Various populations of memory phenotype CD8+ T cells have been described over the last 15–20 years, all of which possess elevated effector functions relative to naïve phenotype cells. Using a technique for isolating antigen specific cells from unprimed hosts, we recently identified a new subset of cells, specific for nominal antigen, but phenotypically and functionally similar to memory cells arising as a result of homeostatic proliferation (HP). We show here that these “Virtual Memory” cells are independent of previously identified “innate memory” cells, arising as a result of their response to IL-15 trans-presentation by lymphoid tissue-resident CD8α+ DCs in the periphery. The absence of IL-15, CD8+ T cell expression of either CD122 or Eomes, or of CD8a+ DCs all lead to the loss of Virtual Memory cells in the host. Our results show that CD8+ T cell homeostatic expansion is an active process within the non-lymphopenic environment, is mediated by IL-15, and produces antigen inexperienced memory cells which retain the capacity to respond to nominal antigen with memory-like function. Preferential engagement of these “Virtual Memory” T cells into a vaccine response could dramatically enhance the rate by which immune protection develops.

Metallothioneins constitute a class of low-molecular-weight, cysteine-rich metal-binding stress proteins which are biosynthetically regulated at the level of gene transcription in response to metals, hormones, cytokines, and other physiological and environmental stresses. In this report, we demonstrate that the Saccharomyces cerevisiae metallothionein gene, designated CUP), is transcriptionally activated in response to heat shock and glucose starvation through the action of heat shock transcription factor (HSF) and a heat shock element located within the CUP) promoter upstream regulatory region. CUP) gene activation in response to both stresses occurs rapidly; however, heat shock activates CUP) gene expression transiently, whereas glucose starvation activates CUP) gene expression in a sustained manner for at least 2.5 h. Although a carboxylterminal HSF transcriptional activation domain is critical for the activation of CUP) transcription in response to both heat shock stress and glucose starvation, this region is dispensable for transient heat shock activation of at least two genes encoding members of the S. cerevisiae hsp7O family. Furthermore, inactivation of the chromosomal SNFI gene, encoding a serine-threonine protein kinase, or the SNF4 gene, encoding a SNF1 cofactor, abolishes CUPI transcriptional activation in response to glucose starvation without altering heat shock-induced transcription. These studies demonstrate that the S. cerevisiae HSF responds to multiple, distinct stimuli to activate yeast metallothionein gene transcription and that these stimuli elicit responses through nonidentical, genetically separable signalling pathways.The activation of gene transcription plays a vital role in the ability of all organisms to mount a protective response to environmental stresses. Upon exposure to a specific stress, cells activate the transcription of genes encoding proteins which either offer protection from the stress or repair stressinduced cellular damage. Although the precise mechanisms by which cells sense and respond to a specific environmental stress to activate the transcription of appropriate target genes are unknown, a growing number of transcription factors which participate in stress signal transduction pathways have been identified (14,19,28,46). Metallothioneins (MTs) are a class of low-molecular-weight, cysteine-rich metal-binding stress-responsive proteins which are present in bacteria, fungi, plants, and animals (25). Since the discovery of MTs, a number of biological roles have been postulated, including protection from metal toxicity, metal homeostasis, free radical detoxification, and protection from ionizing radiation. Indeed, consistent with these possible roles, MT genes in higher eukaryotic species are transcriptionally induced by a variety of stresses such as metals, glucocorticoid hormones, interferon, interleukins, and other agents involved in the inflammatory response or which generate oxidative stress (6,46

