel of 20-mer peptides with 10-aa overlaps, representing the sequence of murine OSP, to induce experimental autoimmune encephalomyelitis (EAE), an animal model for MS. SJL mice challenged with murine OSP peptides 52–71, 82–101, 102–121, 142–161, 182–201, and 192–207 exhibited clinical EAE. OSP:52–71 elicited severe relapsing-remitting EAE in some individuals. All other encephalitogenic peptides elicited, at most, a loss of tail tonicity from which the mice most often completely recovered. Mononuclear cell infiltrates and focal demyelination characteristic of EAE were evident. T cell proliferative responses were seen with all encephalitogenic peptides except 142–161 and 182–201. OSP peptides 72–91 and 132–151 did not cause clinical EAE, but did elicit robust proliferative responses. B10.PL and PL/J mice challenged with the same OSP peptide doses as SJL mice did not exhibit clinical EAE. These results in the SJL EAE model, together with the results from MS patient clinical samples, make OSP a promising candidate for autoantigenic involvement in MS.

Candidate autoantigens in multiple sclerosis

Multiple sclerosis is an inflammatory demyelinating CNS disease of putatively autoimmune origin. Novel models of experimental autoimmune encephalomyelitis (EAE) have demonstrated that T cells specific for various myelin and even nonmyelin proteins are potentially encephalitogenic. The encephalitogenic T cell response directed against different CNS antigens not only determines the lesional topography of CNS inflammation but also the composition of the inflammatory infiltrates. The heterogeneity of the lesional distribution seen in EAE might therefore be useful for the understanding of the various clinical subtypes seen in MS. In this review the possible candidate autoantigens in MS are discussed with special regard to the human T cell and B cell responses against various myelin and nonmyelin proteins.

Immunopathogenesis of multiple sclerosis: the role of T cells

Multiple sclerosis is considered to be an autoimmune disease that results from aberrant immune responses to central nervous system antigens. T cells are considered to be crucial in orchestrating an immunopathological cascade that culminates in damage to the myelin sheath, oligodendrocytes and axons.

Spontaneous regression of primary autoreactivity during chronic progression of experimental autoimmune encephalomyelitis and multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a widely used animal model for multiple sclerosis (MS). EAE is typically initiated by CD4(+) T helper cell type 1 (Th1) autoreactivity directed against a single priming immunodominant myelin peptide determinant. Recent studies have shown that clinical progression of EAE involves the accumulation of neo-autoreactivity, commonly referred to as epitope spreading, directed against peptide determinants not involved in the priming process. This study directly addresses the relative roles of primary autoreactivity and secondary epitope spreading in the progression of both EAE and MS. To this end we serially evaluated the development of several epitope-spreading cascades in SWXJ mice primed with distinctly different encephalitogenic determinants of myelin proteolipid protein. In a series of analogous experiments, we examined the development of epitope spreading in patients with isolated monosymptomatic demyelinating syndrome as their disease progressed to clinically definite MS. Our results indicate that in both EAE and MS, primary proliferative autoreactivity associated with onset of clinical disease invariably regresses with time and is often undetectable during periods of disease progression. In contrast, the emergence of sustained secondary autoreactivity to spreading determinants is consistently associated with disease progression in both EAE and MS. Our results indicate that chronic progression of EAE and MS involves a shifting of autoreactivity from primary initiating self-determinants to defined cascades of secondary determinants that sustain the self-recognition process during disease progression.

The epitope spreading cascade during progression of experimental autoimmune encephalomyelitis and multiple sclerosis

We have made the following observations regarding self-recognition during the development and progression of murine experimental autoimmune encephalomyelitis (EAE) and human multiple sclerosis (MS): 1) chronic progression of EAE is accompanied by a sequential, predictable cascade of neo-autoreactivity, commonly referred to as epitope spreading, presumably caused by endogenous self-priming during autoimmune-mediated tissue damage; 2) there is an invariant relationship between the progression of EAE and the emergence of epitope spreading; 3) progression of EAE can be inhibited by the induction of antigen-specific tolerance to spreading determinants after onset of initial neurologic symptoms; 4) CD4+ Th 1 cells responding to spreading determinants are autonomously encephalitogenic; 5) epitope spreading occurs during the development of MS and in some cases involves HLA-DP class II-restricted self-recognition; and 6) progression of both EAE and MS is accompanied by the decline of primary T-cell autoreactivity associated with disease onset and by the concurrent emergence of the epitope spreading cascade. Our studies directly challenge the traditional view that EAE and MS are initiated and maintained by autoreactivity directed against a single predominant myelin protein or determinant. Our results indicate that progression of EAE and MS involves a shifting of T-cell autoreactivity from primary initiating self-determinants to defined cascades of secondary determinants that sustain the inflammatory self-recognition process during disease progression.

