Reversible phagocytosis in rabbit polymorphonuclear leukocytes.

We have studied the fate of inert phagocytized particles in rabbit neutrophils. Neutrophils release significant quantities of preingested oil emulsion. Roughly 50% of an ingested load is released in 40 min at 37 degrees C. By electron microscopy the process of release appears to be by exocytosis: particles appear extruded through a network of processes often accompanied by membranous vesicles. Exocytosis is temperature and glucose dependent but unlike phagocytosis does not require divalent cations. From Coulter counter measurements virtually the entire cell population appears to undergo the phagocytosis-exocytosis sequence. Neutrophils undergoing exocytosis remain intact as determined by direct counts, electron microscopy, and absence of lactate dehydrogenase release. Moreover, by sequentially feeding differently labeled particles, it is shown that the processes of phagocytosis and exocytosis can occur concurrently. Indeed, it is found that ingestion accelerates release. The implications of these phenomena for membrane recycling, lysosomal enzyme release, and the killing of microorganisms are briefly discussed.