INHIBITION OF PROTEINASE-3 BY ANCA AND ITS CORRELATION WITH DISEASE-ACTIVITY IN WEGENERS GRANULOMATOSIS

Detection of circulating antineutrophil cytoplasmic antibodies (ANCA) to the neutrophil serine proteinase, proteinase 3 (PR3), has proven va luable for the diagnosis of Wegener's granulomatosis (WG). However, th e importance of these autoantibodies in the pathogenesis of WG remains unknown. It was recently reported that anti-PR3 autoantibodies (PR3-A NCA) from some patients with WG inhibit the proteolytic activity of PR 3 and interfere with the inactivation of PR3 by the physiologic inhibi tor, alpha(1)-proteinase inhibitor (alpha(1)-PI). We have studied the effect of PR3-ANCA on the enzymatic activity of PR3 and its correlatio n with disease activity in patients with WG. We purified IgG from 21 P R3-ANCA positive sera obtained from 17 patients with WG, and determine d its effect on the esterolytic and proteolytic activity of purified h uman PR3 using Boc-Ala-O-Nitrophenyl ester and fluoresceinated-elastin as enzyme substrates. Controls included seven sera containing anti-MP O autoantibodies (MPO-ANCA) from patients with systemic vasculitis and seven ANCA-negative sera obtained from healthy individuals. We found that PR3-ANCA from 9 of the 17 patients significantly inhibited the ac tivity of PR3. There was no correlation between the titers of PR3-ANCA and their inhibitory activity. For one extensively characterized auto antibody, the inhibition reached 70 to 95% at 20-fold molar excess of IgG to enzyme, with an apparent K(i)app of 56.5 mu M. This inhibition was non-competitive in nature, and was additive to that produced by (a lpha(1)-PI. A review of the clinical histories of the patients reveale d a strong association between active WG and inhibitory autoantibodies . PR3-ANCA from eight of 10 patients with active disease showed signif icant inhibition of PR3 activity, whereas only one of seven patients i n remission had inhibitory PR3-ANCA. These results suggest that the in hibitory profile of PR3-ANCA may be more reflective of disease activit y in patients with WG than the absolute titer, and suggest possible al ternative mechanisms for the role of these autoantibodies in the patho genesis of WG.