The purpose of this study is to determine the versatility of the
monoclonal antibody anti-Leu-M1 in
histiocytosis X diagnosis. This antibody recognizes an unsialylated
lacto-N-fucopentaose III (hapen X)
carbohydrate moiety that is linked to the
cell membrane protein in interdigitating reticulum cells and Langerhans' cells. Previously, the authors have shown that anti-Leu-M1 can be used to
stain Reed-Sternberg cells, which are likely related to interdigitating reticulum cells. In this study, the authors tested the usefulness of anti-Leu-M1 in staining
formalin-fixed and
paraffin-embedded tissue sections from eight patients with
histiocytosis X. For staining of
histiocytosis X cells, unlike Reed-Sternberg cells in
Hodgkin's disease,
neuraminidase treatment was required for removal of
sialic acid residues from the
Leu-M1 antigen. The staining characteristics of anti-Leu-M1 in
histiocytosis X cells resembled those of normal Langerhans' cells and lymphocyte and histiocyte variants (L & H cells) in the lymphocyte-predominant type of
Hodgkin's disease. The significance of sialylation of
Leu-M1 antigen in
histiocytosis X cells has yet to be determined in order to correlate the prognosis of the disease. The authors suggest that anti-Leu-M1 used together with
neuraminidase treatment is a valuable tool in the diagnosis of
histiocytosis X when electron microscopy or frozen sections for OKT6 immunostaining are not available.