OBJECTIVE: Wegener's granulomatosis (WG) is strongly associated with 
antineutrophil cytoplasmic autoantibodies (ANCAs) directed against proteinase 3 
(PR3). Recent studies have shown that membrane-bound PR3 (mPR3) is 
differentially expressed and colocalizes with CD177/NB1 on circulating 
neutrophils. We undertook this study to assess the differential expression of 
CD177 on neutrophils from patients with ANCA-associated systemic vasculitis 
(ASV) in comparison with patients with systemic lupus erythematosus (SLE), 
patients with rheumatoid arthritis (RA), and healthy individuals, and to 
investigate whether colocalization of mPR3 and CD177 affects anti-PR3-mediated 
neutrophil activation.
METHODS: Expression of CD177 and mPR3 was analyzed by flow cytometry on isolated 
neutrophils from patients with ASV (n=53), those with SLE (n=30), those with RA 
(n=26), and healthy controls (n=31). Neutrophil activation mediated by anti-PR3 
antibodies was assessed by measuring the oxidative burst with a dihydrorhodamine 
assay.
RESULTS: Percentages of CD177-expressing neutrophils were significantly higher 
in patients with ASV and those with SLE than in healthy controls. In 3 healthy 
donors, CD177 expression was not detected. After priming with tumor necrosis 
factor alpha, neutrophils remained negative for CD177 while mPR3 expression was 
induced. Neutrophils from CD177-negative donors or CD177- neutrophils sorted 
from donors with bimodal expression were susceptible to anti-PR3-mediated 
oxidative burst. Variation in the extent of anti-PR3-mediated neutrophil 
activation among different donors occurred independent of the percentage of 
CD177-expressing neutrophils.
CONCLUSION: Membrane expression of CD177 on circulating neutrophils is increased 
in patients with ASV and in those with SLE, but not in RA patients. However, 
primed neutrophils from CD177-negative individuals also express mPR3 and are 
susceptible to anti-PR3-mediated oxidative burst, suggesting that recruitment of 
CD177-independent mPR3 is involved in anti-PR3-induced neutrophil activation.