Monoclonal antibodies can precipitate low-density lipoprotein. I. Characterization and use in determining apolipoprotein B

We produced 20 mouse monoclonal antibodies against human plasma low-density lipoprotein (LDL). Individually they failed to precipitate LDL in agarose gel by the double-immunodiffusion technique; collectively they did, or as few as two combined monoclonal antibodies could do so. To mimic polyclonal antibodies in determination of apolipoprotein B (apo B) by radial immunodiffusion, a combination of four particular monoclonal antibodies (clones A, B, C, and D) was necessary. We characterized these four clones with respect to temperature dependency, affinity, total binding to ¹²⁵I-labeled LDL, and specificity to the different species of apolipoprotein B. Two monoclonal antibodies (B and C) bound 100% of ¹²⁵I-labeled LDL; clones A and D bound 80% and 87%, respectively. All four clones bound maximally to LDL at 4°C. The affinity constants for clones A, B, C, and D were 0.6, 2.1, 3.8, and 2.3 x 10⁹ L/mol, respectively. By the Western blotting technique, the four monoclonal antibodies all reacted with the species B-100 and B-74 of apolipoprotein B, and to various degrees with B-48 and B-26. Radial immunodiffusion (x) and direct enzyme-linked immunosorbent assay (y) with a mixture of the four monoclonal antibodies gave almost identical results for 70 patients: y = 0.921x - 2.58; r = 0.933.