A novel candidate autoantigen in a multiplex family with multiple sclerosis: prevalence of T-lymphocytes specific for an MBP epitope unique to myelination

Myelin basic protein and myelin oligodendrocyte glycoprotein T-cell repertoire in childhood and juvenile multiple sclerosis

Multiple sclerosis (MS) is usually a disease of young adulthood, its clinical onset occurring between 20 and 40 years of age; however, today there is general consensus that MS can also occur in children, adolescents and even in infants. In order to gain further insight into the T-cell repertoire present in this particular group of patients myelin basic protein (MBP)-, MBP exon-2- and myelin oligodendrocyte glycoprotein (MOG)Igd-specific T-cell lines (TCLs) were isolated from 18 patients whose symptoms had started before the age of 16. Epitope specificity was established by measuring proliferative responses, and interferon-g (IFN-g) secretion by using a panel of overlapping synthetic peptides. For MOGIgd, the T-cell response was focused on three main immunodominant epitopes comprising residues 1-26, 36-60 and 63-87. For MBP the predominant immune responses were directed against peptides 83-102, 139-153 and 146-162. When compared to those observed in adult-onset MS patients, anti-MOGIgd specificity and anti-MBP responses showed similar results. Moreover, the number of MBP exon-2 TCLs isolated, and the magnitude of the specific IFN-g secretion induced were similar, both in childhood/juvenile-onset and adult-onset MS patients. Thus, despite differences in the clinical and neuroimaging manifestations of MS, these results would seem to indicate that both the spectrum of MBP found, as well as the MOGIgd epitopes recognized by peripheral blood T cells in MS, appear to be similar for childhood/juvenile-onset and adult-onset patients.

Mechanisms of immunological tolerance in central nervous system inflammatory demyelination

Multiple sclerosis is a complex autoimmune disease of the central nervous system that results in a disruption of the balance between pro-inflammatory and anti-inflammatory signals in the immune system. Given that central nervous system inflammation can be suppressed by various immunological tolerance mechanisms, immune tolerance has become a focus of research in the attempt to induce long-lasting immune suppression of pathogenic T cells. Mechanisms underlying this tolerance induction include induction of regulatory T cell populations, anergy and the induction of tolerogenic antigen-presenting cells. The intravenous administration of encephalitogenic peptides has been shown to suppress experimental autoimmune encephalomyelitis and induce tolerance by promoting the generation of regulatory T cells and inducing apoptosis of pathogenic T cells. Safe and effective methods of inducing long-lasting immune tolerance are essential for the treatment of multiple sclerosis. By exploring tolerogenic mechanisms, new strategies can be devised to strengthen the regulatory, anti-inflammatory cell populations thereby weakening the pathogenic, pro-inflammatory cell populations.

A Truncated Alternative Spliced Isoform of Human Desmoglein 1 Contains a Specific T Cell Epitope Binding to the Pemphigus Foliaceus-Associated HLA Class II DRβ1*0102 Molecule

Desmogleins (Dsg) are transmembrane glycoproteins of the desmosome that allow a cell-cell adhesion between keratinocytes and comprise four different isoforms (Dsg1 to Dsg4). Two Dsg are targeted by pathogenic autoantibodies produced in the course of autoimmune bullous skin diseases, Dsg1 in pemphigus foliaceus (PF), and Dsg3 and Dsg1 in pemphigus vulgaris. The genetic susceptibility to PF is associated with certain HLA class II alleles, which are thought to participate in disease pathogenesis through their capacity to accommodate autoantigen-derived peptides and present them to autoreactive T cells. So far, a unique isoform of Dsg1 has been described in humans, which includes several immunodominant T cell epitopes. In this study, we describe an alternative transcript of DSG1, which contains a 101-bp insertion corresponding to the 3' end of DSG1-intron 6 and introducing a stop codon in the nucleotide sequence. This alternative transcript leads to the synthesis of a truncated isoform of Dsg1 expressed in normal human epidermis. This isoform bears a specific peptide sequence that binds to the PF-associated HLA class II DRbeta1*0102 molecule as shown in a HLA-DR peptide-binding assay, and induces PF T cell proliferation. These data provide an illustration of an autoantigen encoded by alternative spliced transcript that may participate in the pathogenesis of the disease by bearing PF-associated HLA class II restricted-epitope.

