Studies of the Epitopes of Amoxicillin by Monoclonal Antibodies

Four different mice monoclonal antibodies to amoxicillin (AX) were studied (AO 25.2, AO 6.2, AO 21.1, and AO 3.2). The specificity was determined by enzyme-linked immunosorbent assay inhibition using in the fluid phase free and conjugated monomers of AX, ampicillin, and benzylpenicillin with ε-aminocaproic acid. The monoclonal AO 25.2 (IgM isotype) recognized a chemical structure common to all penicillins used, presumably the thiazolidine ring. AO 6.2 (IgE) and AU 3.2 (IgG2a recognized mainly the side chain of AX and the clone AO 21.1 (IgG3) required for optimal inhibition of the conjugated monomer of AX, indicating that both the side chain and the new antigenic determinant were required for optimal inhibition. These results indicate that there are differences in the specificities of these antibodies and that the different parts of the AX molecule contribute to a different extent to the antigen-binding site.