Multiple sclerosis and HLA: is the susceptibility gene really HLA-DR or -DQ?

Genetics of primary progressive multiple sclerosis

Multiple sclerosis (MS) patients are classified as either having relapsing onset or progressive onset disease, also known as primary progressive MS (PPMS). Relative to relapsing onset patients, PPMS patients are older at disease onset, are equally likely to be men or women, and have more rapid accumulation of disability that does not respond well to treatments used in relapsing onset MS. Although estimates vary, 5-15% of all MS patients have a PPMS disease course. Genetic variance is a proposed determinant of MS disease course. If distinct genes associated with PPMS were identified study of these genes might lead to an understanding of the biology underlying disease progression and neural degeneration that are the hallmarks of PPMS. These genes and their biological pathways might also represent therapeutic targets. This chapter systematically reviews the PPMS genetic literature. Despite the intuitively appealing notion that differences between PPMS and relapsing onset MS are due to genetics, definite differences associated with these phenotypes at the major histocompatibility complex or elsewhere in the genome have not been found. Recent large-scale genome wide screens identified multiple genes associated with MS susceptibility outside the MHC. The genetic variants identified thus far make only weak individual contributions to MS susceptibility. If the genetic effects that contribute to the differences between PPMS and relapsing MS are similar in magnitude to those that distinguish MS from healthy controls then, given the relative scarcity of the PPMS phenotype, very large datasets will be needed to identify PPMS associated genes. International collaborative efforts could provide the means to identify such genes. Alternately, it is possible that factors other than genetics underlie the differences between these clinical phenotypes.

Genetics for understanding and predicting clinical progression in multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is a dys-immune disease of the central nervous system with highly variable and unpredictable long-term outcome.

STATE OF THE ART

In the early 1970s association between HLA alleles and MS was established. Very recently, the power of Genome Wide Association Studies (GWAS) enabled the identification of several loci involved in immune functions as genetic risk factors in MS. Recent data suggest that common genetic variations might modulate the clinical phenotype of MS through a regulation of key pathophysiological pathways.

PERSPECTIVES

Identification of modifier genes might offer an opportunity to explore new relevant therapeutic targets and early prognostic markers. To date, studies of modifier genes in MS are numerous but results are still unclear. This research field may now benefit from large cohorts of patients available for association studies.

CONCLUSION

In this context, we propose a review of epidemiological and association studies of genetic modifying effect in MS.

Influence of histocompatibility genes on disease susceptibility and treatment response in patients with relapsing-remitting multiple sclerosis treated with interferon β-1a

Multiple sclerosis (MS) is the most common, non-traumatic cause of neurological disability in young adults. The aim of this study was to investigate the influence of HLA class II alleles DRB1* and DQB1* on susceptibility to relapsing-remitting (RR) MS and response to interferon (IFN) β-1a treatment. A prospective observational study was conducted. Seventeen patients with clinically definite RRMS, attending a tertiary referral center for multiple sclerosis in Israel and receiving treatment with subcutaneous IFN β-1a, 22 mcg three times weekly were recruited between December 1998 and February 2000 and observed for 12 months. HLA genotyping was performed and clinical characteristics (relapse rate and disability progression) assessed at baseline and after 12 months. HLA data for a healthy control group were also used for comparison. HLA and the success of treatment with IFN β-1a in this group of RRMS patients were assessed. The frequency of DRB1*03 was six times higher in patients treated with IFN β-1a than in the healthy control group (n=100): 29% (5/17) versus 5% (5/100), respectively. Additionally, DQB1*03 and DQB1*02 were present in 82% (14/17) and 41% (7/17) of RRMS patients, but in only 33% (33/100) and 18% (18/100) of control patients, respectively. A better response to IFN β-1a treatment was seen in patients carrying these alleles than in patients without these alleles. Our results indicated that DRB1*03, DQB1*03 and DQB1*02 alleles may contribute to MS susceptibility and IFN β-1a responsiveness, and warrant further verification in a larger population.

Relationship between HLA-DRB1 polymorphism and susceptibility or resistance to multiple sclerosis in Caucasians: a meta-analysis of non-family-based studies

OBJECTIVE

To identify the contribution of HLA-DRB1 alleles to susceptibility or resistance to multiple sclerosis (MS) in Caucasians through a meta-analysis of non-family-based studies.

METHODS

A systematic review of case-control studies in Caucasians was performed. Studies examining allele or phenotype frequencies were analyzed separately. Odds ratio (OR) and 95% confidence intervals (CIs) were used. We also used the relatively predispositional effect (RPE) method to analyze several allele frequency studies to avoid skewed results due to some strongly associated alleles.

