Adhesion Between Human Neutrophils and Immobilized Endothelial Ligand Vascular Cell Adhesion Molecule 1: Divalent Ion Effects

Integrin-mediated adhesion of circulating neutrophils to endothelium during inflammation involves multiple adhesion molecules on both neutrophils and endothelium. Most studies of neutrophil adhesion have focused on adhesion to ICAM-1 (mediated by β₂ integrins), but interaction with the endothelial ligand vascular cell adhesion molecule 1 (VCAM-1) may also play a role in neutrophil adhesion to activated endothelium. In this study we demonstrate significant adhesion between neutrophils and VCAM-1 mediated by β₁ integrins, principally via α₄β₁ (VLA-4). We characterize the dynamics of adhesion in terms of rate constants for a two-step bond formation process, the first involving juxtaposition of active molecules with substrate and the second involving bond formation. The results indicate that the first step is rate limiting for VLA-4-VCAM-1 interactions. Changing divalent cation composition affects these coefficients, implicating molecular conformational changes as a key step in the process.