Abstract

The effect of irradiation of thymectomized mice on the incidence of lymphoid tumors in subsequently implanted isologous thymic grafts has been studied. In a series of experiments, it has been found that: 1. Systemic irradiation of the host is essential for the induction of these tumors in more than sporadic numbers. 2. The lymphomogenic effect of irradiation on the host persists for as long as 8 days after the last of a series of fractional exposures. 3. The effect is strikingly inhibited or abolished by shielding one thigh during irradiation or by the intravenous injection of isologous bone marrow cells after irradiation. These effects of irradiation, thigh-shielding, and marrow injection on the incidence of implant lymphomas closely resemble those previously noted for thymic lymphomas arising in situ in intact mice of this strain. * These investigations were supported by grants-in-aid from the National Cancer Institute, National Institutes of Health, U.S. Public Health Service, the Jane Coffin Childs Memorial Fund for Medical Research, and an American Cancer Society Institutional Cancer Research grant to Stanfor University.