Abstract
OBJECTIVE: To determine the specific antibodies present in glomerular immune deposits in patients with systemic lupus erythematosus (SLE). METHODS: Kidney tissue was obtained at autopsy and stored frozen until used. Glomeruli were isolated from the renal cortex, sonicated, and the glomerular basement membrane fragments were extracted with a pH 2.5 buffer or 6 M guanidine hydrochloride. The latter method provided a higher yield and was used in most of the 23 specimens studied. The extracted IgG was quantified by a capture assay using an ELISA with chemiluminescence. IgG antibodies to 14 different antigens were quantified by the same type of assay. The enrichment of antibodies in the extracts was determined in comparison to the initial supernatant of glomeruli that served as a serum surrogate. RESULTS: Antibodies to dsDNA, the collagen-like region of C1q, Sm, SSA, SSB, and chromatin were enriched in glomerular extracts, mainly from patients with proliferative lupus glomerulonephritis. The IgG binding to histones resulted from the presence of immune or non-immune aggregates of IgG. In some specimens all 6 of the above-listed antibodies were enriched. In one specimen antibodies to myeloperoxidase were enriched. Antibodies to cathepsin G, lactoferrin, and beta2-glycoprotein I were not detected. Antibodies to Epstein-Barr viral capsid antigen and nuclear antigen 1 and antibodies to tetanus toxoid were detected in the serum surrogate, but were not enriched in extracts of glomerular basement membrane fragments. CONCLUSION: Autoantibodies with multiple different specificities form the immune deposits in glomeruli of patients with SLE, including antibodies to dsDNA, Sm, SSA, SSB, the collagen-like region of C1q, and chromatin.
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