Detection of anti-neutrophil cytoplasmic antibodies by immunoprecipitation

F. Lucena-Fernandes
G. Dalpé
P. Dagenais
C. Richard
R. Calvert
G. Boire
H.A. Ménard

Division of Rheumatology, Department of Medicine, Centre Hospitalier Universitaire and (Department of Cell Biology) Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Quebec

(Original manuscript submitted 71/11/94; received in revised form 13/1/95; accepted 27/1/95)

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 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 microscopie 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.

Clin Invest Med 1995; 18 (3): 153-162

Table of contents: CIM vol. 18, no. 3