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Michael L Dustin

Publications and source records attributed to Michael L Dustin.

18 recordsLinked to original sources
PubMed2003

In vivo imaging approaches in animal models of rheumatoid arthritis.

The interaction of activated leukocytes with the rheumatoid synovial environment is a key process in arthritis. Understanding this process will play an important role in designing effective treatments. In vivo imaging approaches combined with molecular genetics in animal models provide important tools to address these issues. The present review will focus on approaches to in vivo imaging, with particular attention to approaches that are proving useful for, or have promise for, research on animal models of rheumatoid arthritis. These approaches will probably shed light on the specific local mechanisms involved in chronic inflammation and provide real time monitoring approaches to follow cellular and molecular events related to disease development.

Animals↗
PubMed2003

Coordination of T cell activation and migration through formation of the immunological synapse.

T cell activation is based on interactions of T cell antigen receptors with MHC-peptide complexes in a specialized cell-cell junction between the T cell and antigen-presenting cell-the immunological synapse. The immunological synapse coordinates naïve T cell activation and migration by stopping T cell migration with antigen-presenting cells bearing appropriate major histocompatibility complex (MHC) peptide complexes. At the same time, the immunological synapse allows full T cell activation through sustained signaling over a period of several hours. The immunological synapse supports activation in the absence of continued T cell migration, which is required for T cell activation through serial encounters. Src and Syk family kinases are activated early in immunological synapse formation, but this signaling process returns to the basal level after 30 min; at the same time, the interactions between T cell receptors (TCRs) and MHC peptides are stabilized within the immunological synapse. The molecular pattern of the mature synapse in helper T cells is a self-stabilized structure that is correlated with cytokine production and proliferation. I propose that this molecular pattern and its specific biochemical constituents are necessary to amplify signals from the partially desensitized TCR.

Calcium Signaling↗
PubMed2002

Neural and immunological synaptic relations.

A synapse is a stable adhesive junction between two cells across which information is relayed by directed secretion. The nervous system and immune system utilize these specialized cell surface contacts to directly convey and transduce highly controlled secretory signals between their constituent cell populations. Each of these synaptic types is built around a microdomain structure comprising central active zones of exocytosis and endocytosis encircled by adhesion domains. Surface molecules that may be incorporated into and around the active zones contribute to modulation of the functional state of the synapse.

Animals↗
PubMed2002

Cutting edge: quantitative imaging of raft accumulation in the immunological synapse.

Although the accumulation of lipid rafts at the immunological synapse is now well accepted, the degree of the accumulation, the localization within the fine structure of the immunological synapse, and the region from which lipid rafts are recruited have not been defined. In this work we show that lipid rafts preferentially accumulate in the central zone of the immunological synapse, the central supramolecular activation complex (C-SMAC). However, quantitative analyses indicate that the level of recruitment of lipid rafts to the C-SMAC is relatively small and suggests that rearrangement of lipid rafts from the peripheral zone of the synapse into the C-SMAC can account for this accumulation. We also assessed the effects of CD28 deficiency on lipid raft recruitment to the immunological synapse. The accumulation of lipid occurred independently of the CD28/B7 system and was not measurably altered by CD28.

Animals↗
PubMed2002

Shmoos, rafts, and uropods- the many facets of cell polarity.

The recent Juan March Foundation meeting on "Regulation and functional insights in cellular polarity" focused on cellular polarity in yeasts, Dictyostelium, epithelial cells, fibroblasts, and immune cells. The molecular systems covered included membrane rafts, actin and tubulin cytoskeleton, polarized transcription, signaling, and cell-cell adhesion. Across these diverse biological and molecular systems, important general concepts emerged, including new ideas for establishing and maintaining polarity that are likely to be applicable across models and experimental systems.

Actins↗
PubMed2002

The immunological synapse.

T-cell activation requires interaction of T-cell antigen receptors with proteins of the major histocompatibility complex (antigen). This interaction takes place in a specialized cell-cell junction referred to as an immunological synapse. The immunological synapse contains at least two functional domains: a central cluster of engaged antigen receptors and a surrounding ring of adhesion molecules. The segregation of the T-cell antigen receptor (TCR) and adhesion molecules is based on size, with the TCR interaction spanning 15 nm and the lymphocyte-function-associated antigen-1 (LFA-1) interaction spanning 30-40 nm between the two cells. Therefore, the synapse is not an empty gap, but a space populated by both adhesion and signaling molecules. This chapter considers four aspects of the immunological synapse: the role of migration and stop signals, the role of the cytoskeleton, the role of self-antigenic complexes, and the role of second signals.

