Endogytosis of cationic iron colloid particles by rat peritoneal macrophages and the ferritin synthesis. A morphological study

Observations were made on rat peritoneal macrophages exposed to cationic ferric hydroxide colloid (ferric hydroxide-cacodylate complex, Fe-Cac) in vitro in order to study the process of endocytosis of the cationic particles and their fate after ingestion. Fe-Cac particles given to macrophages were adhered to the cell surface and taken up through endocytosis. The ingested particles were first found in the cytoplasmic tiny vesicles and canals adhering to their inner surfaces. These tiny vesicles seldom fused each other or with lysosomes at the early stage of incubation. By further incubation in the iron-free medium, however, macrophages developed the acid phosphatase positive large vacuoles containing a quantity of iron particles, showing the fusion of some Fe-Cac containing endocytic vacuoles with lysosomes. After 15 hr of chase in iron-free medium ferritin molecules in paracrystalline arrangements appeared in a few siderosomes and also diffusely scattered ones in cytoplasmic matrix. Immunocytochemical observations of ferritin with antirat ferritin antibody and FITC conjugated rabbit IgG showed diffuse staining of cytoplasm after 10 to 15 hr of chase in iron-free medium.