The germline repertoire of T cell receptor beta-chain genes in patients with chronic progressive multiple sclerosis

Genome-wide association studies of multiple sclerosis

Large-scale genetic studies of multiple sclerosis have identified over 230 risk effects across the human genome, making it a prototypical common disease with complex genetic architecture. Here, after a brief historical background on the discovery and definition of the disease, we summarise the last fifteen years of genetic discoveries and map out the challenges that remain to translate these findings into an aetiological framework and actionable clinical understanding.

Clone clusters in autoreactive CD4 T-cell lines from probable multiple sclerosis patients form disease-characteristic signatures

We developed a method for selectively propagating disease-related autoreactive T-cell lines (auTCLs) based on their increased resistance to apoptosis. The generated auTCLs homogeneously co-express CD45RO and CD49a, adhere strongly to extracellular matrix proteins and express high interleukin-17 (IL-17) messenger RNA levels, resembling a T-cell subset proposed to transmigrate into tissues and induce systemic and local inflammation in rheumatoid arthritis. The combinations of T-cell oligoclones that comprise probable multiple sclerosis (pMS) disease-related lines use a unique portfolio of T-cell receptor beta-chain variable allele (BV genes) combinations forming 'disease-specific cluster patterns'. The auTCL derived from different patients and from different myelin epitopes display striking similarities in BV gene allele clusters and are derived primarily from a disease-prone hotspot residing in the BV gene locus between Vbeta6 and Vbeta9. Conversely, healthy subject TCLs use different BV gene allele sets, forming 'healthy responder usage formats'. These formats were absent from the pMS patient V-beta gene allele combinations evaluated in this study. Hierarchical clustering of the BV gene combinations, distinguish three pMS auTCL groups, implying existence of up to three disease-related immune response patterns. These subgroup patterns may reflect different disease subclasses or alternatively they may suggest immune reactivity to different aetiological agents. Analyses of clonal-clustering patterns may potentially aid in subclassification of MS or in characterizing aetiological agents of this disease.

TCR β polymorphisms and multiple sclerosis

A total of 267 families with two or more siblings with multiple sclerosis (MS) were genotyped with 14 restriction fragment length polymorphisms at the TCR beta locus. A nonparametric linkage analysis of the data showed no evidence for linkage to this locus (mlod=0.11). No significant allelic or haplotype transmissions were observed in the total sample of 565 patients. After stratification for the presence of HLA DRB1*15, an association was observed between the BV25S1*1-BV26S1*1-BV2S1*1 haplotype and MS (P=0.00089). This was not significant upon correction for multiple comparisons. It was also not significant when the haplotype frequency in affected individuals was compared to a normal control sample (P=0.77). Furthermore, the associated haplotype was followed-up in an independent sample of 97 nuclear families with a single DRB1*15-positive child with MS. The BV25S1*1-BV26S1*1-BV2S1*1 haplotype did not show significant evidence for transmission distortion but the same trend was seen (P=0.21). There were no significant associations observed in the DRB1*15-negative patients and no detectable difference was seen in the DRB1*15-positive BV25S1*1-BV26S1*1-BV2S1*1 association when comparing different subgroups based on clinical course of MS. These results show no evidence for linkage and fail to establish an association between MS susceptibility and the TCR beta locus.

Multiple Sclerosis

This chapter provides information on the epidemiology of multiple sclerosis (MS), the most common disabling neurological disease in young adults. It describes the clinical and pathologic features of MS and how these features pose challenges for clinical diagnosis and case definition criteria. Information is provided regarding the descriptive epidemiology of MS, including studies of incidence, prevalence, and temporal trends in MS frequency. Also included is a discussion of the interesting geographical features of the MS distribution, including MS disease clusters, the latitude gradient in disease risk, and migrant studies of individuals who move from high-risk to low-risk regions. Other sections of the chapter cover evidence regarding the infectious etiology of MS, including the important role that Epstein-Barr virus appears to play in disease susceptibility. The role of lifestyle factors is receiving increasing emphasis in MS epidemiologic studies, and evidence is summarized regarding the potential role of cigarette smoking, diet, and hormonal factors.

T cell receptor beta chain genotyping in Australian relapsing-remitting multiple sclerosis patients

This study focused on susceptibility to MS within the beta-chain of the T-cell antigen receptor (TCRB locus, 7q35) in a cohort of 122 RR-MS patients compared with 96 normal individuals using biallelic polymorphisms across the bv8s1(Vbeta8.1) to bv11s1 (Vbeta11) TCRB subregion. The markers bv6s5, bv8s1, bv10s1, bv15s1 and bv3s1 were studied for allele and genotype frequencies; haplotypes were assigned with combinations of two of these markers and stratification for HLA-DR15 was also performed. Linkage disequilibrium was found between alleles of the bv8s1, bv10s1/bv15s1 and bv3s1 loci in both patients and controls. An increase among RR-MS patients in the allele frequency of bv8s1*2 (P=0.03) and the haplotype bv8s1*2/bv3s1*1 (P=0.006) was noted and both were found to be statistically significant. In the DR15-positive group, the association between TCRB and MS was seen with the bv8s1*2 allele (Puc=0.05) and the bv8s1*2/bv10s1 haplotypes (Puc=0.048), while the haplotype associations seen among DR15-negative RR-MS patients included the bv3s1*1 allele (bv10s1*1/ bv3s1*1, Puc=0.022; bv8s1*2/bv3s1*1, Puc=0.048). These results support the involvement of the TCRB region in MS susceptibility and encourage further study of the variable gene segments in this region.

