[Histochemical and electron microscopical studies of histiocytoma (author's transl)]

Histiocytoma cutis: a tumour of dermal dendrocytes (dermal dendrocytoma)

The histogenesis of histiocytoma (dermatofibroma) was investigated using new antibodies that demonstrate factor XIIIa (FXIIIa) positive cells and the monocyte macrophage cell series (MAC 387), in formalin fixed tissue. The distribution of S100 protein, vimentin and Ulex europaeus agglutinin I (UEA-I) were also studied. The antibody against FXIIIa labelled the normal dermal population of fixed connective tissue cells (dermal dendrocytes) emphasizing their dendritic processes; cells that are widely distributed, but are most numerous in the papillary dermis. In contrast, the antibody, MAC 387 against monocyte derived macrophages, did not label this cell population. In 30 histiocytomas, intense labelling for FXIIIa was found peripherally, but labelling was rather weaker in cells situated centrally. Only a few cells labelled for S100 protein and with the monoclonal antibody MAC 387, but vimentin positivity was universal. UEA-I labelled only vessels in histiocytomas. However, FXIIIa labelling was negative in 16 dermatofibrosarcomas, three keloids and several other fibroproliferative lesions. These contrasting results with FXIIIa labelling have practical implications for diagnosis of benign and malignant spindle cell tumours of the skin. We conclude that histiocytomas (dermal dendrocytomas) take their origin from dermal fixed connective tissue cells, (dermal dendrocytes), but other spindle cell tumours may differ in histogenesis.

Immunohistologic study of cellular populations of histiocytofibromas ("dermatofibromas")

Histiocytofibromas (HF) are benign tumours of the skin, the cellular composition of which is not yet known with certainty. The immunohistologic characteristics of 5 lesions were studied by using monoclonal antibodies and an indirect immunofluorescence method. All tumours were found to contain HLA-DR(+) cells, and, to a minor degree, OKM1(+) cells. OKT6(+) cells were present in the epidermis overlying the tumours; however in the HF themselves, no OKT6(+) cells were found. The presence of HLA-DR(+) and OKM1(+) cells demonstrates that HF contain cells bearing antigenic characteristics of histiocytes but not of Langerhans' cells, and we feel that the term "histiocytofibroma" is a more accurate designation for these lesions than "dermatofibroma".