Heterogeneity in lysosomal fusion with phagocytic vesicles and cell membrane in non-phagocytosing guinea-pig polymorphonuclear leukocyte.

Abstract

The fusion of lysosomes and other granules with phagocytic vesicles (endo-fusion) and cell membrane (exocytosis) was simultaneously examined in non-phagocytosing guinea-pig polymorphonuclear leukocytes (PMNs). beta-Glucuronidase as a typical lysosomal enzyme, acid phosphatase as another lysosomal enzyme, and alkaline phosphatase as a specific granule enzyme were assayed. PMNs released these three enzymes in the presence of serum but the extents of exocytosis differed considerably: release of beta-glucuronidase, alkaline phosphatase and acid phosphatase was 6.9, 4.3 and 3.3%, respectively. Acid phosphatase was released even in the absence of serum, whereas the other two enzymes were not. These three enzymes showed also different responses in endofusion: the preformed phagocytic vesicles fused with the granules containing beta-glucuronidase and acid phosphatase, but scarcely fused with those containing alkaline phosphatase, although all these enzymes were recovered in increasing amounts in the phagolysosome fraction when the cells were allowed to phagocytose continuously. These results suggest that fusion of these three types of granules with phagocytic vesicles (endo-fusion) and plasma membrane (exocytosis) is heterogeneous and regulated by different mechanisms in guinea-pig PMNs.