Shear forces and high affinity LFA-1 drive PMN recruitment (102.18)

Abstract

Abstract Acute inflammation triggers the innate immune response of neutrophils that efficiently traffic from the blood stream to concentrate at high numbers at the site of tissue infection or wounding. A gatekeeper in this process is activation of β2-integrins, which forms bond clusters with ICAM-1 on the endothelial surface. These bond clusters serve dual functions of providing adhesive strength to anchor neutrophils under the shear forces of blood flow and directional guidance for cell polarization and subsequent transmigration on inflamed endothelium. We hypothesized that shear forces transmitted through high affinity LFA-1 facilitates their cooperation with the calcium release activated channel (CRAC) Orai1 in directing localized cytoskeletal activation and directed migration. Employing vascular mimetic microfluidic channels we observed neutrophils arresting on a substrate of either ICAM-1 or allosteric antibodies that stabilize a high or low affinity conformation of LFA-1. Neutrophils captured via low affinity LFA-1 did not exhibit intracellular calcium flux, F-actin polymerization, cell polarization, or directional migration under shear flow. In contrast, high affinity LFA-1 provided orientation along a uropod-pseudopod axis that required calcium flux through Orai1. We demonstrate how the shear stress of blood flow can transduce distinct outside-in signals at focal sites of high affinity LFA-1 that provides contact mediated guidance for neutrophil emigration.