designed the study, contributed to discussion, and edited the manuscript. and complete by 15 weeks. These in vivo data indicate that peripheral tolerance alone can protect NOD8.3 mice from autoimmune diabetes and that profound changes in T-cell repertoire can follow subtle changes in thymic antigen presentation. By exposing developing thymocytes to self-antigens, the thymus purges the majority of autoreactive T cells by a process called negative selection. Experiments in animal models L-371,257 have demonstrated that stromal medullary thymic epithelial cells (ECs) and bone marrowderived thymic dendritic cells (DCs) play an important role by expressing self-antigens to mediate thymocyte negative selection (1). Many, but not all, tissue-specific antigens that are expressed in medullary thymic ECs are controlled by the autoimmune regulator (AIRE) L-371,257 transcription factor (25). Thymic DCs have been shown to broaden the spectrum of self-antigens presented to developing T cells either by expressing self-antigens or presenting self-antigens after capturing them from medullary ECs (6). Although the expression of self-antigens in medullary thymic ECs and thymic DCs deletes the majority of self-reactive T cells, the central negative selection process is still not complete. This is indicated by the presence of circulating self-reactive effector T cells in healthy individuals (710). For the T cells specific for self-antigens that escape central tolerance, additional protection is provided by peripheral tolerance mechanisms. In peripheral tissue, steady-state DCs and AIRE-expressing ECs make an important contribution to the inactivation/deletion of self-reactive T cells (1115). Despite the crucial role of T-cell deletion in limiting autoimmune attack, the relative Rabbit Polyclonal to MBL2 central and peripheral contributions to self-reactive T-cell tolerance to individual self-antigens are not well documented. In humans with type 1 diabetes and in the NOD mouse, self-reactive T cells escape negative selection in the thymus, emigrate to the periphery, and are activated to differentiate into diabetogenic effector T cells. Thus, autoimmune diseases such as type 1 diabetes represent a failure of both central and peripheral tolerance mechanisms. In the NOD mouse, pathogenic autoimmunity develops against -cell antigens, including L-371,257 insulin and islet-specific glucose 6 phosphatase catalytic subunitrelated protein (IGRP) (1618). Mechanisms of tolerance to these two antigens are very different. Insulin is expressed in medullary thymic ECs in an AIRE-dependent manner. Physiological insulin expression in the thymus does induce tolerance, but it is insufficient to completely protect from diabetes in NOD mice. We have previously shown that increased thymic expression of insulin can completely protect from diabetes (19). In contrast, IGRP is not expressed in the thymus of NOD mice (15,20), and peripheral tolerance is the only protection from autoimmunity to IGRP. In NOD mice, CD8+T cells that target the peptide IGRP206214(IGRP-specific T cells) can be tracked using IGRP206214/Kdtetramer (IGRP tetramer). They can be detected in the peripheral blood and in the islets of most NOD mice (18,21). In NOD-IGRP mice, IGRP is transgenically overexpressed in antigen-presenting cells (APCs) of the thymus and the periphery (16). However, owing to the low frequency of IGRP-specific T cells in the endogenous repertoire, only limited insight could be gained into the relative contribution of central versus peripheral tolerance mechanisms. Thus, despite the clearly established importance of central tolerance, it remains unclear how efficiently thymic negative selection removes autoreactive T cells from the repertoire. Hence, we studied the impact on IGRP-specific T cells by transgenically introducing IGRP expression in the thymus and peripheral lymphoid tissue of T-cell receptor (TCR) transgenic NOD mice with CD8+T cells specific for this disease-relevant epitope (NOD8.3 mice). Our results demonstrate central tolerance of IGRP-specific T.