Nephritogenic Lupus Antibodies Recognize Glomerular Basement Membrane-Associated Chromatin Fragments Released from Apoptotic Intraglomerular Cells

Abstract

Antibodies to dsDNA represent a classification criterion for systemic lupus erythematosus. Subpopulations of these antibodies are involved in lupus nephritis. No known marker separates nephritogenic from non-nephritogenic anti-dsDNA antibodies. It is not clear whether specificity for glomerular target antigens or intrinsic antibody-affinity for dsDNA or nucleosomes is a critical parameter. Furthermore, it is still controversial whether glomerular target antigen(s) is constituted by nucleosomes or by non-nucleosomal glomerular structures. Previously, we have demonstrated that antibodies eluted from murine nephritic kidneys recognize nucleosomes, but not other glomerular antigens. In this study, we determined the structures that bind nephritogenic autoantibodies in vivo by transmission electron microscopy, immune electron microscopy, and colocalization immune electron microscopy using experimental antibodies to dsDNA, to histones and transcription factors, or to laminin. The data obtained are consistent and point at glomerular basement membrane-associated nucleosomes as target structures for the nephritogenic autoantibodies. Terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling or caspase-3 assays demonstrate that lupus nephritis is linked to intraglomerular cell apoptosis. The data suggest that nucleosomes are released by apoptosis and associate with glomerulus basement membranes, which may then be targeted by pathogenic antinucleosome antibodies. Thus, apoptotic nucleosomes may represent both inducer and target structures for nephritogenic autoantibodies in systemic lupus erythematosus.

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

“…We have previously identified chromatin fragments as the glomerular target structure for nephritogenic autoantibodies in lupus nephritis (12,13,38) (for review, see refs. 8 and 9).…”

“…Recent studies have demonstrated that nephritogenic antibodies recognize chromatin fragments (10)(11)(12)(13) which bind glomerular basement membranes (GBMs) and matrix components with high affinity (14). These immune complexes were observed as electron-dense structures in GBMs and the mesangial matrix, and bound IgG was confined to electron-dense structures in both murine (12,14) and human (13) lupus nephritis.…”

“…These immune complexes were observed as electron-dense structures in GBMs and the mesangial matrix, and bound IgG was confined to electron-dense structures in both murine (12,14) and human (13) lupus nephritis. In vivo bound IgG was not observed in regular glomerular structures (15), although anti-DNA antibodies have been shown to cross-react in vitro with other glomerular antigens (16)(17)(18)(19).…”

Type I interferon signaling is involved in the spontaneous development of lupus-like disease in B6.Nba2 and (B6.Nba2 × NZW)F1 mice

“…[20][21][22][23][24] These antibodies were found to bind mainly nuclear antigens such as chromatin, histones and dsDNA, and/or components of the glomerular basement membrane. In particular, anti-dsDNA autoantibodies were found to be pathogenic and it has been shown that some anti-dsDNA autoantibodies can by themselves alter the gene expression profile of mesangial cell lines, turning on the expression of inflammatory molecules.…”

The consequences of apoptosis in autoimmunity

“…Several experimental reports demonstrate the relationship between impaired clearance of apoptotic cells and SLE, and especially the involvement of C1q defects in SLE [64]. Kalaaji et al demonstrated that large chromatin fragments, derived from apoptotic cells, localize in the intraglomerular membrane in murine and human SLE [65], and that those intra-glomerular membrane-associated nucleosomes are targeted by anti-dsDNA autoantibodies in human lupus nephritis [66].…”