Resistance to intravenous tumor metastases in the athymic nude mouse: a paradoxic response.

The role of the host immune response in the abatement or prevention of tumor metastasis is unclear. To investigate possible interaction of lymphocytes with tumor cells, the F10 subline of the B16 melanoma was studied after subcutaneous or intravenous injection in original host C57BL/6 mice, Swiss nude mice, and BALB/c nude mice. The F10 tumor grew rapidly after subcutaneous injection in all strains of mice. Although florid pulmonary metastases were detected in the lungs of C57BL/6 mice after intravenous inoculation, both strains of nude mice were markedly resistant to the development of pulmonary metastases (P less than 0.001). Labeling of the B16 F10 melanoma cells with 3H-thymidine demonstrated that the kinetics of tumor cells after intravenous inoculation were similar in C57BL/6 mice and nude mice. Increased natural killer (NK) activity in the nude mouse play an important role in the prevention of pulmonary metastases.