Apolipoprotein E quantified by enzyme-linked immunosorbent assay.

We developed a sensitive, specific "sandwich"-type enzyme-linked immunosorbent assay in which affinity-purified antibodies are used for coating and also for preparing an antibody-peroxidase conjugate to quantify apolipoprotein E in serum and in its lipoprotein fractions. This technique is rapid (results within 5 h), precise (mean intra- and interassay CVs 4.3 and 8.2%, respectively), accurate, and simple to perform. Sample pretreatment did not enhance apo E immunoreactivity. For 47 normolipidemic subjects, the mean apo E concentration was 38.11 (SD 11.1) mg/L. Above-normal apo E concentrations were measured in all types of hyperlipoproteinemia, especially types III and V. Apo E correlated with triglyceride (r = 0.58) and cholesterol concentrations (r = 0.60). As determined by gel filtration, hypertriglyceridemia was associated with a redistribution of apo E towards the triglyceride-rich lipoprotein fractions, which contained 77.1% (SD 16.8%) of total plasma apo E in Fredrickson type V patients, compared with 12.5% (SD 6.3%) in normal persons.