The role of macrophages in tumor angiogenesis is known to be the production of angiogenic cytokines and growth factors including TNF-α. Recently, macrophage also can produce the INF-γ that is being studied to be involved in angiogenic inhibition. Thus, the importance of macrophages in tumor angiogenesis is might being an angiogenic switch. Thus, the hypothesis tested here is that TNF-α can modulate the INF-γ production in the macrophages from tumor environment as a part of tumor angiogenic switch.

Macrophages in tumor environment were obtained from the peritoneal cavity of C57BL/6 mice injected with B16F10 melanoma cell line for 6 or 11 days. Mac1⁺-macrophages were purified using magnetic bead (MACs™; Milteny Biotech, Germany) and cultured with various concentrations of TNF-α for various time points at 37℃. The supernatants were analyzed for IFN-γ or VEGF by ELISA kit (Endogen, Woburn, MA).

Residential macrophages from the peritoneal cavity did not respond to LPS or TNF-α to produce INF-γ. However, the cells from tumor environment produced IFN-γ as well as VEGF and upregulated by the addition of LPS or TNF-α. RT-PCR analysis revealed the external TNF-α-induced IFN-γ gene expression in the macrophages from tumor environment.

The overall data suggest that the macrophages in tumor environment might have an important role not only in angiogenic signal but also in anti-angiogenic signal by producing related cytokines. And TNF-α might be a key cytokine in tumor angiogenic switch.