Linkage analysis of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in the rat identifies a locus controlling demyelination on chromosome 18

mRNA expression profile reveals differentially expressed genes in splenocytes of experimental autoimmune encephalomyelitis model

Experimental autoimmune encephalomyelitis (EAE) is a mouse model that can be used to investigate aetiology, pathogenesis, and treatment approaches for multiple sclerosis (MS). A novel integrated bioinformatics approach was used to understand the involvement of differentially expressed genes (DEGs) in the spleen of EAE mice through data mining of existing microarray and RNA-seq datasets. We screened differentially expressed mRNAs using mRNA expression profile data of EAE spleens taken from Gene Expression Omnibus (GEO). Functional and pathway enrichment analyses of DEGs were performed by Database for Annotation, Visualization, and Integrated Discovery (DAVID). Subsequently, the DEGs-encoded protein-protein interaction (PPI) network was constructed. The 784 DEGs in GSE99300 A.SW PP-EAE mice spleen mRNA profiles, 859 DEGs in GSE151701 EAE mice spleen mRNA profiles, and 646 DEGs in GSE99300 SJL/J PP-EAE mice spleen mRNA profiles were explored. Functional enrichment of 55 common DEGs among 3 sub-datasets revealed several immune-related terms, such as neutrophil extravasation, leucocyte migration, antimicrobial humoral immune response mediated by an antimicrobial peptide, toll-like receptor 4 bindings, IL-17 signalling pathway, and TGF-beta signalling pathway. In the screening of 10 hub genes, including MPO, ELANE, CTSG, LTF, LCN2, SELP, CAMP, S100A9, ITGA2B, and PRTN3, and in choosing and validating the 5 DEGs, including ANK1, MBOAT2, SLC25A21, SLC43A1, and SOX6, the results showed that SLC43A1 and SOX6 were significantly decreased in EAE mice spleen. Thus this study offers a list of genes expressed in the spleen that might play a key role in the pathogenesis of EAE.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

Immune profile of an atypical EAE model in marmoset monkeys immunized with recombinant human myelin oligodendrocyte glycoprotein in incomplete Freund's adjuvant

Background

Experimental autoimmune encephalomyelitis (EAE) in the common marmoset monkey (Callithrix jacchus) is a relevant preclinical model for translational research into immunopathogenic mechanisms operating in multiple sclerosis (MS). Prior studies showed a core pathogenic role of T and B cells specific for myelin oligodendrocyte glycoprotein (MOG). However, in those studies, the quality of the response against MOG epitopes was strongly biased by bacterial antigens in the complete Freund’s adjuvant (CFA), in which the immunizing recombinant human (rh) MOG protein had been formulated. In response to the need of a more refined EAE model, we have tested whether disease could also be induced with rhMOG in incomplete Freund’s adjuvant (IFA).

Method

Marmosets were immunized with rhMOG emulsified in IFA in the dorsal skin. Monkeys that did not develop neurological deficit were given booster immunizations at 28-day interval with the same antigen preparation. In a second experiment, three marmoset twin pairs were sensitized against MOG peptides in IFA to study a possibility for suppressive activity towards pathogenic T cells directed against the encephalitogenic epitope MOG40-48.

Results

Despite the absence of strong danger signals in the rhMOG/IFA inoculum, all monkeys developed clinically evident EAE symptoms. Moreover, in all monkeys, demyelinated lesions were present in the white matter and in two cases also in the cortical grey matter. Immune profiling at height of the disease showed a dominant T cell response against the overlapping peptides 14–36 and 24–46, but reactivity against the pathogenically most relevant peptide 34–56 was conspicuously absent. In the second experiment, there was an indication for a possible suppressive mechanism.

Conclusions

Immunization of marmoset monkeys with rhMOG in IFA elicits clinical EAE in all animals. Moreover, rhMOG contains pathogenic and regulatory epitopes, but the pathogenic hierarchy of rhMOG epitopes is strongly influenced by the adjuvant in which the protein is formulated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0378-5) contains supplementary material, which is available to authorized users.

Identification of candidate risk gene variations by whole-genome sequence analysis of four rat strains commonly used in inflammation research

Background

The DA rat strain is particularly susceptible to the induction of a number of chronic inflammatory diseases, such as models for rheumatoid arthritis and multiple sclerosis. Here we sequenced the genomes of two DA sub-strains and two disease resistant strains, E3 and PVG, previously used together with DA strains in genetically segregating crosses.

Results

The data uncovers genomic variations, such as single nucleotide variations (SNVs) and copy number variations that underlie phenotypic differences between the strains. Comparisons of regional differences between the two DA sub-strains identified 8 genomic regions that discriminate between the strains that together cover 38 Mbp and harbor 302 genes. We analyzed 10 fine-mapped quantitative trait loci and our data implicate strong candidates for genetic variations that mediate their effects. For example we could identify a single SNV candidate in a regulatory region of the gene Il21r, which has been associated to differential expression in both rats and human MS patients. In the APLEC complex we identified two SNVs in a highly conserved region, which could affect the regulation of all APLEC encoded genes and explain the polygenic differential expression seen in the complex. Furthermore, the non-synonymous SNV modifying aa153 of the Ncf1 protein was confirmed as the sole causative factor.

Conclusion

This complete map of genetic differences between the most commonly used rat strains in inflammation research constitutes an important reference in understanding how genetic variations contribute to the traits of importance for inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-391) contains supplementary material, which is available to authorized users.

Parent-of-origin effects implicate epigenetic regulation of experimental autoimmune encephalomyelitis and identify imprinted Dlk1 as a novel risk gene

Parent-of-origin effects comprise a range of genetic and epigenetic mechanisms of inheritance. Recently, detection of such effects implicated epigenetic mechanisms in the etiology of multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system. We here sought to dissect the magnitude and the type of parent-of-origin effects in the pathogenesis of experimental neuroinflammation under controlled environmental conditions. We investigated inheritance of an MS-like disease in rat, experimental autoimmune encephalomyelitis (EAE), using a backcross strategy designed to identify the parental origin of disease-predisposing alleles. A striking 37–54% of all detected disease-predisposing loci depended on parental transmission. Additionally, the Y chromosome from the susceptible strain contributed to disease susceptibility. Accounting for parent-of-origin enabled more powerful and precise identification of novel risk factors and increased the disease variance explained by the identified factors by 2-4-fold. The majority of loci displayed an imprinting–like pattern whereby a gene expressed only from the maternal or paternal copy exerts an effect. In particular, a locus on chromosome 6 comprises a well-known cluster of imprinted genes including the paternally expressed Dlk1, an atypical Notch ligand. Disease-predisposing alleles at the locus conferred lower Dlk1 expression in rats and, together with data from transgenic overexpressing Dlk1 mice, demonstrate that reduced Dlk1 drives more severe disease and modulates adaptive immune reactions in EAE. Our findings suggest a significant epigenetic contribution to the etiology of EAE. Incorporating these effects enables more powerful and precise identification of novel risk factors with diagnostic and prognostic implications for complex disease.

