We study immune reactions at the single-cell level and we have shown that when a white blood cell (or leukocyte) contacts another cell to attack it or exchange information, the former becomes much stiffer and more viscous within minutes. Studying these mechanical changes in immune cells can help scientists better understand the mechanism by which immune cells identify threats such as cancer cells. Many aspects of the mechanical properties of immune cells remain unclear and require further characterization. This internship will contribute to this characterization. Using a microindentation technique, we can measure the tension of the actomyosin cortex underlying the cell membrane, which can fluctuate over time. We will ask whether these fluctuations are used by leukocytes to sense their environment and whether they can help them to react faster to stimuli brought by other cells. Another question is motivated by preliminary data showing that pressing a T lymphocyte (a leukocyte at the core of immune response) with an adhesive microsphere leads to an apparent higher stiffness of the leukocyte than when the microsphere is not adherent. This effect might be either purely due to adhesive vs. non-adhesive boundary conditions, or might be a signature of a rapid mechanical response of the cell to adhesion. We will address this question by producing sets of microbeads with controlled adhesive strength and by inhibiting specific molecular components of the cell cytoskeleton.