Factor XIIIa-positive dermal dendritic cells in keloids and hypertrophic and mature scars.

Keloids and hypertrophic scars have several common features. Both are reddish, firm, slightly protruding lesions that consist of proliferative fibroblastic cells and collagenous tissues. The aim of the present study was to evaluate the contribution of factor XIIIa (FXIIIa)-positive dermal dendritic cells to formation of keloids and hypertrophic scars. The numbers of FXIIIa-positive cells were counted in the keloid, hypertrophic scar and mature scar, each of which was divided into fibrocollagenous area and superficial dermal area overlying the nodular lesion. The features of the FXIIIa-positive cells were examined using immunohistochemical and immunoelectron microscopic techniques. More FXIIIa-positive cells were present in the overlying dermal area than in the fibrocollagenous area, commonly in three types of dermal lesion. The number of FXIIIa-positive dendritic cells was significantly greater in the overlying dermal area of keloids than in the corresponding area of hypertrophic or mature scar. Immunoelectron microscopic examination showed that the immunoreactivity for FXIIIa was seen mainly at the periphery of the cytoplasm of dermal dendritic cells. These results suggest that FXIIIa-positive dendritic cells in the overlying dermal area play active roles in formation of keloids and may contribute to dermal-epidermal interactions in keloids.