New insights into the T cell synapse from single molecule techniques

• Published in: Nature reviews. Immunology Vol. 11; no. 10; pp. 672 - 684
• Main Authors: Dustin, Michael L, Depoil, David
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2011; Nature Publishing Group
• Subjects: 631/1647/664; 631/250/21/1293; Actin; Actins - genetics; Actins - immunology; Actins - metabolism; adaptor proteins; Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - immunology; Adaptor Proteins, Signal Transducing - metabolism; Animals; Antigen-presenting cells; Antigen-Presenting Cells - immunology; Antigen-Presenting Cells - metabolism; Antigens; Biomedical and Life Sciences; Biomedicine; Cell activation; Cytological Techniques - methods; Gene expression; genomics; Humans; imaging; Immunity; Immunological synapses; Immunological Synapses - chemistry; Immunological Synapses - metabolism; Immunology; Ligands; Lymphocyte Activation - genetics; Lymphocyte Activation - immunology; Lymphocytes T; Major Histocompatibility Complex; Methods; Mice; Microscopy; Molecular Imaging - methods; Physiological aspects; Radicals; Receptors, Antigen, T-Cell - genetics; Receptors, Antigen, T-Cell - immunology; Receptors, Antigen, T-Cell - metabolism; review-article; Signal transduction; Signal Transduction - genetics; Signal Transduction - immunology; T cells; T-cell receptor; T-Lymphocytes - chemistry; T-Lymphocytes - cytology; T-Lymphocytes - immunology; T-Lymphocytes - metabolism; United States; New York; United States > US
• ISSN: 1474-1733; 1474-1741
• DOI: 10.1038/nri3066

Key Points Single molecule methods are leading to advances in our understanding of immune cell activation, but different interpretations of the cutting-edge data can also trigger controversies. Probing single T cell receptor (TCR)–peptide–MHC bonds at early time points has led to the discovery that the two-dimensional on-rate is a crucial parameter that amplifies apparently small chemical differences between different ligand–receptor interactions. Measuring single TCR–peptide–MHC interactions using fluorescence resonance energy transfer reveals that cytoskeletal force increases the off-rate by approximately tenfold, further emphasizing the importance of efficient peptide–MHC capture. Electron microscopy and super-resolution fluorescence microscopy reveal that the TCR and the adaptor protein linker for activation of T cells (LAT) are organized into protein islands in a protein-poor lipid sea and that collisions between TCR + and LAT + islands initiate signalling. By contrast, time-lapse and super-resolution fluorescence microscopy suggest that TCR clusters in the plasma membrane interact in trans with LAT in sub-synaptic vesicles to initiate signalling. Mutations in a putative TCR dimer interface impair central supramolecular activation cluster (cSMAC) formation, a TSG101-dependent process that might transfer nucleic acid messages from T cells to antigen-presenting cells. Unexpected and controversial results regarding the functional organization of the T cell synapse have been obtained from the single molecule imaging techniques that have recently become available. T cell activation depends on extracellular ligation of the T cell receptor (TCR) by peptide–MHC complexes in a synapse between the T cell and an antigen-presenting cell. The process then requires the assembly of signalling complexes between the TCR and the adaptor protein linker for activation of T cells (LAT), and subsequent filamentous actin (F-actin)-dependent TCR cluster formation. Recent progress in each of these areas, made possible by the emergence of new techniques, has forced us to rethink our assumptions and consider some radical new models. These describe the receptor interaction parameters that control T cell responses and the mechanism by which LAT is recruited to the TCR signalling machinery. This is an exciting time in T cell biology, and further innovation in imaging and genomics is likely to lead to a greater understanding of how T cells are activated.