Anti-neutrophil cytoplasmic antibodies (ANCA) from patients with systemic vasculitis recognize restricted epitopes of proteinase 3 involving the catalytic site

ANCA with specificity for proteinase 3 (PR3), a neutrophil primary granule enzyme, are of diagnostic value in Wegener's granulomatosis (WG) and certai n other forms of systemic vasculitis. There is evidence to suggest that the y play a pathogenic role in disease, and that the interaction of ANCA with PR3 is likely to be important. We showed, using a resonant mirror biosensor , that C-ANCA from different patients recognized the same or closely relate d epitopes on PR3. Studies using linear peptides in the SPOT system confirm ed the highly restricted nature of this interaction and identified five lin ear epitopes. Fluid-phase inhibition studies, using a different set of pept ides, validated the sequences involved. Using a computer-generated model of the structure of PR3, four of five epitopes were shown to be intimately li nked with the catalytic site. The restricted number of epitopes, and their location at the catalytic site, has important implications for the role of C-ANCA in the pathogenesis of vasculitis.