Treg-specific deletion of NKAP results in severe, systemic autoimmunity due to peripheral loss of Tregs.

Regulatory T cells are critical for the generation and maintenance of peripheral tolerance. Conditional deletion of the transcriptional repressor NKAP in Tregs using Foxp3-YFP-cre NKAP conditional knockout mice causes aggressive autoimmunity characterized by thymic atrophy, lymphadenopathy, peripheral T cell activation, generation of autoantibodies, immune infiltration into several organs, and crusty skin at 3 weeks of age, similar to that of "scurfy" Foxp3-mutant mice. While Treg development in the thymus proceeds normally in the absence of NKAP, there is a severe loss of thymically-derived Tregs in the periphery. NKAP-deficient Tregs have a recent thymic emigrant phenotype, and are attacked by complement in a cell-intrinsic manner in the periphery. Previously, we demonstrated that NKAP is required for conventional T cell maturation as it prevents complement-mediated attack in the periphery. We now show that Tregs undergo a similar maturation process as conventional T cells, requiring NKAP to acquire complement resistance after thymic egress.