Postpartum cell-mediated immunity induced in the rat following perinatal exposure to iodine-131

Studies were undertaken with the intent to establish the degree of risk experienced by a mother and her immediate offspring in developing gastrointestinal cancer following exposure to iodine-131 during pregnancy. An indirect approach in the identification of tumor induction for risk determination was utilized in this study which relied upon the measurement of antitumor cell-mediated immunity (CMI) occurring in the host following exposure to the radionuclide. Fischer F344 inbred pregnant rats were selected as the animal model, and the radionuclide exposure was accomplished by a single intraperitoneal administration of iodine-131 [Na131] at the stage of 16-18 days of pregnancy; then at two months postpartum, the dams and pups were evaluated for the capacity of their peripheral blood lymphoid cells to express specific cytotoxic responses towards target cells consisting of cultured X-ray induced rat small bowel adenocarcinoma cells. The results indicate that an antitumor immunity was induced in the pups upon such a prenatal exposure, while none could be detected existing in their mothers. In addition, there appeared to be a possible sex or hormonal component as a preliminary consideration of the data suggested the male offspring were approximately 1.7 times more immunoresponsive to the perinatal insult. Threshold detection level for detecting such responses to the iodine-131 was found to be in the range of a 9.25 kBq (250 nCi) quantity of exposure. The implication of these preliminary findings based upon such indirect measurements is that the first generation may be at an increased risk to gastrointestinal cancer following peritanal exposure to iodine-131 in the later stage of pregnancy.