The alternative complement pathway was thought to be critical in the pathogenesis of ANCA-GN for several reasons: 1) depletion of factor B, critical for the alternative complement pathway, could protect mice from this disease (20); 2) the membrane attack complex (MAC), C3d, factor B, and factor P were detected in renal biopsy samples with pauci-immune myeloperoxidase (MPO)-ANCA-GN (21); and 3) both the renal staining and the urinary and plasma levels of the proteins involved in the alternative complement pathway were significantly upregulated in ANCA-GN (20). Here, MPO is linked to ganglioneuroma.