Dose-dependent TCDD-induced increase or decrease in T-lymphocyte subsets in the blood of New World monkeys ( Callithrix jacchus)

Abstract

Dose-dependent opposite effects of TCDD were observed on lymphocyte subsets in the blood of marmoset monkeys during long-term studies: while repeated doses resulting in effective body burdens equivalent to 5 to 10 ng TCDD/kg body wt (1.5 ng/kg body wt, weekly) decreased the percentage and the absolute number of “helper-inducer” T cells (CD4 +CDw29 +), even smaller doses (300 pg/kg body wt, weekly) leading to effective body burdens equivalent to 2 to 3 ng TCDD/kg body wt induced an increase in this lymphocyte subpopulation. The results clearly indicate that immunological effects induced by TCDD in the marmoset at higher doses cannot be expected to also occur (at a decreased incidence) at very low exposures, and no scientific basis exists for a linear extrapolation to very low exposures. The effects are reversed at a lower dose level, and no effects are any longer detectable in our model when the exposure is further decreased to a single dose of 1 ng TCDD/kg body wt or lower.