Fine structural recognition specificities of IgE antibodies distinguishingamoxicilloyl and amoxicillanyl determinants in allergic subjects

IgE antibodies in the sera of subjects allergic to beta -lactam antibiotics detect a spectrum of specificities ranging from side-chain groups to an en tire penicillin or cephalosporin molecule. In addition to such structural h eterogeneity of allergenic determinants, TgE antibodies in the sera of diff erent allergic subjects show heterogeneous recognition responses. Detailed immunochemical studies were carried out on the sera of penicillin-allergic subjects that showed selective and unexpected reactions with the frequently prescribed penicillin, amoxicillin. Antibodies from one subject reacted on ly with the amoxicilloyl determinant while TgE from another subject showed multiple reactivity with penicilloyl and penicillanyl determinants of diffe rent penicillins but not with the amoxicilloyl determinant. Quantitative ha pten inhibition studies revealed that the combining sites of the former ant ibodies were complementary to amoxicillin in a form that permits binding to the hydroxyaminobenzyl side-chain and the thiazolidine ring carboxyl. Thes e conditions are satisfied with the drug in the '-oyl' but not in the '-any l' form which involves linkage through the 2-carboxyl of the thiazolidine r ing. With the second serum, adsorption studies showed that the wide-ranging reactivity of IgE was due to a single population of antibodies that detect ed a common specificity on the different penicillins. Combining site studie s revealed clear recognition of the benzyl portion of the side-chain of ben zylpenicilloyl, benzylpenicillanyl, ampicilloyl, ampicillanyl and amoxicill anyl determinants when free antibody access to the side-chain was possible but little or no recognition of the ring hydroxyl of amoxicillin. Such unin hibited access may not occur, however, when amoxicillin is conjugated in th e '-oyl' form since opening the beta -lactam ring allows increased flexibil ity, and rotation of the molecule and the possibility of close association of the hydroxyaminobenzyl side-chain of amoxicillin with the linked peptide carrier. In such close steric association, H-bonding involving the ring hy droxyl and amino acids of the carrier may prevent antibody access to the si de-chain region of the amoxicilloyl determinant. Copyright (C) 2001 John Wi ley & Sons, Ltd.