Journal of Lipid Research, Vol 29, 1-8, Copyright © 1988 by Lipid Research, Inc.
Interaction of LDL, Lp[a], and reduced Lp[a] with monoclonal antibodies against apoB
A Gries, C Fievet, S Marcovina, J Nimpf, H Wurm, H Mezdour, JC Fruchart and GM Kostner
Institute of Physiology, University of Graz, Austria.
Five monoclonal antibodies (2A, 9A, 6B, L3, L7) produced in mice against
human apolipoprotein B were investigated by competitive and inhibitive
electroimmunoassay (EIA) for their reactivity with low density lipoprotein
(LDL), lipoprotein[a] (Lp[a]), and reduced Lp[a]. All of the antibodies
reacted with apoB of the different lipoproteins indicated by very similar
slopes of the binding curves. None of them gave a positive reaction with
apolipoprotein[a]. The amount of apoB required for 50% inhibition of
antibody binding varied for the different antibodies and lipoproteins.
Antibody 9A showed almost the same affinity for LDL, Lp[a], and reduced
Lp[a]. Antibodies 2A and 6B bound about twofold better to LDL and reduced
Lp[a] than to untreated Lp[a]. Antibodies L3 and L7 needed nearly threefold
higher amounts of Lp[a]-apoB for 50% inhibition of antibody binding than of
apoB of LDL and reduced Lp[a]. The amount of apoB required for 50%
inhibition of antibody binding was somewhat higher in inhibitive assay than
in competitive assay. We suggest that apo[a] covers certain epitopes of
apoB in native Lp[a] leading to a reduced reaction with the monoclonal
antibodies. However, it could also be that the binding of the [a]antigen to
apoB via disulfide bridges causes profound conformational changes of the
apoB region exposed to the surface.
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