Murine lupus glomerulotropic monoclonal antibodies exhibit differing specificities but bind via a common mechanism

We recently identified that the glomerular binding activity in MRL/lpr serum consists of Abs reactive with DNA/histone adherent to glomerular basement membrane (GBM) via type IV collagen. These studies suggest the presence of multiple nephritogenic autoantibodies that bind to glomeruli via a common mechanism, an hypothesis we tested by producing glomerular binding mAbs from a nephritic MRL/lpr mouse. All 7 mAbs produced bound to glomeruli/GBM in a DNase-inhibitable fashion. The 4 mAbs that bound most avidly to glomeruli/GBM (group I) did not bind to DNA per se, and GBM binding after DNase treatment was reconstituted by histones or histone/DNA co-addition. The remaining 3 mAbs (group II) bound well to DNA, and GBM binding after DNase treatment was reconstituted by DNA but not histones. Collagenase (but not heparitinase) inhibited GBM binding of all mAbs and impaired the ability of nuclear Ags to reconstitute binding. None of the mAbs bound to type IV collagen per se. Using defined nuclear Ags, two group I mAbs bound specifically to histone H2A-H2B-DNA complexes, one bound specifically to intact chromatin, and one was polyreactive to histones. Group II mAbs bound to any nuclear Ag-containing DNA. Binding to nuclear Ags by all mAbs was altered if type IV collagen was used as the assay substrate, and in this context the common Ag for all mAbs was intact chromatin. In sum, glomerular binding mAbs exhibit differing antigenic specificities, but can be identified as either predominantly anti-histone/nucleosome (group I) or anti-DNA (group II). Regardless, binding to chromatin adherent to type IV collagen is a common property of all such mAbs.