ABSTRACT
Educational immune tolerance to self-antigens is induced primarily in the thymus where tissue-restricted antigens (TRAs) are presented to T lymphocytes by cells of the thymic stroma - a process known as central tolerance. The expression of these TRAs is controlled in part by a transcription factor encoded by the autoimmune regulatory (Aire) gene. Patients with a mutation of this gene develop a condition known as autoimmune-polyendocrinopathy-candidiasis-ectodermal-dystrophy (APECED), characterized by autoimmune destruction of endocrine organs, fungal infection and dental abnormalities. There is now evidence for TRA expression and for mechanisms of functional tolerance outside the thymus. This has led to a number of studies examining Aire expression and function at these extra-thymic sites. These investigations have been conducted across different animal models using different techniques and have often shown discrepant results. Here we review the studies of extra thymic Aire and discuss the evidence for its expression and function in both human and murine systems.
Subject(s)
Animal Structures/metabolism , Lymphoid Tissue/metabolism , Transcription Factors/physiology , Animal Structures/immunology , Animals , Humans , Lymphoid Tissue/immunology , Mice , Transcription Factors/chemistry , AIRE ProteinABSTRACT
The 5'-flanking sequences of the human macrophage inflammatory protein-3alpha/CCL20 gene were cloned and transfected into G-361 human melanoma cells in a luciferase reporter construct. Tumor necrosis factor-alpha (TNF-alpha) treatment stimulated luciferase expression, and promoter truncations demonstrated that TNF-alpha inducibility is conferred by a region between nt -111 and -77, which contains a non-standard nuclear factor-kappaB (NF-kappaB) binding site. The requirement for NF-kappaB was demonstrated as follows: (i) mutations in this NF-kappaB site abrogated TNF-alpha responsiveness; (ii) TNF-alpha activated a construct containing two copies of the CCL20 NF-kappaB binding site; (iii) overexpression of NF-kappaB p65 activated the CCL20 promoter; (iv) NF-kappaB from nuclear extracts of TNF-alpha-stimulated cells bound specifically to this NF-kappaB site.
