Characterization of immunoreactive forms of pancreatic polypeptide in islet cell tumors using antisera with different regional specificities

Tumor tissue from a heterogeneous group of patients with clinically and histologically diagnosed islet cell tumors has been assessed for pancreatic polypeptide (PP) content using radioimmunoassay. Immunoreactive forms of PP, obtained by gel filtration of tissue extracts, were detected using antisera with different regional specificities. Normal pancreatic tissue contained one form of PP coeluting with human PP whereas, tumor tissue from patients with insulinoma, Zollinger-Ellison, and WDHA (watery diarrhea hypokalemic achlorhydric) syndromes contained, in addition, higher molecular weight forms of immunoreactive PP. Furthermore, a lower molecular weight form was detected in tumor tissue from a Zollinger-Ellison syndrome patient. The high molecular weight forms of immunoreactive PP were not recognized using a C-terminal-specific antiserum, whereas the smaller form was only detected using this antiserum. The variation in cross-reactivity observed with two antisera in this study emphasizes the limitations of using a single antiserum to detect molecular forms of peptide hormones, particularly those in islet cell tumors.