Evaluation of the apo-1/Fas promoter mva I polymorphism in multiple sclerosis

The pathogenesis of multiple sclerosis is under strong genetic control involving several or more genes each of modest effect. Whilst the mechanisms underlying the pathogenesis of MS remain unknown, it has been hypothesised that either decreased apoptosis of autoreactive T cells in the CNS, or increased apoptosis of oligodendrocytes may play an important role. The Apo-1/Fas antigen (CD95), the gene for which is located in a chromosomal region showing linkage in MS genome screens, is a critical inducer of apoptosis and studies have shown aberrant expression of this molecule in MS, correlating with a decrease in T cell apoptosis or increase in CNS tissue damage. This study investigated an Mva I polymorphism in the Apo-1/Fas promoter region in a group of 124 Australian patients with relapsing-remitting MS and in 183 normal controls. Whilst there were increases in the Mva I*2 allele in MS individuals overall (59% vs 52%, P not corrected=0.08), and in HLA-DRB1*1501 negative MS patients (62% vs 55%), these were not significantly different from controls. Interactions were investigated between the Mva I alleles and T cell receptor beta chain variable region (TCRBV) germline polymorphisms, with a trend in MS individuals towards a decrease of the Mva I*1 allele when combined with the TCRBV3S1*2 allele (Relative Risk=0.25, P=0.067), and with the TCRBV8S1*1 allele (Relative Risk=0.44, P=0.12). Overall, the findings of this study indicate a possible effect of the Apo-1/Fas promoter Mva I polymorphism in MS susceptibility, which needs to be confirmed in further studies. Multiple Sclerosis (2000) 6 14 - 18

HLA-DMB gene and HLA-DRA promoter region polymorphisms in Australian multiple sclerosis patients

The MHC region has been shown to contain a susceptibility locus for multiple sclerosis (MS). While the strongest association to date has been between HLA-DRB1*1501 and MS, the exact nature of the MHC association in MS remains unclear. Two candidate polymorphic loci within the MHC class II region, the HLA-DMB gene and the HLA-DRA promoter, which lie close to HLA-DRB1, were therefore examined in an Australian MS population. The HLA-DMB*0103 phenotype was increased in the MS patients (46% vs. 30%) and the frequency of the HLA-DRA promoter A allele was also increased (81% vs. 68%). When the subjects were stratified into HLA-DRB*1501 positive and negative individuals these associations were not significantly different. This is a result of the strong linkage disequilibrium between HLA-DRB*1501 and both HLA-DMB*0103 and the HLA-DRA promoter A allele. The complete linkage between DRB1*1501 and the HLA-DRA promoter A allele indicates that the MS susceptibility haplotype (DRB1*1501-HLA-DQB1*0602-HLA-DQA1* 0102) can be extended out to promoter of the HLA-DRA locus. Interactions between both HLA-DMB and the HLA-DRA promoter and other reported MS susceptibility loci were examined (TCRBV polymorphisms, HLA-DQA1 and HLA-DQB1). Some interactions between specific TCRBV polymorphisms and the HLA-DRA promoter were observed, which is consistent with other published reports suggesting an epistatic interaction between TCRBV and HLA-DRB1.

The genetics of multiple sclerosis. A review

Multiple sclerosis (MS) is characterized by chronic inflammation and demyelination in the central nervous system (CNS). Although the etiology of MS is unknown, both genetic and environmental contributions to the pathogenesis are inferred from epidemiologic studies. Geographic distributions and epidemics of MS and data from migration studies provide evidence for some, thus far unidentified, environmental effects. The co-occurrence of MS with high and low frequencies in ethnic groups often sharing an environment, the increased recurrence rate in families, and the high concordance rate among identical twins point to inheritable determinants of susceptibility. Based on the autoimmune hypothesis of demyelination, genetic studies sought associations between MS and polymorphic alleles of candidate genes which regulate either the immune response or myelin production. The most consistent finding in case-control studies was the association with the major histocompatibility complex (MHC) (also called human leukocyte antigen--HLA) class II, DR15, DQ6, Dw2 haplotype. Studies on other gene products encoded within or close to the MHC complex on chromosome 6p21.3 (e.g., HLA DP, complement components, transporter proteins, tumor necrosis factor, and myelin-oligodendrocyte glycoprotein) resulted in conflicting observations in different patient populations. The potential contribution of polymorphic alleles within the genes of the T-cell receptor alpha beta chains, immunoglobulins, cytokines, and oligodendrocyte growth factors or their receptors to MS susceptibility either remains equivocal or is rejected. Studies on families with multiple affected members have revealed that MS is a complex trait, that the contribution of individual genes to susceptibility is probably small, and that differences are possible between familial and sporadic forms. The development of molecular and computer technologies have facilitated the performance of comprehensive genomic scans in multiplex families, which have confirmed the possible linkage of multiple loci to susceptibility, each with a minor contribution. Several provisional sites were reported, but only 6p21 (MHC complex), 5p14, and 17q22 were positive in more than one study. The British update demonstrated segregation among regions of interest depending on DR15 sharing, and excluded a gene of major effect from 95%, and one with a moderate effect from 65% of the genome. The extended study by the US collaboration group revealed that the MHC linkage was limited to families segregating HLA DR2 alleles, which suggested that linkage to the MHC is related to the HLA DR2 association, and that sporadic and familial MS share at least one common susceptibility marker. Further identification of MS susceptibility loci may involve additional family sets, more polymorphic markers, and the exploration of telomeric chromosomal regions. Data from these studies may further elucidate pathogenic mechanisms of MS.

The role of protective CD8+ T cells in resistance of BALB/c mice to Theiler's murine encephalomyelitis virus-induced demyelinating disease: regulatory vs. lytic

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is an excellent model for human multiple sclerosis. Within the BALB/c strain, BALB/cAnNCr mice are susceptible while BALB/cByJ mice are resistant. BALB/cByJ mice become susceptible when irradiated. Adoptive transfer of CD8+ splenic T cells from resistant BALB/cByJ donors protect irradiated BALB/cByJ, as well as BALB/cAnNCr recipients, from development of TMEV-IDD. Anti-TMEV CTL activities in BALB/cAnNCr, BALB/cByJ and irradiated BALB/cByJ mice are comparable. A population of splenic CD4+ T cells in BALB/cByJ donors has also been identified which can protect both susceptible BALB/cAnNCr and irradiated BALB/cByJ recipients from TMEV-IDD via adoptive transfer.

