The result of such is that selectins exhibit catch and slip bond behavior—under low shear stresses, their bonding affinities are actually increased by an increase in tensile force applied to the bond because of more selectins preferring the ‘open’ conformation. At high stresses, the binding affinities are still reduced because the selectin-ligand bond is still a normal slip bond. It is thought that this shear stress threshold helps select for the right diameter of blood vessels to initiate leukocyte extravasation, and may also help prevent inappropriate leukocyte aggregation during vascular stasis.[12]