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Natural and Immune Antibodies in Mice of Low and High Tumor Strains^*

(From the Mount Sinai Medical Research Foundation and the Chicago Medical School, Chicago 8, Illinois)

1. Natural antisheep agglutinins were determined in the serum of mice of six inbred strains. A striking difference distinguished the C57 Black animals from animals of the other strains: in the former, antisheep agglutinins were found in more than 90 per cent of the animals, and titers of 16 and higher in more than half, whereas the incidence and the titers of the antibodies in the other strains were markedly lower.

2. Natural agglutinins for human red cells were present only infrequently and in low titers in the mouse serum, without any relationship to the strain of the animals tested.

3. In tumor-bearing animals of the C57 Black and of the C3H strains the distribution of antisheep agglutinins was similar to that in tumor-free animals, except that the presence of induced or transplanted tumors tended to raise the incidence and titer of agglutinins.

4. Immune antibodies against sheep red cells and human red cells were produced in C57 Black, C3H, and dba animals. Agglutinins and hemolysins for sheep red cells and human red cells reached higher levels in the majority of C57 Black animals, as compared with the values found in C3H and dba mice.

5. The antibodies were not absorbed by Forssman antigen. The significance of this finding was discussed.

6. The greater frequency of natural antisheep agglutinins, their significantly higher titers, and the more vigorous response to injections of sheep and human red blood cells, seem to justify the conclusion that mice of strain C57 Black have a more active and more responsive agglutinin-producing reticulo-endothelial system than the other five strains.

It would be tempting to correlate the apparent higher efficiency of the reticulo-endothelial tissues of strain C57 Black with the low incidence of spontaneous mammary carcinoma. However, it is equally possible that the two phenomena are not related to each other as cause and effect.

We hope that further study, especially of other strains with low tumor incidence and with high tumor incidence but free of the milk factor, may throw light on this problem.

^* Presented at the fortieth annual meeting of the American Association for Cancer Research at Detroit, Michigan, on April 16, 1949.