Genetic analysis of inflammation, cytokine mRNA expression and disease course of relapsing experimental autoimmune encephalomyelitis in DA rats

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.

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.

iNOS-mediated secondary inflammatory response differs between rat strains following experimental brain contusion

BACKGROUND

Nitric oxide is a key mediator of post-traumatic inflammation in the brain. We examined the expressions of iNOS, nNOS, and eNOS in inbred DA and PVGa rat strains where DA is susceptible to autoimmune neuroinflammation and PVGa-resistant.

METHODS

Parietal contusions using a weight drop model were produced in five rats per genotype. After 24 h, the brains were removed and analyzed using a range of immunohistochemical methods.

RESULTS

PVGa presented significantly increased iNOS expression in infiltrating inflammatory cells in the perilesional area compared to DA (p < 0.05). The amount of w3/13-positive infiltrating inflammatory cells did not differ between strains. eNOS and nNOS expression did not differ between strains. iNOS-positive cells coexpressed neuronal (NeuN), macrophage (ED-1), and leucocyte (w3/13) markers. MnSOD was significantly increased in PVGa (p < 0.05). 3-Nitrotyrosine, a measure of peroxynitrite levels, and fluoro-jade stained neuronal degeneration, did not differ between strains.

CONCLUSIONS

Two inbred rat strains with genetically determined differences in susceptibility to develop autoimmune disease displayed different levels of the inflammatory and anti-inflammatory mediators iNOS and MnSOD, indicating genetic regulation. Interestingly, the increased levels of iNOS did not lead to elevated expression of the neuronal cell-death marker fluoro-jade. The increased iNOS expression was correlated with increased expression of superoxide scavenger MnSOD. Excessive peroxynitrite formation was probably prevented by limitation of available superoxide. Subsequently, the higher expression of potentially deleterious iNOS in PVGa did not result in increased neuronal death.

Lung exposure of titanium dioxide nanoparticles induces innate immune activation and long-lasting lymphocyte response in the Dark Agouti rat

Nanomaterial of titanium dioxide (TiO(2)) is manufactured in large-scale production plants, resulting in risks for accidental high exposures of humans. Inhalation of metal oxide nanoparticles in high doses may lead to both acute and long-standing adverse effects. By using the Dark Agouti (DA) rat, a strain disposed to develop chronic inflammation following exposure to immunoactivating adjuvants, we investigated local and systemic inflammatory responses after lung exposure of nanosized TiO(2) particles up to 90 days after intratracheal instillation. TiO(2) induced a transient response of proinflammatory and T-cell-activating cytokines (interleukin [IL]-1α, IL-1β, IL-6, cytokine-induced neutrophil chemoattractant [CINC]-1, granulocyte-macrophage colony-stimulating factor [GM-CSF], and IL-2) in airways 1-2 days after exposure, accompanied by an influx of eosinophils and neutrophils. Neutrophil numbers remained elevated for 30 days, whereas the eosinophils declined to baseline levels at Day 8, simultaneously with an increase of dendritic cells and natural killer (NK) cells. The innate immune activation was followed by a lymphocyte expansion that persisted throughout the 90-day study. Lymphocytes recruited to the lungs were predominantly CD4(+) helper T-cells, but we also demonstrated presence of CD8(+) T-cells, B-cells, and CD25(+) T-cells. In serum, we detected both an early cytokine expression at Days 1-2 (IL-2, IL-4, IL-6, CINC-1, IL-10, and interferon-gamma [IFN-γ] and a second response at Day 16 of tumor necrosis factor-alpha (TNF-α), indicating systemic late-phase effects in addition to the local response in airways. In summary, these data demonstrate a dynamic response to TiO(2) nanoparticles in the lungs of DA rats, beginning with an innate immune activation of eosinophils, neutrophils, dendritic cells, and NK cells, followed by a long-lasting activation of lymphocytes involved in adaptive immunity. The results have implications for the assessment of risks for adverse and persistent immune stimulation following nanoparticle exposures in sensitive populations.