The DRB1 Val86/Val86 genotype associates with multiple sclerosis in Australian patients

Genetic susceptibility to multiple sclerosis (MS) has so far been strongly localized to the MHC class II region encoding the alleles of the haplotype HLA-DRB1*1501, -DQA1*0102, -DQB1*0602. However, this haplotype is not carried by approximately 40% of MS patients; a potential explanation could be that they carry other MHC class II alleles with similar function due to the sharing of nucleotide sequences encoding critical amino acid residues. The DRB1 gene is polymorphic at residue 86, encoding valine or glycine. In view of the increasing evidence for a functional role for DRB1 aa86 in the binding and presentation of autoantigenic peptides such as myelin basic protein, this study investigated associations with the residue 86 polymorphism in an Australian MS population. A significant increase in the Val86/Val86 genotype was observed in the MS patients, which was still present in the absence of the DRB1*1501 allele (p = 0.032). This suggest that DRB1 aa86 may have an independent role in contributing to MS susceptibility. The Val86/Val86 genotype was correlated with genotyping for other putative MS susceptibility genes, including T cell receptor beta chain germline polymorphisms, HLA-DMB alleles, and -DQA1 and -DQB1 alleles encoding critical amino acid residues, with a significant interaction only observed with DQB1 Leu26 (p = 0.014). Additional studies of the HLA-DRB1 aa86 polymorphism in MS, and its function, are needed to more fully understand this association.

Genome-Wide Linkage Analysis of Chronic Relapsing Experimental Autoimmune Encephalomyelitis in the Rat Identifies a Major Susceptibility Locus on Chromosome 9

The immunization of inbred Dark Agouti (DA) rats with an emulsion containing homogenized spinal cord and CFA induces chronic relapsing experimental autoimmune encephalomyelitis (EAE), a disease with many similarities to multiple sclerosis. We report here the first genome-wide search for quantitative trait loci regulating EAE in the rat using this model. We identified one quantitative trait locus on chromosome 9, Eae4, in a [DA(RT1av1) × BN(RT1n)]F2 intercross showing linkage to disease susceptibility and expression of mRNA for the proinflammatory cytokine IFN-γ in the spinal cord. Eae4 had a larger influence on disease incidence among rats that were homozygous for the RT1av1 MHC haplotype (RT1av1 rats) compared with RT1n/av1 rats, suggesting an interaction between Eae4 and the MHC. Homozygosity for the DA allele at markers in Eae4 and in the MHC was sufficient for EAE. Thus, Eae4 is a major genetic factor determining susceptibility to EAE in this cross of DA rats. In addition, there was support for linkage to phenotypes of EAE on chromosomes 1, 2, 5, 7, 8, 12, and 15. The chromosome 12 region has been shown previously to predispose DA rats to arthritis, and the chromosome 2 region is syntenic to Eae3 in mice. We conclude that Eae4 and probably the other identified genome regions harbor genes regulating susceptibility to neuroinflammatory disease. The identification and functional characterization of these genes may disclose critical events in the pathogenesis of multiple sclerosis; understanding these events could be essential for the development of new therapies against the disease.

Inheritance of susceptibility to multiple sclerosis

In recent years, epidemiological evidence supporting the genetic basis of multiple sclerosis has been extended and whole-genome linkage screening has advanced the mapping of the involved genes. Understanding of the known HLA associations has also improved and many candidate genes have been studied.

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 Cia3 and Oia2 regulate 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.

Susceptibility to relapsing-progressive multiple sclerosis is associated with inheritance of genes linked to the variable region of the TcR beta locus: use of affected family-based controls

We tested the hypothesis that susceptibility to relapsing-progressive (RP) (but not to relapsing-remitting [RR]) multiple sclerosis (MS) is associated with a gene linked to the TcR beta-chain variable region delimited by the Vbeta8-BamHI and Vbeta11-BamHI RFLP alleles in DRw15+ MS patients, using a contingency-table test of patient data and affected family-based controls. Control alleles and haplotypes were composed of parental marker alleles and haplotypes not transmitted to the affected child, in 90 simplex and 31 multiplex families from British Columbia. A total of 6,164 alleles at 11 loci were segregated through families of probands with RP MS or RR MS. The Vbeta8-Vbeta11 subhaplotype frequencies in the DRw15+ RP MS (but not RR MS) patients differed from control frequencies, because of an increase of the 2-1 subhaplotype (P=.02). Vbeta8-BamHI and Vbeta11-BamHI allele frequencies (P=.05 and .009, respectively) in the DRw15+ RP MS (but not RR MS) patients differed from control frequencies. The Vbeta1-Vbeta8 subhaplotype frequencies in the DRw15- RP MS (but not RR MS) patients differed from control frequencies (P=.03), with a significantly increased frequency of the 1-1 subhaplotype (P=.01; RR=7.1) in RP MS versus RR MS patients. Susceptibility to RP MS is associated both with a recessive inheritance of a gene linked to the 3' (Vbeta11) end of the 2-1 subhaplotype defined by the Vbeta8-BamHI and Vbeta11-BamHI alleles in DRw15+ patients and with a gene, located on the 1-1 subhaplotype, defined by the Vbeta1-TaqI and Vbeta8-MspI alleles of the TcR beta-chain complex in DRw15- patients.

