Reduced Self-Reactivity of an Autoreactive T Cell After Activation with Cross-reactive Non–Self-Ligand

Autoreactive CD4+ T lymphocytes are critical to the induction of autoimmune disease, but because of the degenerate nature of T cell receptor (TCR) activation such receptors also respond to other ligands. Interaction of autoreactive T cells with other non–self-ligands has been shown to activate and expand self-reactive cells and induce autoimmunity. To understand the effect on the autoreactivity of naive cross-reactive T cells of activation with a potent nonself ligand, we have generated a TCR transgenic mouse which expresses a TCR with a broad cross-reactivity to a number of ligands including self-antigen. The activation of naive transgenic recombination activating gene (Rag)2−/− T cells with a potent non–self-ligand did not result in a enhancement of reactivity to self, but made these T cells nonresponsive to the self-ligand and anti-CD3, although they retained a degree of responsiveness to the non–self-ligand. These desensitized cells had many characteristics of anergic T cells. Interleukin (IL)-2 production was selectively reduced compared with interferon (IFN)-γ. p21ras activity was reduced and p38 mitogen-activated protein kinase (MAPK) was relatively spared, consistent with known biochemical characteristics of anergy. Surprisingly, calcium fluxes were also affected and the anergic phenotype could not be reversed by exogenous IL-2. Therefore, activation with a hyperstimulating non–self-ligand changes functional specificity of an autoreactive T cell without altering the TCR. This mechanism may preserve the useful reactivity of peripheral T cells to foreign antigen while eliminating responses to self

Field-induced ultrafast modulation of Rashba coupling at room temperature in ferroelectric α\alpha-GeTe(111)

Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, $\alpha$-GeTe(111) is a non-centrosymmetric ferroelectric (FE) semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecond (fs) light pulses requiring exploration of the possible control of ferroelectricity on this timescale. Here, we probe the room temperature transient dynamics of the electronic band structure of $\alpha$-GeTe(111) using time and angle-resolved photoemission spectroscopy (tr-ARPES). Our experiments reveal an ultrafast modulation of the Rashba coupling mediated on the fs timescale by a surface photovoltage (SPV), namely an increase corresponding to a 13 % enhancement of the lattice distortion. This opens the route for the control of the FE polarization in $\alpha$-GeTe(111) and FE semiconducting materials in quantum heterostructures.Comment: 31 pages, 12 figure

Field-induced ultrafast modulation of Rashba coupling at room temperature in ferroelectric alpha-GeTe(111)

Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, α-GeTe(111) is a non-centrosymmetric ferroelectric semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecond light pulses requiring exploration of the possible control of ferroelectricity on this timescale. Here, we probe the room temperature transient dynamics of the electronic band structure of α-GeTe(111) using time and angle-resolved photoemission spectroscopy. Our experiments reveal an ultrafast modulation of the Rashba coupling mediated on the fs timescale by a surface photovoltage, namely an increase corresponding to a 13% enhancement of the lattice distortion. This opens the route for the control of the ferroelectric polarization in α-GeTe(111) and ferroelectric semiconducting materials in quantum heterostructures.Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, α-GeTe(111) is a non-centrosymmetric ferroelectric semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecond light pulses requiring exploration of the possible control of ferroelectricity on this timescale. Here, we probe the room temperature transient dynamics of the electronic band structure of α-GeTe(111) using time and angle-resolved photoemission spectroscopy. Our experiments reveal an ultrafast modulation of the Rashba coupling mediated on the fs timescale by a surface photovoltage, namely an increase corresponding to a 13% enhancement of the lattice distortion. This opens the route for the control of the ferroelectric polarization in α-GeTe(111) and ferroelectric semiconducting materials in quantum heterostructures

Les restes humains de la grotte ornée paléolithique des Deux-Ouvertures (Ardèche, France)

International audienceThe opening of the Deux-Ouvertures cave is on the left bank of the Ardèche River, just before the canyon exit on the land of the village of Saint-Martin d’Ardèche in the Southwest of France. Although it has been known since 1896, the deep part of one of the galleries was not discovered until 1985. The surface of this gallery was covered by animal bones, 90% of which belonged to Ursus spelaeus. In 2007, two osseous human fragments were discovered: the distal part of an adult humerus and the diaphysis of a radius belonging to a young individual. These two specimens are the topic of the present paper. Although the date of the humerus (34,440–33,730 cal BP) corresponds to the period when bears frequented the caves, the dates of the diaphysis of the radius (4410–4570 cal BP), found at the heart of the “decorated Paleolithic sector”, lead us to assume that it was transported there, perhaps deliberately. The study of the two human bones originating in the Deux-Ouvertures cave illustrates that the diaphysis of the radius, belonging to a young individual of the Neolithic period, does not exhibit any differences in comparison to modern radii. By contrast, the distal part of the adult humerus, although it is incomplete and altered, is the first example that has been dated in the Ardèche of adult human remains associated with a decorated Paleolithic cave. This specimen, aside perhaps from the width of its median column, is rather slender and does not present any significant difference in relation to other upper Paleolithic humeri.La grotte des Deux-Ouvertures s’ouvre en rive gauche peu avant la sortie des gorges de l’Ardèche, sur le territoire de la commune de Saint-Martin-d’Ardèche. Bien que connue depuis 1896, ce n’est qu’en 1985 qu’était découverte la partie profonde du réseau : une galerie qui présentait des ossements éparpillés sur le sol, dont plus de 90 % appartiennent à Ursus spelaeus. En 2007, deux fragments osseux humains – une partie distale d’un humérus adulte et une diaphyse de radius appartenant à un jeune sujet – ont été également mis au jour. Ils font l’objet de cet article. La datation de l’humérus (34 440–33 730 cal BP) s’inscrit au sein de la phase de fréquentation par les ours des cavernes, alors que la datation de la diaphyse du radius (4410–4570 cal BP) en plein cœur du « secteur orné paléolithique » laisse supposer qu’il a été déposé, peut-être, de façon délibérée. L’étude des deux os humains provenant de la grotte des Deux-Ouvertures montre que la diaphyse radiale, appartenant à un sujet jeune, d’âge Néolithique, ne présente pas de différence en regard de radius modernes. En revanche, la partie distale de l’humérus d’un sujet adulte, bien qu’incomplète et altérée, est le premier reste humain d’adulte, associé à une grotte ornée paléolithique en Ardèche, à avoir été daté. Ce dernier, exception faite peut-être pour la largeur du pilier médian, est plutôt gracile et ne présente pas de différence significative avec les autres restes du Paléolithique supérieur