Identification of alpha-1-proteinase inhibitor-containing cells in pancreatic islets

By a regular immunoperoxidase method, alpha-1-proteinase inhibitor (Api) was demonstrated in pancreatic islets in individuals with and without genetic deficiency of Api. Subsequently a double immunoperoxidase method, with two different chromogens (diaminobenzidine-brown and 4-chloro-1-naphthol-blue), was applied on the same tissue section in order to identify cells containing Api and cells secreting polypeptide hormones. Api-positive cells and hormone-secreting cells were found to be mutually exclusive indicating that Api is synthesized by previously unrecognized islet cell. The population of Api cells was significantly higher in persons with genetic deficiency than in other individuals, implying a possible compensatory hyperplasia of those cells triggered by a low level of circulating Api.