HEPARAN-SULFATE ELISA GIVES FALSE-POSITIVE RESULTS FOR ANTI-DNA DNA HISTONE IMMUNE-COMPLEXES IN SERA OF PATIENTS WITH SLE

Heparan sulphate-reactive antibodies in lupus sera have been suggested to be anti-DNA-DNA/histone immune complexes and to be associated with lupus nephritis. In this study, 23 anti-DNA-positive lupus sera inclu ding 13 active nephritis sera were tested for the presence of circulat ing anti-DNA-DNA/histone immune complexes by solid phase heparan sulph ate-ELISA. Because of high background binding to protamine chloride-li nked heparan sulphate plates, poly-L-lysine (PLL) was used as a linker and the remaining active sites of PLL were blocked with poly-L-glutam ic acid. The ELISA was capable of detecting small amounts of anti-DNA IgG-DNA/histone immune complexes formed in vitro. However, only three active nephritis sera of the 23 sera tested showed significant binding to heparan sulphate plates. This binding was found to be non-specific , the result of high background binding of IgG to PLL. Anti-heparan su lphate ELISA using positively charged linkers detects non-specific bin ding when lupus sera are tested. Specific assays need to be developed for DNA/histone-related immune complexes present in lupus sera.