Pure anti-dsDNA mAbs need chromatin structures to promote glomerular mesangial deposits in BALB/c mice

Abstract

The glomerular targets for nephritogenic antibodies have been identified as membrane-associated chromatin fragments. The processes responsible for their deposition are poorly understood. To determine early events in antibody-mediated nephritis, we injected highly pure anti-dsDNA mAbs into BALB/c mice. Mice receiving one dose of anti-dsDNA mAbs were sacrificed 6 or 24 h later. No direct binding of mAbs to glomerular membranes or to the mesangial matrix was observed by immune electron microscopy. In contrast, repeated injections of the same antibodies over 4 weeks resulted in deposition of electron dense structures predominantly in the mesangial matrix. These structures contained mAbs and chromatin fragments as determined by co-localization immune electron microscopy. Biotinylated anti-dsDNA mAbs, injected into nephritic (NZB × NZW)F1 or MRL^lpr/lpr mice were detected in newly formed electron dense structures within glomerular capillary membranes. There were no correlation between mAb affinity for DNA, as determined by surface plasmon resonance analyses, and ability to bind chromatin fragments in vivo. No direct binding of mAbs to inherent membrane antigens was observed. Quantification of DNA in sera before and after one single injection of antibodies revealed increased DNA levels at 6 h after injection of anti-dsDNA mAb, and lower levels after 24 h. Repeated injections of anti-dsDNA caused an increase in circulating DNA. These results indicate that availability of chromatin fragments, presumable in circulation, is important for glomerular mesangial matrix deposition of anti-dsDNA antibody-containing immune complexes in context of lupus nephritis.

Keywords::

• Autoimmunity
• autoantibodies
• dsDNA
• lupus nephritis
• systemic lupus erythematosus

Acknowledgements

This work was supported by the Foundation for Health and Rehabilitation through the Norwegian Rheumatology Organization (project 2004/2/0250). We are thankful to Randi Olsen, Helga Marie Bye, and Jørgen Benjaminsen for technical help with the electron microscopic work and to Dr Svetlana Zykova for help with the Agilent analysis. We are indebted to Nina Løvset, Ragnhild Osnes, and Stig Rune Olsen for breeding the mice and to Dr Dmitri Svistonov for help with intravenous injection of the mAbs.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.