Combined effect of HLA-DRB1*1501 and interleukin-1 receptor antagonist gene allele 2 in susceptibility to relapsing/remitting multiple sclerosis

Susceptibility to multiple sclerosis (MS) is associated with HLA-DRB1*1501. Many reports have suggested associations with other loci but these results remain unconfirmed. We studied the IL-1 receptor antagonist (IL-1ra) gene polymorphism and the HLA-DR and DQ allele frequencies by DNA-based methods in both the primary chronic progressive form (PP MS) and the relapsing/remitting form (R/R MS). The frequency of DRB1*1501 and IL-1ra allele 2 were significantly higher in R/R MS. Association was more marked in the female sex and in patients with benign forms of R/R MS. On the other hand DR4 subtypes carrying a Val at position 86 in the DR beta chain were increased in PP MS. The present study indicates that MS is genetically heterogeneous and shows a combined effect of HLA-DR and IL-1ra genes in susceptibility to the R/R form of the disease.

Genomewide scan of multiple sclerosis in Finnish multiplex families

Multiple sclerosis (MS) is a neurological, demyelinating disorder with a putative autoimmune etiology. It is thought to be a multifactorial disease with a complex mode of inheritance. Here we report the results of a two-stage genomewide scan for loci predisposing to MS. The first stage of the screen, with a low-resolution map, was performed in a selection of 16 pedigrees collected from an isolated Finnish population. Multipoint, non-parametric linkage analysis of the 328 markers did not reveal statistically significant results. However, 10 slightly interesting regions (P = .1-.15) emerged, including our previous findings of the HLA complex on 6p21 and a putative locus on 5p14-p12. Eight of these novel regions were further analyzed by use of denser marker maps, in the second stage of the scan. For the chromosomal regions 4cen, 11tel, and 17q, the statistical significance increased, but not conclusively; for 2q32 and 10q21, the statistical significance did not change. Accordingly, genotyping of the high-density markers in these regions was performed, and the data were analyzed by use of two-point, parametric linkage analysis using the complete pedigree information of the 21 Finnish multiplex families. We detected suggestive evidence for a predisposing locus on chromosomal region 17q22-q24. Several markers on 17q22-q24 yielded positive LOD scores, with the maximum LOD score (Zmax) occurring with D17S807 (Zmax = 2.8, theta = .04; dominant model). Interestingly, a suggestive linkage between MS and the markers on 17q22-q24 was also revealed by a recent genomewide scan in MS families from the United Kingdom.

TCRV and TCRJ gene usage in MBP responding T cells from (B10.PL x PL/J)F1 mice is biased towards that of B10.PL mice

We analyzed myelin basic protein (MBP) specific T cell hybridoma clones from (B10.PL x PL/J)F1 mice. MBP-reacting T cell hybridomas from F1 mice preferentially expressed B10.PL TcraV2.3 (53%) and B10.PL TcraV4.2 (13%) with minor expression of TcraV4.4 (13%) gene segments. A dominant expression of TcrbV8.2 (73%) accompanying with TcrbV8.1 (20%) and TcrbV13 (7%) gene segments have been identified in these MBP-reacting T cell hybridomas from F1 mice. There was less restrictive but non-random usage of the TcraJ and TcrbJ gene segments. Overall, the MBP-reacting T cell hybridomas from (B10.PL x PL/J)F1 mice were dominated by the MBP-reacting T cell pattern seen in B10.PL mice.

Identification of multiple sclerosis-associated genes

Multiple sclerosis (MS) is a complex genetic trait. Analyses to identify genetic variants that increase susceptibility to MS have primarily focused on candidate genes, either in family linkage investigations or in association (linkage disequilibrium) studies in sporadic cases and control subjects. Most of the candidate genes considered to date either influence immune function or encode structural myelin proteins. Recently, three preliminary whole genomic surveys were completed, and they reveal multiple loci of possible genetic linkage that are worthy of further study. No convincing evidence for a single strong locus has emerged from analysis of the three studies. Linkage promises to focus the future choice of candidate genes for further investigation.

Immune system genes in multiple sclerosis: genetic association and linkage analyses on TCR beta, IGH, IFN-gamma and IL-1ra/IL-1 beta loci

The role of genetic factors in the etiology of multiple sclerosis (MS) has been clearly demonstrated but the loci determining susceptibility to this disease remain largely unidentified. A contribution from several immune system genes has been suggested based on animal models and association/linkage analyses on MS patients and families. With the exception of the findings from the HLA complex, studies on candidate immune system genes have provided controversial results. Here we have performed genetic association and linkage analyses on four chromosomal regions containing immune system genes. A possible role for each of these loci in MS has been previously suggested. In data-sets derived from the Finnish population we found no evidence for contribution of the T-cell receptor beta chain (TCR beta chromosome 7q35), immunoglobulin heavy chain (IGH chromosome 14q32), interferon-gamma (IFN-gamma chromosome 12q14-q15) or interleukin-1 receptor antagonist/interleukin-1 beta (IL-1ra/IL-1 beta chromosome 2q14-q21) loci in the genetic susceptibility to MS.

Evolution and selection of primate T cell antigen receptor BV8 gene subfamily

The set of potential T cell receptor specificities is highly diverse. The relative contributions of T cell receptor (TCR) V beta gene segment polymorphisms, duplications, deletions, and gene conversions to this final T cell receptor protein diversity are unknown. To study these mechanisms, we sequenced and compared closely related primate TCR gene segments from BV8S1, S2, and S5. Interspecies comparisons show that these gene segments have sustained multiple duplication, gene conversion, and deletion events during the last 35 million years of anthropoid primate evolution. BV8 coding sequences are generally conserved with respect to their flanking noncoding sequences, but we find no evidence for positive or negative selection in sequences coding for the first two putative complementarity-determining (ligand-binding) regions. Sequences of TCRBV8 gene segments from unrelated humans demonstrate no nonsynonymous substitutions in nonleader regions of either the BV8S1 or S2 gene segments. We conclude that gene duplication, deletion, and conversion mechanism contribute in a substantial way to the overall diversity of the TCRBV8 gene segment repertoire in primate evolution and that germline substitutions and consequent polymorphisms in CDRs 1 and 2 of these gene segments probably do not play an active role in generating TCR beta chain protein variation.

