Idiotypic characteristics of immunoglobulins associated with systemic lupus erythematosus. Studies of antibodies deposited in glomeruli of humans.

Indirect immunofluorescence with monoclonal antibodies to 6 different idiotypes was used to characterize immunoglobulins deposited in the glomeruli of renal biopsy samples from 32 patients with systemic lupus erythematosus (SLE) and 19 patients with nonlupus immune glomerulonephritis. IdGN2 was present in 75% of the biopsy specimens from SLE patients and in 6% of those from patients with non-lupus nephritis; IdGN1 occurred in 38% and 6%, respectively. The other idiotypes were not increased in biopsy samples from patients with SLE. Deposition of IdGN2 was associated with a subendothelial location of Ig and proliferative changes in the glomeruli. In studies of glomerular eluates from 4 immunosuppressed SLE patients, an average of 26% of total Ig and 37% of anti-DNA was composed of IdGN2. Compared with IdGN2- immunoglobulin, IdGN2+ immunoglobulin was enriched in IgG1 in all 4 eluates, and was enriched in high-avidity anti-DNA in 2 eluates. IdGN2 is a marker of antibody subsets that are characteristic of SLE and are associated with severe lupus nephritis.