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

Objective: Upregulation of adhesion molecules on endothelial cells followin g irradiation has been shown, but the functional significance of this upreg ulation in various endothelial cells lines is not clear. We have developed an in vitro flow model to study the functional consequences of the radiatio n-induced upregulation of E-selection and intercellular adhesion molecule ( ICAM-1). Methods: Human dermal microvascular endothelial cells (HDMEC), human umbili cal vein endothelial cells (HUVEC), or transformed human microvascular endo thelial cells (HMEC-1) were grown in 35-nm dishes and irradiated with a sin gle does 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/cm(2). Flow cytometry was used t o quantify the expression of E-selectin and ICAM-1 on the various endotheli al cells. Results: Flow cytomeric analysis revealed an upregulation of ICAM-1 express ion on all three cell types postirradiation (post-IR), and an upregulation of E-selection 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 roll ing and firmly adherent HL-60 cells on post-IR HDMEC at shear stress less t han or equal to 1.5 dynes/cm(2); pretreatment of control and irradiated HDM EC with antibodies to E-selectin and ICAM-1 significantly diminished the nu mber of rolling and firmly adherent HL-60 cells, respectively. No rolling o r firm adhesion of HL-60 cells was observed on HUVEC or HMEC-1 monolayers p ost-IR. Conclusion: These findings suggest that ICAM-1 is upregulated on irradiated HDMEC, HUVEC and HMEC-1. E-selectin is upregulated to a function level onl y on irradiated HDMEC, and not on irradiated HUVEC or HMEC-1.