Previous studies in type 1 diabetes (T1D) in the nonobese diabetic mouse demonstrated that a crucial insulin epitope (B:9-23) is presented to diabetogenic CD4 T cells by IA g7 in a weakly bound register. The importance of antigenic peptides with low-affinity HLA binding in human autoimmune disease remains less clear. The objective of this study was to investigate T-cell responses to a lowaffinity self-epitope in subjects with T1D. HLA-DQ8 tetramers loaded with a modified insulin peptide designed to improve binding the lowaffinity register were used to visualize T-cell responses following in vitro stimulation. Positive responses were only detectable in T1D patients. Because the immunogenic register of B:9-23 presented by DQ8 has not been conclusively demonstrated, T-cell assays using substituted peptides and DQ8 constructs engineered to express and present B:9-23 in fixed binding registers were used to determine the immunogenic register of this peptide. Tetramer-positive T-cell clones isolated from T1D subjects that responded to stimulation by B:11-23 peptide and denatured insulin protein were conclusively shown to recognize B:11-23 bound to HLA-DQ8 in the low-affinity register 3. These T cells also responded to homologous peptides derived from microbial antigens, suggesting that their initial priming could occur via molecular mimicry. These results are in accord with prior observations from the nonobese diabetic mouse model, suggesting a mechanism shared by mouse and man through which T cells that recognize a weakly bound peptide can circumvent tolerance mechanisms and play a role in the initiation of autoimmune diseases, such as T1D.antigen presentation | self-antigen | MHCII tetramers T ype 1 diabetes (T1D) is a polygenic T-cell-mediated autoimmune disease with strong genetic linkages to the MHC class II and insulin promoter regions (1). Class II molecules are fundamental for CD4 + T-cell activation, whereas the insulin promoter polymorphism can modulate insulin levels in the thymus thereby influencing the threshold of selection for insulinspecific autoreactive T cells (2, 3). In the nonobese diabetic (NOD) mouse model of autoimmune mediated diabetes, insulinspecific IA g7 -restricted CD4 + T cells have been strongly implicated in β-cell destruction. In prediabetic NOD mice, 50% of the T-cell clones established from islet-infiltrating lymphocytes were insulin-specific and the majority of these clones recognized the insulin B:9-23 (B:9-23 SHLVEALYLVCGERG) epitope (4, 5). Moreover, substitution of a single residue in the B:9-23 region abrogated development of diabetes in a transgenic mouse model (6, 7). Thus, in the murine NOD model, the IA g7 -restricted B:9-23 epitope is considered to be pivotal in the development of diabetes.The position or "register" that B:9-23 occupies within the IA g7 binding groove has been a controversial but important question. At least three binding registers (R) have been considered, defined here by which B:9-23 amino acid occupies the first binding pocket (p1) position in the IA g7 ...

In this report, we show that the Src-like adaptor protein (SLAP) plays an important role in thymocyte development. SLAP expression is developmentally regulated; it is low in CD4-CD8- thymocytes, it peaks in the CD4+CD8+ subset, and it decreases to low levels in more mature cells. Disruption of the SLAP gene leads to a marked upregulation of TCR and CD5 expression at the CD4+CD8+ stage. The absence of SLAP was also developmentally significant because it enhanced positive selection in mice expressing the DO11.10 transgenic T cell receptor. Moreover, SLAP deletion at least partially rescued the development of ZAP-70-deficient thymocytes. These results demonstrate that SLAP participates in a novel mechanism of TCR downregulation at the CD4+CD8+ stage and regulates positive selection.

The adaptor molecule SLAP and E3 ubiquitin ligase c-Cbl each regulate expression of T cell receptor (TCR)-CD3 on thymocytes. Here we provide genetic and biochemical evidence that both molecules function in the same pathway. TCR-CD3 expression was similar in the absence of SLAP and/or c-Cbl. SLAP and c-Cbl were found to interact, and their expression together downregulated CD3epsilon. This required multiple domains in SLAP and the ring finger of c-Cbl. Furthermore, expression of SLAP and c-Cbl together induced TCRzeta ubiquitination and degradation, preventing the accumulation of fully assembled recycling TCR complexes. These studies indicate that SLAP links the E3 ligase activity of c-Cbl to the TCR, allowing for stage-specific regulation of TCR expression.