AIRE activated tissue specific genes have histone modifications associated with inactive chromatin

The Autoimmune Regulator (AIRE) protein is expressed in thymic medullary epithelial cells, where it promotes the ectopic expression of tissue-restricted antigens needed for efficient negative selection of developing thymocytes. Mutations in AIRE cause APECED syndrome, which is characterized by a breakdown of self-tolerance. The molecular mechanism by which AIRE increases the expression of a variety of different genes remains unknown. Here, we studied AIRE-regulated genes using whole genome expression analysis and chromatin immunoprecipitation. We show that AIRE preferentially activates genes that are tissue-specific and characterized by low levels of initial expression in stably transfected HEK293 cell model and mouse thymic medullary epithelial cells. In addition, the AIRE-regulated genes lack active chromatin marks, such as histone H3 trimethylation (H3K4me3) and acetylation (AcH3), on their promoters. We also show that during activation by AIRE, the target genes acquire histone H3 modifications associated with transcription and RNA polymerase II. In conclusion, our data show that AIRE is able to promote ectopic gene expression from chromatin associated with histone modifications characteristic to inactive genes

Editorial: Thymic function at single cell resolution

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Irf4 Expression in Thymic Epithelium Is Critical for Thymic Regulatory T Cell Homeostasis

The thymus is a primary lymphoid organ required for the induction and maintenance of central tolerance. The main function of the thymus is to generate an immunocompetent set of T cells not reactive to self. During negative selection in the thymus, thymocytes with autoreactive potential are either deleted or differentiated into regulatory T cells (Tregs). The molecular basis by which the thymus allows high-efficiency Treg induction remains largely unknown. In this study, we report that IFN regulatory factor 4 (Irf4) is highly expressed in murine thymic epithelium and is required to prime thymic epithelial cells (TEC) for effective Treg induction. TEC-specific Irf4 deficiency resulted in a significantly reduced thymic Treg compartment and increased susceptibility to mononuclear infiltrations in the salivary gland. We propose that Irf4 is imperative for thymic Treg homeostasis because it regulates TEC-specific expression of several chemokines and costimulatory molecules indicated in thymocyte development and Treg induction.status: publishe

Irf4 Expression in Thymic Epithelium Is Critical for Thymic Regulatory T Cell Homeostasis

The thymus is a primary lymphoid organ required for the induction and maintenance of central tolerance. The main function of the thymus is to generate an immunocompetent set of T cells not reactive to self. During negative selection in the thymus, thymocytes with autoreactive potential are either deleted or differentiated into regulatory T cells (Tregs). The molecular basis by which the thymus allows high-efficiency Treg induction remains largely unknown. In this study, we report that IFN regulatory factor 4 (Irf4) is highly expressed in murine thymic epithelium and is required to prime thymic epithelial cells (TEC) for effective Treg induction. TEC-specific Irf4 deficiency resulted in a significantly reduced thymic Treg compartment and increased susceptibility to mononuclear infiltrations in the salivary gland. We propose that Irf4 is imperative for thymic Treg homeostasis because it regulates TEC-specific expression of several chemokines and costimulatory molecules indicated in thymocyte development and Treg induction.status: publishe

Ultrastructure of medullary thymic epithelial cells of autoimmune regulator (Aire)-deficient mice

The significance of the autoimmune regulator (Aire) transcription regulator in establishing central tolerance has recently been elucidated in great detail. Still, the role of Aire in medullary thymic epithelial cell (mTEC) physiology is not fully understood. To shed more light on this issue, we studied the ultrastructure of mTECs in Aire-deficient thymus. We show that all types of mTECs show ultrastructural signs of activation and increased intracellular traffic, which suggests that in the absence of Aire their physiology is impaired. Type 6 ‘large’ mTECs are fully developed in Aire-deficient mice and more frequent than in the normal thymus. The frequency of type 5 ‘undifferentiated’ mTECs is also increased. Collectively, our results suggest that the role of Aire in the physiology of mTECs could be more profound and not restricted only to the presentation of self-tissue-restricted antigens and/or apoptosis of end-stage fully mature cell types.Živana Milićević, Novica M. Milićević, Martti Laan, Pärt Peterson, Kai Kisand, Hamish S. Scott and Jürgen Westerman

Lipopolysaccharide induces tumor necrosis factor receptor-1 independent relocation of lymphocytes from the red pulp of the mouse spleen

It is well known that bacterial lipopolysaccharide (LPS) induces migration of several cellular populations within the spleen. However, there are no data about the impact of LPS on B and T lymphocytes present in the red pulp. Therefore, we used an experimental model in which we tested the effects of intravenously injected LPS on the molecular, cellular and structural changes of the spleen, with special reference to the red pulp lymphocytes. We discovered that LPS induced a massive relocation of B and T lymphocytes from the splenic red pulp, which was independent of the tumor necrosis factor receptor-1 signaling axis. Early after LPS treatment, quantitative real-time PCR analysis revealed the elevated levels of mRNA encoding numerous chemokines and proinflammatory cytokines (XCL1, CXCL9, CXCL10, CCL3, CCL4, CCL5, CCL17, CCL20, CCL22, TNFα and LTα) which affect the navigation and activities of B and T lymphocytes in the lymphoid tissues. An extreme increase in mRNA levels for CCL20 was detected in the white pulp of the LPS-treated mice. The CCL20-expressing cells were localized in the PALS. Some smaller CCL20-expressing cells were evenly dispersed in the B cell zone. Thus, our study provides new knowledge of how microbial products could be involved in shaping the structure of lymphatic organs