Genetic regulation of microglia activation, complement expression, and neurodegeneration in a rat model of traumatic brain injury

Secondary brain damage following traumatic brain injury in part depends on neuroinflammation, a process where genetic factors may play an important role. We examined the response to a standardized cortical contusion in two different inbred rat strains, Dark Agouti (DA) and Piebald Virol Glaxo (PVG). Both are well characterized in models of autoimmune neuroinflammation, where DA is susceptible and PVG resistant. We found that infiltration of polymorphonuclear granulocytes (PMN) at 3-day postinjury was more pronounced in PVG. DA was more infiltrated by T cells at 3-day postinjury, showed an enhanced glial activation at 7-day postinjury and higher expression of C3 complement at 7-day postinjury. Neurodegeneration, assessed by Fluoro-Jade, was also more pronounced in the DA strain at 30-day postinjury. These results demonstrate differences in the response to cortical contusion injury attributable to genetic influences and suggest a link between injury-induced inflammation and neurodegeneration. Genetic factors that regulate inflammation elicited by brain trauma may be important for the development of secondary brain damage.

Genetic analysis of neuropathic pain-like behavior following peripheral nerve injury suggests a role of the major histocompatibility complex in development of allodynia

Neuropathic pain is a common consequence of damage to the nervous system. We here report a genetic analysis of development of neuropathic pain-like behaviors after unilateral photochemically-induced ischemic sciatic nerve injury in a panel of inbred rat strains known to display different susceptibility to autoimmune neuroinflammation. Pain behavior was initially characterized in Dark-Agouti (DA; RT1(av1)), Piebald Virol Glaxo (PVG; RT1(c)), and in the major histocompatibility complex (MHC)-congenic strain PVG-RT1(av1). All strains developed mechanical hypersensitivity (allodynia) following nerve injury. However, the extent and duration of allodynia varied significantly among the strains, with PVG displaying more severe allodynia compared to DA rats. Interestingly, the response of PVG-RT1(avRT1) was similar to that of DA, suggesting regulation by the MHC locus. This notion was subsequently confirmed in an F2 cohort derived from crossing of the PVG and PVG-RT1(av1)strains, where allodynia was reduced in homozygous or heterozygous carriers of the RT1(av1) allele in comparison to rats homozygous for the RT1(c) allele. These results indicate that certain allelic variants of the MHC could influence susceptibility to develop and maintain neuropathic pain-like behavior following peripheral nerve injury in rats.

Recovery from spinal cord injury differs between rat strains in a major histocompatibility complex-independent manner

Inflammation is a common characteristic of spinal cord injury. The nature of this response, whether it is beneficial or detrimental, has been the subject of debate. It has been reported that susceptibility to autoimmunity is correlated with increased functional impairment following spinal cord injury. As the ability to mount an autoimmune response has most consistently been associated with certain haplotypes of the major histocompatibility complex (MHC), we analysed the possible effects of the MHC haplotype on functional impairment and recovery following spinal cord injury. A contusion injury was induced in experimental autoimmune encephalomyelitis-susceptible and -resistant rats [Dark Agouti, Lewis and Piebald Viral Glaxo (PVG), respectively]. We found that locomotion recovered significantly better in Dark Agouti rats compared with PVG and Lewis rats but an F2 intercross (PVG x PVG-RT1(av1)) excluded the possibility that this difference was MHC haplotype-dependent. Thus, we conclude that recovery following spinal cord injury is subject to considerable genetic heterogeneity that is not coupled to the MHC haplotype region. Continued research of genetic variants regulating recovery following spinal cord injury is warranted.

Differential effects of Th1, monocyte/macrophage and Th2 cytokine mixtures on early gene expression for immune-related molecules by central nervous system mixed glial cell cultures

Cytokines secreted within the central nervous system (CNS) are important in the development of multiple sclerosis (MS) lesions. The balance between Th1, monocyte/macrophage (M/M) and Th2 cytokines in the CNS may be pivotal in determining the outcome of lesion development. We examined the effects of mixtures of cytokines on gene expression by CNS glial cells, as mixtures of cytokines are present in MS lesions, which in turn contain mixtures of glial cells. In this initial analysis by gene array, we examined changes at 6 hours to identify early changes in gene expression that represent primary responses to the cytokines. Rat glial cells were incubated with mixtures of Th1, M/M and Th2 cytokines for 6 hours and examined for changes in early gene expression employing microarray gene chip technology. A minimum of 814 genes were differentially regulated by one or more of the cytokine mixtures in comparison to controls, including changes in expression in a large number of genes for immune system-related proteins. Expression of the proteins for these genes likely influences development and inhibition of MS lesions as well as protective and regenerative processes. Analysing gene expression for the effects of various combinations of exogenous cytokines on glial cells in the absence of the confounding effects of inflammatory cells themselves should increase our understanding of cytokine-induced pathways in the CNS.

