Genome-wide analysis of extended pedigrees confirms IL2-IL21 linkage and shows additional regions of interest potentially influencing coeliac disease risk.

Coeliac disease is a chronic inflammatory condition of the small intestine, triggered by dietary exposure to gluten in genetically susceptible individuals. Risk alleles at HLA-DQA1 and HLA-DQB1 are necessary for disease development, but are alone not sufficient for disease onset. We aimed to identify novel loci underlying susceptibility to coeliac disease through the use of extended Finnish and Hungarian families with multiple affected individuals. An initial whole-genome linkage approach yielded several loci that were followed up further using the Immunochip custom array. Loci with a parametric logarithm of odds (LOD) score of >1.3 were identified at 4q, 6p [human leukocyte antigen (HLA) region], 6q, 7p, 17p, 17q and at 22p. The 4q and 6q loci have been identified previously in coeliac disease risk, whereas follow-up analyses indicate that the 17p and 22p loci may be novel risk loci for coeliac disease. These loci harbour previously described risk variants for other autoimmune diseases, but their segregation patterns do not explain the linkage to coeliac disease. We followed up the linkage to the 4q region, containing the previously described interleukin (IL)2 and IL21 genes. The risk variants at 4q in the studied pedigrees are most likely distinct from previously described risk variants, indicating that the observed linkage may be due to rare high-risk variants of still unknown nature. The importance of this locus to coeliac disease risk was further shown by the finding that serum levels of IL21 were elevated in both untreated and treated coeliac patients compared to controls.

The shared CTLA4-ICOS risk locus in celiac disease, IgA deficiency and common variable immunodeficiency.

IgA deficiency (IgAD) and common variable immunodeficiency (CVID) often co-occur in families, associating with chronic inflammatory diseases such as celiac disease (CD). ICOS (inducible co-stimulator) and CTLA4 (cytotoxic T-lymphocyte-associated protein-4) may be important in both disorders, as ICOS is necessary for Ig class-switching and CTLA4 negatively regulates T-cell activation. Linkage and association of CD with CTLA4-ICOS is well documented, we thus aimed to further pinpoint CD susceptibility by haplotype-tagging analysis. We genotyped 663 CD families from Finland and Hungary, 575 additional CD patients from Finland, Hungary and Italy; 275 Swedish and Finnish IgAD individuals and 87 CVID individuals for 14-18 genetic markers in CTLA4-ICOS. Association was found between CTLA4-ICOS and both IgAD (P=0.0015) and CVID (P=0.0064). We confirmed linkage of CTLA4-ICOS with CD (LOD 2.38, P=0.0005) and found association of CTLA4-ICOS with CD (P=0.0009). Meta-analysis of the IgAD, CVID and CD materials revealed intergenic association (P=0.0005). Disease-associated markers were associated with lower ICOS and higher CTLA4 expression, indicating that the risk haplotypes contain functional variants. In summary, we identified a novel shared risk locus for IgAD, CVID and CD, the first report of association between CTLA4-ICOS and IgAD. Association between CD and CTLA4-ICOS was also confirmed in a large European data set.

Humanized transgenic mice expressing HLA DR4-DQ3 haplotype: reconstitution of phenotype and HLA-restricted T-cell responses.

Many autoimmune conditions have close genetic linkages to particular human histocompatibility leukocyte antigen (HLA) class II genes. With the aim of establishing a murine model of autoimmune disease, we have generated an HLA DR4-DQ3 haplotype transgenic (Tg) mouse that expresses a 440-kb yeast artificial chromosome harbouring DRA, DRB1*040101, DRB4*010301, DQA1*030101, DQB1*0302 and all the internal regulatory segments. This Tg mouse line was crossed to human CD4 (hCD4) Tg mice and endogenous class II knockout mice (I-A(o/o) and I-E(o/o)) lines to generate a DR4-DQ3.hCD4.IAE(o/o) Tg line. The Tg DR and DQ molecules are expressed on the physiological cell types in these animals, i.e. on most B cells (>85%), dendritic cells (DCs) and macrophages but not on T cells, with levels of expression comparable with those of human B cells (where DR > DQ expression). The DR4/DQ3 transgenes fully reconstituted the CD4 T-cell compartment, in both the thymus and the periphery, and the analysis of the T-cell receptor repertoire in the Tg mice confirmed that these class II molecules were able to mediate thymic selection of a broad range of Vbeta families. HLA DR4- and DQ3-restricted T-cell responses were elicited following immunization with known T-cell determinants presented by these molecules. Furthermore, the DR4-DQ3-restricted CD4(+) T cells conferred protective antibody-mediated immunity against an otherwise lethal infection with Salmonella enterica var. typhimurium. These new DR4-DQ3 Tg mice should prove to be valuable tools for dissecting the importance of this class II haplotype in autoimmune disorders like rheumatoid arthritis.