Common Alleles of the SLAM/CD2 Family are Associated with Murine Lupus

dc.contributor.advisorWakeland, Edward K.en
dc.creatorLimaye, Nishaen
dc.description.abstractThe Sle1b locus on telomeric mouse chromosome 1 mediates a break in tolerance to chromatin in the NZM2410 model of the autoimmune disease Systemic Lupus Erythematosus (SLE). B6.Sle1b congenic mice produce anti-nuclear autoantibodies (ANAs), and have elevated activated B and CD4+ T cells, and mild splenomegaly. Fine mapping of Sle1b positioned it within a ~900 kb region between 171.3 and 172.2 Mb. A contig of 100 B6-derived Bacterial Artificial Chromosomes (BACs) was constructed across Sle1b, and sequencing of six BACs that form an overlapping tiling path across it revealed that the interval contains 24 genes, 19 of which are expressed in the spleen, and 14 of which are in B and CD4+ T cells. We carried out extensive candidate gene analyses on the spleen-expressed genes, including sequencing of all the exons and flanking introns in the lupus-resistant B6 and susceptible B6.Sle1b parental strains, as well as Quantitative Real-time PCR on B and CD4+ T cell cDNA to detect any potentially functional polymorphisms between them. These analyses showed that the SLAM/CD2 family of seven immunoregulatory receptors, clustered within the locus, are by far the best candidates to be the Sle1b gene(s). The members of this family play important roles in intercellular interactions, activation, and function, by engaging in homophilic interactions with themselves or with each other, on a wide variety of immune cell types. Sequence analyses of their extracellular ligand-binding immunoglobulin (Ig) domains revealed that the cluster forms two stable, linked haplotypes of alleles in 33 common inbred laboratory strains of mice. The B6-like haplotype is found only in a small set of C57-strains, while the B6.Sle1b-like haplotype is found in all of the remaining, including the autoimmune-prone MRL, NOD, and NZB, as well as non-autoimmune strains like 129, Balb/c, and C3H. Introgression of this common haplotype from 129 onto B6 also potentiates autoimmunity, causing phenotypes similar to those of B6.Sle1b mice, which derive this interval from the NZW parent of NZM2410. Autoimmunity is mediated, not by a rare mutation peculiar to the region from NZW, but instead by common polymorphic variants of this family, in combination with the downstream signaling and effector molecules and pathways present in the B6 genetic background, underlining the importance of epistasis in such complex, multigenic autoimmune phenotypes. An examination of the SLAM/CD2 Ig domains in a large group of wild-outbred and wild-derived inbred strains belonging to different species of Mus, and sub-species of Mus musculus, has shown that the "disease" alleles of this family are also very common in these populations, demonstrating that their prevalence in the lab strains is not simply an artifact of their inbreeding. The genes also show the presence of ancestral or trans-species polymorphisms, indicative of maintenance of these alleles by balancing selection, although we do not yet know what precisely drives it. The small size of the Sle1b susceptibility interval, and the presence of this linked cluster of attractive candidate genes within it, makes it hard to identify which gene or combination of genes within this family is actually responsible for the autoimmunity by any further recombinational analysis. We have instead turned to a BAC-transgenic rescue strategy by which to localize the gene to a single B6-derived BAC, by its ability to complement the ANA-production phenotype and rescue autoimmunity in B6.Sle1b mice. We believe the strategy is feasible because Sle1b has a strong allele dose effect, so that the presence of a B6 allele of the Sle1b gene causes a large drop in penetrance of ANA-production, from about 90% in nine month old B6.Sle1b females, to about 33% in (B6 X B6.Sle1b) F1s. Our data show that none of the non-SLAM/CD2 candidates within the region is able to rescue B6.Sle1b mice, despite being demonstrably expressed from their BAC-transgenes. BACs carrying certain SLen
dc.format.digitalOriginborn digitalen
dc.subjectAntibodies, Antinuclearen
dc.subjectLupus Erythematosus, Systemicen
dc.titleCommon Alleles of the SLAM/CD2 Family are Associated with Murine Lupusen
dc.type.materialTexten School of Biomedical Sciencesen Southwestern Medical Centeren of Philosophyen


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