Heterozygous mutations in the C-terminal domain of COPA underlie a complex autoinflammatory syndrome

Mutations in the N-terminal WD40 domain of coatomer protein complex subunit α (COPA) cause a type I interferonopathy, typically characterized by alveolar hemorrhage, arthritis, and nephritis. We described 3 heterozygous mutations in the C-terminal domain (CTD) of COPA (p.C1013S, p.R1058C, and p.R1142X) in 6 children from 3 unrelated families with a similar syndrome of autoinflammation and autoimmunity. We showed that these CTD COPA mutations disrupt the integrity and the function of coat protein complex I (COPI). In COPAR1142X and COPAR1058C fibroblasts, we demonstrated that COPI dysfunction causes both an anterograde ER-to-Golgi and a retrograde Golgi-to-ER trafficking defect. The disturbed intracellular trafficking resulted in a cGAS/STING-dependent upregulation of the type I IFN signaling in patients and patient-derived cell lines, albeit through a distinct molecular mechanism in comparison with mutations in the WD40 domain of COPA. We showed that CTD COPA mutations induce an activation of ER stress and NF-κB signaling in patient-derived primary cell lines. These results demonstrate the importance of the integrity of the CTD of COPA for COPI function and homeostatic intracellular trafficking, essential to ER homeostasis. CTD COPA mutations result in disease by increased ER stress, disturbed intracellular transport, and increased proinflammatory signaling.

[Monogenic auto-inflammatory diseases associated with actinopathies: A review of the literature]

Auto-inflammatory diseases (AIDs) are diseases resulting from an inappropriate activation of innate immunity in the absence of any infection. The field of monogenic AIDs is constantly expanding, with the discovery of new pathologies and pathophysiological mechanisms thanks to pangenomic sequencing. Actinopathies with auto-inflammatory manifestations are a new emerging group of AIDs, linked to defects in the regulation of the actin cytoskeleton dynamics. These diseases most often begin in the neonatal period and combine to varying degrees a more or less severe primary immune deficiency, cytopenias (especially thrombocytopenia), auto-inflammatory manifestations (especially cutaneous and digestive), atopic and auto-immune manifestations. The diagnosis is to be evoked essentially in front of a cutaneous-digestive auto-inflammation picture of early onset, associated with a primary immune deficiency and thrombocytopenia or a tendency to bleed. Some of these diseases have specificities, including a risk of macrophagic activation syndrome or a tendency to atopy or lymphoproliferation. We propose here a review of the literature on these new diseases, with a proposal for a practical approach according to the main associated biological abnormalities and some clinical particularities. However, the diagnosis remains genetic, and several differential diagnoses must be considered. The pathophysiology of these diseases is not yet fully elucidated, and studies are needed to better clarify the inherent mechanisms that can guide the choice of therapies. In most cases, the severity of the picture indicates allogeneic marrow transplantation.

The tumor suppressor adenomatous polyposis coli regulates T lymphocyte migration

Adenomatous polyposis coli (APC) is a tumor suppressor whose mutations underlie familial adenomatous polyposis (FAP) and colorectal cancer. Although its role in intestinal epithelial cells is well characterized, APC importance in T cell biology is ill defined. APC regulates cytoskeleton organization, cell polarity, and migration in various cell types. Here, we address whether APC plays a role in T lymphocyte migration. Using a series of cell biology tools, we unveiled that T cells from FAP patients carrying APC mutations display impaired adhesion and motility in constrained environments. We further dissected the cellular mechanisms underpinning these defects in APC-depleted CEM T cell line that recapitulate the phenotype observed in FAP T cells. We found that APC affects T cell motility by modulating integrin-dependent adhesion and cytoskeleton reorganization. Hence, APC mutations in FAP patients not only drive intestinal neoplasms but also impair T cell migration, potentially contributing to inefficient antitumor immunity.

