Recognition of the immunodominant myelin basic protein peptide by autoantibodies and HLA-DR2-restricted T cell clones from multiple sclerosis patients. Identity of key contact residues in the B-cell and T-cell epitopes

Genetic linkage analysis of the antibody responses to myelin basic protein and myelin oligodendrocyte glycoprotein in rats immunized with rat spinal cord homogenate

The genetic control of the antibody response to myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) was analysed in F1 and F2 crosses of DA and E3 rats, immunized with rat spinal chord homogenate. The DA rats were highly susceptible to encephalomyelitis and made antibody responses to both MBP and MOG, whereas the E3 rats were disease-resistant and responded only to MOG. The anti-MBP response was mainly controlled by the disease-promoting MHC region of the DA strain together with several disease loci outside MHC. In contrast, the anti-MOG response was associated with loci not related to or actually conferring resistance to 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 cells of multiple sclerosis patients target a common environmental peptide that causes encephalitis in mice

Multiple sclerosis (MS) is a chronic autoimmune disease triggered by unknown environmental factors in genetically susceptible hosts. MS risk was linked to high rates of cow milk protein (CMP) consumption, reminiscent of a similar association in autoimmune diabetes. A recent rodent study showed that immune responses to the CMP, butyrophilin, can lead to encephalitis through antigenic mimicry with myelin oligodendrocyte glycoprotein. In this study, we show abnormal T cell immunity to several other CMPs in MS patients comparable to that in diabetics. Limited epitope mapping with the milk protein BSA identified one specific epitope, BSA(193), which was targeted by most MS but not diabetes patients. BSA(193) was encephalitogenic in SJL/J mice subjected to a standard protocol for the induction of experimental autoimmune encephalitis. These data extend the possible, immunological basis for the association of MS risk, CMP, and CNS autoimmunity. To pinpoint the same peptide, BSA(193), in encephalitis-prone humans and rodents may imply a common endogenous ligand, targeted through antigenic mimicry.

The fine specificity of the myelin oligodendrocyte glycoprotein autoantibody response in patients with multiple sclerosis and normal healthy controls

Antibodies directed against the extracellular immunoglobulin (Ig)-like domain of the myelin oligodendrocyte glycoprotein (MOG(Igd)) mediate demyelination in experimental autoimmune encephalomyelitis (EAE) and are implicated in the immunopathogenesis of multiple sclerosis (MS). In this study we investigated the epitope specificity of MOG(Igd)-specific autoantibodies immunopurified from MS patients (n=17) and normal healthy controls (HD; n=9). ELISA, using a panel of synthetic MOG(Igd) peptides, revealed that the epitope specificity of this response was heterogeneous in both groups. The most frequently recognised epitopes were located in amino acid sequences (a.a.) 1-26 (13/17) and 63-87 (15/17) in MS patients, and 14-39 (6/9) and 63-87 (6/9) in HDs, but there was no association between MS and any particular peptide specificity. We therefore investigated the ability of the immunopurified antibodies to recognise native MOG(Igd) expressed on at the membrane surface by FACS. Unexpectedly, antibodies fulfilling this essential criterion for a demyelinating antibody response were detected only in one of the MS samples. These results indicate that the epitope specificity of the human B cell response to MOG is not only heterogeneous, but may only mediate demyelination in a limited subset of MS patients.

Antigen specific immunotherapy of multiple sclerosis

The development of antigen specific therapy for multiple sclerosis (MS) involves specifically suppressing undesired immune responses targeting the myelin sheath and underlying axon. We have recently reported some success with altered peptide ligands for a major target of the autoimmune response in MS. Antigen specific therapy has the potential to suppress undesirable autoimmunity, while leaving the rest of the immune system intact. Induction of an antigen specific Th1-to-Th2 shift could achieve this aim, once side effects, such as allergic responses, are minimized with optimal dosing.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

Contribution of the MHC class II antigens to the etiology of infantile spasm in Mexican Mestizos

PURPOSE

Infantile spasms (ISs) are age-dependant epileptic seizures, which may be flexor, extensor, lightning or nods, or mixed. The aim of this study was the analysis of genetic factors within the human leukocyte antigen (HLA) complex associated with ISs.

