Immunohistochemical study of secretory proteins in the developing human exocrine pancreas

We have studied, by immunohistochemical methods using specific antisera, the development of three glycoproteins of human pancreatic secretion: lipase, carboxyl ester hydrolase (CEH) and the P19 protein (precursor of the non glycosylated protein X or "pancreatic thread/stone protein"). We have compared their development to that of trypsinogens (Tgs) and chymotrypsinogen A (ChTgA), as well as to that of FAP (feto acinar pancreatic protein), a glycoprotein associated with the differentiation of human pancreas. Our studies show the characteristic appearance and development of lipase, the immunoreactivity of which appears later (at the 21st week of pregnancy) than it does for Tgs and ChTg (at the 16th week of pregnancy). Moreover, the lipase labelling is first observed in a few acini dispersed in the pancreas and then spreads out progressively to be present in all the acini after the age of 15 days. By contrast, as soon as they appear, Tgs and ChTg are observed uniformly in all acinar cells. The intensities of the lipase, Tgs and ChTg labellings increase greatly at birth. The ontogenesis of CEH does not follow that of lipase but that of Tgs and ChTg. The ontogenesis of P19 is parallel to that of Tgs. As previously observed, FAP presents a maximal immunoreactivity at the 24th-27th weeks of pregnancy, which decreases slowly up until birth.