Plasma Membrane Synthesis in the Macrophage following Phagocytosis of Polystyrene Latex Particles

Phagocytosis of polystyrene latex beads by mouse peritoneal macrophages results in the interiorization of large amounts of plasma membrane to form the phagolysosomal membrane. The isolated membrane of the phagolysosomes is initially similar to the plasma membrane in cholesterol and phospholipid content, and carries 5′-nucleotidase activity with the characteristics of the plasma membrane marker enzyme. Immediately after ingestion, the amount of the plasma membrane has descreased as judged by a reduction in cell volume, spreading, pinocytosis, and phagocytosis. During the next 6 hours, the phagolysosomal 5′-nucleotidase activity decreases with a half-life of about 2 hours. Total cellular 5′-nucleotidase also decreases to a degree accounted for by the decrease in the phagolysosomal enzyme and in proportion to the amount of latex interiorized. After a lag of about 6 hours, cellular levels of the membrane constituents cholesterol and phospholipid begin to increase. The final net increase is linearly proportional to the amount of latex initially ingested and to the amount of plasma membrane interiorized. Only at this time do the macrophages begin to spread out on the glass surface, resume pinocytosis, and regain the ability to phagocytize a new test particle. The cellular levels of 5′-nucleotidase also begin to increase reaching control levels by 10 to 12 hours after phagocytosis. This activity is not associated with the phagolysosomes. These changes suggest the net synthesis of plasma membrane to replace the membrane interiorized during phagocytosis. This synthesis requires the presence of exogenous cholesterol molecules for use in the membrane. In the absence of cholesterol, plasma membrane functions are not restored and 5′-nucleotidase activity does not return to control levels. The inhibition of protein and RNA synthesis after phagocytosis blocks the net increment in cellular cholesterol, phospholipid, and 5′-nucleotidase activity.