Phagosomal-phagolysosomal membrane dynamics of stimulated mouse peritoneal macrophages.

Freeze-fracture replication was used to study the membrane events of stimulated mouse peritoneal macrophages during phagocytosis. An increase in intramembrane particles (IMPs) was observed on the protoplasmic fracture (PF) face of the freeze-fractured plasma membrane of phagocytosing macrophages as compared to those of the plasma membrane of nonphagocytosing cells. On the basis of freeze-fracture patterns of membranes, three types of phagosomal membranes were found following the ingestion of the streptomycin-dependent mutant (avirulent) of Salmonella typhimurium (SMD). Most phagosomes 10 min after bacterial uptake had membranes that were structurally similar to the plasma membranes of phagocytosing cells. Structural transformations, i.e., changes in IMP number and size distribution, were observed in phagosomal membranes as the time from bacterial uptake increased. Similar types of phagosomal membranes were also found in phagocytosing macrophages when wild-type Salmonella typhimurium (virulent) was used as the phagocytic challenge. Some indirect morphological evidence suggested that membranes may be pinched off from the phagosomes-phagolysosomes which would be available for recycling back to the cell surface. In the systems studied thus far it appears that the freeze-fracture structure of phagolysosomal membranes is significantly different from that of the plasma membranes. In addition, freeze-fracture evidence suggested that fusion can take place between adjacent phagosomes or phagolysosomes.