Identification of endothelial cell membrane proteins that bind anti-DNA antibodies from patients with systemic lupus erythematosus by direct or indirect mechanisms.

Abstract A subgroup of murine monoclonal anti-DNA antibodies bind to vascular endothelial cells either directly as a result of cross-reactivity, or indirectly through immunoglobulin-bound DNA and DNA-binding proteins on the endothelial cell membrane. To determine whether these mechanisms apply in human systemic lupus erythematosus (SLE), and to identify endothelial cell membrane protein(s) that bind human anti-DNA antibodies, we examined, by Western blotting, the binding of human polyclonal anti-DNA antibodies (PoAb) isolated from eight patients with SLE to human umbilical vein endothelial cell membrane proteins. PoAbs bind to endothelial membrane proteins with M r 84,000 and 46,000, which correspond to the DNA-binding proteins previously reported. Such binding is diminished after removal of DNA by DNase treatment. In addition, PoAbs bind to membrane proteins with M r 180,000, 110,000, 68,000, 44,000, and 35,000–30,000. Such binding is unaffected by alterations in DNA concentration. Anti-dsDNA and anti-ssDNA PoAbs from individual patients exhibit identical binding patterns, as are PoAbs isolated during active disease or remission. The results show that human anti-DNA antibodies can bind to endothelial cells both indirectly via immunoglobulin-bound DNA, and directly due to cross-reactivity. These mechanisms of cellular binding by anti-DNA antibodies may depict patho-genetic steps in human SLE.