The genetic analysis of multiple sclerosis

Although monogenic diseases often show extreme clinical phenotypes, the major burden of genetic ill health lies in the more prevalent polygenic disorders, such as diabetes, hypertension and multiple sclerosis. These conditions affect many thousands of individuals and their management consumes vast amounts of health care resources: in the UK some 80,000 people have multiple sclerosis; the estimated financial cost to society of introducing treatments, such as beta interferon, could be as high as 250 million pounds per year. Knowledge on the genetics of these common diseases is poor, but has potentially received a considerable boost with the arrival of whole genome screening. The genome screen in insulin-dependent diabetes mellitus (IDDM) reported in 1994 was the first in a human polygenic disease. Since this publication, whole genome screening has been performed in a variety of human polygenic diseases, including schizophrenia, bipolar affective disorder, non-insulin-dependent diabetes mellitus (NIDDM), inflammatory bowel disease, asthma and multiple sclerosis.

Association between susceptibility to Theiler's virus-induced demyelination and T-cell receptor Jbeta1-Cbeta1 polymorphism rather than Vbeta deletion

Theiler's murine encephalomyelitis virus (TMEV) induces demyelinating disease in susceptible mouse strains after intracerebral inoculation. The clinical symptoms and histopathology of the central nervous system appear to be similar to those of human multiple sclerosis (MS), and thus, this system provides an excellent infectious animal model for studying MS. The virus-induced demyelination is immune mediated, and the genes involved in the immune response such as those for the T-cell receptor beta-chain and major histocompatibility complex (MHC) haplotypes are known to influence disease susceptibility. To define whether the T-cell receptor Jbeta-Cbeta or Vbeta genes are associated with susceptibility, we have analyzed F2 mice from crosses of susceptible SJL/J (Vbeta(a)-JCbeta(b)) mice and resistant C57L (Vbeta(a)-JCbeta(a)) mice. Our results indicate that susceptibility to TMEV-induced demyelination is associated with restriction fragment length polymorphism reflecting the T-cell receptor Jbeta1-Cbeta1 region rather than the Vbeta polymorphism. This association becomes stronger when the MHC haplotype is considered in the linkage analysis. However, differences in the T-cell receptor alpha-chain haplotype have no significant influence on the pathogenesis of TMEV-induced demyelination.

Genetic predisposition to multiple sclerosis as revealed by immunoprinting

This study was designed to examine the immunogenetic background predisposing to multiple sclerosis (MS). Three hundred fifty-eight clinically well-characterized MS patients from Germany were investigated and compared to 395 healthy control subjects. Each individual was genotyped for 22 polymorphic markers located within or close to immunorelevant candidate genes including HLA-DRB1*, T-cell receptor (TCR), cell interaction molecules, cytokines, and cytokine receptor genes. Altogether, approximately 17,000 genetic analyses were performed. Patients were grouped according to the course of MS-relapsing-remitting or chronic progressive. Most of the genetic markers were not associated with increased risk or their exact contribution was not clear (e.g., tumor necrosis factor). The relative risks for HLA-DRB1*15+ and DRB1*03+ individuals were 3.64 and 1.42, respectively. In both groups of patients, certain TCRB gene polymorphisms were risk factors. In DRB1*03+ individuals the relative risk was increased (> 22) when a specific TCRBV6S3 allele was also inherited. Furthermore, distinct linkage disequilibria of TCRBV6S1/TCRBV6S3 elements in patients and control subjects strongly suggested an additional risk factor in the TCRBV region for DRB1*15+ individuals. These findings are discussed with respect to the pathogenesis and rational approaches to the therapy of MS.

Interaction between certain major histocompatibility complex class II and T-cell receptor V beta alleles promotes the antibody production to extractable nuclear antigen-related peptides

Our objective was to study the interaction between major histocompatibility complex (MHC) class II and T-cell receptor (TCR) alleles in the recognition of extractable nuclear antigen-derived peptides in 32 patients with systemic lupus erythematosus and 173 of their family members. MHC genes were analyzed using sequence specific oligonucleotides, and TCR beta-chain gene polymorphism using restriction fragment-length polymorphism. One dominant peptide (as defined by enzyme-linked immunosorbent assay autoantibody reactivity) was identified in each antigen studied: peptide 1-20 in Sm-D, peptide 35-58 in U1-RNP-A, and peptide 304-324 in the Ro/SSA 60 Kd protein. None of the MHC class II and TCR beta haplotypes was directly associated with any of the autoantibodies. Twenty-six subjects had antibodies to the peptide Sm-D1-20; nine of them were DRB1*0101/DQB1*0501. Among subjects with this haplotype, the number of responders was higher (p < 0.028, p corrected, pc = 0.336) in those with the 2-25-9 TCR beta haplotype than in the remainder. Conversely, the number of DRB1*04/DQB1*0302 responders was lower (p < 0.030, pc = 0.360) among subjects with the 23-20-9 TCR beta haplotype than in those without. The odds ratios (OR) were 4.23 and 0.21, respectively. Of the 54 subjects positive for anti-U1-RNP-A 35-38, 13 were DRB1*0101/DQB1*0501 and eight DRB1*04/DQB1*0302. The percentage of responders was higher (p < 0.041, pc = 0.492, OR = 3.48) in the former group of subjects with the 2-25-9 TCR beta haplotype, and lower (p < 0.02, pc = 0.024, OR = 0.09) in the latter with the 23-20-9 TCR beta haplotype. Three of the 12 anti Ro/SSA 60Kd 304-324-positive subjects were DRB1*0101/DQB1*0501. All had the 2-25-9 TCR beta haplotype (p < 0.046, pc = 0.552, OR = 6.29) and none the 23-20-9 (p < 0.031, pc = 0.372, OR = 0.10). The same combinations of genes were associated with high/low response toward the three peptides. These data provide evidence for an interplay of the MHC class II and TCR beta alleles in the control of specific autoantibody response to well-defined nuclear Ag peptides.

