Methods: Autoreactive IgM antibodies of various specificities, including antibodies against double-stranded DNA (dsDNA), from AID-deficient MRL/lpr mice were given to asymptomatic MRL/lpr mice, and the levels of cytokines, proteinuria, immune complex deposition in the kidneys, and glomerulonephritis were examined. Novel AID-deficient MRL/lpr mice that lack any antibodies were generated for comparison to AID-deficient MRL/lpr mice that secrete only IgM.
Results: Treatment with IgM anti-dsDNA resulted in a dramatic improvement in lupus nephritis. Other autoreactive IgM antibodies, such as antiphospholipid and anti-Sm, did not alter the pathologic changes. Secretion of proinflammatory cytokines by macrophages and the levels of inflammatory cells and apoptotic debris in the kidneys were lower in mice receiving IgM anti-dsDNA. Protective IgM derived from AID-deficient MRL/lpr mice displayed a distinct B-cell repertoire, with a bias toward members of the VH7183 family.
Conclusion: IgM anti-dsDNA protected MRL/lpr mice from lupus nephritis, likely by stopping the inflammatory cascade leading to kidney damage. A distinct repertoire of VH usage in IgM anti-dsDNA hybridomas from AID-deficient mice suggests that there is enrichment of a dedicated B-cell population that secretes unmutated protective IgM in these mice.
Heparin exerts a dual effect on murine lupus nephritis by enhancing enzymatic chromatin degradation and preventing chromatin binding in glomerular membranes. (Arthritis Rheum. 2011;63:1065-1075.)
Abstract
Objective: Association of nucleosome–IgG immune complexes with glomerular basement membranes (GBMs) is an important event in the development of lupus nephritis. Preventing this binding and/or increasing nuclease sensitivity of nucleosomes may be viable strategies for the prevention of the disease. Theoretically, heparin may alter nucleosomal structure and increase sensitivity to proteinases and nucleases, and may also inhibit binding of nucleosomes and nucleosome–IgG complexes to basement membrane structures. The aim of this study was to investigate whether and eventually how heparin prevents murine lupus nephritis.
Methods: Surface plasmon resonance was used to analyze if heparin inhibits binding of nucleosomes to laminin and collagen. The effect of heparin on nuclease- and proteinase-mediated degradation of nucleosomes was analyzed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and agarose gel electrophoresis. In vitro results were compared with analyses in vivo in heparin-treated (NZB × NZW)F1 mice. Anti–double-stranded DNA antibody production, deposition of nucleosome–IgG complexes in GBMs, and development of proteinuria were monitored, and circulating chromatin fragments were quantified using quantitative polymerase chain reaction.
Results: In vitro studies demonstrated that heparin increased enzymatic degradation of nucleosomes and almost completely inhibited binding of nucleosomes to laminin and collagen. (NZB × NZW)F1 mice treated with heparin demonstrated delayed or no antibody production and higher variation of circulating chromatin levels compared with untreated control mice. This effect was accompanied by highly reduced nucleosome–IgG complexes in GBMs and delayed development of nephritis.
