title: ANCA-induced neutrophil F-actin polymerization: implications for microvascular inflammation.
abstract: BACKGROUND
  The antineutrophil cytoplasmic antibody (ANCA)-positive vasculitides are characterized by a necrotizing vasculitis of small vessels with neutrophil infiltration. The reasons behind the selectivity for small vessels remain unclear, but may relate to the necessity for neutrophils to deform in order to pass through capillaries. The resistance to deformation of neutrophils largely arises from their actin cytoskeleton. It is hypothesized that ANCA, by inducing actin polymerization, increases neutrophil rigidity and contributes to their sequestration in capillaries.
  
  
  METHODS
  To test this hypothesis, neutrophils were treated with IgG-ANCA and the following characterizations: formation of filamentous F-actin (by flow cytometry); changes in morphology (by fluorescence and electron microscopy); and the potential to obstruct microvessels (by measuring entry times into micropipettes with comparable diameters to capillaries). The neutrophil signaling mechanisms activated by IgG-ANCA were investigated using blocking antibodies to Fcgamma receptors and inhibitors of tyrosine phosphorylation. Protein tyrosine phosphorylation was examined by immunoblotting of cell lysates, and calcium fluxes were measured by spectrofluorimetry of Fura-2 pentakis (acetoxymethyl) ester (Fura 2-AM) labeled neutrophils.
  
  
  RESULTS
  IgG-ANCA led to a significant dose-dependent actin polymerization over about 10 minutes. Over the same period, neutrophils became distorted in shape and more resistant to micropipette aspiration. Treatment with normal IgG caused less marked and delayed changes in these parameters. Actin polymerization required engagement of FcgammaRIIa receptor, tyrosine phosphorylation, and calcium fluxes.
  
  
  CONCLUSIONS
  These novel findings reveal signaling mechanisms that underlie ANCA-induced actin polymerization and might explain the predilection for small vessels in IgG-ANCA-associated vasculitis.
authors.affiliation: Department of Nephrology, University of Birmingham, United Kingdom. yee-wai.tse@phnt.swest.nhs.uk
authors.forename: Wai Y
authors.initials: WY
authors.lastname: Tse
authors.forename: Gerard B
authors.initials: GB
authors.lastname: Nash
authors.forename: Peter
authors.initials: P
authors.lastname: Hewins
authors.forename: Caroline O S
authors.initials: CO
authors.lastname: Savage
authors.forename: Dwomoa
authors.initials: D
authors.lastname: Adu
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000378:metabolism* / Q000494:pharmacology; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D020013:Calcium Signaling; D048430:Cell Shape; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D008833:Microcirculation / Q000276:immunology / Q000293:injuries / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism* / Q000648:ultrastructure; D010766:Phosphorylation; D017452:Receptors, IgG / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry; D014657:Vasculitis / Q000209:etiology / Q000276:immunology / Q000378:metabolism
chemical_list: D000199:Actins; D019268:Antibodies, Antineutrophil Cytoplasmic; D001704:Biopolymers; D007074:Immunoglobulin G; D017452:Receptors, IgG; D014443:Tyrosine