cAMP Bursts Control T Cell Directionality by Actomyosin Cytoskeleton Remodeling

T lymphocyte migration is an essential step to mounting an efficient immune response. The rapid and random motility of these cells which favors their sentinel role is conditioned by chemokines as well as by the physical environment. Morphological changes, underlaid by dynamic actin cytoskeleton remodeling, are observed throughout migration but especially when the cell modifies its trajectory. However, the signaling cascade regulating the directional changes remains largely unknown. Using dynamic cell imaging, we investigated in this paper the signaling pathways involved in T cell directionality. We monitored cyclic adenosine 3′-5′ monosphosphate (cAMP) variation concomitantly with actomyosin distribution upon T lymphocyte migration and highlighted the fact that spontaneous bursts in cAMP starting from the leading edge, are sufficient to promote actomyosin redistribution triggering trajectory modification. Although cAMP is commonly considered as an immunosuppressive factor, our results suggest that, when transient, it rather favors the exploratory behavior of T cells.

Fam65b Phosphorylation Relieves Tonic RhoA Inhibition During T Cell Migration

We previously identified Fam65b as an atypical inhibitor of the small G protein RhoA. Using a conditional model of a Fam65b-deficient mouse, we first show that Fam65b restricts spontaneous RhoA activation in resting T lymphocytes and regulates intranodal T cell migration in vivo. We next aimed at understanding, at the molecular level, how the brake that Fam65b exerts on RhoA can be relieved upon signaling to allow RhoA activation. Here, we show that chemokine stimulation phosphorylates Fam65b in T lymphocytes. This post-translational modification decreases the affinity of Fam65b for RhoA and favors Fam65b shuttling from the plasma membrane to the cytosol. Functionally, we show that the degree of Fam65b phosphorylation controls some cytoskeletal alterations downstream active RhoA such as actin polymerization, as well as T cell migration in vitro. Altogether, our results show that Fam65b expression and phosphorylation can finely tune the amount of active RhoA in order to favor optimal T lymphocyte motility.

FAM65B controls the proliferation of transformed and primary T cells

Cell quiescence is controlled by regulated genome-encoded programs that actively express genes which are often down-regulated or inactivated in transformed cells. Among them is FoxO1, a transcription factor that imposes quiescence in several cell types, including T lymphocytes. In these cells, the FAM65B encoding gene is a major target of FOXO1. Here, we show that forced expression of FAM65B in transformed cells blocks their mitosis because of a defect of the mitotic spindle, leading to G2 cell cycle arrest and apoptosis. Upon cell proliferation arrest, FAM65B is engaged in a complex containing two proteins well known to be involved in cell proliferation i.e. the HDAC6 deacetylase and the 14.3.3 scaffolding protein. In primary T cells, FAM65B is down-regulated upon T cell receptor engagement, and maintaining its expression blocks their proliferation, establishing that the decrease of FAM65B expression is required for proliferation. Conversely, inhibiting FAM65B expression in naive T lymphocytes decreases their activation threshold. These results identify FAM65B as a potential new target for controlling proliferation of both transformed and normal cells.

Profiling the lymphoid-resident T cell pool reveals modulation by age and microbiota

Despite being implicated in non-lymphoid tissues, non-recirculating T cells may also exist in secondary lymphoid organs (SLO). However, a detailed characterization of this lymphoid-resident T cell pool has not yet been done. Here we show that a substantial proportion of CD4 regulatory (Treg) and memory (Tmem) cells establish long-term residence in the SLOs of specific pathogen-free mice. Of these SLOs, only T cell residence within Peyer's patches is affected by microbiota. Resident CD4 Treg and CD4 Tmem cells from lymph nodes and non-lymphoid tissues share many phenotypic and functional characteristics. The percentage of resident T cells in SLOs increases considerably with age, with S1PR1 downregulation possibly contributing to this altered homeostasis. Our results thus show that T cell residence is not only a hallmark of non-lymphoid tissues, but can be extended to secondary lymphoid organs.

