Background: The role of macrophages in tumor angiogenesis has been known to influence in the production of angiogenic cytokines and growth factors including TNF-alpha. Recently, macrophages were also found to produce INF-gamma, 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-alpha can modulate the INF-gamma production in macrophages in tumor environment as part of the tumor angiogenic switch.
Methods: Macrophages 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-alpha at various time points at 37 degrees C. The supernatants were analyzed for IFN-gamma or VEGF by ELISA kit.
Results: Residential macrophages from peritoneal cavity did not respond to LPS or TNF-alpha to produce INF-gamma. However, the cells from tumor environment produced IFN-gamma as well as VEGF. Upregulation of IFN-gamma production by the addition of LPS or TNF-alpha was observed in macrophages from the tumor bearing peritoneal cavity. RT-PCR analysis revealed external TNF-alpha-induced IFN-gamma gene expression in macrophages from tumor environment.
Conclusion: The 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-alpha might be a key cytokine functioning as a tumor angiogenic switch.