Myeloperoxidase (MPO)-specific antineutrophil cytoplasmic antibody (ANCA) is associated with rapidly progressive glomerulonephritis (RPGN) in microscopic polyangiitis (MPA). MPO-ANCA activates neutrophils by binding to cell surface MPO expressed on tumor necrosis factor-α (TNF-α)-primed neutrophils and induces neutrophil degranulation and production of reactive oxygen species, consequently resulting in glomerular endothelial damage. Recently, anti-MPO antibody has been found to activate glomerular endothelial cells, leading to an upregulation of adhesion molecules. MPO-ANCA, however, is not always correlated with disease activity in MPA. Accordingly, the molecule(s) responsible for the anti-MPO antibody have been explored on mouse glomerular endothelial cells. The molecule was identified as moesin, which is a heparin-binding protein and belongs to the ezrin/radixin/moesin family of proteins distributed in the plasma membrane in the cellular cortex. Interestingly, anti-moesin is observed in sera of SCG/Kj mice, which spontaneously develop MPO-ANCA-associated RPGN, and of patients with MPO-AAV. The activation of glomerular endothelial cells by the anti-MPO antibody appears to be associated with signaling through moesin.