ELISA of IgG antibody to oxidized low-density lipoprotein: effects of blocking buffer and method of data expression.

We describe an ELISA for serum IgG antibodies against malondialdehyde-modified low-density lipoprotein (mLDL). Optimal antigen concentration, serum dilution, and dilution of enzyme-conjugated second antibody were 25 mg/L, 1:250, and 1:5000, respectively, when 5 g/L human serum albumin was used for blocking. When data were expressed as mLDL/LDL (the ratio of IgG binding to mLDL vs LDL), within-run and between-run CVs were 7.0% and 8.9%, respectively. Antibody concentrations expressed as mLDL/LDL or as mLDL-LDL (the difference between IgG binding to mLDL and to LDL) were higher in women with systemic lupus erythematosus (n = 20) than in controls (n = 20) (P < 0.001). With bovine serum albumin or Superblock blocking buffers, only the mLDL-LDL data were significant. Thus, the choice of blocking agent and the method of data expression should be carefully considered when assaying IgG antibodies against mLDL.