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.

Genetics of demyelinating diseases

Multiple sclerosis (MS), the prototypic demyelinating disease in humans, is the most common cause of acquired neurological dysfunction arising between early to mid adulthood. MS is an inflammatory disorder and is believed to result from an autoimmune response, directed against myelin proteins and perhaps other antigens, resulting in demyelination and dense astrogliosis. A genetic component in MS is indicated by an increased relative risk to siblings compared to the general population (lambda s) of 20-40, and an increased concordance rate in monozygotic compared to dizygotic twins. Association and/or linkage studies to candidate genes have yielded a considerable number of reports showing significant genetic effects for the major histocompatibility complex (MHC), immunoglobulin heavy chain, T cell antigen receptor, and myelin basic protein loci. With the exception of the MHC, however, these results have been difficult to replicate or apply beyond isolated populations. Recently, a multi-analytical genomic screen effort was completed to identify genomic regions potentially harboring MS susceptibility genes. Nineteen such regions were identified. The data confirm the reported genetic effect of the MHC region. However, no single locus generated overwhelming evidence of linkage. These results suggest a multifactorial etiology, including both environmental and multiple genetic factors of moderate effect.

TCR gene polymorphisms and autoimmune disease

Autoimmunity may result from abnormal regulation within the immune system. As the T cell is the principal regulator of the immune system and its normal function depends on immune recognition or self/non-self discrimination, abnormalities of the idiotypic T-cell receptor (TCR) may be one cause of autoimmune disease. The TCR is a clonally distributed, cell-surface heterodimer which binds peptide antigen when complexed with HLA molecules. In order to recognize the variety of antigens it may possibly encounter, the TCR, by necessity, is a diverse structure. As with immunoglobulin, it is the variable domain of the TCR which interacts with antigen and exhibits the greatest amount of amino acid variability. The underlying genetic basis for this structural diversity is similar to that described for immunoglobulin, with TCR diversity relying on the somatic recombination, in a randomly imprecise manner, of smaller gene segments to form a functional gene. There are a large number of gene segments to choose from (particularly the TCRAV, TCRAJ and TCRBV gene segments) and some of these also exhibit allelic variation. Finally, polymorphisms in non-coding regions of TCR genes, leading to biased recombination or expression, are also beginning to be recognized. All these factors contribute to the polymorphic nature of the TCR, in terms of both structure and repertoire formation. It follows that inherited abnormalities in either coding or regulatory regions of TCR genes may predispose to aberrant T-cell function and autoimmune disease. This review will outline the genomic organization of the TCR genes, the genetic mechanisms responsible for the generation of diversity, and the results of investigations into the association between germline polymorphisms and autoimmune disease.

The Dai minority population of southwest China: heterogeneity of DR2-associated HLA-DRB1,DRB5,DQA1, and DQB1 haplotypes

HLA-DR2 is the most common DR specificity (60.3%) identified in the Dai minority population of Xishuangbanna, Yunna Province, China. We characterized the DRB1, DRB5, DQA1, and DQB1 alleles of 44 unrelated DR2-positive individuals, 11 of whom (15%) were DR2 homozygous. Four DRB1 and four DRB5 alleles encoding DR2 were identified in this population. The most frequent DR2-associated DRB1 alleles were *1602 (gf = 0.164) and *1502 (gf = 0.151). DRB1*1501 (gf = 0.048) and a new allele designated DRB1*1504 (gf = 0.014) were also detected, but *1601 and *1503 were absent. The most frequent DR2-associated DRB5 alleles were *0101 (gf = 0.233) and *0102 (gf = 0.110). Nine different DR2-associated DR/DQ haplotypes were identified. The two most common DR2 haplotypes were DRB1*1602, DRB5*0101, DQA1*0102, DQB1*0502 (hf = 0.142) and DRB1*1502, DRB5*0102, DQA1*0101, DQB1*0501 (hf = 0.075). The new DRB1*1504 allele was found on a single haplotype: DRB1*1504, DRB5*0101, DQA1*0102, DQB1*0502 (hf = 0.017). The Dw2, Dw12, Dw21, and Dw22 haplotypes, present in many other Asian and Mongoloid populations, were not identified in this unique group. However, the Dai minority population is characterized by a relatively large number of diverse DR2 haplotypes and a new DRB1 allele encoding DR2.

Cloning of myelin basic protein-reactive T cells from the experimental allergic encephalomyelitis-resistant rat strain, LER

Rats of the LER inbred strain are resistant to the active induction of experimental allergic encephalomyelitis (EAE), although they are susceptible to adoptively transferred EAE when they are injected with encephalitogenic T cells from EAE-susceptible Lewis rats. The mechanism of resistance remains to be elucidated. We report here that myelin basic protein (MBP)-specific T cells can be cloned from LER rats immunized with MBP, that these CD4+ LER T cells can recognize the encephalitogenic peptide (MBP-EP) and will divide vigorously when it is presented to them, and that these T cells bear V beta 8 + TCR chains. Nevertheless, in contrast to Lewis T cells with the same specificity and TCR beta chains, LER T cells from MBP-EP-specific clones cannot induce EAE when adoptively transferred into naive rats of either strain. Thus, LER T cells can assemble and use a TCR with the canonical encephalitogenic V beta 8.2-D beta-J beta region in response to immunization with MBP, yet they continue to display resistance to EAE.

