Abstract
During phagocytosis of serum-opsonized zymosan by guinea-pig polymorphonuclear neutrophils, the leucine aminopeptidase activity decreased significantly, whereas 5'-nucleotidase and alkaline phosphodiesterase activities remained unchanged. Inactivation of leucine aminopeptidase activity was not observed by exposure of neutrophils to non-opsonized zymoan, IgG-coated zymosan or polystyrene latex particles. Pretreatment of neutrophils with cytochalasin B, which prevents phagocytosis but not surface binding of particles, did not prevent leucine aminopeptidase from inactivation. On the other hand, the inactivation during phagocytosis was protected by serine protease inhibitors. These findings suggest that loss of leucine aminopeptidase activity from phagocytosing cells may be mediated by certain serine protease inhibitor-sensitive factor (s) which are probably activated by the attachement of an opsonized zymosan particle to a specific membrane recptor, probably the C3b receptor.
