Myelin basic protein-specific T-cell responses in identical twins discordant or concordant for multiple sclerosis

Mechanistic and Biomarker Studies to Demonstrate Immune Tolerance in Multiple Sclerosis

The induction of specific immunological tolerance represents an important therapeutic goal for multiple sclerosis and other autoimmune diseases. Sound knowledge of the target antigens, the underlying pathomechanisms of the disease and the presumed mechanisms of action of the respective tolerance-inducing approach are essential for successful translation. Furthermore, suitable tools and assays to evaluate the induction of immune tolerance are key aspects for the development of such treatments. However, investigation of the mechanisms of action underlying tolerance induction poses several challenges. The optimization of sensitive, robust methods which allow the assessment of low frequency autoreactive T cells and the long-term reduction or change of their responses, the detection of regulatory cell populations and their immune mediators, as well as the validation of specific biomarkers indicating reduction of inflammation and damage, are needed to develop tolerance-inducing approaches successfully to patients. This short review focuses on how to demonstrate mechanistic proof-of-concept in antigen-specific tolerance-inducing therapies in MS.

Antigen-Specific Immune Tolerance in Multiple Sclerosis-Promising Approaches and How to Bring Them to Patients

Antigen-specific tolerance induction aims at treating multiple sclerosis (MS) at the root of its pathogenesis and has the prospect of personalization. Several promising tolerization approaches using different technologies and modes of action have already advanced to clinical testing. The prerequisites for successful tolerance induction include the knowledge of target antigens, core pathomechanisms, and how to pursue a clinical development path that is distinct from conventional drug development. Key aspects including patient selection, outcome measures, demonstrating the mechanisms of action as well as the positioning in the rapidly growing spectrum of MS treatments have to be considered to bring this therapy to patients.

Autoantibodies to Non-myelin Antigens as Contributors to the Pathogenesis of Multiple Sclerosis

For years, investigators have sought to prove that myelin antigens are the primary targets of autoimmunity in multiple sclerosis (MS). Recent experiments have begun to challenge this assumption, particularly when studying the neurodegenerative phase of MS. T-lymphocyte responses to myelin antigens have been extensively studied, and are likely early contributors to the pathogenesis of MS. Antibodies to myelin antigens have a much more inconstant association with the pathogenesis of MS. Recent studies indicate that antibodies to non-myelin antigens such as neurofilaments, neurofascin, RNA binding proteins and potassium channels may contribute to the pathogenesis of MS. The purpose of this review is to analyze recent studies that examine the role that autoantibodies to non-myelin antigens might play in the pathogenesis of MS.

Innate immunity in the central nervous system

Immune responses in the CNS are common, despite its perception as a site of immune privilege. These responses can be mediated by resident microglia and astrocytes, which are innate immune cells without direct counterparts in the periphery. Furthermore, CNS immune reactions often take place in virtual isolation from the innate/adaptive immune interplay that characterizes peripheral immunity. However, microglia and astrocytes also engage in significant cross-talk with CNS-infiltrating T cells and other components of the innate immune system. Here we review the cellular and molecular basis of innate immunity in the CNS and discuss what is known about how outcomes of these interactions can lead to resolution of infection, neurodegeneration, or neural repair depending on the context.

Human T cell expansion and experimental autoimmune encephalomyelitis inhibited by Lenaldekar, a small molecule discovered in a zebrafish screen

Immune-mediated diseases [multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE)] are driven by proliferating, highly activated autoreactive T-cells that are unresponsive to in vivo immunoregulatory mechanisms. The compound Lenaldekar (LDK) was identified in a zebrafish screen by inhibiting T-cell expansion. By monitoring mitogen- and antigen-driven proliferation, we found that LDK inhibited human and murine T-cell expansion in a non-cytolytic manner. This suppressive activity directly correlated with the degree of activation/proliferation of the T-cells. In testing LDK in an EAE model of MS, exacerbations were suppressed in treated animals. Therefore, LDK represents a novel therapeutic approach to T-cell-mediated autoimmune diseases.

