Humans expressing a defective form of the transcription factor AIRE (autoimmune regulator) develop multiorgan autoimmune disease. We used aire- deficient mice to test the hypothesis that this transcription factor regulates autoimmunity by promoting the ectopic expression of peripheral tissue- restricted antigens in medullary epithelial cells of the thymus. This hypothesis proved correct. The mutant animals exhibited a defined profile of autoimmune diseases that depended on the absence of aire in stromal cells of the thymus. Aire-deficient thymic medullary epithelial cells showed a specific reduction in ectopic transcription of genes encoding peripheral antigens. These findings highlight the importance of thymically imposed "central" tolerance in controlling autoimmunity.

Aire promotes the tolerization of thymocytes by inducing the expression of a battery of peripheral-tissue antigens in thymic medullary epithelial cells. We demonstrate that the cellular mechanism by which Aire exerts its tolerance-promoting function is not primarily positive selection of regulatory T cells, but rather negative selection of T effector cells. Surprisingly, supplementing its influence on the transcription of genes encoding peripheral-tissue antigens, Aire somehow enhances the antigen-presentation capability of medullary epithelial cells. Thus, this transcriptional control element promotes central tolerance both by furnishing a specific thymic stromal cell type with a repertoire of self antigens and by better arming such cells to present these antigens to differentiating thymocytes. In Aire's absence, autoimmunity and ultimately overt autoimmune disease develops.

Autoimmune regulator (aire) is a transcription factor that controls the self-reactivity of the T cell repertoire. Although previous results indicate that it exerts this function in part by promoting ectopic expression of a battery of peripheral-tissue antigens in epithelial cells of the thymic medulla, recent data argue for additional roles in negative selection of thymocytes by medullary cells. As one approach to exploring such roles, we performed computational analyses of microarray data on medullary RNA transcripts from aire-deficient versus wild-type mice, focusing on the genomic localization of aire-controlled genes. Our results highlight this molecule's transcriptional activating and silencing roles and reveal a significant degree of clustering of its target genes. On a local scale, aire-regulated clusters appeared punctate, with aire-controlled and aire-independent genes often being interspersed. This pattern suggests that aire's action may not be a simple reflection of the wide action of a chromatin remodeling enzyme. Analysis of the identity of certain of the clustered genes was evocative of aire's potential roles in antigen presentation and the coordination of intrathymic cell migration: for example, major histocompatibility complex class I and class II gene products and certain chemokine genes are targets of aire-regulated transcription.autoimmunity ͉ microarray ͉ T cell tolerance ͉ thymus ͉ gene expression

The lymphotoxin pathway is critical for the development and maintenance of peripheral lymphoid organs. Mice with deficiencies in members of this pathway lack lymph nodes and Peyer’s patches and have abnormal spleen architecture. These animals also develop autoantibodies to and lymphocytic infiltrates of multiple organs, provoking speculation that the lymphotoxin pathway may play a role in central tolerance induction. Indeed, a series of reports has claimed that lymphotoxin signals control the expression of Aire, a transcriptional regulator that is expressed in medullary epithelial cells of the thymus, mediates ectopic transcription of genes encoding a variety of peripheral tissue Ags, and promotes clonal deletion of self-reactive thymocytes. However, one report argued that lymphotoxin signals regulate the composition and organization of the thymus, particularly of the medullary epithelial compartment. Herein, we resolve this controversy in favor of the latter view. The expression and function of Aire were unaffected in medullary epithelial cells of mice lacking either lymphotoxin β receptor or the lymphotoxin α-chain, and there was minimal overlap between the sets of genes controlled by Aire and lymphotoxin. Instead, both knockout lines showed abnormal medullary epithelial cell organization, and the line lacking the β receptor had significantly fewer medullary epithelial cells. In short, the lymphotoxin pathway drives the developmental rather than selectional properties of thymic stromal cells.

Given the importance of the NOD mouse as a model of type 1 diabetes, there is a surprising lack of published information on the overall composition of the thymic and peripheral T-cell compartments. In this study, we revisited some earlier reports of T-cell abnormalities in this strain and examined a number of additional parameters to provide a global view of T-cells in prediabetic NOD mice. In some cases, we concur with past conclusions, but in other important areas, we find that NOD mice closely resemble nonautoimmune strains. Specifically, and contrary to published reports, the thymocyte subset distribution, the rate and composition of thymic export, and the composition of the peripheral T-cell pool, including the proportion of CD25 ؉ CD4 ؉ T-cells, are essentially normal in prediabetic NOD mice. These factors are therefore unlikely to be involved in the loss of tolerance that leads to autoimmunity within this strain. Diabetes 52:327-334, 2003

The Aire transcription factor plays an important role in immunological self-tolerance by mediating the ectopic expression of peripheral self-antigens by thymic medullary epithelial cells (MECs), and the deletion of thymocytes that recognize them. In Airedeficient humans or mice, central tolerance is incomplete and multiorgan autoimmune disease results. We examined the variability of Aire's effects on ectopic transcription among individual mice of three different inbred strains. Aire's function was, overall, quite similar in the three backgrounds, although generally stronger in C57BL/6 than in BALB/c or NOD mice, and a minority of Aireregulated genes did show clear differences. Gene expression profiling of wild-type MECs from single mice, or from the two thymic lobes of the same mouse, revealed significantly greater variability in Aire-controlled ectopic gene expression than in Aire-independent transcripts. This ''noisy'' ectopic expression did not result from parental or early developmental imprinting, but from programming occurring after the formation of the thymic anlage, resulting from epigenetic effects or from the stochastic nature of Aire activity. Together, genetic and nongenetic variability in ectopic expression of peripheral antigens in the thymus make for differences in the portion of self determinants presented for tolerance induction. This variable self may be beneficial in preventing uniform holes in the T-cell repertoire in individuals of a species, but at the cost of variable susceptibility to autoimmunity.gene expression ͉ immunological tolerance ͉ microarray ͉ thymus ͉ autoimmune regulator

Successful microarray experimentation can generate enormous amounts of data, potentially very rich but also very unwieldy. Bold outlooks and new methods for data analysis and presentation should yield additional insight into the complexities of the immune system.

There's always a catch. The post‐translational modification of proteins with ubiquitin (Ub) or ubiquitin‐like (Ubl) modifiers is an important signal in the regulation of a variety of biological processes, such as degradation and regulation of gene expression. Here we report the synthesis of a panel of peptide vinyl sulfones (see scheme) harboring various portions of the Ub C terminus by using a safety‐catch linker. Depending on their length, such compounds can efficiently target Ubl‐specific proteases.