ACTIVATED NEUTROPHILS EXPRESS PROTEINASE-3 ON THEIR PLASMA-MEMBRANE IN-VITRO AND IN-VIVO

Apart from the diagnostic value of anti-neutrophil cytoplasmic antibod ies (ANCA), their detailed characterization and that of their correspo nding antigens have opened new ways for the exploration of the pathoge nesis of primary systemic vasculitis. ANCA are now thought to play an important functional role via activation of phagocytic cells (e.g. pol ymorphonuclear neutrophils (PMN)). In this study we examined the mecha nisms by which ANCA could gain access to proteinase 3 (PR3) in intact PMN, at two levels: ex vivo by analysing the presence of PR3 on the pl asma membrane of PMN from patients with ANCA-associated vasculitis, an d in vitro by stimulation of PMN using different cytokines, including recombinant tumour necrosis factor-alpha (rhTNF-alpha) and two forms o f IL-8 (produced by monocytic and endothelial cells). Using immunocyto chemical staining techniques (FACS and immunoelectronmicroscopy) PR3 h as been detected on the plasma membrane of PMN from patients with acti ve ANCA-associated vasculitis. However, this phenomenon is also seen i n patients with sepsis who do not have ANCA. In addition, TNF-alpha an d both forms of IL-8 act synergistically and induce a translocation of PR3 from the intragranular loci to the cell surface of PMN. These res ults provide strong evidence for the hypothesis that ANCA are directly pathogenic by binding to PR3 which is expressed on the cell surface o f primed/activated PMN.