METHODS

Sixty-five patients diagnosed according to the established international criteria were compared with 229 healthy individuals; all of them were Mexican Mestizos. Five families were also analyzed (seven affected and five healthy sibs); HLA class I and class II antigens were typed using the standard microlymphocytotoxicity methods.

RESULTS

The findings showed female gender preference (2:1). Two thirds were symptomatic, and prevalent seizures were of mixed type (67%). A strong association with HLA-DR17 was detected in the IS group (pc < 0.01; OR = 3.6; EF = 0.20). DR17 was also found increased in the symptomatic patients (p = 0.009; OR = 3.16) and in those with other types of seizures (p = 0.001; OR = 2.0). Conversely, HLA-DQ6 was significantly decreased (pc < 0.002; PF = 0.37) in the total and in the symptomatic groups (p < 0.01). Haplotype linkage was not confirmed in the families; however, those with more than one affected sib shared at least one haplotype.

CONCLUSIONS

These findings suggest the contribution of DR locus to the susceptibility and the participation of DQ region in the resistance to IS. Severity seems also to be influenced by HLA-DR17, and therefore class II typing may be a helpful tool for disease prognosis.

B cells and antibodies in CNS demyelinating disease

There is much evidence to implicate B cells, plasma cells, and their products in the pathogenesis of MS. Despite unequivocal evidence that the animal model for MS, EAE, is initiated by myelin-specific T cells, there is accumulating evidence of a role for B cells, plasma cells, and their products in EAE pathogenesis. The role(s) played by B cells, plasma cells, and antibodies in CNS inflammatory demyelinating diseases are likely to be multifactorial and complex, involving distinct and perhaps opposing roles for B cells versus antibody.

Epitopes targeted by bullous pemphigoid T lymphocytes and autoantibodies map to the same sites on the bullous pemphigoid 180 ectodomain

Bullous pemphigoid is a blistering skin disease characterized by autoantibodies directed against the NC16A domain of bullous pemphigoid 180 (collagen XVII), a transmembrane protein of epidermal basal cells. Passive transfer studies in mice have shown that antibodies that bind to this immunodominant region of bullous pemphigoid 180 are capable of inducing a skin disease that closely mimics bullous pemphigoid, supporting the hypothesis that epitopes within NC16A are involved in the pathogenesis of bullous pemphigoid. In this study, we examined the autoimmune T cell response in bullous pemphigoid patients. T cells from eight of 12 bullous pemphigoid patients, all of whom had circulating anti-bullous pemphigoid 180 autoantibodies, showed a specific proliferative response to recombinant forms of NC16A. T cell lines and clones developed from four of these patients recognize the same NC16A peptides as those targeted by autoantibodies from the corresponding individuals. These NC16A-responding T lymphocytes express alpha/beta T cell receptors and CD4 memory T cell surface markers and exhibited a Th1/Th2 mixed cytokine profile that may support the production of antibodies. This new information will aid in defining the key steps involved in the development of the autoimmune response in bullous pemphigoid.

Human autoimmunity genes in mice

In the post-genomic era, the expression and investigation of human (auto)immunity genes seems more relevant than ever. The generation of humanized animal models of human diseases will be useful to study the interplay between genetic and non-genetic factors in disease development and may form a basis for the development of new drugs that act more specifically than the ones currently in use. Transgenic mice have been generated that express various human proteins--candidate autoantigens, disease-associated MHC class II molecules, TCRs and/or CD4--in order to study diseases such as rheumatoid arthritis, multiple sclerosis and diabetes.

