Katrien L. de Graaf

T cell epitopes of human myelin oligodendrocyte glycoprotein identified in HLA-DR4 (DRB1*0401) transgenic mice are encephalitogenic and are presented by human B cells.

Myelin oligodendrocyte glycoprotein (MOG) is an Ag present in the myelin sheath of the CNS thought to be targeted by the autoimmune T cell response in multiple sclerosis (MS). In this study, we have for the first time characterized the T cell epitopes of human MOG restricted by HLA-DR4 (DRB1*0401), an MHC class II allele associated with MS in a subpopulation of patients. Using MHC binding algorithms, we have predicted MOG peptide binding to HLA-DR4 (DRB1*0401) and subsequently defined the in vivo T cell reactivity to overlapping MOG peptides by testing HLA-DR4 (DRB1*0401) transgenic mice immunized with recombinant human (rh)MOG. The data indicated that MOG peptide 97–108 (core 99–107, FFRDHSYQE) was the immunodominant HLA-DR4-restricted T cell epitope in vivo. This peptide has a high in vitro binding affinity for HLA-DR4 (DRB1*0401) and upon immunization induced severe experimental autoimmune encephalomyelitis in the HLA-DR4 transgenic mice. Interestingly, the same peptide was presented by human B cells expressing HLA-DR4 (DRB1*0401), suggesting a role for the identified MOG epitopes in the pathogenesis of human MS.

Quantitative trait loci disposing for both experimental arthritis and encephalomyelitis in the DA rat; impact on severity of myelin oligodendrocyte glycoprotein‐induced experimental autoimmune encephalomyelitis and antibody isotype pattern

Quantitative trait loci (QTL) controlling inflammatory diseases with different organ specificity may hypothetically either be unique for one disease or shared among different diseases. We have investigated whether five non‐MHC QTL controlling susceptibility to experimental arthritis in the DA rat also influence myelin oligodendrocyte glycoprotein (MOG)‐induced experimental autoimmune encephalomyelitis (EAE) in an F2 intercross between inbred DA and PVG.RT1a rats. Two of the five chromosome regions affecting arthritis in the DA rat also regulate phenotypes of EAE. The DA allele at markers in Cia3(collagen‐induced arthritis QTL) on chromosome 4 is associated with more severe EAE and high levels of anti‐MOG antibodies of the IgG2c subclass. Since production of antibodies of the IgG2c subclass may be stimulated by Th1 cells, and there is previous evidence that such cells promote EAE, it is possible that both of the studied phenotypes are controlled by the same gene or genes regulating Th1/Th2 cell differentiation. Furthermore, we show that Oia2(oil‐induced arthritis QTL) on chromosome 4 regulates levels of anti‐MOG antibodies of the IgG1 subclass and of anti‐MOG IgE, but that this gene region does not affect clinical disease severity in our study. Since production of IgE and IgG1 may be stimulated by Th2 cells, this QTL may also control Th1/Th2 bias. We conclude that Cia3and Oia2regulate MOG‐induced EAE in rats. Furthermore, since both EAE and arthritis phenotypes co‐localize to these gene regions, they may harbor genes which are key regulators of pathogenic immune responses.

MHC Class II-Regulated Central Nervous System Autoaggression and T Cell Responses in Peripheral Lymphoid Tissues Are Dissociated in Myelin Oligodendrocyte Glycoprotein-Induced Experimental Autoimmune Encephalomyelitis

We dissected the requirements for disease induction of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis in MHC (RT1 in rat) congenic rats with overlapping MOG peptides. Immunodominance with regard to peptide-specific T cell responses was purely MHC class II dependent, varied between different MHC haplotypes, and was linked to encephalitogenicity only in RT1.Ba/Da rats. Peptides derived from the MOG sequence 91–114 were able to induce overt clinical signs of disease accompanied by demyelinated CNS lesions in the RT1.Ba/Da and RT1n haplotypes. Notably, there was no detectable T cell response against this encephalitogenic MOG sequence in the RT1n haplotype in peripheral lymphoid tissue. However, CNS-infiltrating lymphoid cells displayed high IFN-γ, TNF-α, and IL-4 mRNA expression suggesting a localization of peptide-specific reactivated T cells in this compartment. Despite the presence of MOG-specific T and B cell responses, no disease could be induced in resistant RT1l and RT1u haplotypes. Comparison of the number of different MOG peptides binding to MHC class II molecules from the different RT1 haplotypes suggested that susceptibility to MOG-experimental autoimmune encephalomyelitis correlated with promiscuous peptide binding to RT1.B and RT1.D molecules. This may suggest possibilities for a broader repertoire of peptide-specific T cells to participate in disease induction. We demonstrate a powerful MHC class II regulation of autoaggression in which MHC class II peptide binding and peripheral T cell immunodominance fail to predict autoantigenic peptides relevant for an autoaggressive response. Instead, target organ responses may be decisive and should be further explored.

