Dissociation between phagocytosis and phagosome-lysosome fusion

The acridine orange technique was used to explore phagosome-lysosome fusion (P-L fusion) in thioglycollate-elicited rat peritoneal macrophages. Sheep red blood cells were coated with IgG or IgM plus complement, or treated with neuraminidase, tannic acid or glutaraldehyde; then both their capacity to be ingested by macrophages and their ability to induce P-L fusion after ingestion were assayed. Their capacity to be engulfed by macrophages was similar, but glutaraldehyde-treated erythrocytes were far more efficient than the other particles in triggering P-L fusion. Hence, both processes must be driven by different mechanisms. No correlation was found between the surface charge of test particles (as assayed by cell electrophoresis) and their ability to trigger phagocytosis or P-L fusion. However, glutaraldehyde-treated erythrocytes were found to be more hydrophobic than the other particles, as previously reported. Hence, particle hydrophobicity might favor P-L fusion. The implication of these findings are discussed.