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The mechanisms by which Lat (a key adaptor in the T cell antigen receptor (TCR) signaling pathway) and the TCR come together after TCR triggering are not well understood. We investigate here the role of SNARE proteins, which are part of protein complexes involved in the docking, priming and fusion of vesicles with opposing membranes, in this process. Here we found, by silencing approaches and genetically modified mice, that the vesicular SNARE VAMP7 was required for the recruitment of Lat-containing vesicles to TCR-activation sites. Our results indicated that this did not involve fusion of Lat-containing vesicles with the plasma membrane. VAMP7, which localized together with Lat on the subsynaptic vesicles, controlled the phosphorylation of Lat, formation of the TCR-Lat-signaling complex and, ultimately, activation of T cells. Our findings suggest that the transport and docking of Lat-containing vesicles with target membranes containing TCRs regulates TCR-induced signaling.

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Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that patrol tissues to sense danger signals and activate specific immune responses. In addition, they also play a role in inflammation and tissue repair. Here, we show that oxygen availability is necessary to promote full monocyte-derived DC differentiation and maturation. Low oxygen tension (hypoxia) inhibits expression of several differentiation and maturation markers (CD1a, CD40, CD80, CD83, CD86, and MHC class II molecules) in response to lipopolysaccharide (LPS), as well as their stimulatory capacity for T-cell functions. These events are paralleled by impaired up-regulation of the chemokine receptor CCR7, an otherwise necessary event for the homing of mature DCs to lymph nodes. In contrast, hypoxia strongly upregulates production of proinflammatory cytokines, particularly TNF␣ and IL-1␤, as well as the inflammatory chemokine receptor CCR5. Subcutaneous injection of hypoxic DCs into the footpads of mice results in defective DC homing to draining lymph nodes, but enhanced leukocyte recruitment at the site of injection. Thus, hypoxia uncouples the promotion of inflammatory and tissue repair from sentinel functions in DCs, which we suggest is a safeguard mechanism against immune reactivity to damaged tissues. (Blood. 2008;112:3723-3734) IntroductionLow oxygen tension (hypoxia) has been described at virtually every site of extensive inflammation, including necrotic foci and cutaneous sites of infection and wounding. 1 Sites of inflammation are also characterized by extensive infiltration of inflammatory leukocytes, which need to move against oxygen gradients. As a consequence, immune effector cells in hypoxic sites, including dendritic cells (DCs), have an acute need to respond to these demanding conditions to maintain their viability and activity. DCs are powerful antigen-presenting cells (APCs) specialized for the activation of resting T cells and the initiation and regulation of many types of immune response. [2][3][4][5] Because of this, we have investigated the functional changes that accompanying the metabolic adaptation of DCs to hypoxia, as these events are likely to affect the development of both inflammatory and immune functions.The capacity of DCs to activate and regulate T-cell responses is acquired during a complex differentiation and maturation program. [2][3][4][5] DCs originate from bone marrow and, at an "immature" stage, they patrol peripheral tissues for the presence of pathogenassociated antigens. In order to perform this function, DCs express a rich repertoire of pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), which permit DCs to recognize distinct pathogen-associated molecules. 6,7 The engagement of TLRs initiates a cascade of signaling events in DCs that leads, in the process of "maturation," to the secretion of inflammatory and immunomodulatory factors, which mediate protective immunity. 6,7 For instance, stimulation of DC by lipopolysaccharide (LPS), through the participation of TLR4, lead...

Whether human IL-10-producing regulatory T cells ("Tr1") represent a distinct differentiation lineage or an unstable activation stage remains a key unsolved issue. Here, we report that Eomesodermin (Eomes) acted as a lineage-defining transcription factor in human IFN-γ/IL-10 coproducing Tr1-like cells. In vivo occurring Tr1-like cells expressed Eomes, and were clearly distinct from all other CD4 + T-cell subsets, including conventional cytotoxic CD4 + T cells. They expressed Granzyme (Gzm) K, but had lost CD40L and IL-7R expression. Eomes antagonized the Th17 fate, and directly controlled IFN-γ and GzmK expression. However, Eomes binding to the IL-10 promoter was not detectable in human CD4 + T cells, presumably because critical Tbox binding sites of the mouse were not conserved. A precommitment to a Tr1-like fate, i.e. concominant induction of Eomes, GzmK, and IFN-γ, was promoted by IL-4 and IL-12-secreting myeloid dendritic cells. Consistently, Th1 effector memory cells contained precommitted Eomes + GzmK + T cells. Stimulation with T-cell receptor (TCR) agonists and IL-27 promoted the generation of Tr1-like effector cells by inducing switching from CD40L to IL-10. Importantly, CD4 + Eomes + T-cell subsets were present in lymphoid and nonlymphoid tissues, and their frequencies varied systemically in patients with inflammatory bowel disease and graft-versus-host disease. We propose that Eomes + Tr1-like cells are effector cells of a unique GzmK-expressing CD4 + T-cell subset.