Peanut agglutinin. A useful marker for histiocytosis X and interdigitating reticulum cells.

We studied the peanut agglutinin (PNA) staining patterns of histiocytosis X (H-X) (three cases, including one case of Letterer-Siwe disease) and well-characterized cases of malignant histiocytosis (two cases) and monoblastic leukemia (one case) in paraffin-embedded specimens. H-X cells showed staining identical to that of interdigitating reticulum cells, with unique paranuclear and cell surface deposits of reaction products. Thus, H-X cells were easily distinguished from benign macrophage-histiocytes, which show diffuse cytoplasmic staining, and malignant cells of malignant histiocytosis and monoblastic leukemia, which did not stain with PNA, PNA staining proved more useful than Leu-M1 antibody for this purpose, since neither interdigitating reticulum cells in ten reactive lymph nodes nor Langerhans'-type cells in three cases of H-X were stained with Leu-M1 antibody. These observations support a close relationship between H-X cells and interdigitating reticulum cells, and demonstrate the usefulness of PNA for the identification of these cells in paraffin-embedded material.