Penicillin derivatives are true monovalent elicitors of anaphylactic reactions.

Conjugates carrying a single 2-carboxy-4,6-dinitrophenyl hapten and as auxiliary group various thiazolidine substituents related to penicilloyl, were prepared and studied in guinea-pig passive cutaneous anaphylaxis (PCA). Included are monohaptenic model conjugates with discrete hydrocarbon auxiliary groups. One of the conjugates with the 3-formyl-2,2-dimethyl-1,3-thiazolidine-(4S)-oyl auxiliary group, characterized by the blocked chemical reactivity of the thiazolidine, was an anaphylactogen. This rules out formation of oligohaptenic antigens via chemical conjugation as a step in the PCA reactions observed. Rather, the non-covalent interactions of the auxiliary group, which has very strict structural requirements not yet mapped out in full, are necessary. Data from the model conjugates show that planar ring structures in conjunction with unsubstituted carboxyl groups constitute effective auxiliary groups. Benzylpenicilloyl antigens may act as monovalent elicitors of immediate reactions when the antibody population is predominantly directed against the benzyl side-chain. Under these conditions the benzyl residue is expected to serve as the haptenic part and the thiazolidine moiety as the auxiliary group.