The sad plight of multiple sclerosis research (low on fact, high on fiction): critical data to support it being a neurocristopathy

The literature for evidence of autoimmunity in multiple sclerosis (MS) is analysed critically. In contrast to the accepted theory, the human counterpart of the animal model experimental autoimmune demyelinating disease, experimental allergic encephalomyelitis (EAE), is not MS but a different demyelinating disorder, i.e. acute disseminated encephalomyelitis and acute haemorrhagic leucoencephalitis. Extrapolation of EAE research to MS has been guided largely by faith and a blind acceptance rather than sound, scientific rationale. No specific or sensitive immunological test exists that is diagnostic of MS despite the extensive application of modern technology. Immunosuppression has failed to have any consistent effect on prognosis or disease progression. The available data on MS immunotherapy are conflicting, at times contradictory and are based on findings in animals with EAE. They show predominantly a 30% effect in relapsing/remitting MS which suggests powerful placebo effect. Critical analysis of the epidemiological data shows no association with any specific autoimmune diseases, but does suggest that geographic factors and age at development posit an early onset possibly dependent on environmental influences. Certain neurological diseases are, however, found in association with MS, namely hypertrophic peripheral neuropathy, neurofibromatosis-1, cerebral glioma, glioblastoma multiforme and certain familial forms of narcolepsy. These share a common genetic influence possibly from genes on chromosome 17 affecting cell proliferation. A significant number of these disorders are of neural crest origin, the classical example being abnormalities of the Schwann cell. These and other data allow us to propose that MS is a developmental neural crest disorder, i.e. a cristopathy, implicating glial cell dysfunction with diffuse blood-brain barrier breakdown. The data on transcription factor SOX10 mutations in animals may explain these bizarre clinical associations with MS and the phenotypic variability of such alterations (Cossais et al. 2010). Research directed to the area of neural crest associations is likely to be rewarding.

Toll-like receptors: a new target in rheumatoid arthritis?

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases. It is characterized by chronic inflammation of the joint leading to its destruction. Although the initiating cause remains elusive, environmental factors and genetic background are known to contribute to the etiology of RA. The role of Toll-like receptors (TLRs) in innate immunity and their ability to recognize microbial products has been well characterized. TLRs are able to recognize endogenous molecules released upon cell damage and necrosis, and are present in RA synovial fluid. Although it appears unlikely that a pathogen underlies the pathogenesis or progression of RA, the release of endogenous TLR ligands during inflammation may activate TLRs and perpetuate the disease. An increasing body of circumstantial evidence implicates TLR signaling in RA, although, at present, their involvement is not defined comprehensively. Targeting individual TLRs or their signaling transducers may provide a more specific therapy without global suppression of the immune system.

Meningeal mast cells affect early T cell central nervous system infiltration and blood-brain barrier integrity through TNF: a role for neutrophil recruitment?

Mast cells contribute to the pathogenesis of experimental autoimmune encephalomyelitis, a rodent model of the human demyelinating disease multiple sclerosis. Yet their site and mode of action is unknown. In both diseases, myelin-specific T cells are initially activated in peripheral lymphoid organs. However, for disease to occur, these cells must enter the immunologically privileged CNS through a breach in the relatively impermeable blood-brain barrier. In this study, we demonstrate that a dense population of resident mast cells in the meninges, structures surrounding the brain and spinal cord, regulate basal CNS barrier function, facilitating initial T cell CNS entry. Through the expression of TNF, mast cells recruit an early wave of neutrophils to the CNS. We propose that neutrophils in turn promote the blood-brain barrier breach and together with T cells lead to further inflammatory cell influx and myelin damage. These findings provide specific targets for intervention in multiple sclerosis as well as other immune-mediated CNS diseases.

Islet-specific glucose-6-phosphatase catalytic subunit-related protein-reactive CD4+ T cells in human subjects

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is recognized as a major autoantigen for autoimmune type 1 diabetes (T1D) in the NOD mouse model. This study was undertaken to examine CD4+ T cell responses toward IGRP in human subjects. The tetramer-guided epitope mapping approach was used to identify IGRP-specific CD4+ T cell epitopes. IGRP(23-35) and IGRP(247-259) were identified as DRA1*0101/DRB1*0401-restricted epitopes. IGRP(13-25) and IGRP(226-238) were identified as DRA1*0101/DRB1*0301-restricted epitopes. IGRP-specific tetramers were used to evaluate the prevalence of IGRP-reactive T cells in healthy and T1D subjects. More than 80% of subjects with either DRB1*0401 or DRB1*0301 haplotype have IGRP-specific CD4+ T cell responses for at least one IGRP epitope. IGRP-specific T cells from both healthy and T1D groups produce both gamma-IFN and IL-10. DRA1*0101/DRB1*0401 IGRP(247-259)-restricted T cells also show cross-reactivity to an epitope derived from liver/kidney glucose-6-phosphatase. The detection of IGRP-reactive T cells in both type 1 diabetic subjects and healthy subjects and recent reports of other autoreactive T cells detected in healthy subjects underscore the prevalence of potentially autoreactive T cells in the peripheral immune system of the general population.