Human herpesvirus 6 and multiple sclerosis: systemic active infections in patients with early disease

By means of immunohistochemical staining, cells actively infected with human herpesvirus 6 (HHV-6) were found in central nervous system tissues from 8 (73%) of 11 patients with definite multiple sclerosis (MS). Interestingly, 17 (90%) of 19 tissue sections showing active demyelination were positive for HHV-6-infected cells compared with only 3 (13%) of 23 tissue sections free of active disease (P<.0001). Central nervous system tissues from 2 of 28 normal persons and patients with other inflammatory demyelinative diseases were positive for HHV-6-infected cells (P<.0001), and the 2 positive cases were diagnosed as having HHV-6 leukoencephalitis. By use of a rapid culture assay, blood samples from 22 (54%) of 41 patients with definite MS were found to contain active HHV-6 infections, compared with 0 of 61 normal controls (P<.0001). No significant difference was found between HHV-6 viremia-positive and HHV-6 viremia-negative MS patients with respect to type of disease (relapsing/remitting or progressive). In contrast, patients with active HHV-6 viremia were significantly younger and had shorter durations of disease than did HHV-6 viremia-negative patients.

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

Peptide dose, MHC affinity, and target self-antigen expression are critical for effective immunotherapy of nonobese diabetic mouse prediabetes

Cross-reactive T cells that recognize both Tep69 (dominant nonobese diabetic (NOD) T cell epitope in ICA69 (islet cell autoantigen of 69 kDa)) and ABBOS (dominant NOD T cell epitope in BSA) are routinely generated during human and NOD mouse prediabetes. Here we analyzed how systemic administration of these mimicry peptides affects progressive autoimmunity in adoptively transferred and cyclophosphamide-accelerated NOD mouse diabetes. These models were chosen to approximate mid to late stage prediabetes, the typical status of probands in human intervention trials. Unexpectedly, high dose (100 microg) i.v. ABBOS prevented, while Tep69 exacerbated, disease in both study models. Peptide effects required cognate recognition of endogenous self-Ag, because both treatments were ineffective in ICA69null NOD congenic mice adoptively transferred with wild-type, diabetic splenocytes. The affinity of ABBOS for NOD I-A(g7) was orders of magnitude higher than that of Tep69. This explained 1) the expansion of the mimicry T cell pool following i.v. Tep69, 2) the long-term unresponsiveness of these cells after i.v. ABBOS, and 3) precipitation of the disease after low dose i.v. ABBOS. Disease precipitation and prevention in mid to late stage prediabetes are thus governed by affinity profiles and doses of therapeutic peptides. ABBOS or ABBOS analogues with even higher MHC affinity may be candidates for experimental intervention strategies in human prediabetes, but the dose translation from NOD mice to humans requires caution.

Autoantibodies to Abl and Bcr proteins

Formation of an aberrant, chimeric Bcr-Abl protein is the hallmark of Philadelphia (Ph) chromosome-positive leukemias. The Bcr-Abl protein, as well as its normal cellular counterparts--Abl and Bcr--are intracellular molecules with postulated roles in a variety of critical biologic functions. In this study, we demonstrate the existence of autoantibodies against these proteins. Plasma from 18 of 31 individuals (58%), including 14 of 20 Ph-positive CML patients (70%), two of four normal volunteers (50%), and two of seven patients with Ph-negative leukemia (29%) recognized p210Bcr-Abl when used in immunoprecipitation followed by immunoblotting experiments. In all 18 patients, plasma was able to recognize baculovirus-expressed Abl protein; in four patients, recognition of baculovirus-expressed Bcr protein was also demonstrated. These observations suggest that a humoral immune response to p210Bcr-Abl is discernible in both Ph-positive and -negative leukemias and in healthy individuals, and is most likely due to autoantibodies which recognize normal Abl and, to a lesser extent, normal Bcr proteins.

The pyruvate dehydrogenase complex as a target autoantigen in primary biliary cirrhosis

Mitochondrial autoantigens and their B and T cell autoepitopes have been well defined in primary biliary cirrhosis (PBC). However, the relationships of the antimitochondrial antibodies and the mechanisms of bile duct destruction in PBC remain an enigma. The serological hallmark of PBC remains the presence of antibodies to mitochondria, particularly to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). However, several mechanisms may now be proposed which may explain the immune-mediated bile duct damage in PBC. These include the possible role of T cell-mediated cytotoxicity as well as the interaction between the IgA class of antimitochondrial antibodies and the mitochondrial autoantigens. A prominent feature in this discussion is the highly directed and specific immune response to the mitochondrial antigens, including PDC-E2 as well as other members of the 2-oxo-acid dehydrogenase complexes. Ultimately, the mechanisms that lead to this immune reaction should provide data on other questions in PBC, including the reasons for female predominance, the absence of PBC in children and the relative ineffectiveness of immunosuppressive agents.