Rapid and robust analysis of cellular and molecular polarization induced by chemokine signaling

Cells respond to chemokine stimulation by losing their round shape in a process called polarization, and by altering the subcellular localization of many proteins. Classic imaging techniques have been used to study these phenomena. However, they required the manual acquisition of many cells followed by time consuming quantification of the morphology and the co-localization of the staining of tens of cells. Here, a rapid and powerful method is described to study these phenomena on samples consisting of several thousands of cells using an imaging flow cytometry technology that combines the advantages of a microscope with those of a cytometer. Using T lymphocytes stimulated with CCL19 and staining for MHC Class I molecules and filamentous actin, a gating strategy is presented to measure simultaneously the degree of shape alterations and the extent of co-localization of markers that are affected by CCL19 signaling. Moreover, this gating strategy allowed us to observe the segregation of filamentous actin (at the front) and phosphorylated Ezrin-Radixin-Moesin (phospho-ERM) proteins (at the rear) in polarized T cells after CXCL12 stimulation. This technique was also useful to observe the blocking effect on polarization of two different elements: inhibition of actin polymerization by a pharmacological inhibitor and expression of mutants of the Par6/atypical PKC signaling pathway. Thus, evidence is shown that this technique is useful to analyze both morphological alterations and protein redistributions.

Fam65b is a new transcriptional target of FOXO1 that regulates RhoA signaling for T lymphocyte migration

Forkhead box O (FOXO) transcription factors favor both T cell quiescence and trafficking through their control of the expression of genes involved in cell cycle progression, adhesion, and homing. In this article, we report that the product of the fam65b gene is a new transcriptional target of FOXO1 that regulates RhoA activity. We show that family with sequence similarity 65 member b (Fam65b) binds the small GTPase RhoA via a noncanonical domain and represses its activity by decreasing its GTP loading. As a consequence, Fam65b negatively regulates chemokine-induced responses, such as adhesion, morphological polarization, and migration. These results show the existence of a new functional link between FOXO1 and RhoA pathways, through which the FOXO1 target Fam65b tonically dampens chemokine-induced migration by repressing RhoA activity.

Rho GTPases: masters of T lymphocyte migration and activation

Rho GTPases are key signal transducer elements activated in T cells by both chemokine and antigen receptors. These two signalling pathways control the two main functions of T lymphocytes: motility and activation. Rho GTPases are thus crucial for the development of an adequate immune response. In this review, we mostly focus on the roles of RhoA, Rac1 and Cdc42 in T cells. We show their importance in phenomena such as adhesion, morphological polarization, migration and antigen recognition.

Activation of the ancestral polarity regulator protein kinase C zeta at the immunological synapse drives polarization of Th cell secretory machinery toward APCs

A key feature in T lymphocyte biology is that Th cells rapidly polarize their secretory machinery toward cognate APCs. The molecular mechanisms of these dynamic Th cell responses and their impact on APC biology remain to be elucidated. In this study, we demonstrate that protein kinase Czeta (PKCzeta) is rapidly activated at the immunological synapse (IS) in human Th cells interacting with cognate dendritic cells (DCs) and that a functional PKCzeta is required for the polarization of Th cell secretory machinery toward DCs. We also show that PKCzeta-dependent Th cell polarization allows dedicated delivery of IFN-gamma and CD40L at the IS and is required for the activation of cognate DCs to IL-12 production. PKCzeta synaptic activation is a low-threshold phenomenon and, in Th cells interacting with multiple DCs, selectively occurs at the IS formed with the DCs offering the strongest stimulus leading to dedicated Th cell polarization. Our results identify the PKCzeta signaling pathway as a key component of the Th cell polarization machinery and provide a molecular basis for T cell-dedicated activation of cognate DCs.

