title: Role of the MyD88 transduction signaling pathway in endothelial activation by antiphospholipid antibodies.
abstract: Antiphospholipid syndrome (APS) is an autoimmune disease characterized by the persistent presence of antiphospholipid antibodies (aPLs) and recurrent thrombosis or fetal loss. The thrombophilic state has been partially related to the induction of a proinflammatory and procoagulant endothelial cell (EC) phenotype induced by anti-beta(2)-glycoprotein I (beta(2)-GPI) antibodies that bind beta(2)-GPI expressed on the EC surface. Anti-beta(2)-GPI antibody binding has been shown to induce nuclear factor-kappa B (NF-kappa B) translocation leading to a proinflammatory EC phenotype similar to that elicited by interaction with microbial products (lipopolysaccharide [LPS]) and proinflammatory cytokines (interleukin 1 beta [IL-1 beta], tumor necrosis factor alpha [TNF-alpha]). However, the upstream signaling events are not characterized yet. To investigate the endothelial signaling cascade activated by anti-beta(2)-GPI antibodies, we transiently cotransfected immortalized human microvascular endothelial cells (HMEC-1) with dominant-negative constructs of different components of the pathway (Delta TRAF2, Delta TRAF6, Delta MyD88) together with reporter genes (NF-kappa B luciferase and pCMV-beta-galactosidase). Results showed that both human anti-beta(2)-GPI IgM monoclonal antibodies as well as polyclonal affinity-purified anti-beta(2)-GPI IgG display a signaling cascade comparable to that activated by LPS or IL-1. Delta TRAF6 and Delta MyD88 significantly abrogate antibody-induced as well as IL-1- or LPS-induced NF-kappa B activation, whereas Delta TRAF2 (involved in NF-kappa B activation by TNF) does not affect it. Moreover, anti- beta(2)-GPI antibodies and LPS followed the same time kinetic of IL-1 receptor-activated kinase (IRAK) phosphorylation, suggesting an involvement of the toll-like receptor (TLR) family. Our findings demonstrate that anti-beta(2)-GPI antibodies react with their antigen likely associated to a member of the TLR/IL-1 receptor family on the EC surface and directly induce activation.
authors.affiliation: Istituto di Ricovero e Aura a Carattere Scientifico Istituto Auxologico Italiano, Allergy and Clinical Immunology Unit, Department of Internal Medicine, University of Milan, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Raschi
authors.forename: Cinzia
authors.initials: C
authors.lastname: Testoni
authors.forename: Daniela
authors.initials: D
authors.lastname: Bosisio
authors.forename: Maria O
authors.initials: MO
authors.lastname: Borghi
authors.forename: Takao
authors.initials: T
authors.lastname: Koike
authors.forename: Alberto
authors.initials: A
authors.lastname: Mantovani
authors.forename: Pier Luigi
authors.initials: PL
authors.lastname: Meroni
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D017152:Antibodies, Antiphospholipid / Q000276:immunology / Q000494:pharmacology*; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D000943:Antigens, Differentiation / Q000235:genetics / Q000502:physiology*; D016736:Antiphospholipid Syndrome / Q000150:complications / Q000276:immunology; D002461:Cell Line, Transformed; D019040:E-Selectin / Q000096:biosynthesis / Q000235:genetics; D004730:Endothelium, Vascular / Q000276:immunology*; D005260:Female; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases; D008070:Lipopolysaccharides / Q000494:pharmacology; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000235:genetics / Q000502:physiology; D011971:Receptors, Immunologic / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D047992:TNF Receptor-Associated Factor 2; D048029:TNF Receptor-Associated Factor 6; D019851:Thrombophilia / Q000209:etiology / Q000276:immunology; D014162:Transfection; D053482:beta 2-Glycoprotein I
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D017152:Antibodies, Antiphospholipid; D000911:Antibodies, Monoclonal; D000943:Antigens, Differentiation; D019040:E-Selectin; D006023:Glycoproteins; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D011506:Proteins; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D047992:TNF Receptor-Associated Factor 2; D048029:TNF Receptor-Associated Factor 6; D053482:beta 2-Glycoprotein I; D011494:Protein Kinases; D053592:Interleukin-1 Receptor-Associated Kinases