Immunohistochemical localization of dipeptidyl aminopeptidase IV in thyroid papillary carcinoma

The localization of dipeptidyl aminopeptidase IV expressed aberrantly in thyroid carcinoma was studied by immunoelectron microscopy using a monoclonal antibody to the enzyme with special reference to enzyme-histochemical staining of the enzyme. Five thyroid papillary carcinomas were investigated including two lymph-node metastases. All cases showed the dense immunoreaction product on the apical membrane and only traces of the product on lateral membranes, endoplasmic reticulum and nuclear membranes. In one case only, the dense product was observed on basal tubular structures. Analysis, using immunogold labelling on pre-embedded cryosections, revealed that dipeptidyl aminopeptidase IV was localized on the luminal surface of cancer cells. Two different distribution patterns of dipeptidyl aminopeptidase IV activity staining, diffuse and apical patterns, reported previously were thought to be due to different amounts of dipeptidyl aminopeptidase IV in the cytoplasm of cancer cells. This enzyme-histochemical staining method is useful for pathological diagnosis of thyroid tumours and can be applied to clinical materials. The enzyme localization is revealed by the staining pattern.