Localization of anti-Leu-M1 (CD15) binding sites in Hodgkin's disease by immunoelectron microscopic examination

Anti-Leu-M1 (CD15) is a monoclonal antibody used in surgical pathology to diagnoses Hodgkin's disease. By light microscopic immunohistochemistry, anti-Leu-M1 reacts with Reed-Sternberg cells and their variants, notably lacunar cells in nodular sclerosing Hodgkin's disease, as well as granulocytes in Hodgkin's disease. The immunostaining of Reed-Sternberg cells has been characteristically described as a diffuse cytoplasmic pattern with a prominent perinuclear globular component. In addition, irregular plasma membrane reactivity has been observed. To define the intracellular localization of Leu-M1 precisely, the authors performed postembedding immunoelectron microscopy with the protein A-gold technique on sections embedded in Lowicryl K4M from a patient with nodular-sclerosing-type Hodgkin's disease. At the electron microscopic level, gold particle staining indicative of Leu-M1 binding was found within cytoplasmic granules and the Golgi apparatus, as well as focally at the plasma membrane. The cytoplasmic granules were located in a perinuclear region and in the cell periphery. Although the morphology of the granules was suggested of lysosomal structures, immunolabel was not detected on serial sections of these granules with three different antibodies directed against lysosomal antigens.