Susceptibility to actively-induced murine experimental allergic encephalomyelitis is not linked to genes of the T cell receptor or CD3 complexes

The role of the T cell receptor (TCR) in the genetic control of susceptibility to autoimmune demyelinating diseases remains shrouded in controversy. We have used the CXD2 series of recombinant inbred lines (RIL) and a (B10.S/DvTe x SJL/J) x B10.S/DvTe backcross (BC1) population to test for linkage between susceptibility to actively-induced EAE and the different TCR and CD3 loci. The two populations were inoculated for induction of EAE, phenotyped for both clinical and histological parameters of disease, and genotyped using markers flanking the loci of interest in the CXD2 RIL and an SJL/J allele-specific TCR V beta assay in the BC1 mice. Comparisons between the CXD2 strain distribution pattern (SDP) for disease and the SDPs for the chromosomal regions containing the TCR alpha, beta, gamma, delta, and CD3 delta, epsilon, gamma and zeta loci showed no linkage to these loci. Additional tests between EAE susceptibility and several other immunologically important loci for which the SDPs were known also showed no linkage to the minor lymphocyte-stimulating antigen gene Mlsl, Hc, the gene encoding complement component C5, Cd8a, or Cd5. Furthermore, our data from the BC1 mice demonstrate that the Tcrb locus segregates independent of disease and does not modulate disease severity. We conclude that while autoreactive TCRs are undoubtedly necessary for disease pathogenesis, the principle non-MHC-linked loci controlling susceptibility to murine EAE in BALB/c mice are not linked to any of the individual TCR-CD3 complex genes. Similarly, the major disease genes in the SJL/J mouse are not linked to TCR V beta. Our data cannot, however, preclude the possibility that TCR/CD3 alleles are involved in epigenetic phenomena or susceptibility in other mouse strains or animal systems.

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.

Genetic susceptibility to multiple sclerosis

Twin studies have established that susceptibility to multiple sclerosis (MS) is partly genetic. Attempts to identify the relevant genetic loci have involved population-based studies, to detect associations between a genetic marker and MS, and family studies, to detect linkage between a putative marker and MS. Most of this genetic work is driven by the view that MS is an autoimmune disease. Thus, the focus has been mainly on genes known to be important in the immune response: human leukocyte antigen (HLA) genes, T-cell receptor genes, and immunoglobulin genes. To date, only the particular HLA-DR2 haplotype that is common in Caucasians can be concluded to be important in MS susceptibility in most populations. Studies of other genetic loci have been few, the data obtained often have been conflicting or controversial, and further studies are needed to clarify the biological significance of these loci in MS. Recommendations for further studies are provided in order to overcome some of the problems that have plagued earlier work in MS such as nonreproducibility of results.

No linkage or association between multiple sclerosis and the myelin basic protein gene in affected sibling pairs

Myelin basic protein was examined as a candidate gene for susceptibility to multiple sclerosis using two adjacent amplification fragment length polymorphisms (AmpFLPs), containing seven and six highly informative alleles respectively. No allelic association was found with multiple sclerosis, comparing 77 cases and 88 controls, and there was no evidence for linkage in 73 affected sibling pairs, using the methods of identity by descent and identity by state.

Polymorphism of the tumour necrosis factor beta gene in multiple sclerosis and rheumatoid arthritis

We evaluated the TNF-beta gene polymorphism in two HLA-associated autoimmune diseases, multiple sclerosis (MS) and rheumatoid arthritis (RA). The TNF-beta allele and genotype frequencies were not significantly different in the patient populations, compared to controls. An increased frequency of the TNF-beta*2 allele was observed in HLA-DR2+ vs. HLA-DR2- MS patients. No such association was seen in HLA-DR4+ RA patients.

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.

T-cell antigen receptors in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic disease of unknown etiology characterized by chronic inflammation mainly in the joints. Several lines of evidence suggest that T cells are involved in the pathogenesis of the disease. RA is associated with certain HLA-DR alleles. Studies analyzing T-cell receptor transcripts in RA have found biased or preferential usage of certain V alpha and/or V beta gene segments by T cells infiltrating the synovial membrane or extravasating into the synovial fluid compared to peripheral blood. In certain patients few T-cell antigen receptor (TCR) clones dominated the infiltrating T cells, suggesting that T cells from the synovial membrane or the synovial fluid comprise oligoclonal populations of T cells. However, other studies have found a polyclonal population of T cells. In interpreting these results the phase of the disease (early vs. late RA), the source of T cells and the limitations of the methods used in these studies should be taken into consideration. However, it appears that synovial T cells comprise oligoclonal populations of T cells and that there is a bias towards particular TCR gene segments, although a specific TCR gene segment in RA has not emerged.

No linkage between multiple sclerosis and the T cell receptor alpha chain locus

Susceptibility to multiple sclerosis (MS) is genetically determined but it is thought that more than one gene contributes to development of the disease. We report a study of linkage to one candidate, the T cell receptor alpha chain locus, on chromosome 14, in affected sibling pairs. Markers with high polymorphism information contents were used to assign haplotypes identical by descent and state. Forty nine pairs were studied using restriction fragment length polymorphisms (RFLP) and 82 pairs were investigated using a microsatellite repeat polymorphism. In neither case did genotype or haplotype sharing differ significantly from expected rates. Stratification of patients according to DR15 status did not alter the distribution of haplotypes in affected siblings. We conclude that the T cell receptor alpha locus is not linked to susceptibility in patients with MS from the United Kingdom.