Animals↗
PubMed2002

Polar redistribution of the sialoglycoprotein CD43: implications for T cell function.

Contact between T cells and APCs results in the orchestrated segregation of molecules at the cell-cell interface and formation of a specialized structure termed the immunological synapse. This model predicts the topological seclusion of large molecules such as CD43 from the site of closest contact between the T cell and APC, allowing for the close apposition of cell membranes and effective TCR engagement. Similarly, during T cell migration segregation of CD43 to the uropod is thought to aid integrin adhesion at the leading edge of the cell by removing steric hindrance. We show in this work that CD43 distribution on T cells is regulated by a membrane proximal ezrin binding site and that failure to displace CD43 from the immunological synapse has no inhibitory effects on primary T cell activation. We also report that CD43 expression at the contact zone between T cells and matrix does not negatively regulate motility but may regulate LFA-1 de-adhesion. These results suggest that the steric barrier model of CD43 is inadequate and that alternative mechanisms account for the negative regulatory properties of CD43.

Animals↗
PubMed2002

T cell receptor signaling precedes immunological synapse formation.

The area of contact between a T cell and an antigen-presenting cell (APC) is known as the immunological synapse. Although its exact function is unknown, one model suggests that it allows for T cell receptor (TCR) clustering and for sustained signaling in T cells for many hours. Here we demonstrate that TCR-mediated tyrosine kinase signaling in naïve T cells occurred primarily at the periphery of the synapse and was largely abated before mature immunological synapses had formed. These data suggest that many hours of TCR signaling are not required for T cell activation. These observations challenge current ideas about the role of immunological synapses in T cell activation.

Animals↗
PubMed2002

T-cell activation: a multidimensional signaling network.

Naïve T cell activation requires the interactions of antigen receptors, adhesion molecules and co-stimulatory molecules. Antigen receptors and adhesion molecules are involved in spatio-temporal movement to form a stable immunological synapse. This stable junction interrupts T cell migration, and provides a platform for temporally regulated co-stimulatory receptor signaling spanning a period of days.

Animals↗
PubMed2002

WIP deficiency reveals a differential role for WIP and the actin cytoskeleton in T and B cell activation.

WIP stabilizes actin filaments and is important for filopodium formation. To define the role of WIP in immunity, we generated WIP-deficient mice. WIP(minus sign/minus sign) mice have normal lymphocyte development, but their T cells fail to proliferate, secrete IL-2, increase their F-actin content, polarize and extend protrusions following T cell receptor ligation, and are deficient in conjugate formation with superantigen-presenting B cells and anti-CD3 bilayers. In contrast, WIP-deficient B lymphocytes have enhanced proliferation and CD69 expression following B cell receptor ligation and mount normal antibody responses to T-independent antigens. Both WIP-deficient T and B cells show a profound defect in their subcortical actin filament networks. These results suggest that WIP is important for immunologic synapse formation and T cell activation.

Actins↗
PubMed2002

Immature CD4(+)CD8(+) thymocytes form a multifocal immunological synapse with sustained tyrosine phosphorylation.

The immunological synapse formed during mature T cell activation consists of a central cluster of TCR and MHC molecules surrounded by a ring of LFA-1 and ICAM-1. We examined synapse formation in thymocytes undergoing activation in a lipid bilayer system by following the movement of fluorescent MHC and ICAM-1 molecules. Immature CD4(+)CD8(+) thymocytes formed a decentralized synapse with multiple foci of MHC accumulation corresponding to areas of exclusion of ICAM-1. The MHC clusters and ICAM-1 holes were mobile and transient and correlated with active and sustained signaling, as shown by staining with antibodies against phosphotyrosine and activated Lck. Our findings show that signaling in immature thymocytes can result from a novel, multifocal pattern of receptor accumulation.

Animals↗
PubMed2002

Correlation of a dynamic model for immunological synapse formation with effector functions: two pathways to synapse formation.

