IMMUNOLOGICAL PROPERTIES OF APO-B-CONTAINING LIPOPROTEIN PARTICLES INHUMAN ATHEROSCLEROTIC ARTERIES

In this study, we have documented immunochemical properties of apolipo protein (apo) B-containing particles (LpB) extracted from human athero sclerotic lesions obtained during vascular reconstructive surgery of p atients. These properties were compared to those of particles purified from corresponding atherosclerotic plasma and healthy control plasma. LpB immunoreactivities were tested in solid phase competitive binding radioimmunoassays using five anti-apoB monoclonal antibodies (MAb) fo r which epitopes have been previously located on the protein. The regi ons encompassed amino acids 405 to 539 (MAb B1), 1854 to 1879 (MAb B4) , 3506 (MAb BA11), and 4355 (MAb BL3). The fifth antibody (MAb BL5) re cognizes a conformationally expressed epitope. LpB from lesions presen ted a significantly decreased immunoreactivity as compared to LpB from respective plasma except for the epitope recognized by MAb BA11 locat ed precisely in the low density lipoprotein (LDL) receptor binding sit e. The accessibility of the four sequential epitopes was similar on Lp B from atherosclerotic and healthy plasma while it was decreased for t he conformational one in LpB from atherosclerotic samples. These alter ed immunoreactivities were not related to changes in chemical composit ion of LpB as this was quite comparable in all preparations. With rega rd to electronegativity, apoB fragmentation, immunological accessibili ty, and size distribution of the particles, changes seem to increase i n the following order from healthy plasma, atherosclerotic plasma, and the corresponding lesions. The results confirm some structural charac teristics of oxidatively modified particles from human atherosclerotic lesions and to a lesser degree from respective plasma, but more speci fically demonstrate a global conformational change in LpB from lesions , this change being perhaps initiated in the plasma.