Identification of corticotrophs in the human pituitary with mAB lu-5, a novel immunocytochemical marker.

The presence of mAB lu-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 pars tuberalis and several cells lining pars 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 lu-5 immunoreactivity was evident. GH-, PRL-, TSH-, FSH-, LH-, alpha-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 lu-5 did not stain ACTH. Immunoreactivity with mAB lu-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 lu-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.