AIM: To understand the mechanism by which anti-β4 integrin monoclonal antibody (mAb) inhibits apoptosis of vascular endothelial cells (VEC). METHODS: Viability was determined by counting the cells that attached to dishes after treatments. DNA fragmentation was analyzed by agarose gel electrophoresis and fluorescence microscopy. The intracellular content of cAMP was measured by radioimmunoassay (RIA). The levels of p53 and Ras expres- sions were analyzed by fluorescence microscopy combined with immunofluorescence under laser scanning confo- cal microscopy. RESULTS: After the cells were deprived of fibroblast growth factor (FGF) and serum were exposed to the mAb 5 mg/L for 24 h, the detachment and DNA fragmentation of these cells were suppressed. When cells were deprived of FGF and serum, the intracellular cAMP level and Ras protein content decreased (P<0.05), while the level of p53 protein expression increased (P<0.05). But in the presence of anti-β4 integrin mAb, VEC apoptosis was inhibited, and at the same time, the changes mentioned above were obviously blocked (P<0.05). CONCLUSION: Anti-4 integrin mAb inhibited apoptosis by affecting the level of cAMP, and blocking down- regulation of Ras protein and up-regulation of p53 protein in VEC. AIM: To understand the mechanism by which anti-β4 integrin monoclonal antibody (mAb) inhibits apoptosis of vascular endothelial cells (VEC). METHODS: Viability was determined by counting the cells that attached to dishes after treatments. DNA fragmentation was analyzed by agarose gel electrophoresis and fluorescence microscopy. The intracellular content of cAMP was measured by radioimmunoassay (RIA). The levels of p53 and Ras expres- sions were analyzed by fluorescence microscopy combined with immunofluorescence under laser scanning confocal microscopy. RESULTS: After the cells were deprived of fibroblast growth factor (FGF) and serum were exposed to the mAb 5 mg / L for 24 h, the detachment and DNA fragmentation of these cells were suppressed. When cells were deprived of FGF and serum, the intracellular cAMP level and Ras protein content decreased (P <0.05) while the level of p53 protein expression increased (P <0.05). But in the presence of anti-β4 integrin mAb, VEC apoptos CONCLUSION: Anti-4 integrin mAb in apoptosis by affecting the level of cAMP, and blocking down-regulation of Ras protein and up- regulation of p53 protein in VEC.