Immunotoxicologic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rabbits

Male white New Zealand rabbits were exposed orally to 0, 0.01, 0.1, 1 and 10 micrograms/kg/wk of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for a period of 8 weeks. After 4 and 6 weeks of first TCDD administration, the rabbits were inoculated with a mixture of tetanus toxoid and Freund's adjuvant. TCDD exposure reduced the serum antitoxin titers, skin sensitivity to tuberculin, and the number of antibody producing cells in popliteal lymph nodes. At the end of the treatment period serum IgG levels were increased at the lowest dose of TCDD treatment while a marked depression was noticed at the highest dose level. An increase in the thymidine uptake by splenic lymphocytes in culture was noted at all levels of TCDD treatment whereas the response of these cells to phytomitogens was decreased at high levels of TCDD exposure. All different immunologic effects were not altered at the lowest TCDD treatment but both humoral and cell-mediated immune responses were depressed at the highest level of TCDD exposure.