[Blocking factors in human blood which inhibit the cytotoxicity of lymphocytes].

The cytotoxicity of human peripheral blood lymphocytes against malignant tumor cell lines was significantly inhibited by human plasma or sera. In addition to so-called blocking factors such as antigens, antibodies, antigen-antibody complexes, IAP and ferritin, some substances which could be removed by heat or centrifugation were considered to play a significant role.