T-cell responses to myelin antigens in multiple sclerosis; relevance of the predominant autoimmune reactivity to myelin oligodendrocyte glycoprotein

Until recently, the search for the 'culprit' autoantigen towards which deleterious autoimmunity is directed in multiple sclerosis (MS) centered mostly on myelin basic protein (MBP) and proteolipid (PLP), the two most abundant protein components of central nervous system (CNS) myelin, the target tissue for the autoimmune attack in MS. Although such research has yielded important data, furthering our understanding of the disease and opening avenues for possible immune-specific therapeutic approaches, attempts to unequivocally associate MS with MBP or PLP as primary target antigens in the disease have not been successful. This has led in recent years to a new perspective in MS research, whereby different CNS antigens are being investigated for their possible role in the initiation or progression of MS. Interesting studies in laboratory animals show that T-cells directed against certain non-myelin-specific CNS antigens are able to cause inflammation of the CNS, albeit without expression of clinical disease. However, reactivity to these antigens by MS T-cells has not been demonstrated. Conversely, reactivity by MS T-cells to non-myelin-specific antigens such as heat shock proteins, could be observed, but the pathogenic potential of such reactivity has not been corroborated with the encephalitogenicity of the antigen. More relevant to MS pathogenesis may be, as we outlined in this review, the autoimmune reactivity directed against minor myelin proteins, in particular the CNS-specific myelin oligodendrocyte glycoprotein (MOG). Here, we review the current knowledge gathered on T-cell reactivity to possible target antigens in MS in the context of their encephalitogenic potential, and underline the facets which make MOG a highly relevant contender as primary target antigen in MS, albeit not necessarily the only one.

T cell recognition of myelin proteolipid protein and myelin proteolipid protein peptides in the peripheral blood of multiple sclerosis and control subjects

Myelin proteolipid protein (PLP) is a prime candidate autoantigen for multiple sclerosis. In order to define potential immunodominant epitopes, T cell lines (TCL) from the peripheral blood of HLA-DR 15(2) MS patients were established which responded to the intact molecule of PLP. These TCL were then tested in individual proliferation assays with a variety of PLP peptides spanning most of the PLP molecule. Multiple peptides were recognized by TCL from the MS population, with more than one peptide often recognized by lines from the same individual. Three immunodominant peptides were identified which were recognized by the majority of MS patients. Estimated frequency analyses were then performed on the peripheral blood of HLA-DR15(2)-positive MS and control subjects using TCL initiated by the three immunodominant peptides, 40-60, 95-117, and 185-206. TCL from HLA-DR15 MS subjects recognized peptide 95-117 significantly more often than TCL from control subjects.

CD8+ Myelin Peptide-Specific T Cells Can Chemoattract CD4+ Myelin Peptide-Specific T Cells: Importance of IFN-Inducible Protein 10

The demyelination process that occurs in the central nervous system (CNS) of patients with multiple sclerosis (MS) is due, in part, to an inflammatory response in which CD4+ and CD8+ T cells and macrophages infiltrate white matter. While it is thought that the inflammatory and demyelination process in MS is the product of Th1-associated cytokines secreted by CD4+ myelin protein-specific T cells present in the CNS, the mechanisms that are responsible for the recruitment and maintenance of these myelin-reactive CD4+ T cells in the CNS have not been elucidated. We have shown previously that CD8+CTL that recognize peptides derived from sequences of the myelin proteolipid protein (PLP) presented by HLA class I molecules can be generated in vitro, and that these PLP-specific CD8+CTL secrete the proinflammatory chemokines macrophage-inflammatory protein-1α and -1β, IL-16, and IP-10. In this study, we demonstrate that soluble products of these PLP-specific CD8+CTL can chemoattract CD4+ T cells that are specific for a myelin basic protein peptide and a PLP peptide, and that the majority of this chemotactic activity is mediated by IFN-inducible protein 10. These results demonstrate that PLP-specific CD8+ T cells can play a role in the recruitment and retention of myelin-derived peptide-specific CD4+ T cells, and indicate that they may play a proinflammatory role in the pathogenesis of MS.

