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MR Fibi, M Aslan, P Hintz-Obertreis, JU Pauly, M Gerken, G Luben, L Lauffer, B Siebold, W Stuber and G Nau
Department of Preclinical Development of Therapeutics, BEHRINGWERKE AG,
Marburg, Germany.
Recombinant human erythropoietin (rhuEpo)-specific mouse monoclonal
antibodies (MoAbs) have been produced and characterized. All antibodies
were specifically reactive with rhuEpo in enzyme-linked immunosorbent assay
(ELISA). Epitope exclusion studies showed three distinct epitope regions,
A, B, and C, recognized by neutralizing MoAbs. An additional epitope region
D was recognized by non-neutralizing MoAbs. Antibodies defining an epitope
region competed with each other for binding sites, but did not compete with
antibodies defining a different epitope region. Group B antibodies were
able to compete for the receptor binding site on rhuEpo with a soluble
human Epo-receptor-lg fusion protein. No single peptide sequences were
found to specifically interact either with group B MoAbs or with the
rhuEpo-receptor. Therefore, it is suggested that epitope region B and the
receptor binding site share binding determinants that are primarily
composed of conformational epitopes. Because group A and group C antibodies
did not compete with the receptor for binding to the receptor binding site
of the rhuEpo molecule, it is suggested that neutralization via epitope
regions A and C is mediated through binding inhibition caused by
conformational changes, transmuting the binding site(s) for the receptor.
Conversely, binding to the receptor seems to induce conformational changes
in the hormone molecule, eliminating epitopes for group A and C antibodies.
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