OBJECTIVE To investigate the molecular mechanism of allogeneic CD8+ T cell-induced apoptosis of vascular endothelial cells. METHODS Allogeneic CD8+ T cells were isolated from PBMC by positive selection using magnetic beads coated with anti-CD8 antibody. Apoptosis of human umbilical vein endothelial cells (HUVEC) and human dermal microvascular endothelial cells (HDMEC) were detected by Annexin V-FITC labeling. Gene and protein expression of proteinase-activated receptor-1 (PAR-1) in vascular endothelial cells were tested by RT-PCR and Western blot. Western blotting was also used to detect the change of MAPK and Caspase-3 expression in vascular endothelial cells. The effects of SFLLRN (PAR-1 agonist), ATAP2 (PAR-1 antibody), SB203580 (inhibitor of p38MAPK), SP600125 (inhibitor of JNK) upon apoptosis were also examined. RESULTS After co-culturing with allogeneic CD8+ T cells for 24 h and 48 h, the apoptotic rates of HUVEC were 51.7% +/- 4.1% and 29.4% +/- 3.3% respectively (P < 0.01, vs untreated HUVEC) and those of HDMECs 28.9% +/- 2.2% and 15.2% +/- 1.8% respectively (P < 0.01, vs untreated HDMEC). The effect of PAR-1 agonist upon apoptosis of HUVEC and HDMEC similar to that of allogeneic CD8+ T cells. These effects were largely prevented by ATAP2 and SB203580 (P < 0.05). Allogeneic CD8+ T cells and PAR-1 agonist enhanced the cleavage of Caspase-3 and led to p38MAPK phosphorylation. CONCLUSIONS Allogeneic CD8+ T cells induced the apoptosis of vascular endothelial cells through PAR-1 dependent modulation of intrinsic apoptotic pathway via the cleavage of Caspase-3 and the phosphorylation of p38MAPK.