HLA-DP: a class II restriction molecule involved in epitope spreading during the development of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system. It is widely believed that complex polygenic inheritance patterns involving HLA-DR and -DQ class II genes contribute to MS susceptibility, and current evidence indicates that disease risk vs disease outcome may be associated with distinctly different HLA class II alleles. We have recently shown that the early development of MS is accompanied by an extensive plasticity of myelin self-recognition with the acquisition of neo-autoreactivity, or epitope spreading, as a prominent feature. Although we did not observe a common determinant recognized by patients sharing identical HLA-DR or -DQ class II alleles, we did observe epitope spreading to the p50-63 determinant of myelin proteolipid protein (PLP) in two study subjects showing complete disparity at HLA-DR and -DQ but identity at the HLA-DP allele DPB1*0301. In the present study we show that self-recognition during the early stages in the development of MS involves HLA-DP class II restricted responses to the PLP 50-63 spreading determinant. Our results suggest that self-presentation by HLA-DP may play an important role in epitope spreading and in the propagation of self-recognition during the clinical progression of MS.

Immune tolerance mediated by recombinant proteolipid protein prevents experimental autoimmune encephalomyelitis

Proteolipid protein (PLP), a transmembrane protein expressed only in the central nervous system (CNS), is a candidate target autoantigen for autoimmune-mediated demyelination. We have evaluated the effect of a recombinant form of the PLP protein, delta PLP4, in a murine model of experimental autoimmune encephalomyelitis (EAE). PLP-specific T-cell responses were observed following immunization of SJL/J, PL/J and SWR mice with delta PLP4, demonstrating processing of the protein to several distinct antigenic epitopes. Clinical EAE associated with inflammation and demyelination in the CNS also developed after sensitization of mice with delta PLP4 in adjuvant. Conversely, tolerance to delta PLP4 in adult mice and prevention of PLP peptide 139-151-induced EAE was induced by intravenous injection of soluble delta PLP4. The prevention of disease onset was paralleled by a significant reduction in demyelination and CNS inflammatory cell infiltration and diminished PLP139-151-specific T-cell proliferative responses. These results are consistent with the establishment of peripheral T-cell tolerance and reinforce the notion that recombinant myelin antigens and intravenous tolerance induction may prove useful in the modulation of the human demyelinating disease, multiple sclerosis (MS).

HPRT mutant T-cell lines from multiple sclerosis patients recognize myelin proteolipid protein peptides

Mutation of the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene in a T-cell is believed to be an indication that the T-cell has been activated and has proliferated in vivo. HPRT mutant T-cell lines were generated from peripheral blood mononuclear cells from patients with MS and control subjects. More lines were isolated from the MS patients than from the control subjects. Using stringent criteria for recognition, none of the lines from MS-affected or control subjects recognized intact myelin basic protein (MBP) or myelin proteolipid protein (PLP) molecules. Using stringent criteria, two of the 10 MS patients harbored mutant lines each recognizing distinct PLP peptides (PLP peptide 40-60 recognized by 3 lines from one patient and PLP peptide 178-191 recognized by 2 lines from the other patient). A single line recognizing PLP peptide 89-106 was derived from 1 of 7 normal controls. HPRT mutant lines recognizing multiple epitopes of PLP which spanned much of the molecule could be isolated from MS patients, and to a lesser extent, normal subjects.

Diversity and plasticity of self recognition during the development of multiple sclerosis

Recent studies using murine animal model systems indicate that clinical progression of autoimmune disease may be due to the sequential accumulation of neoautoreactivity characterized by extensive plasticity of self recognition. In the present study, we addressed the question of whether a similar paradigm of self recognition is implicated in the development of multiple sclerosis (MS), a demyelinating disease with a presumed autoimmune etiology. Our approach was to determine serial changes over a 12-18-mo period in response to an epitope-mapping series of 265 12-mer peptides of myelin proteolipid protein (PLP) by patients with isolated monosymptomatic demyelinating syndromes (IMDS), a group of distinct clinical disorders with variable rates of progression to MS. Our data showed that an extensive array of proteolipid protein peptides could elicit autoreactivity. Moreover, differential autoreactive patterns were evident within IMDS patient subpopulations. Monocentric monophasic IMDS patients with no evidence of prior subclinical disease typically showed fully sustained autoreactivity characterized by extensive plasticity, epitope focusing, shifting, and spreading of responses to new self determinants. In contrast, multicentric monophasic IMDS patients with putative evidence of prior asymptomatic lesion formation typically showed partially sustained autoreactivity characterized by abrupt abrogation of responses to an extensive array of self determinants. No sustained autoreactivity was observed in normal control subjects or in patients with other neurologic diseases. Our results indicate that self recognition associated with the development of MS is a developmental process characterized by autoreactive diversity, plasticity, and instability.

