Irradiation induced expression of CD31, ICAM-1 and VCAM-1 in human microvascular endothelial cells

The adherence and migration of leukocytes through the endothelium of blood vessels is an important Early event which occurs in normal tissues followin g ionizing irradiation but the underlying mechanisms ale not fully understo od. ICAMI-1/CAM-1 anti CD31 are membrane proteins of endothelial cells, med iate this process when the vasculature is exposed to other inflammatory sti muli. In this study, expression of ICAM-1, VCAM-1 and CD31 on human dermal microvascular endothelial cells (HDMECs) at 72 hours post-irradiation risin g flow cytometry ann northern analysis was determined. Dose-dependent incre ases in surface expression and mRNA of ICAM-1 and CD31 were observed. In co ntrast VCAM-1 was practically undetectable on both control and irradiated H DMECs but was strongly expressed in TNF-alpha activated positive control HD MECs. The upregulation in ICAM-1 and CD31 was independent of radiation-indu ced changes in cell size number and cell cycle stage. We suggest that ICAM- 1 is active over a prolonged period whereas VCAM-1 acts only transiently in lenkocyte-endothelial interactions in the irradiated microvasculature. The late upregulation of CD31 is a novel finding and may have a function in ra diation-induced leukocyte extravasation, platelet adherence to the vascular wall and abnormal endothelial cell proliferation. Both ICAM-1 and CD31 see m to be therapeutic targets for. the amelioration of radiation-induced norm al tissue damage.