Sinus histiocytosis with massive lymphadenopathy (Rosai Dorfman disease): evidence for a dendritic cell derivation?

Sinus histiocytosis with massive lymphadenopathy or Rosai-Dorfman disease is a rare histiocytic disorder of unknown origin. Both dendritic cell and monocyte-macrophage lineage have been considered as the origin of the histiocytes that are classical of the disorder. We analyzed seven cases of Rosai-Dorfman disease to determine the immunophenotypic profile of these cells. Immunohistochemical analysis was undertaken by using: (a) fascin as a novel mature dendritic cell marker; (b) S-100 protein; (c) CD68 (both KP1 and PGM1) as macrophage related markers; (d) CD79a and (e) CD3. The Rosai-Dorfman histiocytes exhibited strong cytoplasmic staining for fascin in all the cases and demonstratedformation of a meshwork of fine dendritic processes emanating from the cell cytoplasm. S-100 protein was uniformly expressed in all the cases. Expression of both KP1 and PGM1 epitopes of CD68 was found to be weak and variable. The phagocytosed lymphocytes were composed of an admixture of both B and T-lymphocytes. The characteristic expression pattern of the histiocytes for fascin along with co-expression of S-100 protein and a consistently weaker and variable expression of macrophage-lineage markers point more towards a dendritic cell ontogeny of these cells. Further, abundant fascin expression and presence of dendritic processes indicate a differentiated or mature dendritic cell phenotype for these cells.