Phagocyte NADPH oxidase restrains the inflammasome in ANCA-induced GN.

ANCA-activated phagocytes cause vasculitis and necrotizing crescentic GN (NCGN). ANCA-induced phagocyte NADPH oxidase (Phox) may contribute by generating tissue-damaging reactive oxygen species. We tested an alternative hypothesis, in which Phox restrains inflammation by downregulating caspase-1, thereby reducing IL-1β generation and limiting NCGN. In an antimyeloperoxidase (anti-MPO) antibody-mediated disease model, mice transplanted with either gp91(phox)-deficient or p47(phox)-deficient bone marrow showed accelerated disease with increased crescents, necrosis, glomerular monocytes, and renal IL-1β levels compared with mice transplanted with wild-type bone marrow. IL-1β receptor blockade abrogated aggravated NCGN in gp91(phox)-deficient mice. In vitro, challenge with anti-MPO antibody strongly enhanced caspase-1 activity and IL-1β generation in gp91(phox)-deficient and p47(phox)-deficient monocytes compared with wild-type monocytes. This enhanced IL-1β generation was abrogated when caspase-1 was blocked. ANCA-induced superoxide and IL-1β generation were inversely related in human monocytes. Furthermore, transplantation of gp91(phox)/caspase-1 double-deficient bone marrow rescued the accelerated NCGN phenotype in gp91(phox) bone marrow-deficient mice. These results suggest that Phox-generated reactive oxygen species downregulate caspase-1, thereby keeping the inflammasome in check and limiting ANCA-induced inflammation. IL-1 receptor blockade may provide a promising strategy in NCGN, whereas our data question the benefit of antioxidants.