Thymic resilience and T cell output require Liver X Receptors

The thymus is a primary lymphoid organ necessary for optimal T cell development. Here we show that liver X receptors, which are a class of nuclear receptors and transcription factors with diverse functions in metabolism and immunity, critically contribute to thymic integrity and function. LXRαβ-deficient mice develop a fatty, rapidly-involuting thymus, and acquire a shrunken and prematurely senescent peripheral T cell repertoire. The functions of LXRαβ are cell specific and the resulting phenotypes mutually independent. Whereas macrophages require LXRαβ for reverse cholesterol transport and lipid removal, thymic epithelial cells (TEC) and thymocytes respectively utilize LXRαβ for self-renewal and negative selection. Consequently, TEC-derived LXRαβ protect against premature involution in homeostasis and orchestrate thymic regeneration following stress, while thymocyte-derived LXRαβ limit cell disposal during negative selection and confer heightened sensitivity to experimental autoimmune encephalomyelitis. These results identify three distinct but complementary mechanisms by which LXRαβ govern T lymphocyte education. Cortical and medullary thymic epithelial cells sorted from LXRalpha-flox LXRbeta-flox control versus FoxN1-Cre LXRalpha-flox LXRbeta-flox (4 total groups)