Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on maternal immune response during pregnancy

Whether pregnancy-induced immunosuppression when combined with exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) could exacerbate immunotoxicity has not been previously investigated. The current study evaluated the immune status of C57BL/6 pregnant and virgin mice following exposure to TCDD. To this end, syngeneically pregnant or virgin female mice were injected intraperitoneally with 10 mug/ kg TCDD. Pregnancy alone significantly decreased thymic cellularity and J11d expression as well as induced changes in T-cell subsets. TCDD treatment caused significant thymic atrophy in pregnant mice as early as 48 h after exposure, but this effect was apparent in virgin mice only after 72 h. TCDD treatment also caused more marked alterations in thymic T-cell subpopulations of pregnant mice when compared to the virgin mice, with a decrease in the percentage of double-positive T cells and an increase in the percentage of single-positive (sP CD4(+) or sP CD8(+)) and double-negative T cells. Moreover, the proliferative responses of thymocytes, but not splenocytes, to mitogens were significantly altered in TCDD-treated pregnant mice when compared to the TCDD-treated virgin mice. Furthermore, no significant changes in the expression of CD4, CD8, B220 and NK1.1 markers were found in splenocytes from TCDD-treated virgin and pregnant mice. Immunization of mice with a superantigen caused a similar immunotoxic response in TCDD-treated pregnant and virgin mice with a decreased lymph node cellularity and lower percentages and cell numbers of Vbeta3(+) and Vbeta11(+) T cells. Together, the results of the current study demonstrate for the first time that pregnancy augments the sensitivity to TCDD-induced immunotoxicity in the thymus, but not in secondary lymphoid organs.