Delayed Contact Sensitivity to Catechols: IV. Stereochemical Conformation of the Antigenic Determinant¹

Guinea pigs sensitized with catechols having cyclic and linear hydrocarbon side-chains did not exhibit reciprocal cross-reactivity. Those sensitized with catechols having cyclic hydrocarbon side-chains reacted to almost the same degree when tested with catechols having linear hydrocarbon side-chains with approximately the same number of carbon atoms. Guinea pigs sensitized with catechols having linear side-chains reacted poorly or not at all when tested with catechols having cyclic side-chains. This indicates the importance of the hydrocarbon side-chain in determining antigenic specificity and provides a chemical basis for non-reciprocal cross-reactivity. Specificity that could be attributed to a carrier molecule was minimal or absent. The data are compatible with a linear conformation of n-alkyl side-chains but indicate that, because of their flexibility, they can conform to other shapes. Aromatic character in the hydrocarbon side-chain did not markedly affect specificity, which seemed to be almost completely determined by size and shape.