AN ELECTRON MICROSCOPIC STUDY OF DEGRANULATION OF MAST CELL GRANULES IN URTICARIA PIGMENTOSA

[摘要] Electron microscopic examination of 4 human cases of urticaria pigmentosa revealed that the nodular type lesions were mainly composed of round mast cells, while the majority of mast cells in macular type of lesions were elongated. The elongated type of mast cells were found in normal skin and in the stroma of benign skin tumors. When mast cells are young, they contain more mitochondria and endoplasmic reticulum than older cells, but the total amount of these organelles is not large in comparison to other connective tissue cells. The 3 major components of mast cell granules were fine, parallel filaments, thick lamellae and a dense particulate material. Formation of the granules was initiated by a concentration of the fine filaments. This was followed by an accumulation of thick lamellae and the subsequent deposition of the dense particulate material on the lamellae. There seemed to be no direct participation of the endoplasmic reticulum in the synthesis of the mast cell granules. Disintegration of the mast cell granules began with fragmentation of the lamellae and a loss of density throughout the granule but most marked at the periphery of the granule. The center of the granules became coarsely reticular. Progression of this process resulted in complete dissolution of the granules. Mast cell granules not only disintegrated within mast cells but also were discharged into the surrounding connective tissue at different stages of disintegration.