Shear-induced capping of l-selectin on the neutrophil surface during centrifugation

l-selectin on leukocytes is critical in leukocyte tethering and adhesion to inflamed endothelium and lymphocyte homing to lymphoid organs. The spatial distribution of l-selectin on leukocytes controls cellular adhesive function in hydrodynamic shear. How l-selectin changes its position on the cell membrane remains an open question, but a possible candidate is shear stress encountered on the cell surface. Here we demonstrate shear-induced l-selectin polarization on the membrane during the process of centrifugation of resting neutrophils via immunofluorescent microscopy. It was found that randomly distributed l-selectin on neutrophils moves to a polar cap at one end of the cell after centrifugation (300 ×g for 2 min) without inflammatory stimuli. This l-selectin redistribution under shear was predicted by Monte Carlo simulations that show how convection dominates over diffusion, leading to l-selectin cap formation during centrifugation at 280 ×g or during leukocyte adhesion to the endothelial wall at 1 dyn/cm2. Those results point to a role for shear stress in the modulation of l-selectin distribution, and suggest a possible alternate mechanism and reinterpretation of previous in vitro studies of l-selectin mediated adhesion of neutrophils isolated via centrifugation.