Immunohistochemical demonstration of salivary proline rich peptide P-C like immunoreactivity in human pancreatic B-cells

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Abstract
Antisera against proline rich peptide P-C, recently isolated from human whole saliva were raised in rabbits by injections of peptide P-C bovine serum albumin conjugates. Immunohistochemical study using the antisera was carried out on human salivary glands, gut and pancreas. Peptide P-C like immunoreactivity was present not only in the salivary glands but also in the pancreatic islets, though not in the gut. Furthermore, immunostaining of adjacent thin sections revealed that cells reacting with antisera against peptide P-C were identical to those reacting with insulin antisera. As the antisera against peptide P-C did not have any cross-reactivities to insulin, glucagon, somatostatin, pancreatic polypeptide, vasoactive intestinal polypeptide and human C-peptide, the antisera were considered to recognize specifically either peptide P-C related antigen or peptide P-C itself in human pancreatic .beta.-cells. A novel substance, peptide P-C like immunoreactivity, may be present in pancreatic .beta.-cells independent of pro-insulin and insulin. Morphological similarity between the salivary glands and the pancreas has been reported, and amylase, kallikrein and glucagon are present in both. These findings seem to suggest some functional relation between the pancreas and salivary glands. Detection of peptide P-C like immunoreactivity in the pancreas and salivary glands would be additional support for this idea. Although it is suggested that peptide P-C like immunoreactivity in pancreatic .beta.-cells may play some role in the function of .beta.-cells, its exact pathophysiological role remains obscure.