Analysis of antibody responses to predominant linear epitopes of Theiler's murine encephalomyelitis virus

Using synthetic peptides, we have defined the major linear antibody epitopes of Theiler's murine encephalomyelitis virus (TMEV), i.e., A1A (VP1(12-25)), A1Ba (VP1(146-160)), A1Cb (VP1(262-276)), A2A (VP2(2-16)), A2B (VP2(165-179)), and A3A (VP3(24-37)). A time course study with either pooled or individual sera indicates that susceptible SJL mice intracerebrally infected with TMEV strongly and selectively recognize the A1Cb epitope of VP1, compared with resistant BALB/c or C57BL/6 mice, which broadly recognize most of the epitopes on the different capsid proteins. However, antibodies from SJL mice subcutaneously immunized with TMEV recognize primarily A1Ba, A1Cb, and A2A epitopes. A similar predominant recognition of the A1Cb epitope was found with antibodies from the cerebrospinal fluid of intracerebrally virus-infected SJL mice. Interestingly, a substantial level of antibodies against the A1Cb epitope in virus-infected SJL mice is of the immunoglobulin G2a subclass, in contrast to an undetectable level of this immunoglobulin G subclass in virus-immunized SJL mice. The level of in vitro viral neutralization by antibodies did not correlate with the clinical signs. Antibodies to A1Cb, A2A, and A2B were able to neutralize viral plaque formation in vitro, while antibodies to A3A, A1A, and A1Ba were not.

Different distribution of T cell receptor beta-chain haplotypes in mixed connective tissue disease and systemic lupus erythematosus

Mixed connective tissue disease (MCTD) and systemic lupus erythematosus (SLE) are autoimmune diseases with a genetic background, and it is reasonable to suggest that aberrations in T cell receptor (TCR) genes could contribute to these diseases, as they play an important role in immune regulation. We studied TCR beta-chain gene segments V beta 8, V beta 11 and C beta with restriction fragment length polymorphism (RFLP) in MCTD and SLE patients and controls. Haplotypes could be assigned in individuals who were homozygous for two or three of these three loci, whereupon the haplotype 2/25/10 (V beta 8/V beta 11/C beta) was found to be under-represented in MCTD (P = 0.029). The frequencies of individual alleles in both groups were similar to those of the controls, whereas the number of homozygotes within V beta 8 gene (23/23 kb and 2/2 kb) was increased in MCTD (P = 0.028). It is concluded that the distribution of TCR beta-chain genes could be aberrant in MCTD and could play a role in susceptibility, whereas the TCR beta-chain gene distribution in the SLE patients did not differ from that of the controls.

The HLA-Dw2 haplotype segregates closely with multiple sclerosis in multiplex families

Multiple sclerosis (MS) is associated with the HLA class II specificity Dw2, but the importance of its influence has been questioned, since sib-pair analysis has failed to show linkage with this haplotype. However, the use of 'identity by descent' (IBD) analysis may not be ideal, since it does not make use of the facts that (i) the Dw2-haplotype is the only haplotype with a confirmed role in MS, and (ii) it performs its influence in a dominant manner. We have investigated nine Swedish multiplex MS families. In eight of the families, the Dw2 haplotype occurred in MS patients. Within these families, Dw2 was shared by all 17 individuals with MS. In a compilation of 48 published multiplex MS families in which at least one patient carried Dw2, only three of 107 individuals with MS did not carry the Dw2 haplotype. This indicates that the Dw2 haplotype, when present in familial MS, may confer a stronger influence in MS susceptibility than generally recognized.

Influence of deletion of T cell receptor V beta genes on the Theiler's virus model of multiple sclerosis

To determine the role of TCR V beta genes in a model of multiple sclerosis (MS), we studied Theiler's virus infection in congenic mice with deletion of TCR V beta chromosome. Congenic mice expressing the V beta a [50% deletion of TCR V beta] or V beta c 70% deletion of TCR V beta] haplotype were generated in mice resistant [B10 (H-2b)], intermediate [B10.K (H-2k), B10.RIII (H-2r)] or susceptible [B10.S (H-2s), and B10.Q (H-2q)] to Theiler's virus induced demyelination. Deletion of TCR V beta genes (V beta a or V beta c) did not convert B10 or B10.K congenic mice to susceptibility. In contrast, congenic B10.RIII-V beta c developed prominent demyelination and 10- to 100-fold increase in virus-antigen expression in spinal cord compared to B10.RIII mice. No effect on the extent of demyelination was observed in B10.S-V beta a, B10.S-V beta c or B10.Q-V beta c mice. These experiments illustrate the critical interactions between MHC, TCR, and background genes in susceptibility to immune-mediated disease.

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

Although multiple sclerosis (MS) is thought to be an autoimmune disease, the target antigen of the immune response is unknown. Both myelin basic protein (MBP) and proteolipid protein (PLP) have been considered candidate autoantigens. Because the immune response to either foreign or self antigens is influenced by the genetic background of the host, the importance of these candidate antigens has been difficult to establish in humans because of genetic diversity. To eliminate genetic differences in MS patients and healthy controls, we have studied the MBP-specific T-cell response in 6 sets of identical twins, 3 of which were concordant and 3 discordant for MS. A total of 638 short-term T-cell lines were established and characterized for MBP-specific proliferative and cytotoxic activity, fine specificity, and human leukocyte antigen (HLA) restriction. Similar frequencies of MBP-specific T cells were observed in affected and unaffected individuals. A slightly higher percentage of cytotoxic T-cell lines was found in affected individuals. For most of the cell lines, the restriction elements were the HLA class II antigens that have been reported previously to be associated with MS; no important differences with respect to HLA restriction were found between the patients and healthy individuals. The peptide epitopes of MBP that were recognized most frequently by the T-cell lines were those previously shown to be immunodominant. Differences in specificity were seen in some discordant twins indicating that, despite genetic identity, the MBP-specific T-cell repertoire may be shaped differently. These findings indicate that differences in frequency, peptide specificity, or HLA restriction are not sufficient to implicate MBP-specific T cells in the pathogenesis of MS. However, the T-cell response to MBP may still represent one necessary component with disease occurring when this response is combined with other host characteristics such as regulation of cytokine-, adhesion molecule-, or HLA-antigen expression in the nervous system or immunoregulatory mechanisms.