Dynamic shifts in LFA-1 affinity regulate neutrophil rolling, arrest, and transmigration on inflamed endothelium.

Polymorphonuclear leukocyte (PMN) recruitment to vascular endothelium during acute inflammation involves cooperation between selectins, G-proteins, and beta2-integrins. LFA-1 (CD11a/CD18) affinity correlates with specific adhesion functions because a shift from low to intermediate affinity supports rolling on ICAM-1, whereas high affinity is associated with shear-resistant leukocyte arrest. We imaged PMN adhesion on cytokine-inflamed endothelium in a parallel-plate flow chamber to define the dynamics of beta2-integrin function during recruitment and transmigration. After arrest on inflamed endothelium, high-affinity LFA-1 aligned along the uropod-pseudopod major axis, which was essential for efficient neutrophil polarization and subsequent transmigration. An allosteric small molecule inhibitor targeted to the I-domain stabilized LFA-1 in an intermediate-affinity conformation, which supported neutrophil rolling but inhibited cell polarization and abrogated transmigration. We conclude that a shift in LFA-1 from intermediate to high affinity during the transition from rolling to arrest provides the contact-mediated signaling and guidance necessary for PMN transmigration on inflamed endothelium.