Nephritogenicity of anti-proteoglycan antibodies in experimental murine lupus nephritis

BACKGROUND: Cross-reactivity between anti-DNA antibodies and heparan sulfate (HS)/heparan sulfate-proteoglycan (HS-PG) of glomerular basement membrane has been previously reported. Conceivably, this determines the final outcome of glomerular injury in lupus nephritis. EXPERIMENTAL DESIGN: We investigated the status of glomerular injury in NZB/NZW F1 mice after the administration of rabbit anti-HS-PG antibody (experiment group). The controls received normal rabbit IgG only. RESULTS: All experimental animals became proteinuric 2 weeks after the administration of anti-HS-PG. The animals of the older age group (16 weeks) had significant hematuria as well. Their glomeruli exhibited hypercellularity with a heavy influx of polymorphonuclear leukocytes and monocytes into their capillaries, and some of them exhibited crescentic changes. Electron-dense deposits were present in subepithelial, subendothelial, and mesangial regions of the glomeruli. The control group had normocellular glomeruli with a few mesangial deposits. Mouse IgG and C₃ displayed a granular pattern of immunofluorescence in the experimental group. Anti-rabbit IgG titers in the serum were higher in the control group, which lower in the renal glomerular eluates. No significant differences were observed in the concentrations of anti-dsDNA and -ssDNA either in the sera or in the eluates. There was also no difference between the control and experimental group in terms of antibody synthesis by the splenic lymphocytes and their proliferation subsequent to antigenic challenge. CONCLUSIONS: Data suggest that administration of anti-HS-PG accentuates the glomerular injury during the natural course of lupus nephritis in (NZB/NZW F1 mice; seemingly these two antibodies (anti-HS-PG and -DNA) do not competitively inhibit the binding of the other to the same anionic sites of glomerular basement membrane enriched with heparan sulfate in vivo.