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Inhibition of Fc gamma R-dependent functions by N-formylmethionylleucylphenylalanine in human neutrophils.

Human polymorphonuclear neutrophils (PMN) participate in different cellular functions, including phagocytosis, antibody-dependent cell-mediated cytotoxicity (ADCC), and release of reactive oxygen intermediates. Each of these functions can be triggered by receptors for the Fc portion of IgG molecules (Fc gamma R). Normal resting neutrophils possess Fc gamma RII and Fc gamma RIIIB receptors. They also have specific membrane receptors for formylated peptides such as the prototype N-formylmethionylleucylphenylalanine (FMLP). In this report, we present evidence that preincubation of PMN with FMLP inhibits different PMN Fc gamma R-dependent functions such as phagocytosis, ADCC, and immune complex-dependent cytotoxicity. These inhibitory effects can be explained, at least in part, by downregulation of both Fc gamma RII and Fc gamma RIII. Unexpectedly, preincubation of FMLP with PMN was not necessary for ADCC inhibition. Taking into account that the FMLP-dependent Fc gamma R downregulation is not observed before 30 min of incubation, and the onset of ADCC occurs rapidly (seconds), it is possible that FMLP can modify this function by altering early intracellular events.