Fibrocyte: a missing piece in the pathogenesis of fibrous epulis

Objective To investigate the significant role of fibrocytes in pathogenesis of fibrous epulis. Material Human epulis specimens and human peripheral blood mononuclear cells (PBMCs) were used in this study. Methods Different subtypes of human fibrous epulides and normal gingival tissue specimens were collected for histological and immunofluorescence analyses. Electron microscopy and elemental analysis were used to characterize the extracellular microenvironment in different subtypes of fibrous epulides. Human PBMCs were subsequently isolated from peripheral blood to identify the factor that trigger fibrocyte differentiation in vitro. Results We demonstrated the presence of circulation-derived fibrocytes in fibrous epulides. These fibrocytes differentiate into myofibroblasts or osteoblasts under the local inflammatory environment in fibrous epulides. TGF-β1 promotes fibrocytes differentiation into myofibroblasts in a concentration-dependent manner. The TGF-β1 along with a high calcium and phosphorus extracellular environment stimulates the fibrocytes to differentiate into osteoblasts. The fibrocytes-derived myofibroblasts and osteoblasts are responsible for the fibrogenesis and osteogenesis of fibrous epulides, respectively. The persistent local inflammatory environment drived the differentiation of circulation-derived fibrocytes and drived the recurrence of fibrous epulides. Conclusions Fibrocytes play an important role in the fibrogenesis and osteogenesis in fibrous epulis, and might serve as a therapeutic target for the recurrence of fibrous epulides.