Anti-dsDNA antibodies bind to mesangial annexin II in lupus nephritis

Production of anti-dsDNA antibodies is a hallmark of lupus nephritis, but how these antibodies deposit in organs and elicit inflammatory damage remains unknown. In this study, we sought to identify antigens on the surface of human mesangial cells (HMC) that mediate the binding of human anti-dsDNA antibodies and the subsequent pathogenic processes. We isolated anti-dsDNA antibodies from patients with lupus nephritis by affinity chromatography. We used multiple methods to identify and characterize antigens from the plasma membrane fraction of mesangial cells that crossreacted with the anti-dsDNA antibodies. We found that annexin II mediated the binding of anti-dsDNA antibodies to HMC. After binding to the mesangial cell surface, anti-dsDNA antibodies were internalized into the cytoplasm and nucleus. This also led to induction of IL-6 secretion and annexin II synthesis, mediated through activation of p38 MAPK, JNK, and AKT. Binding of anti-dsDNA antibodies to annexin II correlated with disease activity in human lupus nephritis. Glomerular expression of annexin II correlated with the severity of nephritis, and annexin II colocalized with IgG and C3 deposits in both human and murine lupus nephritis. Gene silencing of annexin II in HMC reduced binding of anti-dsDNA antibody and partially decreased IL-6 secretion. In summary, our data demonstrate that annexin II mediates the binding of anti-dsDNA antibodies to mesangial cells, contributing to the pathogenesis of lupus nephritis. This interaction provides a potential target for therapeutic intervention.