Phagocytosis and Degradation of Melanosomes by the Mast Cells*

Vol. 53, No.3

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PHAGOCYTOSIS AND DEGRADATION OF MELANOSOMES BY THE MAST CELLS* SYOZO SATO, MD., ATSIJSHI KUK1TA, MD. AND SHIN-ICHI SATO, M.D. ABSTRACT

In this electron microscopic study, the melanosomes were always seen as degradative conglomerates within phagocytie vacuoles of the mast cells of skin lesions of dermal melanocytosis and blue nevus. Neither individual premelanosomes nor melanosomes occurring free in the mast cells were observed. The present investigation did not find evi-

dence for melanin biosynthesis in the mast cells, but it suggests phagocytosis and degradation of melanosomes in these cells.

l\'fany microscopic and ultrastructural observations of the intimate association of mast cells and pigment cells and the coexistence of melanin with metachromatic granules in the

magnification of 5,000 with a Hitachi HU-ilA electron microscope operated at an accelerating voltage of 75 Ky.

OBSERVATION

mast cells have been reported (1—11). All these

The mast cells of the skin lesions possess a findings have long suggested a capability for number of villi-like projections on the plasma melanin formation in mast cells. In this paper, the authors report on studies membrane and a round nucleus with indentaof lesions of dermal melanocytosis (12) and tions. Rough surfaced endoplasmic reticulum, blue nevus with an electron microscope. We mitochondria, ribosomes, fine filaments and the Golgi complex were observed in the cytoconclude that melanosomesi may be phago- plasm. The characteristic mast cell granules, cytized by mast cells. Problems of biosynthesis round or oval in shape, were easily observed. of melanin in mast cells and their phagocytic acThe internal structure of the mast cell grantivity will be discussed. ides was composed of parallel, scroll or concentric lamellae and a granular substance.

MATERIALS AND METHODS

Several melanosomes as seen in melanophages were found in the cytoplasm of the sis and blue nevus. The materials were cut into mast cells. These melariosomes in the mast Biopsy specimens were obtained from the skin lesions of four patients with dermal melanocyto-

cells were all confined within the phagocytic 2 per cent osmium tetroxide with phosphate vacuoles outside the mast cell granules, and small pieces, and fixed for 2 hours in ice-cooled buffer at pH 7.3. After fixation, the specimens were dehydrated in increasing concentrations of ethanol

solution, and transferred through two changes of propylene oxide. All specimens were embedded in Epon 812. Sections for electron microscopy were cut with glass and diamond knives on a Porter-

some of the malanosomes were broken up into small pieces with a decrease in their electron density. Individual premelanosomes and melanosomes lying free in the cytoplasm of the mast

Blum ultramicrotome MT-2 at a thickness of cells were not recognized (Figs. 1—3). 500 A. They were electron stained with saturated

uranyl acetate and lead citrate for 5 minutes

DISCUSSION

each. Electron micrographs were taken at direct In light microscopic investigations, Weill This study was supported by grants from the (13), Bertolotto (3), and Quevedo et al. (14) Ministry of Education, Japan, the Far East Basic Research Fund of Sears, Roebuck and Co., Inc.. stated that rat and human mast cells neither Chicago, Illinois, and Japan O'Leary Inc. Fund produced melanin pigment nor contributed to for Pigment Research. the melanogenic activity of the melanocytes in Received January 16, 1969; accepted for publithe hair follicles and in the epidermis. They cation March 5. 1969. * From the Department of Dermatology, Sap- concluded that melanin pigment found in the poro Medical College. Sapporo, Japan. t Nomenclature of the melanin granules was mast cells was considered to have been phagodescribed after the recommended terminology of cytized by these cells. Akai (15) described that melanin-containing organelles, proposed at the no parallelism was present between the numSixth International Pigment Cell Conference in ber of the mast cells and the degree of the skin 1965. 183

184

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Fxo. 1. A small number of phagocytic vacuoles with degradative conglomerates of melanosomes found in the mast cells in blue nevus. Mast cell (Mc), Melanosomes within phagocytic vacuole(m), Melanophage (mp). X 15,700

S

S U

p

brn

a

Fic. 2. Mast cell (top) intimately associated with a dermal melanocyte (bottom)

containing phagocytic vacuoles with melanosomes in the lesion of dermal melanocytosis. Mast cell (Mc), Melanosome in. phagocytic vacuole (m), Individual melanosome lying free in dermal melanocyte (M), Basement membrane (bm). X 17150

½

Fie. 3. Conglomerate of melanosomes within the phagocytic vacuole is seen in the

mast cell of cellular blue nevus. Mast cell (Mc), Melanosome in phagocytic vacuole (m), Melanophage (mp). X

19.600

18ô

186

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pigmentation in the cases of urticaria pigmen- capable of melanin biosynthesis, and that the tosa and other dermatoses.

On the other hand, Woringer (16) believed

melanosomes synthesized in the dermal pigment

cells may be phagoeytized by the mast cells.

that the mast cells played a role in melanogene- We may say that mast cells are capable of sis because their number increased in many phagocytosis of melanin granules formed in the dermatoses associated with hyperpigmentation. melanin-synthesizing cells. Nay (1) found that the mast cells of the mouse REFERENCES not only produced melanin under certain con-

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