Abstract: Objective: To investigate whether there is inhibition of the human lung cancer cell line A549 induced by the culture supernatant of Toxoplasma gondii in vitro and the mechanism of the inhibition. Methods A549 cells 5×104mL-1 were cultured and harvested in the different cell culture plates. The cells were treated for different hours with different concentrations of Toxoplasma gondii culture supernatant (the concentrations of tachyzoites were 4×107mL-1, 8×107mL-1, 16×107mL-1 respectively). Growth inhibition rates were measured with the MTT method；Cell cycle was checked with Flow Cytometer. Western blot was used to detect the leves of cyclinB1、cdc2 of cells. Results The culture supernatants of Toxoplasma gondii could inhibit the proliferation of A549 cells in a time-dose dependent manner. Cell cycle was significantly stopped at G2/M phase by the culture supernatants with FCM technology. The culture supernatant of Toxoplasma gondii reduced the expressions of gene cyclinB1and cdc2 of A549 cells. Conclusion The culture supernatant of Toxoplasma gondii may inhibit A549 cell and arrest the cell cycle of A549 cells mainly by regulating the expression of gene cyclinB1 and cdc2

Key words: Toxoplasma gondii, Lung cancer cell A549 cell, cell cycle