Alterations in the Developing Immune System of the Rat after Perinatal Exposure to Methoxychlor

Abstract

We previously demonstrated that apoptotic cell death occurred in the thymus of rat pups of both sexes after perinatal exposure to methoxychlor (MXC) through dams. Based on that result, we have undertaken a further investigation to determine whether perinatal exposure to MXC persistently influences the rat immune system until a mature age. For the present study, male and female pups were obtained from dams receiving MXC at dietary dose levels of 0, 30, 100, 300 and 1000 ppm. Dietary administration of MXC to the parental rats was started from 3 weeks prior to mating for both sexes and was continued for females (dams) throughout the period of gestation and lactation. The pups of both sexes in all dose groups were maintained on a normal diet from weaning up to 10 weeks of age and then were examined for the effect of MXC on the immune system. Males and females showed a significant increase in thymic CD3⁺/CD4^-CD8^- cells in the 1000 ppm group and a significant decrease in splenic CD3⁺/CD8⁺ cells in the 300 and 1000 ppm groups. In addition, females in the 300 and 1000 ppm groups showed significant decreases and/or decreasing trends in splenic cellularity, splenic CD3⁺ T cells, CD45RA⁺ B cells, and CD3⁺/CD4⁺ T cells. These results suggest that perinatal exposure to MXC may exhibit profound and long-lasting effects on the developing rat immune system, especially in females, which continues into adulthood.