Even with recent progress in determining the genetic basis of complex diseases, the issue of ‘missing heritability’ remains and its potential sources are frequently speculated about but rarely explained. Parent-of-origin effects might contribute to the ‘missing heritability’ and involve genetic and epigenetic mechanisms of inheritance. Our study is the first that establishes (i) the magnitude and (ii) the type of parent-of-origin effects in the pathogenesis of a multiple sclerosis-like disease, experimental autoimmune encephalomyelitis (EAE) in rat, using a strategy designed to identify genes that confer risk only when inherited from either mother or father. A striking 37-54% of all risk loci depended on parental origin. Accounting for parent-of-origin enabled more powerful and precise identification of novel risk factors for EAE, such as the imprinted Dlk1gene. Disease-predisposing alleles conferred lower Dlk1 expression in rats and transgenic Dlk1 mice demonstrated that lower Dlk1 drives more severe EAE and modulates adaptive immune responses. Because parental-origin effects are epigenetically regulated, our data implicate a contributory role for epigenetic mechanisms in complex diseases. Considering parent-of-origin effects in complex disease has enabled more powerful and precise identification of novel risk factors.

Gene expression in the spinal cord in female lewis rats with experimental autoimmune encephalomyelitis induced with myelin basic protein

Background

Experimental autoimmune encephalomyelitis (EAE), the best available model of multiple sclerosis, can be induced in different animal strains using immunization with central nervous system antigens. EAE is associated with inflammation and demyelination of the nervous system. Micro-array can be used to investigate gene expression and biological pathways that are altered during disease. There are few studies of the changes in gene expression in EAE, and these have mostly been done in a chronic mouse EAE model. EAE induced in the Lewis with myelin basic protein (MBP-EAE) is well characterised, making it an ideal candidate for the analysis of gene expression in this disease model.

Methodology/Principal Findings

MBP-EAE was induced in female Lewis rats by inoculation with MBP and adjuvants. Total RNA was extracted from the spinal cords and used for micro-array analysis using AffimetrixGeneChip Rat Exon 1.0 ST Arrays. Gene expression in the spinal cords was compared between healthy female rats and female rats with MBP-EAE. Gene expression in the spinal cord of rats with MBP-EAE differed from that in the spinal cord of normal rats, and there was regulation of pathways involved with immune function and nervous system function. For selected genes the change in expression was confirmed with real-time PCR.

Conclusions/Significance

EAE leads to modulation of gene expression in the spinal cord. We have identified the genes that are most significantly regulated in MBP-EAE in the Lewis rat and produced a profile of gene expression in the spinal cord at the peak of disease.

Expression of Ccl11 associates with immune response modulation and protection against neuroinflammation in rats

Multiple sclerosis (MS) is a polygenic disease characterized by inflammation and demyelination in the central nervous system (CNS), which can be modeled in experimental autoimmune encephalomyelitis (EAE). The Eae18b locus on rat chromosome 10 has previously been linked to regulation of beta-chemokine expression and severity of EAE. Moreover, the homologous chemokine cluster in humans showed evidence of association with susceptibility to MS. We here established a congenic rat strain with Eae18b locus containing a chemokine cluster (Ccl2, Ccl7, Ccl11, Ccl12 and Ccl1) from the EAE- resistant PVG rat strain on the susceptible DA background and utilized myelin oligodendrocyte glycoprotein (MOG)-induced EAE to characterize the mechanisms underlying the genetic regulation. Congenic rats developed a milder disease compared to the susceptible DA strain, and this was reflected in decreased demyelination and in reduced recruitment of inflammatory cells to the brain. The congenic strain also showed significantly increased Ccl11 mRNA expression in draining lymph nodes and spinal cord after EAE induction. In the lymph nodes, macrophages were the main producers of CCL11, whereas macrophages and lymphocytes expressed the main CCL11 receptor, namely CCR3. Accordingly, the congenic strain also showed significantly increased Ccr3 mRNA expression in lymph nodes. In the CNS, the main producers of CCL11 were neurons, whereas CCR3 was detected on neurons and CSF producing ependymal cells. This corresponded to increased levels of CCL11 protein in the cerebrospinal fluid of the congenic rats. Increased intrathecal production of CCL11 in congenic rats was accompanied by a tighter blood brain barrier, reflected by more occludin⁺ blood vessels. In addition, the congenic strain showed a reduced antigen specific response and a predominant anti-inflammatory Th2 phenotype. These results indicate novel mechanisms in the genetic regulation of neuroinflammation.

Fine-mapping resolves Eae23 into two QTLs and implicates ZEB1 as a candidate gene regulating experimental neuroinflammation in rat

Background

To elucidate mechanisms involved in multiple sclerosis (MS), we studied genetic regulation of experimental autoimmune encephalomyelitis (EAE) in rats, assuming a conservation of pathogenic pathways. In this study, we focused on Eae23, originally identified to regulate EAE in a (LEW.1AV1xPVG.1AV1)F2 cross. Our aim was to determine whether one or more genes within the 67 Mb region regulate EAE and to define candidate risk genes.

Methodology/Principal Findings

We used high resolution quantitative trait loci (QTL) analysis in the 10th generation (G10) of an advanced intercross line (AIL) to resolve Eae23 into two QTLs that independently regulate EAE, namely Eae23a and Eae23b. We established a congenic strain to validate the effect of this region on disease. PVG alleles in Eae23 resulted in significant protection from EAE and attenuated CNS inflammation/demyelination. Disease amelioration was accompanied with increased levels of Foxp3⁺ cells in the CNS of the congenic strain compared to DA. We then focused on candidate gene investigation in Eae23b, a 9 Mb region linked to all clinical phenotypes. Affymetrix exon arrays were used to study expression of the genes in Eae23b in the parental strains, where none showed differential expression. However, we found lower expression of exon 4 of ZEB1, which is specific for splice-variant Zfhep1. ZEB1 is an interleukin 2 (IL2) repressor involved in T cell development. The splice-specific variance prompted us to next analyze the expression of ZEB1 and its two splice variants, Zfhep1 and Zfhep2, in both lymph node and spleen. We demonstrated that ZEB1 splice-variants are differentially expressed; severity of EAE and higher IL2 levels were associated with down-regulation of Zfhep1 and up-regulation of Zfhep2.

Conclusions/Significance

We speculate that the balance between splice-variants of ZEB1 could influence the regulation of EAE. Further functional studies of ZEB1 and the splice-variants may unravel novel pathways contributing to MS pathogenesis and inflammation in general.

A role for VAV1 in experimental autoimmune encephalomyelitis and multiple sclerosis

Multiple sclerosis, the most common cause of progressive neurological disability in young adults, is a chronic inflammatory disease. There is solid evidence for a genetic influence in multiple sclerosis, and deciphering the causative genes could reveal key pathways influencing the disease. A genome region on rat chromosome 9 regulates experimental autoimmune encephalomyelitis, a model for multiple sclerosis. Using interval-specific congenic rat lines and association of single-nucleotide polymorphisms with inflammatory phenotypes, we localized the gene of influence to Vav1, which codes for a signal-transducing protein in leukocytes. Analysis of seven human cohorts (12,735 individuals) demonstrated an association of rs2546133-rs2617822 haplotypes in the first VAV1 intron with multiple sclerosis (CA: odds ratio, 1.18; CG: odds ratio, 0.86; TG: odds ratio, 0.90). The risk CA haplotype also predisposed for higher VAV1 messenger RNA expression. VAV1 expression was increased in individuals with multiple sclerosis and correlated with tumor necrosis factor and interferon-gamma expression in peripheral blood and cerebrospinal fluid cells. We conclude that VAV1 plays a central role in controlling central nervous system immune-mediated disease and proinflammatory cytokine production critical for disease pathogenesis.

