title: IgG subclass distribution, affinity of anti-myeloperoxidase antibodies in sera from patients with Wegener's granulomatosis and microscopic polyangiitis.
abstract: OBJECTIVE
  Our previous study suggested that patients with MPO-ANCA (myeloperoxidase antineutrophil cytoplasmic autoantibodies)-positive Wegener's granulomatosis (WG) were common in Chinese, indicating that patients with MPO-ANCA could manifest as either WG or microscopic polyangiitis (MPA). The aim of this study was to compare the immunological characteristics of MPO-ANCA in patients with WG and MPA.
  
  
  METHODS
  Fifteen patients with WG and 21 patients with MPA were enrolled in the current study. Anti-MPO IgG subclasses and their titres were detected by antigen-specific enzyme-linked immunosorbent assays (ELISA); affinity was assessed by antigen-inhibition ELISAs. The sera from all patients were employed to inhibit biotin conjugated affinity-purified human anti-MPO antibodies (Probe-biotin), from plasma exchange of a patient with MPA, in a competitive inhibition ELISAs system.
  
  
  RESULTS
  All four anti-MPO subclasses could be detected in sera from patients with WG and MPA. The titres of anti-MPO IgG4 subclass in patients with WG were significantly higher than those with MPA (1:1878 vs 1:218, P < 0.005). The affinity constants of MPO-ANCA were comparable between patients with WG and MPA (0.3-70/M vs 0.3-140/M respectively). Eleven out of the 15 sera and 18 out of the 21 sera could inhibit the binding of the Probe-biotin in patients with WG and MPA respectively. The average inhibition rate was 47.7% +/- 11.5% and 61.7% +/- 14.5% respectively (P < 0.05).
  
  
  CONCLUSIONS
  MPO-ANCA IgG4 subclass might play a role in the development of WG. The MPO-ANCA in WG and MPA might recognize overlapping but different epitopes on native MPO molecule. The difference in immunological characteristics of MPO-ANCA might contribute to different disease entities.
authors.affiliation: Renal Division, Department of Medicine Peking University First Hospital, Institute of Nephrology, Peking University, Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China.
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Liu
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Feng
authors.initials: F
authors.lastname: Yu
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Zhao
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000276:immunology*; D000915:Antibody Affinity; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D014890:Granulomatosis with Polyangiitis / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000145:classification*; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000276:immunology*; D014657:Vasculitis / Q000276:immunology*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D007074:Immunoglobulin G; D009195:Peroxidase