During antigen recognition by T cells different receptors and ligands form a pattern in the intercellular junction called the immunological synapse, which might be involved in T-cell activation. Recently, a synapse assembly model has been proposed, which enables the calculation of the propensity for synapse assembly driven by membrane-constrained protein binding interactions. We bring together model predictions of mature synapse assembly with data on the dependence of T-cell responses on T-cell receptor (TCR)-MHC-peptide (pMHC) binding kinetics. Predictions of mature synapse assembly, based on TCR-pMHC binding kinetics, correlate well with observed cytokine responses by T cells bearing the relevant TCR but not with cytotoxic T lymphocyte-mediated killing. We discuss the suggested different role for the synapse in pre- and post-nuclear activation events in T cells. The view of immunological synapse assembly given here emphasizes the importance of both the on and off rates for the TCR-pMHC interaction and in this context recent data on a positive role for analogs of self-peptides in synapse assembly is considered.

Animals↗
PubMed2002

The synapse assembly model.

A framework for quantitative analysis of the mechanisms underlying immunological synapse assembly has been recently developed. This model uses partial differential equations to describe the binding interactions of receptors and ligands, with the constraint that they are embedded in apposed deformable membranes linked to a cytoskeletal complex.

Animals↗
PubMed2002

The immunological synapse: integrins take the stage.

Adhesive interactions play important roles in coordinating T-cell migration and activation, specifically in the formation of the immunological synapse (IS), a specialized cell-cell junction. Recent demonstrations show several molecules implicated in T-cell signaling, including Vav, ADAP, and Rap-1, have major roles in integrin regulation and place adhesion molecules at center stage in addressing the question: what are the signals involved in the formation of the IS and full T-cell activation? This review focuses on the role of integrins as an essential system for both physical adhesion and signaling in T-cell activation. The role of integrins appears to be quite distinct from classical costimulation and has been largely overlooked due to the ubiquitous use of serum in lymphocyte functional assays. Each major signal transduction pathway has branches leading to the nucleus and others that feed back on cytoskeletal and membrane regulation at the IS.

Animals↗
PubMed2002

Stimulation of naïve T-cell adhesion and immunological synapse formation by chemokine-dependent and -independent mechanisms.

Chemokines adsorbed to the cell surface play an important role in the initial interactions of T cells with endothelial cells, and may also have a role in T-cell interactions with dendritic cells. Therefore, we examined the effect of surface-adsorbed chemokines on the interaction of naïve murine splenic T cells with supported bilayers containing intercellular adhesion molecule (ICAM)-1, or with bone marrow-derived cultured dendritic cells in the presence and absence of relevant MHC-peptide complexes. Naïve T cells formed immunological synapses, defined as a ring of lymphocyte function associated (LFA)-1-ICAM-1 interactions surrounding a central cluster of MHC-peptide complexes, on supported planar bilayers containing ICAM-1 and relevant MHC-peptide complexes. Chemokines stimulated an increase in the percentage of naïve cells that adhered to ICAM-1, but did not increase the average number of LFA-1-ICAM-1 interactions in the contact area. In contrast, relevant MHC-peptide complexes resulted in a small increase in the proportion of interacting T cells, but stimulated an 8-fold increase in the number of LFA-1-ICAM-1 interactions in each contact formed. Naïve T cells displayed a significant basal adhesion to bone marrow dendritic cells that was further increased when relevant chemokines were adsorbed to the dendritic cell surface. However, basal and antigen-stimulated T-cell adhesion to dendritic cells was not sensitive to pertussis toxin. Thus, there are chemokine-independent mechanisms that initiate adhesion between T cells and dendritic cells.

Animals↗
PubMed2001

Costimulation and endogenous MHC ligands contribute to T cell recognition.

To initiate an immune response, key receptor-ligand pairs must cluster in "immune synapses" at the T cell-antigen-presenting cell (APC) interface. We visualized the accumulation of a major histocompatibility complex (MHC) class II molecule, I-E(k), at a T cell-B cell interface and found it was dependent on both antigen recognition and costimulation. This suggests that costimulation-driven active transport of T cell surface molecules helps to drive immunological synapse formation. Although only agonist peptide-MHC class II (agonist pMHC class II) complexes can initiate T cell activation, endogenous pMHC class II complexes also appeared to accumulate. To test this directly, we labeled a "null" pMHC class II complex and found that, although it lacked major TCR contact residues, it could be driven into the synapse in a TCR-dependent manner. Thus, low-affinity ligands can contribute to synapse formation and T cell signaling.

Animals↗