Bcl10 controls TCR- and FcgammaR-induced actin polymerization

Bcl10 plays an essential role in the adaptive immune response, because Bcl10-deficient lymphocytes show impaired Ag receptor-induced NF-kappaB activation and cytokine production. Bcl10 is a phosphoprotein, but the physiological relevance of this posttranslational modification remains poorly defined. In this study, we report that Bcl10 is rapidly phosphorylated upon activation of human T cells by PMA/ionomycin- or anti-CD3 treatment, and identify Ser(138) as a key residue necessary for Bcl10 phosphorylation. We also show that a phosphorylation-deficient Ser(138)/Ala mutant specifically inhibits TCR-induced actin polymerization yet does not affect NF-kappaB activation. Moreover, silencing of Bcl10, but not of caspase recruitment domain-containing MAGUK protein-1 (Carma1) induces a clear defect in TCR-induced F-actin formation, cell spreading, and conjugate formation. Remarkably, Bcl10 silencing also impairs FcgammaR-induced actin polymerization and phagocytosis in human monocytes. These results point to a key role of Bcl10 in F-actin-dependent immune responses of T cells and monocytes/macrophages.

ERM proteins regulate cytoskeleton relaxation promoting T cell–APC conjugation

During activation, T cells associate with antigen-presenting cells, a dynamic process that involves the formation of a broad area of intimate membrane contact known as the immunological synapse. The molecular intermediates that link initial antigen recognition to the cytoskeletal changes involved in this phenomenon have not yet been defined. Here we demonstrate that ezrin-radixin-moesin proteins are rapidly inactivated after antigen recognition through a Vav1-Rac1 pathway. The resulting disanchoring of the cortical actin cytoskeleton from the plasma membrane decreased cellular rigidity, leading to more efficient T cell-antigen-presenting cell conjugate formation. These findings identify an antigen-dependent molecular pathway that favors immunological synapse formation and the subsequent development of an effective immune response.

Imaging of T-cell interactions with antigen presenting cells in culture and in intact lymphoid tissue

The development of an effective immune response requires cell-cell contact between T cells and antigen-bearing cells of several types (dendritic cells, B cells, infected tissue cells). Recent advances in light microscopy have led to intense investigation of the molecular events that accompany these cell interactions, especially the redistribution of membrane proteins into discrete organized subdomains within the zone of cell-cell contact termed the 'immunological synapse'. Here we discuss two aspects of our own studies in this area. First, we highlight results from our in vitro analysis of the role of the cytoskeletal ezrin, radixin, moesin adapter proteins in the exclusion of CD43 from the well-defined T cell receptor (TCR) and integrin-rich zones of the synapse. Based on the molecular mechanism uncovered in this work, we propose a new model for how TCR-signaled changes in cytoskeletal organization indirectly influence both protein distributions and the efficiency of signaling between T cell and presenting cell. We then discuss the development of a new method for dynamic visualization of T cell - dendritic cell interactions in intact lymphoid tissue. The remarkable longevity of monogamous lymphocyte-presenting cell interactions is discussed, differences between our observations and those of others are laid out in detail, and prospects for future application of this technical approach to analysis of early immune responses in lymphoid organs and of effector lymphocyte function in tissues are presented.

Dynamic imaging of T cell-dendritic cell interactions in lymph nodes

T cell immune responses begin within organized lymphoid tissues. The pace, topology, and outcomes of the cellular interactions that underlie these responses have, so far, been inferred from static imaging of sectioned tissue or from studies of cultured cells. Here we report dynamic visualization of antigen-specific T cells interacting with dendritic cells within intact explanted lymph nodes. We observed immunological synapse formation and prolonged interactions between these two cell types, followed by the activation, dissociation, and rapid migration of T cells away from the antigenic stimulus. This high-resolution spatiotemporal analysis provides insight into the nature of cell interactions critical to early immune responses within lymphoid structures.

Exclusion of CD43 from the immunological synapse is mediated by phosphorylation-regulated relocation of the cytoskeletal adaptor moesin

Formation of the immunological synapse requires TCR signal-dependent protein redistribution. However, the specific molecular mechanisms controlling protein relocation are not well defined. Moesin is a widely expressed phospho-protein that links many transmembrane molecules to the cortical actin cytoskeleton. Here, we demonstrate that TCR-induced exclusion of the large sialoprotein CD43 from the synapse is an active event mediated by its reversible binding to moesin. Our results also reveal that relocalization of moesin is associated with changes in the phosphorylation status of this cytoskeletal adaptor protein. Finally, these findings raise the possibility that the change in moesin localization resulting from TCR engagement modifies the overall topology of the lymphocyte membrane and facilitates molecular interactions at the site of presenting cell contact.

