[Reticulohistiocytic tumors of the skin. New concepts].

Recent findings of the cytochemical, immunological and fine structural properties of dermal infiltrate cells in various skin conditions do not support the existence of a so called "reticular cell" (Aschoff). Reticulohistiocytic tumors of the skin obviously derive from histiocytes, a member of the mononuclear phagocytic system (MPS, monocyte leads to histiocyte leads to macrophage). Histiocytes may be differentiated from other tissue cells according to their appearance under the electron microscope, their distinct enzymatic properties and their receptors for Fc-IgG and C3 complement. Since several conditions such as mycosis fungoides, Sézary syndrome and various reticuloses of the traditional european literature were proved to be lymphomas (B- or T-cell type), only the following skin tumors were classified as being at least of partly histiocytic origin: Histiocytoma (better dermatofibroma), reticulohistiocytoma (juvenile xanthogranuloma), systemic reticulohistiocytosis, malignant histiocytoma and histiocytosis, histiocytic or mixed lymphoma and histiocytosis X. The last entity reflects the differentiation of histiocytes into proliferating atypical Langerhans cells, which were shown to have similar enzymatic and immunologic properties, however, the proliferating Langerhans cells in the histiocytosis X do not phagocytize.