Changes in immune response to sheep red blood cells during growth of transplantable rat tumor

The number of direct plaque-forming cells and the titer of circulating hemolytic antibodies were studied at different times after transplantation of Guérin tumor in rats. A stimulating effect was observed 5 days after tumor transplantation. In the terminal stage of tumor development the immune responsiveness was reduced. When irradiated, nongrowing tumor tissue was transplanted, an increased immune response could be observed shortly after transplantation while a loss in immune response did not develop up to the 21st day after transplantation.