Fetoacinar pancreatic protein in the developing human pancreas.

The distribution of the 110-kilodalton fetoacinar pancreatic (FAP) protein was examined in 56 pancreases obtained from human embryos and fetuses (ranging 6 from weeks of gestation to full term) and 10 normal adult pancreases. This recently discovered protein is a concanavalin-A-binding glycoprotein that is specific for acinar cells of the pancreas. Using a murine monoclonal antibody for either immunoperoxidase or immunofluorescence procedures, FAP-protein expression was not found in embryos at less than 9 weeks of gestation. At 9-10 weeks, a clear staining was observed in the terminal portions of dilated buds in primitive pancreatic tubular structures (i.e., the site of the first development of the future acinus). At 11-12 weeks, acinar structuration began, and FAP-protein expression increased as shown by the higher number of stained acini and the greater staining intensity. Maximal expression occurred at 15-22 weeks and then gradually decreased; from 28 to 32 weeks until full term, the pancreas was almost negative for this protein. In the adult pancreases, the protein was either absent or only present in acinar cells surrounding the islets of Langerhans. The pancreatic ducts and endocrine cells remained negative throughout gestation and in adults. FAP-protein thus appears to be a marker of acinar-cell differentiation. Its function remains unknown at present. Its close association with the growth and development of the pancreas together with the fact that, in a previous study, it was found to be re-expressed in pancreatitis and in cancer, suggest that it may play a role in developmental regenerative and neoplastic processes in the pancreas.