Objective: Cross-reactivity with kidney antigens is believed to be a critical determinant in the renal pathogenicity of anti-double-stranded DNA (anti-dsDNA) antibodies. Murine nephritogenic anti-dsDNA antibodies have been shown to cross-react with alpha-actinin, and anti-alpha-actinin antibodies have been found to be deposited in the kidneys of lupus mice with active nephritis. Furthermore, in humans with systemic lupus erythematosus (SLE), it has been found that a greater proportion of polyclonal IgG anti-dsDNA antibodies from patients with renal involvement bind to alpha-actinin than do those from patients without renal disease. We undertook this study to substantiate a direct link between cross-reactive anti-dsDNA/anti-alpha-actinin antibodies and the pathogenesis of lupus nephritis in humans.
Methods: A panel of 10 anti-dsDNA and/or anti-alpha-actinin antibodies was generated by Epstein-Barr virus transformation of lymphocytes from patients with SLE and was extensively characterized. Antibody binding was studied by enzyme-linked immunosorbent assay and Western blotting. Antibody potential for pathogenicity was assessed by measuring binding to isolated glomeruli and mesangial cells and by evaluation of histologic features of the kidney following injection in vivo.
Results: All anti-dsDNA antibodies isolated also bound alpha-actinin. Cross-reactive antibodies bound to mesangial cells and to isolated glomeruli ex vivo. Binding to glomeruli was not inhibited by DNase treatment, but could be abrogated by alpha-actinin. Furthermore, histopathologic abnormalities seen in mice injected intraperitoneally with a cross-reactive cell line included fusion of podocyte foot processes and subepithelial and subendothelial deposition.
Conclusion: These studies provide strong support for the hypothesis that alpha-actinin is a major cross-reactive target for anti-dsDNA antibodies in SLE patients. Cross-reactive anti-dsDNA/anti-alpha-actinin antibodies from SLE patients are pathogenic and may contribute to the kidney lesions in lupus nephritis.