Correspondence to Francisco S á nchez-Madrid: fsanchez.hlpr@salud.madrid.org Abbreviations used in this paper: ACF, autocorrelation function; EAP, endothelial adhesive platform; FCS, fl uorescence correlation spectroscopy; FLIM, fl uorescence lifetime imaging microscopy; FN, fi bronectin; FRET, F ö rster resonance energy transfer; FRETeff, FRET effi ciency; GPI, glycosylphosphatidylinositol; HUVEC, human umbilical vein endothelial cell; knn, k nearest neighbor; LEL, large extracellular loop; mEGFP, monomeric EGFP; TEM, tetraspanin-enriched microdomain; VE-cadherin, vascular endothelial cadherin.The online version of this article contains supplemental material.

Data presented here provide evidence for a new direct interaction of the GTPase Rac with the C-terminal cytoplasmic domain of tetraspanin CD81. Tetraspanin-enriched, microdomain-dependent compartmentalization is a novel regulatory mechanism of Rac activity turnover, which provides a novel mechanism for regulation of cell motility by tetraspanins.

In this study, we investigated the dynamics of the molecular interactions of tetraspanin CD81 in T lymphocytes, and we show that CD81 controls the organization of the immune synapse (IS) and T cell activation. Using quantitative microscopy, including fluorescence recovery after photobleaching (FRAP), phasor fluorescence lifetime imaging microscopy-Föster resonance energy transfer (phasorFLIM-FRET), and total internal reflection fluorescence microscopy (TIRFM), we demonstrate that CD81 interacts with ICAM-1 and CD3 during conjugation between T cells and antigen-presenting cells (APCs). CD81 and ICAM-1 exhibit distinct mobilities in central and peripheral areas of early and late T cell-APC contacts. Moreover, CD81-ICAM-1 and CD81-CD3 dynamic interactions increase over the time course of IS formation, as these molecules redistribute throughout the contact area. Therefore, CD81 associations unexpectedly define novel sequential steps of IS maturation. Our results indicate that CD81 controls the temporal progression of the IS and the permanence of CD3 in the membrane contact area, contributing to sustained T cell receptor (TCR)-CD3-mediated signaling. Accordingly, we find that CD81 is required for proper T cell activation, regulating CD3, ZAP-70, LAT, and extracellular signal-regulated kinase (ERK) phosphorylation; CD69 surface expression; and interleukin-2 (IL-2) secretion. Our data demonstrate the important role of CD81 in the molecular organization and dynamics of the IS architecture that sets the signaling threshold in T cell activation. The interaction between T lymphocytes and antigen-presenting cells (APCs) is essential for the initiation of the immune response. The dynamic structure formed at cell-to-cell contacts between T cells and APCs, called the immune synapse (IS), is characterized by controlled recruitment of membrane receptors to specific subcellular sites (1). Upon activation by an APC, T cell molecules involved in the IS redistribute in highly organized structures at the T cell-APC contact (2). The T cell receptor (TCR) and associated molecules concatenate into the central area (central supramolecular activation cluster [cSMAC]), whereas adhesion receptors rearrange in a surrounding external ring called the peripheral supramolecular activation cluster (pSMAC) (3). During IS formation, preclustered TCR "protein islands" converge into larger aggregates that translocate toward the cSMAC (4, 5), from where they are internalized and degraded (6). The balance between the generation and degradation of TCR microclusters is critical for sustained T cell activation (5, 7) and is modulated by ligand mobility (8). However, the mechanisms regulating protein receptor movement and the basis for IS molecular segregation are still poorly understood.A plethora of molecules are translocated to the IS during T cell activation (9). These include the tetraspanins CD81 (10) and CD82 (11), which are known to associate with several IS components such as major histocompatibility complex class II (MHCII) molecules, CD4, and LF...

Because severe G6PD deficiency can be a phenocopy of chronic granulomatous disease with regard to the cellular and clinical phenotype, careful evaluation of neutrophil function seems mandatory in these patients to decide on appropriate anti-infective preventive measures. Determining the level of G6PD enzyme activity should be followed by analysis of reactive oxygen species production and NET formation to decide on required antibiotic and antimycotic prophylaxis.

