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Study of destructive mechanisms of the immune response to sarcoma I allograft in mice.

In B10 mice (H-2b) the Sarcoma I allograft (H-2a) was after a period of temporary progression definitely rejected by the allo-transplantation reaction. After a treatment of B10 mice with xenogeneic antithymocyte serum (ATS) the primary growth of the Sa I allograft was enhanced, later the allograft grew either permanently or, after a short regression, exhibited secondary growth, or permanently regressed. The destructive activity of spleen cells from untreated recipients, as measured according to the Winn neutralization test, increased at the time of tumor rejection and remained elevated. In ATS-treated recipients the destructive activity was markedly suppressed during primary tumor growth, at the time of temporary regression significantly increased and in permanent regressors remained elevated. In progressors there was again a decrease of this activity. The destructive activity in the spleen of regressors was found mainly in the cell fraction which did not adhere to nylon wool; these cells significantly accelerated the development and enhanced the destructive activity of normal spleen cells. The decrease of destructive activity in recipients with progressively growing tumors was detected both in cells adhering and in those which did not adhere to nylon wool. Besides this defect, the defect of proliferative activity of spleen cells was detected by the local graft-versus-host reaction test in non-treated as well as ATS-treated recipients. It could not be directly proven that the suppression of the alloimmune reactivity was caused by suppressor cells--in spleens of progressors there were found no cells capable to suppress the activity of effector cells nor the evolution of the destructive activity of normal spleen cells.