Information transfer at the immunological synapse

Antigen-specific activation of T lymphocytes requires the interaction of their clonally distributed T-cell receptors with plasma membrane ligands composed of foreign peptide antigens bound to major histocompatibility complex molecules. For proliferation and differentiation to ensue, a variety of other adhesive and accessory proteins must also interact with their counter-receptors on the antigen-presenting cell to facilitate and complement the T-cell receptor-antigen recognition event. Recent studies have revealed that these various proteins show an unexpected degree of spatial organization in the zone of cell-cell contact. This region of membrane approximation is now referred to as the "immunological synapse" because of its functional analogy to the site of intercellular information transfer between neurons. Here, we review the evidence for signaling-dependent control of the dynamic changes in protein distribution that gives rise to the synapse and try to relate the emerging spatio-temporal information on synapse formation to T-cell biology.

Crippling of CD3-zeta ITAMs does not impair T cell receptor signaling

We evaluated the importance of CD3-zeta ITAMs in T cell responses by breeding the P14 transgenic TCR into mice in which CD3-zeta chains lacking all or part of their ITAMs were genetically substituted for wild-type CD3-zeta chains. In contrast to the H-Y TCR, the P14 TCR permitted the development of peripheral CD8+ T cells harboring signaling-defective CD3-zeta subunits. The absence of functional CD3-zeta ITAMs did not reduce the spectrum of activation events and effector functions that constitute the normal attributes of mature CD8+ T cells. The only detectable differences were quantitative and noted only when T cells were challenged with suboptimal peptide concentrations. Therefore, the ITAMs present in the CD3-gammadeltaepsilon module are sufficient for qualitatively normal TCR signaling and those present in CD3-zeta have no exclusive role during T cell activation.

Chronic intravenous injections of antigen induce and maintain tolerance in T cell receptor-transgenic mice

Antigen-specific T cell tolerance can be induced by systemic injection of high-dose antigen. In particular, a single intravenous (i.v.) injection of influenza virus hemagglutinin peptide in HNT-TCR transgenic mice induces T cell tolerance through thymocyte apoptosis as well as anergy and deletion of peripheral CD4+ T cells. We now show that this tolerance is reversed after 8 weeks probably due to the short in vivo half-life of the peptide. Since durable tolerance is required for this strategy to be of therapeutic value, we tested whether weekly i.v. injections of peptide (up to 12 weeks) could maintain the CD4+ T cell tolerance. Each injection induces a profound deletion of thymocytes, although their level recovers before the next injection. Therefore, during the treatment period, the thymus undergoes cycles of contraction/expansion. In the periphery, the number of CD4+ T cells is stably decreased and the persisting CD4+ T cells are hyporeactive both in vitro and in vivo. This tolerance is essentially peripheral since comparable results were obtained in thymectomized HNT-TCR mice injected weekly. Our data show that stable antigen-specific tolerance can be induced by repeated i.v. injections of antigen. These findings might have implications for the treatment of T cell-mediated autoimmune diseases.

Chronic intravenous injections of antigen induce and maintain tolerance in T cell receptor-transgenic mice