Naturally Presented Peptides on Major Histocompatibility Complex I and II Molecules Eluted from Central Nervous System of Multiple Sclerosis Patients

Tandem mass spectrometry was used to identify naturally processed peptides bound to major histocompatibility complex (MHC) I and MHC II molecules in central nervous system (CNS) of eight patients with multiple sclerosis (MS). MHC molecules were purified from autopsy CNS material by immunoaffinity chromatography with monoclonal antibody directed against HLA-A, -B, -C, and -DR. Subsequently peptides were separated by reversed-phase HPLC and analyzed by mass spectrometry. Database searches revealed 118 amino acid sequences from self-proteins eluted from MHC I molecules and 191 from MHC II molecules, corresponding to 174 identified source proteins. These sequences define previously known and potentially novel autoantigens in MS possibly involved in disease induction and antigen spreading. Taken together, we have initiated the characterization of the CNS-expressed MHC ligandome in CNS diseases and were able to demonstrate the presentation of naturally processed myelin basic protein peptides in the brain of MS patients.

Suppressive DNA Vaccination in Myelin Oligodendrocyte Glycoprotein Peptide-Induced Experimental Autoimmune Encephalomyelitis Involves a T1-Biased Immune Response

Vaccination with DNA encoding a myelin basic protein peptide suppresses Lewis rat experimental autoimmune encephalomyelitis (EAE) induced with the same peptide. Additional myelin proteins, such as myelin oligodendrocyte glycoprotein (MOG), may be important in multiple sclerosis. Here we demonstrate that DNA vaccination also suppresses MOG peptide-induced EAE. MOG91–108 is encephalitogenic in DA rats and MHC-congenic LEW.1AV1 (RT1av1) and LEW.1N (RT1n) rats. We examined the effects of DNA vaccines encoding MOG91–108 in tandem, with or without targeting of the hybrid gene product to IgG. In all investigated rat strains DNA vaccination suppressed clinical signs of EAE. There was no requirement for targeting the gene product to IgG, but T1-promoting CpG DNA motifs in the plasmid backbone of the construct were necessary for efficient DNA vaccination, similar to the case in DNA vaccination in myelin basic protein-induced EAE. We failed to detect any effects on ex vivo MOG-peptide-induced IFN-γ, TNF-α, IL-6, IL-4, IL-10, and brain-derived neurotropic factor expression in splenocytes or CNS-derived lymphocytes. In CNS-derived lymphocytes, Fas ligand expression was down-regulated in DNA-vaccinated rats compared with controls. However, MOG-specific IgG2b responses were enhanced after DNA vaccination. The enhanced IgG2b responses together with the requirement for CpG DNA motifs in the vaccine suggest a protective mechanism involving induction of a T1-biased immune response.

High Immunogenicity of Intracellular Myelin Oligodendrocyte Glycoprotein Epitopes

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the CNS with associated axonal loss. There is strong evidence for an autoimmune pathogenesis driven by myelin-specific T cells. Myelin oligodendrocyte glycoprotein (MOG) induces a type of experimental autoimmune encephalomyelitis in animals which is very MS-like since there are demyelinating CNS lesions and axonal loss. This underscores the potential role of MOG in MS pathogenesis. We performed a T cell reactivity pattern analysis of MS patients at the onset of relapse or progression of neurological deficits and controls that were stratified for the genetic risk factor HLA-DRB1*1501. For the first time, we show that there is an HLA-DR-restricted promiscuous dominant epitope for CD4+ T cells within the transmembrane/intracellular part of MOG comprising aa 146–154 (FLCLQYRLR). Surprisingly, controls had broader T cell reactivity patterns toward MOG peptides compared with MS patients, and the transmembrane and intracellular parts of MOG were much more immunogenic compared with the extracellular part. Measurements of in vitro binding affinities revealed that HLA-DRB1*1501 molecules bound MOG 146–154 with intermediate and HLA-DRB1*0401 molecules with weak affinities. The binding of MOG 146–154 was comparable or better than myelin basic protein 85–99, which is the dominant myelin basic protein epitope in context with HLA-DRB1*1501 molecules in MS patients. This is the first study in which the data underscore the need to investigate the pathogenic or regulatory role of the transmembrane and intracellular part of MOG for MS in more detail.

