Enzyme-linked immunoassay for Lp[a].
Based on our findings that rabbit antisera raised against human Lp[a] or apo[a] have the potential to cross-react with plasminogen, and in some cases have nearly equal affinities for plasminogen and Lp[a], we have developed an assay for plasma Lp[a] based on a "sandwich" ELISA that is insensitive to the presence of plasminogen. This was accomplished through the use of anti-apo[a] as a capture antibody and quantitation of the bound Lp[a], i.e., the apoB-100-apo[a] complex, with an anti-apoB antibody. Although apo[a] is heterogeneous in size, all Lp[a] particles tested, either in pure form or contained in whole plasma, gave parallel dose-response curves and were immunologically equivalent. However, when purified Lp[a] particles with different apo[a] isoforms were studied, those having larger isoforms were, on a weight basis, less reactive than those having a smaller size. Nearly equivalent reactivity was observed when protein concentration was expressed on a molar basis. The distribution of Lp[a] in a population of 84 subjects was skewed with one-third of the individuals having less than 1 mg/dl Lp[a] protein. All subjects tested had measurable concentrations of Lp[a] with a lower limit of detection of 0.030 mg/dl Lp[a] protein. The mean level was 3.2 mg/dl with a range of 0.045 to 13.3 mg/dl. These studies demonstrate the successful development of an ELISA for Lp[a] protein that is insensitive to the presence of plasminogen; that heterogeneity of Lp[a] and apo[a] are an important source of variation in the assay; and the need for an appropriate Lp[a] standard in order to minimize this variation.
Fless
G M
GM
Department of Medicine, Pritzker School of Medicine, University of Chicago, IL 60637.
Snyder
M L
ML
Scanu
A M
AM
D000293:Adolescent; D000328:Adult; D001054:Apolipoproteins A / Q000097:blood; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D017270:Lipoprotein(a); D008074:Lipoproteins / Q000097:blood* / Q000276:immunology / Q000592:standards; D008297:Male; D008875:Middle Aged; D010958:Plasminogen / Q000032:analysis / Q000276:immunology; D012015:Reference Standards; D012016:Reference Values; D014280:Triglycerides / Q000097:blood
D001054:Apolipoproteins A; D017270:Lipoprotein(a); D008074:Lipoproteins; D014280:Triglycerides; D010958:Plasminogen