Antibody-Dependent Cell-Mediated Cytotoxicity in X-Irradiation-Induced Adenocarcinoma of the Rat Small Bowel

Antibody-dependent cell-mediated cytotoxicity (ADCC) was detected in the serum of Holtzman rats which had only their hypoxic ileum and jejunum exposed to 1700-2000 R of X rays, among which 10-25% would develop visible lesions in 4-6 months. All irradiated animals possessed serum which induced the in vitro injury of allogeneic cultured cells of an X-ray-induced rat small bowel adenocarcinoma by effector peripheral-blood lymphoid cells isolated from normal unexposed rats. The active serum component was apparently an IgG, on the basis of its solubility in ammonium sulfate solution, reactivity with anti-rat IgG and matrix-bound Protein A, molecular weight, and inactivity of F( ab′)2fragments. The in vivo significance of this ADCC is presently unclear since it existed in the serum of all rats exposed to the ionizing radiation regardless of whether they developed visible lesions. However, the results do suggest that if this immunological responsiveness plays a role in host tumor defense, then the deficiency in those rats developing the cancer may lie in their circulating effector cells.