Genomics studies of immune-mediated diseases using the BN-LEW rat model

LEW and BN rats, that behave in opposite ways for their susceptibility to various immune-mediated diseases, provide a powerful model to investigate the molecular and genetic bases of immune system physiology and dysregulation. Using this model, we addressed the question of the genetic control of central nervous system autoimmunity, of xenobiotic-induced allergic diseases, and of T cell subsets that differ by their cytokine profiles. By linkage analysis and genetic dissection, using a panel of congenic rats, we identified a 120 Kb region on chromosome 9 that controls all these phenotypes, indicating that this region contains a gene or set of genes that plays an important role in the immune system homeostasis and susceptibility to immune mediated diseases. In this review, we will describe these rat genomics studies and will discuss the cellular and genetic factors that may be involved in the differences between these rat strains.

Genetic variants of CC chemokine genes in experimental autoimmune encephalomyelitis, multiple sclerosis and rheumatoid arthritis

Multiple sclerosis (MS) is a complex disorder of the central nervous system, causing inflammation, demyelination and axonal damage. A limited number of genetic risk factors for MS have been identified, but the etiology of the disease remains largely unknown. For the identification of genes regulating neuroinflammation we used a rat model of MS, myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), and carried out a linkage analysis in an advanced intercross line (AIL). We thereby redefine the Eae18b locus to a 0.88 Mb region, including a cluster of chemokine genes. Further, we show differential expression of Ccl2, Ccl11 and Ccl11 during EAE in rat strains with opposite susceptibility to EAE, regulated by genotype in Eae18b. The human homologous genes were tested for association to MS in 3841 cases and 4046 controls from four Nordic countries. A haplotype in CCL2 and rs3136682 in CCL1 show a protective association to MS, whereas a haplotype in CCL13 is disease predisposing. In the HLA-DRB1* 15 positive subgroup, we also identified an association to a risk haplotype in CCL2, suggesting an influence from the human leukocyte antigen (HLA) locus. We further identified association to rheumatoid arthritis in CCL2, CCL8 and CCL13, indicating common regulatory mechanisms for complex diseases.

Multiple loci comprising immune-related genes regulate experimental neuroinflammation

A 58 Mb region on rat chromosome 4 known to regulate experimental autoimmune encephalomyelitis (EAE) was genetically dissected. High-resolution linkage analysis in an advanced intercross line (AIL) revealed four quantitative trait loci (QTLs), Eae24-Eae27. Both Eae24 and Eae25 regulated susceptibility and severity phenotypes, whereas Eae26 regulated severity and Eae27 regulated susceptibility. Analyses of the humoral immune response revealed that the levels of serum anti-myelin oligodendrocyte glycoprotein (MOG) immunoglobin G1 (IgG1) antibodies are linked to Eae24 and anti-MOG IgG2b antibodies are linked to both Eae24 and Eae26. We tested the parental DA strain and six recombinant congenic strains that include overlapping fragments of this region in MOG-EAE. Eae24 and Eae25 showed significant protection during the acute phase of EAE, whereas Eae25 and Eae26 significantly modified severity but not susceptibility. The smallest congenic fragment, which carries Eae25 alone, influenced both susceptibility and severity, and protected from the chronic phase of disease. These results support the multiple QTLs identified in the AIL. By demonstrating several QTLs comprising immune-related genes, which potentially interact, we provide a significant step toward elucidation of the polygenically regulated pathogenesis of MOG-EAE and possibly multiple sclerosis (MS), and opportunities for comparative genetics and testing in MS case-control cohorts.

A resource for the simultaneous high-resolution mapping of multiple quantitative trait loci in rats: the NIH heterogeneous stock

The laboratory rat (Rattus norvegicus) is a key tool for the study of medicine and pharmacology for human health. A large database of phenotypes for integrated fields such as cardiovascular, neuroscience, and exercise physiology exists in the literature. However, the molecular characterization of the genetic loci that give rise to variation in these traits has proven to be difficult. Here we show how one obstacle to progress, the fine-mapping of quantitative trait loci (QTL), can be overcome by using an outbred population of rats. By use of a genetically heterogeneous stock of rats, we map a locus contributing to variation in a fear-related measure (two-way active avoidance in the shuttle box) to a region on chromosome 5 containing nine genes. By establishing a protocol measuring multiple phenotypes including immunology, neuroinflammation, and hematology, as well as cardiovascular, metabolic, and behavioral traits, we establish the rat HS as a new resource for the fine-mapping of QTLs contributing to variation in complex traits of biomedical relevance.

Comparative genomics for detecting human disease genes

Originally, comparative genomics was geared toward defining the synteny of genes between species. As the human genome project accelerated, there was an increase in the number of tools and means to make comparisons culminating in having the genomic sequence for a large number of organisms spanning the evolutionary tree. With this level of resolution and a long history of comparative biology and comparative genetics, it is now possible to use comparative genomics to build or select better animal models and to facilitate gene discovery. Comparative genomics takes advantage of the functional genetic information from other organisms, (vertebrates and invertebrates), to apply it to the study of human physiology and disease. It allows for the identification of genes and regulatory regions, and for acquiring knowledge about gene function. In this chapter, the current state of comparative genomics and the available tools are discussed in the context of developing animal model systems that reflect the clinical picture.

Combined-cross analysis of genome-wide linkage scans for experimental autoimmune encephalomyelitis in rat

Unbiased genetic analysis of experimental autoimmune encephalomyelitis (EAE) can provide insights into the pathogenesis of multiple sclerosis. To date five genome-wide scans using F2 crosses between different inbred rats have been performed with the aim of defining EAE-regulating quantitative trait loci (QTLs) as the starting point for identification of the underlying genes. We here report the first combined-cross analysis of three F2 crosses previously performed in our group. The majority of QTLs was shared between the different strain combinations and was therefore reproduced by the combined-cross analysis. Consequently, combined-cross analysis improved the power to detect QTLs with modest effects and narrowed QTL confidence intervals. The findings also demonstrate a lack of power in previous F2 crosses and encourage future use of larger populations. Moreover, the allelic states of shared QTLs could be established, thus providing critical information for narrowing QTLs and identifying the key polymorphism by subsequent haplotype analysis.

