MPO and histiocytoma: However, immunohistochemically, HS cells are positive for histiocytic markers such as CD68, CD163, CD204, and lysozyme; they express one or more histiocytoma markers, namely, Langerhans cell markers (CD1a and langerin) and follicular dendritic cell markers, but they do not express morphological markers (e.g., CD21 and CD35) and myelocytic markers (e.g., CD34 and myeloperoxidase) [2].