Modulation of IFN-γ production by TNF-α in macrophages from the tumor environment: Significance as an angiogenic switch

BackgroundThe role of macrophages in tumor angiogenesis has been known to influence in the production of angiogenic cytokines and growth factors including TNF-α. Recently, macrophages were also found to produce INF-γ, which were found to be involved in angiogenic inhibition. Thus, the importance of macrophages in tumor angiogenesis might be the angiogenic switch. The hypothesis tested here is that TNF-α can modulate the INF-γ production in macrophages in tumor environment as part of the tumor angiogenic switch.MethodsMacrophages in tumor environment were obtained from peritoneal cavity and s.c. grown tumor of C57BL/6 mice injected with B16F10 melanoma cell line for 6 and 11 days, respectively. Mac1+-macrophages were purified using magnetic beads (MACs™; Milteny Biotech, Germany) and cultured with various concentrations of TNF-α at various time points at 37 °C. The supernatants were analyzed for IFN-γ or VEGF by ELISA kit.ResultsResidential macrophages from 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. Upregulation of IFN-γ production by the addition of LPS or TNF-α was observed in macrophages from the tumor bearing peritoneal cavity. RT-PCR analysis revealed external TNF-α-induced IFN-γ gene expression in macrophages from tumor environment.ConclusionThe overall data suggest that the macrophages in tumor environment might play an important role not only in angiogenic signal but also in anti-angiogenic signal by producing related cytokines. Moreover, TNF-α might be a key cytokine functioning as a tumor angiogenic switch.