Expression and functional significance of adhesion molecules on cultured endothelial cells in response to ionizing radiation.

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Upregulation of adhesion molecules on endothelial cells following irradiation has been shown, but the functional significance of this upregulation in various endothelial cell lines is not clear. We have developed an in vitro flow model to study the functional consequences of the radiation-induced upregulation of E-selectin and intercellular adhesion molecule (ICAM-1). Human dermal microvascular endothelial cells (HDMEC), human umbilical vein endothelial cells (HUVEC), or transformed human microvascular endothelial cells (HMEC-1) were grown in 35-mm dishes and irradiated with a single dose of 10 Gy. HL-60 (human promyelocytic leukemia) cells were perfused over the irradiated endothelial cells in a parallel plate flow chamber at shear stress ranging from 0.5 to 2.0 dynes/cm2. Flow cytometry was used to quantify the expression of E-selectin and ICAM-1 on the various endothelial cells. Flow cytomeric analysis revealed an upregulation of ICAM-1 expression on all three cell types postirradiation (post-IR), and an upregulation of E-selectin expression only on HDMEC post-IR. E-selectin expression was detected on control HDMEC, but at a lower level than that detected on post-IR HDMEC. Flow assays revealed a significant increase in the number of rolling and firmly adherent HL-60 cells on post-IR HDMEC at shear stress < or =1.5 dynes/cm2; pretreatment of control and irradiated HDMEC with antibodies to E-selectin and ICAM-1 significantly diminished the number of rolling and firmly adherent HL-60 cells, respectively. No rolling or firm adhesion of HL-60 cells was observed on HUVEC or HMEC-1 monolayers post-IR. These findings suggest that ICAM-1 is upregulated on irradiated HDMEC, HUVEC, and HMEC-1. E-selectin is upregulated to a functional level only on irradiated HDMEC, and not on irradiated HUVEC or HMEC-1.