Evidence for induction of apoptosis in T cells from murine fetal thymus following perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes thymic atrophy, but the precise mechanism of such toxicity remains unresolved. The current study investigated the role of apoptosis in TCDD-induced thymic involution follow-ing perinatal exposure to TCDD. To this end, C57BL/6 pregnant mice were injected intraperitoneally on gestational day (GD) 14 with a single dose of 10 g/kg TCDD. Analysis of the thymus on GDs 15, 16, 17, and 18, and on postnatal day (PD) 1, showed a remarkable reduction in thymic cellularity 3–7 days post-TCDD exposure. TCDD treatment also caused marked changes in the proportions of T-cell subsets, particularly on GD 17 and GD 18 thymocytes. In vitro culture of thymocytes from mice exposed perinatally to TCDD showed increased apoptosis when compared to the controls, which peaked on day 3 post-TCDD exposure. Triple-color staining showed that TCDD induced apoptosis in al