[The analysis of immunosuppressive substance derived from choriocarcinoma cell lines].

By virtue of the release of myriad metabolites from tumor cells into the tumor-bearing host, malignant transformed cells may escape from the host immune surveillance system. One of the mechanisms for such an escape phenomenon may be mediated by the activation of the host's suppressor pathway. To analyze the immunosuppressive circuit by means of a tumor cell-derived factor, we have used the choriocarcinoma cell lines as a model and obtained the following experimental results. 1. In the choriocarcinoma cell lines' supernatant, we found two distinct factors: One was an immunosuppressive factor and the other was a non-specific lymphocyte proliferating factor. 2. The immunosuppressive factor induced the suppressor T cell which produced the potent suppressor T cell factor in the human and mouse system. 3. The immunosuppressive activity was found to have a strong affinity for the Fc portion of IgG. This factor was therefore suggested to be a Fc gamma receptor-like molecule. 4. The supernatant derived from various human cancer cell lines also contained similar Fc gamma receptor-like molecules. The pathophysiological significance of the immunosuppressive factor derived from tumor cells will be discussed in the context of the immunosuppression widely seen in the tumor-bearing state, and the properties of the substance will be related with the Fc-binding immunosuppressive factor derived from normal trophoblast.