Proteolysis of classic anti-neutrophil cytoplasmic autoantibodies (C-ANCA) by neutrophil proteinase 3

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Abstract
SUMMARY: C-ANCA, which are directed against neutrophil proteinase 3 (PR3), are specific markers for the diagnosis of active Wegener's granulomatosis (WG). The correlation between C-ANCA titre and WG disease activity suggests that these autoantibodies are involved in the development of WG, We have previously observed that C-ANCA interfere with PR3 proteolytic activity and with complexation of PR3 with its major physiologic inhibitor α1-antitrypsin (α1-AT). The possible pathogenic importance of C-ANCA may be related to the stability of C-ANCA IgG PR3 complexes. In the present study we tested proteolysis by PR3 of human IgG and proteolysis of C-ANCA IgG complexed to the enzyme. All human IgG subclass proteins were cleaved by PR3, Digestion products were compared with those obtained by human neutrophil elastase (HNE)-mediated proteolysis of human IgG subclass proteins. Although cleavage products of similar size could be identified, the proteolytic activity of both enzymes towards human IgG differed. Furthermore, inhibiting C-ANCA IgG were cleaved into small peptides when complexed to PR3. The possible pathogenic consequences or these findings will be discussed.

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