Investigating the active role of mechanical force during T-cell activation

The role of mechanical force has gained increasing interest in the field of cell biology owing to the realisation that cells are continually subject to stresses and strains induced by the cellular environment. Cells are known to be able to sense and react to forces imposed on them by their local environment as well as being able to directly impart force during motility, adhesion and cell division. This is also true for cells of the adaptive immune system, specifically during the intimate cell-cell interaction occurring between the T-cell and Antigen Presenting Cell (APC), known as the Immunological Synapse (IS). This highly selective process by which a T cell is able to bind, recognise and react to only foreign antigens has been the focus of intense study due to its crucial importance in the adaptive immune response. The actin cytoskeleton is known to play an essential role in the formation and maintenance of the IS, but questions remain regarding the influence of forces generated by actin during this process. With the aim of measuring mechanical force generated at the IS, we present a novel method combining the super resolution imaging technique, Stimulated Emission Depletion (STED) microscopy and Traction Force Microscopy (TFM). Using the tunable kinetics of the 1G4 Jurkat T-cell system in combination with high spatial and temporal resolution microscopy we demonstrate that actin dynamics at the IS is antigen dependent and show by TFM that force generation occurs on two distinct time scales during activation, mediated by the actin cytoskeleton. Together, the results highlight the intimate links between the dynamics of the actin cytoskeleton, force generation and the antigen response of T cells during activation.