Abstract
Peritoneal mast cells and eosinophils were incubated with cationized ferritin (CF) an electron dense marker that binds to the plasma membrane. In both cell types, CF was internalized from the plasma membrane in tubular invaginations. Vesicles of various shapes and sizes containing CF were found in the cytoplasm. Trimetaphosphatase (TMPase) positive lysosomes were found near the nucleus and at the cell periphery. In mast cells, the secretory granules were not reactive for TMPase, while in the eosinophils an occasional specific granule contained reaction product. Vesicles containing CF were observed close to the TMPase positive lysosomes and some of these vesicles seemed to fuse with TMPase positive lysosomes. Vesicles containing both CF and TMPase reaction product were also observed. The presence of both CF and positive TMPase reaction in the same granule suggests that they are secondary lysosomes responsible for degradation of endocytosed material. The CF also induced a partial degranulation of the secretory granules and CF was seen associated with the granule matrix.
