Characterization of monoclonal antibodies against apolipoproteins A-I and A-II. Epitope expression in LpA-I and LpA-I : A-II particles

Two monoclonal antibodies (MAbs) against apolipoprotein A-I (apo A-I), 6B9 and FF9B10, and one MAb against apolipoprotein A-II (apo A-II), 3F5, were c haracterized. To establish the epitope of apo A-I recognized by these antib odies, different experimental approaches were performed. First, competition between MAbs and the related epitopes on the same antigen was performed us ing double-determinant tests with previously characterized MAbs, Second, co mpetition of different synthetic peptides of apo A-I in solution with apo A -I immobilized to solid phase was carried out. The MAbs against apo A-I (6B 9 and FF9B10) appear to recognize discontinuous epitopes located in the ami no-terminal region of the apo A-I. In competition experiments Mab 3F5 did n ot recognize central- or carboxy-terminal peptides of apo A-II. Furthermore , apo A-II was stronger recognized when it was included in HDL or LpA-I:A-I I than in its purified form. So the epitope for 3F5 is better expressed in the lipoprotein structure. Finally, to establish the epitopes expression in different antigens in solution, competition of purified apo A-I, apo A-II, LpA-I, and LpA-I:A-II particles or HDL3, with apo A-I or HDL immobilized t o solid phase, was carried out, The results showed that both MAbs against a po A-I reacted with poor affinity against free apo A-I, with high and simil ar affinities against Lp A-I and Lp A-I:A-II lipoparticles and with the hig hest affinity against HDL3. The MAb 3F5 against apo A-II recognized only Lp A-I:A-II and not LpA-I lipoparticles.