Virus, liver and autoimmunity

The immune system's ability to distinguish self from nonself is essential for both host defence against microbial antigens and protection of self-antigens from autoimmune destruction. Such discrimination is complicated by extensive structural homology shared between micro-organisms and self-antigens, a condition known as molecular mimicry. Molecular mimicry provides the foundation for an immune response directed against an exogenous agent such as a virus to cross-react with mimicked host self sequences, leading to autoimmunity, and in some cases, tissue injury and autoimmune disease. In this review we analyse studies investigating the role of molecular mimicry and cross-reactive immunity in liver-related autoimmunity.

Highly related immunoglobulin light chain sequences in different multiple sclerosis patients

Although immunoglobulin G and free light (L) chains of oligoclonal origin in cerebrospinal fluid (CSF) are the most common immunologic abnormalities in multiple sclerosis (MS), it is unknown whether homologous CSF L chain sequences are present in different individuals with MS. Using Southern blotting, a particular kappa (kappa) L chain variable region (V) probe was recently found to hybridize to Vkappa cDNA from CSF B cells from almost one half of the MS patients tested but only 10% of normal or other neurologic disease controls [Zhou, S.-R., Maier, C.C., Mitchell, G.W., LaGanke, C.C., Blalock, J.E., Whitaker, J.N., 1998. A cross-reactive idiotope in cerebrospinal fluid cells in multiple sclerosis: further evidence for the role of myelin basic protein. Neurology 50, 411-417.] Here, we report that this likely results from remarkable sequence similarity in certain Vkappa from CSF B cells from different individuals with MS. The high degree of sequence homology even extended to all three complementarity determining regions (CDR) which in part form an antibody combining site. In addition, marked sequence homology was observed between the light chains from the MS patients and those from certain mouse antibodies against myelin basic protein (MBP). The results establish, in principle, that the same or very similar kappa light chain variable regions can be shared between CSF B lymphocytes from different individuals with MS as well as with certain antibodies against MBP.

Molecular mapping of the major epitopes of BP180 recognized by herpes gestationis autoantibodies

Herpes gestationis (HG) is an autoantibody-mediated subepidermal bullous dermatosis associated with pregnancy. The primary target of HG autoantibodies is BP180, a 180-kDa hemidesmosomal glycoprotein. We previously showed that autoantibodies and autoimmune T lymphocytes from HG patients recognize the MCW-1 antigenic site (AA 507-520), which is located in the membrane-proximal noncollagenous domain (NC16A) of BP180. Here, we analyzed the sera of 37 HG patients to further define the sites on BP180 that are targeted by autoantibodies. All of the HG sera, but none of the control sera, were immunoreactive with sec180e, a 120-kDa recombinant protein encompassing the entire BP180 extracellular domain. HG sera depleted of reactivity to NC16A no longer reacted with sec180e, indicating that the major HG-associated epitopes on BP180 are restricted to the NC16A domain. The vast majority of the HG sera (34 of 37) reacted with a 7 amino acid peptide corresponding to the N-terminal half of MCW-1 (MCW-1A). Eleven HG sera (including the 3 that failed to react with MCW-1A) recognized one or more of three antigenic sites located within a 15 amino acid stretch immediately downstream of MCW-1A. In summary, we have identified four major HG-associated epitopes clustered within a 22 amino acid region of the BP180 ectodomain. These findings support the hypothesis that an autoimmune response to the BP180 NC16A domain is a crucial step in the pathogenesis of HG.

