Immunohistochemical and ultrastructural analysis of the proliferating cells in histiocytosis X.

The cellular nature of the proliferating histiocytes in 6 cases of histiocytosis X was studied immunohistochemically and ultrastructurally. Immunohistochemically, S-100 protein was detected both in the cytoplasm and the nuclei of histiocytosis X cells as well as Langerhans cells in normal oral epithelium. These cells were always negative for lysozyme, alpha 1-antitrypsin, alpha 1-antichymotrypsin and immunoglobulins. S-100 protein was not detected in lysozyme-positive histiocytes and multinucleated giant cells often showed the signs of phagocytosis. Thus, S-100 protein appears to be a useful immunohistochemical marker for histiocytosis X cells. Ultrastructurally, Birbeck granules noticed in histiocytosis X cells were never seen in the phagocytic histiocytes with numerous lysosomes and phagosomes. These results emphasized the heterogeneous nature of the proliferating histiocytes involved in the lesions. Since histiocytosis X cells share characteristics, not only ultrastructurally but also immunohistochemically, with Langerhans cells, the hypothesis that histiocytosis X may be fundamentally an abnormal proliferation of Langerhans cells has been further supported.