Cytotoxic effects of antibodies to proteinase 3 (C‐ANCA) on human endothelial cells

SUMMARY Autoantibodies directed against cytoplasmic antigens of neutrophils (ANCA), especially those with specificity for proteinase 3 (PR‐3) and myeloperoxidase, are valuable markers for differential diagnosis and monitoring of disease activity in Wegener's granulomatosis (WG) and other vasculitides. Till now, several concepts concerning a direct role of antibodies against PR‐3 in the pathogenesis of WG have been discussed. Recently we were able to show that these antibodies recognize PR‐3 translocated into the membrane of human endothelial cells. The aim of this study was to investigate putative cytotoxic effects of antibodies to PR‐3 on human endothelial cells. Antibodies were obtained by affinity purification of sera from patients with active WG, Purified antibodies to Ro (SS‐A), La (SS‐B) and RNP served as controls. Purified antibodies to PR‐3 displayed a lytic activity against endothelial cells treated with tumour necrosis factor‐alpha (TNF‐α:) with the help of cytokine‐primed neutrophils as measured in a Cr‐release assay. About 100% specific cytotoxicity occurred after 4 h and was independent of complement, Cytotoxic effects were inhibited by coincubation with unprimed ncutrophils or preincubation of PR‐3 antibodies with purified antigen. Antibodies to Ro (SS‐A), La (SS‐B) or RNP had no cytotoxic effect. In summary, PR‐3 antibody‐induced cytotoxicity required (i) expression of PR‐3 on the surface of TNF‐α‐treated endothelial cells: and (ii) co‐cultivation of cytokine‐primed neutrophils. This is to the best of our knowledge the first report on direct cytotoxic effects of PR‐3 antibodies on vascular endothelium. Our data give a hint at a PR‐3 antibody‐mediated mechanism of endothelial injury via antibody‐dependent cellular cytotoxicity in WG and other ANCA‐related vasculitides.