title: Detection of anti-neutrophil cytoplasmic antibodies by immunoprecipitation.
abstract: Immunoprecipitation (IP) of radiolabeled PMN extracts was used as the gold standard for anti-proteinase 3 (PR-3) autoantibody detection to validate immunofluorescence (IF) and alpha granule (alpha) ELISA. A myeloperoxidase (MPO) ELISA was also used in parallel. We studied 48 patients with strictly defined vasculitic syndromes in the initial active phase of their disease. The 3 methods confirmed the high (> 90%) sensitivity and specificity of anti-PR-3 for patients with Wegener's granulomatosis (WG). Similarly, a high (86%) sensitivity of MPO-ELISA was found in microscopic polyarteritis as defined. Using alpha-ELISA, we could not improve the detection rate of anti-PR-3 obtained by IF-cANCA-pattern reading. Moreover, a small proportion (< 15%) of biopsy-proven WG patients had anti-MPO antibodies detected by IF, usually as pANCA but also, even if rarely, as bona fide cANCA (< 5%). Thus, IF would seem to be the most reliable screening method and alpha-ELISA should be used for confirmation. On the other hand, because MPO-ELISA detected twice as many anti-MPO positive sera as did pANCA pattern reading by IF, we suggest that in the clinical context of a vasculitis, MPO-ELISA should also be used as a screening test. Although IP is not designed for routine clinical use, it should be required when reporting the presence of anti-PR-3 in vasculitis-like diseases that are fertile grounds for false positive reactions.
authors.affiliation: Department of Medicine, Centre Hospitalier Universitaire, Faculty of Medicine, Université de Sherbrooke, Quebec.
authors.forename: F
authors.initials: F
authors.lastname: Lucena-Fernandes
authors.forename: G
authors.initials: G
authors.lastname: Dalpé
authors.forename: P
authors.initials: P
authors.lastname: Dagenais
authors.forename: C
authors.initials: C
authors.lastname: Richard
authors.forename: R
authors.initials: R
authors.lastname: Calvert
authors.forename: G
authors.initials: G
authors.lastname: Boire
authors.forename: H A
authors.initials: HA
authors.lastname: Ménard
mesh_terms: D000328:Adult; D000368:Aged; D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies / Q000032:analysis* / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005455:Fluorescent Antibody Technique; D014890:Granulomatosis with Polyangiitis / Q000175:diagnosis / Q000276:immunology; D006801:Humans; D007531:Isoflurophate; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000276:immunology*; D010488:Polyarteritis Nodosa / Q000175:diagnosis / Q000276:immunology; D011233:Precipitin Tests; D012680:Sensitivity and Specificity; D014657:Vasculitis / Q000175:diagnosis*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies; D007531:Isoflurophate