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Ltβr Signaling Does Not Regulate Aire-Dependent Transcripts in Medullary Thymic Epithelial Cells¹

Max-Planck-Institute-for-Immunobiology, Department for Developmental Immunology, Freiburg, Germany

Thymic medullary epithelial cells (mTECs) play a major role in central tolerance induction by expressing tissue-specific Ags (TSAs). The expression of a subset of TSAs in mTECs is under the control of Aire (autoimmune regulator). Humans defective for AIRE develop a syndrome characterized by autoimmune disease in several endocrine glands. Aire has been proposed to be regulated by lymphotoxin β receptor (Ltβr) signaling and there is evidence that, additionally, Aire-independent transcripts may be regulated by this pathway. Given the potential clinical importance of Aire regulation in mTECs for the control of autoimmunity, we investigated the relation between Ltβr signaling and TSA expression by whole genome transcriptome analysis. In this study, we show that the absence of Ltβr has no effect on the expression of Aire and Aire-dependent TSAs. Also, the lack of Ltβr signaling does not disturb regulatory T cells or the distribution of dendritic cells in the thymus. However, mTECs in Ltβr-deficient mice show an aberrant distribution within the thymic medulla with disruption of their three-dimensional architecture. This is predicted to impair the interaction between mTECs and thymocytes as shown by the reduced surface uptake of MHCII by mature thymocytes in Ltβr-deficient mice. We propose that the physiological medullary architecture ensures negative-selection by supporting lympho-epithelial interaction through a large epithelial cell surface distributed evenly across the medulla.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ V.C.M. was supported by a fellowship from Fundação para a Ciência e Tecnologia, Portugal.

² Address correspondence and reprint requests to Dr. Conrad C. Bleul, Max-Planck-Institute-for-Immunobiology, Stuebeweg 51, Freiburg 79108, Germany. E-mail address: bleul{at}immunbio.mpg.de

³ Abbreviations used in this paper: T_reg, regulatory T cell; TSA, tissue-specific Ag; mTEC, medullary thymic epithelial cell; Ltβr, lymphotoxin β receptor; DC, dendritic cell; wt, wild type; KO, knockout; Hprt, hypoxanthine-guanine phosphoribosyltransferase; qPCR, quantitative PCR; T_eff, T effector cell; RTE, recent thymic emigrant.

⁴ The online version of this article contains supplemental material.