A role for histones and ubiquitin in lupus nephritis?

Glomerulonephritis frequently develops in Systemic lupus erythematosus (SLE) but the pathogenesis is still poorly understood. Experimental evidence now suggests that histones can participate in immune complex formation in lupus nephritis. In a retrospective study, using samples from Northern and Southern Europe, Japan and South America, we searched for glomerular deposits of histones, both in native and ubiquitinated forms, in renal biopsy specimens from 48 patients with SLE and 70 cases of glomerulonephritis from patients without SLE. Positive glomerular immunofluorescent staining was revealed with rabbit antibodies to synthetic peptide 1-21 of histone H3, 22-45 of ubiquitin and to the branched region of ubiquitinated histone H2A (U-H2A) in 65% (31/48), 29% (14/48) and 54% (26/48) of the cases of SLE respectively. In total positive staining with at least one of the antibodies was seen in 36/48 (75%) cases. The staining was granular in nature and was present in capillary and mesangial areas. Only 3% (2/70) of non-SLE renal biopsies revealed positive staining with the above antibodies. None of the biopsy specimens from SLE patients were positive for ss- or ds-DNA, when tested with intercalating dyes. Serum samples were available from 15/48 SLE cases and were analysed with peptides and parent proteins by ELISA; epitopes in the N-terminal regions of core histones and in the C-terminus of histone H1 were often recognised by IgG antibodies in SLE sera, as was ubiquitin and the branched octapeptide of U-H2A. These results support the notion that the nuclear autoantigens histone and ubiquitin may be involved in the induction of glomerulonephritis in human SLE.