Nephritogenic antibodies bind in glomeruli through interaction with exposed chromatin fragments and not with renal cross-reactive antigens

Abstract

Cross-reactivity of anti-double stranded DNA (anti-dsDNA) antibodies with glomerular antigens has been postulated as a key factor in the development of lupus nephritis. Because no direct proof has been presented on anti-dsDNA antibodies binding in vivo to glomerular structures, we have analysed the binding of potentially nephritogenic anti-dsDNA antibodies to α-actinin and laminin. By enzyme-linked immunosorbent assay and surface plasmon resonance (SPR) analyses, we demonstrate that monoclonal antibodies (mAbs) bind both double-stranded DNA and α-actinin at high affinity. However, when added to nephritic kidney sections they did not bind to such structures, but rather to nucleosome-containing structures within the mesangial matrix or the glomerular basement membranes (GBMs). Nucleosomes, anti-nuclear antibodies and complexes of them were tested for their binding to glomerular components such as agrin, perlecan and laminin using SPR analysis. Nucleosomes bound to laminin, marginally to agrin, but not to perlecan or heparan sulphate-depleted agrin. Anti-histone H2B and anti-nucleosome antibodies in complex with nucleosomes slightly increased the binding of nucleosomes to agrin, while binding to laminin was slightly decreased compared to nucleosomes alone. In conclusion, the availability of nucleosomal antigens and the binding of these antigens to components of the mesangial matrix and GBM seem crucial for the glomerular deposition of immune complexes.

Keywords::

• Anti-dsDNA antibodies
• anti-α-actinin antibodies
• systemic lupus erythematosus
• lupus nephritis
• anti-nucleosome antibodies

Acknowledgements

We thank Dr Dan Eilat for providing us with the anti-dsDNA antibodies A52 and D42, and Dr Tony N Marion for monoclonal antibodies against dsDNA. Randi Olsen and Helga Marie Bye are appreciated for their technical help with the electron microscopic work. Wim Tamboer is gratefully acknowledged for the purification of agrin.

Declaration of interest: This work was funded by the Foundation for Health and Rehabilitation through the Norwegian Rheumatology Organization (project 2008/2/0229). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.