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

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Abstract
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.