Fig. 1. Time evolution of formation of protrusion of macrophage induced by application of an external force pulse with an amplitude of 2 nN and 90 seconds duration. The phase contrast images (A,B) correspond to the beginning and the end of the pulse. The position of the magnetic tweezers in the direction of the force is plotted as a function of time. The inset shows the initial state of the deformation at higher time resolution to expose the initial elastic response more clearly.