Mouse forestomach carcinoma cells immunosuppress macrophages through TGF-β1

Peritoneal implantation metastasis of gastric cancer cells is associated with poor prognosis. Peritoneal macrophages are the most important immune cells in the abdominal cavity to control tumor metastasis. In the present study, the immunosuppressive effects of mouse forestomach cells on macrophages were examined.

Conditioned medium from mouse forestomach cell cultures were used to treat isolated peritoneal macrophages. A colorimetry-based phagocytosis assay was performed to investigate the functional change of macrophages. The alternation in cytokine secretion by macrophages was measured by enzyme-linked immunosorbent assay. Specific markers of macrophage polarization were analyzed by real-time reverse transcription polymerase chain reaction. The transforming growth factor-β1 signaling was evaluated by Western blotting. Neutralization experiments were performed by using transforming growth factor-β1 antibody.

The conditioned medium reduced the phagocytotic capability of macrophages. Lower tumor necrosis factor-α and interleukin-1β levels and higher interleukin-10 and vascular endothelial growth factor levels were observed. Real-time reverse transcription polymerase chain reaction showed increased mRNA levels of M2 macrophage markers. Further study revealed that transforming growth factor-β1 was significantly elevated in the conditioned medium and transforming growth factor-β1 signaling was activated in the macrophages with treatment with conditioned medium. Neutralization of transforming growth factor-β1 reversed the immunosuppressive effects on macrophages.

Immunosuppressive macrophages can be induced by conditioned medium from mouse forestomach cell cultures. These effects seemed to be through the production of transforming growth factor-β1 by the tumor cells. Targeting transforming growth factor-β1 intervention might help in the control of peritoneal metastasis of gastric cancers.