[Immunological assay of apolipoprotein A-I]

Since lipid free apo A-I and lipid rich apo A-I (HDL, LP A, LP A-I) have different accessible antigenic sites, the electroimmunoassay ("rocket") does not allow the determination of the apo A-I concentration in both lipoproteins and serum when lipid free apo A-I are taken as controls. The results are found more significant when an isolated HDL or serum are used as reference. A comparison is made with the results (height of the pics) obtained for the same sample with different antibodies anti apo A-I, checked with the same HDL control, great differences two to one is observed. It is only explained by the various composition of antibodies directed against different apo A-I antigenic sites. Differences obtained in the levels of apo A-I in HDL2 and in HDL3 by immunoprecipitation show that the more lipoproteins are lipid rich the less their apo A-I are reached by antibodies.