Transplantation Immunity to Simian Virus 40-Transformed Cells in Tumor-Bearing Mice. II. Evidence for Macrophage Participation at the Effector Level of Tumor Cell Rejection2
Experiments were performed to determine if normal macrophages are recruited in vivo, as a result of specific interaction between immune lymphoid cells and tumor cells, to serve an effector role in the inhibition of tumor development by simian virus 40 (SV40)-transformed cells in syngeneic BALB/c mice. The results obtained indicate that spleen cells from mice with tumors induced by SV40-transformed cells (TU-5 line) could prevent tumor development by admixed TU-S cells when inoculated together into normal adults at ratios as low as 1:1. Tumor-neutralizing activity of the immune lymphoid cells was not diminished after treatment of lymphoid cells with 500 R γ-radiation. Neutralizing activity of immune lymphoid cells was lost after 2000 R. Tumor cell neutralization by immune lymphoid cells was less efficient in newborn mice and adult mice given 500 R whole-body γ-radiation, which suggests that immune lymphoid cells cooperate with cells lacking in number or function in newborn and irradiated mice. Normal bone marrow cells supplied the function necessary for tumor cell neutralization by immune lymphoid cells in irradiated mice(700 R). Tumor cell neutralization by immune lymphoid cells occurred less efficiently in mice treated with silica, a specific macrophage toxin. Thus normal macrophages are involved in tumor cell rejection in vivo as a consequence of specific immune lymphoid cell-tumor cell interaction.