In vitro demonstration of an antigen in red blood cells of C3H mice.

In previous experiments with the spontaneous C3H mouse mammary tumor it was observed that antisera produced in rabbits with filtrates from this tumor inhibited the hemolytic effect of 10 per cent saline suspensions of mammary tumors on mouse red blood cells (2). This inhibition was achieved only by sensitization of the mouse red blood cells, which in the nonsensitized state were hemolyzed by the tumor suspension. It was not achieved by mixing the antitumor serum with the tumor suspensions. The inhibition produced by the antimammary tumor serum was, on the average, 8 times greater than that produced by normal rab bit serum. These findings suggested further studies with antisera produced in rabbits with other mouse tumor filtrates, to determine whether this inhibi tion of hemolysis by suspensions from mammary tumors is specific for the antimammary tumor serum. Accordingly, experiments were made with antitumor rabbit sera prepared with two different brain tumors induced in mice with methylcholanthrene (6) : (a) an undifferentiated malignant gli oma grown in the C3H mouse strain (which is sus ceptible to spontaneous mammary tumor) and (6) an ependymoma grown in the C57BL strain (which is resistant to mammary tumor). It has also been found that there are striking differences in the hemagglutinating and hemolytic behavior between the red blood cells of the C57BL mice, which are mammary tumor-resistant, and those of the C3H mice, which are susceptible (1, 2). And, most significantly, there is a difference between the red blood cells from tumor-bearing and those from nontumor-bearing animals of com parable ages (over 1 year) of the C3H strain. Thus, the questions arise : (a) Does this difference in the hemagglutinating and/or hemolytic behavior rep resent a difference in the antigenic constitution of