CATHEPSIN-D AND CATHEPSIN-E COEXPRESSION IN SINUS-HISTIOCYTOSIS WITH MASSIVE LYMPHADENOPATHY (ROSAI-DORFMAN-DISEASE) AND LANGERHANS CELL HISTIOCYTOSIS - FURTHER EVIDENCES OF A PHENOTYPIC OVERLAP BETWEEN THESE HISTIOCYTIC DISORDERS

Nosological classification of sinus histiocytosis with massive lymphad enopathy (SHML; Rosai-Dorf man disease) is difficult, and the normal c ellular counterpart of Rosai-Dorfman (RD) cells is uncharacterised. Th e peculiar S-100+ phenotype of RD cells suggests a relationship with t he dendritic cell family. Recent investigations have revealed cathepsi n E to be selectively concentrated in antigen-presenting cells, wherea s cathepsin D was found to be expressed in cells of macrophage Lineage . Cathepsin D and E distribution was investigated by immunohistochemis try in a series of SHML biopsies and in two types of dendritic cell pr oliferative lesions: dermatopathic lymphadenitis (DL) and Langerhans' cell histiocytosis (LCH). In SHML biopsies, RD cells and monocyte-rela ted elements of the sinuses and pulp co-expressed cathepsin D and E. L CH cells also stained for both these aspartic proteinases. Conversely, in DL cathepsin E and D were localised to separate cells that resembl ed Langerhans' cells (LC) or macrophages, respectively, in morphology and distribution. Our data outline the peculiar immunophenotype of RD and LCH cells and suggest that caution should be exercised in the iden tification of their normal cellular counterpart. The common expression of cathepsin D and E and of S-100 protein suggests some phenotypic ov erlap between SHML and LCH cells, despite their striking morphological divergence.