EVIDENCE FOR POLYMORPHISM OF MERKEL CELLS IN THE ADULT HUMAN ORAL-MUCOSA

We recently reported that Merkel cells in the normal palatine mucosa o f adult rodents are highly polymorphic. In order to ascertain whether or not this polymorphism is also evident in the human oral mucosa, pal atine mucosae from cadavers without oral diseases and perilesional pal atine mucosae of patients with pleomorphic adenoma were examined by im munohistochemistry using an antibody against cytokeratin 20. Findings showed that Merkel cells in the human normal palatine mucosa were poll -morphic, and a number of irregular-shaped Merkel cells (dendritic Mer kel cells) with apparent cytoplasmic projections were present among ty pical oval to round Merkel cells. The mucosa usually contained a small number of oval to round Merkel cells residing in ectopic places such as prickle and granular cell layers. On the other hand, the slightly i nflamed perilesional palatine mucosa contained an increased incidence of dendritic Merkel cells. Ectopic Merkel cells were rare in the peril esional palatine mucosa. Characteristics of dendritic Merkel cells mer e examined using specimens from perilesional palatine mucosae by means of immunohistochemistry and electron microscopy. It was shown that ev ery dendritic Merkel cell and most roundish Merkel cells in the perile sional mucosa lacked innervation. Electron microscopy suggested that d endritic Merkel cells release secretory granules from the tip of the c ytoplasmic process and the basal cytoplasm towards the lamina propria mucosae, in a manner resembling the case of similar cells in rodents.