B-cell responses to myelin basic protein and its epitopes in autoimmune encephalomyelitis induced by Semple rabies vaccine

Semple rabies vaccine is composed of rabies virus-infected sheep or goat brain inactivated with phenol and is administered daily after exposure for 14-21 days. Semple rabies vaccine-induced autoimmune encephalomyelitis (SAE) has clinico-pathological findings of demyelination similar to experimental autoimmune encephalomyelitis (EAE) caused by injection of central nervous system tissue or purified myelin proteins into experimental animals and frequently studied as a model for the human demyelinating disease, multiple sclerosis (MS). T-cell-mediated immune responses play a major role in induction of EAE, and antibody responses enhance disease severity. We studied the antibody responses to myelin basic protein (MBP) in 24 Thai patients with SAE and 77 control individuals to define the linear epitopes in human MBP that are encephalitogenic. Antibody levels were assessed by ELISA using native human MBP or synthetic MBP peptides of 20 amino acids. The major B-cell epitope was MBP61-80 and a minor epitope was MBP106-140 in SAE while in MS the major B-cell epitope is MBP84-96. MBP61-80-specific IgG1 and IgG3 levels were significantly higher in patients than controls while IgG2 and IgG4 were not. The data support the hypothesis that autoreactive Th1 cells induce SAE. The difference in B-cell epitope recognition may be due to differences in the genetic backgrounds of the populations studied or may reflect underlying differences in the pathogenesis of SAE and MS.

Autoimmunity to the glutamate receptor in mice--a model for Rasmussen's encephalitis?

We investigated the in vivo pathogenic potential of murine autoimmunity to peptides of the glutamate/AMPA receptor subunit 3 (GluR3). Antibodies to GluR3 are found in human epilepsy, Rasmussen's encephalitis (RE). In our accompanying paper in this issue we found that murine antibodies to the GluR3B peptide (amino acids 372-395) bind neurons in culture, evoke GluR channel activity, and kill neurons in a complement-independent excitotoxic manner, mimicking the pathophysiologic effects of excess of glutamate. In the present study, we immunized four mouse strains (BALB/c, C3H/HeJ, SJL/J and C57BL/6) with the GluR3B peptide, and investigated the development of (1) anti-GluR3B antibodies; (2) anti-GluR3 T cells; (3) clinical symptoms and abnormal behaviour; (4) brain pathology. We found that BALB/c, C3H/HeJ and SJL/J mice strains developed high titres of anti-GluR3B antibodies. The low levels anti-GluR3B antibodies raised in C57BL/6 mice suggest that the genetic background of mice influences their ability to mount a humoral autoimmune response towards the GluR3B peptide. The GluR3B-immunized mice also developed anti-GluR3B T cells, and their splenocytes showed significantly biased frequencies of particular (Vbeta11, Vbeta7 and Vbeta8) TCR Vbeta families. Surprisingly, GluR3B-immunized mice also raised high anti-ssDNA humoral immunoreactivity. GluR3B-immunized mice exhibited multiple brain pathology, partially resembling that observed in RE, and subclinical behavioral abnormalities, but no epilepsy, even upon facilitating the entry of the autoreactive antibodies into the brain, by weakening the blood-brain barrier. Taken together, these results suggest that autoimmunity to the GluR3B epitope may account for the neuronal death and brain pathology seen in neurodegenerative diseases like RE, but may not be sufficient to underly epilepsy, at least not in mice.

Detection of an autoantibody from Pug dogs with necrotizing encephalitis (Pug dog encephalitis)

An autoantibody against canine brain tissue was detected in the cerebrospinal fluid (CSF) and serum of two Pug dogs (Nos. 1 and 2) by indirect immunofluorescence assay (IFA). Dog No. 1, a 2-year-old male, exhibited severe depression, ataxia, and generalized seizures and died 2 months after the onset of symptoms. Dog No. 2, a 9-month-old male, exhibited severe generalized seizures and died 17 months after the onset of symptoms. Histopathologic examination revealed a moderate to severe multifocal accumulation of lymphocytes, plasma cells, and a few neutrophils in both the gray and white matter of the cerebrum in dog No. 1. In dog No. 2, the cellular infiltrates were mild, but there was a severe, diffuse, and multifocal necrosis in the cerebral cortex with prominent astrocytosis. With the aid of IFA using fluorescein isothiocyanate-labeled antidog IgG goat serum and a confocal imaging system, specific reactions for glial cells were detected in the CSF of these Pug dogs but not in six canine control CSF samples. Double-labeling IFA using CSF from these Pug dogs and a rabbit antiserum against glial fibrillary acidic protein (GFAP) revealed that the autoantibody recognized GFAP-positive astrocytes and their cytoplasmic projections. By immunoblot analysis, the autoantibody from CSF of these Pug dogs recognized two common positive bands at 58 and 54 kd, which corresponded to the molecular mass of human GFAP. The role of this autoantibody for astrocytes is not yet clear. However, if the presence of the autoantibody is a specific feature of Pug dog encephalitis, it will be a useful clinical diagnostic marker and a key to the pathogenesis of this unique canine neurologic disease.