RESULTS

A total of 5464 cases and 7809 controls from 14 allele frequency studies and a total of 5401 cases and 7538 controls from 23 phenotype frequency studies were analyzed. DRB1*15 was definitely the strongest risk factor for MS (allele group, Pc<0.00013, OR 2.59, 95%CI 2.34-2.87; phenotype group, Pc<0.00013, OR 3.35, 95%CI 2.95-3.80). DRB1*03 frequencies were significantly increased among MS cases in the phenotype group (Pc= 0.0013, OR 1.21, 95%CI 1.09-1.33) but not in the allele group. DRB1*14 and DRB1*07 showed protective effects against MS in both groups (DRB1*14, allele group, Pc<0.00013, OR 0.53, 95%CI 0.42-0.66; phenotype group, Pc<0.00013, OR 0.57, 95%CI 0.45-0.71; DRB1*07, allele group, Pc<0.0026, OR 0.75, 95%CI 0.64-0.87; phenotype group, Pc<0.00013, OR 0.67, 95%CI 0.61-0.73). By RPE method, DRB1*14, and DRB1*07 showed protective effects after excluding DRB1*15 from the analysis. DRB1*03 was significantly higher in MS cases than controls after removing both DRB1*15 and DRB1*14.

CONCLUSIONS

In Caucasians, we highlighted the definite protective role of HLA-DRB1*14 and DRB1*07 for MS. DRB1*03 is probably the only risk factor for MS besides DRB1*15 and a common genetic foundation for autoimmune disease. Targeting to these alleles may have potential values in prevention or therapy for MS in the specific population.

A transcription factor map as revealed by a genome-wide gene expression analysis of whole-blood mRNA transcriptome in multiple sclerosis

Background

Several lines of evidence suggest that transcription factors are involved in the pathogenesis of Multiple Sclerosis (MS) but complete mapping of the whole network has been elusive. One of the reasons is that there are several clinical subtypes of MS and transcription factors that may be involved in one subtype may not be in others. We investigate the possibility that this network could be mapped using microarray technologies and contemporary bioinformatics methods on a dataset derived from whole blood in 99 untreated MS patients (36 Relapse Remitting MS, 43 Primary Progressive MS, and 20 Secondary Progressive MS) and 45 age-matched healthy controls.

Methodology/Principal Findings

We have used two different analytical methodologies: a non-standard differential expression analysis and a differential co-expression analysis, which have converged on a significant number of regulatory motifs that are statistically overrepresented in genes that are either differentially expressed (or differentially co-expressed) in cases and controls (e.g., V$KROX_Q6, p-value <3.31E-6; V$CREBP1_Q2, p-value <9.93E-6, V$YY1_02, p-value <1.65E-5).

Conclusions/Significance

Our analysis uncovered a network of transcription factors that potentially dysregulate several genes in MS or one or more of its disease subtypes. The most significant transcription factor motifs were for the Early Growth Response EGR/KROX family, ATF2, YY1 (Yin and Yang 1), E2F-1/DP-1 and E2F-4/DP-2 heterodimers, SOX5, and CREB and ATF families. These transcription factors are involved in early T-lymphocyte specification and commitment as well as in oligodendrocyte dedifferentiation and development, both pathways that have significant biological plausibility in MS causation.

The genetics of clinical outcome in multiple sclerosis

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS), the clinical course of which varies considerably between patients. Genetic complexity and interactions with as yet unknown environmental factors have hindered researchers from fully elucidating the aetiology of the disease. In addition to influencing disease susceptibility, epidemiological evidence suggests that genetic factors may affect phenotypic expression of the disease. Genes that affect clinical outcome may be more effective therapeutic targets than those which determine susceptibility. We present in this review a comprehensive survey of the genes (both MHC- and non-MHC-related) that have been investigated for their role in disease outcome in MS. Recent studies implicating the role of the genotype and epistatic interactions in the MHC in determining outcome are highlighted.

