␥␦ T lymphocytes in the intestinal intraepithelial layer (␥␦ IELs) are thought to contribute to immune competence, but their actual function remains poorly understood. Here we used DNA microarrays to study the gene expression profile of ␥␦ IELs in a Yersinia infection system to better define their roles. To validate this approach, mesenteric lymph node CD8 ؉ ␣␤ T cells were similarly analyzed. The transcription profiles show that, whereas lymph node CD8 ؉ ␣␤ T cells must be activated to become cytotoxic effectors, ␥␦ IELs are constitutively activated and appear to use different signaling cascades. Our data suggest that ␥␦ IELs may respond efficiently to a broad range of pathological situations irrespective of their diverse T cell antigen receptor repertoire. ␥␦ IELs may modulate local immune responses and participate in intestinal lipid metabolism, cholesterol homeostasis, and physiology. This study provides a strong basis for further investigations of the roles of these cells as well as mucosal immune defense in general.D espite intense efforts, the functional roles of ␥␦ T cells in maintaining host immune defense remain enigmatic. One unique feature of ␥␦ T cells that distinguishes them from ␣␤ T cells is their tissue distribution. Although ␥␦ T cells represent a small percentage (Ͻ5%) of the lymphocytes in the central immune system of humans and mice, they are a sizable population (10 -50%) in the mucosal epithelia (1, 2). The murine ␥␦ T lymphocytes in the intestinal intraepithelial layer (␥␦ IELs) exhibit a diverse T cell antigen receptor (TCR) repertoire (3, 4) and thus have the potential to recognize a variety of antigens. These cells have been implicated in regulating the development of epithelial cells (5) and in controlling intestinal ␣␤ T cell responses in an Eimeria vermiformis infection model (6). Recently, we found that mice lacking ␥␦ T cells (TCR␦ Ϫ/Ϫ ) are much less resistant than either normal mice or mice without ␣␤ T cells (TCR␤ Ϫ/Ϫ ) to the dissemination of the enteric pathogen Yersinia pseudotuberculosis to the liver and spleen 1-4 days after oral infection (7). To gain insight into the scope of ␥␦ IEL responses in this system, we compared the gene expression of ␥␦ IELs isolated from mice orally infected with Yersinia to that of ␥␦ IELs isolated from uninfected animals by using the Affymetrix (Santa Clara, CA) GENECHIP technology (8). This approach allowed us to examine a large number of transcripts including many not associated with lymphocyte functions and to gain insight into the cellular mechanisms operating in ␥␦ IELs. To validate the experimental approach, and to serve as a basis of comparison for the ␥␦ IEL data, we also analyzed the expression profiles of mesenteric lymph node (MLN) CD8 ϩ ␣␤ T cells at the peak of the peripheral responses to oral Yersinia infection (7).We find that, whereas transcripts associated with cytotoxic functions and activation are significantly induced in CD8 ϩ ␣␤ T cells by the infection, ␥␦ IELs from infected and uninfected animals appear to be constituti...

The cause of common polygenic autoimmune diseases is not understood because of genetic and cellular complexity. Here, we pinpoint the action of a subset of autoimmune susceptibility loci in the NOD mouse strain linked to D1mit181, D2mit490, D7mit101, and D15mit229, which cause a generalized resistance to thymic deletion in vivo that applies equally to Aire-induced organ-specific gene products in the thymic medulla and to systemic antigens expressed at high levels throughout the thymus and affects CD4(+), CD4(+)8(+), and CD4(+)25(+) thymocytes. Resistance to thymic deletion does not reflect a general deficit in TCR signaling to calcineurin- or ERK-induced genes, imbalance in constitutive regulators of apoptosis, nor excessive signaling to prosurvival genes but is distinguished by failure to induce the proapoptotic gene and protein, Bim, during in vivo encounter with high-avidity autoantigen. These findings establish defects in thymic deletion and Bim induction as a key mechanism in the pathogenesis of autoimmunity.

To understand how orally introduced antigen regulates peripheral immune responses, we fed cytochrome c protein to mice transgenic for the beta chain of a cytochrome c-specific TCR and followed the antigen-specific T cell responses with a cyt c/I-Ek tetramer staining reagent. We find that within 6 hr of cytochrome c administration, antigen-specific systemic T cell activation is induced, and spleen cells gain the ability to stimulate cytochrome c-specific T cell responses. Feeding multiple low doses of cytochrome c down-regulates the systemic immune response, which can be correlated with a reduction of antigen-specific T cells and not with immune deviation. These results suggest that systemic distribution of antigen contributes significantly to oral tolerance induction.