Organized spatial patterns of activated β2integrins in arresting neutrophils

The transition from leukocyte rolling to firm adhesion is called arrest. β2integrins are required for neutrophil arrest1. Chemokines can trigger neutrophil arrest in vivo2and in vitro3. Resting integrins4exist in a “bent-closed” conformation, i.e., not extended (E−) and not high affinity (H−), unable to bind ligand. Electron microscopic images of isolated β2integrins in “open” and “closed” conformations5inspired the switchblade model of integrin activation from E−H−to E+H−to E+H+67. Recently8, we discovered an alternative pathway of integrin activation from E−H−to E−H+to E+H+. Spatial patterning of activated integrins is thought to be required for effective arrest, but so far only diffraction-limited localization maps of activated integrins exist8. Here, we combine superresolution microscopy with molecular modeling to identify the molecular patterns of H+E−, H−E+, and H+E+activated integrins on primary human neutrophils. At the time of neutrophil arrest, E+H+integrins form oriented (non-random) nanoclusters that contain a total of 4,625±369 E+H+β2integrin molecules.