Mouse strains with different susceptibility to aryl hydrocarbon hydroxylase (AHH) induction and with different levels and/or affinity for a specific cytosolic binding protein ("receptor") were used to investigate the immunosuppressive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Humoral antibody production was strongly inhibited in C57B1 6 and C3H HeN mice (more susceptible strains) with very low, single doses of TCDD (1.2 μg/kg), while other strains ( DBA 2 and AKR) required higher doses (at least 6 μg/kg) to be partially suppressed. Longer exposure (8 weeks) did not increase the sensitivity of DBA 2 mice. A good correlation between the degree of enzyme inducibility and immunosuppression was observed in studies with B6D2F1 mice and backcrosses. Similar results were obtained with 2,3,7,8-tetrachlorodibenzo-furan (TCDF), the most powerful competitor for TCDD "receptor" in vitro and in vivo. TCDD immnotoxic effects appeared to be associated with the presence of a specific cytosolic binding protein which mediates AHH induction.
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