Clonal expansion of IgA-positive plasma cells and axon-reactive antibodies in MS lesions

Immunoglobulin A (IgA), the predominant immunoglobulin class in mucosal secretions, has been found in the cerebrospinal fluid of patients with multiple sclerosis (MS). In this study we examined the infiltration of clonally expanded IgA plasma cells in lesions of MS brains. Sequences of complementarity-determining region 3 of IgA variable heavy chain (V(H)) genes demonstrated the clonal expansion of IgA-bearing plasma cells in MS lesions. Somatic mutations and ongoing intra-clonal mutations occurred in their V(H) genes. Immunohistochemical study demonstrated infiltration of dimer and polymer IgA1- and A2-positive plasma cells in perivascular spaces, in the parenchyma of MS lesions, and in the adjacent white matter. Double immunofluorescence staining showed binding of IgA antibody on axons and walls of microvessels in the areas of chronic active and inactive demyelination. Bielshowsky's silver impregnation revealed axonal damage in these areas. These findings suggest that IgA in the CNS are localized on axons in lesions and may contribute to axonal damage in 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.

TLR4 contributes to disease-inducing mechanisms resulting in central nervous system autoimmune disease

Environmental factors strongly influence the development of autoimmune diseases, including multiple sclerosis. Despite this clear association, the mechanisms through which environment mediates its effects on disease are poorly understood. Pertussis toxin (PTX) functions as a surrogate for environmental factors to induce animal models of autoimmunity, such as experimental autoimmune encephalomyelitis. Although very little is known about the molecular mechanisms behind its function in disease development, PTX has been hypothesized to facilitate immune cell entry to the CNS by increasing permeability across the blood-brain barrier. Using intravital microscopy of the murine cerebromicrovasculature, we demonstrate that PTX alone induces the recruitment of leukocytes and of active T cells to the CNS. P-selectin expression was induced by PTX, and leukocyte/endothelial interactions could be blocked with a P-selectin-blocking Ab. P-selectin blockade also prevented PTX-induced increase in permeability across the blood-brain barrier. Therefore, permeability is a secondary result of recruitment, rather than the primary mechanism by which PTX induces disease. Most importantly, we show that PTX induces intracellular signals through TLR4, a receptor intimately associated with innate immune mechanisms. We demonstrate that PTX-induced leukocyte recruitment is dependent on TLR4 and give evidence that the disease-inducing mechanisms initiated by PTX are also at least partly dependent on TLR4. We propose that this innate immune pathway is a novel mechanism through which environment can initiate autoimmune disease of the CNS.

The voltage-gated Kv1.3 K(+) channel in effector memory T cells as new target for MS

Through a combination of fluorescence microscopy and patch-clamp analysis we have identified a striking alteration in K(+) channel expression in terminally differentiated human CCR7(-)CD45RA(-) effector memory T lymphocytes (T(EM)). Following activation, T(EM) cells expressed significantly higher levels of the voltage-gated K(+) channel Kv1.3 and lower levels of the calcium-activated K(+) channel IKCa1 than naive and central memory T cells (T(CM)). Upon repeated in vitro antigenic stimulation, naive cells differentiated into Kv1.3(high)IKCa1(low) T(EM) cells, and the potent Kv1.3-blocking sea anemone Stichodactyla helianthus peptide (ShK) suppressed proliferation of T(EM) cells without affecting naive or T(CM) lymphocytes. Thus, the Kv1.3(high)IKCa1(low) phenotype is a functional marker of activated T(EM) lymphocytes. Activated myelin-reactive T cells from patients with MS exhibited the Kv1.3(high)IKCa1(low) T(EM) phenotype, suggesting that they have undergone repeated stimulation during the course of disease; these cells may contribute to disease pathogenesis due to their ability to home to inflamed tissues and exhibit immediate effector function. The Kv1.3(high)IKCa1(low) phenotype was not seen in glutamic acid decarboxylase, insulin-peptide or ovalbumin-specific and mitogen-activated T cells from MS patients, or in myelin-specific T cells from healthy controls. Selective targeting of Kv1.3 in T(EM) cells may therefore hold therapeutic promise for MS and other T cell-mediated autoimmune diseases.

