Phagocytosis-induced modulation of human neutrophil chemotaxis receptors

Abstract

We investigated the effect of a major physiologic event, phagocytosis, on the ability of human neutrophils (PMN) to bind the synthetic chemotactic peptide, 3H-formyl-methio-nyl-leucyl-phenylalanine (3H-FMLP). We found that both latex and opsonized zymosan (OPZ) particles caused dose-dependent suppression of 3H-FMLP binding and abolition of 3H-FMLP binding with concentrations of OPZ greater than 2 mg/ml. This “particle effect” was completely inhibited by incubation of PMN with 10 mM 2-deoxyglucose before, but not after, phagocytosis. The particle effect was partially inhibited (28%) by anaerobic conditions and CGD neutrophils, but not by superoxide dismutase, catalase, or oxygen radical scavengers. In addition, supernatants from PMN that had been incubated with OPZ caused 55% reduction of 3H-FMLP binding by fresh PMN. The effect of PMN-OPZ supernatants was inhibited by 1 mM phenylmethylsulfonylfluoride (PMSF), suggesting an additional role for release of neutrophil proteases in the particle effect. The finding that the particle effect was not inhibited by cytochalasin-B or under conditions in which 3H-FMLP was bound to PMN prior to OPZ, indicated that membrane ingestion was not responsible for phagocytosis-induced suppression of 3H-FMLP binding. Finally, we found that low concentrations of OPZ (0.167 mg/ml) decreased the affinity but not total number of 3H-FMLP receptors, but higher OPZ concentrations (>2 mg/ml) totally abolished 3H-FMLP binding. These data indicate that the act of phagocytosis initiates at least two distinct mechanisms that may result in the modulation of chemotactic peptide receptors and perhaps other membrane proteins on neutrophils.