Immunocytochemical localization and identification of prosomatostatin gene products in medullary carcinoma of human thyroid gland

Practical markers used in the diagnosis of endocrine tumors

Endocrine tumors constitute a large group of neoplasms that are widely dispersed throughout the body. They are made up mostly of neuroendocrine tumors (NE), which are characterized by the presence of secretory granules and production of peptide hormones, and non-NE tumors such as those derived from thyroid follicular cells and adrenal cortical cells. Immunohistochemical markers have been used to characterize these lesions and distinguish them from other histologically similar tumors. Chromogranin and synaptophysin are the most widely used broad-spectrum neuroendocrine tumor markers. The use of antibodies to transcription factors, keratins, and specific peptides is quite valuable in the diagnosis of endocrine tumors. This article reviews the common markers used to characterize endocrine tumors and to recognize tumors involved in the differential diagnosis of specific lesions.

Histopathological and immunohistochemical features of thyroid carcinoma

Thyroid-specific malignant tumors are derived from follicle cells (papillary and follicular carcinoma), and from parafollicular, calcitonin-producing C-cells (medullary carcinoma). The main criterion for diagnosis of papillary carcinoma is the occurrence of ground glass, hypochromic nuclei, often associated with papillae as the prominent pattern of the tumor, and psammoma bodies. The diagnosis of follicular carcinoma is based on the true infiltration of the venous vessels outside the tumor capsule and the fungus-like infiltration through the tumor capsule into the surrounding parenchyma. Anaplastic carcinoma is mostly detected by the pathologist by fine-needle aspiration biopsy, or tumor reduction specimen. Medullary thyroid carcinoma is typically composed of solid nests and infiltrating formations of polygonal or spindle-shaped cells and amyloid deposits within the stroma of the tumor. Two main discriminatory immunohistochemical markers for tumors with follicular and parafollicular origin are thyroglobulin and calcitonin, respectively. Thyroglobulin is present in more than 95% of papillary and follicular carcinomas, whereas anaplastic thyroid carcinomas are mostly immunonegative for thyroglobulin. Medullary carcinoma is characteristically positive for calcitonin, pan-neuroendocrine markers, and often numerous peptides.

Immunocytochemical detection and characterization of intrahepatic human pancreatic islets after combined liver-islet allotransplantation

The unique availability of an explanted liver-islet allograft, removed for primary nonfunction of the liver, led us to evaluate distribution and phenotype of exocrine and endocrine components of the pancreatic graft. Immunocytochemistry was used to map patterns of gene products for islet hormones, proprotein processing enzymes, panneuroendocrine markers, and pancreatic exocrine markers. When compared with age-matched control pancreases, insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-producing cells were similarly represented and distributed within the grafted islet. We also demonstrate that the intrahepatic transplanted islets retained the enzyme machinery able to process the hormone precursors into bioactive fragments. In the clinical setting, this resulted in an immediate functioning of the graft and insulin-independence of the patient one month after transplantation. The purity in islets, as assessed by immunocytochemistry with antibodies to tissue constituents of endocrine and exocrine lineages, was around 40%. Despite the massive intraportal presence of pancreatic acinar tissue, no signs or symptoms attributable to ectopic hypersecretion of exocrine enzymes occurred. In fact, when tested with antibodies to such enzymes, low levels of immunoreactivity were observed in the grafted acinar cells.

The use of fixed-frozen tissue in routine ultrastructural evaluation and immunogold labeling

A method of freezing fixed surgical tissue specimens for long-term storage and subsequent resin embedding was developed. The method entails fixation of the specimens in Karnowsky's liquid, cryoprotecting with 10% sucrose, freezing in melting Freon gas, and storage at -80 degrees C. When needed, even after years, the frozen tissue pieces are thawed in lukewarm (37 degrees C) buffer and embedded in resin (Epon or Lowicryl). Ultrastructural detail as well as immunocytochemical reactivity of a wide variety of cellular constituents are well preserved. The method is practical and allows retrospective embedding in Lowicryl resin (a technique not easily applicable in everyday routine) for subsequent ultrastructural immunolocalization studies.

Somatostatin cells in human somatotropic adenomas

Data from our group have shown that the human adenomatous and normal anterior pituitary may be the source of somatostatin (SRIH). SRIH-producing cells were identified in two somatotropic adenomas. Immunoreactive SRIH cells were present in both cases. In case 2, material was available for RNA studies, in situ hybridization and electron microscopy. The size of the transcript identified by Northern blot analysis was identical to that of hypothalamic SRIH mRNA. In situ hybridization showed that the SRIH gene was expressed in a cell subset superimposable to that identified by immunocytochemistry. Co-localization studies revealed that SRIH and growth hormone (GH) immunoreactivities were not present in the same cells. Ultrastructural immunogold labelling showed that SRIH cells had features distinct from those of the somatotropes. The results confirm that the somatotropic adenomas have the ability to synthesize SRIH, indicate that SRIH expression is restricted to a subset of adenoma cells different from GH-producing cells, and imply that SRIH cells are involved in paracrine regulation of neighbouring somatotropes.

Immunocytochemical localization and identification of members of the pancreatic polypeptide (PP)-fold family in human thyroid C cells and medullary carcinomas

An increasing number of regulatory peptides not coded by the calcitonin genes are known to occur in the thyroid C cells. We have now carried out light and electron microscopic immunocytochemical analyses on specimens of normal human thyroids and medullary carcinomas to establish the occurrence of members of the PP-PYY-NPY family in the C cell system. By means of site-directed immunocytochemistry we provide the first evidence that a molecule closely related to proNPY is present in normal and pathologic C cells, and is co-stored with calcitonin in the cytoplasmic dense-core granules. Preliminary observations also suggest that high levels of expression of NPY-gene products help to define a subset of tumours with a less aggressive behaviour.