Genetics of autoimmune neuroinflammation

Detection of gene variants affecting the risk for multiple sclerosis provides insights into mechanisms central for autoaggressive neuroinflammation. Major histocompatibility complex (MHC) class II genes, and probably also MHC class I genes, regulate both human multiple sclerosis and rodent experimental autoimmune encephalomyelitis. However, the functional understanding of the MHC regulation requires further experimentation. Genome scans in human multiple sclerosis have failed to demonstrate significant non-MHC loci with genome-wide significance, but approximately 50 such loci have been described in different rodent experimental autoimmune encephalomyelitis models. Positional cloning of individual rodent genes is difficult, but genes or small genome regions now emerge. Association studies in large human cohorts are needed to confirm the human relevance of rodent genes and such cohorts will also be used for single nucleotide polymorphism-based whole-genome screening. It is realistic to assume that several non-MHC genes regulating autoimmune neuroinflammation, including target tissue responses, will be pinpointed in the next ten years. At the moment there are a few hot candidates, including MHC2TA, PRKCA and IL7R.

Advanced Intercross Line Mapping ofEae5RevealsNcf-1andCLDN4as Candidate Genes for Experimental Autoimmune Encephalomyelitis

Eae5 in rats was originally identified in two F(2) intercrosses, (DA x BN) and (E3 x DA), displaying linkage to CNS inflammation and disease severity in experimental autoimmune encephalomyelitis (EAE), respectively. This region overlaps with an arthritis locus, Pia4, which was also identified in the (E3 x DA) cross. Two congenic strains, BN.DA-Eae5 and BN.DA-Eae5.R1, encompassing the previously described Eae5 and Pia4, were established. DA alleles within the chromosome 12 fragment conferred an increase in disease susceptibility as well as increased inflammation and demyelination in the CNS as compared with BN alleles. To enable a more precise fine mapping of EAE regulatory genes, we used a rat advanced intercross line between the EAE-susceptible DA strain and the EAE-resistant PVG.1AV1 strain. Linkage analysis performed in the advanced intercross line considerably narrowed down the myelin oligodendrocyte glycoprotein-EAE regulatory locus (Eae5) to a approximately 1.3-megabase region with a defined number of candidate genes. In this study we demonstrate a regulatory effect of Eae5 on MOG-EAE by using both congenic strains as well as fine mapping these effects to a region containing Ncf-1, a gene associated with arthritis. In addition to structural polymorphisms in Ncf-1, both sequence polymorphisms and expression differences were identified in CLDN4. CLDN4 is a tight junction protein involved in blood-brain barrier integrity. In conclusion, our data strongly suggests Ncf-1 to be a gene shared between two organ-specific inflammatory diseases with a possible contribution by CLDN4 in encephalomyelitis.

Definition of a 1.06-Mb region linked to neuroinflammation in humans, rats and mice

Unbiased identification of susceptibility genes might provide new insights into pathogenic mechanisms that govern complex inflammatory diseases such as multiple sclerosis. In this study we fine mapped Eae18a, a region on rat chromosome 10 that regulates experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. We utilized two independent approaches: (1) in silico mapping based on sequence similarity between human multiple sclerosis susceptibility regions and rodent EAE quantitative trait loci and (2) linkage mapping in an F10 (DA x PVG.AV1) rat advanced intercrossed line. The linkage mapping defines Eae18a to a 5-Mb region, which overlaps one intergenomic consensus region identified in silico. The combined approach confirms experimentally, for the first time, the accuracy of the in silico method. Moreover, the shared intersection between the results of both mapping techniques defines a 1.06-Mb region containing 13 candidate genes for the regulation of neuroinflammation in humans, rats, and mice.

Evidence for linkage and association between autoimmune thyroid diseases and the 18q12-q21 region in a large Tunisian family

Many studies have shown linkage between IDDM6 locus on 18q12-q21 chromosome and several autoimmune diseases, suggesting that it might harbour susceptibility genes common to autoimmunity. Using 12 families deriving from a large Tunisian multiplex family (the Akr family) from which 38 people were affected with autoimmune thyroid diseases (AITD), and 193 unrelated AITD patients, tested against 100 healthy subjects, we tried to replicate the positive results previously reported for the IDDM6. Akr members were genotyped with eight microsatellite markers harbouring the IDDM6 region. Multipoint non-parametric linkage analysis have shown a clear peak values of NPL score around D18S41 marker (Z = 3.72, P = 0.0001). Family-based association test (FBAT) and transmission disequilibrium test (TDT) have confirmed linkage results. In particular, a significant association with allele 3 of D18S41 and allele 2 of D18S57 markers was found. Case-control studies, using one intragenic microsatellite (locus CTG18.1) marker in the immunoglobulin transcription factor (ITF2) gene, a 5' flanking AC repeat of the anti-apoptotic BCL-2 gene as well as two SNPs at positions +52 and +1955 from transcription start site of BCL-2, showed no significant association between neither genes and AITD. Our study is the first replication of the 18q12-q21 chromosome region as a potential candidate to AITD genetic susceptibility. The Akr family has shown evidence for linkage between IDDM6 locus and AITD. Moreover, case-control study does not support the involvement of ITF2 and BCL2 genes in AITD pathogenesis.

Cerebrospinal fluid levels of neurofilament light in chronic experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG) is a chronic relapsing-remitting animal model of multiple sclerosis (MS). Neurofilament light (NF-L), a structural protein expressed in neuronal cells can be used to quantify the amount of neuronal damage in MS patients. An immunoassay was used to measure levels of neurofilament light in cerebrospinal fluid (CSF) in rats with myelin oligodendrocyte glycoprotein-induced EAE. Significantly increased levels of neurofilament were found in the immunized animals compared to the controls, strengthening the similarities in the diseases and the progression pattern between the animal model and MS. The turnover of NF-L during this disease is increased since significantly elevated levels also were identified in the spinal cord of the diseased animals and immunohistochemistry gave support for this observation. Monitoring neurofilament levels in EAE can be used to follow disease progression and effects of therapy.

Impact of genomics on research in the rat

The need to translate genes to function has positioned the rat as an invaluable animal model for genomic research. The significant increase in genomic resources in recent years has had an immediate functional application in the rat. Many of the resources for translational research are already in place and are ready to be combined with the years of physiological knowledge accumulated in numerous rat models, which is the subject of this perspective. Based on the successes to date and the research projects under way to further enhance the infrastructure of the rat, we also project where research in the rat will be in the near future. The impact of the rat genome project has just started, but it is an exciting time with tremendous progress.

Genetic dissection of neurodegeneration and CNS inflammation

Inflammation and neurodegeneration characterize multiple sclerosis, as well as many other diseases of the central nervous system (CNS). The understanding of the molecular pathways that regulate these processes is of fundamental importance for the development of new therapies. Nerve lesions paradigms in animals can serve as important tools to dissect central features of human CNS disease and by using these models certain key regulators have also been identified. However, our knowledge of how aspects of neurodegeneration and CNS inflammation are regulated on a genomic level is very limited. Such knowledge may help to unravel disease mechanisms. By using a standardized nerve trauma model, ventral root avulsion (VRA), in a series of inbred rat strains we here demonstrate a potent genetic regulation of the degree of neuron death and glial activation. Genome wide mapping of these phenotypes in experimental rat strain crosses identifies several quantitative trait loci (QTLs) controlling nerve lesion-induced nerve cell death, local T cell accumulation and expression of MHC class II on microglia. This approach may lead to the identification of evolutionary conserved genetic polymorphisms in key controlling genes, which can serve as prime candidates for association studies in several human CNS diseases.

