TSCOT + Thymic Epithelial Cell-Mediated Sensitive CD4 Tolerance by Direct Presentation

Sejin Ahn,Seunghyuk Lee,Graham Anderson,Min Cheol Kim,Nicholas P Restifo,Gwanghee Lee,Douglas C Palmer,Kee Nyung Lee,Soo Jung Yang,Hyo Sun Shin,Deokjae Lee,Eric J Jenkinson,Moon Gyo Kim,Marc R Theoret,Avinash Bhandoola

doi:10.1371/journal.pbio.0060191

Abstract

Although much effort has been directed at dissecting the mechanisms of central tolerance, the role of thymic stromal cells remains elusive. In order to further characterize this event, we developed a mouse model restricting LacZ to thymic stromal cotransporter (TSCOT)-expressing thymic stromal cells (TDLacZ). The thymus of this mouse contains approximately 4,300 TSCOT+ cells, each expressing several thousand molecules of the LacZ antigen. TSCOT+ cells express the cortical marker CDR1, CD40, CD80, CD54, and major histocompatibility complex class II (MHCII). When examining endogenous responses directed against LacZ, we observed significant tolerance. This was evidenced in a diverse T cell repertoire as measured by both a CD4 T cell proliferation assay and an antigen-specific antibody isotype analysis. This tolerance process was at least partially independent of Autoimmune Regulatory Element gene expression. When TDLacZ mice were crossed to a novel CD4 T cell receptor (TCR) transgenic reactive against LacZ (BgII), there was a complete deletion of double-positive thymocytes. Fetal thymic reaggregate culture of CD45- and UEA-depleted thymic stromal cells from TDLacZ and sorted TCR-bearing thymocytes excluded the possibility of cross presentation by thymic dendritic cells and medullary epithelial cells for the deletion. Overall, these results demonstrate that the introduction of a neoantigen into TSCOT-expressing cells can efficiently establish complete tolerance and suggest a possible application for the deletion of antigen-specific T cells by antigen introduction into TSCOT+ cells.

Highlights

T cell tolerance is established mainly in the thymus where the T cell population develops and learns by a process called negative selection to avoid harmful reactivity against selfantigens expressed in that thymus
Discovery of the AIRE gene and its expression in medullary thymic epithelial cell (mTEC) has led to an understanding of its critical regulatory role in the removal of autoreactive T cells, against tissuespecific antigens expressed in the endocrine system
While developing in the thymus, thymocytes are selected for the ability to recognize harmful antigen, while those that respond to antigens present in their own body are eliminated

Summary

Introduction

T cell tolerance is established mainly in the thymus where the T cell population develops and learns by a process called negative selection to avoid harmful reactivity against selfantigens expressed in that thymus (reviewed in [1,2]). Organ-specific tolerance can be established by various other mechanisms, including anergy [3], ignorance [4], and regulatory T cells [5]. For a diverse T cell repertoire, this negative selection process occurs primarily in the thymic medullary compartment (reviewed in [7,8]). It is widely accepted that thymic medullary epithelial cells (mTEC) that express low levels of tissue-specific peripheral antigens in a promiscuous/ ectopic fashion [9,10] can initiate clonal deletion. Discovery of the AIRE gene and its expression in mTEC has led to an understanding of its critical regulatory role in the removal of autoreactive T cells, against tissuespecific antigens expressed in the endocrine system

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Discussion

Conclusion