Embryonic or fetal antigens (EAs) are expressed on developing rodent fetus (mouse, hamster, rat, guinea pig) and on human fetus. EAs on the embryo cells arouse cellular and humoral immune responses in their syngeneically pregnant mothers which have been partially characterized. Antigens cross-reactive with EAs have been detected on every major histologic class of rodent and human tumor. These reexpressed EAs or fetal gene products on tumors are termed oncofetal antigens (OFAs). Little is known about the expression or regulation of the immune responses to ionizing radiation promoted neoplasia or the effects of radiation on immune responses to OFAs. The specific goals of the proposed study are to confirm the presence of specific OFAs on radiation-induced primary tumors of mice using unique monoclonal antibodies prepared against phasespecific mouse embryonic antigens by immunization with syngeneic fetus. The EA epitopes reactive with these selected monoclonal antibodies have been partially characterized. Then, the time course of OFA expression in radiation promoted neoplasia would be assessed in vitro and in vivo. The irradiated host's immunoregulatory responses to specific OFAs will be carefully catalogued. The effects of acute whole body irradiation on the specific immune response potential to OFA expression on primary and passaged radiation-induced tumors would be determined from these studies. The objectives of the project are to determine (1) if specific OFA expression is a fundamental trait of radiation-induced tumors in mice and (2) whether radiation-induced damage of the immune response contributes to lymphoma or sarcoma development. We will determine if activation of c onc-gene expression parallels OFA expression and if c-onc or v-onc gene encoded products and OFAs are interrelated.