The Non-MHC Quantitative Trait Locus Cia5 Contains Three Major Arthritis Genes That Differentially Regulate Disease Severity, Pannus Formation, and Joint Damage in Collagen- and Pristane-Induced Arthritis

Cia5 is a locus on rat chromosome 10 which regulates the severity of collagen- and pristane-induced arthritis (CIA and PIA). To refine the region toward positional identification, Cia5 subcongenic strains were generated and studied in PIA and CIA. The protective effect of the telomeric locus Cia5a was confirmed in both models. A second arthritis severity locus (Cia5d) was identified within the most centromeric portion of Cia5. DA.F344(Cia5d) rats had a significantly lower median arthritis severity index in PIA, but not in CIA, compared with DA. On histologic analyses DA.F344(Cia5a) and DA.F344(Cia5d) congenics with PIA preserved a nearly normal joint architecture compared with DA, including significant reduction in synovial hyperplasia, pannus, angiogenesis, inflammatory infiltration, bone and cartilage erosions. Cia5 and Cia5a synovial levels of IL-1beta mRNA were reduced. Although both DA.F344(Cia5) and DA.F344(Cia5a) rats were protected in CIA, the arthritis scores of DA.F344(Cia5) were significantly higher than those of DA.F344(Cia5a), suggesting the existence of a third locus where F344-derived alleles centromeric from Cia5a contribute to increased arthritis severity. The existence of the third locus was further supported by higher levels of autoantibodies against rat type II collagen in DA.F344(Cia5) congenics compared with DA.F344(Cia5a). Our results determined that Cia5 contains three major arthritis severity regulatory loci regulating central events in the pathogenesis of arthritis, and differentially influencing CIA and PIA. These loci are syntenic to regions on human chromosomes 17q and 5q implicated in the susceptibility to rheumatoid arthritis, suggesting that the identification of these genes will be relevant to human disease.

Eae19, a new locus on rat chromosome 15 regulating experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) and its animal model, myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), share a complex genetic predisposition with contributions from the major histocompatibility complex class II genes and many other genes. Linkage mapping in F(2) crosses between the susceptible DA rat strain and the resistant ACI or BN rat strains in various models of autoimmune neuroinflammation have repeatedly displayed suggestive linkage to a region on rat chromosome 15. A direct study of this region was undertaken in congenic strains by transferring resistant ACI alleles to the susceptible DA background. Phenotypic analysis demonstrated lower maximal and cumulative EAE scores in the DA.ACI-D15Rat6-D15Rat71 (C15), DA.ACI-D15Rat6-D15Rat48, D15Rat126-D15Rat71 (C15R3b), and DA.ACI-D15Rat23-D15rat71 (C15R4) strains compared to the parental DA rat strain. Linkage analysis was then performed in a (DA x PVG.AV1)F(7) advanced intercross line, resulting in a LOD score of 4.7 for the maximal EAE score phenotype at the peak marker D15Rat71 and a confidence interval of 13 Mb, overlapping with the congenic fragment defined by the C15R3b and the C15R4 strains. Thus, a new MOG-EAE locus with the designation Eae19 is identified on rat chromosome 15. There are 32 confirmed or predicted genes in the confidence interval, including immune-responsive gene 1 and neuronal ceroid lipofuscinose gene 5. Definition of loci such as Eae19 enables the characterization of genetically regulated, evolutionary conserved disease pathways in complex neuroinflammatory diseases.

The non-major histocompatibility complex quantitative trait locus Cia10 contains a major arthritis gene and regulates disease severity, pannus formation, and joint damage

OBJECTIVE

To construct rats congenic for the chromosome 2 arthritis-regulatory quantitative trait locus Cia10, originally identified in a (DA x ACI)F(2) intercross rat strain that had been assessed for collagen-induced arthritis (CIA), and to determine the effect of this congenic interval on arthritis severity, joint histologic structure, and cytokine transcription in rats with pristane-induced arthritis (PIA).

METHODS

A 52.6-MB interval derived from the ACI (CIA- and PIA-resistant) strain and containing the Cia10 interval was introgressed into the DA (arthritis-susceptible) background through genotype-guided congenic breeding. Homozygous male and female DA.ACI(Cia10) congenic rats were studied for their susceptibility to and severity of PIA, and were compared with same-sex DA rats. Histologic analyses were done on hind paws collected on day 32 following the pristane injection. Levels of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) messenger RNA (mRNA) were measured with real-time polymerase chain reaction on synovial tissues from day-32 ankles.

RESULTS

Both male and female DA.ACI(Cia10) congenic rats developed a significantly milder form of arthritis, with a 95% and 92% reduction in the arthritis severity index compared with DA male and female controls, respectively (males P < or = 0.001 and females P = 0.003). DA.ACI(Cia10) congenic rat synovial tissue was more likely to preserve its normal histologic architecture, including minimal to no cartilage and bone erosions, synovial hyperplasia, and pannus formation, and reduced numbers of vessels (angiogenesis), when compared with DA synovial tissue. There was a 2.7- and 2.4-fold reduction in the amount of IL-1beta and TNFalpha mRNA, respectively, in the synovial tissue of DA.ACI(Cia10) congenic rats compared with DA rats. Sequencing analyses of complementary DNA for the Cia10-predicted candidate gene Ptpn8, the rat homolog of the rheumatoid arthritis (RA)-susceptibility gene PTPN22, revealed no polymorphisms between the DA and ACI strains.

CONCLUSION

This study determined that Cia10 harbors a major autoimmune arthritis-regulatory gene. This gene regulates clinical disease severity, histologic damage, and the levels of at least two central proinflammatory cytokines. We are in the process of narrowing down the critical region for positional cloning of the Cia10 gene. The identification of this gene will provide novel targets or pathways for focused candidate-gene studies in RA.

Resolution of a 16.8-Mb Autoimmunity-Regulating Rat Chromosome 4 Region into Multiple Encephalomyelitis Quantitative Trait Loci and Evidence for Epistasis

To investigate effects of a 16.8-Mb region on rat chromosome 4q42-43 on encephalomyelitis, we performed a high-resolution mapping using a 10th generation advanced intercross line between the susceptible DA strain and the MHC identical but resistant PVG.1AV1 strain. Clinical signs of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) developed in 29% of 772 F(10) rats. Three regions controlling disease, Eae20, Eae21, and Eae22, were mapped using 15 microsatellite markers spanning 16.8 Mb. Eae20 was a major genetic determinant within the region whereas Eae21 modified disease severity. Eae22 was identified as an epistatic region because it only displayed an effect together with Piebald Virol Glaxo (PVG) alleles on Eae20. Disease down-regulation by PVG alleles in the telomeric part of Eae20 was also demonstrated in DA rats made congenic for a approximately 1.44-Mb chromosomal region from PVG. As the region containing Eae20-Eae22 also regulates arthritis, together with the fact that the syntenic mouse 6F(2)-F(3) region regulates experimental lupus and diabetes, and the syntenic human 12p13.31-13.2 region regulates multiple sclerosis and rheumatoid arthritis, the present data point to genes that control several inflammatory diseases. The pairscan analyses of interaction, which here identified Eae22, are novel in the encephalomyelitis field and of importance in the design of further studies of this region in other diseases and species. The limited number of genes identified in Eae20, Eae21, and Eae22 enables focused examination of their relevance in mechanistic animal studies and screening of their association to human diseases.

