Early T-cell signalling
One of the most striking features of our immune system is its inherent ability to distinguish harmful from harmless based on the primary protein structure of antigens. T-cells embody this trait of adaptive immunity through their unique capability for detecting antigenic peptides. It is driven by αβT-cell receptors (TCRs) on the T-cell binding to particular antigenic peptide-loaded MHC molecules (pMHC) displayed by antigen-presenting cells. T-cells are exquisitely sensitive to antigen: they can detect even a single antigenic pMHC molecule among a great number of structurally similar yet non-stimulatory pMHCs. The molecular/cellular mechanisms underlying this remarkable quality are not at all understood, even though their relevance for both disease progression and intervention can hardly be overestimated: inappropriate changes in T-cell reactivity can be harmful if not fatal as they can weaken the body’s defense against pathogens and cancer, and cause allergies or trigger autoimmunity.
It is of critical importance to consider the properties of the interface between a T-cell and an APC, termed immunological synapse. Imaging approaches revealed non-homogeneous and highly orchestrated distributions of various key components of the early T-cell signaling machinery at the plasma membrane. In our lab, we are often using a model system for specific T-cell activation, in which the APC is mimicked by a functionalized fluid supported lipid bilayer. This model has the advantage that the immunological synapse is aligned with the focal plane of the microscope. It further enables total internal reflection illumination, thereby significantly reducing intracellular background.
Our key publications
TCRs are randomly distributed on the plasma membrane of resting antigen-experienced T cells
Rossboth, B., A.M. Arnold, H. Ta, R. Platzer, F. Kellner, J.B. Huppa, M. Brameshuber, F. Baumgart, and G.J. Schütz. 2018. TCRs are randomly distributed on the plasma membrane of resting antigen-experienced T cells. Nature Immunology. 19:821-827, opens an external URL in a new window.
Single molecule localization microscopy (SMLM) and STED microscopy were used to study the spatial distribution of the TCR in the plasma membrane of resting T cells. Our data indicate a completely random distribution.
Monomeric TCRs drive T cell antigen recognition
Brameshuber, M., F. Kellner, B.K. Rossboth, H. Ta, K. Alge, E. Sevcsik, J. Göhring, M. Axmann, F. Baumgart, N.R.J. Gascoigne, S.J. Davis, H. Stockinger, G.J. Schütz, and J.B. Huppa. 2018. Monomeric TCRs drive T cell antigen recognition. Nature Immunology. 19:487–496, opens an external URL in a new window.
Previous experiments indicated higher TCR oligomers before activation, yet the approaches were rather indirect. We applied TOCCSL, single-molecule coincidence analysis, photon-antibunching-based FCS and FRET to revisit these findings. We observed purely monomeric TCR before activation, and even upon activation the mutual distances of TCR within microclusters were larger than the Förster distance of 5nm.
TCR-peptide-MHC interactions in situ show accelerated kinetics and increased affinity
Huppa, J.B., M. Axmann, M.A. Mörtelmaier, B.F. Lillemeier, E.W. Newell, M. Brameshuber, L.O. Klein, G.J. Schütz, and M.M. Davis. 2010. TCR-peptide-MHC interactions in situ show accelerated kinetics and increased affinity. Nature. 463:963-967, opens an external URL in a new window.
We used single molecule FRET between TCR and pMHC to measure the interaction lifetime directly in the immunological synapse. Up to fivefold faster interaction kinetics compared to in vitro systems using purified proteins were observed.
Phenotypic models of T cell activation
Lever, M., P.K. Maini, P.A. van der Merwe, and O. Dushek. 2014. Phenotypic models of T cell activation. Nat Rev Immunol. 14:619-629., opens an external URL in a new window
Comparison of different models describing T cell activation
Functional Anatomy of T Cell Activation and Synapse Formation
Fooksman, D.R., S. Vardhana, G. Vasiliver-Shamis, J. Liese, D. Blair, J. Waite, C. Sacristán, G. Victora, A. Zanin-Zhorov, and M.L. Dustin. 2010. Functional Anatomy of T Cell Activation and Synapse Formation. Annual Reviews of Immunology. 28:79-105, opens an external URL in a new window.
Nicely summarizes the concepts behind the immunological synapse between a T cell and an antigen-presenting cell.
Early T-cell signalling