Phosphatidylserine-dependent adhesion of T cells to endothelial cells

Phosphatidylserine (PS) was exposed at the surface of human umbilical vein endothelial cells (HUVECs) and cultured cell lines by agonists that increas e cytosolic Ca2+, and factors governing the adhesion of T cells to the trea ted cells were investigated. Thrombin, ionophore A23187 and the Ca2+-ATPase inhibitor 2,5-di-tert-butyl-1,4-benzohydroquinone each induced a PS-depend ent adhesion of Jurkat T cells. A23187, which was the most effective agonis t in releasing PS-bearing microvesicles, was the least effective in inducin g the PS-dependent adhesion of Jurkat cells. Treatment of ECV304 and EA.hy9 26 cells with EGTA, followed by a return to normal medium, resulted in an i nflux of Ca2+ and an increase in adhering Jurkat cells. Oxidised low-densit y lipoprotein induced a procoagulant response in cultured ECV304 cells and increased the number of adhering Jurkat cells, but adhesion was not inhibit ed by pretreating ECV304 cells with annexin V. PS was not significantly exp osed on untreated Jurkat cells, as determined by flow cytometry with annexi n V-FITC. However, after adhesion to thrombin-treated ECV304 cells for 10 m in followed by detachment in 1 mM EDTA, there was a marked exposure of PS o n the Jurkat cells. Binding of annexin V-FITC to the detached cells was inh ibited by pretreating them with unlabelled annexin V. Contact with thrombin -treated ECV304 cells thus induced the exposure of PS on Jurkat cells and, as Jurkat cells were unable to adhere to thrombin-treated ECV304 cells in t he presence of EGTA, the adhesion of the two cell types may involve a Ca2bridge between PS on both cell surfaces. The number of T cells from normal, human peripheral blood that adhered to ECV304 cells was not increased by t reating the latter with thrombin. However, findings made with several T cel l lines were generally, but not completely, consistent with the possibility that adhesion to surface PS on endothelial cells may be a feature of T cel ls that express both CD4+ and CD8+ antigens. Possible implications for PS-d ependent adhesion of T cells to endothelial cells in metastasis, and early in atherogenesis, are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.