Since its discovery, Aire has been the topic of numerous studies in its role as a transcriptional regulator in the thymus where it promotes the "promiscuous" expression of a large repertoire of tissue-restricted antigens (TRAs) that are normally expressed only in the immune periphery. This process occurs in specialized medullary thymic epithelial cells (mTECs) and mediates the elimination of self-reactive T cells or promotes their conversion to the Foxp3+ regulatory T cell lineage, both of which are required for the prevention of autoimmunity. In recent years, there has been increasing interest in the role of extrathymic Aire expression in peripheral organs. The focus has primarily been on the identification of the cellular source(s) and mechanism(s) by which extrathymic AIRE affects tolerance-related or other physiological processes. A cadre of OMICs tools including single cell RNA sequencing and novel transgenic models to trace Aire expression to perform lineage tracing experiments have shed light on a phenomenon that is more complex than previously thought. In this chapter, we provide a deeper analysis of how extrathymic Aire research has developed and progressed, how cellular sources were identified, and how the function of AIRE was determined. Current data suggests that extrathymic AIRE fulfills a function that differs from what has been observed in the thymus and strongly argues that its main purpose is to regulate transcriptional programs in a cell content-dependent manner. Surprisingly, there is data that also suggests a non-transcriptional role of extrathymic AIRE in the cytoplasm. We have arrived at a potential turning point that will take the field from the classical understanding of AIRE as a transcription factor in control of TRA expression to its role in immunological and non-immunological processes in the periphery.

• Keywords
• AIRE, Fertility, Immune periphery, Non-immune function, RORγt+ eTACs, Sertoli cells, Th17 responses, Transcription function, eTACs, mTECs,
• MeSH
• Antigens MeSH
• Autoimmunity MeSH
• Epithelial Cells metabolism   MeSH
• Gene Expression Regulation * MeSH
• Thymus Gland MeSH
• Transcription Factors * genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antigens MeSH
• Transcription Factors * MeSH

Male infertility affects approximately 14% of all European men, of which ~44% are characterized as idiopathic. There is an urgency to identify the factors that affect male fertility. One such factor, Autoimmune Regulator (AIRE), a protein found in the thymus, has been studied in the context of central tolerance functioning as a nuclear transcription modulator, responsible for the expression of tissue-restricted antigens in specialized thymic cells that prevent autoimmunity. While its expression in the testes remains enigmatic, we recently observed that sterility in mice correlates with the absence of Aire in the testes, regardless of the deficient expression in medullary thymic epithelial cells or cells of the hematopoietic system. By assessing the Aire transcript levels, we discovered that Sertoli cells are the exclusive source of Aire in the testes, where it most likely plays a non-immune role, suggesting an unknown mechanism by which testicular Aire regulates fertility. Here, we discuss these results in the context of previous reports which have suggested that infertility observed in Aire deficient mice is of an autoimmune aetiology. We present an alternative point of view for the role of Aire in testes in respect to fertility altering the perspective of how Aire's function in the testes is currently perceived.

• Keywords
• Aire 1, Sertoli cells 5, autoimmunity 2, spermatogenesis 6, sterility 3, testis 4,
• MeSH
• Autoimmunity * MeSH
• Cell Nucleus MeSH
• Epithelial Cells * metabolism   MeSH
• Fertility MeSH
• Mice MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

The autoimmune regulator (Aire) serves an essential function for T cell tolerance by promoting the "promiscuous" expression of tissue antigens in thymic epithelial cells. Aire is also detected in rare cells in peripheral lymphoid organs, but the identity of these cells is poorly understood. Here, we report that Aire protein-expressing cells in lymph nodes exhibit typical group 3 innate lymphoid cell (ILC3) characteristics such as lymphoid morphology, absence of "classical" hematopoietic lineage markers, and dependence on RORγt. Aire+ cells are more frequent among lineage-negative RORγt+ cells of peripheral lymph nodes as compared with mucosa-draining lymph nodes, display a unique Aire-dependent transcriptional signature, express high surface levels of MHCII and costimulatory molecules, and efficiently present an endogenously expressed model antigen to CD4+ T cells. These findings define a novel type of ILC3-like cells with potent APC features, suggesting that these cells serve a function in the control of T cell responses.

• MeSH
• Epithelial Cell Adhesion Molecule metabolism   MeSH
• Antigen-Presenting Cells immunology   MeSH
• CD11 Antigens metabolism   MeSH
• Phenotype MeSH
• Transcription, Genetic MeSH
• Nuclear Receptor Subfamily 1, Group F, Member 3 metabolism   MeSH
• Lymph Nodes cytology   MeSH
• Lymphocytes immunology   metabolism   MeSH
• Histocompatibility Antigens Class II metabolism   MeSH
• Mice, Inbred BALB C MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Immunity, Innate MeSH
• AIRE Protein MeSH
• Gene Expression Regulation MeSH
• Transcription Factors genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Epithelial Cell Adhesion Molecule MeSH
• CD11 Antigens MeSH
• Itgax protein, mouse MeSH Browser
• Nuclear Receptor Subfamily 1, Group F, Member 3 MeSH
• Histocompatibility Antigens Class II MeSH
• Rorc protein, mouse MeSH Browser
• Transcription Factors MeSH