Tetrachlorodibenzo-p-Dioxin (TCDD) Inhibits Differentiation and Increases Apoptotic Cell Death of Precursor T-Cells in the Fetal Mouse Thymus

Figures & data

TABLE 1. The effect of gestational exposure to TCDD on thymic weight and cellularity

Fetal litter weight, number of pups/litter, individual fetal thymic weight and cellularity on gestation day 18
	Litter weights (mg)	Number of pups/litter	Thymic weights (μ g)	Cellularity^1
A
Control	8.5 ± 2.0	7.0 ± 2.0	2.86 ± 0.39	3.80 ± 1.24
5. μg/kg TCDD	8.1 ± 2.4	6.8 ± 2.1	1.65 ± 0.44	1.35 ± 0.69
B
Control	7.9 ± 0.8	6.8 ± 1.5	3.01 ± 0.75	4.26 ± 1.50
10. μg/kg TCDD	9.2 ± 2.2	7.8 ± 1.7	1.17 ± 0.10	1.18 ± 0.57

¹Cellularity is ×10⁶ cells

*Significantly different from control, p < 0.05

Thymic weights are in micrograms. Thymic cellularity is ×10⁶ cells per thymus. Weights and cellularity are presented on a per organ basis (mean ± SEM) as the total is divided by the number of individuals in the litter. (A) Comparison of control and 5 μg/kg TCDD treatment. (B) Comparison of control and 10 μg/kg TCDD treatment

FIG. 1 (A) Representative histograms from control and dioxin exposed gestation day 18 mice, showing 7-AAD fetal thymocyte fluorescence in all CD4CD8 cell compartments. (B) Representative histograms from control and dioxin-exposed gestation day 18 mice, showing 7-AAD fluorescence in CD4⁺CD8⁺ fetal thymocytes. Abbreviations: V—viable cells; EA—early apoptotic cells; LA/N- late apoptotic/necrotic cells. Numbers immediately above labeled compartments represent percentages of cells in each compartment. *Significantly different at p < 0.05.

TABLE 2. The effect of gestational exposure to TCDD on thymocyte populations defined by CD4 and CD8 cell surface antigens

Fetal thymocyte surface antigen expression
	CD4^−8^−	CD4^−8^+	CD4^+8^−	CD4^+8^+
A
Control	11.13 ± 3.87	1.83 ± 0.22	2.18 ± 1.30	84.86 ± 3.68
5. μ g/kg TCDD	18.46 ± 2.17	3.69 ± 0.76	1.79 ± 0.87	76.04 ± 2.26
B
Control	10.67 ± 4.25	1.90 ± 0.39	1.38 ± 0.48	86.08 ± 3.75
10. μ g/kg TCDD	25.80 ± 11.0	5.04 ± 1.21	1.72 ± 0.75	67.42 ± 9.80

*Significantly different from control, p < 0.05

Numbers are percentages (mean ± SEM) of cells within each phenotype. (A) Controls compared to 5 μ g/kg TCDD. (B) Controls compared to 10 μ g/kg TCDD

TABLE 3. Cellularity in thymocyte phenotypes defined by CD4 and CD8 expression

Fetal thymocyte numbers in populations defined by CD4 and CD8 expression
	CD4^−8^−	CD4^−8^+	CD4^+8^−	CD4^+8^+
A
Control	0.42 ± 0.15	0.07 ± 0.01	0.08 ± 0.05	3.22 ± 0.14
5. μ g/kg TCDD	0.26 ± 0.03	0.05 ± 0.01	0.02 ± 0.01	1.02 ± 0.03
B
Control	0.45 ± 0.18	0.08 ± 0.02	0.06 ± 0.02	3.67 ± 0.16
10. μ g/kg TCDD	0.28 ± 0.12	0.06 ± 0.01	0.02 ± 0.01	0.82 ± 0.11

*Significantly different from control, p < 0.05

Calculated as total cellularity multiplied by the percentage of cells within each phenotype. Numbers are × 10⁶ cells per thymus

FIG. 2 Representative gestation day 18 fetal thymi, 40× magnification. (A) is a control thymus, while (B) is a 10 μg/kg TCDD-exposed thymus. Note the increased cellularity and size of the control thymus.

FIG. 3 Gestation day 18 fetal thymus at 100× magnification. (A) is the control thymus, (B) is the 10 μg/kg TCDD-exposed thymus. The cortex is labeled C and the medulla is labeled M. Note the clear demarcation of the cortical/medullary junction for the control thymus.

FIG. 4 Gestation Day 18 Fetal Thymus, 500× magnification. (A) is the control thymus, (B) is the 10 μg/kg TCDD-exposed thymus. The long thin arrows indicate mitotic figures seen in the control thymus, while the short thick arrows indicate pyknotic nuclei in the TCDD-exposed thymus.