Exposure of chromatin and not high affinity for dsDNA determines the nephritogenic impact of anti-dsDNA antibodies in (NZB×NZW)F1 mice

Abstract

Recent studies have demonstrated that the nephritogenicity of antibodies to dsDNA and nucleosomes confers to binding of glomerular membrane-associated nucleosomes, and not to cross-reacting glomerular antigens. There is no known parameter that determines antibody pathogenicity aside from specificity for dsDNA/nucleosomes, and systemic lupus erytheomatosus (SLE) patients may have high titer anti-dsDNA antibodies irrespective whether they have lupus nephritis or not. One parameter may be antibody affinity, as theoretically only high affinity antibodies may bind in vivo in a stable way. This was analyzed in (NZB x NZW)F1 mice with full-blown lupus nephritis. These mice had serum antibodies to dsDNA, and IgG autoantibodies bound in situ in glomerular membrane-associated electron dense structures as determined by immune electron microscopy (IEM). Intrinsic affinity of purified circulating and glomerular IgG anti-dsDNA antibodies was determined by surface plasmon resonance. The results demonstrate that affinity of glomerular-bound anti-dsDNA antibodies was higher than for those in circulation. However, affinity of glomerular in situ-bound antibodies from different mice varied considerably, from K(D) in the range from 10(- 8) to 10(- 13). These results indicate that antibody affinity is not a decisive pathogenic factor, but rather that availability of chromatin fragments may be the factor that determines whether an anti-dsDNA antibody binds in glomeruli or not.

Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players

“…In the severe combined immunodeficient (SCID) mice it was confirmed that the binding of human anti-dsDNA AAb to the kidney causes proteinuria and thus tissue damage, probably through different mechanisms [134]. Mjelle et al demonstrated that the availability of glomerular chromatin fragments is prerequisite for renal anti-dsDNA AAb binding [135]. Accordingly, the development of lupus nephritis in humans is strongly associated with high titres of anti-dsDNA AAb [136], which precede the clinical onset of SLE [137] and of disease flares [138].…”

Heparin exerts a dual effect on murine lupus nephritis by enhancing enzymatic chromatin degradation and preventing chromatin binding in glomerular membranes

“…SPR kinetic analyses for unfractionated heparin mixed with nucleosomes at the same molar ratios were performed at 30 l/minute for 180 seconds (association step) followed by 600 seconds of dissociation time. Binding of 163c3 anti-dsDNA mAb (without or with heparin at 1:10 or 1:100 molar ratio) to the DNA chip was analyzed by the kinetic/ affinity assay (35). Regeneration of the chips and all calculations were performed as described (14).…”

The anti-DNA antibody: origin and impact, dogmas and controversies

“…We further analysed anti bodies in sera and glomerular eluates with respect to their specifi city and intrinsic affinity. 99,110 The data were surprisingly clear, and demonstrated that nephritogenic anti-B-DNA antibodies exert their pathogenic effect only when chroma tin fragments are exposed in the mesangial matrix and in the GBM.…”

“…associated with lupus nephritis, the renal manifestation of this disease. This concept derived from three facts: DNA binds collagen, a component of the glomerular basement membrane (GBM); 98 the nephritogenic antibodies bind DNA; 93,99 and anti-dsDNA antibodies can be eluted from nephritic kidneys. [99][100][101] These facts do not necessarily provide information about the real targets for the antibodies in kidneys in the context of lupus nephritis, only that in vivo-bound IgG antibodies recognize at least DNA.…”

“…These and similar data 113 indicate that anti-B-DNA antibodies exert their nephritogenic effect by binding to exposed chromatin fragments in glomerular membranes and matrices, which is consistent with the fact that antibodies eluted from nephritic kidneys show specificity for nucleosomes, histones and DNA as a common denominator, although several other specificities have also been detected in such eluates. [99][100][101] The origin of chromatin fragments The next step was to determine the origin of the GBMassociated chromatin fragments. During the transition from mild to severe lupus nephritis, a marked decrease in the major renal endonuclease DNase I has been observed at the mRNA and enzyme activity levels.…”