Phagocytosis, the uptake of external objects, such as bacteria is a key function of immune cells. It is a process that is driven by a deformation of the cell membrane with the aim of engulfing the target. The signaling pathways that drive phagocytosis have been extensively studied but little is known about the inherent mechanical aspects. We study the mechanics of phagocytosis by measuring the time-resolved changes of the membrane stiffness around a particle that acts as a phagocytic target. We use magnetic microparticles coated with immunoglobulin G to trigger phagocytosis upon binding. To quantify the translational and rotational motion of the magnetic particles, we tag them with fluorescent fiduciary markers. We exert a mechanical torque on the particles by applying a modulating magnetic field and simultaneously measure the rotational and translational particle displacements to quantify the mechanical properties of the binding site. Our measurements show an irreversible stiffening of the contact site by at least a factor five within a time span of a few hundred seconds. We hypothesize that the observed increase in stiffness originates from the cell membrane wrapping around the particle. By considering the energy of a deformed membrane, we describe the size of the phagocytic cup as a function of the measured stiffness. Our technique provides a new tool to quantitatively study the dynamics of membrane processes such as phagocytosis.
|Title of host publication||Proceedings of the 76th Annual Meeting of the German Physical Society, 25-30 March 2012, Berlin, Germany|
|Publication status||Published - 2012|
|Event||conference; the 76th Annual Meeting of the German Physical Society, 25-30 March 2012, Berlin, Germany; 2012-03-25; 2012-03-30 - |
Duration: 25 Mar 2012 → 30 Mar 2012
|Conference||conference; the 76th Annual Meeting of the German Physical Society, 25-30 March 2012, Berlin, Germany; 2012-03-25; 2012-03-30|
|Period||25/03/12 → 30/03/12|
|Other||the 76th Annual Meeting of the German Physical Society, 25-30 March 2012, Berlin, Germany|