Kinetics of CCR7 expression differ between primary activation and effector memory states of T(H)1 and T(H)2 cells

We explored the kinetics of CCR7 expression on T(H)1 and T(H)2 polarized cells as well as on antigen-specific T cell lines at various stages of differentiation. A striking pattern of early (days 7-14) inducible CCR7 expression was seen preferentially on primary T(H)1 cell lines, as compared to T(H)2 cells, and was dependent on the strength and duration of the T cell receptor signal. Upon repeated restimulation (days 21-28) and differentiation, a switch occurred in which T(H)2 cells had high CCR7 expression, whereas T(H)1 cells lost CCR7 expression. Chronic (8 weeks and later) effector memory cell lines were 95% CCR7 negative. These data demonstrate an ordered pattern of CCR7 expression that suggest more rapid priming of T(H)1 cells in the lymph node, and delayed priming with prolonged CCR7 expression during T(H)2 responses, and may have implications for tracking T(H)1 effector T cells ex vivo in autoimmune diseases.

Chemokine receptor expression on MBP-reactive T cells: CXCR6 is a marker of IFNgamma-producing effector cells

Cytokine-polarized T cells have distinct chemokine receptor (CKR) expression patterns associated with their cytokine secretion profiles. In order to investigate this paradigm in autoreactive human T cells, we have determined the CKR expression pattern of myelin basic protein (MBP)-reactive T cell lines (TCL) and compared these profiles to those of TCL-generated in response to tetanus toxoid (TT). Expression of CXCR6 and CXCR3 on TCL was significantly positively correlated with IFNgamma, and inversely correlated with IL-5 production. TT TCL had significantly higher expression of CCR7(-)/CD45RA(-) T effector memory (Tem) cells than MBP TCL. However, in MBP-specific TCL, CXCR6 was found to be the best marker of conversion to the Tem phenotype. CXCR6 and CXCR3 are likely to be important in the migration of effector memory T cells in Th1-mediated inflammatory diseases such as multiple sclerosis (MS).

Costimulation of memory T-cells by ICOS: a potential therapeutic target for autoimmunity?

Approaches that target costimulatory receptors are independent of T-cell receptor specificity and may be useful for T-cell-mediated diseases in which the antigens involved are not well defined. However, the proper costimulatory pathways need to be targeted. For example, therapies for human T-cell-mediated diseases need to be effective against previously activated memory cells. In this review, we use autoimmune demyelination as a paradigm for established immune-mediated pathogenesis. Studies with the human disease multiple sclerosis and the rodent model experimental autoimmune encephalomyelitis have suggested that the effectiveness of CD28 blockade, as a therapeutic strategy for established autoimmune demyelination, may be limited. ICOS, a receptor that appears to be involved in the costimulation of previously activated T-cells, may be an attractive alternative.

The role of costimulation in autoimmune demyelination

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

Twins: mirrors of the immune system

Twin studies are a powerful tool to assess genetic and nongenetic factors in multifactorial, immune-mediated diseases. Here, Marco Salvetti and colleagues review important results from such studies and highlight their potential value. Future developments that should help to realize the potential of twin studies are discussed.

The critical role of IL-12 and the IL-12R beta 2 subunit in the generation of pathogenic autoreactive Th1 cells

Experimental Allergic Encephalomyelitis (EAE) is a demyelinating disease of the central nervous system which is an animal model for the human autoimmune disease, multiple sclerosis. EAE is mediated by CD4+ T cells and the T cells responsible for disease induction produce Th1 cytokines. IL-12 produced by monocytes and dendritic cells is the most critical factor which influences the development and differentiation of pathogenic autoreactive Th1 cells. Here, we review our recent studies on the critical contributions of IL-12 and the IL-12R beta 2 subunit to the generation of autoreactive effector cells which mediate EAE. In addition, we discuss the potential contribution of IL-18 to the upregulation of the IL-12/IL-12R beta 2 pathway and the contribution of the suppressor cytokines, IL-4 and IL-10, in downregulating this pathway. Collectively, our studies demonstrate that the IL-12/IL-12R beta 2 pathway is a critical intermediary in the process of Th1 differentiation which can be both positively or negatively regulated. This pathway remains an attractive immunotherapeutic target for blockade of function with inhibitory reagents or downregulation by Th2 cytokines.

Decrypting the spectrum of antigen-specific T-cell responses: the avidity repertoire of MBP-specific T-cells

Myelin basic protein (MBP) is a well-characterized autoantigen potentially involved in the pathogenesis of the most common human demyelinating disease of the central nervous system (CNS), multiple sclerosis (MS). It is known that MBP-specific T-cell responses differ widely among different individuals and also within a single donor in terms of fine specificity and functional characteristics including the avidity in antigen recognition. In this report, we demonstrate that the in vitro selection of MBP-reactive T-cell repertoire is strictly dependent upon the antigen dose used in the primary cultures. MBP-specific T-cell lines (TCLs) were generated from MS patients and healthy donors using different antigen concentration in cultures (0.1 to 50 microg/ml). In both MS patients and controls, the number of obtained T-cell lines was affected by the antigen concentration. In addition, low and high antigen concentrations selected in vitro different T-cell populations in terms of peptide specificity patterns and different functional avidities in antigen recognition. Low concentrations of MBP in the primary cultures yielded a small number of TCLs recognizing the specific antigen with higher avidity whereas high antigen concentrations allowed the in vitro expansion of a higher numbers of T-cells recognizing MBP with lower avidity. The use of different antigen concentrations in the primary cultures can be applied as a simple experimental system to investigate the overall avidity repertoire of antigen-specific T-cell response in humans.

