Fig. 4.

The role of tumor-associated macrophages (TAMs) during tumor angiogenesis. TAMs (blue) can promote tumor growth in at least two different ways: 1. TAMs, actively suppress the hosts immune response to tumors by secretion of immunosuppressive mediators, such as IL-6 and IL-10. 2. TAMs are a significant source of angiogenic factors (e.g., FGF2, MMPs, VEGF) that promote tumor neovessel formation and thereby contribute to malignant progression. Macrophages are thought to participate in and support the process of anastomosis, the fusion of two vascular sprouts to establish a direct connection. During this setting, macrophages (blue) can be found intimately associated with endothelial tip cells (red). It is hypothesized that their recruitment to sites of vessel fusion is driven by tip cell secreted Ang-2 (orange) that can attract macrophages in a Tie2-dependent or Tie-2 independent pathway, with the latter being mediated by beta2-integrins