Organized spatial patterns of activated β2 integrins in arresting neutrophils

The transition from leukocyte rolling to firm adhesion is called arrest. Beta2 integrins are required for neutrophil arrest. Chemokines can trigger neutrophil arrest in vivo and in vitro. Resting integrins exist in a bent-closed conformation, i.e., not extended (E-) and not high affinity (H-), unable to bind ligand. Electron microscopic images of isolated beta2 integrins in open and closed conformations inspired the switchblade model of integrin activation from E-H- to E+H- to E+H+. Recently, 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 exist. 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 E+H+ beta2 integrin molecules.