A study was carried out on effects of IL-6 on the proliferation and apoptosis of tumor cells and the ex- pression of apoptosis relavent genes ( p53

bcl-2 ) in tumor cells for three kinds of fractional total-body-irradiated tu- mor-bearing mice.The apoptotic index

proliferative index

S phase fraction of S180 sarcoma

H22 hepatocarcinoma and Lewis lung cancer cells were measured by flowcytometry ( FCM ) after total-body-irradiation and irradiation plus IL-6. The protein expression level of p53

bcl-2 in three kinds of tumors were also determined by the immunohisto- chemical method ( UltraSensitive S-P ) . The results showed that the S phase fraction and proliferation index in Lewis lung cancer cells were lower in the irradiated plus IL-6 group than in the control

while apoptotic index was higher ( P < 0.05). However

the experimental results for S180 sarcoma cells were opposite ( P < 0.01 ) . In addition

no significant effects were observed in H22 hepatocarcinoma. These results revealed that IL-6 promoted the apoptosis of irradiated Lewis lung cancer cells ( P < 0.05 )

while the apoptosis of S180 sarcoma ( P < 0.05 ) was restrained

and there was no significant effects on the cellular cycle of H22 hepatocarcinoma (P > 0.05 ) . In Lewis lung cancer the expression level of p53 was lower in the IL-6 group and highter in S180 sarcoma ( P < 0.05 )

while unvaried in H22 hepatocarcinoma as compared to the control ( P > 0.05 ) . It is considered that tumor cell’s proportion in the cellular cycle is changed by IL-6 and the effects of IL-6 on the expression of p53

bcl-2 in different three kinds of tumors are different. IL-6 has radio-sensitive effects on some tumors and opposite effects on other tumors

it may be related to the expression of P53 and Bcl-2 in tumor cells.