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.

Antigen-Specific Therapy of Murine Lupus Nephritis Using Nucleosomal Peptides: Tolerance Spreading Impairs Pathogenic Function of Autoimmune T and B Cells

In the (SWR × NZB)F1 mouse model of lupus, we previously localized the critical autoepitopes for nephritogenic autoantibody-inducing Th cells in the core histones of nucleosomes at aa positions 10–33 of H2B and 16–39 and 71–94 of H4. A brief therapy with the peptides administered i.v. to 3-mo-old prenephritic (SWR × NZB)F1 mice that were already producing pathogenic autoantibodies markedly delayed the onset of severe lupus nephritis. Strikingly, chronic therapy with the peptides injected into 18-mo-old (SWR × NZB)F1 mice with established glomerulonephritis prolonged survival and even halted the progression of renal disease. Remarkably, tolerization with any one of the nucleosomal peptides impaired autoimmune T cell help, inhibiting the production of multiple pathogenic autoantibodies. However, cytokine production or proliferative responses to the peptides were not grossly changed by the therapy. Moreover, suppressor T cells were not detected in the treated mice. Most interestingly, the best therapeutic effect was obtained with nucleosomal peptide H416–39, which had a tolerogenic effect not only on autoimmune Th cells, but autoimmune B cells as well, because this peptide contained both T and B cell autoepitopes. These studies show that the pathogenic T and B cells of lupus, despite intrinsic defects in activation thresholds, are still susceptible to autoantigen-specific tolerogens.

Microbial epitopes act as altered peptide ligands to prevent experimental autoimmune encephalomyelitis

Molecular mimicry refers to structural homologies between a self-protein and a microbial protein. A major epitope of myelin basic protein (MBP), p87-99 (VHFFKNIVTPRTP), induces experimental autoimmune encephalomyelitis (EAE). VHFFK contains the major residues for binding of this self-molecule to T cell receptor (TCR) and to the major histocompatibility complex. Peptides from papilloma virus strains containing the motif VHFFK induce EAE. A peptide from human papilloma virus type 40 (HPV 40) containing VHFFR, and one from HPV 32 containing VHFFH, prevented EAE. A sequence from Bacillus subtilis (RKVVTDFFKNIPQRI) also prevented EAE. T cell lines, producing IL-4 and specific for these microbial peptides, suppressed EAE. Thus, microbial peptides, differing from the core motif of the self-antigen, MBPp87-99, function as altered peptide ligands, and behave as TCR antagonists, in the modulation of autoimmune disease.

High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

The smaller isoform of the GABA-synthesizing enzyme, glutamic acid decarboxylase 65 (GAD65), is unusually susceptible to becoming a target of autoimmunity affecting its major sites of expression, GABA-ergic neurons and pancreatic beta-cells. In contrast, a highly homologous isoform, GAD67, is not an autoantigen. We used homolog-scanning mutagenesis to identify GAD65-specific amino acid residues which form autoreactive B-cell epitopes in this molecule. Detailed mapping of 13 conformational epitopes, recognized by human monoclonal antibodies derived from patients, together with two and three-dimensional structure prediction led to a model of the GAD65 dimer. GAD65 has structural similarities to ornithine decarboxylase in the pyridoxal-5'-phosphate-binding middle domain (residues 201-460) and to dialkylglycine decarboxylase in the C-terminal domain (residues 461-585). Six distinct conformational and one linear epitopes cluster on the hydrophilic face of three amphipathic alpha-helices in exons 14-16 in the C-terminal domain. Two of those epitopes also require amino acids in exon 4 in the N-terminal domain. Two distinct epitopes reside entirely in the N-terminal domain. In the middle domain, four distinct conformational epitopes cluster on a charged patch formed by amino acids from three alpha-helices away from the active site, and a fifth epitope resides at the back of the pyridoxal 5'-phosphate binding site and involves amino acid residues in exons 6 and 11-12. The epitopes localize to multiple hydrophilic patches, several of which also harbor DR*0401-restricted T-cell epitopes, and cover most of the surface of the protein. The results reveal a remarkable spectrum of human autoreactivity to GAD65, targeting almost the entire surface, and suggest that native folded GAD65 is the immunogen for autoreactive B-cells.