Maternal MHC Regulates Generation of Pathogenic Antibodies and Fetal MHC-Encoded Genes Determine Susceptibility in Congenital Heart Block

Congenital heart block develops in fetuses of anti-Ro52 Ab-positive women. A recurrence rate of 20%, despite the persistence of maternal autoantibodies, indicates that there are additional, yet unidentified, factors critical for development of congenital heart block. In this study, we demonstrate that besides the maternal MHC controlling Ab specificity, fetal MHC-encoded genes influence fetal susceptibility to congenital heart block. Using MHC congenic rat strains, we show that heart block develops in rat pups of three strains carrying MHC haplotype RT1av1 (DA, PVG.AV1, and LEW.AV1) after maternal Ro52 immunization, but not in LEW rats (RT1l). Different anti-Ro52 Ab fine specificities were generated in RT1av1 versus RT1l animals. Maternal and fetal influence was determined in an F2 cross between LEW.AV1 and LEW strains, which revealed higher susceptibility in RT1l than RT1av1 pups once pathogenic Ro52 Abs were present. This was further confirmed in that RT1l pups more frequently developed heart block than RT1av1 pups after passive transfer of RT1av1 anti-Ro52 sera. Our findings show that generation of pathogenic Ro52 Abs is restricted by maternal MHC, whereas the fetal MHC locus regulates susceptibility and determines the fetal disease outcome in anti-Ro52–positive pregnancies.

Characterization of the encephalitogenic immune response in a model of multiple sclerosis.

Experimental autoimmune encephalomyelitis (EAE) can be actively induced with the extracellular domain of myelin oligodendrocyte glycoprotein (MOG 1–125). MOG‐EAE closely mimics multiple sclerosis (MS) especially as far as demyelination, lesion formation and axonal pathology are concerned. MOG 91–108 is the encephalitogenic stretch within MOG 1–125 in two EAE‐susceptible MHC congenic LEW rat strains [LEW.1AV1 (RT1av1) and LEW.1N (RT1n)] and DA (RT1av1) rats. In LEW.1AV1 rats, disease could be induced with MOG 96–104 and to a lesser extent with MOG 98–106, whereas in LEW.1N rats, only MOG 98–106 was pathogenic. Both peptides bound well to their restricting MHC class II molecules, i.e., RT1.Dn in the LEW.1N rat and RT1.Ba in the LEW.1AV1 rat. TCR spectratyping of MOG 91–108 immunized LEW.1N, LEW.1AV1 and DA rats revealed that MHC class II determined the TCRBV preference of CNS infiltrating T cells. The data demonstrate that the most critical factor in inducing MS like pathology is presentation of autoantigenic peptides on MHC class II molecules resulting in demyelination and axonal pathology.

MHC class II isotype- and allele-specific attenuation of experimental autoimmune encephalomyelitis.

Most autoimmune diseases are associated with certain MHC class II haplotypes. Autoantigen-based specific immune therapy can lead either to beneficial or, in the context of inflammatory conditions, detrimental outcomes. Therefore, we designed a platform of peptides by combinatorial chemistry selected in a nonbiased Ag-independent approach for strong binding to the rat MHC class II isotype RT1.Dn allelic product of the RT1n haplotype that is presenting autoantigen in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in LEW.1N rats. Peptide p17 (Ac-FWFLDNAPL-NH2) was capable of suppressing the induction of and also ameliorated established experimental autoimmune encephalomyelitis. MHC class II isotype and allele specificity of the therapeutic principle were demonstrated in myelin basic protein-induced experimental autoimmune encephalomyelitis in LEW rats bearing the RT1l haplotype. A general immunosuppressive effect of the treatment was excluded by allogeneic heart transplantation studies. In vitro studies demonstrated the blocking effect of p17 on autoantigenic T cell responses. We thus demonstrate a rational design of strong MHC class II-binding peptides with absolute isotype and allele specificity able to compete for autoantigenic sequences presented on disease-associated MHC class II molecules.

Autoantigen conformation influences both B- and T-cell responses and encephalitogenicity.

Background: The influence of protein conformation of autoantigens to induce disease has not been assessed in detail. Results: Protein conformation of myelin oligodendrocyte glycoprotein determined encephalitogenicity and the degree of T- and B-cell responses. Conclusion: Protein conformation has a strong impact on the potential of an autoantigen to induce autoimmune disease. Significance: Autoantigen conformation needs to be taken into consideration in studies regarding disease-inducing capacity. It has become increasingly clear that only antibodies recognizing conformation-dependent epitopes of myelin oligodendrocyte glycoprotein (MOG) have a demyelinating potential in the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Nevertheless, for the induction of EAE, most studies to date have used MOG peptides or bacterially expressed MOG, neither of which contain the tertiary structure of the native antigen. Non-refolded recombinant human MOG does not induce EAE in DA rats. Therefore, we refolded this protein in order to assess the influence of MOG conformation on its pathogenicity in DA rats. DA rats immunized with refolded human MOG developed severe acute EAE. As expected, rats immunized with the refolded protein had a higher amount of conformational MOG antibodies present in serum. But in addition, a striking effect of MOG refolding on the generation of T-cell responses was found. Indeed, T-cell responses against the encephalitogenic MOG 91–108 epitope were greatly enhanced after refolding. Therefore, we conclude that refolding of MOG increases its pathogenicity both by generating conformation-dependent MOG antibodies and by enhancing its processing or/and presentation on MHC molecules. These data are important in regard to investigations of the pathogenic potential of many (auto)antigens.