The impact of HLA-A and -DRB1 on age at onset, disease course and severity in Scandinavian multiple sclerosis patients

The human leucocyte antigen (HLA) class II haplotype DRB1*15-DQB1*06 (DR15-DQ6) is associated with susceptibility to multiple sclerosis (MS), and HLA class I associations in MS have also been reported. However, the influence of HLA class I and II alleles on clinical phenotypes in MS has not yet been completely studied. This study aimed at evaluating the impact of HLA-A and -DRB1 alleles on clinical variables in Scandinavian MS patients. The correlation between HLA-A or -DRB1 alleles and age at onset, disease course and Multiple Sclerosis Severity Score (MSSS) were studied in 1457 Norwegian and Swedish MS patients by regression analyses and Kruskal-Wallis rank sum test. Presence of HLA-DRB1*15 was correlated with younger age at onset of disease (corrected P = 0.009). No correlation was found between HLA-A and the variables studied. This study analysed the effect of HLA-A on clinical variables in a large Scandinavian sample set, but could not identify any significant contribution from HLA-A on the clinical phenotype in MS. However, associations between HLA-DRB1*15 and age at onset of MS were reproduced in this extended Scandinavian MS cohort.

Analysis of extended HLA haplotypes in multiple sclerosis and narcolepsy families confirms a predisposing effect for the class I region in Tasmanian MS patients

Human leucocyte antigen (HLA)-DRB1*15 is associated with predisposition to multiple sclerosis (MS), although conjecture surrounds the possible involvement of an alternate risk locus in the class I region of the HLA complex. We have shown previously that an alternate MS risk allele(s) may be encompassed by the telomerically extended DRB1*15 haplotype, and here, we have attempted to map the putative variant. Thirteen microsatellite markers encompassing a 6.79-megabase (D6S2236-G51152) region, and the DRB1 and DQB1 genes, were genotyped in 166 MS simplex families and 104 control families from the Australian State of Tasmania and 153 narcolepsy simplex families (trios) from the USA. Complementary approaches were used to investigate residual predisposing effects of microsatellite alleles comprising the extended DRB1*15 haplotype taking into account the strong predisposing effect of DRB1*15: (1) Disease association of the extended DRB1*15 haplotype was compared for MS and narcolepsy families--predisposing effects were observed for extended class I microsatellite marker alleles in MS families, but not narcolepsy families; (2) disease association of the extended DRB1*15 haplotype was investigated after conditioning MS and control haplotypes on the absence of DRB1*15--a significant predisposing effect was observed for a 627-kb haplotype (D6S258 allele 8-MOGCA allele 4; MOG, myelin oligodendrocyte glycoprotein) spanning the extended class I region. MOGCA allele 4 displayed the strongest predisposing effect in DRB1*15-conditioned haplotypes (p = 0.0006; OR 2.83 [1.54-5.19]). Together, these data confirm that an alternate MS risk locus exists in the extended class I region in Tasmanian MS patients independent of DRB1*15.

Human leucocyte antigen class II polymorphism in Irish patients with multiple sclerosis

The contribution of human leucocyte antigen (HLA) to the genetic risk for multiple sclerosis (MS) in patients of Northern European Caucasoid ancestry has been known since the 1970s. The northern part of Ireland, including county Donegal, is known to be a high-risk area for the development of MS. Recorded prevalence rates for county Wexford in the south-east Ireland have been markedly lower and suggest the existence of a prevalence gradient within the island. To evaluate the association of HLA-DRB1 and -DQB1 haplotypes with MS in both Wexford and Donegal, we examined a total of 118 patients and 400 regionally matched controls. The aim of this exploratory study was to test the possibility of heterogeneity in HLA class II associations with MS and to identify potential predisposing or protective haplotypes, associated with MS risk in Ireland. We confirmed the association of DRB1*1501-DQB1*0602 haplotype carriage with MS in both Wexford [odds ratio (OR) = 2.95, P= 0.0020, P(cor)= 0.0220] and Donegal (OR = 2.29, P= 0.0030, P(cor)= 0.0420). A higher frequency and a significantly higher homozygosity rate of this haplotype in Donegal are likely contributing factors to the higher prevalence of MS in Donegal compared with Wexford. The distribution of HLA class II alleles among Irish MS patients and controls establishes that there is heterogeneity in HLA class II associations with MS within Ireland.

Quantitative and qualitative changes in gene expression patterns characterize the activity of plaques in multiple sclerosis

