Specificity of Antisera to Mouse Ascites Tumor in Rabbits Immunologically Depressed with Mouse Red Cells

Summary The concept tested is whether antisera showing increased specificity against a mouse ascites tumor can be obtained by immunizing with this tumor rabbits that were immunologically depressed by injection of mouse red cells when newborn. One-half the young in three litters of rabbits (depressed) were injected with washed mouse red cells on the day of birth and several times thereafter until day 38 after birth. The other half (controls) were left uninjected. At 9 ½ to 12 months, one-half the rabbits in both depressed and control groups were immunized with mouse red cells, the other half with L4946 mouse tumor. Antisera from depressed rabbits finally immunized with red cells had hemagglutination, hemolysin and cytolytic titers respectively 17, 6 and 6 times lower than their controls, indicating considerable immunologic depression. Antisera from depressed rabbits finally immunized with tumor cells had titers respectively 6, 2 and 2 times lower than their controls, indicating some cross-depression against tumor cells. The specificity of antisera against L4946 tumor was precisely the same in depressed rabbits and in nondepressed controls; absence of results for the latter control group in recent studies by Levi et al. and by Garb et al. throws serious doubt on a positive interpretation of their data.