UVB RADIATION SUPPRESSES THE TNF-ALPHA-INDUCED EXPRESSION OF E-SELECTIN AND ICAM-1 ON CULTURED HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS

Endothelial cells, which are involved in the development of inflammato ry and immune responses, can express various kinds of cell adhesion mo lecules (CAM) including E-selectin and intercellular adhesion molecule -1 (ICAM-1). These cell adhesion molecules and their ligands on leukoc ytes play an essential role in the control of extravasation of inflamm atory cells. Ultraviolet B (UVB) radiation can reach the upper dermis and modulate CAM expressions on vascular endothelial cells (EC). We ex amined the direct effect of UVB on E-selectin and ICAM-1 expression on cultured human umbilical vein endothelial cells (HUVEC) and also exam ined its effect on these cells induced by tumour necrosis factor-alpha (TNF-alpha), which is a potent CAM-inducer and is released by UVB rad iation on the skin. Various doses of UVB were exposed to human umbilic al vein endothelial cells (HUVEC) and these expressions were examined by flow cytometric analysis using FACScan; 5, 10 and 25 mJ/cm(2) UVB i nduced neither E-selectin nor ICAM-1 expression. Irradiation of HUVEC with UVB 30 min after treatment with TNF-alpha inhibited these express ions. Although the inhibition of E-selectin was observed until 12 h in a dose-dependent manner, ICAM-1 expression was almost completely inhi bited, even at 5 mJ/cm(2) UVB. UVB irradiation before TNF-alpha stimul ation showed similar effects to those obtained post-irradiation. This study has demonstrated that UVB can directly down-regulate EC function s, and the results may have implications in action mechanisms of UVB t herapy.