Complex alternative splicing of the myelin oligodendrocyte glycoprotein gene is unique to human and non-human primates

Myelin/oligodendrocyte glycoprotein (MOG) is a minor integral membrane protein specific to CNS myelin, encoded by a gene located in the major histocompatibility complex. MOG is an highly encephalitogenic autoantigen and a target for autoaggressive immune responses in CNS inflammatory demyelinating diseases. We performed transcriptomic analyses for a gene expressed only in mammalian CNS, myelin oligodendrocyte glycoprotein (MOG). Complex splicing patterns were exclusively found in primates and not in mice, unlike patterns found for other myelin protein genes. In addition to those shared with rodents, these multiple MOG isoforms likely support functions unique to the primate order, in particular maintenance of myelin structure, intracellular signaling, and modulation of CNS autoimmunity via exposure of specific MOG determinants. Developmentally, in human brain the splice variants of MOG appear at a late stage compared to the major isoform, coincidental with myelination and myelin maturation, unlike other myelin proteins. These findings are discussed within the framework of a biological basis for phenotype diversity in recent mammalian evolution and for the notoriously variable clinical expression of diseases such as multiple sclerosis.

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

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

T-cell properties determine disease site, clinical presentation, and cellular pathology of experimental autoimmune encephalomyelitis

Two distinct clinical phenotypes of experimental autoimmune encephalomyelitis are observed in BALB interferon-gamma knockout mice immunized with encephalitogenic peptides of myelin basic protein. Conventional disease, characterized by ascending weakness and paralysis, occurs with greater frequency after immunizing with a peptide comprising residues 59 to 76. Axial-rotatory disease, characterized by uncontrolled axial rotation, occurs with greater frequency in mice immunized with a peptide corresponding to exon 2 of the full length 21.5-kd protein. The two clinical phenotypes are histologically distinguishable. Conventional disease is characterized by inflammation and demyelination primarily in spinal cord, whereas axial-rotatory disease involves inflammation and demyelination of lateral medullary areas of brain. Both types have infiltrates in which neutrophils are a predominating component. By isolating T cells and transferring disease to naive recipients, we show here that the type of disease is determined entirely by the inducing T cell. Furthermore, studies using CXCR2 knockout recipients, unable to recruit neutrophils to inflammatory sites, show that although neutrophils are critical for some of these T cells to effect disease, there are also interferon-gamma-deficient T cells that induce disease in the absence of both interferon-gamma and neutrophils. These results highlight the multiplicity of T-cell-initiated effector pathways available for inflammation and demyelination.

Activation of APCs through CD40 or Toll-like receptor 9 overcomes tolerance and precipitates autoimmune disease

Some autoreactive T cells normally escape thymic selection and persist in the periphery. This is true of myelin-reactive CD4(+) T cells, the effectors of experimental autoimmune encephalomyelitis (EAE) in laboratory animals and the presumed mediators of multiple sclerosis in humans. Nonetheless, most individuals do not succumb to autoimmune disease. There is growing evidence that while peripheral APCs stimulate immune responses against foreign Ags in the setting of tissue destruction and "danger," they actually maintain tolerance against self Ags under steady state conditions. We hypothesized that tolerance against candidate autoantigens could be reversed by activation of APCs via CD40 or Toll-like receptor 9 signaling. Adult SJL mice injected i.p. with a peptide fragment of proteolipid protein (a candidate autoantigen in multiple sclerosis) emulsified in IFA fail to mount lymphoproliferative or cytokine responses and are protected from EAE upon subsequent challenge with the Ag combined with adjuvants. Here we report that tolerized proteolipid protein-specific lymph node cells regain the ability to divide, differentiate along a Th1 lineage, and transfer EAE when reactivated in the presence of agonistic Abs against CD40 or CpG oligonucleotides. The effects of both anti-CD40 and CpG oligonucleotides are dependent upon induction of IL-12. Our findings suggest two mechanisms to explain the well-documented association between infectious illnesses and flare-ups of multiple sclerosis. Microbial pathogens could 1) release molecules that bind Toll-like receptors, and/or 2) stimulate microbe-specific T cells to express CD40 ligand, thereby licensing APCs that bear both microbial and autoantigens to break tolerance.

