Immunohistochemical and cytochemical evidences for a possible localization of leucine aminopeptidase in the Merkel cell granule

Localization of leucine aminopeptidase (LAP) in the Merkel cell-axon complex was studied immuno-histochemically and cytochemically in the labial tissues of the mouse, rat, dog, and monkey. Anti-LAP was obtained in rabbits by the injection of commercially supplied swine LAP which was confirmed as electrophoretically pure. The Merkel cells of the mouse, rat, and monkey were positively stained by treatment with anti-LAP but the Merkel cells of the dog were negative. When ultrathin sections of the hair follicle from the rat whisker pad, which contain an adundance of Merkel cells, were processed by immuno-peroxidase or by the immuno-gold method, the reaction products were predominantly deposited on the Merkel cells granules. Furthermore, an immuno-blot assay revealed that an extract of the hair follicles from murine whisker pads contained a molecule of relative molecular mass M1 = 60 000 which is similar in size to a subunit of swine LAP. Thus, it appears that Merkel cell granules of rodents and the monkey contain a protein which resembles lucine aminopeptidase.