Application of catalyzed signal amplification in immunodetection of gonadotropin subunits in clinically nonfunctioning pituitary adenomas

Abstract

Pituitary adenomas that are characterized by the absence of a particular clinical syndrome and the absence of excessive hormone secretion have been classified as nonfunctioning adenomas. Recent development of immunohistochemical analysis and hormonal assay have suggested that many of these tumors have function to secret the gonadotropin subunits. A novel procedure biotin amplification in immunohistochemistry, catalyzed signal amplification (CSA) has been reported recently. In this study, the authors applied this new method to tissues from 50 eases of clinically nonfunctioning adenomas. These cases had no evidence of endocrinological signs by hormone secretion. When the CSA system was applied in normal pituitary bland, each of subunits was positive even when the antibody was diluted 1:1,000,000, which is 1,000 folds of standard indirect immunoperoxidase method. Immunohistochemical staining by indirect immunohistochemical method revealed that all 50 adenomas were negative for all the anterior hormones, including growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH), beta-subunit of luteinizing hormone (LHβ), follicle-stimulating hormone (FSHβ), thyroid stimulating hormone (TSHβ), and a-subunit of glycoprotein (αSU;). Using avidin-biotin complex (ABC) method, two cases were positive for FSHβ and four cases were positive for αSU, respectively, and the immunopositivities were observed weakly in scattered cells. By CSA system, 26 cases of 50 nonfunctioning adenoma were positive for FSHβ, 16 cases were positive for LHβ, and 29 cases were positive for αSU, respectively. The immunoreactivities were clearly observed in cytoplasm of many adenoma cells. This amplification procedure provides a means of greatly increasing the sensitivity of the immunohistochemistry including subunits of glycoproteins that are difficult to detect by previous indirect immunoperoxidase method or ABC method. This amplification procedure provides a great increase in the sensitivity of the immunohistochemistry for the detection of gonadotropin subunits and suggest that significant proportion of the nonfunctioning adenomas are gonadotropin subunit producing adenomas.