T cells participate in bone remodeling during the rapid palatal expansion

Palatal expansion has been widely used for the treatment of transverse discrepancy or maxillae hypoplasia, but the biological mechanism of bone formation during this procedure is largely unknown. Osteoclasts, which could be regulated by T cells and other components of the immune system, play a crucial role in force-induced bone remodeling. However, whether T cells participate in the palatal expansion process remains to be determined. In this study, we conducted the tooth borne rapid palatal expansion model on the mouse, and detect whether the helper T cells (Th) and regulatory T cells (Treg) could affect osteoclasts and further bone formation. After bonding open spring palatal expanders for 3-day, 5-day, 7-day, and retention for 28-day, micro-computed tomography scanning, histologic, and immunofluorescence staining were conducted to evaluate how osteoclasts were regulated by T cells during the bone remodeling process. We revealed that the increased osteoclast number was downregulated at the end of the early stage of rapid palatal expansion. Type 1 helper T (Th1) cells and Type 17 helper T (Th17) cells increased initially and promoted osteoclastogenesis. Thereafter, the regulatory T (Treg) cells emerged and maintained a relatively high level at the late stage of the experiment to downregulate the osteoclast number by inhibiting Th1 and Th17 cells, which governed the new bone formation. In conclusion, orchestrated T cells are able to regulate osteoclasts at the early stage of rapid palatal expansion and further facilitate bone formation during retention. This study identifies that T cells participate in the palatal expansion procedure by regulating osteoclasts and implies the potential possibility for clinically modulating T cells to improve the palatal expansion efficacy.