Leucine Aminopeptidase Activity in Mast Cells

Abstract

DURING investigations of the behaviour of leucine aminopeptidase activity of blood-serum in patients with dermatoses and tumours^1–3, in a case of diffuse skin mastocytosis of a new-born, we detected heightened activity of leucine aminopeptidase. After mechanical friction of the affected skin, greater activity of leucine aminopeptidase occurred. From this we supposed a release of leucine aminopeptidase from the mast cell infiltrates of the skin. As is well known, in urticaria pigmentosa mechanical irritation of the skin lesions give rise to a degranulation of mast cells^4,5 with liberation of histamine and serotonin. Indeed, there is no doubt that mast cells contain the enzyme leucine aminopeptidase. Using Burstone and Folk's histochemical method⁶, we were able to demonstrate a strong positive cytoplasmic leucine aminopeptidase reaction in the mast cell infiltrates of the cutis in the above-mentioned case. Also in the mesentery of rats, mast cells likewise show a weak positive but distinct cytoplasmic leucine aminopeptidase reaction (Fig. 1), while other connective tissue cells are free of histochemically demonstrable activity of leucine aminopeptidase. To answer the question, whether with degranulation of mast cells there is a release of leucine aminopeptidase in the surrounding tissue, some experiments on rats were performed. Following Fawcett's method⁷ for the release of histamine by mast cells, eight black rats (150–200 gm.) were killed and, after being bled, the abdomen was opened, the mesentery detached in its entirety at the root and separated from the intestine. After incubation in 2 ml. aqua bidest. or Tyrode's solution for 20 min. at 20° C. in 0.5 c.c. of the filtrate, the activity of leucine aminopeptidase was determined by a modified method of Green et al. ¹. Histological controls showed no greater morphological alterations of the mast cells by treatment with Tyrode's solution; however, after treatment by aqua bidest., the well-known osmotic rupture of the mast cells with degranulation^5,7 resulted (Table 1).