On the origin of the phagocytic membrane

Abstract

Phagocytic vesicles and plasma membranes were isolated from mouse L cell fibroblasts which had ingested latex particles in the presence of labelled protein, sugar or lipid precursors. In some experiments the cell surface was specifically marked before phagocytosis with labelled sialic acid using the CMP-sugar donor. Each marker was found to be differentially incorporated in comparisons between plasma membranes and phagosomes. The inhibition of protein synthesis with cycloheximide during phagocytosis did not decrease the rate of particle ingestion, but had only a slight effect on the marker distribution pattern. However, this pattern was highly sensitive to a variation in the culture history of the cells. The characteristic differential marker incorporation between membranes indicates that the phagocytic membrane is not derived entirely from an invagination of the pre-existing cell surface. Rather, much newly synthesised material of a unique composition may also coat particles during their ingestion. It is proposed that the mechanism of phagocytosis differs only superficially from that of lamellipodial locomotion of cells.