ULTRASTRUCTURE OF HUMAN DERMAL MAST-CELLS IN 29 DIFFERENT LYSOSOMAL STORAGE DISEASES

The effect of lysosomal storage diseases on the ultrastructure of huma n mast cells has not previously been reported. Indeed, there has been little published evidence indicating that mast cells contain typical l ysosomes. However, mast cell cytoplasmic granules contain hydrolases s imilar to those found in lysosomes, but which differ from lysosomal hy drolases in exhibiting optimal activity at higher pH. We therefore exa mined by transmission electron microscopy the dermal mast cells in 58 biopsies of patients exhibiting 1 of 29 different lysosomal storage di seases. We found mast cells containing abnormal lysosomes in 16 of the se disorders. In 6 of these 16 diseases, the mast cells' cytoplasmic g ranules appeared normal. These observations indicate that human mast c ells can contain lysosomes, and provide evidence that the enzymes affe cted by lysosomal storage diseases are active in mast cells.