title: Anti-citrullinated protein antibodies bind surface-expressed citrullinated Grp78 on monocyte/macrophages and stimulate tumor necrosis factor alpha production.
abstract: OBJECTIVE
  Anti-citrullinated protein antibodies (ACPAs), which are the most specific autoantibody marker in patients with rheumatoid arthritis (RA), correlate with disease activity; however, the role of ACPAs in RA pathogenesis has not been elucidated. We hypothesized that ACPAs may directly stimulate mononuclear cells to produce inflammatory cytokines. Thus, we identified cognate antigens of ACPAs on monocyte/macrophages and examined their immunopathologic roles in the pathogenesis of RA.
  
  
  METHODS
  ACPAs were purified from pooled ACPA-positive RA sera by cyclic citrullinated peptide-conjugated affinity column. After coculture of U937 cells with ACPAs, the tumor necrosis factor alpha (TNFalpha) production and NF-kappaB DNA binding activity of the cells were measured by enzyme-linked immunosorbent assay. The cognate antigens of ACPAs on the U937 cell surface were probed by ACPAs, and the reactive bands were examined via proteomic analysis.
  
  
  RESULTS
  ACPAs specifically enhanced TNFalpha production and increased the DNA-binding activity of NF-kappaB in U937 cells. Proteomic analysis revealed that Grp78 protein (72 kd) was one of the cognate antigens of ACPAs. The truncated form of cell surface-expressed Grp78 (55 kd) on U937 cells contained citrulline capable of binding with ACPAs. After citrullination, glutathione S-transferase-tagged recombinant Grp78 (97.52 kd) became a 72-kd fragment and bound with ACPAs. ACPAs also bound to human monocytes and lymphocytes to promote TNFalpha production.
  
  
  CONCLUSIONS
  We clearly demonstrated that ACPAs enhance NF-kappaB activity and TNFalpha production in monocyte/macrophages via binding to surface-expressed citrullinated Grp78.
authors.affiliation: Buddhist Dalin Tzu-Chi General Hospital, Chia-Yi, Taiwan, National Taiwan University College of Medicine, Taipei, Taiwan, and School of Medicine, Tzu-Chi University, Hualien, Taiwan.
authors.forename: Ming-Chi
authors.initials: MC
authors.lastname: Lu
authors.forename: Ning-Sheng
authors.initials: NS
authors.lastname: Lai
authors.forename: Hui-Chun
authors.initials: HC
authors.lastname: Yu
authors.forename: Hsien-Bin
authors.initials: HB
authors.lastname: Huang
authors.forename: Song-Chou
authors.initials: SC
authors.lastname: Hsieh
authors.forename: Chia-Li
authors.initials: CL
authors.lastname: Yu
mesh_terms: D000954:Antigens, Surface / Q000276:immunology / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism; D001323:Autoantibodies / Q000097:blood / Q000276:immunology / Q000494:pharmacology; D015153:Blotting, Western; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000276:immunology*; D006801:Humans; D047468:Immunoprecipitation; D008214:Lymphocytes / Q000276:immunology / Q000378:metabolism; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D010456:Peptides, Cyclic / Q000276:immunology*; D040901:Proteomics; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*; D020298:U937 Cells
chemical_list: D000954:Antigens, Surface; D001323:Autoantibodies; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D016328:NF-kappa B; D010456:Peptides, Cyclic; D014409:Tumor Necrosis Factor-alpha; C487763:cyclic citrullinated peptide