[Immunosuppressive substance derived from choriocarcinoma (author's transl)]

Addition of choriocarcinoma culture fluid (CCF) inhibited mixed lymphocyte reaction (MLR) in vitro antibody production and in vitro allo-killer induction. This suppression was not mediated by HCG, and predominant when CCF was added at the initial phase of culture. The suppression of antibody production was observed when stimulated by T cell-dependent antigen but not by T cell-independent antigens. This suppression was mediated by suppressor T cell, since CSF induced antigen-nonspecific suppressor T cell during 24 hr-incubation. The suppressor T cell once induced was X-ray resistant, but sensitive at precursor level before incubation with CCF. The specific antiserum was raised in rabbit by immunization with a fraction of CCF. After appropriate absorbtion, the obtained antiserum reacted with choriocarcinoma cell lines and normal human chorionic trophoblast, but not with other human cells as tested by immunofluorescent antibody technique. Interestingly, this antiserum effectively neutralized the immunosuppressive activity of CCF, but this neutralizing activity was absorbed out with normal human chorionic villi. Thus, the trophoblasts of choriocarcinoma released them from maternal attack.