Membrane proteinase 3 and Wegener's granulomatosis.

Proteinase 3 (PR3) is found in neutrophil and monocyte lysosomal granules. Anti-neutrophil cytoplasmatic antibodies (ANCA) with specificity for PR3 are characteristic for patients with Wegener's granulomatosis. The interaction of ANCA with neutrophilic ANCA antigens is necessary for the development of ANCA-associated diseases. ANCA bind to membrane-expressed PR3 and induce full-blown activation in primed neutrophils. We discuss two different aspects of membrane PR3 (mPR3). The first aspect is the amount of PR3 and mechanisms controlling this issue. The second aspect is the presence of two neutrophil subsets that differ in the mPR3 expression phenotype.