Identification of Corticotrophs in the Human Pituitary with mAB 1u-5, a Novel Immunocytochemical Marker

Abstract

The presence of mAB 1u-5, a panepithelial, monoclonal antibody was studied in human adenohypophyses and pituitary adenomas by immunohistochemistry using the avidinbiotin-peroxidase complex technique. In nontumorous adenohypophyses, only corticotrophs showed strong immunoreactivity, whereas other adenohypophysial cell types exhibited little or no staining. Positive immunostaining was observed in corticotrophs spreading to the, posterior lobe, in cells of squamous nests located in the gars tuberalis and several cells lining gars intermedia cavities. The Crooke's hyaline material in the cytoplasm of corticotrophs was immunopositive. In adenomatous corticotrophs and cytoplasmic fibrous bodies of sparsely granulated adenomatous somatotrophs, distinct mAB 1u-5 immunoreactivity was evident. GH-, PRL-, TSH-, FSH-, LH-, a-subunit-producing adenomas, null cell adenomas and oncocytomas showed no convincing staining. Immunopositivity in corticotroph adenomas was diffusely distributed in the cytoplasm and was not located in secretory granules, indicating that mAB 1u-5 did not stain ACTH. Immunoreactivity with mAB 1u-5 was not specific for pituitary corticotrophs, since the antibody stained nontumorous epithelial cells and epithelial tumor cells in other organs as well. It can be concluded that mAB 1u-5 is a valuable immunocytochemical marker in pituitary related studies, especially in those pituitary adenomas in which immunostaining for ACTH is weak or equivocal; in these cases, it can confirm the diagnosis of corticotroph adenoma. The antibody yields similar results as keratin antisera. In our experience, however, it gives a stronger, more distinct immunopositivity with less nonspecific background staining.