Intercalated duct cells in the rat parotid gland may behave as tissue stem cells

This study was conducted to determine whether intercalated duct cells in the rat parotid gland have the properties of tissue stem cells. After induction of cellular proliferation by repeated administration of isoproterenol (IPR), a β-adrenergic agonist, proliferation activity in acinar, intralobular, and intercalated ductal cells was quantified using Ki-67 immunohistochemistry. The total number of each type of component cell in a gland was also estimated in the course of IPR treatment. IPR was found to induce proliferation of acinar and intercalated duct cells, but not intralobular duct cells. The total number of acinar cells in a gland on day 5 of IPR treatment was 1.6 times of that at day 0 (baseline). In contrast, the total numbers of intercalated and intralobular duct cells did not change from baseline, indicating a high possibility that the proliferated intercalated duct cells differentiated into acinar cells. On days 2 to 3 of IPR treatment, intercalated duct cells with amylase-positive secretory granules were recognized in a region very close to the acini, and were suspected of being transitional cells from intercalated duct to acinar cells. This quantitative study indicates that intercalated duct cells may have the properties of tissue stem cells upon IPR stimulation.