DIRECT INTERACTION WITH PRIMED CD4+ CD45R0+ MEMORY LYMPHOCYTES-T INDUCES EXPRESSION OF ENDOTHELIAL LEUKOCYTE ADHESION MOLECULE-1 AND VASCULAR CELL-ADHESION MOLECULE-1 ON THE SURFACE OF VASCULAR ENDOTHELIAL-CELLS

The process of recruitment of leukocytes at sites of inflammation involves direct cell-to-cell interactions between leukocytes and vascular endothelial cells (EC) mediated by various adhesion receptors on leukocytes and their inducible endothelial ligands. In this study we have examined the induction on EC of endothelial leukocyte adhesion molecule-1 (ELAM-1), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) upon their interaction with subpopulations of human T cells. When co-cultured with EC both resting CD4+ T and CD8+ T cells caused a modest increase in the expression of endothelial ICAM-1. Moreover, resting CD4+ but not CD8+ T cells induced expression of ELAM-1 and VCAM-1 on a small fraction of unstimulated EC. Prior activation with phorbol 12-myristate 13-acetate (PMA) significantly increased the ability of T cells to up-regulate endothelial ICAM-1 and also induced the expression of both ELAM-1 and VCAM-1. PMA-primed CD4+ T cells induced both VCAM-1 and ELAM-1 on EC more efficiently than CD8+ T cells. Furthermore, the ability to induce the expression of ELAM-1 and VCAM-1 was confined to the CD4+CD45R0+ memory/primed subpopulation of T cells. This induction of various endothelial adhesion ligands could also be mediated by antigen-primed CD4+ T cell lines. The CD4+ T cell-mediated induction of adhesion ligands required direct intercellular contact with EC because neither cultures of EC and PMA-primed CD4+ T cells separated by a microporous membrane insert nor the conditioned medium of PMA-primed T cells induced expressio of ELAM-1 and VCAM-1 on EC. Cyclosporin A significantly inhibited the activation of T cells with PMA but had no effect on the ability of PMA-primed T cells to up-regulate endothelial CAM. Thus, CD4+CD45R0+ T cells via as yet unknown mechanism can significantly enhance the expression of each of the three endothelial adhesion ligands and, thereby, may facilitate the process of recruitment of additional leukocytes to exacerbate inflammation.