MHC and non-MHC gene regulation of disease susceptibility and disease course in experimental inflammatory peripheral neuropathy

With a panel of rat strains, we demonstrate a strong impact of the MHC genotype on susceptibility and disease course in experimental autoimmune neuritis induced with peripheral nerve myelin or the P2 peptide 58-81 (KNTEISFKLGQEFEETTADNRKTK). Beside the MHC genotype, non-MHC genes determined disease susceptibility and resistance. The type of disease induced with P2 58-81 was strongly correlated to the strength of the MHC class II isotype interaction with P2 58-81. These findings suggest a link between susceptibility and acute versus chronic disease courses on one hand and the strength of the MHC class II molecule/peptide affinity on the other hand.

Identification of two novel female-specific non-major histocompatibility complex loci regulating collagen-induced arthritis severity and chronicity, and evidence of epistasis

OBJECTIVE

To identify additional sex-specific and epistatic quantitative trait loci (QTL) regulating collagen-induced arthritis (CIA) severity overall, as well as within different stages during the disease course, in an intercross between major histocompatibility complex-identical inbred rat strains DA/Bkl (susceptible) and ACI/Hsd (resistant).

METHODS

Arthritic male (DA x ACI)F2 intercross offspring (n = 143) were analyzed separately from the females (n = 184). Phenotypic extremes (maximum arthritis scores [MAS]) were genotyped and used for QTL analysis. All 327 rats were genotyped with the simple sequence-length polymorphism (SSLP) markers closest to the peak of Cia7 and Cia10, the major loci previously identified in this intercross, and with SSLPs covering chromosomes 12 and 18. Phenotypes studied were disease onset, arthritis severity scores on days 14-39, MAS, mean and cumulative arthritis scores, delayed-type hypersensitivity, and antibody responses to rat type II collagen.

RESULTS

A new female-specific arthritis-severity recessive locus was identified on rat chromosome 12 (Cia25), with a maximum effect observed on day 28 (logarithm of odds [LOD] 4.7). The homozygous DA genotype at Cia25 was associated with a 45% higher median arthritis score in females. Sequencing analyses of the Cia25 candidate gene Ncf1 revealed polymorphisms between DA and ACI. The previously identified locus, Cia10, was found to be male-specific. A 2-locus interaction model analysis identified a novel recessive chromosome 18 QTL, Cia26, which was dependent on Cia7, with its maximum effect observed at later stages during the disease course (peak LOD score of 3.6 for arthritis scores on day 39).

CONCLUSION

This study identified 2 novel female-specific loci, and 1 male-specific locus. Cia25 regulates MAS and disease severity during the mid-to-late stages of the disease course and may be accounted for by Ncf1 polymorphisms. Cia26 is in epistasis with Cia7 and regulates later stages of disease, suggesting an involvement in disease perpetuation and/or chronicity.

Gene-expression profiling of the early stages of MOG-induced EAE proves EAE-resistance as an active process

Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG) is a well-established animal model of multiple sclerosis (MS) in rodents. It reflects the wide spectrum of disease pathology and serves as a valuable tool for studying the pathogenesis and for testing new therapies of MS. In order to identify genes responsible for resistance to and modulation of the disease, we compared the mRNA expression profile of more than 12,000 genes by DNA microarray technique in lymph nodes of the highly EAE-susceptible mouse strain C57Bl/6 (B6) and the resistant strain C57Bl/10.S (B10). The disease onset in B6 mice was day 15. We identified 84 genes that were up-regulated more than two-fold in B10 mice compared to vehicle-treated controls, whereas only two genes were up-regulated in B6 mice after 7 and 15 days post-immunization (p.i.), respectively. We were able to match five up-regulated genes in B10 mice to known quantitative trait loci (QTLs), which control for EAE susceptibility. Only 17, respectively 5, genes were down-regulated at both time points in B10 and B6 mice. Tests for immunoreactivity to MOG (T cell proliferation and interferon-gamma (IFN-gamma) secretion) revealed no stronger immune response in B6 compared to B10 mice supporting the hypothesis of an immunosuppressive effect as a target to prevent EAE in the B10 mice. We conclude that resistance to EAE (and possibly to MS) is an active process mediated by multiple genes up-regulated in peripheral lymphatic organs of resistant animals. Thus, monitoring of the expression of these new candidate genes may serve as a tool for the disease progression and the pharmaceutical treatment.

Current Gene-Mapping Strategies in Experimental Models of Multiple Sclerosis

Both family-based linkage analyses and population-based association studies have failed to identify disease-regulatory non-human leucocyte antigen genes of importance in multiple sclerosis (MS). Instead, investigators have employed experimental models, which offer major advantages in genetic studies. We summarize the current main methodologies used and the status of both the human and experimental approaches. Why is it important to find genes regulating MS? There is an immense number of cellular and molecular interactions defined in the immunological field and it is very difficult to unravel those that are critical to an inflammatory disease, such as MS, by classical hypothesis-driven research. Unbiased genetics defines evolutionary conserved gene polymorphisms and pathways regulated by these genes, which are central in the pathogenesis. These, in turn, are of interest as therapeutic targets and pharmacogenetic markers.

An Advanced Intercross Line Resolves Eae18 into Two Narrow Quantitative Trait Loci Syntenic to Multiple Sclerosis Candidate Loci

Identification of polymorphic genes regulating inflammatory diseases may unravel crucial pathogenic mechanisms. Initial steps to map such genes using linkage analysis in F(2) intercross or backcross populations, however, result in broad quantitative trait loci (QTLs) containing hundreds of genes. In this study, an advanced intercross line in combination with congenic strains, was used to fine-map Eae18 on rat chromosome 10 in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE). Myelin oligodendrocyte glycoprotein-induced EAE is a chronic relapsing disease that closely mimics key features of multiple sclerosis. Congenic DA.ACI rat strains localized Eae18 to an approximately 30-Mb large region. Fine-mapping was then performed in an advanced intercross line consisting of a (DA x PVG.1AV1)F(7) intercross, resulting in two adjacent EAE-regulating QTLs designated Eae18a and Eae18b. The two QTLs span 5.5 and 3 Mb, respectively, and the 3-Mb Eae18b contains as few as 10 genes, including a cluster of chemokine genes (CCL1, CCL2, CCL7, and CCL11). Eae18a and Eae18b are syntenic to human chromosome 17p13 and 17q11, respectively, which both display linkage to multiple sclerosis. Thus, Eae18 consists of at least two EAE-regulating genes, providing additional evidence that clustering of disease-regulating genes in QTLs is an important phenomenon. The overlap between Eae18a and Eae18b with previously identified QTLs in humans and mice further supports the notion that susceptibility alleles in inflammatory disease are evolutionary conserved between species.

