LATE AND PERSISTENT UP-REGULATION OF INTERCELLULAR-ADHESION MOLECULE-1 (ICAM-1) EXPRESSION BY IONIZING-RADIATION IN HUMAN ENDOTHELIAL-CELLSIN-VITRO

Adhesion molecules play a key role in cellular traffic through vascula r endothelium, in particular during the inflammatory response when leu kocytes migrate from blood into tissues. Since inflammation is one of the major consequences of radiation injury, we investigated the effect of ionizing radiation on cell-surface expression of the intercellular adhesion molecule-1 (ICAM-1), the vascular cell adhesion molecule-1 ( VCAM-1) and E-selectin in cultured human umbilical Vein endothelial ce lls (HUVEC). Flow cytometry performed on irradiated HUVEC revealed bot h a time- (from 2 to 10 days) and dose- (from 2 to 10 Gy) dependent up -regulation of basal expression of ICAM-1, and no induction of VCAM-1 or E-selectin. The radiation-induced increase in ICAM-1 expression on HUVEC was correlated with augmented adhesion of neutrophils on irradia ted endothelial cells. Interleukin-6 (IL-6) or other soluble factors r eleased by irradiation were not involved in the enhanced ICAM-1 expres sion by irradiation. Northern blot analysis showed an overexpression o f ICAM-1 mRNA from 1 to 6 days after a 10 Gy exposure. Our data sugges t that ICAM-1 participates in the radiation-induced inflammatory react ion of the endothelium.