Lymphocyte cytotoxicity in X-irradiation induced rat small bowel adenocarcinoma. IV. Activation of cellular immunity by X irradiation.

Exposure of only the ileum and jejunum of Holtzman male rats to 100--2000 R resulted in almost immediate and dose-dependent activation of anti-tumor cellular immune mechanisms, as measured in vitro by the cytotoxicity of the animals' peripheral blood lymphoid cells to allogeneic cultured cells from an x-irradiation induced Holtzman rat small bowel adenocarcinoma. These cytotoxic responses were somewhat specific; the lymphoid cells did not kill prostatic adenocarcinoma target cells and cytotoxicity could not be induced by x-irradiation of some tissues other than the small bowel. Results suggest that exposure of an organ to ionizing radiation results in changes which sensitize the lymphoid cells in the animal to recognize and kill cancer cells of the particular tissue. Immunologic suppression by ionizing radiation presumably did not occur because only a small portion of the body was exposed.