Objective To investigate the effect of interleukin-6 （IL-6） on the apoptosis of annulus fibrosus （AF） cell induced by interleukin-1β （IL-1β）. Methods Cultured AF cells were divided into 6 groups and treated with no drug

10 ng/mL IL-6

10 ng/mL IL-1β

10 ng/mL IL-1β and Z-VAD-FMK （a caspase-9 inhibitor）

10 ng/mL IL-1β and 10 ng/mL IL-6

10 ng/mL IL-1β and 100 ng/mL IL-6

respectively. After three days of culture

the apoptosis rate

the positive rates of caspase-3

-8

and -9 of AF cells were detected with flow cytometry. Results The apoptosis rates of cells in group 1 to 6 were 2.67%±1.08%

2.71%±0.53%

20.37%±1.57%

11.34%±0.67%

18.17%±0.74%

and 9.42%±1.08%

respectively. There was no significant difference between group 1 and 2

while the apoptosis rates of group 4

5

and 6 were significantly lower than group 3 （P=0.001

P=0.172

and P=0.001

respectively）. Positive rates of caspase-3 in group 5 （12.35%±0.64%） and 6 （9.26%±0.36%） were significantly lower than group 3 （17.14%±0.72%; P=0.001 and P<0.001

respectively）. And positive rates of caspase-9 in group 5 （15.13%±1.45%） and 6 （10.17%±2.50%） were significantly lower than group 3 （19.4%±0.98%; P=0.014 and P=0.004

respectively）. But there was not obvious change of caspase-8 activity after IL-6 was added. Conclusion IL-6 is capable of protecting AF cells from IL-1β induced apoptosis in vitro. Mechanism of the protection is related with the inhibition of caspase-3 and -9 activities.