| Abstract: | The proliferative responses of peripheral blood lymphocytes of inbred SJL/J mice to the mitogens phytohemagglutinin and concanavalin A were evaluated serially in individual animals before and after induction of lymphomas by transplantation. Tumor-bearing mice exhibited marked suppression of mitogen responsiveness. Proliferative responses in mixed lymphocyte-tumor cell culture and mixed lymphocyte culture were also suppressed. Suppression of responses was tumor related, and responsiveness was restored in animals whose tumors regressed. There was no deficiency of responder T-cells in the peripheral blood of tumor-bearing animals, and suppressor cell activity was not demonstrable in a number of in vitro assays. However, plasma from tumor-bearing animals exhibited potent immunosuppressive activity. The presence of plasma suppressive activity was similarly tumor related. Thus this study demonstrates nonspecific suppression of cell-mediated immune responses following tumor induction, apparently mediated by a plasma suppressor factor. |