Genetic variation in myelin oligodendrocyte glycoprotein expression and susceptibility to experimental autoimmune encephalomyelitis

Myelin oligodendrocyte glycoprotein (MOG) is encoded within the RT1.M region of the rat MHC a susceptibility locus for MOG-induced experimental autoimmune encephalomyelitis (EAE). We report that the enhanced susceptibility of Brown Norway (BN) rats to MOG-EAE is associated with higher expression of MOG mRNA and protein in the nervous system than in the less susceptible Lewis (LEW) strain. MOG mRNA was also detected in the immune system, but there was no correlation with disease susceptibility. These results suggest that differences in the expression of MOG in the target organ, rather than in the immune system may influence susceptibility to MOG-EAE.

New loci regulating rat myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis

Myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease in rats that closely mimics many clinical and histopathological aspects of multiple sclerosis. Non-MHC quantitative trait loci regulating myelin oligodendrocyte glycoprotein-induced EAE have previously been identified in the EAE-permissive strain, DA, on rat chromosomes 4, 10, 15, and 18. To find any additional gene loci in another well-known EAE-permissive strain and thereby to assess any genetic heterogeneity in the regulation of the disease, we have performed a genome-wide linkage analysis in a reciprocal (LEW.1AV1 x PVG.1AV1) male/female F(2) population (n = 185). We examined reciprocal crosses, but no parent-of-origin effect was detected. The parental rat strains share the RT1(av1) MHC haplotype; thus, non-MHC genes control differences in EAE susceptibility. We identified Eae16 on chromosome 8 and Eae17 on chromosome 13, significantly linked to EAE phenotypes. Two loci, on chromosomes 1 and 17, respectively showed suggestive linkage to clinical and histopathological EAE phenotypes. Eae16 and Eae17 differ from those found in previously studied strain combinations, thus demonstrating genetic heterogeneity of EAE. Furthermore, we detected a locus-specific parent-of-origin effect with suggestive linkage in Eae17. Further genetic and functional dissection of these loci may disclose critical disease-regulating molecular mechanisms.

Gene-expression profiling of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a mouse model that serves as an experimental tool for studying the etiology, pathogenesis, as well as new therapeutic approaches of multiple sclerosis (MS). EAE is a polygenic chronic inflammatory demyelinating disease of the nervous system that involves the interaction between genetic and environmental factors. Previous studies have identified multiple quantitative trait loci (QTL) controlling different aspects of disease pathogenesis. However, progress in identifying new susceptibility genes outside the MHC locus has been slow. With the advent of new global methods for genetic analysis such as large-scale sequencing, gene expression profiling combined with classic linkage analysis and congenic and physical mapping progress is considerably accelerating. Here we review our preliminary work on the use of gene expression mapping to identify new putative genetic pathways contributing to the pathogenesis of EAE.

T- and B-cell responses to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis and multiple sclerosis

The identification of myelin oligodendrocyte glycoprotein (MOG) as a target for autoantibody-mediated demyelination in experimental autoimmune encephalomyelitis (EAE) resulted in the re-evaluation of the role of B cell responses to myelin autoantigens in the immunopathogenesis of multiple sclerosis. MOG is a central nervous system specific myelin glycoprotein that is expressed preferentially on the outermost surface of the myelin sheath. Although MOG is only a minor component of CNS myelin it is highly immunogenic, inducing severe EAE in both rodents and primates. In rat and marmoset models of MOG-induced EAE demyelination is antibody-dependent and reproduces the immunopathology seen in many cases of MS. In contrast, in mice inflammation in the CNS can result in demyelination in the absence of a MOG-specific B cell response, although if present this will enhance disease severity and demyelination. Clinical studies indicate that autoimmune responses to MOG are enhanced in many CNS diseases and implicate MOG-specific B cell responses in the immunopathogenesis of multiple sclerosis. This review provides a summary of our current understanding of MOG as a target autoantigen in EAE and MS, and addresses the crucial question as to how immune tolerance to MOG may be maintained in the healthy individual.

Polygenic control of autoimmune peripheral nerve inflammation in rat

Experimental autoimmune neuritis (EAN) is the principal animal model for Guillain-Barré syndrome (GBS), an inflammatory disease of the peripheral nervous system. Little is known on the genetic regulation of these diseases. We provide the first genetic linkage analysis of EAN. Susceptibility to EAN in a rat F2 population segregated with high levels of anti-PNM IgG, as well as IgG2b and IgG2c isotype levels, which support that disease genes regulate preferential Th1/Th2 differentiation. Linkage analysis demonstrated co-localization of EAN loci with reported susceptibility loci for experimental arthritis and/or encephalomyelitis and a new region on chromosome 17. Further dissection of these loci may disclose disease pathways in GBS.

MHC class II-regulated central nervous system autoaggression and T cell responses in peripheral lymphoid tissues are dissociated in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis

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

Linkage analysis in multiple sclerosis of chromosomal regions syntenic to experimental autoimmune disease loci

Multiple sclerosis is a demyelinating disorder of the central nervous system with a putative autoimmune aetiology in which several genes are thought to be involved. Four published genomic screens have confirmed that a gene influencing MS resides within or close to the HLA class II region in 6p21. Still, this locus is likely to confer only a part of the genetic susceptibility in MS. Further, all four studies identified a number of other regions with possible linkage. We have investigated eight chromosomal intervals syntenic to loci of importance for experimental autoimmune model diseases in the rat in 74 Swedish MS families. Possible linkage (a non-parametric linkage NPL score of 1.16 by GENEHUNTER computer package) was observed with markers in 12p13.3, a region syntenic to the rat Oia2 locus which is importance for oil induced arthritis (OIA). Four markers in the T cell receptor beta chain gene region in 7q35 showed possible linkage (highest NPL score of 1.16). This locus is syntenic to the rat Cia3 locus (collagen induced arthritis). These two loci at least partially overlap with chromosomal regions showing indicative evidence for linkage in the previous MS genomic screens. Indeed, both Oia2 and Cia3 were recently found to be linked also with experimental autoimmune encephalomyelitis, a commonly used model for MS. Markers in 2p12, 3p25, 10q11.23, 17q21-25, 19q13.1, and 22q12-13 failed to provide evidence for linkage. We conclude that evidence is amounting that 12p13-12 and 7q34-36 may harbour genes with an importance for MS. The synteny with experimental loci may eventually facilitate their identification.

Immune responses against the myelin/oligodendrocyte glycoprotein in experimental autoimmune demyelination

Myelin/oligodendrocyte glycoprotein (MOG) is a surface-exposed antigen of myelin and an important target for autoimmune responses which mediate inflammatory demyelination in the central nervous system. Experimentally, MOG induces strong pathogenic T cell responses in many strains of laboratory animals. Immunological studies in humans also identify MOG as a surprisingly prevalent antigenic molecule among the myelin proteins. In addition, the encephalitogenic properties of MOG are linked to the induction of antibody responses which have been demonstrated to directly promote central nervous system demyelination, a hallmark neuropathological feature in disorders such as human multiple sclerosis. Factors responsible for autoimmunity to MOG likely include genetic influences as well as other mechanisms, which are the subject of intense investigation. This article reviews experimental data currently available on specificity and pathogenic roles of T cell and antibody responses against MOG, which have implications relevant to multiple sclerosis and related disorders.

