Mechanical Forces in T-Cell Recognition and Signaling

The project Mechanical Forces in T-Cell Antigen Recognition addresses T-cell antigen recognition, a process of fundamental importance for adaptive immunity. Functional integrity of antigen recognition is of utmost importance, since T-cells recognize and kill infected cells, and help B-cells in the production of antibodies neutralizing pathogens. For the specific interaction of a T-cell with its target cell, specialized surface molecules are needed, namely the T-cell receptor (TCR) on the T-cell and the MHC on the target cell. The MHC is capable of presenting different fragments of molecules originating from pathogens or healthy cellular components. As soon as a T-cell recognizes a pathogen-derived fragment, it issues a defense response. There is now increasing evidence that mechanical forces acting on TCRs are instrumental for this process, rendering them very interesting for academic research and relevant for medical applications, e.g. cancer immunotherapies. The proposed project will determine the impact of such forces by directly reading out a molecular force sensor at the base of the MHC, anchored to an artificial or natural cell surface. As soon as the T-cell receptor binds to the MHC, the force sensor registers any applied strain. The sensor consists of a spring which extends to a certain degree under force. The distance separating the ends of the spring can be precisely measured by single molecule microscopy: If attached to the respective ends of the spring and illuminated by laser light, one fluorescent dye transfers parts of its light energy to the second dye, but only when it is close by. The efficiency of this light energy transfer process is strictly dependent on the distance of the two participating dyes. Eventually, it is possible to calculate the force necessary to extend the spring to the observed degree. The molecular force sensor used here has an extraordinary high resolution (1-12 pico-Newton), and can be detected by single molecule microscopy in real time in living cells. Using this sensor I was able to directly observe mechanical forces exerted by T-cells. Based on these results, I now wish to address following questions in the proposed project: (i) Do TCR-imposed forces become modulated by other accessory surface molecules? (ii) Are such forces required for the activation of T-cells? (iii) Do mechanical forces improve or worsen the discrimination capabilities of the T-cells for the MHC- presented fragments? In order to answer these question, I will employ highly resolving microscopy which allows me to look at the behavior of single molecules present in the T-cell:APC contact. I expect to advance our understanding regarding the mechanisms underlying the phenomenal sensitivity of T-cells towards antigens, which is critical to accelerate the development of better and more versatile T-cell-based immunotherapies targeting autoimmune diseases, allergy and cancer.

"The Gentle Tip-Toe of T-Cells: Mastering Immune Precision" Our immune system relies on a set of powerful defenders called T-cells, which play a central role in identifying and responding to harmful invaders, such as viruses and bacteria. These immune warriors can detect even the smallest differences between dangerous foreign particles and the body's own cells, a skill essential to preventing disease while avoiding attacks on healthy tissue. But how do T-cells achieve this level of precision? Scientists have long believed that the forces exerted by T-cells during target recognition could help them distinguish between threats and harmless elements. However, the mechanics of this process have remained a mystery. Our research team set out to uncover whether these forces are strong enough to influence how T-cells recognize and respond to foreign particles. We developed an experimental approach using cutting-edge techniques to measure the pulling forces T-cells apply when interacting with target molecules. Our findings revealed that these forces are surprisingly weak and infrequent, averaging less than 5 piconewtons-an extremely gentle tug. Importantly, only a small fraction of these interactions involved detectable forces, suggesting that T-cells rarely rely on physical pulling to assist in identification. Moreover, we explored how varying the strength of these forces affected the duration of molecular interactions, or bond lifetimes, between T-cells and their targets. Contrary to popular theories, we found that changes in pulling force had no impact on these bond lifetimes. Even when we adjusted the conditions to increase or decrease force, the T-cells maintained stable interactions with their targets. This groundbreaking discovery challenges the current understanding of how T-cells perform their duties. Rather than using force to enhance recognition, T-cells seem to create a stable, controlled environment that protects against mechanical disturbances. By doing so, they can focus on detecting bond lifetimes accurately-a critical factor in distinguishing between genuine threats and the body's own cells. These insights lead to new avenues for research into immune function and has far-reaching implications for developing treatments for autoimmune diseases and enhancing immune therapies. Understanding how T-cells achieve such precise recognition without relying on force may inspire innovative strategies to modulate immune responses in various medical applications. Our study provides a fresh perspective on the elegant and precise mechanisms T-cells use to keep our immune system functioning effectively and highlights the complexity of our body's natural defence strategies.