Antiserum directed against chromogranin A and B (CAB) is a useful marker for peptide hormone-producing endocrine cells and tumors.

Certain proteins, such as the chromogranins, have a ubiquitous occurrence in nearly ail peptide hormone-producing cells. To date, little is known about their functional role as structural proteins, precursors of bioactive peptides, or enzymes. Such proteins may serve as markers for endocrine cells and tumors. In the present study, we have used an antiserum that recognizes both chromogranin A and B (CAB) to demonstrate peptide hormone-producing endocrine cells and tumors in humans. The antiserum demonstrated endocrine cells all along the gastrointestinal tract, most of the islet cells, the adrenomedullary cells, the thyroid C cells, scattered endocrine cells in the respiratory tract, and numerous cells in the adenohypophysis. The CAB-positive cells outnumbered those storing chromogranin A as studied in the intestines and the anterior pituitary. An array of different peptide hormone-producing tumor cells were also CAB-positive, including several types of islet cell tumors, gastric, intestinal, and bronchial carcinoids, medullary thyroid carcinomas, and pheochromocytomas. Thus, the CAB antiserum may help identify peptide hormone-producing cells and tumors.