Constitutive membrane expression of proteinase 3 (PR3) and neutrophil activation by anti-PR3 antibodies.

Antineutrophil cytoplasm autoantibodies with specificity for proteinase 3 (PR3) are thought to play a major role in the pathogenesis of Wegener's granulomatosis (WG), presumably by their potential to activate neutrophils. In patients with WG, high expression of PR3 on the surface of nonprimed neutrophils is associated with an increased incidence and rate of relapse. In this study, we analyzed the functional significance of constitutive PR3 expression for neutrophil activation as induced by anti-PR3 antibody. Therefore, primed and nonprimed neutrophils were stimulated with the monoclonal anti-PR3 antibody PR3G-3. Activation was measured as actin polymerization by the phalloidin assay as an early, detectable activation event and oxidative burst by the dihydrorhodamine assay, as a late, detectable activation event. In contrast to the oxidative burst, we found that anti-PR3 antibody-induced actin polymerization could be triggered in neutrophils without priming with tumor necrosis factor alpha (TNF-alpha). In addition, a correlation was found between the level of PR3 expression on the surface of these nonprimed neutrophils and the degree of actin polymerization. However, after priming with TNF-alpha, no correlation was found between membrane expression of PR3 and the level of actin polymerization or respiratory burst as induced by anti-PR3 antibody. These data suggest that the presence of PR3 on the surface of nonprimed neutrophils has consequences for their susceptibility to the initial activation step by anti-PR3 antibodies. These data may be relevant in view of the observed relation between membrane expression of PR3 on nonprimed neutrophils of patients with WG and their susceptibility for relapses.

Recombinant protein to analyze autoantibodies to proteinase 3 in systemic vasculitis.

The presence of antineutrophil cytoplasmic autoantibodies with specificity for proteinase 3 (PR3-ANCA) usually is detected by enzyme-linked immunosorbent assay (ELISA) with purified PR3 as a substrate. We studied the technical performance of direct and capture ELISA using a recombinant proteolytically inactive form of PR3 produced in the baculovirus expression system for the detection of PR3-ANCA in 114 patients with systemic vasculitis at diagnosis. We found that ELISA using recombinant PR3 produced in insect cells is a promising alternative for ELISA with native PR3. We found a correlation between tests using recombinant or native PR3, as well as correlation of the ELISA results with ANCA titers measured by the indirect immunofluorescence technique. However, the specificity for ANCA-associated vasculitis of ELISA with recombinant PR3 was lower than ELISA using native PR3. Compared with the direct assay, capture ELISA is a more sensitive method for PR3-ANCA detection, with both native and recombinant PR3, and its results depend on the monoclonal antibody used to capture the antigen.

Neutrophil-activating potential of antineutrophil cytoplasm autoantibodies.

Accumulating in vivo and in vitro evidence supports the hypothesis that antineutrophil cytoplasm autoantibodies (ANCA) with specificity for proteinase 3 (PR3) and myeloperoxidase (MPO) are involved in the pathophysiology of small-vessel vasculitis. The best-described effector function of these autoantibodies is stimulation of neutrophils to produce reactive oxygen species and to release proteolytic enzymes. Neutrophil activation requires interaction of monomeric ANCA with PR3/MPO and Fcgamma receptors, but also other mechanisms--for instance, stimulation by ANCA-containing immune complexes--cannot be excluded. This review focuses on the mechanisms of neutrophil activation by ANCA. We discuss the molecules involved in ANCA binding to the neutrophil surface and in triggering the functional responses. We summarize current knowledge on the signal-transduction pathways initiated by ANCA and on the factors determining susceptibility of neutrophils to activation by these autoantibodies.

Diversity of PR3-ANCA epitope specificity in Wegener's granulomatosis. Analysis using the biosensor technology.

Wegener's granulomatosis is a systemic disease characterized by the presence of antineutrophil cytoplasm autoantibodies specific for proteinase 3 (PR3-ANCA). The functional characteristics of PR3-ANCA differ between quiescent and active disease, suggesting changes in the properties of the autoantibodies in time. Using biosensor technology, we found that PR3-ANCA of different patients (n = 8) recognize a limited number of overlapping regions on PR3 at the time of diagnosis of Wegener's granulomatosis. This area might cover an immunodominant epitope, common for PR3-ANCA from all patients, irrespective of the size of the total area recognized by an individual autoantibody. Experiments with sera (n = 4) collected at the moment of diagnosis and at the time of relapse showed that the individual epitope specificities of PR3-ANCA change during the course of the disease. These changes in epitope specificity of PR3-ANCA may be responsible for the differences in functional properties of these autoantibodies between various stages of the disease.

Neutrophil membrane expression of proteinase 3 (PR3) is related to relapse in PR3-ANCA-associated vasculitis.

Wegener granulomatosis (WG) is strongly associated with the presence of antineutrophil cytoplasm autoantibodies (ANCA) with specificity for proteinase 3 (PR3). Relapses of WG are frequently preceded by a rise of autoantibody titer and PR3-ANCA are able to activate primed neutrophils in vitro. Except being stored intracellularly and translocated to the cell surface upon neutrophil stimulation, PR3 can also be detected on the surface of non-stimulated neutrophils (membrane PR3 or mPR3), with an interindividual variability in percentages of mPR3(-)-positive cells and level of mPR3 expression. This study began with the hypothesis that the presence of PR3 on the surface of non-stimulated neutrophils enables interaction with PR3-ANCA and influences clinical manifestations of the disease. It analyzed mPR3 expression on neutrophils of 89 WG patients in complete remission and 72 healthy controls to evaluate whether the presence of PR3 on the surface of resting neutrophils is related to clinical manifestations of WG and/or to the susceptibility to develop relapses. The number of patients with a bimodal mPR3 expression on resting neutrophils did not differ between patients and controls. However, in WG patients, an increased percentage of mPR3(+) neutrophils and an elevated level of mPR3 expression compared with healthy individuals (P = 0.037) were found. Within the group of WG patients, an elevated level of mPR3 expression was significantly associated with an increased risk for relapse (P = 0.021) and with an increased relapse rate (P = 0.011), but not with the disease extent or particular manifestations at diagnosis or at relapse. These data support the hypothesis that PR3 expression on the membrane of neutrophils plays a role in the pathophysiology of PR3-ANCA associated vasculitis.