Identification of an epitope derived from human proteolipid protein that can induce autoreactive CD8+ cytotoxic T lymphocytes restricted by HLA-A3: evidence for cross-reactivity with an environmental microorganism

The demyelination process that occurs in the central nervous system (CNS) of patients with multiple sclerosis (MS) is in part due to an inflammatory response in which CD4+ and CD8+ T cells and macrophages infiltrate white matter. In this study, we have identified a peptide sequence derived from the CNS-specific myelin protein proteolipid protein (PLP) which could bind to HLA-A3 and induce a HLA-A3-restricted CD8+ CTL response from HLA-A3+ donors. These PLP peptide-specific CTL could lyse HLA-A3+ target cells pulsed with a homologous peptide derived from the CRM1 protein of Saccharomyces cerevisae. These findings demonstrate the immunogenic potential of a PLP-derived peptide for generation of autoreactive HLA-A3-restricted CD8+ CTL, and further show that these CTL can be activated by a peptide derived from a common environmental microorganism.

Treatment of experimental encephalomyelitis with a novel chimeric fusion protein of myelin basic protein and proteolipid protein

It has been shown that peripheral T cell tolerance can be induced by systemic antigen administration. We have been interested in using this phenomenon to develop antigen-specific immunotherapies for T cell-mediated autoimmune diseases. In patients with the demyelinating disease multiple sclerosis (MS), multiple potentially autoantigenic epitopes have been identified on the two major proteins of the myelin sheath, myelin basic protein (MBP) and proteolipid protein (PLP). To generate a tolerogenic protein for the therapy of patients with MS, we have produced a protein fusion between the 21.5-kD isoform of MBP (MBP21.5) and a genetically engineered form of PLP (deltaPLP4). In this report, we describe the effects of treatment with this agent (MP4) on clinical disease in a murine model of demyelinating disease, experimental autoimmune encephalomyelitis (EAE). Treatment of SJL/J mice with MP4 after induction of EAE either by active immunization or by adoptive transfer of activated T cells completely prevented subsequent clinical paralysis. Importantly, the administration of MP4 completely suppressed the development of EAE initiated by the cotransfer of both MBP- and PLP-activated T cells. Prevention of clinical disease after the intravenous injection of MP4 was paralleled by the formation of long-lived functional peptide-MHC complexes in vivo, as well as by a significant reduction in both MBP- and PLP-specific T cell proliferative responses. Mice treated with MP4 were resistant to disease when rechallenged with an encephalitogenic PLP peptide emulsified in CFA, indicating that MP4 administration had a prolonged effect in vivo. Administration of MP4 was also found to markedly ameliorate the course of established clinical disease. Finally, MP4 therapy was equally efficacious in mice defective in Fas expression. These results support the conclusion that MP4 protein is highly effective in suppressing disease caused by multiple neuroantigen epitopes in experimentally induced demyelinating disease.

T cell response to two immunodominant proteolipid protein (PLP) peptides in multiple sclerosis patients and healthy controls

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system in which autoimmune T lymphocytes reacting with myelin antigens are believed to play a pathogenic role. Since HLA binding is involved in the selection of T cell responses, we have examined PLP peptide binding to HLA DR2, an HLA allele frequently found in MS patients. Both PLP 40-60 and PLP 89-106 show significant, high affinity binding to HLA DR2. We then tested whether responses to PLP peptides 40-60 and 89-106 are elevated in multiple sclerosis patients compared to matched controls. We also analysed T cell responses to MBP 87-106, which is considered to be the immunodominant region of MBP in humans. Here we demonstrate heterogenous T cell responses to PLP 40-60, PLP 89-106 and MBP 87-106 in both MS patients and controls. The overall number of TCL and the HLA restriction of those TCL did not vary significantly in the two groups. PLP 40-60 specific cytolytic TCL were increased in MS patients, whereas healthy controls had increased percentages of cytolytic TCL responding to PLP 89-106 and MBP 87-106. Although the data presented here shows heterogenous responses in T cell numbers, differences in numbers and specificity of cytolytic cells could be involved in the pathogenesis of autoimmune demyelinating disease.