Analysis of the T cells that are potentially involved in autoantibody production in pemphigus vulgaris

Pemphigus vulgaris (PV) is a classical example of an antibody-mediated autoimmune disease of the skin. Direct evidence exists that autoantibodies against the desmosomal adhesion molecule, desmoglein 3 (Dsg3), are critical in the pathogenesis of this disease. The transfer of serum IgG antibodies reactive with Dsg3 into newborn mice induces a bullous skin disease resembling PV. Autoreactive T cell responses to Dsg3 may be critical in the pathogenesis of PV because 1) antibody production generally requires T cell help, 2) the involvement of CD4+ T lymphocytes in PV has been suggested by the strong association with distinct HLA class II alleles, and 3) T cell recognition of epitopes of Dsg3 may be crucial for the initiation and perpetuation of the production of Dsg3-specific autoantibodies by B cells. We and others have identified autoreactive T cells recognizing distinct epitopes of the extracellular portion of Dsg3 in PV patients. These autoreactive CD4+ T cells preferentially produced TH2 cytokines such as IL-4, and IL-10. Autoantibodies of the TH2-dependent IgG4 subtype are preferentially seen in active stages of PV disease, while autoantibodies of the TH1-dependent IgG1 subclass are predominant upon remission of PV. Healthy individuals who carried HLA class II alleles similar or identical to those found to be highly prevalent in PV also developed autoreactive T cell responses to Dsg3. Autoreactive T cells from PV patients produced both TH1 and TH2 cytokines; autoreactive T cells from normals produced TH0 cytokines. These observations suggest that Dsg3-specific T cells may provide targets to eventually modulate the T cell-dependent production of pathogenic autoantibodies in PV.

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.

Regulation of interleukin (IL)-12 receptor beta2 subunit expression by endogenous IL-12: a critical step in the differentiation of pathogenic autoreactive T cells

The interleukin (IL)-12 receptor (R)beta2 subunit is the critical molecule involved in maintaining IL-12 responsiveness and controlling T helper cell type 1 lineage commitment. We demonstrate that IL-12 and interferon (IFN)-gamma play separate, but complementary, roles in regulating IL-12Rbeta2 expression on antigen-specific CD4(+) T cells. These results are consistent with our previous observation that IL-12 can promote autoimmune disease through IFN-gamma-independent as well as -dependent pathways. Therefore, we compared the induction of IL-12 by, and the expression of the IL-12Rbeta2 subunit on, myelin basic protein (MBP)-specific T cells from experimental allergic encephalomyelitis (EAE)-susceptible SJL (H-2(s)) mice and from EAE- resistant B10.S mice (H-2(s)). B10.S mice had an antigen-specific defect in their capacity to upregulate the IL-12Rbeta2 subunit. Defective expression was not secondary to the production of suppressive cytokines, but to a failure of B10.S MBP-specific T cells to upregulate CD40 ligand expression and to induce the production of IL-12. IL-12Rbeta2 expression as well as encephalitogenicity of these cells could be restored by the addition of IL-12. These results suggest that the development of immunotherapies that target the IL-12Rbeta2 subunit may be useful for the treatment of autoimmune diseases.

Identification and characterization of autoreactive T cell responses to bullous pemphigoid antigen 2 in patients and healthy controls

Antibodies against the extracellular domain of bullous pemphigoid antigen 2 (BPAG2) are thought to play a key role in the pathogenesis of bullous pemphigoid (BP), the most frequent autoimmune bullous disease of the skin. Autoreactive T cell responses to BPAG2 were investigated in 16 BP patients and 24 healthy controls by coculture of PBMC with two recombinant BPAG2 proteins (extracellular domain of BPAG2). Primary in vitro T cell responses to BPAG2 were observed in 10/12 BP patients expressing the BP-associated HLA-DQB1*0301 allele and 8/10 DQB1*0301 positive healthy individuals. DQB1*0301 also restricted three autoreactive T cell lines from two BP patients and a healthy donor. In contrast, PBMC from 14 normal patients carrying HLA class II alleles other than DQB1*0301 were not stimulated by BPAG2. Autoreactive BPAG2-specific CD4(+) T cell lines and clones from five BP patients produced both Th1 and Th2 cytokines, whereas three autoreactive T cell lines from three DQB1*0301 positive normal patients produced exclusively IFN-gamma. The absence of BPAG2-specific Th2 cells in healthy individuals strongly suggests that autoreactive Th2 responses to BPAG2 are restricted to BP patients and may thus be critical in the pathogenesis of BP.