Design and synthesis of a potent cyclic analogue of the myelin basic protein epitope MBP72-85: importance of the Ala81 carboxyl group and of a cyclic conformation for induction of experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP), such as guinea pig sequence MBP72-85. Two linear and one cyclic analogues based on MBP72-85 have been synthesized and evaluated for EAE induction in Lewis rats. The linear peptide Gln1-Lys2-Ser3-Gln4-Arg5-Ser6-Gln7-+ ++Asp8-Glu9-Asn10-Pro11-Val12 (1) was found to induce EAE, while substitution of the Asp residue at position 8 with Ala resulted in an analogue (2) which suppressed the induction of EAE by its parent peptide. Nuclear magnetic resonance studies of analogue 1 in dimethyl sulfoxide (DMSO) using TOCSY/ROESY techniques revealed a head-to-tail intramolecular interaction (ROE connectivity between betaVal12-gammaGln1), indicating a pseudocyclic conformation for the immunogenic peptide 1. A conformational model was developed using NMR constraints and molecular dynamics. Based on this model, a novel amide-linked cyclic analogue has been designed and synthesized by connecting the side-chain amino and carboxyl groups of Lys and Glu at positions 2 and 9, respectively, of linear analogue 1. The cyclic analogue (3) had similar activity to the linear peptide 1, and the EAE effects induced by cyclic analogue 3 were completely suppressed by co-injection with the Ala81-substituted analogue 2 in Lewis rats. The similar potencies of analogues 1 and 3 support the proposed cyclic comformation suggested for analogue 1 from NMR studies and computer modeling and provides the basis for designing more potent molecules with improved properties such as increased resistance to degradation.15 The present findings suggest that a cyclic conformation for the MBP72-85 epitope positions the carboxyl group of Asp81 correctly and presumably other side groups of the peptide such as Arg78 in a manner which enables functional binding of the trimolecular complex MHC-peptide-T cell receptor resulting in EAE.

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 Epitopes Targeted by the Rheumatoid Arthritis-Associated Antifilaggrin Autoantibodies are Posttranslationally Generated on Various Sites of (Pro)Filaggrin by Deimination of Arginine Residues

Antifilaggrin autoantibodies (AFA) are a population of IgG autoantibodies associated to rheumatoid arthritis (RA), which includes the so-called “antikeratin” Abs and antiperinuclear factor. AFA are the most specific serological markers of RA. We previously showed that they recognize human epidermal filaggrin and other profilaggrin-related proteins of various epithelial tissues. Here, we report further characterization of the protein Ags and epitopes targeted by AFA. All the Ags that exhibit numerous neutral/acidic isoelectric variants were immunochemically demonstrated to be deiminated proteins. In vitro deimination of a recombinant human filaggrin by a peptidylarginine deiminase generated AFA epitopes on the protein. Moreover, two of three filaggrin-derived synthetic peptides with a citrulline in the central position were specifically and widely recognized by AFA affinity-purified from a series of RA sera. These results indicate that citrulline residues are constitutive of the AFA epitopes, but only in the context of specific amino acid sequences of filaggrin. In competition experiments, the two peptides abolished the AFA reactivity of RA sera, showing that they present major AFA epitopes. These data should help in the identification of a putative deiminated AFA-inducing or cross-reactive articular autoantigen and provide new insights into the pathogenesis of RA. They could also open the way toward specific immunosuppressive and/or preventive therapy of RA.

