Chemoattractant Signals and β2 Integrin Occupancy at Apical Endothelial Contacts Combine with Shear Stress Signals to Promote Transendothelial Neutrophil Migration

Lymphocyte transendothelial migration (TEM) is promoted by fluid shear signals and apical endothelial chemokines. Studying the role of these signals in neutrophil migration across differently activated HUVEC in a flow chamber apparatus, we gained new insights into how neutrophils integrate multiple endothelial signals to promote TEM. Neutrophils crossed highly activated HUVEC in a β 2 integrin-dependent manner but independently of shear. In contrast, neutrophil migration across resting or moderately activated endothelium with low-level β 2 integrin ligand activity was dramatically augmented by endothelial-presented chemoattractants, conditional to application of physiological shear stresses and intact β 2 integrins. Shear stress signals were found to stimulate extensive neutrophil invaginations into the apical endothelial interface both before and during TEM. A subset of invaginating neutrophils completed transcellular diapedesis through individual endothelial cells within 2 integrins by adherent neutrophils can mediate TEM only if properly coupled to stimulatory shear stress and chemoattractant signals transduced at the apical neutrophil-endothelial interface.