Julien Husson (LadHyX, École Polytechnique, Palaiseau). Mechanics of leukocyte activation.

Leukocytes perform diverse functions, including killing, phagocyting other cells, or forming immunological synapses. While activating, leukocytes generate forces and change their mechanical properties. We have developed a micropipette-based rheometer to quantify these forces and time-dependent viscoelastic properties. We activate leukocytes with an anti-coated microbead. A flexible micropipette is used as a force sensor that the leukocyte can bend by exerting pN to nN- forces1-4. We exert a small oscillatory compressive force on the leukocyte and record its deformation to access its stiffness and viscosity.

We show that viscoelastic properties of T lymphocytes, B lymphocytes, and neutrophils change drastically during the first minutes of activation. Mechanical changes start within the first seconds following contact with an activating microbead, preceding cell morphological changes. We show that activating leukocytes have a specific mechanical signature during activation.  A detailed characterization of time-dependent leukocyte mechanics will help better understanding immune response, including antitumoral response.