Genetic regulation of nerve avulsion-induced spinal cord inflammation

In the animal model for multiple sclerosis (MS), experimental autoimmune encephalitis (EAE), genetic loci correlating with incidence or severity of disease are located both within and outside of the major histocompatibility complex (MHC). Whereas polymorphisms within MHC class I and II molecules are likely to be a major determinant of MHC gene influence in rat EAE, it is still unclear how non-MHC gene regions influence disease. Genetic control of inflammation can hypothetically be either general or specific for a particular target tissue. For the latter, gene regulation of pathomechanisms in the CNS could affect reactivity of microglia or astrocytes, local cytokine/chemokine production, or even neuronal vulnerability. We have obtained strong support for this notion by observations of rat strain-dependent variation in the inflammatory response after ventral root avulsion, a model in which mainly non-antigen-specific elements of the immune system promote inflammation. A comparison of strains with similar MHC haplotypes on different backgrounds and strains with different MHC haplotypes on the same background, respectively, demonstrates that the inflammatory phenotype is regulated mainly by non-MHC genes. Interestingly, different features of the inflammatory response, such as induction of MHC class II expression, glial activation, cytokine expression, and neuronal vulnerability, varied between rat strains and were largely independent of each other. The genetic control of several basic features of inflammation in the CNS is of great relevance not only for MS/EAE, but also for several other neurological conditions with inflammatory components such as cerebrovascular and neurogenerative dieases and trauma.

Suggestive evidence for association of human chromosome 18q12-q21 and its orthologue on rat and mouse chromosome 18 with several autoimmune diseases

Some immune system disorders, such as type 1 diabetes, multiple sclerosis (MS), and rheumatoid arthritis (RA), share common features: the presence of autoantibodies and self-reactive T-cells, and a genetic association with the major histocompatibility complex. We have previously published evidence, from 1,708 families, for linkage and association of a haplotype of three markers in the D18S487 region of chromosome 18q21 with type 1 diabetes. Here, the three markers were typed in an independent set of 627 families and, although there was evidence for linkage (maximum logarithm of odds score [MLS] = 1.2; P = 0.02), no association was detected. Further linkage analysis revealed suggestive evidence for linkage of chromosome 18q21 to type 1 diabetes in 882 multiplex families (MLS = 2.2; lambdas = 1.2; P = 0.001), and by meta-analysis the orthologous region (also on chromosome 18) is linked to diabetes in rodents (P = 9 x 10(-4)). By meta-analysis, both human chromosome 18q12-q21 and the rodent orthologous region show positive evidence for linkage to an autoimmune phenotype (P = 0.004 and 2 x 10(-8), respectively, empirical P = 0.01 and 2 x 10(-4), respectively). In the diabetes-linked region of chromosome 18q12-q21, a candidate gene, deleted in colorectal carcinoma (DCC), was tested for association with human autoimmunity in 3,380 families with type 1 diabetes, MS, and RA. A haplotype ("2-10") of two newly characterized microsatellite markers within DCC showed evidence for association with autoimmunity (P = 5 x 10(-6)). Collectively, these data suggest that a locus (or loci) exists on human chromosome 18q12-q21 that influences multiple autoimmune diseases and that this association might be conserved between species.

Mapping and identification of autoimmunity genes

Over the past several years, intense effort has been made to map the chromosomal locations of genes involved in the susceptibility to autoimmune diseases. The first phase of this mapping effort-performed in most cases by using microsatellite markers to scan the genome for loci that are linked with disease-has generated first-draft maps for numerous autoimmune diseases in humans, mice and rats, pointing to as many as 20 different loci in some diseases. The second phase is now beginning, with efforts focused on narrowing the loci sufficiently to allow the positional cloning of disease-associated alleles. From these mapping data it is clear that some of these loci overlap between various autoimmune diseases and preliminary results suggest that indeed there is a sharing of 'autoimmunity genes' between various autoimmune diseases.

Genetic dissection of a rat model for rheumatoid arthritis: significant gender influences on autosomal modifier loci

Rheumatoid arthritis (RA) is a common, chronic, autoimmune, inflammatory disease that is influenced by genetic factors including gender. Many studies suggest that the genetic risk for RA is determined by the MHC, in particular class II alleles with a 'shared epitope' (SE), and multiple non-MHC loci. Other studies indicate that RA and other autoimmune diseases, in particular insulin-dependent diabetes mellitus (IDDM) and autoimmune thyroid disease (ATD), share genetic risk factors. Rat collagen-induced arthritis (CIA) is an experimental model with many features that resemble RA. The spontaneous diabetes-resistant bio-breeding rat, BB(DR), is of interest because it is susceptible to experimentally induced CIA, IDDM and ATD, and it has an SE in its MHC class II allele. To explore the genetics of CIA, including potential gender influences and the genetic relationships between CIA and other autoimmune diseases, we conducted a genome-wide scan for CIA regulatory loci in the F(2) progeny of BB(DR) and CIA-resistant BN rats. We identified 10 quantitative trait loci (QTLs), including 5 new ones (Cia15, Cia16*, Cia17, Cia18* and Cia19 on chromosomes 9, 10, 18 and two on the X chromosome, respectively), that regulated CIA severity. We also identified four QTLs, including two new ones (Ciaa4* and Ciaa5* on chromosomes 4 and 5, respectively), that regulated autoantibody titer to rat type II collagen. Many of these loci appeared to be gender influenced, and most co-localized with several other autoimmune trait loci. Our data support the view that multiple autoimmune diseases may share genetic risk factors, and suggest that many of these loci are gender influenced.

Genetics of rat neuroinflammation

The definition of genes regulating the pathogenetic pathways of autoimmune neuroinflammation, may provide targets for new therapeutic strategies. This is not easily accomplished in human disease. Such genetic dissection can more readily be done by the use of inbred rodent strains. With these, genetic heterogeneity is avoided and variation in the environmental influences is minimized. Close mimicking of the human disease characteristics is desirable in such endeavors. Chronic relapsing experimental autoimmune encephalomyelitis (EAE) with MS-like histopathology is achieved after immunization of certain rat strains with myelin oligodendrocyte glycoprotein (MOG) or spinal cord homogenate. The major histocompatibility complex (MHC) regulate the ease by which the environmental trigger in the form of immunisation induces disease. Use of intra-MHC recombinant strains demonstrated major influences from the MHC class II genome region, but additional influences from both the MHC class I and III regions. These findings now provide a basis for studies of the mechanisms for MHC-controlled autoimmune pathogenicity leading to MS-like disease. Gene mapping of F2 crosses between susceptible and resistant rat strains demonstrated nine genome regions outside the MHC which regulate different phenotypes of rat EAE. Many of these co-localize with genome regions regulating other organ-specific disease such experimental arthritis, suggesting a sharing of disease pathways. Further finemapping can lead to the exact identification of disease regulating genes. Interestingly, we have also demonstrated a non-MHC gene control of the inflammatory response, in the form of glial cell activation, and neuronal degeneration, subsequent to anterior nerve root avulsion in rats. The genetic dissection of these influences may unravel pathways controlling CNS vulnerability.