Procollagen-positive fibroblasts predominantly express fibrogenic growth factors and their receptors in human encapsulation process against foreign body

This paper addresses the in situ expression of transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), and their receptors in the encapsulation process against a foreign body, using 20 cases of the titanium miniplate as a model of the foreign body, used clinically to fix a fractured mandible. Fibrous tissue formed during the encapsulation process was composed of scar-like and fibrogenic layers, with the former directly facing the foreign body. By immunohistochemistry using pre-fixed frozen sections, only the fibrogenic layer was characterized by expression of type I procollagen (PC-I). Spindle-shaped mesenchymal cells in the fibrogenic layer expressed TGF-beta isoforms and receptors, PDGF isoforms, and PDGF beta-receptor. In contrast, the scar-like layer had few such cells. In both layers, spindle-shaped cells did not express Ki-67 in their nuclei. Double immunofluorescence microscopy for cell identification revealed that most PC-I-positive fibroblasts expressed both isoforms and receptors of TGF-beta and PDGF in the fibrogenic layer, while in contrast, they were expressed by only a small number of CD68-positive macrophages. These results suggest that in the maintenance stage of the human encapsulation process against a foreign body, both TGF-beta and PDGF function cooperatively via their receptors in the fibrogenic layer, with such stimuli markedly diminished in the scar-like layer.