Neutrophils can adhere via α4β1-integrin under flow conditions

Abstract

In this study we investigated the possibility that an alternative pathway exists for neutrophil recruitment, namely an α4β1-dependent pathway. A parallel plate chamber was used to investigate whether neutrophils could tether, roll, and adhere to tumor necrosis factor α (TNPα)-stimulated endothelium via α4β1, α4β1-integrin was induced on neutrophils using dihydrocytochalasin B and either an endogenous (endothelial-derived) chemotactic agent or an exogenous chemotactic molecule. α4β1-expressing neutrophils could stably adhere under shear force (2 dyne/cm2) to TNFα- stimulated endothelium independent of the β2 -integrin. The firm adhesion was entirely abolished by antibodies directed against either the α4 or β1-integrin subunits. However, the rolling interaction was not dependent on α4β1 but was abolished by antiselectin therapy. Neutrophils expressing αα4β1 could also tether to the endothelium in the presence of antiselectin therapy, but at shear stresses less than 2 dyne/cm2, α4β1 expressing neutrophils also tethered to and stably adhered (no rolling) to VCAM-1- but not to ICAM-l-transfected L cells. The interaction only occurred at shear stress less than 2 dyne/cm2. A cell line (Ramos) known to express high quantities of α4β1-integrin interacted with VCAM-l-transfected L cells at very similar shear conditions. α4β1-expressing neutrophils were also able to adhere to a second α4-integrin ligand, fibronectin; however, this interaction only occurred under static conditions. These data suggest that, under certain conditions, neutrophils can adhere independently of the β2-integrin pathway and adhere via the α4β1-integrin. This study refutes the concept that α4β1-integrin adhesion is restricted to mononuclear leukocytes and is not functional on human neutrophils.