Multiple sclerosis (MS) is a complex autoimmune disorder of the CNS with both genetic and environmental contributing factors. Clinical symptoms are broadly characterized by initial onset, and progressive debilitating neurological impairment. In this study, RNA from MS chronic active and MS acute lesions was extracted, and compared with patient matched normal white matter by fluorescent cDNA microarray hybridization analysis. This resulted in the identification of 139 genes that were differentially regulated in MS plaque tissue compared to normal tissue. Of these, 69 genes showed a common pattern of expression in the chronic active and acute plaque tissues investigated (Pvalue<0.0001, rho=0.73, by Spearman's rho analysis); while 70 transcripts were uniquely differentially expressed (> or = 1.5-fold) in either acute or chronic active tissues. These results included known markers of MS such as the myelin basic protein (MBP) and glutathione S-transferase (GST) M1, nerve growth factors, such as nerve injury-induced protein 1 (NINJ1), X-ray and excision DNA repair factors (XRCC9 and ERCC5) and X-linked genes such as the ribosomal protein, RPS4X. Primers were then designed for seven array-selected genes, including transferrin (TF), superoxide dismutase 1 (SOD1), glutathione peroxidase 1 (GPX1), GSTP1, crystallin, alpha-B (CRYAB), phosphomannomutase 1 (PMM1) and tubulin beta-5 (TBB5), and real time quantitative (Q)-PCR analysis was performed. The results of comparative Q-PCR analysis correlated significantly with those obtained by array analysis (r=0.75, Pvalue<0.01, by Pearson's bivariate correlation). Both chronic active and acute plaques shared the majority of factors identified suggesting that quantitative, rather than gross qualitative differences in gene expression pattern may define the progression from acute to chronic active plaques in MS.

Past exposure to sun, skin phenotype, and risk of multiple sclerosis: case-control study

OBJECTIVE

To examine whether past high sun exposure is associated with a reduced risk of multiple sclerosis.

DESIGN

Population based case-control study.

SETTING

Tasmania, latitudes 41-3 degrees S.

PARTICIPANTS

136 cases with multiple sclerosis and 272 controls randomly drawn from the community and matched on sex and year of birth.

MAIN OUTCOME MEASURE

Multiple sclerosis defined by both clinical and magnetic resonance imaging criteria.

RESULTS

Higher sun exposure when aged 6-15 years (average 2-3 hours or more a day in summer during weekends and holidays) was associated with a decreased risk of multiple sclerosis (adjusted odds ratio 0.31, 95% confidence interval 0.16 to 0.59). Higher exposure in winter seemed more important than higher exposure in summer. Greater actinic damage was also independently associated with a decreased risk of multiple sclerosis (0.32, 0.11 to 0.88 for grades 4-6 disease). A dose-response relation was observed between multiple sclerosis and decreasing sun exposure when aged 6-15 years and with actinic damage.

CONCLUSION

Higher sun exposure during childhood and early adolescence is associated with a reduced risk of multiple sclerosis. Insufficient ultraviolet radiation may therefore influence the development of multiple sclerosis.

Genetic and functional studies in multiple sclerosis patients from Martinique attest for a specific and direct role of the HLA-DR locus in the syndrome

Among candidate genes involved in multiple sclerosis (MS) genetic susceptibility, MHC genes and particularly HLA-DRB1*1501-DQB1*0602 haplotype play a major role. Based on the strong linkage disequilibrium observed in Caucasians between DRB1*1501 and DQB1*0602 alleles, it is still impossible to draw a firm conclusion about the DRB1 or DQB1 locus involvement. In order to address this issue a strategy associating a genetic and a functional approach was conducted in a population of-non-Caucasian MS patients. We observed that in Martinicans (55 MS and 100 controls), the DRB1*15 and DRB1*07 alleles were positively associated with the disease. However in Martinicans the most common DRB1*15 subtype was *1503 and not *1501. Moreover, in Martinicans, the frequency of DQB1*0602, found in association with other DRB1 alleles than DRB1*15 (42% of DQB1*0602 haplotypes), was not increased in DRB1*15-negative MS patients, suggesting a neutral role of DQB1*0602 in MS genetics. In a second step, we demonstrated the capability of the DRB1*1503 allele associated with MS in Martinicans to present the immunodominant autoantigen MBP 85-99 peptide to a DRB1*1501 restricted MBP specific T cell line. Interestingly, structural features of DRB1*1501 or DRB1*1503 molecules are in good fit with the hypothesis that *1501 and *1503 molecules may act similarly in MS development by presenting the same immunodominant MBP peptide. On the whole, our results show a prominent role of the DRB1 locus (DRB1*1501 and/or DRB1*1503 alleles) in the immunodominant MBP 85-99 peptide presentation to genetically different MS patients and suggest a neutral role of the DQB1 encoded molecule in MS susceptibility.

