Bone Marrow-Derived Fibrocytes are Involved in Human Dental Pulp Repair

Objectives: Fibrocytes are circulating mesenchymal progenitor cells with macrophage and fibroblast-like features. To date, there have been no data to show the existence of fibrocytes in human dental pulp repair. The present study aimed to explore the expression profile of CD45 (a pan-hematopoietic marker)+/pro-collagen I (a fibroblast product)+ fibrocytes in intact and during wound healing after pulp capping of adult dental pulp tissue.
Methods: This study was undertaken in accordance with the declaration of Helsinki and has been approved by the Niigata University Ethics Committee (No. 21-R17-09-10). Human healthy permanent teeth were obtained from patients undergoing orthodontic treatment, who had provided informed consent. Routine pulp capping with mineral trioxide aggregate (MTA) was performed under local anesthesia to induce a mineralized barrier at the exposed surface. Teeth were extracted from patients after 7, 14, and 35 days as part of orthodontic treatment. Sections of the extracted teeth were prepared and stained for various markers using indirect immunofluorescence.
Results: Most of the CD45-positive cells were negative for pro-collagen I in normal pulp tissue. At 7 days post-operatively, CD68 (a general macrophage marker)-positive cells occupied the wounded layer, and CD45+/pro-collagen I+ fibrocytes were scattered under the wounded area. At day 14, CD68-positive macrophages were confined along the fibrous matrix in contact with MTA. Fibrocytes were detected underneath the fibrous matrix, and noted to infiltrate into regions of new blood capillary formation and were positively stained for vascular endothelial growth factor (VEGF). By 35 days, when the injured site was covered with a dentine bridge, there were few fibrocytes.
Conclusions: This is the first report to show the presence of fibrocytes in human dental pulp wound healing. The spatiotemporal distribution of fibrocytes in the present study suggests that fibrocytes are involved in the early stages of dental pulp wound healing.