Demonstration by gel diffusion of antigen in spontaneous mouse tumors.

immunize rabbits. The rabbit antiserum was absorbed with normal mouse tissues and tested by gel immunodiffusion with a 2nd group of tumors. The latter were pooled to form 3 distinct groups—strong, weak, and negative reactors. The 3 tumor pools were then used to immunize 3 additional groups of rabbits. The rabbit antisera harvested from the secondary groups were absorbed with spleen homogenate, serum, and mammary gland homogenate from normal mice of the same origin. If antiserum reacted positively in gel diffusion with tumor homogenate, it was also absorbed with contralateral mammary gland extract from the same tumor mice. After the final absorption, the rabbit antisera were tested in gel immunodiffusion against tumor extract, serum and extracts of 2 organs from the same tumorbearing mice, serum and 4 organ extracts from normal mice, extracts of normal mouse embryo, extracts of 2 transplantable mammary carcinomas, and extracts of contaminating bacteria. Of 15 rabbits immunized, 12 produced antisera which reacted with the tumor extract, but not with the other materials. Each rabbit produced the reacting antibodies for a short period of time only. Extracts of very small tumors did not react with the rabbit antisera. The results suggest that there are distinctive antigens in spontaneous tumors, or that the concentration of some normal antigens may be greatly increased. The antigens in question are not weak, but may require special technics for identification.