Identification and precursor frequency analysis of a common T cell epitope motif in mitochondrial autoantigens in primary biliary cirrhosis

The immunodominant antimitochondrial antibody response in patients with primary biliary cirrhosis (PBC) is directed against the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Based on our earlier observations regarding peripheral blood mononuclear cell (PBMC) T cell epitopes, we reasoned that a comparative analysis of the precursor frequencies of PDC-E2 163-176-specific T cells isolated from PBMC, regional hepatic lymph nodes, and from the liver of PBC patients would provide insight regarding the role of T cells in PBC. Results showed a disease-specific 100-150-fold increase in the precursor frequency of PDC-E2 163-176-specific T cells in the hilar lymph nodes and liver when compared with PBMC from PBC patients. Interestingly, autoreactive T cells and autoantibodies from PBC patients both recognize the same dominant epitope. In addition, we demonstrated cross-reactivity of PDC-E2 peptide 163-176-specific T cell clones with PDC-E2 peptide 36-49 and OGDC-E2 peptide 100-113 thereby identifying a common T cell epitope "motif" ExETDK. The peptide 163-176-specific T cell clones also reacted with purified native PDC-E2, suggesting that this epitope is not a cryptic determinant. These data provide evidence for a major role for PDC-E2 peptide 163-176 and/or peptides bearing a similar motif in the pathogenesis of PBC.

In vivo survival of viral antigen-specific T cells that induce experimental autoimmune encephalomyelitis

A peptide derived from the human papillomavirus L2 protein is recognized by a myelin basic protein (MBP)-specific T cell clone from a multiple sclerosis patient and by MBP-specific autoantibodies purified from multiple sclerosis brain tissue. We now show in mice that low doses of this papillomavirus peptide were optimal in selecting a subpopulation of papillomavirus peptide-specific T cells that cross-reacted with MBP(87-99) and with an unrelated viral peptide derived from the BSLF1 protein of Epstein-Barr virus (EBV). These low dose viral peptide- specific T cell lines were highly encephalitogenic. Splenocytes from mice transferred with viral peptide-specific T cells showed a vigorous response to both the papillomavirus and MBP peptides, indicating that viral antigen-specific T cells survived for a prolonged time in vivo. The EBV peptide, unable to prime and select an autoreactive T cell population, could still activate the low dose papillomavirus peptide-specific cells and induce central nervous system (CNS) autoimmunity. Cytokine profiles of papillomavirus peptide-specific encephalitogenic T cells and histopathology of CNS lesions resembled those induced by MBP. These results demonstrate conserved aspects in the recognition of the self-antigen and a cross-reactive viral peptide by human and murine MBP-specific T cell receptors. We demonstrate that a viral antigen, depending on its nature, dose, and number of exposures, may select autoantigen-specific T cells that survive in vivo and can trigger autoimmune disease after adoptive transfer.

Recent advances in immunology in multiple sclerosis

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system that is of possible autoimmune origin. This article is divided into three parts, reviewing recent advances in three selected topics regarding the immunology of multiple sclerosis. The first part addresses the consequences of T cell and oligodendrocyte death in the inflammatory lesions. The second covers the recent experimental evidence favouring the involvement of infectious agents in the pathophysiology of central nervous system autoimmune diseases. The third part concerns the mode of action of interferon-beta in multiple sclerosis. These new advances have lead to a better understanding of the immunopathology of multiple sclerosis and therefore open new therapeutic possibilities.

Activation of autoreactive T cells by peptides from human pathogens

Activation of autoreactive T cells is a necessary-but not sufficient-step in the development of T cell mediated autoimmunity. Autoreactive T cells can be activated by viral and bacterial peptides that meet the structural requirements for MHC molecule binding and T cell receptor recognition. Due to the degenerate nature of MHC class II molecule binding motifs and a certain degree of flexibility in T cell receptor recognition, such microbial peptides have been found to be quite distinct in their primary sequence from the self-peptide they mimic.