Two mechanisms for IgG Fc-receptor-mediated phagocytosis by human neutrophils.
Neutrophils (PMN) stimulated with the chemo-attractant FMLP, with platelet activating factor (PAF), and with phorbol dibutyrate exhibited a three- to fivefold increase in phagocytosis of IgG-opsonized sheep E (ElgG). Enhancement of phagocytosis occurred even when stimulants were washed away before the ElgG were added, showing that they could prime PMN for enhanced phagocytosis. When PMN were loaded with MAPTAM, a cell permeant analog of EGTA that prevented any rise in [Ca2+]i, they showed no FMLP-stimulated phagocytosis but had a normal phagocytic response to PAF and phorbol dibutyrate. Addition of MAPTAM after FMLP priming abolished enhanced ingestion, even in the presence of optimal extracellular Ca2+. Thus, the [Ca2+]i rise that occurred on ligation of PMN IgG FcR by ElgG was required for FMLP-stimulated phagocytosis. We determined which FcR were involved in this [Ca2+]i rise and in FMLP-stimulated phagocytosis. Aggregated (agg-IgG) IgG and the anti FcRIII mAb 3G8 both caused increases in [Ca2+]i, removal of FcRIII with phosphatidylinositol-specific phospholipase C (PIPLC) abolished the 3G8-dependent rise in [Ca2+]i without affecting the agg-IgG-dependent rise. Moreover, IV.3 (anti FcRII mAb) completely inhibited the agg-IgG-induced increase in [Ca2+]i in PIPLC-treated PMN, showing that ligation of FcRII is sufficient for a normal IgG-induced [Ca2+]i rise. FMLP-stimulated phagocytosis also was unaffected by PIPLC, suggesting that the rise in [Ca2+]i required for FMLP-stimulated phagocytosis could come from FcRII ligation. From these studies we conclude that there are two molecular mechanisms for IgG-mediated phagocytosis in activated PMN. One, stimulated by FMLP, is dependent on an increase of intracellular Ca2+ during the ingestion process; the other, activated by phorbol esters and PAF, is capable of effecting high levels of ingestion at very low concentrations of [Ca2+]i. These data are consistent with the hypothesis that ligation of FcRII by IgG opsonized targets is sufficient for this Ca(2+)-dependent mechanism of stimulated phagocytosis.
Rosales
C
C
Department of Medicine, Washington University, School of Medicine, St. Louis, MO 63110.
Brown
E J
EJ
D002118:Calcium / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D066298:In Vitro Techniques; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis / Q000187:drug effects; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000494:pharmacology; D011961:Receptors, Fc / Q000502:physiology*
D007074:Immunoglobulin G; D010972:Platelet Activating Factor; D011961:Receptors, Fc; D015240:Phorbol 12,13-Dibutyrate; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002118:Calcium