Tether formation.

Video micrographs show tether formation from a marrow reticulocyte (left column) and a normoblast (right column). The top images show the cell morphology and the resting position of the cantilever. As the cells are withdrawn, the cantilever deflects, providing a measure of the force (middle panels). When the force gets big enough, the surface yields, and a strand of membrane is pulled out between the cell and its attachment site on the bead. After a length of 10 to 30 μm is reached, the cell is held stationary and the force on the tether is allowed to relax to a steady value (bottom panels).