title: Toll-like receptor triggering augments activation of human mast cells by anti-citrullinated protein antibodies.
abstract: OBJECTIVE
  Mast cells may play a role in rheumatoid arthritis (RA), but activation of human mast cells in autoimmune settings has been little studied. Toll-like receptors (TLR) and Fcγ receptors (FcγR) are important receptors for cellular activation in the joint, but expression and stimulation of these receptors in human mast cells or the functional interplay between these pathways is poorly understood. Here, we analysed triggering of human mast cells via these receptors in the context of anti-citrullinated protein antibody-positive (ACPA+) RA.
  
  
  METHODS
  RNA and protein expression of TLRs and FcγR was quantified using PCR and flow cytometry, respectively. Mast cells were stimulated with TLR ligands (including HSP70) combined with IgG immune complexes and IgG-ACPA.
  
  
  RESULTS
  Human mast cells expressed TLRs and produced cytokines in response to TLR ligands. Both cultured and synovial mast cells expressed FcγRIIA, and triggering of this receptor by IgG immune complexes synergised with activation by TLR ligands, leading to two- to fivefold increased cytokine levels. Mast cells produced cytokines in response to ACPA immune complexes in a citrulline-specific manner, which synergised in the presence of HSP70.
  
  
  CONCLUSIONS
  Our data show that synovial mast cells express FcγRIIA and that mast cells can be activated by IgG-ACPA and TLR ligands. Importantly, combined stimulation via TLRs and immune complexes leads to synergy in cytokine production. These findings suggest mast cells are important targets for TLR ligands and immune complexes, and that combined activation of mast cells via these pathways greatly enhances inflammation in synovial tissue of RA patients.
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Suurmond
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: F
authors.initials: F
authors.lastname: Rivellese
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: A L
authors.initials: AL
authors.lastname: Dorjée
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: Bakker
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Y J P C
authors.initials: YJ
authors.lastname: Rombouts
authors.affiliation: Sanquin Research and Landsteiner Laboratorium, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Rispens
authors.affiliation: Sanquin Research and Landsteiner Laboratorium, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Wolbink
authors.affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Zaldumbide
authors.affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: R C
authors.initials: RC
authors.lastname: Hoeben
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: T W J
authors.initials: TW
authors.lastname: Huizinga
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: R E M
authors.initials: RE
authors.lastname: Toes
mesh_terms: D000936:Antigen-Antibody Complex / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D008024:Ligands; D008407:Mast Cells / Q000276:immunology*; D010003:Osteoarthritis / Q000276:immunology; D010456:Peptides, Cyclic / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D017452:Receptors, IgG / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology; D051193:Toll-Like Receptors / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology
chemical_list: D000936:Antigen-Antibody Complex; D016207:Cytokines; C080568:Fc gamma receptor IIA; D007074:Immunoglobulin G; D008024:Ligands; D010456:Peptides, Cyclic; D012333:RNA, Messenger; D017452:Receptors, IgG; D051193:Toll-Like Receptors; C487763:cyclic citrullinated peptide
keywords: Ant-CCP; Autoantibodies; Rheumatoid Arthritis