The use of paired labeling in the determination of tumor-localizing antibodies.

A paired-label technic has been developed which permits the direct measurement of tumor-localizing antibodies in a single tumor over and above nonspecific background localization of control material. The technic involves labeling of the globulin fraction of the antiserum with one radioisotope, I131, and of the globulin fraction of normal serum with another isotope, I133. The two preparations are mixed and injected simultaneously into a tumor-bearing host. Localization of antibody in the tumor specimen is determined by analysis of the specimen for the two isotopes present. It was shown that the labeling technics are reproducible and that the method is valid. By this method it was found that localization of antibody in the Murphy lymphosarcoma of rats is not uniform and does not parallel localization of normal serum globulin preparations, and that different parts of the tumor have different abilities to absorb antibody. It is postulated that this probably is connected with the rapidity of circulation of blood to the tumor.