Lymphocytes bound at endothelial cell junctions extravasate within minutes. Lymphocyte-endothelial cell binding is mediated by receptors such as vascular cell adhesion molecule 1 (VCAM-1). VCAM-1 activates endothelial cell nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in minutes, and this activity is required for VCAM-1-dependent lymphocyte migration. In this report, we examined mechanisms for activation of matrix metalloproteinases (MMPs) during VCAM-1-dependent lymphocyte migration. Lymphocyte binding to VCAM-1 rapidly activated endothelial cell-associated MMPs. Furthermore, inhibition of MMPs on the endothelial cells but not on the lymphocytes blocked VCAM-1-dependent lymphocyte migration across endothelial cells. The activation of endothelial cell MMPs required VCAM-1-stimulated endothelial cell NADPH oxidase activity as determined by scavenging of reactive oxygen species (ROS) and by pharmacologic or antisense inhibition of NADPH oxidase. Exogenous addition of 1 microM H(2)O(2), the level of H(2)O(2) generated by VCAM-1-stimulated endothelial cells, rapidly activated endothelial cell-associated MMPs. In contrast, activation of lymphocyte-associated MMPs was delayed by hours after binding to VCAM-1, and this activation was blocked by inhibition of endothelial cell ROS generation. There was also a delay in H(2)O(2)-induced decrease in lymphocyte-associated tissue inhibitors of metalloproteinases (TIMPs), resulting in an increase in MMP/TIMP ratio. In summary, this is the first report of a mechanism for ROS function in VCAM-1 activation of endothelial cell MMPs during VCAM-1-dependent lymphocyte migration.