Ultrastructural alterations in macrophages after phagocytosis of acrylic microspheres.

The effect of microparticles on the survival of cultured mouse peritoneal macrophages was investigated using doses of 0.01-0.1 mg of lyophilized particles/ml of medium and 5 X 10(5) cells, corresponding to approximately 4000-40,000 particles per cell. The lowest dose did not significantly change the survival time as compared with the controls, while approximately 75% of the cells were lost during the first 48 h on exposure to the highest dose. High doses of particles induce cellular damage. The morphology and stability of the lysosomal apparatus was followed with electron microscopy, acid phosphatase cytochemistry, and acridine orange uptake. Alteration of the lysosomal vacuome was characterized by a greatly enhanced rate of autophagocytosis, the formation of huge secondary lysosomes containing microparticles, and labilization of the vacuome with loss of acidity and a tendency to leak acid phosphatase into the cell sap.