T-cell response to myelin basic protein and lipid-bound myelin basic protein in patients with multiple sclerosis and healthy donors

An autoimmune T-cell response to myelin proteins is thought to be involved in the pathogenesis of multiple sclerosis (MS) and myelin basic protein (MBP) is the most widely studied potential target antigen. We investigated the T-cell response to MBP in MS patients and controls using two different molecular forms of the protein: the classical hydrophilic MBP (lipid-free MBP, LF-MBP) and a lipid-bound, native-like preparation of MBP isolated in a molecular form retaining the binding to all myelin lipids (lipid-bound-MBP, LB-MBP). Short term T-cell lines (TCL) were generated using either LF- or LB-MBP and tested for their reactivity to the in vitro stimulating antigen. No differences were detected between MS patients and healthy donors in the percentage of T-cell cultures responsive to the LF-MBP. In contrast, the number of LB-MBP reactive cultures was higher in MS patients than in controls. This difference was almost entirely due to the presence of high numbers of LB-MBP-specific TCL in MS patients which did not cross-react with LF-MBP and were not present in healthy subjects. LB-MBP may represent a novel antigen worth to be investigated in MS.

Recognition of desmoglein 3 by autoreactive T cells in pemphigus vulgaris patients and normals

Pemphigus vulgaris (PV) is an autoimmune blistering disease of the skin and is caused by autoantibodies against desmoglein 3 (Dsg3) on epidermal keratinocytes. Because the production of autoantibodies is presumably T cell dependent, Dsg3-specific T cell reactivity was investigated in 14 PV patients and 12 healthy donors. Peripheral blood mononuclear cells from seven PV patients with active disease showed a primary in vitro response to a recombinant protein containing the extracellular portion (EC1-5) of Dsg3, whereas two of seven PV patients in remission or under immunosuppressive treatment exhibited only secondary (2 degrees) or tertiary (3 degrees) T cell responses to Dsg3. T cell responses to Dsg3 were also observed in four of 12 healthy individuals upon 2 degrees or 3 degrees stimulation with Dsg3. Both PV patients and healthy responders were either positive for DRbeta1*0402 -- which is highly prevalent in PV -- or positive for DR11 alleles homologous to DRbeta1*0402. Two CD4+ Dsg3-specific T cell lines and 12 T cell clones from two PV patients and two CD4+ T cell lines and eight T cell clones from two normals were also stimulated by a Dsg3 protein devoid of the EC2-3 (deltaN1), suggesting that epitopes were located in the EC1, EC4, and/or EC5. Using Dsg3 peptides, one immunodominant peptide (residues 161-177) was also identified in the EC2. These observations demonstrate that T cell responses to Dsg3 can be detected in PV patients and in healthy donors carrying major histocompatibility class II alleles identical or similar to those highly prevalent in PV.

Immunodominance of a low-affinity major histocompatibility complex-binding myelin basic protein epitope (residues 111-129) in HLA-DR4 (B1*0401) subjects is associated with a restricted T cell receptor repertoire

The pathogenesis of multiple sclerosis (MS) is currently ascribed in part to a T cell-mediated process targeting myelin components. The T cell response to one candidate autoantigen, myelin basic protein (MBP), in the context of HLA-DR15Dw2, has been previously studied in detail. However, the characteristics of cellular immunity in the context of other MS-associated HLA-DR haplotypes are scarcely known. MBP-specific T cell lines (TCL) were generated from HLA-DR4 (B1*0401)-positive MS subjects. Out of 275 MBP-specific TCL, 178 (64. 7%) specifically recognized region MBP(111-129), predominantly in the context of DRB1*0401. The major T cell epitope for MBP recognition corresponded to residues MBP(116-123). These TCL expressed disparate profiles of cytokine secretion and cytotoxicity. T cell receptor analysis, on the other hand, revealed a strikingly limited heterogeneity of rearrangements. In contrast to MBP(81-99), which binds with high affinity to HLA-DR15 and is recognized by a diverse T cell repertoire, MBP(111-129) binds weakly to DRB1*0401, suggesting that only high affinity T cell receptors might be able to efficiently engage such unstable MHC/peptide complexes, thus accounting for the T cell receptor restriction we observed. This study provides new insight about MBP recognition and proposes an alternative mechanism for immunodominance of self-antigen T cell epitopes in humans.

