Murine Lupus Susceptibility Locus Sle1a Requires the Expression of two Subloci to Induce Inflammatory T Cells

The NZM2410-derived Sle1a lupus susceptibility locus induces activated autoreactive CD4(+) T cells and reduces the number and function of Foxp3(+) regulatory T cells. In this study, we first showed that Sle1a contributes to autoimmunity by increasing anti-nuclear antibody production when expressed on either NZB or NZW heterozygous genomes, and by enhancing the chronic graft vs. host disease response indicating an expansion of the autoreactive B cell pool. Screening two non-overlapping recombinants, the Sle1a.1 and Sle1a.2 intervals that cover the entire Sle1a locus, revealed that both Sle1a.1 and Sle1a.2 were necessary for the full Sle1a phenotype. Sle1a.1, and to a lesser extent Sle1a.2, significantly affected CD4(+) T cell activation as well as Treg differentiation and function. Sle1a.2 also increased the production of autoreactive B cells. Since the Sle1a.1 and Sle1a.2 intervals contain only one and 15 known genes, respectively, this study considerably reduces the number of candidate genes responsible for the production of autoreactive T cells. These results also demonstrate that the Sle1 locus is an excellent model for the genetic architecture of lupus, in which a major obligate phenotype results from the co-expression of multiple genetic variants with individual weak effects.