Interaction of anti-cholesterol antibodies with human lipoproteins

Inoculation of mice with cholesterol-rich liposomes containing the adjuvant monophosphoryl lipid A results in the production of antiserum containing IgM Ab to cholesterol. The specificity of the Ab was to cholesterol and structurally similar sterols containing a 3 beta-hydroxyl group. Anti-cholesterol binding activity was significantly diminished if the 3 beta-hydroxyl was altered by either epimerization, substitution, oxidation, or esterification. A similar specificity for 3 beta-hydroxy-sterols was observed for an anti-cholesterol IgM mAb. Both hyperimmune serum and the mAb reacted with intact human very-low-/intermediate-density lipoprotein (VLDL/IDL) and low-density lipoproteins (LDL), but not high-density lipoproteins (HDL), in an ELISA, but could react with total lipid extracts containing cholesterol that were prepared from all three lipoprotein classes. Functionally, immune serum or the mAb aggregated and induced a fusion-like reaction with VLDL/IDL and LDL at low temperatures: these aggregates result in spherical structures visible with light microscopy. Similarly, binding of anti-cholesterol A to small cholesterol-rich liposomes resulted in the appearance of vesicular structures with approximately 20- to 200-fold increased diameters. These data demonstrate that the anti-cholesterol Ab recognize unesterified cholesterol in VLDL/IDL and LDL; high-density lipoprotein cholesterol in the intact lipoprotein, however, appears to be protected from reaction with these Ab.