Inhibitory effects of IL-12 on experimental tooth movement and root resorption in mice

Objective: Interleukin (IL)-12 is an important cytokine for innate and adaptive immunity. We previously reported that IL-12 inhibits tumour necrosis factor (TNF)-α-mediated osteoclast formation by inducing apoptosis. We also reported that TNF-α plays an important role in mechanical loading-induced osteoclast formation and bone resorption during orthodontic tooth movement. In this study, we investigated the effects of IL-12 on mechanical tooth movement in mice. Design: A Ni-Ti closed coil spring was inserted between the upper incisors and the upper left first molar in mice. IL-12 was injected locally adjacent to the first molar every other day during the experimental period, at doses varying from 0 to 1.5 μg/day. After 12 days, the animals were killed and their jaws were processed for histological evaluation using tartrate-resistant acid phosphatase (TRAP) and TdT-mediated dUTP-biotin nick end-labelling (TUNEL) staining, and measurements of the root resorption area. Results: In the IL-12-treated mice, tooth movement and root resorption appeared to be reduced. In TUNEL-stained sections, many apoptotic cells were recognized on the pressure side in the IL-12-treated mice. Conclusions: Our findings suggest that IL-12 inhibits not only mechanical tooth movement, but also root resorption during orthodontic tooth movement. These findings may arise through apoptosis induced by IL-12.