Autoreactive IgG to intracellular proteins in sera of MS patients

IgG binding to multiple protein constituents in lysates of Jurkat cells was detected by Western blot in sera of patients with multiple sclerosis (MS) and systemic lupus erythematosus (SLE). The distribution patterns of bands with sera tested against protein lysates from normal Jurkat cells or from Jurkat cells exposed to apoptosis or oxidative stress inducing conditions were similar in most patients, but with inter-individual differences. The number of bands with sera of both patient populations far exceeded those (0 or 2 bands) detected with sera of healthy controls. Proteinase K, RNase and DNase pre-treatment of cell lysates suggested a protein nature for all of the antigens and a ribonucleoprotein (RNP) nature for some of the antigens recognized by serum IgG of MS and SLE patients. Only two MS patients had positive anti-nuclear antibody (ANA) titers, while all of them had positive Western blots. In addition to similarities, dissimilarities were also recognized between the humoral immune responses in MS and SLE. No IgG molecules were detected against phosphorylated proteins in the sera of MS patients, while multiple phosphoproteins were recognized by IgG molecules of SLE patients in immunoprecipitation experiments. These data suggest that in addition to ANA, the sera of MS patients contain autoantibodies directed against multiple intracellular proteins. The protein recognition patterns of immunoglobulins in MS share similarities, but also have distinct features when compared to those in SLE. The biological significance of these autoantibodies in MS remains to be understood.

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.

Differential recognition of MBP epitopes in BALB/c mice determines the site of inflammatory disease induction

Although myelin basic protein (MBP)-recognizing T cells are not readily obtained after immunization of BALB/c mice with MBP (reflecting the BALB/c resistance to actively induced experimental autoimmune encephalomyelitis (EAE)), they can be expanded and cloned after several rounds of in vitro culture. The majority of BALB/c-derived clones recognize an epitope defined by MBP peptide 59-76. When transferred to naive BALB/c recipients, these clones cause classical EAE, with characteristic inflammation and demyelination of the central nervous system (CNS). We previously showed that two related clones recognizing a minor epitope, defined by MBP peptide 151-168, cause inflammation and demyelination preferentially of the peripheral nervous system (PNS). Because MBP has alternatively spliced isoforms, residues 151-168 are not present contiguously in all MBP isoforms. In order to determine whether induction of PNS disease is idiosyncratic to these sister clones, or related to their properties of epitope recognition, an independent T-cell line with similar recognition properties was studied. Clone 116F, derived from a BALB/c shiverer mouse, expresses a different T-cell receptor (TCR), with distinct TCR contact residues, but like the previously described T cells, this clone requires residues from both exons 6 and 7 for optimal stimulation. When adoptively transferred to BALB/c recipients, this clone preferentially induces disease of the PNS. A control BALB/c shiverer-derived MBP 59-76-recognizing clone, in contrast, induces CNS disease. These data strongly suggest that the site of disease initiation may correlate with epitope recognition, particularly when alternative isoforms are involved.

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

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

Golli-MBP gene in multiple sclerosis susceptibility

Multiple sclerosis (MS) is an oligo- or polygenic disease but no specific susceptibility genes have been identified so far. In the Finnish population we have previously found evidence for linkage between MS and the myelin basic protein gene (here called Golli-MBP gene) suggesting that either Golli-MBP or another gene in its vicinity contributes to MS suceptibility. Here we have screened the Golli-MBP gene for nucleotide variations and carried out multipoint association analyses in a Finnish case-control data-set as well as in an independent data-set composed of 151 MS families from Finland and Sweden. In both data-sets we found association between MS and alleles in the 1.27 kilobase (kb) range at a tetranucleotide repeat element (TGGA)n which is located 1 kb upstream of the MBP exon 1. Haplotype analyses suggested that the MS-associated 1.27 kb alleles can be split into predisposing and non-predisposing variants and provided evidence that the candidate DNA region contributing to MS susceptibility should be located at the Golli-MBP gene within a 20-25 kb segment that was conserved in the predisposing haplotypes. These findings suggest a role for the Golli-MBP locus in MS susceptibility, at least in a subset of patients, and serve as a basis for highly focused attempts to identify predisposing mutation(s).