Antigen-specific T cell tolerance can be induced by systemic injection of high-dose antigen. In particular, a single intravenous (i.v.) injection of influenza virus hemagglutinin peptide in HNT-TCR transgenic mice induces T cell tolerance through thymocyte apoptosis as well as anergy and deletion of peripheral CD4+ T cells. We now show that this tolerance is reversed after 8 weeks probably due to the short in vivo half-life of the peptide. Since durable tolerance is required for this strategy to be of therapeutic value, we tested whether weekly i.v. injections of peptide (up to 12 weeks) could maintain the CD4+ T cell tolerance. Each injection induces a profound deletion of thymocytes, although their level recovers before the next injection. Therefore, during the treatment period, the thymus undergoes cycles of contraction/expansion. In the periphery, the number of CD4+ T cells is stably decreased and the persisting CD4+ T cells are hyporeactive both in vitro and in vivo. This tolerance is essentially peripheral since comparable results were obtained in thymectomized HNT-TCR mice injected weekly. Our data show that stable antigen-specific tolerance can be induced by repeated i.v. injections of antigen. These findings might have implications for the treatment of T cell-mediated autoimmune diseases.

Antigen-dependent and -independent Ca2+ responses triggered in T cells by dendritic cells compared with B cells

Dendritic cells (DCs) are much more potent antigen (Ag)-presenting cells than resting B cells for the activation of naive T cells. The mechanisms underlying this difference have been analyzed under conditions where ex vivo DCs or B cells presented known numbers of specific Ag-major histocompatibility complex (MHC) complexes to naive CD4(+) T cells from T cell antigen receptor (TCR) transgenic mice. Several hundred Ag-MHC complexes presented by B cells were necessary to elicit the formation of a few T-B conjugates with small contact zones, and the resulting individual T cell Ca2+ responses were all-or-none. In contrast, Ag-specific T cell Ca2+ responses can be triggered by DCs bearing an average of 30 Ag-MHC complexes per cell. Formation of T-DC conjugates is Ag-independent, but in the presence of the Ag, the surface of the contact zone increases and so does the amplitude of the T cell Ca2+ responses. These results suggest that Ag is better recognized by T cells on DCs essentially because T-DC adhesion precedes Ag recognition, whereas T-B adhesion requires Ag recognition. Surprisingly, we also recorded small Ca2+ responses in T cells interacting with unpulsed DCs. Using DCs purified from MHC class II knockout mice, we provide evidence that this signal is mostly due to MHC-TCR interactions. Such an Ag-independent, MHC-triggered calcium response could be a survival signal that DCs but not B cells are able to deliver to naive T cells.

CD8 expression allows T cell signaling by monomeric peptide-MHC complexes

Physiologically, TCR signaling is unlikely to result from the cross-linking of TCR-CD3 complexes, given the low density of specific peptide-MHC complexes on antigen-presenting cells. We therefore have tested directly an alternative model for antigen recognition. We show that monomers of soluble peptide-MHC trigger Ca2+ responses in CD8alphabeta+ T cells. This response is not observed in CD8- T cells and when either the CD8:MHC or CD8:Lck interactions are prevented. This demonstrates that an intact CD8 coreceptor is necessary for effective TCR signaling in response to monomeric peptide-MHC molecules. We propose that this heterodimerization of TCR and CD8 by peptide-MHC corresponds to the physiological event normally involved during antigen-specific signal transduction.

Modifications of CD8+ T cell function during in vivo memory or tolerance induction

Naive monoclonal T cells specific for the male antigen can be stimulated in vivo to eliminate male cells and become memory cells or to permit survival of male cells and become tolerant. Memory cells responded to TCR ligation by cyclic oscillations of calcium levels and immediate secretion of very high levels of IL-2 and interferon-gamma. Tolerant cells did not proliferate in response to ionomycin and phorbol myristate acetate, failing to mobilize calcium to produce IL-2 or express IL-2R, but survived for long time periods in vivo and secreted IL-10. These results emphasize that tolerance is not an absence of all functional activity and may be associated with modifications of behavior conferring important regulatory functions on tolerant T cells.