Genetic dissection of the human leukocyte antigen region by use of haplotypes of Tasmanians with multiple sclerosis

Association of multiple sclerosis (MS) with the human leukocyte antigen (HLA) class II haplotype DRB1*1501-DQB1*0602 is the most consistently replicated finding of genetic studies of the disease. However, the high level of linkage disequilibrium (LD) in the HLA region has hindered the identification of other loci that single-marker tests for association are unlikely to resolve. In order to address this issue, we generated haplotypes spanning 14.754 Mb (5 cM) across the entire HLA region. The haplotypes, which were inferred by genotyping relatives of 152 patients with MS and 105 unaffected control subjects of Tasmanian ancestry, define a genomic segment from D6S276 to D6S291, including 13 microsatellite markers integrated with allele-typing data for DRB1 and DQB1. Association to the DRB1*1501-DQB1*0602 haplotype was replicated. In addition, we found that the class I/extended class I region, defined by a genomic segment of approximately 400 kb between MOGCA and D6S265, harbors genes that independently increase risk of, or provide protection from, MS. Log-linear modeling analysis of constituent haplotypes that represent genomic regions containing class I (MOGCA-D6S265), class III (TNFa-TNFd-D6S273), and class II (DRB1-DQB1) genes indicated that having class I and class II susceptibility variants on the same haplotype provides an additive effect on risk. Moreover, we found no evidence for a disease locus in the class III region defined by a 150-kb genomic segment containing the TNF locus and 14 other genes. A global overview of LD performed using GOLD identified two discrete blocks of LD in the HLA region that correspond well with previous findings. We propose that the analysis of haplotypes, by use of the types of approaches outlined in the present article, should make it possible to more accurately define the contribution of the HLA to MS.

Identifying disease modifying genes in multiple sclerosis

Evidence is mounting that genetic variation influences not only susceptibility to multiple sclerosis (MS), but also its course and severity. Identification of disease modifying genes, however, poses unique challenges, especially on how to classify the course and outcome of the disease in ways that may be relevant to analysis of biological factors that might be influenced by genes. The power of the statistical approaches to detect small effects of individual genes in complex disorders such as MS is problematic, and approaches to estimate power must be appropriate for the data. Nonetheless, using contemporary schemes of classification, genetic variants that influence disease course have been found; in fact, a small number have been confirmed to influence disease course in two or more independent studies. This review addresses strategies relevant to identification of disease modifying genes in MS, and summarizes and critically evaluates the current state of knowledge in this area.

The fine specificity of human T cell lines towards myelin basic protein peptides in southern Italian multiple sclerosis patients

We studied the relationship between the HLA specificities associated with multiple sclerosis (MS) susceptibility in southern Italy and the reactivity of the human myelin basic protein (hMBP) immunogenic peptides 84-98 and 143-168, using short-term T-cell lines established from 9 MS patients and from 8 healthy individuals. In our population, DR15 was significantly associated with MS (34.9% in MS versus 13.7% in healthy controls, P < 0.05). This result is in agreement with the association found in northern Europe, but not with data obtained in a population from the island of Sardinia (Italy). In MS patients the frequency of reactive T-cell lines (TCL), tested for fine specificity against the immunodominant hMBP peptides 84-98 and 143-168, was increased for the hMBP 143-168 peptide (P < 0.05) but not for the 84-98 peptide. Although this reactivity was higher in DR15+ MS patients than in DR 15- MS patients, it seemed not to be associated with DR15 specificity in the MS population. Furthermore, there were no significant differences in frequency of reactive TCL to hMBP peptide 84-98 in DR15-positive or DR15-negative MS patients. Consequently, it appears that peptide 84-98, considered as a relevant autoantigen, is not implicated in the pathogenesis of MS in our population from southern Italy.

Sex and age at diagnosis are correlated with the HLA-DR2, DQ6 haplotype in multiple sclerosis

The HLA-DR2, DQ6 (i.e., HLA-DRB1*1501, DQA1*0102, DQB1*0602) haplotype contributes to the risk of developing multiple sclerosis (MS) in Caucasoids of Northern European heritage. A correlation between the clinical expression of MS and the presence of HLA-DR2, DQ6 has, however, not convincingly been shown. In this study conventional bivariate analysis and logistic regression analysis were used to study the relationship between HLA-DR2, DQ6 and four disease variables in a cohort of 286 Norwegian MS patients from the Oslo area. Logistic regression analysis showed that HLA-DR2, DQ6 was significantly more frequent among female than male patients (P=0. 0251), and was negatively correlated with age at diagnosis regardless of sex (P=0.0254). No significant correlation was observed between HLA-DR2, DQ6 and type of disease (relapsing-remitting versus primary chronic progressive MS) or presence/absence of oligoclonal bands in the cerebrospinal fluid.

