Overall, approximately 85% of patients with pauci-immune crescentic glo-merulonephritis or pauci-immune small-vessel vasculitis have circulating ANCA. The two major antigen specificities of ANCA are for proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). Either specificity can occur in any clinicopathologic variant of ANCA-disease, but MPO-ANCA is most prevalent in renal-limited disease and PR3-ANCA is most prevalent in Wegener's granulomatosis.
There is compelling in vitro (14) and animal model (15,16) experimental data showing that ANCA IgG causes glomerulonephritis and vasculitis, probably by direct interaction with neutrophils (and possibly monocytes) resulting in activation with release of lytic enzymes and reactive oxygen radicals that cause the inflammatory injury to glomeruli and vessels. Strong clinical support is provided by the observation that a neonate developed pulmonary hemorrhage and nephritis following transplacental transfer of maternal MPO-ANCA IgG (17).
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