Effects of Radiation on Living Organisms Radiosensitivity of Immune Responses and Mechanisms of Project Title: Immune Reactions RX-03-O1-(b) 14. Scope: (Conc'd.) observed suscepcibility of mice to murine lymphoid leukemia and to rejection of allografts. (Stoner) Although extensive research interest has been given to the carcinogenic effects of ionizing radiation, little is known about che effects of radiation on latent RNA and DNA tumor virus infections and the influence of radiation on virus-induced tumors, Also, little is known of radiation effects upon the immune system of genetically susceptible and resistant hosts in determining the pathogenesis of tumor virus infections and virus-induced tumors. [n this respect, the chicken, with its known indigenous tumor viruses and established genetically susceptible and resistant lines, offers a unique animal model system to study the effects of graded doses of radiation on the virus-host relationship in leukosis. The well-known repressant action of ionizing radiation on immune systems provides an opportunity to assess the relative role of cellular and humcral immunity in resistance to avian leukosis. The overall significance of the proposed research is that it is possible with this model system to work with known, well-described leukemic DNA and RNA viruses in both susceptible and resistant lines of chickens and to explore the virus-host relationship of leukemia as well as the effects of radiation on the virus-host relationship of leukemia that cannot be studied in man. The vast majority of avian tumors have their histogenesis in the hematopoietic system and have been classified as the avian leukosis complex. A recent classification of the avian leukosis complex has been established by Sevoian as follows: Avian Leukosis Complex: LYMPHOID Type I (Myxovirus) Subtype A B Cc Type II (Herpesvirus) Type III (Myxovirus) MYELOID ERYTHROID Type I NON-LEUKOSIS TUMORS Type I Osteopetrosis Fibrosarcomas Endotheliomas Nephroblastomas, etc. Type I . two distinct types of viruses--RNA (RIF-virus, T-virus) and DNA bus) --can cause leukemic tumors. The etiologic identification of eases has led to the terms lymphoid leukosis for RIF-RNA virus tumors, reticuloendotheliosis for T-RNA tumors and Marek's disease for JM-DNA virus It is estimated that Marek's disease makes up the majority of naturally tumors. Nearly all field flocks are infected with Marek's occurring tumors in poultry. and remain chronically infected. Though infection age disease virus at an early levels with Marek's disease are as high as 100% in some cases, neoplasia (See Continuation Sheec) [119210 RX-177