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 epitope spreading cascade during progression of experimental autoimmune encephalomyelitis and multiple sclerosis

We have made the following observations regarding self-recognition during the development and progression of murine experimental autoimmune encephalomyelitis (EAE) and human multiple sclerosis (MS): 1) chronic progression of EAE is accompanied by a sequential, predictable cascade of neo-autoreactivity, commonly referred to as epitope spreading, presumably caused by endogenous self-priming during autoimmune-mediated tissue damage; 2) there is an invariant relationship between the progression of EAE and the emergence of epitope spreading; 3) progression of EAE can be inhibited by the induction of antigen-specific tolerance to spreading determinants after onset of initial neurologic symptoms; 4) CD4+ Th 1 cells responding to spreading determinants are autonomously encephalitogenic; 5) epitope spreading occurs during the development of MS and in some cases involves HLA-DP class II-restricted self-recognition; and 6) progression of both EAE and MS is accompanied by the decline of primary T-cell autoreactivity associated with disease onset and by the concurrent emergence of the epitope spreading cascade. Our studies directly challenge the traditional view that EAE and MS are initiated and maintained by autoreactivity directed against a single predominant myelin protein or determinant. Our results indicate that progression of EAE and MS involves a shifting of T-cell autoreactivity from primary initiating self-determinants to defined cascades of secondary determinants that sustain the inflammatory self-recognition process during disease progression.

HLA-DP: a class II restriction molecule involved in epitope spreading during the development of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system. It is widely believed that complex polygenic inheritance patterns involving HLA-DR and -DQ class II genes contribute to MS susceptibility, and current evidence indicates that disease risk vs disease outcome may be associated with distinctly different HLA class II alleles. We have recently shown that the early development of MS is accompanied by an extensive plasticity of myelin self-recognition with the acquisition of neo-autoreactivity, or epitope spreading, as a prominent feature. Although we did not observe a common determinant recognized by patients sharing identical HLA-DR or -DQ class II alleles, we did observe epitope spreading to the p50-63 determinant of myelin proteolipid protein (PLP) in two study subjects showing complete disparity at HLA-DR and -DQ but identity at the HLA-DP allele DPB1*0301. In the present study we show that self-recognition during the early stages in the development of MS involves HLA-DP class II restricted responses to the PLP 50-63 spreading determinant. Our results suggest that self-presentation by HLA-DP may play an important role in epitope spreading and in the propagation of self-recognition during the clinical progression of MS.

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.

Rational clinical immunotherapy for multiple sclerosis

In this article, we assess the roles and the efficacy of immunopharmacologic agents in the treatment of multiple sclerosis (MS) and other demyelinating disease syndromes. The initial clinical manifestations of demyelinating disease, immunotherapeutic goals, efficacy of individual agents, and specific immunopharmacologic recommendations are discussed. MS and other idiopathic demyelinating disease syndromes can be effectively managed with immunotherapy. Exacerbations are treatable, and the frequency and severity of exacerbations can be reduced. Although some agents have a minor effect on progression of disability, current approaches have not proved to have a major influence on treatment of progressive MS. Immunotherapy for inflammatory demyelinating disease necessitates a high degree of clinical certainty about the diagnosis. Because all available therapeutic agents have limitations and significant toxic effects, careful consideration is necessary before use. Treatment should be individualized on the basis of the clinical course of the disease and the degree of patient disability.

Distribution of HLA-Dw2 in optic neuritis and multiple sclerosis indicates heterogeneity

The human leukocyte antigen (HLA) phenotype Dw2 is known to be increased in multiple sclerosis (MS), but only slightly in optic neuritis (ON).

MATERIAL AND METHODS

127 consecutive patients with unilateral monosymptomatic ON were typed genomically for HLA-DR and -DQ genes.

RESULTS

The frequency of HLA-Dw2 among ON patients (47%) was found to be significantly higher than among 250 controls (30%) but significantly lower than in a group of 245 MS patients (60%), all of the same ethnic origin. At the group level, these figures can be calculated to indicate that 53% of the ON patients belong to the group of "MS-type ON" (95% confidence limits 25-78%). A compilation of published data on the frequency of the HLA-DR17(3), DQ2 haplotype, prompted by a slight increase in this material, revealed a significant association with this haplotype in ON, after compensation for the increase of Dw2.

CONCLUSION

ON differs from both MS and controls regarding HLA-Dw2. Thus, a substantial number of patients with ON may suffer from conditions not immuno-genetically related to MS, which might be designated as non-MS type ON. This condition may be more common in men and in young patients of both sexes.

