Identification of carcinogens by measurement of cell-mediated immunity. IV. Antitumor immunity following perinatal exposure to 1,2-dimethylhydrazine.

This study was initiated to investigate the possible perinatal carcinogenic effects of the colon carcinogen 1,2-dimethylhydrazine (DMH) in Fischer F344 inbred rats. Pregnant female animals during their 16-18th day of gestation were administered the chemical by intraperitoneal injections, and beginning at 4 months postparturition, the antitumor cell-mediated immunity (CMI) was delineated in the dams and pups as an indirect measure of carcinogenesis. The CMI status was established by the ability of peripheral blood lymphoid cells obtained from the rats to injure and kill target tumor cells derived from an X-ray-induced rat small bowel adenocarcinoma cell line with the degree of damage being reflected in the quantity of loss of radioiodinated peripheral and integral membrane proteins from the target cells. A significant antitumor CMI was observed in the exposed offsprings although there was no apparent difference between the immunoresponsiveness observed in either the males or the female siblings. Unexpectedly, the mothers exhibited little such antitumor cellular immunity following the carcinogenic insult; even though all previous investigations of adult animals always demonstrated such an immunological response following exposure to the quantities of DMH that were administered (0.1 to 20 mg per kg body wt). As a consequence, these findings tentatively implied that the state of pregnancy alters a female's response to chemical carcinogenic insults and may actually serve as a device for protection from environmentally caused cancer. The threshold detection level for DMH exposure utilizing immune measurements was found to be approximately 10 times smaller for the perinatal susceptibility to the chemical insult intimating that such tests might usefully be incorporated in those bioassays utilized for determining the cancer-causing potential of weak carcinogens. Our findings now suggest that DMH may indeed be a perinatal carcinogen and that immune responsiveness may be readily employed for identifying such substances. However, the definitive studies of actually identifying cancer following such in utero exposures remain to be accomplished.