Effect of low-density lipoprotein (LDL) antigen source on an enzyme-linkedimmunosorbent assay for autoantibodies against oxidized LDL

We examined the effect of antigen source on an enzyme-linked immunosorbent assay (ELISA) for autoantibodies against oxidized low-density lipoprotein ( LDL). Serum samples from 20 subjects with systemic lupus erythematosus (SLE ) and from 20 controls were assayed for immunoglobulin G (IgG) and immunogl obulin M (IgM) autoantibodies against oxidized LDL, using either a pooled o r individual (n=3) LDL preparation as antigen. For IgG autoantibodies again st oxidized LDL there was a relationship (r similar to 0.5, P<0.01) between data obtained using individual versus pooled antigen preparations. Bias pl ots demonstrated consistent inverse, concentration-dependent relationships (r similar to-0.6, P<0.001). The difference in IgG autoantibodies against o xidized LDL levels between SLE patients and controls was underestimated (39 -58%) when assays used individual rather than pooled LDL antigen. For Igh? autoantibodies against oxidized LDL the direct relationships were stronger (r similar to 0.8, P<0.001) and the concentration-dependent relationships w eaker (r similar to-0.3, significance variable) than for Ige autoantibodies against oxidized LDL. Variations between LDL preparations suggested that a pooled antigen would give a more stable assay. Thus, LDL antigen source is important in assays for both IgG and IgM autoantibodies against oxidized L DL.