Multiple sclerosis: re-expression of a developmental gene in chronic lesions correlates with remyelination

Central nervous system tissue from multiple sclerosis and non-multiple sclerosis subjects was studied for the expression of exon 2 myelin basic protein gene products at the protein and message levels by immunocytochemistry and in situ hybridization, respectively. The exon 2-encoded protein sequence is normally expressed during development (myelination) within the 21.5- and 20.2-kd isoforms of myelin basic protein and is downregulated in the adult central nervous system where the 18.5- and 17.2-kd isoforms predominate, the latter devoid of exon 2 owing to alternative splicing. Exon 2 myelin basic protein gene products were readily demonstrable in multiple sclerosis samples, the highest levels correlating with remyelination in chronic lesions while normal adult central nervous system and non-multiple sclerosis material showed very low levels and fetal human central nervous system tissue (a positive control) showed high levels. We conclude that recapitulation of ontogenetic events during myelin repair accounts for the increased expression of the exon 2-encoded protein sequence in the adult central nervous system during multiple sclerosis, an event that might underly the previously observed T-cell activation to this protein sequence during relapses.

A study of human T-cell lines generated from multiple sclerosis patients and controls by stimulation with peptides of myelin basic protein

We generated T-cell lines from the peripheral blood of controls and of patients with multiple sclerosis (MS) by stimulation with overlapping synthetic peptides representing the entire sequences of all four isoforms of human myelin basic protein (MBP). The T-cell lines reacted to a wide range of epitopes in the major isoforms of MBP and to epitopes that were present only in the minor isoforms. Many MS patients and controls had T-cells responding to one or more cryptic MBP epitopes, as indicated by the generation of a peptide-specific T-cell line(s) by stimulation with synthetic peptides but not by stimulation with whole MBP. About one-third of the peptide-generated lines were cytotoxic. Although we have shown that this technique of peptide stimulation is effective in generating human antiviral cytotoxic CD8+ T-cell lines, all the cytotoxic MBP-specific lines generated by this method were predominantly CD4+. Our study did not reveal any significant differences, between MS patients and controls, in reactivity to epitopes within any of the isoforms of MBP.

Biochemistry of demyelination

The myelin sheath, a lipid-rich multilamellar membrane of relative stability, both insulates and enhances conduction in nerve axons. A notable feature of myelin-specific proteins, in particular myelin basic protein, is their susceptibility to proteolytic activity and their encephalitogenicity, which induces inflammatory demyelination in the CNS. The final common pathway of myelin breakdown in vivo is well documented and there is evidence that myelin disruption can be mediated directly by soluble (circulating) factors and for following receptor-driven phagocytosis by macrophages. However the exact mechanism(s) of demyelination in multiple sclerosis is still unresolved, both antigen-specific and--non-specific events having the potential to generate the myelinolytic process.

Purification of immunologically active recombinant 21.5 kDa isoform of human myelin basic protein

We have designed and expressed in bacteria a recombinant fetal form of human myelin basic protein (21.5 kDa isoform; rhMBP21.5), a candidate autoantigen in multiple sclerosis. An exon 2 insertion, carboxy-terminal histidine tag and preferred bacterial codons differentiate the MBP21.5 gene from that encoding the adult, brain-derived form of human MBP (18.5 kDa isoform; hMBP18.5). MBPs were expressed at high levels in E. coli and extracted from whole cells by simultaneous acid solubilization and mechanical disruption. A nearly two-fold increase in recombinant protein was detected in strains harboring MBP genes with bacterial preferred codons compared to genes containing human codons. The recombinant molecules were purified in two steps, first by reversed-phase chromatographic separation and then by metal affinity chromatography. Dimeric forms of recombinant MBP21.5 were detected under physiological conditions, however, substitution of a serine for the single cysteine at amino acid residue 81 resulted in only monomer formation. All forms of recombinant MBPs induced proliferative responses of human T lymphocytes specific for epitopes in MBP18.5 kDa. In contrast, human T cell lines that recognize an exon 2-encoded epitope of MBP responded to the 21.5 kDa isoform of MBP, but not the 18.5 kDa isoform.

