Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the immune system of laboratory animals.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most toxic compounds known. TCDD and other chlorinated dibenzodioxins have been associated with occupational chloracne in workers engaged in the manufacture of technical chlorophenols and their derivatives such as the herbicide 2,4, 5-trichlorophenoxyacetic acid (2,4,5-T) (1), in lethal liver necrosis in rabbits (2), and in the chick edema disease (3). More recently TCDD has been shown to be highly teratogenic (4). Laboratory studies have found TCDD to cause severe atrophy of the thymus at sublethal dose levels (5, 6). Because the thymus is the central lymphoid organ for cellmediated immunity and other environmental chemicals have produced immunosuppression (7), studies to test the immune response in TCDD-treated laboratory animals were conducted. Methods selected to assess cell-mediated immunity were delayed type hypersensitivity to tuberculin in guinea pigs and rats, and a local graft versus host reaction in mice. The effect of TCDD on the humoral immunity was also studied in guinea pigs.