LYMPHODEPLETION OF THE THYMUS CORTEX IN RATS AFTER SINGLE ORAL INTUBATION OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN

Atrophy of the thymus and thymic lymphodepletion occurs after exposure to sublethal doses of TCDD. Previous studies using high doses of TCDD (150 mu g/kg) have indicated a preferential lymphodepletion of the th ymus cortex on day 4 after a single oral intubation. Here we describe the effects of a single oral intubation of lower dose levels of TCDD ( 1, 5, and 25 mu g/kg) on thymic weights and thymocyte subpopulations i n Wistar rats on day 4 after exposure. A single administration of 1 mu g/kg TCDD induced a significant reduction in the number of immature C D4(+)CD8(+) double-positive (DP) thymocytes. At this time point the nu mbers of mature CD3(high) medullary thymocytes were not affected at an y dose level tested. We conclude that also lower dose levels of TCDD i nduce thymic atrophy via a preferential lymphodepletion of the thymus cortex.