Understanding how the immune response is activated and amplified requires detailed knowledge of the stages in the formation of the immunological synapse (IS) between T lymphocytes and antigen-presenting cells (APCs). We show that tetraspanins CD9 and CD151 congregate at the T-cell side of the IS. Silencing of CD9 or CD151 blunts the IL-2 secretion and expression of the activation marker CD69 by APC-conjugated T lymphocytes, but does not affect the accumulation of CD3 or actin to the IS, or the translocation of the microtubule-organizing center toward the T-B contact area. CD9 or CD151 silencing diminishes the relocalization of α4β1 integrin to the IS and reduces the accumulation of high-affinity β1 integrins at the cell-cell contact. These changes are accompanied by diminished phosphorylation of the integrin downstream targets FAK and ERK1/2. Our results suggest that CD9 and CD151 support integrin-mediated signaling at the IS.Keywords: CD9 r CD151 r Immune synapse r Integrins r T-cell activation Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionInteraction between T lymphocytes and antigen-presenting cells (APCs) is critical for antigen presentation and for the initiation of the immune response. This process is characterized by the formation of a dynamic structure called the immune synapse (IS) at the contact between T cells and APCs [1]. At the T cell side of the IS, T-cell receptors (TCRs) and Correspondence: Dr.Francisco Sánchez-Madrid e-mail: fsmadrid@salud.madrid.org associated molecules accumulate in the central area (central supramolecular activation cluster; cSMAC), while adhesion receptors and integrins reorganize in a surrounding external ring called peripheral SMAC (pSMAC) [1]. The increased IS stability enhances T-cell sensitivity, stimulates cytoskeletal processes, induces downstream signaling, and drives effective T-cell differentiation [2,3]. How integrins regulate these processes is not fully understood.Several membrane receptors and integrins concentrated at the IS -CD3, CD4, ICAM-1, lymphocyte function-associated antigen 1 (LFA-1), and very late antigen 4 (VLA-4) -are associated with tetraspanins [4,5] 1968 Rocha-Perugini Vera et al. Eur. J. Immunol. 2014. 44: 1967-1975 organize membrane macrocomplexes called tetraspanin-enriched microdomains (TEMs) [6]. Tetraspanins modulate the function of their associated partners and play important roles in immunity, inflammation, and other processes [6]. Tetraspanins that accumulate at the IS include CD81, which regulates IS architectural organization and maturation [5], and CD82, which contributes to T-cell activation through Rho GTPase-dependent regulation of the actin cytoskeleton [7]. CD82 also increases the adhesion of LFA-1 integrin to its ligand ICAM-1 expressed on APCs [4]. The tetraspanins CD81, CD82, CD53, and CD9 provide T cell costimulatory signals, and CD9 localizes together with TCR signaling molecules in lipid microdomains [4]. Moreover, the T cells of mice deficien...

Correspondence to Francisco S á nchez-Madrid: fsanchez.hlpr@salud.madrid.org Abbreviations used in this paper: ACF, autocorrelation function; EAP, endothelial adhesive platform; FCS, fl uorescence correlation spectroscopy; FLIM, fl uorescence lifetime imaging microscopy; FN, fi bronectin; FRET, F ö rster resonance energy transfer; FRETeff, FRET effi ciency; GPI, glycosylphosphatidylinositol; HUVEC, human umbilical vein endothelial cell; knn, k nearest neighbor; LEL, large extracellular loop; mEGFP, monomeric EGFP; TEM, tetraspanin-enriched microdomain; VE-cadherin, vascular endothelial cadherin.The online version of this article contains supplemental material.

SummaryIn this study, we describe that the PDZ protein syntenin-1 is a crucial element for the generation of signaling asymmetry during the cellular response to polarized extracellular cues. We analyze the role of syntenin-1 in the control of asymmetry in two independent models of T cell polarization -the migratory response to chemoattractants and the establishment of cognate interactions between T cells and antigenpresenting cells (APCs). A combination of mutant, biochemical and siRNA approaches demonstrate that syntenin-1 is vital for the generation of polarized actin structures such as the leading edge and the contact zone with APCs. We found that the mechanism by which syntenin-1 controls actin polymerization relies on its mandatory role for activation of the small GTPase Rac. Syntenin-1 controls Rac through a specific association with the myosin phosphatase Rho interacting protein (M-RIP), which occurs in response to phosphorylation of syntenin-1 by Src at Tyr4. Our data indicate the key role of syntenin-1 in the generation of functional asymmetry in T cells and provide a novel mechanistic link between receptor activation and actin polymerization and accumulation in response to extracellular stimulation.

In the absence of clinical trials to test the benefits and possible applications of ultrasound contrast agents for molecular imaging and therapy, we have developed a novel ex vivo human model using umbilical cords that is valid for the detection of inflammation and for exogenous expression of proteins by sonoporation.