Immunohistochemical and ultrastructural analysis of the proliferating cells in histiocytosis X

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Abstract
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, α‐antitrypsin, α,‐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.