Binding of peptides of the human acetylcholine receptor alpha-subunit to HLA class II of patients with myasthenia gravis

MG is an autoimmune disease in which T cells specific to T-cell epitopes of the human acetylcholine receptor play a role. We have identified two peptides, p195-212 and p259-271, of the human acetylcholine receptor alpha-subunit, to which PBLs of MG patients responded by proliferation. Nevertheless, proliferation assays are relatively complicated to perform and might be affected by medications taken by the patients. Therefore, we tested the possibility of using a different assay to determine recognition of these peptides by MG patients. Thus, we performed a direct binding assay using biotinylated peptides and APCs from peripheral blood of MG patients and healthy controls. With this assay we detected the binding of the two peptides to the surface of intact APCs of both MG patients and control donors. Moreover, the presentation of peptide p259-271 by individuals with MG was significantly higher than that observed in healthy subjects. The peptides were specifically bound to HLA class II determinants on the APCs, as shown by inhibition with antibodies to the HLA class II haplotypes of the individuals investigated. Moreover, the binding of these peptides was in correlation with their ability to induce specific proliferative responses of peripheral blood T cells of these patients. The ability to screen for potentially pathogenic epitopes in each patient is of importance for the future design of specific inhibitory analogues that might be used to treat MG.

Bilateral simultaneous optic neuropathy in adults: clinical, imaging, serological, and genetic studies

To elucidate the cause(s) of acute or subacute bilateral simultaneous optic neuropathy (BSON) in adult life, a follow up study of 23 patients was performed with clinical assessment, brain MRI, HLA typing, and mitochondrial DNA analysis. The results of CSF electrophoresis were available from previous investigations in 11 patients. At follow up, five (22%) had developed clinically definite multiple sclerosis, four (17%) had mitochondrial DNA point mutations indicating a diagnosis of Leber's hereditary optic neuropathy (LHON). The remaining 14 patients (61%) still had clinically isolated BSON a mean of 50 months after the onset of visual symptoms: three of 14 (21%) had multiple MRI white matter lesions compatible with multiple sclerosis, three of 14 (21%) had the multiple sclerosis associated HLA-DR15/DQw6 haplotype, and one of seven tested had CSF oligoclonal IgG bands; in total only five (36%) had one or more of these risk factors. The low frequency of risk factors for the development of multiple sclerosis in these 14 patients suggests that few will develop multiple sclerosis with more prolonged follow up. It is concluded that: (a) about 20% of cases of BSON without affected relatives are due to LHON; (b) multiple sclerosis develops after BSON in at least 20% of cases, but the long term conversion rate is likely to be considerably less than the rate of over 70% seen after an episode of acute unilateral optic neuritis in adult life.

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.

TAP 1 and TAP 2 transporter gene polymorphisms in multiple sclerosis: no evidence for disease association with TAP

Multiple sclerosis (MS) is known to be associated with HLA-DR2, but it is possible that additional major histocompatibility complex (MHC) genes confer disease susceptibility. The most recent candidate genes for MHC-encoded susceptibility are the TAP genes, which are located between the HLA-DQ and DP loci, and encode for proteins believed to transport antigenic peptides from the cytoplasm into the endoplasmic reticulum. We studied TAP 1 and TAP 2 gene polymorphisms in 65 chronic progressive MS patients and 66 healthy subjects. No significant differences in the frequencies of TAP polymorphisms were observed between both groups. These data suggest that TAP is not a susceptibility gene for MS and that the disease-predisposing haplotype does not extend as far as TAP.

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.

HLA and prognosis in multiple sclerosis

The patients of a multiple sclerosis (MS) incidence cohort with 25 years of longitudinal follow-up were typed for HLA-DR and DQ. This type of cohort provides reliable data for gene frequencies and prognostic studies. The influence of sampling bias, mainly due to mortality during the long follow-up, was accounted for. A positive association between MS and DR15,DQ6 was confirmed, but this haplotype did not influence prognosis. There was no difference in haplotype frequency between relapsing-remitting and primary chronic progressive MS. DR17,DQ2 was significantly over-represented in the quartile with the most malignant course. The haplotype DR1,DQ5, which was found rather less frequently in MS patients, also tended to be associated with a poorer prognosis.

