Fig. 3.

Macrophage functions in the tumor microenvironment with special emphasis on immunosuppression, metastasis, lymphangiogenesis and angiogenesis. During immunosuppression, TAM generated molecules prevent the accumulation of cytotoxic T cells (anti-tumorigenic cells). During metastasis, tumor cells secrete soluble factors that prime specific cells such as macrophages that help in seeding tumor cells at distant locations. In hypoxic areas, TAMs and TEMs (Tie2-expressing monocytes) upregulate several angiogenic factors that promote angiogenesis. During lymphangiogenesis, TAMs secrete various factors that initiate the formation of lymphatics.