Distribution of tractional stresses in a migrating neutrophil. (A) A time series of images showing a neutrophil migrating chemokinetically to the right on a 10-kPa gel. The DIC images show that the cell has moved over a full body length in 300 seconds (supplemental Video 2). The images to the right of the DIC images are the corresponding traction images for those time points. The white outline over the traction images represents the approximate boundary as determined from the DIC images. The largest stresses occurred in the posterior of the neutrophil, a feature independent of gel stiffness. The full series of images for this particular example can be seen in supplemental Video 3. (B) A larger version of the last traction image in the series from panel A is shown. The white arrows represent the overall direction and magnitude of the applied tractional stresses. The few large tractions in the center of the cell were balanced by more numerous small tractions in the surrounding areas.