Human leukocyte antigen studies in multiple sclerosis

Multiple sclerosis (MS) has been associated with HLA-DR2 for more than 20 years, and a large number of studies have addressed the relation between MS and the HLA class II genes, which are our major immune-response genes. This has produced a complex and confusing picture that is difficult to interpret. With the advent of reliable and comprehensive DNA-based typing techniques, it is now possible to extract a coherent pattern from this mass of data. The associated haplotype has been specified to HLA-Dw2 in cellular typing nomenclature, which equals DR15,DQ6 by serology, and DRB1*1501,DQA1*0102,DQB1*0602 in sequence-based terminology. This haplotype is increased among groups of MS patients worldwide, although most strongly in North and West Europeans, and it is the only haplotype with a clear importance in MS. Attempts to map this association within the haplotype have not been successful.

The influence of HLA-DR and -DQ alleles on progression to multiple sclerosis following a clinically isolated syndrome

A 5-year follow-up study was performed on 70 Caucasian patients presenting with isolated neurological syndromes of the optic nerve, brain stem, or spinal cord to assess the risk of progression to MS. The influence on patient prognosis of HLA-DR and -DQ alleles and presentation with disseminated brain lesions, demonstrated by MRI scanning, was determined. Clinical progression to MS was observed in 61% of optic neuritis patients, 50% of patients with a brain-stem syndrome, and 35% of patients with a spinal cord disturbance. MS and the isolated clinical syndromes were positively associated with DRB1*1501, DQA1*0102, and DQB1*0602; the frequency of these alleles in the latter group was intermediate between that seen in MS patients and healthy controls. Conversion to MS was positively associated with the DRB1*1501.DQA1*0102.DQB1*0602 haplotype, but the influence of HLA was only significant in patients with disseminated brain lesions at presentation (MRI positive); MS developed in 86% of MRI-positive, DRB1*1501-positive patients compared with 55% of MRI-positive, DRB1*1501-negative patients (p < 0.025). The data suggest that these HLA alleles are involved in susceptibility to initial demyelinating lesion formation and are important in the subsequent development of MS in MRI-positive patients.

Binding of myelin basic protein peptides to human histocompatibility leukocyte antigen class II molecules and their recognition by T cells from multiple sclerosis patients

Multiple sclerosis (MS) is an autoimmune disease in which myelin proteins have been implicated as autoantigens recognized by pathogenic autoreactive T cells. To study the relationship between human myelin basic protein (hMBP) and HLA alleles associated to MS susceptibility, such as DRB1*1501, the binding of synthetic peptides spanning the entire hMBP sequence to 10 purified HLA-DR molecules was determined. All the hMBP peptides tested showed binding affinity for at least one of the DR molecules analyzed, but three hMBP peptides, included in sequences 13-32, 84-103, and 144-163 were found capable of binding to three or more DR molecules. The hMBP peptide 84-103 was the most degenerate in binding, in that it bound to 9 out of 10 DR molecules tested. Interestingly, it bound with highest affinity to DRB1*1501 molecules. To correlate the binding pattern of hMBP peptides to HLA class II molecules with their recognition by T cells, 61 hMBP-specific T cell lines (TCL) were established from the peripheral blood of 20 MS patients, who were homozygous, heterozygous, or negative for DRB1*1501. Analysis of hMBP epitopes recognized by these TCL and their HLA restriction demonstrated a very good correlation between binding data and T cell proliferation to hMBP peptides. Although virtually all hMBP peptides tested could be recognized by at least one TCL from MS patients, three immunodominant T cell epitopes were apparent among the TCL examined, corresponding exactly to the hMBP peptides capable of binding to several DR molecules. No major difference could be detected in the recognition of immunodominant hMBP peptides by TCL from DRB1*1501 positive or negative MS patients. These results have implications for the role of hMBP as relevant autoantigen, and of DRB1*1501 as susceptibility allele in MS.

HLAs and genes in Japanese patients with multiple sclerosis: evidence for increased frequencies of HLA-Cw3, HLA-DR2, and HLA-DQB1*0602

The distribution of HLA-A, B, C, DR and DRB1, DQB1, DPB1 alleles was studied in 60 Japanese patients with clinically definite multiple sclerosis (MS) using serologic and genomic analysis. We found significant associations with HLA-Cw3 (p = 0.002, pc = 0.012, RR = 3.2), DR2 (p = 0.007, RR = 2.6), and DQB1*0602 (p = 0.04, RR = 4.0) in Japanese patients for the first time. The combined presence of Cw3 and DR2 gave a higher risk than each antigen alone. The reported increase in the frequency of DPw4 in Japanese MS patients [12] could not be confirmed by our genomic study. The frequencies of all of the residues in each variable region of the amino acid sequences of DQ beta and DP beta chains were not different between the MS patients and the controls. These results suggest that MS susceptibility may result from polygenic influences and from the presence of environmental factors.