Immunological assays of apolipoproteins in plasma: methods and instrumentation

A number of immunological techniques--radioimmunoassay, enzyme-linked immunosorbent assay (ELISA), electroimmunoassay, radial immunodiffusion, and a variety of immunoprecipitin assays--have been used to quantify apolipoproteins in plasma. This paper outlines their technical details and discusses their major advantages and drawbacks. The most sensitive procedures, RIAs and ELISAS, are best suited to quantifying those apoproteins found in low concentration in plasma. Immunoturbidimetric assays, on the other hand, which are readily automated, are being widely used to quantify apolipoproteins A-I and B. Apolipoprotein quantification is complicated by the interaction of the proteins with lipids, which can often mask their antigenic determinants. This problem may be circumvented by pretreatment of the samples, by selection of appropriate standards, or by the use of polyclonal or monoclonal antibodies that interact with permanently exposed epitopes on the lipoproteins' surfaces. Our proposed methods for measurement of the individual apolipoproteins give consideration to these approaches.