Primary graft dysfunction is a major complication of orthotopic liver transplantation, and hepatic ischemic reperfusion injury is considered to be its major determinant cause. Although oxygen free radicals play an important role, leukocytes, cytokines, and adhesion molecules also contribute to hepatic ischemic reperfusion injury. Prostaglandin E1 (PGE1) has been shown to protect against impairment and dysfunction of transplanted livers in various experimental models as well as in clinical liver transplantation. In this study, the role of PGE1 on leukocyte adherence and transendothelial migration was investigated in cultured human liver vascular endothelial cells (HLVEC). Our results indicated that stimulated, but not resting, leukocytes exhibited high adhesion and transmigration capacity. HLVEC incubated with tumor necrosis factor (TNF) promoted leukocyte adherence and transendothelial migration. PGE1 inhibited leukocyte adherence to HLVEC when it was preincubated with either HLVEC or leukocytes. Moreover, PGE1 also suppressed stimulated leukocyte transendothelial migration in a dose-dependent manner. The inhibitory activity of PGE1 was further investigated on both HLVEC and leukocytes with attention to adhesion molecules. On HLVEC, PGE1 down-regulated TNF-induced expression of endothelial cell leukocyte adhesion molecule 1 and vascular adhesion molecule 1, but not intercellular adhesion molecule 1. On leukocytes, PGE1 inhibited expression of CD11a/CD18 and membrane-bound TNF on PHA-stimulated leukocytes. PGE1 also suppressed TNF release from the stimulated leukocytes. These results indicated that inhibition of leukocyte adherence and transendothelial migration is one of the mechanisms by which PGE1 protects liver grafts.