High-Affinity Bent β-Integrin Molecules in Arresting Neutrophils Face Each Other through Binding to ICAMs In cis.

Leukocyte adhesion requires β-integrin activation. Resting integrins exist in a bent-closed conformation-i.e., not extended (E) and not high affinity (H)-unable to bind ligand. Fully activated EH integrin binds intercellular adhesion molecules (ICAMs) expressed on the opposing cell in trans. EH transitions to EH through EH or through EH, which binds to ICAMs on the same cell in cis. Spatial patterning of activated integrins is thought to be required for effective arrest, but no high-resolution cell surface localization maps of activated integrins exist. Here, we developed Super-STORM by combining super-resolution microscopy with molecular modeling to precisely localize activated integrin molecules and identify the molecular patterns of activated integrins on primary human neutrophils. At the time of neutrophil arrest, EH integrins face each other to form oriented (non-random) nanoclusters. To address the mechanism causing this pattern, we blocked integrin binding to ICAMs in cis, which significantly relieved the face-to-face orientation.