title: Absence of cross-reactivity to myeloperoxidase of anti-thyroid microsomal antibodies in patients with autoimmune thyroid diseases.
abstract: BACKGROUND
  Thyroperoxidase is the major antigen of the thyroid microsomal antibodies (TMA) detected in autoimmune thyroid diseases. Its amino acid sequence has 44% homology with myeloperoxidase (MPO), an enzyme present in the primary granules of neutrophils and one of the major antineutrophil cytoplasmic antibodies (ANCA) antigens. The objective of the present study was to investigate the presence of cross-reactivity to MPO of TMA.
  
  
  METHODS
  We studied sera from 51 patients with autoimmune thyroid diseases, all of them TMA-positive. The presence of ANCA was investigated by indirect immunofluorescence and by capture enzyme-linked immunosorbent assay.
  
  
  RESULTS
  ANCA were positive in 3.9% of the TMA-positive sera and none of them reacted with MPO. In contrast, the ANCA-positive sera revealed antielastase activity. None of the ANCA-positive cases presented clinical signs of vasculitis. However, these 2 patients had been on prolonged treatment with propylthiouracil.
  
  
  CONCLUSIONS
  We conclude that there is no cross-reactivity to MPO of TMA in patients with autoimmune thyroid diseases, possibly because of difference in the spatial configuration of the immunodominant region. The presence of ANCA in patients with autoimmune thyroid diseases without evidence of vasculitis might result from propyIthiouracil-induced polyclonal activation.
authors.affiliation: Department of Internal Medicine, Botucatu Medical School-UNESP, State of São Paulo, Brazil.
authors.forename: B A
authors.initials: BA
authors.lastname: Freire
authors.forename: I D
authors.initials: ID
authors.lastname: Paula
authors.forename: F
authors.initials: F
authors.lastname: Paula
authors.forename: C G
authors.initials: CG
authors.lastname: Kallenberg
authors.forename: P C
authors.initials: PC
authors.lastname: Limburg
authors.forename: T T
authors.initials: TT
authors.lastname: Queluz
mesh_terms: D000328:Adult; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000097:blood / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D001324:Autoantigens / Q000737:chemistry / Q000276:immunology*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006111:Graves Disease / Q000097:blood / Q000276:immunology*; D006801:Humans; D007453:Iodide Peroxidase / Q000737:chemistry / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000737:chemistry / Q000276:immunology*; D017386:Sequence Homology, Amino Acid; D013967:Thyroiditis, Autoimmune / Q000097:blood / Q000276:immunology*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; C056626:thyroid microsomal antibodies; D009195:Peroxidase; D007453:Iodide Peroxidase