Protective role of the cytokine-inducible isoform of nitric oxide synthase induction and nitrosative stress in experimental autoimmune encephalomyelitis of the DA rat

The pathogenic role of nitric oxide (NO) in multiple sclerosis (MS) remains controversial. Some groups have reported a pathogenic role of NO in experimental autoimmune encephalomyelitis (EAE), an animal model of some aspects of MS, whereas we and others have found a disease-suppressive effect of NO in EAE. Because the previously used EAE models have a mainly monophasic inflammatory disease course, distinct from MS, we here studied EAE in the DA rat, which better models the demyelinating and relapsing disease course of human MS. The induction of EAE in DA rats led to 1) severe inflammatory infiltrates mainly in the lumbar spinal cord; 2) an up-regulation of the activity of the cytokine-inducible isoform of NO synthases (NOS-II); and 3) increased tissue protein tyrosine nitration, as indicated by peroxynitrite (ONOO(-)), as a marker of nitrosative stress. Sources of superoxide metabolism, i.e., NADPH oxidase, myeloperoxidase, and superoxide dismutase, remained unchanged. Early treatment of animals with aminoguanidine, a relatively selective inhibitor of NOS-II, lowered nitrotyrosine immunoreactivity but at the same time led to more severe disease and pronounced inflammatory infiltrates in the lumbar spinal cord. Our results suggest a rather protective role of NOS-II induction and nitrosative stress in EAE in DA rats and support the hypothesis of a disease-mitigating immunomodulatory role of NO in this animal model of MS.

The arthritogenic adjuvant squalene does not accumulate in joints, but gives rise to pathogenic cells in both draining and non-draining lymph nodes

A single intradermal injection of the adjuvant-oil squalene induces T cell-mediated arthritis in DA rats. The chain of events leading from non-specific provocation of the immune system to arthritis, with clinical similarities to rheumatoid arthritis, is largely undetermined. Here, we combined in vivo tracking of tritium-labelled squalene with lymph node (LN) cell transfer experiments to determine where critical activation events may take place. The majority of squalene remained at the injection site (79%). The amounts recovered in peripheral joints (<1%) were equal to that recovered in other organs that can be targets in autoimmune diseases. This argues that arthritis does not develop as a consequence of adjuvant accumulation in joints. In contrast, substantial amounts of squalene were recovered in hyperplastic LN draining the injection site (1-13%). The adjuvant was deposited to a larger extent in cells than in extracellular matrix. The draining LN cells could transfer arthritis to naïve irradiated DA rats following in vitro stimulation with conA. Interestingly, non-draining LN were also hyperplastic and harboured arthritogenic cells, although they contained low amounts of squalene (<1%). Consequently, the amount of arthritogenic adjuvant in a particular LN is not closely linked to the development of pathogenic cells. The distribution pattern of squalene was similar in MHC-identical but arthritis-resistant PVG.1AV1 and LEW.1AV1 rats, and it was unaffected by T cell depletion with a monoclonal antibody (R73). Thus, T cells and non-MHC genes do not regulate dissemination of squalene, but rather determine arthritis development at the level of adjuvant response.

Genetic linkage analysis of the antibody responses to myelin basic protein and myelin oligodendrocyte glycoprotein in rats immunized with rat spinal cord homogenate

The genetic control of the antibody response to myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) was analysed in F1 and F2 crosses of DA and E3 rats, immunized with rat spinal chord homogenate. The DA rats were highly susceptible to encephalomyelitis and made antibody responses to both MBP and MOG, whereas the E3 rats were disease-resistant and responded only to MOG. The anti-MBP response was mainly controlled by the disease-promoting MHC region of the DA strain together with several disease loci outside MHC. In contrast, the anti-MOG response was associated with loci not related to or actually conferring resistance to disease.

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.

Analysis of adrenocortical secretory responses during acute an prolonged immune stimulation in inflammation-susceptible and -resistant rat strains

