A Role for the Macrophage in in Vivo and in Vitro Resistance to Murine Bladder Tumor Cell Growth1

Studies were performed to determine the role of macrophages in inhibition of growth of the same tumor cell type both in vitro and in vivo. Bladder transitional epithelium tumor cells were injected s.c. into Toxoplasma-infected mice, previously shown to contain activated macrophages, and into uninfected controls. The subsequent growth of solid tumor was significantly less in the Toxoplasma-infected animals. Bladder tumor cells from the same cell line were grown in vitro either alone or in the presence of peritoneal lymphocytes and/or macrophages from Toxoplasma-infected and control, uninfected mice. [3H]Thymidine incorporation by the tumor cells was inhibited only in the presence of macrophages from the Toxoplasma-infected animals. Lymphocytes alone did not appear to be cytotoxic under the conditions used. Moreover, lymphocytes from Toxoplasma-infected mice did not convey cytotoxicity to macrophages from control animals under the experimental conditions used.