“…Suppressive activity was generated by monocyte-macrophages in cases B and F, and by T lymphocytes in case A. Suppressor macrophages have been observed in both human tumors [2,10,29] and various animal tumors [I, 7, 21]. In most cases, the suppressive activity appeared to be more pronounced against the induction phase of immune responses [14,17,21] and lymphoproliferative responses [7,10,23,26]. In these studies, suppressor activities were analyzed in animal hosts bearing highly immunogenic tumors induced by viruses or chemicals, and the effector phase was generally not affected [5,17,20].…”