Endogenous corticosterone secreted during immune challenge restricts the inflammatory process and genetic variations in this neuroendocrine-immune dialogue have been suggested to influence an individuals sensitivity to develop chronic inflammatory disorders. We have tested inflammation-susceptible Dark Agouti (DA) rats and resistant, MHC-identical, PVG.1AV1 rats for their abilities to secrete corticosterone in response to acute challenge with bacterial lipopolysaccharide (LPS) or a prolonged activation of the nonspecific immune system with arthritogenic yeast beta-glucan. Intravenous injection of LPS triggered equipotent secretion of corticosterone in both rat strains. Interestingly, peak concentrations of corticosterone did not differ significantly between the strains. Intradermal injection of beta-glucan caused severe, monophasic, polyarthritis in DA rats while PVG.1AV1 responded with significantly milder joint inflammation. Importantly, serial sampling of plasma from glucan-injected DA and PVG.1AV1 rats did not reveal elevated concentrations of plasma corticosterone at any time from days 1-30 postinjection compared to preinjection values, in spite of the ongoing inflammatory process. Interestingly, adrenalectomized, beta-glucan-challenged DA rats responded with an aggravated arthritic process, indicating an anti-inflammatory role for the basal levels of corticosterone that were detected in intact DA rats challenged with beta-glucan. Moreover, substitution with subcutaneous corticosterone-secreting pellets, yielding moderate stress-levels, significantly attenuated the arthritic response. In contrast, adrenalectomized and glucan-challenged PVG.1AV1 rats did not respond with an elevated arthritic response, suggesting that these rats contain the arthritic process via corticosterone-independent mechanisms. In conclusion, the hypothalamic-pituitary-adrenal axis in both rat strains exhibited strong activation after challenge with LPS. This contrasted to the basal corticosterone levels observed strains during a prolonged arthritic process. No correlation between ability to secrete corticosterone and susceptibility to inflammation could be demonstrated. Basal levels of endogenous corticosterone appeared to restrain inflammation in beta-glucan-challenged DA rats whereas resistance to inflammation in PVG.1AV1 rats may be mediated via corticosterone-independent mechanisms.

Characterization of acute versus chronic relapsing autoimmune encephalomyelitis in DA rats

This study was undertaken to better understand the role of cytokines in the pathogenesis, especially in the mechanisms of relapse, of experimental autoimmune encephalomyelitis (EAE). For this purpose, we induced acute and chronic relapsing (CR) EAE in DA rats and determined several immunological parameters in rats at various stages of two types of EAE. Histopathological analysis revealed that there was no significant difference in the severity of inflammation in the spinal cord lesions between the two groups. However, demyelination was observed only in rats with CR EAE. Cytokine analysis by competitive PCR demonstrated that levels of TNF-alpha, IL-6 and IL-12 p40 mRNA in the spinal cord at the first attack of CR EAE were significantly higher than those at the peak stage of acute EAE. The mRNA expression of anti-inflammatory cytokines, IL-10 and TGF-beta1, was generally low in both acute EAE and the first attack of CR EAE and upregulated at later stages of CR EAE. These findings suggest that persistent high-level expression of pro-inflammatory cytokines is closely associated with demyelination and relapse of EAE. In contrast, anti-inflammatory cytokines play only a minor role in the relapse.

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.

Further evidence for a role of nitric oxide in experimental allergic encephalomyelitis: aminoguanidine treatment modifies its clinical evolution

The role of nitric oxide (NO) in inflammatory/demyelinating diseases is undergoing extensive investigation as a potential target for therapeutic intervention. However, interference with NO production has resulted in contrasting effects on the development of experimental allergic encephalomyelitis (EAE), the most widely used experimental model for multiple sclerosis (MS). Purpose of this paper was both the analysis of the individual clinical evolution of EAE induced in Lewis female rats by active immunisation and the evaluation of the effect of treatment with aminoguanidine, a selective inhibitor for the inducible isoform of nitric oxide synthase (iNOS). In our experimental model, relapse occurred in 66% of animals. Aminoguanidine treatment, started 3 days before immunisation, guaranteed a complete recovery from the acute phase and a delayed, milder relapse. Moreover, 79 days after immunisation inflammatory cellular infiltrates in the spinal cord were reduced. These data further support the involvement of NO in EAE evolution.

Non-MHC gene regulation of nerve root injury induced spinal cord inflammation and neuron death

Spinal ventral root avulsion leads to an inflammatory response around lesioned motoneurons and the subsequent degeneration of a large proportion of the neurons. We demonstrate here differences in the regulation of cytokine mRNAs, microglia/macrophage activation, MHC expression and nerve cell survival in the two inbred rat strains DA and ACI. These strains have similar major MHC haplotypes, but differ in their non-MHC background genes. T cells were rare in the lesioned segments and depletion of T cells did not affect the response. Thus, non-MHC gene(s) regulate the inflammation and neuron death after nerve trauma by mechanisms not involving antigen-specific immune responses.

Familial factors influence disability in MS multiplex families. French Multiple Sclerosis Genetics Group

BACKGROUND

Both genetic and environmental factors play a role in the pathophysiology of MS and may influence the clinical expression of the disease.

OBJECTIVE

To determine the contribution of familial factors to the clinical expression of MS.