Imaging antigen recognition by naive CD4+ T cells: compulsory cytoskeletal alterations for the triggering of an intracellular calcium response

Antigen recognition was analyzed at the single-cell level by using for the first time T cells which were not altered by in vitro selection, transfection or immortalization. The first consequence of antigen recognition by ex vivo naive CD4+ T cells from T cell receptor (TCR)-transgenic mice is the formation of a "contact zone" with the B cell presenting the antigen. The T cell intracellular calcium (Ca2+) response begins after a delay of 30 s on average, following the formation of the contact zone. The T cell response is entirely inhibited by either protein tyrosine kinase or actin polymerization inhibitors but, surprisingly, it is insensitive to inhibitors of phosphoinositide 3-kinase. Moreover, inhibition of microtubule polymerization and use of Ca2+-free medium do not prevent the beginning of the T cell response, but do reduce the stability of the contact zone and/or the amplitude of the Ca2+ plateau. The critical involvement of the cytoskeleton in antigen recognition on B cells introduces a checkpoint in T cell activation: the initial TCR engagement triggers a Ca2+ response only after an amplification step corresponding to a cytoskeleton-controlled increase in the number of engaged TCR.

Reconstituted killer cell inhibitory receptors for major histocompatibility complex class I molecules control mast cell activation induced via immunoreceptor tyrosine-based activation motifs

Natural killer and T cells express at their surface, members of a multigenic family of killer cell inhibitory receptors (KIR) for major histocompatibility complex Class I molecules. KIR engagement leads to the inhibition of natural killer and T cell activation programs. We investigated here the functional reconstitution of KIR in a non-lymphoid cell type. Using stable transfection in the RBL-2H3 mast cell line, we demonstrated that (i) KIR can inhibit signals induced by FcepsilonRIgamma or CD3zeta polypeptides that bear immunoreceptor tyrosine-based activation motifs; (ii) two distinct immunoreceptor tyrosine-based inhibition motifs-bearing receptors, i.e. KIR and FcgammaRIIB, use distinct inhibitory pathways since KIR engagement inhibits the intracellular Ca2+ release from endoplasmic reticulum stores, in contrast to FcgammaRIIB, which only inhibits extracellular Ca2+ entry; (iii) KIR require co-ligation with an immunoreceptor tyrosine-based activation motif-dependent receptor to mediate their inhibitory function. This latter finding is central to the mechanism by which KIR selectively inhibit only the activatory receptors in close vicinity. Taken together our observations also contribute to define and extend the family of immunoreceptor tyrosine-based inhibition motif-bearing receptors involved in the negative control of cell activation.

The CD8 beta polypeptide is required for the recognition of an altered peptide ligand as an agonist

T cell activation is triggered by the specific recognition of cognate peptides presented by MHC molecules. Altered peptide ligands are analogs of cognate peptides which have a high affinity for MHC molecules. Some of them induce complete T cell responses, i.e. they act as agonists, whereas others behave as partial agonists or even as antagonists. Here, we analyzed both early (intracellular Ca2+ mobilization), and late (interleukin-2 production) signal transduction events induced by a cognate peptide or a corresponding altered peptide ligand using T cell hybridomas expressing or not the CD8 alpha and beta chains. With a video imaging system, we showed that the intracellular Ca2+ response to an altered peptide ligand induces the appearance of a characteristic sustained intracellular Ca2+ concentration gradient which can be detected shortly after T cell interaction with antigen-presenting cells. We also provide evidence that the same altered peptide ligand can be seen either as an agonist or a partial agonist, depending on the presence of CD8beta in the CD8 co-receptor dimers expressed at the T cell surface.

Effects of nocodazole and taxol on glycine evoked currents on rat spinal cord neurones in culture

We examined the effect of altering the cytoskeleton polymerization state by treatment with nocodazole and taxol on glycine-evoked currents in patch-clamp recordings from cultured spinal cord neurones. Adding ATP and GTP to the pipette solution did not prevent the rundown of the peak current. In the absence or in the presence of ATP, the proportion of the non-desensitizing part of the glycine evoked-current declined with time. Adding intracellular GTP and ATP stabilized glycine-evoked responses although the proportion of non-inactivating current was reduced. Nocodazole reduced by itself the proportion of the non-inactivating current whereas taxol (with ATP and GTP) had an opposite effect. These results suggest that the polymerization state of microtubules has functional consequences on glycine receptors.