The murine lupus susceptibility locus Sle1c2 is a sublocus of the NZM2410-derived Sle1 major lupus susceptibility locus and contributes to CD4 T cell activation, increased IFNγ-expressing T cells, and increased susceptibility to chronic graft vs. host disease (cGVHD), When crossed into the NZB lupus-prone mice, Sle1c2 enhanced B cell activation, autoantibodies, and renal pathology. The gene discussed is CD4; the disease is systemic lupus erythematosus.