Objective:The purpose of this paper is to investigate the effects of allicin on the apoptosis of THP-1 cells and expressions of Fas/FasL. Methods:The proliferation inhibition rates of THP-1 cells after various treatments were examined by MTT assay. After the treatment of THP-1 cells by allicin,morphological change of apoptotic cells was investigated by AO/EB fluorescent staining under fluorescent microscope. Apoptosis rate was determined with Annexin V-FITC/PI double staining by flow cytometry. Flow cytometry was used to observe the effect of allicin on apoptosis and cell cycle distribution of THP-1 cells. The expression changes of Fas and FasL were detected by immunohistochemical staining. The changes of Fas/FasL proteins were detected by Western blot. Results:The proliferations of THP-1 cells were inhibited by allicin. MTT assay showed that the allicin inhibited the proliferation of the THP-1 cells,and the inhibition was dependent on both dose and time. The IC50 of 72 h was 12.8 mg/L. Apoptosis rate detected by Annexin V-FITC/PI was proportional to the concentration of the allicin. The percentage of G0/Gl phase cells was increased,but the S phase cell was decreased when treated with allicin for 72 h. 72 h after exposure to 6.4,12.8 mg/L allicin,the apoptotic rates of THP-1 cells were(22.93±2.93)% and(36.73±2.88)%,respectively. They were also dose dependent,and statistically significant when compared with the controls(P < 0.01). The cells could be classificated into:early apoptotic cells,late apoptotic cells,alive cells and dead cells under the fluorescent microscope. After the immunohistochemical staining test,the expression of Fas/FasL increased in THP-1cells was induced by allicin. Fas/FasL was located in the cytoplasm and cytolemma. Western blot test showed that the Fas/FasL protein expression was proportional to the concentration of allicin and it was also dose dependent. After treated with 0,6.4 and 12.8 mg/L allicin for 72 h,the levels of Fas proteins were 0.287±0.009,0.427±0.008 and 0.597±0.011,respectively and the levels of FasL proteins were 0.212±0.014,0.299±0.028 and 0.409±0.027,respectively. The difference was statistically significant(P < 0.01). Conclusion:Allicin induced apoptosis of human THP-1 cells is partly by up-regulating the expressions of Fas/FasL.