Genetics of multiple sclerosis--how could disease-associated HLA-types contribute to pathogenesis?

Multiple sclerosis is a chronic demyelinating disease of the central nervous system in young adults. It is considered a T cell-mediated autoimmune disease which is probably triggered by exogenous events, e.g. infectious agents, in susceptible individuals. Population, family and twin studies indicate that genetic factors and most likely several genes are associated with disease, but it is clear from the concordance rates of identical twins (25-30%) that genetic background as well as exogenous or somatic events are required to develop disease. Among many candidate genes which have been analyzed during recent years, the strongest association was shown for genes of the HLA-class II complex, in particular HLA-DR15 Dw2 and -DQw6. At present, it is not clear how the expression of a particular HLA-class II gene translates into susceptibility to develop an organ-specific autoimmune disease. Potential explanations how this could occur will be discussed.

Gender differences in autoimmune demyelination in the mouse: implications for multiple sclerosis

Gender-related differences in experimental allergic encephalomyelitis (EAE) were examined in the SJL mouse with the purpose of characterizing an animal model ideal for the study of gender-related differences in multiple sclerosis (MS). For the model to allow for study of the induction and the effector phase of disease, the adoptive EAE model was characterized. First, the SJL strain was shown to be nonresponsive with regard to the development of antisyngeneic HY-specific responses in females, thereby permitting intergender adoptive transfers of T lymphocytes during EAE induction. Then, when myelin basic protein (MBP)-specific T cells derived from females were adoptively transferred into female and male recipients, female recipients demonstrated a more rapid onset of disease (p = 0.01), greater maximal acute-phase clinical scores (p < 0.0001) and greater mean clinical scores (p < 0.0001) compared with male recipients. When MBP-specific T cells derived from males were adoptively transferred, female recipients again tended to be more severely affected. Histopathologic analysis revealed quantitative differences between genders that paralleled clinical expression. These results document a clear gender-related difference in adoptive EAE in the SJL, with clinical and histopathologic disease greater in females compared with males. This model will be a useful tool for addressing autoimmune mechanisms underlying gender-related differences in MS.

The immune response to mycobacterial 70-kDa heat shock proteins frequently involves autoreactive T cells and is quantitatively disregulated in multiple sclerosis

Heat shock proteins (HSP) are the most conserved molecules known to date that may also function as immune targets during infection. Hence, theoretically there is a high chance of cross-reactive responses to epitopes shared by host and microbe HSP. If not properly regulated, these responses may contribute to the pathogenesis of autoimmune disease. To determine if immune responses to HSP could contribute to the pathogenesis of multiple sclerosis, we raised T lymphocyte lines specific for the purified protein derivative of Mycobacterium tuberculosis (PPD) from patients with multiple sclerosis, patients with tuberculosis and from healthy individuals. These lines were then screened for their proliferative response to a M. tuberculosis 70-kDa heat shock protein (M.tb.HSP70). The relative frequency of the recognition of highly conserved sequences of M.tb.HSP70 compared to variable ones was also assessed by mapping experiments on those PPD specific T lymphocyte lines which also recognized the mycobacterial 70-kDa heat shock protein. In patients with multiple sclerosis, we observed a significantly higher estimated frequency of PPD-specific T lines responding to M.tb.HSP70 compared to healthy individuals and patients with tuberculosis. Furthermore, mapping experiments using recombinant proteins representing mycobacterial and human HSP70 sequences and a panel of synthetic peptides encompassing the whole sequence of Mycobacterium leprae HSP70, showed that the response to conserved epitopes of HSP70 is a frequent event in each of the three conditions studied, often leading to the cross-recognition of microbial and human sequences. These findings implicate the 70-kDa heat shock proteins as potential autoantigens in multiple sclerosis.

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.

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.

Major T-cell responses in multiple sclerosis

Evidence is emerging that the major T- and B-cell response in multiple sclerosis (MS) is directed to a region of myelin basic protein (MBP) between residues 84 and 103. In rodent models of MS, immunization to this component of MBP evokes experimental autoimmune encephalomyelitis (EAE). T cells found in EAE lesions show similarities in the VJ and VDJ regions of their alpha and beta chains with T cells in MS lesions, and with T cells that are specific for MBPp84-103 isolated from patients with MS. If this region of MBP is critical in the pathogenesis of MS, then therapy aimed at controlling the immune response to this immunodominant region of MBP may be beneficial in treating MS.

