The role of macrophages in preventing metastasis of a homotransplantable hamster lymphoma.

The roles of macrophages in preventing metastasis of a homotransplantable lymphoma were studied in Syrian golden hamsters. Removal of the primary tumor led to enhanced development of metastatic foci. Macrophage activities as demonstrated by macrophage spreading and cytostatic activity were augmented in tumor-bearing hosts, but depressed in tumor-resected hosts. Metastases were facilitated by treatment with silica, an agent that blocks macrophage functions. These results may suggest that immune-activated macrophages contribute to the inhibition of metastases. Metastases were completely inhibited by local irradiation of the primary tumors but such an effect was abolished by the resection of irradiated tumors. Irradiated tumor cells may work as potent immunogens to augment the generation of immune-activated macrophages.