Intravenous antigen administration as a therapy for autoimmune demyelinating disease

Experimental allergic encephalomyelitis is a prototypic autoimmune disease characterized by central nervous system inflammation and demyelination. Previously, we demonstrated that intravenous administration of high doses of myelin basic protein abrogated the clinical and pathological signs of experimental allergic encephalomyelitis by causing the deletion of encephalitogenic, CD4+, myelin basic protein-specific T cells through antigen-induced programmed cell death. In the present study, we further characterized the ability of intravenous antigen administration to attenuate an immune response by myelin basic protein-reactive encephalitogenic T cells. We demonstrated that multiple injections of myelin basic protein are required to achieve a therapeutic response, and that this form of therapy is effective even after prolonged chronic disease. These studies showed that although interleukin-2-stimulated cell cycling is an important factor leading to T-cell death, the administration of exogenous interleukin-2 with antigen can result in the aggravation of clinical disease compared to administration of antigen alone. More importantly, administration of myelin basic protein alone without interleukin-2 was sufficient to reduce autoreactive T cells and clinical disease in experimental autoimmune encephalomyelitis. Our experiments support the rationale for antigen-specific therapy aimed at inducing the programmed death of autoreactive T cells in autoimmune diseases, potentially including the human demyelinating disease multiple sclerosis.

Experimental autoimmune encephalomyelitis in rodents as a model for human demyelinating disease

The cause of multiple sclerosis (MS) is unknown, but the pathology is consistent with an immunological etiology. Studies conducted with the animal model of MS, experimental autoimmune encephalomyelitis (EAE), have provided insight into how the immune system can provoke an immunopathological response characteristic of that seen in MS. The use of inbred rats and mice for studies of EAE has been especially rewarding with respect to the identification of the epitopes of encephalitogenic antigens responsible for the induction of this autoimmune disease and in elucidating the effector mechanism underlying EAE. Moreover, it has also been possible to ascertain how EAE can be regulated, leading to therapeutic modalities which have been applied in clinical studies of MS patients. This review briefly summarizes studies of EAE in rodents, drawing comparisons with immunological findings reported in patients with MS. It is clear that important lessons can be learned from the detailed investigation of animal models that may be applicable to human immunological disorders.

Multiple sclerosis: immune mechanism and update on current therapies

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) afflicting approximately 250,000 individuals in the United States. This inflammatory disease has variable clinical manifestations, ranging from a relapsing-remitting course to a chronic progressive disease. Approximately one third of MS patients have chronic progressive disease often leading to severe impairment of mobility, paralysis, poor vision, and disturbances of bladder and bowel function. Although the etiology and pathogenesis remain unknown, accumulating evidence supports the hypothesis that exposure to an as-yet-unidentified infectious agent(s) triggers an aberrant immune response against self nervous tissue in genetically susceptible individuals. The tenfold higher concordance rate for MS in monozygotic twins compared to dizygotic twins, the increased incidence of MS in women compared to men (2:1), and the familial and racial occurrence of MS provide strong evidence that genetic factors influence susceptibility to MS. The major predisposing genes in MS are the human leukocyte antigen (HLA) class II molecules, DR15 and DQw6, molecularly defined as HLA-DRB1, 1501-DQA1 0102-DQB1 0602. In certain ethnic groups, MS susceptibility is more strongly associated with other DR molecules. Environmental factors are also believed to play a role, as suggested by the unique worldwide prevalence, migration effects, and epidemiological studies. Increased serum and cerebrospinal fluid antibody titers to numerous viruses have been reported; however, there have been no confirmed studies detecting viral RNA or antigen in MS brain tissue. At the present time, no known treatment can significantly alter the progression of MS. Based on the postulate that MS is an autoimmune disease associated with abnormalities in immunoregulation, a number of different immunosuppressive and immunomodulating agents have been tested as therapeutic modalities. In this article, we review the circumstantial evidence suggesting that immune system abnormalities are associated with the disease process, and provide an update on current therapies used in MS.