Cytochemical localization of arylsulfatase B in rat basophils and mast cells

Basophils and mast cells possess large metachromatically staining granules which contain sulfated glycosaminoglycans as well as vasoactive compounds. To determine whether these granules might also have lysosomal properties, we used electron microscopy and cytochemistry to localize arylsulfatase B in rat basophils and mast cells. In basophils of bone marrow, enzymatic reaction product was consistently seen in many, but not all, of the basophil granules. In some cells, the enzyme could also be demonstrated in the Golgi region, restricted to a single cisterna and small vesicles. It was never seen in rough endoplasmic reticulum (RER), although the paucity of cells made adequate sampling difficult. In mast cells of bone marrow and the peritoneal cavity, enzymatic reaction product was consistently found in some cytoplasmic granules of varying sizes and shapes where it characteristically rimmed the periphery of the granule just beneath the limiting membrane. It should be emphasized, however, that the majority of granules were not reactive. Reaction product could also be found occasionally in segments of RER, and in the Golgi region with a distribution similar to that of the basophil. The presence of lysosomal arylsulfatase in granules of developing basophils in bone marrow suggests that some basophil granules, like those of neutrophils, eosinophils, and monocytes are primary lysosomes. Some mast cell granules also contain this lysosomal enzyme, although it is not clear from the present data whether these granules are primary or secondary lysosomes.