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.

Definition of arthritis candidate risk genes by combining rat linkage-mapping results with human case-control association data.

OBJECTIVE: To define genomic regions that link to rat arthritis and to determine the potential association with rheumatoid arthritis (RA) of the corresponding human genomic regions. METHODS: Advanced intercross lines (AIL) between arthritis susceptible DA rats and arthritis resistant PVG.1AV1 rats were injected with differently arthritogenic oils to achieve an experimental situation with substantial phenotypic variation in the rat study population. Genotyping of microsatellite markers was performed over genomic regions with documented impact on arthritis, located on rat chromosomes 4, 10 and 12. Linkage between genotypes and phenotypes were determined by R/quantitative trait loci (QTL). Potential association with RA of single nucleotide polymorphisms (SNPs) in homologous human chromosome regions was evaluated from public Wellcome Trust Case Control Consortium (WTCCC) data derived from 2000 cases and 3000 controls. RESULTS: A high frequency of arthritis (57%) was recorded in 422 rats injected with pristane. Maximum linkage to pristane-induced arthritis occurred less than 130 kb from the known genetic arthritis determinants Ncf1 and APLEC, demonstrating remarkable mapping precision. Five novel quantitative trait loci were mapped on rat chromosomes 4 and 10, with narrow confidence intervals. Some exerted sex-biased effects and some were linked to chronic arthritis. Human homologous genomic regions contain loci where multiple nearby SNPs associate nominally with RA (eg, at the genes encoding protein kinase Calpha and interleukin 17 receptor alpha). CONCLUSIONS: High-resolution mapping in AIL populations defines limited sets of candidate risk genes, some of which appear also to associate with RA and thus may give clues to evolutionarily conserved pathways that lead to arthritis.

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.

Identification of rat quantitative trait loci that regulate LPS-induced pro-inflammatory cytokine responses.

Bacterial lipopolysaccharides (LPSs) trigger innate immune effector functions, such as the production of pro-inflammatory cytokines. Here we utilized major histocompatibility complex (MHC)-congenic rats to dissect the genetic basis of strain-dependent variations of LPS-induced tumour necrosis factor-alpha (TNF-alpha) levels in a whole blood in vitro assay. PVG.1AV1 background was associated with a high response, ACI background with a medium response, and LEW.1AV1 and DA backgrounds were associated with low responses. To determine the location of regulating non-MHC genes, a genome-wide linkage analysis with 236 microsatellite markers was performed on 186 F2 progeny of high TNF-alpha responder PVG.1AV1 and MHC identical but low TNF-alpha responder LEW.1AV1 rats. A region on rat chromosome 1 displayed linkage to LPS-induced TNF-alpha responses (P = 3.3 x 10-5). In addition, a locus on chromosome 2 was linked to responses of both interleukin-6 (IL-6) (P = 2.3 x 10-5) and TNF-alpha (possible linkage, P = 8 x 10-3). Both chromosome regions have been linked to inflammatory diseases in rats, and so have the homologous regions in mice and humans. We therefore suggest that continued genetic dissection of the described in vitro phenotypes will give clues to both normal physiological regulation of LPS-induced TNF-alpha production and disease pathways.