Effects of TCDD and its Congeners 3,3′,4,4′‐Tetraehloroazoxybenzene and 3,3′,4,4′‐Tetrachlorobiphenyl on Lymphoid Development in the Thymus of Avian Embryos

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Abstract
Thymus anlagen from 11‐day‐old chick and 14‐day‐old turkey and duck embryos were cultured in media containing 2, 3, 7, 8‐tetrachlorodibenzo‐p‐dioxin (TCDD) for 5 days. The maximal TCDD‐induced decrease in lymphoid cell number of chick embryo thymus (to about 60% of the control number) occured at concentrations of 10−10M and above. To produce the same effect on lymphoid cell number in the cultures of thymus anlagen from turkey and duck embryos, about a 100‐fold higher concentration of TCDD was needed. The toxicity of the TCDD congeners 3,3′4,4′‐tetrachloroazoxybenzene (TCAOB) and 3,3′,4,4′‐tetrachlorobiphenyl (TCB) to embryonic chicken thymus was testedin vitroandin ovo.In chick embryo thymus cultures, TCAOB and TCB were about two orders of magnitude less toxic than TCDD. Injection of TCAOB and TCB into chicken eggs preincubated for 11 days resulted in a dose‐dependent decrease in thymic lymphoid cell number 5 days later, declining to about 14% of the controls at 10 μg TCAOB/kg egg. The ED50value was estimated to be 3.6 and 60 μg/kg egg for TCAOB and TCB, respectively.

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