Signaling through CD50 (ICAM-3) stimulates T lymphocyte binding to human umbilical vein endothelial cells and extracellular matrix proteins via an increase in β1 and β2 integrin function

Regulated adhesion of T lymphocytes to antigen-presenting cells, endothelial cells and extracellular matrix proteins is crucial in T lymphocyte activation and migration to the sites of injury. In this study, we show that three monoclonal antibodies (mAb) recognizing different epitopes on the CD50 (ICAM-3) molecule increase T lymphocyte adhesion to tumor necrosis factor (TNF)-stimulated human umbilical vein endothelial cells and extracellular matrix proteins. These phenomena are mediated by an increase in β1 and β2 integrin avidity since (a) CD50-induced adhesion to endothelial cells was abrogated by simultaneous blocking of β1- and β2-mediated adhesion pathways but not by interfering with either one individually, (b) CD50 mAb increased β1 integrin-mediated adhesion to extracellular matrix proteins and to fibronectin-derived synthetic peptides, (c) CD50 mAb enhanced T lymphocyte binding to ICAM-1 transfectants, and (d) CD50 mAb did not modify surface expression patterns of β1 or β2 integrins on T lymphocytes. Our data suggest that constitutively expressed CD50 (ICAM-3) can play a pivotal role in initiating a cascade of adhesion events which may be crucial in immune activation and in the development of inflammatory lesions.