Activated lymphocytes promote endothelial cell detachment from matrix: A role for modulation of endothelial cell beta(1) integrin affinity

In vivo, MHC class I-restricted injury of allogeneic tissue or cells infect ed by intracellular pathogens occurs in the absence of classical cytolytic effector mechanisms and Ab. Modulation of the target cell adhesion to matri x may be an additional mechanism used to injure vascular or epithelial cell s in inflammation. We studied the mechanisms of human umbilical vein endoth elial cell (EC) detachment from matrix-coated plastic following contact by concanamycin A-treated lymphocytes as an in vitro model of perforin-indepen dent modulation of EC basement membrane adhesion. Human PBL were depleted o f monocytes, stimulated, then added to an EC monolayer plated on either fib ronectin or type I collagen matrices. Activated, but not resting, PBL induc ed progressive EC detachment from the underlying matrix. Injury of the EC m onolayer required direct cell contact with the activated lymphocytes becaus e no detachment was seen when the PBL were placed above a Transwell membran e. Moreover plasma membranes prepared from activated but not resting PBL in duced EC detachment. Adherent EC stimulated with activated PBL did not show evidence of apoptosis using TUNEL and annexin V staining at time points be fore EC detachment was observed. Finally, neither the matrix metalloprotein ase inhibitors o-phenanthroline and BB-94 nor aprotinin blocked EC detachme nt. However, activation of EC beta(1) integrin using mAb TS2/16 or Mg2+ dec reased EC detachment. These data indicate that cell-cell contact between ac tivated PBL and EC reduces adhesion of EC to the underlying matrix, at leas t in part by inducing changes in the affinity of the endothelial beta(1) in tegrin.