ABSTRACT
Histiocytosis X is characterized by aggregates of Langerhans cells with other inflammatory cells. These Langerhans cells are antigen-presenting cells to T lymphocytes and identified by characteristic morphology, ultrastructural demonstration of Birbeck granules and immunologic reactivity with OKT-6 and HLA-DR antibodies. In this report, the tumor arising in a 2-years-old baby was examined byimmunostaining with several macrophage/dendritic cell markers. The main tumor cells showed cytoplasmic and nuclear staining with S-100 protein and ring-like surface and paranuclear staining with PNA. However, they were negative for follicular dendritic cell marker CD21, macrophage markers lysozyme, Mac 387, alpha-1 antitrypsin and CD68, and interdigitating reticulum cell marker ID4 and ID5. These observations demonstrate the usefulness of S-100 protein and PNA for the identification of Langerhans cells in paraffin-embedded tissue.