Slings enable neutrophil rolling at high shear

Most leukocytes can roll along the walls of venules at low shear stress (1 dyn cm ^-2), but neutrophils have the ability to roll at tenfold higher shear stress in microvessels in vivo. The mechanisms involved in this shear-resistant rolling are known to involve cell flattening and pulling of long membrane tethers at the rear. Here we show that these long tethers do not retract as postulated, but instead persist and appear as slings at the front of rolling cells. We demonstrate slings in a model of acute inflammation in vivo and on P-selectin in vitro, where P-selectin-glycoprotein-ligand-1 (PSGL-1) is found in discrete sticky patches whereas LFA-1 is expressed over the entire length on slings. As neutrophils roll forward, slings wrap around the rolling cells and undergo a step-wise peeling from the P-selectin substrate enabled by the failure of PSGL-1 patches under hydrodynamic forces. The step-wise peeling of slings is distinct from the pulling of tethers reported previously. Each sling effectively lays out a cell-autonomous adhesive substrate in front of neutrophils rolling at high shear stress during inflammation.