Serum glomerular binding activity is highly correlated with renal disease in MRL/lpr mice

The pathogenesis of lupus nephritis is felt to be mediated by anti-DNA antibodies. However, the anti-DNA response and renal disease do not entirely correspond. We recently developed a new assay which detects immune elements based on their ability to bind glomeruli as an alternative approach to understanding the pathogenesis of this disorder. The glomerular binding activity (GBA) defined by this assay consists of immune elements containing IgG which interact specifically with renal tissue, the binding of which is DNase-inhibitable, but which do not bind to DNA directly. In the current study we assessed the relationship between GBA and renal disease in MRL/lpr mice (both untreated and cyclophosphamide-treated) and compared it with the anti-DNA assay. Both assays were highly correlated with renal disease in untreated mice in terms of proteinuria. In cyclophosphamide-treated mice, however, only a weak correlation between the anti-DNA assay and proteinuria was apparent. GBA, in contrast, was more strongly correlated with proteinuria in treated mice. This correlation improved substantially when the DNase-sensitive component of the GBA was used. GBA appeared related to, but not covariant with, the anti-DNA response. These results demonstrate that GBA is a better correlate of murine lupus nephritis than the anti-DNA assay, and suggest that the immune elements detected by this assay, the DNase-sensitive component in particular, may be pathogenically important.