Reactivity of normal T-cell lines to MBP isolated from normal and multiple sclerosis white matter

T-cell reactivity to human myelin basic protein (MBP) has been extensively studied using T-cell lines and clones generated from both peripheral blood and cerebrospinal fluid, from normal controls and multiple sclerosis (MS) patients. These studies have largely utilized myelin basic protein isolated from control human adult white matter. In our study, we used MBP reactive T-cell lines as a probe to investigate antigenic differences in a series of MBP preparations isolated from either control human white matter or white matter from the central nervous system (CNS) of MS patients. Autologous peripheral blood derived mononuclear cells were used as antigen presenting cells (APC). Although the majority of T-cells were found to react equally well with all preparations of MBP isolated from both control and MS white matter, we were also able to identify T-cell lines which reacted well with all preparations of MBP isolated from controls but failed to react with MBP isolated from MS white matter. These differences were unlikely to reflect differences in degradation products or excess peptides present in the MS brain since SDS-PAGE and HPLC did not show any difference in the MS samples compared to the controls, and the concentration response curves for a human T-cell clone specific for the 84-102 region of MBP were similar for all the MBP preparations. We did not detect differences in amino acid content amongst MBP preparations although single amino acid substitutions cannot be ruled out. These results raise the possibility that MBP isolated from MS brain may differ in charge microheterogeneity which would affect antigenic determinants.(ABSTRACT TRUNCATED AT 250 WORDS)

TCR V gene usage in autoimmunity

With the use of polymerase chain reaction technology, investigators now have the ability to assess, in a comprehensive and rapid manner, the entire repertoire of T cell antigen receptors expressed by pathogenic cells present in virtually any disease site. A summary of studies of T cell receptor variable gene usage suggests that preferential expression can be identified most reproducibly when cells are isolated directly from pathogenic lesions. This provides a framework for future investigations in other autoimmune settings.

Self-determinants in autoimmune demyelinating disease: changes in T- cell response specificity

Recent research developments support the following views regarding antigen recognition in autoimmune demyelinating disease: there may be no single autoimmune target protein; diverse peptide self-determinants from multiple myelin proteins can be recognized; target determinant epitopes may differ among individuals; and target epitope recognition can change with time during the course of disease.

Experimental allergic encephalomyelitis induced by the peptide encoded by exon 2 of the MBP gene, a peptide implicated in remyelination

The discovery of T lymphocytes reactive to the peptide encoded by exon 2 of the myelin basic protein (MBP) gene in multiple sclerosis (MS) patients has drawn attention to MBP isoforms harboring that peptide as candidate autoantigens. Previously, immunological studies in MS had almost exclusively used the more abundant 18.5 kDa isoform of MBP, which does not contain the exon 2 peptide. Investigations of experimental allergic encephalomyelitis (EAE) have also focussed on the 18.5 kDa MBP isoform and its peptides. Since EAE is an animal model widely used to study MS, we examined the encephalitogenic potential of exon 2 peptide in the SJL/J mouse. Evidence for increased expression of exon 2-containing isoforms during remyelination in mouse CNS suggested that exon 2-sensitized T cells, with encephalitogenic capacity, might be important in the perpetuation of relapsing EAE (rEAE). Our experiments have demonstrated that exon 2 peptide is inherently immunogenic in SJL mice and that EAE could be induced by the adoptive transfer of exon 2-sensitized lymphocytes. Furthermore, the disease could be accentuated by the transfer of short-term exon 2-reactive lines or by a combination of adoptive transfer and antigenic challenge with exon 2 peptide. The immunodominant epitope(s) appeared to localize to the segment bordered by amino acids 59-85.