title: In vitro effect of anti-β₂ glycoprotein I antibodies on P-selectin expression, a marker of platelet activation.
abstract: OBJECTIVE
  Antiphospholipid antibodies (aPL) associated with thrombembolic events and/or pregnancy morbidity characterize the so-called antiphospholipid syndrome (APS). Beta2glycoprotein I (β2GPI) represents the major target antigen for aPL, but the pathogenic role of anti-β2GPI antibodies (aβ2GPI) is still unclear. Some authors assume they play a role in activating platelets. The effects of aβ2GPI antibodies on platelet P-selectin expression were evaluated in this study.
  
  
  METHODS
  Aβ2GPI antibodies in the plasma of a pregnant APS patient were isolated by affinity chromatography during two different stages (catastrophic and quiescent) of the disease. Gel filtered platelets (100,000/μl) from healthy volunteers were incubated with β2-GPI (20 μg/ml) and with different concentrations (5, 25 e 50 μg/ml) of aβ2GPI antibodies. P-selectin surface expression on platelets was assessed by flow cytometry using a specific fluorescent antibody directed against P-selectin.
  
  
  RESULTS
  Aβ2GPI antibodies induced platelet activation only in the presence of thrombin receptor activator for peptide 6 (TRAP-6), a platelet agonist, at a subthreshold concentration. Aβ2GPI antibody enhancement on platelet surface P-selectin expression was stronger in the catastrophic than in the quiescent phase of the disease (47% versus 15%).
  
  
  CONCLUSIONS
  TRAP-6 dependent platelet activation by aβ2GPI antibodies is consistent with the “two hit” pathogenetic hypothesis for thrombosis. Aβ2GPI antibodies induce higher platelet P-selectin expression during the active rather than in the acute phases.
authors.affiliation: Cattedra e U.O.C. di Reumatologia, Dipartimento di Medicina Clinica e Sperimentale, Università di Padova, Italy. agnese.bontadi@unipd.it
authors.forename: A
authors.initials: A
authors.lastname: Bontadi
authors.forename: A
authors.initials: A
authors.lastname: Ruffatti
authors.forename: S
authors.initials: S
authors.lastname: Giannini
authors.forename: E
authors.initials: E
authors.lastname: Falcinelli
authors.forename: M
authors.initials: M
authors.lastname: Tonello
authors.forename: A
authors.initials: A
authors.lastname: Hoxha
authors.forename: P
authors.initials: P
authors.lastname: Gresele
authors.forename: L
authors.initials: L
authors.lastname: Punzi
mesh_terms: D000208:Acute Disease; D000328:Adult; D016736:Antiphospholipid Syndrome / Q000097:blood* / Q000150:complications / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology*; D001324:Autoantigens / Q000276:immunology* / Q000302:isolation & purification; D002846:Chromatography, Affinity; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D019007:P-Selectin / Q000096:biosynthesis* / Q000235:genetics; D010446:Peptide Fragments / Q000494:pharmacology; D015539:Platelet Activation; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood* / Q000276:immunology; D011250:Pregnancy Complications, Hematologic / Q000097:blood / Q000209:etiology / Q000276:immunology; D019851:Thrombophilia / Q000097:blood / Q000209:etiology* / Q000276:immunology; D053482:beta 2-Glycoprotein I / Q000276:immunology* / Q000302:isolation & purification / Q000494:pharmacology
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D019007:P-Selectin; D010446:Peptide Fragments; D053482:beta 2-Glycoprotein I; C082835:thrombin receptor peptide (42-47)