Freeze-fracture of membrane fusions in phagocytosing polymorphonuclear leukocytes.

Freeze-fracture of rabbit polymorphonuclear leukocytes in the process of phagocytosing yeast cells shows changes in storage granule and phagosome membranes essentially similar to those described in mammalian secretroy cells during exocytosis. These changes consist of the clearing of intramembrane particle from limited zones of the fusing granule and phagosome membranes. After the completion of fusion, which leads to the incorporation of storage granule membrane into the phagosome membrane, particle-free patches are no longer visible, but the phagosome membrane contains some loose aggregates of particles. These data suggest that intracellular membrane fusion in polymorphonuclear leukocytes occurs through interaction of protein-depleted areas of the involved membranes.