Competitive enzyme inhibition immunoassay of apolipoprotein A-I: use of monoclonal antibodies.

An original competitive enzyme inhibition immunoassay has been developed for determination of total apolipoprotein A-I (apo A-I) in serum and in plasma. This specific assay involves a single monoclonal antibody (F59 4A12 2F4, directed to the -COOH terminal region of the apo A-I molecule) and a stable secondary plasma standard. Delipidation of serum samples exposed no additional antigenic sites, which suggests that all the apo A-I molecules express the epitope detected by Mab 4A12 on the surface of the apo A-I-containing particles. Within- and between-run CVs were, respectively, 6.1% and 7.5% at a 1.47 g/L concentration of apo A-I, 7.1% and 8.2% at 1.21 g/L, and 6.5% and 7.3% at 1.80 g/L. Results (y) correlated with those obtained with an electroimmunoassay (x), in which we used a mixture of three monoclonal antibodies, including Mab 4A12, as follows: y = 250x - 7, r = 0.744, P less than 0.001.