Rat skin main neutral protease: immunohistochemical localization.

Specific antiserum against the purified rat skin main neutral protease was used in double layer immunofluorescent method to localize the enzyme in normal rat skin. The specific immunofluorescence was seen in dermal cells that were identified as mast cells on basis of their metachromatic granules. Enzyme histochemical staining with naphthol AS-D chloroacetate localized to the same cells that exhibited specific immunofluorescence. The granules of isolated rat mast cells also gave a specific reaction with the immunohistochemical technique. The results provide further evidence for the suggestion that rat skin main neutral protease is identical with the rat mast cell "chymase."