METHODS

The French Multiple Sclerosis Genetics Group identified 87 sibling pairs. For each patient, sex, age at onset, duration of the disease, and disease course from onset were recorded. Disability was determined by the progression index (PI), defined as the ratio of the Expanded Disability Status Scale (EDSS) score disease duration when the latter exceeded 5 years. Statistical analyses were performed either with a group of patients (clinical features, relation between human leukocyte antigen and clinical features) or with a group of sibpairs (concordance for clinical features).

RESULTS

The mean age at onset was 29.6 years, the ratio of women to men was 59:28, and the mean PI was 0.27. There was no correlation for disease course and age at onset between sibs with MS. In contrast, we observed a weak but significant correlation of the PI in MS sibpairs (r = 0.234, p = 0.03).

CONCLUSION

This study revealed a concordance in MS sibling pairs for the disease severity, supporting the hypothesis that the degree of disability might be partly influenced by familial factors (environmental or genetic).

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

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

A Genome-Wide Search Identifies Two Susceptibility Loci for Experimental Autoimmune Encephalomyelitis on Rat Chromosomes 4 and 10

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease of the central nervous system that exhibits many pathologic similarities with multiple sclerosis. The genetic loci that contribute to mononuclear cell infiltration of the central nervous system and clinical manifestations of EAE in the rat were investigated in the F2 progeny of the highly susceptible Lewis and resistant Brown Norway strains. The data confirmed that the Lewis allele of a MHC-linked gene is necessary, but not sufficient, to confer EAE susceptibility in the F2 progeny. Subsequent analyses were thus restricted to the subset of the F2 animals with EAE-predisposing MHC genotypes. A genome-wide scan approach was performed using 103 microsatellite markers covering 85% of the genome. Two non-MHC regions were identified, one near the centromere of chromosome 4 and the other on the long arm of chromosome 10, that significantly contributed to the disease. In addition, three regions on chromosomes 9, 13, and 17 were suggestive for linkage. Congenic mapping is now needed to reduce the support intervals encoding the loci of interest to sizes amenable to physical mapping and to eventually demonstrate the involvement of some of the candidate genes of immunologic importance localized in these regions.

Genetics of susceptibility to chronic experimental encephalomyelitis and arthritis

The recent developments in genetic techniques and the development of more appropriate animal models for rheumatoid arthritis and multiple sclerosis make it possible to use a new approach for understanding these complex diseases. Thus it is now meaningful to address the question of which genes are causing the diseases. Several new associations with loci outside the MHC region have now been identified in models for both rheumatoid arthritis and multiple sclerosis. Some of these are shared between diseases - for example loci on mouse chromosome 3 (experimental allergic encephalomyelitis, collagen-induced arthritis and Theiler's encephalomyelitis) and rat chromosome 4 (collagen-induced arthritis and the experimental allergic encephalomyelitis induced by myelin oligodendrocytic glycoprotein).

Inheritance of susceptibility to multiple sclerosis

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

Resistance and susceptibility to experimental autoimmune neuritis in Sprague-Dawley and Lewis rats correlate with different levels of autoreactive T and B cell responses to myelin antigens

Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated, inflammatory demyelinating disease of the peripheral nervous system (PNS) that serves as a model for Guillain-Barré syndrome (GBS) in humans. Various mouse and rat strains show different susceptibilities to EAN that can be induced by immunization with bovine PNS myelin (BPM) + Freund's complete adjuvant (FCA). We examined PNS-induced T and B cell responses and cytokine protein production as well as mRNA expression to study the mechanisms behind susceptibility to EAN in Lewis rats and resistance in Sprague-Dawley (SD) rats. Lewis rats with EAN have elevated PNS myelin-reactive interferon-gamma (IFN-gamma) production, TNF-alpha mRNA expression, and increased B cell responses to PNS myelin antigens, but low PNS myelin-reactive transforming growth factor-beta (TGF-beta) and interleukin (IL)-10 mRNA expression in lymph node mononuclear cells (MNC). In contrast, resistance to EAN in SD rats is associated with reduced BPM and P2 peptide-reactive IFN-gamma production, TNF-alpha mRNA expression, and suppressed B cell responses to PNS myelin antigens as well as up-regulation of TGF-beta and IL-10 mRNA expression. Resistance to EAN is also associated with low-grade inflammation or absence of histological evidence of EAN. These results suggest that differential autoreactive T and B cells responses to PNS myelin antigens are strain specific, and the susceptibility to EAN is related to quantitative rather than qualitative differences in distribution between proinflammatory and anti-inflammatory cytokines.

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

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