Proliferation of HSP47-positive skin fibroblasts in dermatofibroma.

BACKGROUND: The cell origin of dermatofibroma (DF) has not been clarified satisfactorily. This study was undertaken to assess the distribution of fibroblasts and the relationship between fibroblasts and other constituent cells in DF by 47-kDa heat-shock protein (HSP47), a cell marker for skin fibroblast.

METHODS: Immunohistochemistry was performed to evaluate the expression of HSP47 and other cell markers in histological variants of DF.

RESULTS: Almost all spindle-shaped cells showed strong immunoreactivity for HSP47 in DF. In the fibrocollagenous type, a common type of DF, HSP47-positive fibroblasts were the major constituent cells. In the cellular and atypical types, many constituent cells were positive for HSP47. Huge cells with bizarre nuclei, which are distinctive of the atypical type, showed immunoreactivity for HSP47, not for CD68 or factor XIIIa (FXIIIa). In the histiocytic and angiomatous types, CD68-positive histiocytes were the major constituent cells, but many scattered spindle cells were positive for HSP47. FXIIIa-positive dermal dendritic cells were increased, irrespective of DF variants, whereas the cell number varied from case to case.

CONCLUSIONS: Skin fibroblast is one of the major constituent cells in DF, and DF may be composed chiefly of two types of cell lineages, fibroblasts and bone marrow-derived monocyte/macrophages (dermal dendritic cells and/or histiocytes).