title: Neutrophil functional responses depend on immune complex valency.
abstract: Ligand-induced cross-linking of Fc gamma receptors (Fc gamma R) on neutrophils plays a significant role in their stimulation, shown here by contrasting the responses induced by low valency immune complexes (LICs) and high valency immune complexes (HICs) and by cross-linking LICs in situ (L/Ab) after their addition to the cells. Multiparameter flow cytometry was used to measure immune complex (IC)-elicited changes in cytoplasmic Ca2+ concentration and initiation of the oxidative burst simultaneously in the same cell and to correlate these with Fc gamma R occupancy. We have previously shown that subpopulations of neutrophils respond maximally to subsaturating concentrations of HIC; saturating dosages stimulate the entire population. This discrepancy was not due to differences in receptor occupancy. The magnitude of the transient Ca2+ increase was independent of the dose of HIC but depended on the dose when an LIC was used. As shown here, L/Ab cross-linking elicited Ca2+ responses similar to those observed in HIC-stimulated cells. In contrast, LIC elicited only minimal intracellular delta pH and no oxidative burst or membrane potential changes at all unless Fc gamma R was cross-linked, accomplished by HIC or by L/Ab. However, azurophilic degranulation, as determined by elastase release, was not observed in cells stimulated by the in situ cross-linking method, whereas the HIC preparation triggered azurophilic degranulation. Thus, some Fc gamma R-mediated neutrophil effector functions such as azurophilic degranulation and oxidative burst initiation have an absolute requirement for Fc gamma R cross-linking, whereas signaling functions such as changes in membrane potential, intracellular pH, and intracellular Ca2+ concentration can occur, albeit more slowly and to a lesser extent, if single Fc gamma R are occupied.
authors.affiliation: Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: Strohmeier
authors.forename: B A
authors.initials: BA
authors.lastname: Brunkhorst
authors.forename: K F
authors.initials: KF
authors.lastname: Seetoo
authors.forename: J
authors.initials: J
authors.lastname: Bernardo
authors.forename: G J
authors.initials: GJ
authors.lastname: Weil
authors.forename: E R
authors.initials: ER
authors.lastname: Simons
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000906:Antibodies / Q000494:pharmacology; D000936:Antigen-Antibody Complex / Q000737:chemistry* / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005434:Flow Cytometry; D005453:Fluorescence; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019272:Leukocyte Elastase; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D018375:Neutrophil Activation / Q000502:physiology; D009504:Neutrophils / Q000378:metabolism / Q000502:physiology*; D010084:Oxidation-Reduction; D010196:Pancreatic Elastase / Q000032:analysis / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism / Q000502:physiology; D016897:Respiratory Burst / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction; D013268:Stimulation, Chemical; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D000906:Antibodies; D000936:Antigen-Antibody Complex; D003574:Cytochrome c Group; D017452:Receptors, IgG; C039465:5-dimethylamiloride; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000584:Amiloride; D013482:Superoxide Dismutase; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; D002118:Calcium