Factor XIIIa expression in juvenile xanthogranuloma

Dermal dendrocytes constitute the largest population among cells of dermatofibromas. In other histiocytic tumours, the exact nature of histiocytic cells is not known. We have searched for the presence of dermal dendrocytes in juvenile xanthogranulomas. The immunohistochemical study was performed on 9 juvenile xanthogranulomas. We used monoclonal or polyclonal antibodies: anti-XIIIa, HAM56, anti-S100, anti-NSE, anti-HLA-DR, anti-CD68 and anti-lysozyme. Phagocytic mononuclear cells (histiocytes, giant cells, Touton cells) did not express Langerhans' cell markers (S100, NSE ou HLA-DR). They weakly expressed markers of macrophages (CD68, lysozyme). There was a very strong binding by HAM56 and anti-XIIIa. This expression was more evident on xanthomatous and newly appeared tumours than on fibrous tumours. The largest population of juvenile xanthogranuloma cells appeared to be constituted by dermal dendrocytes. These cells are perhaps the key-cells of a continuum of benign tumours, from juvenile xanthogranuloma to dermatofibroma, with different stages corresponding to different proportions of dendrocytes, lymphocytes and fibroblasts.