Inhibition of Tumor Angiogenesis by Interferon-γ by Suppression of Tumor-Associated Macrophage Differentiation

Tumor-associated macrophages (TAMs) differentiate from monocytes and are the M2-polarized macrophages in most human tumors, secreting generous vascular endothelial growth factor (VEGF) to promote angiogenesis. Although it has been shown in vitro that interferon-γ (IFN-γ) can inhibit monocytes differentiating to M2 macrophages in the tumor microenvironment and switch TAMs from M2 into M1, suppressing the ability of secreting VEGF, its effects on TAMs in vivo remains unknown. Here we tried to examine the effects of IFN-γ on the recruitment of monocyte/macrophage differentiation of TAMs and tumor angiogenesis in vivo. We built a gallbladder cancer model by inoculating subcutaneously the human gallbladder cancer cell line (GBC-SD) into BALB/C nude mice and injected the recombinant mouse IFN-γ intratumorally. We found that in the IFN-γ group, the number of monocytes/macrophages was significantly higher than that in the control group (p < 0.01), and TAM differentiation rate, which we defined as the number of TAMs / the number of monocytes/macrophages × 100%, mice-VEGF concentration, and microvessels density (MVD) were significantly lower than those in the control group (p < 0.01, p < 0.05, and p < 0.01). Our results suggest that IFN-γ can induce monocytes/macrophages recruiting into the tumor microenvironment, but inhibit them, differentiating to TAMs in vivo, which may reduce the concentration of VEGF and angiogenesis in tumor.