Interactions of 2,3,7,8-TCDD and PCB mixtures/congeners: Immunotoxicity studies

Several commercial PCBs, including Aroclors 1260, 1254, 1248, 1242 and 1232, were immunotoxic in C57BL/6 mice, however the results showed that the lower chlorinated biphenyls (Aroclor 1232 and 1242) were less toxic than the higher chlorinated mixtures. Treatment of C57BL/6J mice with an immunotoxic dose of 2,3,7,8-TCDD (3.7 nmol/kg) and a dose (25 mg/kg) of the commercial PCBs which was not immunotoxic showed that the PCB mixtures antagonized the 2,3,7,8-TCDD-mediated decrease in the plaque-forming cell response to sheep erythrocytes. The structure-dependent effects of individual PCB congeners to act as 2,3,7,8-TCDD antagonists were also investigated and only 2 compounds, namely 2,2′,4,4′,5,5′-and 2,3,3′,4,5,5′-hexachlorobiphenyl exhibited antagonist activity comparable to that observed for Aroclor 1254 as a 2,3,7,8-TCDD antagonist. The implications of these results will be discussed.