Mononuclear cell adhesion and cell adhesion molecule liberation after X-irradiation of activated endothelial cells in vitro

Purpose: Increased expression of cell adhesion molecules on endothelial cells is an important early event in inflammation. Low-dose radiotherapy is very effective anti-inflammatory treatment. The hypothesis that it may act by modulation of cell adhesion molecule expression in activated endothelial cells and the subsequent adhesion of mononuclear cells onto the activated endothelial cells was tested. Materials and methods: EA.hy.926 endothelial cells were irradiated with 0.3-10 Gy X-rays at different times before or after stimulation with TNFalpha. ICAM-1 E-selectin expression was measured by ELISA and FACS. Isolated peripheral blood mononuclear cells were incubated with an activated and irradiate confluent monolayer of endothelial cells 4 h. 12 h or 24 h after stimulation, and adhesion was determined in dynamic and static adhesion assays. Results: In the static adhesion assay, where integrin-mediate adhesion dominates, radiation doses of 0.3-0.6 Gy reduced the adhesion of mononuclear cells onto EA.hy.926-EC in vitro by 25-40% and 15-25% of the control level 4 h and 21 h after stimulation, respectively, but increased adhesion 12 h after stimulation. In the dynamic adhesion assay, where selectin-mediated adhesion dominates, radiation doses of 0.3-0.6 Gy reduced the adhesion events by 40 50% and 30 40% of the control level 4 h and 24 h after stimulation, respectively, and again increased adhesion 12 h after stimulation. X-ray doses of less than or equal to5 Gy did not induce ICAM-1 expression, or modulate TNFalpha-induced ICAM-1 expression. E-selectin expression was, however, increased in a dose-dependent way 6 h after irradiation. In contrast, X-irradiation 2-5 h before stimulation decreased the characteristic transient expression of E-selectin after TNFalpha stimulation. Conclusions: Modulation of E-selectin liberation on activated endothelial cells may be one mechanism to decrease leukocyte adhesion after low-dose irradiation in vitro, and could be involved in the therapeutic action of anti-inflammatory radiotherapy.