Quantitation of apolipoprotein E in rabbit sera with a competitive enzyme-linked immunosorbent assay

A competitive enzyme-linked immunosorbent assay was developed to quantitate apoE levels in normal and cholesterolemic rabbit serum. The assay can detect 1 ng of apoE and has an interassay coefficient of variation of 5.1%. The assay's antigen specificity was established by the generation of a competitive displacement curve with rabbit apoE, but not with rabbit albumin nor with rabbit apoC. Nonimmune serum was not able to produce a detectable response in the assay. Lipid-protein interactions did not interfere with the assay and color development was linear throughout the incubation time. Rabbits fed a normal diet had 5.3 +/- 0.4 mg of apoE/dl serum. Rabbits fed a diet containing 1% (w/w) cholesterol for 14 days had 86 +/- 11 mg of apoE/dl serum.