Enzyme-immunoassays for polychlorinated biphenyls: structural aspects of hapten-antibody binding

The syntheses of 4,4′-dichlorobiphenyl- and 3′,4,4′,5-tetrachlorobiphenyl-2-azo-protein immunogens and the corresponding haptens conjugated to peroxidase through the amidoadipate spacer arm are described. Only one sheep of the 24 immunized animals yielded an antiserum with superior antibody titres. The direct competitive enzyme-linked immunosorbent assay (ELISA) incorporating this antiserum showed IC50 values for commercial polychlorinated biphenyl (PCB) mixtures Delor 103, 104, 105, and 106 (the corresponding formulations are Aroclor 1242, 1248, 1254 and 1260) of about 200, 250, 600, and 900 μg l−1, respectively. No cross-reactions with chlorinated phenols, phenoxyalkanoic acids, or chlorinated herbicides were observed and only a 5% cross-reactivity was found for DDE (Delor 103 = 100%). Molecular models of hapten determinants were constructed to examine potential conformational changes in the biphenyl nucleus in relation to tracer immunoreactivity and assay selectivity. The structural data were not consistent with the lack of immunoreactivity for peroxidase tracers in conjunction with almost all of the tested antisera. Influence of the various molecular factors on the binding and competitive characteristics is discussed.