Immunological aspects of experimental allergic encephalomyelitis and multiple sclerosis

Multiple sclerosis (MS) is the most frequent, demyelinating disease of the central nervous system (CNS) in Northern Europeans and North Americans. Despite intensive research its etiology is still unknown, but a T cell-mediated autoimmune pathogenesis is likely to be responsible for the demyelination. This hypothesis is based both on findings in MS patients and studies of an experimental animal model for demyelinating diseases, experimental allergic encephalomyelitis (EAE). Experiments in EAE have not only demonstrated which myelin antigens are able to induce the demyelinating process but also have determined the characteristics of encephalitogenic T cells, that is, their fine specificity, major histocompatibility complex (MHC) restriction, lymphokine secretion, activation requirements, and T cell receptor (TCR) usage. Based on these findings, highly specific and efficient immune interventions have been designed in EAE and have raised hopes that similar approaches could modulate the disease process in MS. Although the examination of the myelin-specific T cell response in MS patients has shown parallels to EAE, this remains an area of intensive research because a number of questions remain. This review summarizes the important lessons from EAE, examines recent findings in MS, and discusses current concepts about how the disease process develops and which steps might be taken to modulate it.

Healthy monozygous twins do not recognize identical T cell epitopes on the myelin basic protein autoantigen

The T cell response against myelin basic protein (MBP) has been extensively studied in humans because of its putative role in the pathophysiology of multiple sclerosis (MS). Higher concordance rates in monozygous twins as well as an increased risk in relatives suggest the role of genetic factors in MS susceptibility. Very little is known about the shaping of T cell repertoire towards self antigens in humans and their contribution to disease susceptibility in autoimmune disorders. Here we report the comparative T cell epitope recognition patterns towards the MBP auto-antigen in healthy identical twins. We have established MBP-specific T cell lines from eight sets of twins and characterized their fine epitope specificity. Intra-pair comparison showed the co-existence of shared as well as distinct epitopes in six of eight pairs and a complete absence of concordant epitope recognition within two other pairs. These findings indicate that important differences in T cell repertoires against a self antigen may be observed between genetically identical healthy individuals, rendering difficult the interpretation of the differences which may be observed between identical twins discordant for an autoimmune disease.

Multiple sclerosis: multiple etiologies, multiple genes?

Multiple sclerosis is a chronic inflammatory disease characterized by multifocal damage of the central nervous system myelin. Both humoral and cell-mediated immune abnormalities have been observed in patients with multiple sclerosis, but their relation to the demyelination process is not understood. The etiology of the disease is still unknown; however, evidence exists for an interplay between environmental and genetic factors. Several genes are involved in determining the disease susceptibility, at least one of them encoded within human leukocyte antigen gene complex. Other genomic regions coding for components of the immune system or myelin have also been suggested. Clinical, immunological and genetic data suggest that multiple sclerosis may turn out to be a heterogeneous disease. Therefore, molecular genetic dissection of this complex disease should provide important clues to its pathogenesis as well as unravel metabolic pathways for potential therapeutic or preventive strategies. This review will give an overview of recent progress and future challenges in identifying susceptibility genes for multiple sclerosis.

Twin studies in auto-immune disease

Immune-mediated diseases affect up to 5% of the population and are a major cause of morbidity and mortality. These diseases can be organ specific, such as insulin-dependent diabetes (IDDM) and non-organ specific, such as Rheumatoid Arthritis (RA). Identical and non-identical twins have been used to establish whether these diseases are determined by genetic or environmental factors. The results of these studies have been collated in a new section of the Mendel Institute in Rome. Diseases included in these studies included IDDM, RA, Systemic Lupus Erythematosus (SLE), Multiple Sclerosis (MS) and Myasthenia. Striking differences in concordance rates between identical and non-identical twins in all these studies suggest that genetic factors are important in causing these diseases. All the diseases are known to be associated with HLA genes on chromosome 6 which may account for some or all of the genetic susceptibility. However, in the majority of pairs the affected twin has an unaffected co-twin. These observations suggest that non-genetically determined factors, probably environmental factors and not somatic mutations, are critical. The study of unaffected co-twins, who are at high disease-risk, has allowed the identification of changes which precede and predict the clinical disease. The immune-mediated destruction in many of these diseases is probably caused by T-lymphocytes. Twin studies have shown the importance of genetic factors in determining T-cell responses. Identical twins should, therefore, provide the perfect test bed to assess the role of T-cells in immune-mediated diseases.