A pathogenic role of Th2 cells and their cytokine products on the pulmonary metastasis of murine B16 melanoma

The role of Th2 cells and the cytokines produced by these cells on experimental pulmonary metastasis of B16 melanoma was investigated in a murine model implanted with high metastatic (B16F10) or low metastatic (B16F1) melanoma cell. An average of 250 colonies of metastasis in the lungs was counted in mice (BF10 mice) at 14 days after the inoculation of 2 x 10⁵ B16F10 cells/mouse, while <20 colonies were detected in mice (BF1 mice) inoculated with the same number of B16F1 cells. CD4⁺CD11b⁺TCR-αβ⁺ T cells (BF10-Th2 cells) were produced in the spleens of BF10 mice, while these cells were not detected in BF1 mice. The BF10-Th2 cells produced IL-4 and IL- 10 into culture fluids when stimulated in vitro with anti-CD3 mAb. However, IL-2 and IFN-γ were not produced. The level of a pulmonary metastasis in BF1 mice increased to the level observed in BF10 mice, when BF10-Th2 cells were adoptively transferred to BF1 mice. Also, an increase in the number of pulmonary melanoma was demonstrated in BF1 mice treated with 10 μg/kg murine rIL-4. The level of pulmonary metastasis in BF10 mice or in BF1 mice inoculated with BF10-Th2 cells decreased to the level observed in BF1 mice when mice were treated with an anti-IL-4 mAb at a dose of 250 μg/kg on days 1, 3, and 5 after tumor inoculation. These results suggest that the severity of pulmonary metastasis in mice receiving B16 melanoma cells is strongly influenced by the IL-4 released from tumor-associated Th2 cells.