LAUSR

T cells screen the surfaces of antigen presenting cells (APC) for peptides originating from potentially harmful foreign matter in order to trigger an immunological response if necessary. The pivotal interaction in this process takes place between the T cell receptor (TCR) and peptide-presenting MHC (pMHC) complexes. It enables the T cell to detect even very subtle differences in the antigenic peptides while at the same time only very low densities of agonistic pMHCs are required to cause T cell signaling. Little is known about the precise mechanisms behind this exceptional sensitivity and specificity, but recent findings suggest that mechanical forces play an important role.In order to gain further insights, we develop a force sensor for insertion in the immunological synapse, the site of interaction between T cells and APCs. A short peptide forms the core of this sensor, acting as a molecular spring. Depending on the amount of force exerted by the cells, the end-to-end distance of the peptide will change. The peptide carries one fluorophore at each end, chosen such that the fluorophores constitute a FRET pair. Therefore the change in distance can be detected with nanometer precision by means of fluorescence microscopy.After calibration of the sensor, we will have a tool that will enable us, among other things, to measure molecular forces between T cells and APCs, to correlate forces and T cell activation, and to create high resolution force maps of the immunological synapse. Preliminary data demonstrating the validity of the approach will be presented.